低氧诱导因子与乳腺癌转移

Hypoxia-inducible factor 1 and breast cancer metastasis 低氧诱导因子与乳腺癌转移 1 first-author 2 1 corresp ‡Corresponding Author ‡Corresponding Author †E-mail:hzhang22@ustc.edu.cn †E-mail:hzhang22@ustc.edu.cn hzhang22@ustc.edu.cn CAS Key Laboratory of Innate Immunity and Chronic Disease, Innovation Center for Cell Biology, School of Life Sciences, University of Science and Technology of China, Hefei 230027, China CAS Key Laboratory of Innate Immunity and Chronic Disease, Innovation Center for Cell Biology, School of Life Sciences, University of Science and Technology of China, Hefei 230027, China Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA Accumulating evidence has shown that the hypoxic microenvironment, which is critical during cancer development, plays a key role in regulating breast cancer progression and metastasis. The effects of hypoxia-inducible factor 1 (HIF-1), a master regulator of the hypoxic response, have been extensively studied during these processes. In this review, we focus on the roles of HIF-1 in regulating breast cancer cell metastasis, specifically its effects on multiple key steps of metastasis, such as epithelial-mesenchymal transition (EMT), invasion, extravasation, and metastatic niche formation. We also discuss the roles of HIF-1-regulated non-coding RNAs in breast cancer metastasis, and therapeutic opportunities for breast cancer through targeting the HIF-1 pathway. 概要 2 肿瘤，特别是实体瘤，其内部微环境处于一种低氧或缺氧的状态，肿瘤的这种低氧微环境将诱导活化低氧诱导因子（HIF-1）信号通路。HIF-1信号通路在乳腺癌的转移中发挥着重要的作用。乳腺癌的转移涉及肿瘤细胞的浸润、进入血管、通过血液循环迁移、到达远端毛细血管内壁、穿透血管壁进入新的器官以及在新的部位形成转移灶等步骤，过程非常复杂。本文重点围绕HIF-1在转移各个步骤中的作用进行综述。 Breast cancer Hypoxia-inducible factor 1 (HIF-1) Metastasis 乳腺癌 低氧诱导因子 肿瘤转移 Hypoxic microenvironment and breast cancer 1 Hypoxia has been extensively studied for decades within the tumor microenvironment, which influences malignant cells in various ways (Hu and Polyak, 2008 2008 ). While the O 2 supply matches the need of cell growth in normal tissues, the diffusion of O 2 from a blood capillary in a tumor mass that reaches a size of 1–2 mm 3 is limiting because of structural and functional abnormalities of the newly formed tumor vessels, thus leading to the development of hypoxic areas in the tumor mass (Vaupel et al., 2004 2004 ). Breast cancer is the most frequently diagnosed cancer and a major cause of death in women worldwide (Jemal et al., 2011 2011 ; Lech and Przemyslaw, 2011 2011 ). About 25%–40% of invasive breast cancers exhibit hypoxic regions (Lundgren et al., 2007 2007 ). Studies using polarographic electrodes have shown that the median partial pressure of oxygen (pO 2 ) in normal human breast tissue is 65 mmHg (1 mmHg=133.3 Pa). In contrast, human breast cancers have a median pO 2 of 10 mmHg. In addition, more than half of all breast cancers studied had a pO 2 of less than 2.5 mmHg (Vaupel et al., 1991 1991 ; 2007 2007 ; Hohenberger et al., 1998 1998 ). Studies have shown that intra-tumoral hypoxia has negative implications for survival of breast cancer patients, independent of prognostic parameters, such as the clinical tumor stage, histological grade, and lymph node status. Hypoxic tumors are associated with a more aggressive phenotype, increased risk of metastasis, increased resistance to radiotherapy and chemotherapy, and induced cancer immune suppression (Brizel et al., 1996 1996 ; Mees et al., 2009 2009 ). Basic biology of hypoxia-inducible factor 1 (HIF-1) 1 In most human solid tumors, adaptation to decreased O 2 availability is achieved primarily through the activity of two hypoxia-inducible factors (HIF-1 and HIF-2), which regulate the expression of over 1000 target genes (Semenza, 2012 2012 ). Overexpression of HIF-1 has been confirmed in many solid tumors, including ovarian, bladder, uterus, breast, colon, brain, pancreatic, renal, and prostate (Zhong et al., 1999 1999 ; Talks et al., 2000 2000 ). HIF-1 is a hetero-dimeric transcription factor consisting of a constitutively expressed HIF-1β subunit (also known as the aryl hydrocarbon receptor nuclear translocator [ARNT]) and a tightly regulated HIF-1α subunit (Wang et al., 1995 1995 ). Both HIF-1α and HIF-1β are members of the bHLH-PAS superfamily of proteins containing basic-helix-loop-helix (bHLH) and PER-ARNT-SIM (PAS) domains involved in DNA binding and dimerization, respectively (Wang et al., 1995 1995 ). HIF-1α also contains an oxygen-dependent degradation (ODD) domain and two transactivation domains (N-TAD and C-TAD). O 2 regulates HIF-1α stability and activity through hydroxylation of proline and asparagine residues. Under normoxic conditions, two proline residues (P402 and P564) in the human HIF-1α ODD domain are hydroxylated by prolyl hydroxylase domain proteins (PHDs). Hydroxylation is required for binding of the HIF-1α protein to the von Hippel-Lindau protein (VHL). VHL is the recognition subunit of an E3 ubiquitin ligase that adds a poly-ubiquitin chain to HIF-1α, which targets the protein for degradation in the proteasome. Morever, O 2 -dependent hydroxylation of asparagine residue 803 (N803) in HIF-1α by factor inhibiting HIF-1 (FIH-1) suppresses the interaction of HIF-1α with the coactivators p300 and CBP (CREB binding protein), and therefore inhibits the HIF-1α transactivation function under normoxic conditions (Mahon et al., 2001 2001 ; Lando et al., 2002 2002 ). Under hypoxic conditions, both the prolyl and asparaginyl hydroxylation reactions are inhibited, leading to the stabilization of HIF-1α protein and increased interaction with its co-activators. Thus, in hypoxic cells, HIF-1α protein accumulates, hetero-dimerizes with HIF-1, binds to the consensus DNA sequence 5'-RCGTG-3' within hypoxia response elements (HREs) located in target genes, and activates their transcription (Fig. 1 1 ). It is not only that the HIF-1 pathway is regulated by oxygen tension, but also that hypoxia-independent growth factor stimulation, loss of tumor suppressor function, and oncogenic activation have been reported to regulate HIF-1α activity (Semenza, 2003 2003 ). Growth factor signals affecting the HIF-1α pathway include human insulin-like growth factor, human epidermal growth factor (EGF), and prostaglandin E2 (Feldser et al., 1999 1999 ; Laughner et al., 2001 2001 ; Fukuda R. et al., 2002 2002 ; Liu et al., 2002 2002 ; Fukuda N. et al., 2003 2003 ; Grimshaw, 2007 2007 ). Function loss of tumor suppressor proteins, such as VHL, phosphatase, and phosphatase and tension homolog deleted on chromosome 10 (PTEN) and p53 in cancer cells, impairs the degradation of HIF-1α protein, or increases the synthesis of HIF-1 (Krieg et al., 2000 2000 ; Zhong et al., 2000 2000 ; Zundel et al., 2000 2000 ; Ravi et al., 2001 2001 ), thus leading to HIF-1α protein accumulation. Activation of the oncogenic PI3K/Akt signaling pathway stimulates HIF-1α expression through mTOR-dependent translation (Zhong et al., 2000 2000 ; Laughner et al., 2001 2001 ). In addition, cellular reactive oxygen species and nitric oxide have also been shown to stabilize HIF-1α, causing protein accumulation (Kasuno et al., 2004 2004 ; Quintero et al., 2006 2006 ; Gao et al., 2007 2007 ). HIF-1 and breast cancer metastasis 1 Over 90% of all breast cancer deaths are the result of metastasis, primarily to the bone, lung, liver, brain and lymph nodes. Tumor metastasis is the dissemination of cancer cells from the initial site of primary tumor growth to distant organs where they survive, proliferate, and form secondary tumors. Metastasis is a complex process containing a series of discrete steps: (1) epithelial-mesenchymal transition (EMT), during which cancer cells lose cell-to-cell contact and gain motility; (2) local tissue invasion, which is facilitated by the degradation of extracellular matrix (ECM); (3) intravasation, during which cancer cells penetrate the wall of a blood vessel and enter the circulation; (4) homing, during which cancer cells must survive within the circulation; (5) extravasation, during which cancer cells pass through the vascular wall and exit the blood stream at distant organs; and, (6) metastatic niche formation at the metastatic site to create a milieu that is favorable for cancer cell growth. A high level of HIF-1α at diagnosis is predictive of early relapse and metastasis, and correlates with poor clinical outcomes in human breast cancer (Bos et al., 2003 2003 ; Gruber et al., 2004 2004 ; Generali et al., 2006 2006 ). It has been reported that expression of HIF-1 target genes is increased in the triple-negative breast cancer subgroup (Zhong et al., 1999 1999 ; Cancer Genome Atlas Network, 2012 2012 ). HIF-1 plays key roles in many crucial aspects of breast cancer biology, including angiogenesis, stem cell maintenance, metabolic reprogramming, EMT, invasion, metastasis, and resistance to radiation therapy and chemotherapy (Semenza, 2012 2012 ). Inhibition of HIF-1 activity in mice after orthotopic transplantation of triple-negative breast cancer cells has a dramatic effect on primary tumor growth as well as metastasis to lymph nodes and lungs (Zhang et al., 2012 2012 ). Understanding the molecular and cellular mechanisms underlying metastasis is required for accurate prognoses and for developing new therapeutic strategies. Recent studies have shown that the HIF-1 pathway regulates breast cancer metastasis through multiple mechanisms. Next, we will focus on the regulatory roles of HIF-1 in a series of discrete steps of breast cancer metastatic progression. HIF-1 mediates EMT 2 During metastasis, epithelial cells detach from the primary tumor, adhere to and invade the surrounding stroma, intravasate into the bloodstream, and disseminate to distant tissues where they extravasate out of blood vessels and form secondary tumors. The process of epithelial cells detaching from primary tumors closely resembles that of cells undergoing EMT, and EMT has been regarded as the possible first step in the complex process of metastasis (Chaffer and Weinberg, 2011 2011 ; Valastyan and Weinberg, 2011 2011 ). Epithelial cells that undergo EMT lose their epithelial phenotype and acquire mesenchymal cell-associated characteristics (Thiery, 2002 2002 ; Kalluri and Weinberg, 2009 2009 ; Creighton et al., 2010 2010 ; Singh and Settleman, 2010 2010 ; May et al., 2011 2011 ). Thus, EMT is characterized by cellular and molecular changes that include loss of cell-to-cell adhesion, which involves E-cadherin in adherent junctions and claudins in tight junctions, upregulation of the mesenchymal protein vimentin, reorganization of the cytoskeleton to acquire a more spindle-like morphology, and increased motility that involves dynamic actin microfilament networks. HIF-1 provokes EMT through up-regulating EMT-associated transcription factors or repressors, activating the EMT-associated signaling pathways, modulating EMT-associated inflammatory cytokines, as well as regulating other pathways like epigenetic regulators (Bao et al., 2012 2012 ). For instance, HIF-1 induces EMT through the transcriptional control of E-cadherin, SNAIL (zinc finger protein snail), ZEB1 (zinc finger E-box-binding homeobox 1), TWIST, and TCF3 (transcription factor 3, also known as E47) (Krishnamachary et al., 2006 2006 ; Moreno-Bueno et al., 2008 2008 ). In breast cancer cells, EMT was activated by ZEB1-MYB-E-cadherin signaling under hypoxic stress, which induced higher expression of ZEB1 and lower expression of MYB (Hugo et al., 2013 2013 ). Recently, it has been discovered that hypoxia-induced biomolecules, including Jagged2, cyclooxygenase-2 (COX-2), and urokinase receptor (uPAR) (Jo et al., 2009 2009 ; Xing et al., 2011 2011 ; Bocca et al., 2014 2014 ), also contribute to EMT changes and invasive ability of breast cancer cells. The HIF-1 pathway may also regulate EMT via regulating long non-coding RNAs (lncRNAs; such as H19 lncRNA) and calcium signaling in breast cancer cells to promote cancer cell invasion in hypoxic microenvironments (Lock et al., 2013 2013 ; Davis et al., 2014 2014 ; Matouk et al., 2014 2014 ). HIF-1 mediates invasion and intravasation 2 To invade the surrounding tissues, cancer cells need to degrade the surrounding basement membrane (BM) and extracellular matrix barriers. Matrix metallo-proteinases (MMPs) are members of zinc-dependent endo-peptidases that degrade many of the components of the ECM, including the BM. Among MMPs, MMP-2 and MMP-9 degrade type IV collagen, which is a major component of the BM. MMP-2 and MMP-9 have been positively correlated with a higher incidence of metastases and with a poor prognosis in breast cancer (Duffy et al., 2000 2000 ; Pritchard et al., 2001 2001 ; Incorvaia et al., 2007 2007 ). Cells at the invasive front of solid tumors are frequently found to have a high expression level of HIF-1α (Horrée et al., 2007 2007 ). Many reports suggest that hypoxia and HIF-1 upregulate the expression levels and/or activities of MMP-2 and MMP-9 (Krishnamachary et al., 2006 2006 ; Munoz-Najar et al., 2006 2006 ). Type I collagen is very important for cell migration during invasion. When tumor size increases, collagen fibers straighten and align, which facilitates cancer cell invasion (Maglione et al., 2006 2006 ; Provenzano et al., 2006 2006 ; Conklin et al., 2011 2011 ). Recent studies showed that HIF-1α plays a critical role in collagen biogenesis in breast cancers by upregulating the expression levels of pro-collagen prolyl (P4HA1 and P4HA2) and lysyl (PLOD1 and PLOD2) hydroxylases in both cancer and stromal cells (Gilkes et al., 2013a 2013a ; 2013b 2013b ; 2013c 2013c ). P4HA1 and P4HA2 are required for collagen deposition, while PLOD2 is important for collagen fiber crosslinking (Gilkes et al., 2013a 2013a ). Expression of P4HA1, P4HA2, and PLOD2 is required for breast cancer metastasis. HIF-1 and extravasation 2 Breast cancer cells may spread via either the lymphatic or vascular circulation (Weigelt et al., 2005 2005 ). However, less than 0.1% of cancer cells that enter the vascular circulation establish a metastatic lesion (Fidler, 1970 1970 ). This indicates that extravasation of cancer cells from the circulation into a tissue microenvironment where cancer cells can survive and proliferate is a limiting step in the metastatic process. To extravasate, a cancer cell must first adhere to endothelial cells (ECs) in the lung vasculature, a process known as margination, and then disrupt the tight interactions between ECs to penetrate out of the blood vessel. Zhang et al. ( 2012 2012 ) showed that HIF-1 promoted the extravasation of breast cancer cells in the lung. In addition, the invasion of naive breast cancer cells through EC monolayers increased when the cells were exposed to conditioned medium generated by hypoxic breast cancer cells. Biophysical measurement of EC-EC interactions using transendothelial electrical resistance showed decreased EC-EC interactions in the presence of conditioned medium generated by hypoxic breast cancer cells. These effects were not observed when conditioned medium from hypoxic breast cancer cells expressing shRNAs-targeting HIF-1 was used (Zhang et al., 2012 2012 ). Further experiments identified angiopoietin-like 4 (ANGPTL4) as a factor secreted from cancer cells that was induced by hypoxia in an HIF-1-dependent manner. ANGPTL4 expression in cancer cells disrupts vascular EC-EC junctions, increases the permeability of lung capillaries, and facilitates the extravasation of cancer cells (Padua et al., 2008 2008 ). In vivo studies also showed that ANGPTL4 induced vascular leakiness and facilitated lung metastasis in mice (Huang et al., 2011 2011 ). ANGPTL4 expression in primary breast cancers is associated with lung metastasis (Padua et al., 2008 2008 ). Hypoxic breast cancer cells also showed increased adherence to EC monolayers in an HIF-1-dependent manner. Microarray analysis of metastasis-related genes identified a cell surface receptor, L1 cell adhesion molecule (L1CAM), which is a direct transcriptional target of HIF-1 induced by hypoxia in triple negative breast cancer cells (Zhang et al., 2012 2012 ). L1CAM is a protein involved in mediating cell-cell adherence by homophilic and heterophilic interactions with integrins, neuropilin 1, or CD24 (Semenza, 2012 2012 ). Overexpression of L1CAM in cancer cells promoted the adhesion of cancer cells to EC monolayers in vitro , and increased the number of extravasated cancer cells in lung tissue after tail vein injection (Zhang et al., 2012 2012 ). HIF-regulated SDF-1/CXCR4 (stromal cell-derived factor-1/CXC chemokine receptor 4) signaling in ECs under hypoxic conditions may also promote the adhesion of breast cancer cells to ECs (Jin et al., 2012 2012 ). HIF-1 and metastatic niche formation 2 HIF-1 also regulates premetastatic niche formation at distant organs prior to cancer cell arrival (Erler et al., 2006 2006 ; 2009 2009 ; Wong et al., 2011 2011 ; 2012 2012 ). During metastasis, bone marrow-derived cells (BMDCs) are recruited to metastatic sites, where they form cell clusters that precede tumor cell arrival and are subsequently colonized by metastatic cancer cells (Kaplan et al., 2005 2005 ; Xing et al., 2011 2011 ). Hypoxic breast cancer cells produce multiple members of the lysyl oxidase (LOX) family, including LOX, LOXL2, and LOXL4, in an HIF-1-dependent manner (Erler et al., 2009 2009 ; Wong et al., 2011 2011 ; 2012 2012 ). LOX family members are enzymes secreted from primary breast cancer cells that catalyze collagen crosslinking at hydroxylated lysine residues. LOX was initially found to remodel ECM in the primary tumor. Recent studies revealed that LOX can remodel ECM at sites distant from the primary tumor. Primary breast cancer cells secrete LOX family members into the circulation, leading to collagen crosslinking in metastatic tissues, which facilitates the recruitment of BMDCs and, subsequently, breast cancer premetastatic niche formation (Erler et al., 2006 2006 ; 2009 2009 ; Wong et al., 2011 2011 ; 2012 2012 ). In addition, CD11b + /Ly6C med /Ly6G + myeloid cells and CD3 − /NK1.1 + natural killer cells are two BMDC populations that promote metastasis. Indeed, it has been found that recruitment of CD11b + /Ly6C med /mLy6G + cells was enhanced by hypoxic breast cancer cells (Sceneay et al., 2012 2012 ). Interestingly, LOX family members, LOX, LOXL2, and LOXL4 have variable expression in human breast cancers and breast cancer cell lines (Wong et al., 2011 2011 ). A clinical study revealed that LOX expression was associated with intra-tumoral oxygen tension and metastases of breast cancer in patients (Erler et al., 2006 2006 ). Since LOX family members are extracellular secreted proteins that play critical roles in metastasis, a monoclonal antibody or small molecule inhibitor directed against LOX might be useful for breast cancer therapy. HIF-1-regulated non-coding RNA in breast cancer metastasis 1 HIF-1 plays important roles in breast cancer metastasis by mediating hypoxia-induced expression of mRNA-encoding genes. HIF-1 also regulates the expression of non-coding RNAs, which are critical regulators of migration, invasion, and metastasis. Various types of non-coding RNAs have been implicated in cancer progression, such as microRNAs (miRNAs), lncRNAs, endogenous small interfering RNAs (end-siRNAs), PIWI-interacting RNAs (piRNAs), circular RNAs (circRNAs), and long intergenic non-coding RNAs (lincRNAs) (Ling et al., 2013 2013 ). Non-coding RNAs play pivotal roles in migration and invasion of breast carcinoma cells, and provide new insights into the molecular mechanisms that determine metastatic propensity. In this section, we summarize the published research reporting HIF-1-regulated non-coding RNAs in the pathogenesis of breast cancer metastasis, with an emphasis on miRNAs and lncRNAs. HIF-1 regulates the expression of many miRNAs in breast cancer cells. In MCF-7 breast cancer cells, 41 miRNAs were significantly up-regulated and 28 miRNAs were down-regulated by the hypoxic treatment (Camps et al., 2014 2014 ). Expression of miR-210, for instance, which is induced by HIF-1 in most cancer cells, promotes tumor proliferation and invasion, and is associated with a poor clinical outcome in breast cancer (Volinia et al., 2012 2012 ). miR-10b is activated by HIF-1/TWIST1 (twist-related protein 1) signaling, and overexpression of miR-10b initiates robust invasion and metastasis in otherwise non-metastatic breast cancers (Ma et al., 2007 2007 ; 2010 2010 ; Haque et al., 2011 2011 ). miR-20a and miR-20b, which are co-expressed with vascular endothelial growth factor (VEGF)-A and HIF-1α, also play important roles in breast cancer metastasis (Li et al., 2012 2012 ) (Table 1 1 ). chr: chromosome; lncRNA: long non-coding RNA; HOXD10: homeobox D10; VEGF-A: vascular endothelial growth factor A; BRCA1: breast cancer 1; FANCD: Fanconi anemia, complementation group D; FANCF: Fanconi anemia, complementation group F; PARP1: poly(ADP-ribose) polymerase 1; RB1: retinoblastoma 1; PTPN9: protein tyrosine phosphatase, non-receptor type 9; PTPRF: protein tyrosine phosphatase, receptor type F; RECK: reversion-inducing-cysteine-rich protein with Kazal motifs; NF-κB: nuclear factor of kappa light polypeptide gene enhancer in B cells; TGF-β: transforming growth factor β; REDD1: DNA-damage-inducible transcript 4; FGF18: fibroblast growth factor 18; ZEB2: zinc finger E-box binding homeobox 2; p27: p27 protein; UCA1: urothelial cancer associated 1 ncRNA Type (genomic location) Regulation by hypoxia Effect on metastasis Target gene or effector Reference miR-10b MicroRNA (chr 2) ↑ ↑ HOXD10 Ma et al., 2007 2007 ; Haque et al., 2011 2011 miR-20a MicroRNA (chr 13) ↓ ↓ VEGF-A Li et al., 2012 2012 miR-20b MicroRNA (chr X) ↓ ↓ VEGF-A Cascio et al., 2010 2010 ; Li et al., 2012 2012 miR-210 MicroRNA (chr 11) ↑ ↑ BRCA1, FANCD, FANCF, PARP1, E-cadherin, Rb1 Camps et al., 2008 2008 ; Rothé et al., 2011 2011 ; Volinia et al., 2012 2012 miR-24 MicroRNA (chr X) ↑ ↑ PTPN9, PTPRF, Sprouty2 (SPRY2) Kulshreshtha et al., 2007 2007 ; Du et al., 2013 2013 ; Li et al., 2013 2013 ; Camps et al., 2014 2014 miR-27a MicroRNA (chr 19) ↑ ↑ Sprouty2 (SPRY2) Kulshreshtha et al., 2007 2007 ; Camps et al., 2014 2014 ; Li et al., 2013 2013 miR-372/373 MicroRNA (chr 19) ↑ ↑ RECK, NF-κB, and TGF-β pathways Loayza-Puch et al., 2010 2010 ; Keklikoglou et al., 2012 2012 miR-495 MicroRNA (chr 14) ↑ ↑ E-cadherin, REDD1 Hwang-Verslues et al., 2011 2011 miR-675 MicroRNA (chr 11) ↑ ↑ RECK, NF-κB, and TGF-β pathways Loayza-Puch et al., 2010 2010 ; Keklikoglou et al., 2012 2012 Oncofetal H19 RNA lncRNA (chr 11) ↑ ↑ Slug, E-cadherin, angiogenin, FGF18 Matouk et al., 2007 2007 ; 2010 2010 ; 2014 2014 linc-RoR lncRNA (chr 18) ↑ ↑ mi-205, ZEB2 Takahashi et al., 2013 2013 ; Hou et al., 2014 2014 UCA1 lncRNA (chr 19) ↑ ↑ p27 (Kip1) Huang et al., 2014 2014 ; Xue et al., 2014 2014 lncRNAs are novel molecules that participate in a broad range of biological processes and complex diseases, especially in cancer progression. For example, the oncofetal H19 lncRNA is concomitantly induced by both transforming growth factor beta (TGF-β) and hypoxia in a mouse breast cancer model, and regulates E-cadherin expression and stimulates tumor metastasis through a positive feedback loop between Slug and H19/miR-675 (Matouk et al., 2014 2014 ). Several other lncRNAs, such as linc-RoR (regulator of reprogramming) and UCA1 (urothelial cancer associated 1), have been proved to be regulated by hypoxia/HIF-1α, but their detailed mechanistic functions remain elusive (Takahashi et al., 2013 2013 ; Hou et al., 2014 2014 ; Huang et al., 2014 2014 ; Xue et al., 2014 2014 ) (Table 1 1 ). HIF-1 as a therapeutic target 1 Solid tumors, including breast cancers, contain a hypoxic microenvironment due to poor vascularization in the rapidly growing tumor tissues and fast proliferation of cancer cells. HIF-1 plays a pivotal role in the adaptation of cancer cells to hypoxia by activating transcription of target genes that regulate angiogenesis, cell proliferation and survival, glucose metabolism, pH regulation, migration, invasion, and metastasis (Kim et al., 2006 2006 ; Fukuda et al., 2007 2007 ; Zhang et al., 2007 2007 ; Semenza, 2011 2011 ; 2012 2012 ). Increased HIF-1 expression shows strong correlations with poor prognostic outcomes and low survival rates of patients with breast cancers (Rose et al., 2003 2003 ). Therefore, targeting the HIF pathway provides an attractive strategy to treat hypoxic tumors. The HIF-1 pathway is activated in the basal molecular subtype of breast cancer (Cancer Genome Atlas Network, 2012 2012 ), suggesting that HIF-1 inhibitors may be particularly effective in the treatment of triple negative breast cancers. The current HIF-1 inhibitors are classified by their mechanism of action and include those that affect HIF-1α protein levels, HIF-1 dimerization, HIF-1 DNA binding, or HIF-1 transactivation of target genes (Table 2 2 ). Inhibitors that decrease HIF-1α protein levels can be further divided into two groups, inhibitors of HIF-1α translation and inducers of HIF-1α proteasomal degradation. HIF-1 inhibitors, such as digoxin and acriflavine, showed convincing potential therapeutic effects by decreasing primary tumor growth, vascularization, invasion and metastasis in animal models of breast cancer (Lee et al., 2008 2008 ; Zhang et al., 2008 2008 ; 2012 2012 ; Wong et al., 2011 2011 ; 2012 2012 ; Schito et al., 2012 2012 ). HSP90: heat-shock protein 90; 17-AAG: 17-allylamino-demethoxygeldanamycin; HDAC: histone deacetylase; MSC: methylselenocysteine; 17-DMAG: 17-dimethylaminoethylamino-17-demethoxygeldanamycin Mechanism of action Inhibitor Inhibition of HIF-1α mRNA Aminoflavone, GL331 Inhibition of HIF-1α protein synthesis Topoisomerase inhibitors (such as rapamycin, temsirolimus, and everolimus); cardiac glycosides (such as digoxin and digtoxin), microtubule targeting agents (such as 2-methoxyestradiol, epothilone B, and taxotere), topoisomerase inhibitors (such as camptothecin, topotecan, and NSC 644221), oligonucleotides, AF, PX-478 Inhibition of HIF-1α protein stabilization HSP90 inhibitors (such as 17-AAG, 17-DMAG, and apigenin), HDAC inhibitors (such as FK228 and LAQ824), antioxidants (such as ascorbic acid), oligonucleotides, selenium compound (such as berberine and MSC), PX-12, YC-1 Inhibition of HIF-1α:HIF-1β dimerization Acriflavine Inhibitions of HIF-1:DNA binding Anthracyclines, echinomycin Inhibition of HIF-1 transactivity Bortezomib The combination of HIF inhibitors with existing treatments may prove to be useful clinically. Currently, for breast cancer therapy, the selective estrogen receptor (ER) modulator tamoxifen is widely used. Combination chemotherapy using trastuzumab targeting human epidermal growth factor receptor 2 (HER2) and bevacizumab targeting VEGF is another widely used therapeutic strategy. However, triple negative breast cancers respond poorly to currently available therapies. Since the HIF-1 pathway is highly activated in triple negative breast cancers, HIF-1 inhibitors could be effective in treatment of such cancers. Clinical trials are warranted to determine if they may increase the survival of breast cancer patients alone or in combination with current therapeutic regimens. Concluding remarks and future directions 1 HIF-1, as a master regulator of cell response to hypoxic stress, plays important roles in breast cancer metastasis. As summarized in Fig. 2 2 , HIF-1 is involved in almost every key step of the metastatic process, such as EMT, invasion, intravasation, extravasation, and metastatic niche formation, as discussed in detail in this review. While most current studies have focused on HIF-1-regulated proteins, such as transcription factors, repressors and cytokines, recently, there has been growing appreciation of the role of ncRNAs, especially miRNAs and lncRNAs connected with HIF-1 controlled breast cancer metastasis. More comprehensive studies in this regard will shed light on the mechanisms underlying the regulation of hypoxia in breast cancer metastasis. A new concept has also been proposed that involves cancer stem cells in the connections between hypoxia and cancer metastasis (Hill et al., 2009 2009 ). The metastasis-promoting effects of HIF-1 help to maintain an expanding/renewing population of cancer stem cells ready to be distributed much like seeds or pollen blowing in the wind (Philip et al., 2013 2013 ). A few studies have supported this point of view by demonstrating that hypoxia/HIF-1 induces cancer stem-like cells by Jagged2 or mediates paracrine signaling between breast cancer cells and mesenchymal stem cells to promote metastasis (Xing et al., 2011 2011 ; Chaturvedi et al., 2013 2013 ). Further studies along these lines will be potentially valuable for dissecting the mechanisms of breast cancer metastasis. Thus, while intensive mechanistic studies are under way, targeting HIF-1 has emerged as a new therapeutic approach for treating breast cancer patients. Novel strategies targeting HIF-1 are likely to be useful in combination with current therapeutic regimens. Future work is warranted to identify more selective HIF-1 inhibitors, to study their mechanism of action, and to incorporate them in clinical trials. References B Bao , AS Azmi , S Ali , 等 . The biological kinship of hypoxia with CSC and EMT and their relationship with deregulated expression of miRNAs and tumor aggressiveness . BBA Rev Cancer , 2012 . 1826 ( 2 ): 272 - 296 . DOI: 10.1016/j.bbcan.2012.04.008 http://doi.org/10.1016/j.bbcan.2012.04.008 . The biological kinship of hypoxia with CSC and EMT and their relationship with deregulated expression of miRNAs and tumor aggressiveness C Bocca , M Ievolella , R Autelli , 等 . Expression of Cox-2 in human breast cancer cells as a critical determinant of epithelial-to-mesenchymal transition and invasiveness . Exp Opin Therap Targets , 2014 . 18 ( 2 ): 121 - 135 . DOI: 10.1517/14728222.2014.860447 http://doi.org/10.1517/14728222.2014.860447 . Expression of Cox-2 in human breast cancer cells as a critical determinant of epithelial-to-mesenchymal transition and invasiveness R Bos , P van der Groep , AE Greijer , 等 . Levels of hypoxia-inducible factor-1α independently predict prognosis in patients with lymph node negative breast carcinoma . Cancer , 2003 . 97 ( 6 ): 1573 - 1581 . 12627523 DOI: 10.1002/cncr.11246 http://doi.org/10.1002/cncr.11246 . Levels of hypoxia-inducible factor-1α independently predict prognosis in patients with lymph node negative breast carcinoma DM Brizel , SP Scully , JM Harrelson , 等 . Tumor oxygenation predicts for the likelihood of distant metastases in human soft tissue sarcoma . Cancer Res , 1996 . 56 ( 5 ): 941 - 943 . 8640781 . Tumor oxygenation predicts for the likelihood of distant metastases in human soft tissue sarcoma C Camps , FM Buffa , S Colella , 等 . hsa-miR-210 is induced by hypoxia and is an independent prognostic factor in breast cancer . Clin Cancer Res , 2008 . 14 ( 5 ): 1340 - 1348 . 18316553 DOI: 10.1158/1078-0432.CCR-07-1755 http://doi.org/10.1158/1078-0432.CCR-07-1755 . hsa-miR-210 is induced by hypoxia and is an independent prognostic factor in breast cancer C Camps , HK Saini , DR Mole , 等 . Integrated analysis of microRNA and mRNA expression and association with HIF binding reveals the complexity of microRNA expression regulation under hypoxia . Mol Cancer , 2014 . 13 28 24517586 DOI: 10.1186/1476-4598-13-28 http://doi.org/10.1186/1476-4598-13-28 . Integrated analysis of microRNA and mRNA expression and association with HIF binding reveals the complexity of microRNA expression regulation under hypoxia Cancer Genome Atlas Network . Comprehensive molecular portraits of human breast tumours . Nature , 2012 . 490 ( 7418 ): 61 - 70 . 23000897 DOI: 10.1038/nature11412 http://doi.org/10.1038/nature11412 . Comprehensive molecular portraits of human breast tumours S Cascio , A D'Andrea , R Ferla , 等 . miR-20b modulates VEGF expression by targeting HIF-1α and STAT3 in MCF-7 breast cancer cells . J Cell Physiol , 2010 . 224 ( 1 ): 242 - 249 . 20232316 DOI: 10.1002/jcp.22126 http://doi.org/10.1002/jcp.22126 . miR-20b modulates VEGF expression by targeting HIF-1α and STAT3 in MCF-7 breast cancer cells CL Chaffer , RA Weinberg . A perspective on cancer cell metastasis . Science , 2011 . 331 ( 6024 ): 1559 - 1564 . 21436443 DOI: 10.1126/science.1203543 http://doi.org/10.1126/science.1203543 . A perspective on cancer cell metastasis P Chaturvedi , DM Gilkes , CC Wong , 等 . Hypoxia-inducible factor-dependent breast cancer-mesenchymal stem cell bidirectional signaling promotes metastasis . J Clin Invest , 2013 . 123 ( 1 ): 189 - 205 . 23318994 DOI: 10.1172/JCI64993 http://doi.org/10.1172/JCI64993 . Hypoxia-inducible factor-dependent breast cancer-mesenchymal stem cell bidirectional signaling promotes metastasis MW Conklin , JC Eickhoff , KM Riching , 等 . Aligned collagen is a prognostic signature for survival in human breast carcinoma . Am J Pathol , 2011 . 178 ( 3 ): 1221 - 1232 . 21356373 DOI: 10.1016/j.ajpath.2010.11.076 http://doi.org/10.1016/j.ajpath.2010.11.076 . Aligned collagen is a prognostic signature for survival in human breast carcinoma CJ Creighton , JC Chang , JM Rosen . Epithelial-mesenchymal transition (EMT) in tumor-initiating cells and its clinical implications in breast cancer . J Mammary Gland Biol Neopl , 2010 . 15 ( 2 ): 253 - 260 . DOI: 10.1007/s10911-010-9173-1 http://doi.org/10.1007/s10911-010-9173-1 . Epithelial-mesenchymal transition (EMT) in tumor-initiating cells and its clinical implications in breast cancer FM Davis , I Azimi , RA Faville , 等 . Induction of epithelial-mesenchymal transition (EMT) in breast cancer cells is calcium signal dependent . Oncogene , 2014 . 33 ( 18 ): 2307 - 2316 . 23686305 DOI: 10.1038/onc.2013.187 http://doi.org/10.1038/onc.2013.187 . Induction of epithelial-mesenchymal transition (EMT) in breast cancer cells is calcium signal dependent WW Du , L Fang , M Li , 等 . MicroRNA miR-24 enhances tumor invasion and metastasis by targeting PTPN9 and PTPRF to promote EGF signaling . J Cell Sci , 2013 . 126 ( 6 ): 1440 - 1453 . 23418360 DOI: 10.1242/jcs.118299 http://doi.org/10.1242/jcs.118299 . MicroRNA miR-24 enhances tumor invasion and metastasis by targeting PTPN9 and PTPRF to promote EGF signaling MJ Duffy , TM Maguire , A Hill , 等 . Metalloproteinases: role in breast carcinogenesis, invasion and metastasis . Breast Cancer Res , 2000 . 2 ( 4 ): 252 - 257 . 11250717 DOI: 10.1186/bcr65 http://doi.org/10.1186/bcr65 . Metalloproteinases: role in breast carcinogenesis, invasion and metastasis JT Erler , KL Bennewith , M Nicolau , 等 . Lysyl oxidase is essential for hypoxia-induced metastasis . Nature , 2006 . 440 ( 7088 ): 1222 - 1226 . 16642001 DOI: 10.1038/nature04695 http://doi.org/10.1038/nature04695 . Lysyl oxidase is essential for hypoxia-induced metastasis JT Erler , KL Bennewith , TR Cox , 等 . Hypoxia-induced lysyl oxidase is a critical mediator of bone marrow cell recruitment to form the premetastatic niche . Cancer Cell , 2009 . 15 ( 1 ): 35 - 44 . 19111879 DOI: 10.1016/j.ccr.2008.11.012 http://doi.org/10.1016/j.ccr.2008.11.012 . Hypoxia-induced lysyl oxidase is a critical mediator of bone marrow cell recruitment to form the premetastatic niche D Feldser , F Agani , NV Iyer , 等 . Reciprocal positive regulation of hypoxia-inducible factor 1α and insulin-like growth factor 2 . Cancer Res , 1999 . 59 ( 16 ): 3915 - 3918 . 10463582 . Reciprocal positive regulation of hypoxia-inducible factor 1α and insulin-like growth factor 2 IJ Fidler . Metastasis: quantitative analysis of distribution and fate of tumor emboli labeled with 125 I-5-iodo-2'-deoxyuridine . J Natl Cancer Inst , 1970 . 45 ( 4 ): 773 - 782 . 5513503 . Metastasis: quantitative analysis of distribution and fate of tumor emboli labeled with 125I-5-iodo-2'-deoxyuridine N Fukuda , M Nakayama , T Jian , 等 . Leukocyte angiotensin II levels in patients with essential hypertension: relation to insulin resistance . Am J Hypertens , 2003 . 16 ( 2 ): 129 - 134 . 12559679 DOI: 10.1016/S0895-7061(02)03145-X http://doi.org/10.1016/S0895-7061(02)03145-X . Leukocyte angiotensin II levels in patients with essential hypertension: relation to insulin resistance R Fukuda , K Hirota , F Fan , 等 . Insulin-like growth factor 1 induces hypoxia-inducible factor 1-mediated vascular endothelial growth factor expression, which is dependent on MAP kinase and phosphatidylinositol 3-kinase signaling in colon cancer cells . J Biol Chem , 2002 . 277 ( 41 ): 38205 - 38211 . 12149254 DOI: 10.1074/jbc.M203781200 http://doi.org/10.1074/jbc.M203781200 . Insulin-like growth factor 1 induces hypoxia-inducible factor 1-mediated vascular endothelial growth factor expression, which is dependent on MAP kinase and phosphatidylinositol 3-kinase signaling in colon cancer cells R Fukuda , HF Zhang , JW Kim , 等 . HIF-1 regulates cytochrome oxidase subunits to optimize efficiency of respiration in hypoxic cells . Cell , 2007 . 129 ( 1 ): 111 - 122 . 17418790 DOI: 10.1016/j.cell.2007.01.047 http://doi.org/10.1016/j.cell.2007.01.047 . HIF-1 regulates cytochrome oxidase subunits to optimize efficiency of respiration in hypoxic cells P Gao , HF Zhang , R Dinavahi , 等 . HIF-dependent antitumorigenic effect of antioxidants in vivo . Cancer Cell , 2007 . 12 ( 3 ): 230 - 238 . 17785204 DOI: 10.1016/j.ccr.2007.08.004 http://doi.org/10.1016/j.ccr.2007.08.004 . HIF-dependent antitumorigenic effect of antioxidants in vivo D Generali , A Berruti , MP Brizzi , 等 . Hypoxia-inducible factor-1α-expression predicts a poor response to primary chemoendocrine therapy and disease-free survival in primary human breast cancer . Clin Cancer Res , 2006 . 12 ( 15 ): 4562 - 4568 . 16899602 DOI: 10.1158/1078-0432.CCR-05-2690 http://doi.org/10.1158/1078-0432.CCR-05-2690 . Hypoxia-inducible factor-1α-expression predicts a poor response to primary chemoendocrine therapy and disease-free survival in primary human breast cancer DM Gilkes , S Bajpai , P Chaturvedi , 等 . Hypoxia-inducible factor 1 (HIF-1) promotes extracellular matrix remodeling under hypoxic conditions by inducing P4HA1, P4HA2, and PLOD2 expression in fibroblasts . J Biol Chem , 2013 . 288 ( 15 ): 10819 - 10829 . 23423382 DOI: 10.1074/jbc.M112.442939 http://doi.org/10.1074/jbc.M112.442939 . Hypoxia-inducible factor 1 (HIF-1) promotes extracellular matrix remodeling under hypoxic conditions by inducing P4HA1, P4HA2, and PLOD2 expression in fibroblasts DM Gilkes , S Bajpai , CC Wong , 等 . Procollagen lysyl hydroxylase 2 is essential for hypoxia-induced breast cancer metastasis . Mol Cancer Res , 2013 . 11 ( 5 ): 456 - 466 . 23378577 DOI: 10.1158/1541-7786.MCR-12-0629 http://doi.org/10.1158/1541-7786.MCR-12-0629 . Procollagen lysyl hydroxylase 2 is essential for hypoxia-induced breast cancer metastasis DM Gilkes , P Chaturvedi , S Bajpai , 等 . Collagen prolyl hydroxylases are essential for breast cancer metastasis . Cancer Res , 2013 . 73 ( 11 ): 3285 - 3296 . 23539444 DOI: 10.1158/0008-5472.CAN-12-3963 http://doi.org/10.1158/0008-5472.CAN-12-3963 . Collagen prolyl hydroxylases are essential for breast cancer metastasis MJ Grimshaw . Endothelins and hypoxia-inducible factor in cancer . Endocr Rel Cancer , 2007 . 14 ( 2 ): 233 - 244 . DOI: 10.1677/ERC-07-0057 http://doi.org/10.1677/ERC-07-0057 . Endothelins and hypoxia-inducible factor in cancer G Gruber , RH Greiner , R Hlushchuk , 等 . Hypoxia-inducible factor 1α in high-risk breast cancer: an independent prognostic parameter? . Breast Cancer Res , 2004 . 6 ( 3 ): R191 - R198 . 15084243 DOI: 10.1186/bcr775 http://doi.org/10.1186/bcr775 . Hypoxia-inducible factor 1α in high-risk breast cancer: an independent prognostic parameter? I Haque , S Banerjee , S Mehta , 等 . Cysteine-rich 61-connective tissue growth factor-nephroblastoma-overexpressed 5 (CCN5)/Wnt-1-induced signaling protein-2 (WISP-2) regulates microRNA-10b via hypoxia-inducible factor-1α-TWIST signaling networks in human breast cancer cells . J Biol Chem , 2011 . 286 ( 50 ): 43475 - 43485 . 22020939 DOI: 10.1074/jbc.M111.284158 http://doi.org/10.1074/jbc.M111.284158 . Cysteine-rich 61-connective tissue growth factor-nephroblastoma-overexpressed 5 (CCN5)/Wnt-1-induced signaling protein-2 (WISP-2) regulates microRNA-10b via hypoxia-inducible factor-1α-TWIST signaling networks in human breast cancer cells RP Hill , DT Marie-Egyptienne , DW Hedley . Cancer stem cells, hypoxia and metastasis . Semin Radiat Oncol , 2009 . 19 ( 2 ): 106 - 111 . 19249648 DOI: 10.1016/j.semradonc.2008.12.002 http://doi.org/10.1016/j.semradonc.2008.12.002 . Cancer stem cells, hypoxia and metastasis P Hohenberger , C Felgner , W Haensch , 等 . Tumor oxygenation correlates with molecular growth determinants in breast cancer . Breast Cancer Res Treat , 1998 . 48 ( 2 ): 97 - 106 . 9596481 DOI: 10.1023/A:1005921513083 http://doi.org/10.1023/A:1005921513083 . Tumor oxygenation correlates with molecular growth determinants in breast cancer N Horrée , PJ van Diest , MDSG Daisy , 等 . The invasive front in endometrial carcinoma: higher proliferation and associated derailment of cell cycle regulators . Human Pathol , 2007 . 38 ( 8 ): 1232 - 1238 . DOI: 10.1016/j.humpath.2007.01.008 http://doi.org/10.1016/j.humpath.2007.01.008 . The invasive front in endometrial carcinoma: higher proliferation and associated derailment of cell cycle regulators P Hou , Y Zhao , Z Li , 等 . lincRNA-RoR induces epithelial-to-mesenchymal transition and contributes to breast cancer tumorigenesis and metastasis . Cell Death Dis , 2014 . 5 ( 6 ): e1287 24922071 DOI: 10.1038/cddis.2014.249 http://doi.org/10.1038/cddis.2014.249 . lincRNA-RoR induces epithelial-to-mesenchymal transition and contributes to breast cancer tumorigenesis and metastasis M Hu , K Polyak . Microenvironmental regulation of cancer development . Curr Opin Genet Dev , 2008 . 18 ( 1 ): 27 - 34 . 18282701 DOI: 10.1016/j.gde.2007.12.006 http://doi.org/10.1016/j.gde.2007.12.006 . Microenvironmental regulation of cancer development J Huang , N Zhou , K Watabe , 等 . Long non-coding RNA UCA1 promotes breast tumor growth by suppression of p27 (Kip1) . Cell Death Dis , 2014 . 5 ( 1 ): e1008 24457952 DOI: 10.1038/cddis.2013.541 http://doi.org/10.1038/cddis.2013.541 . Long non-coding RNA UCA1 promotes breast tumor growth by suppression of p27 (Kip1) RL Huang , ZQ Teo , HC Chong , 等 . ANGPTL4 modulates vascular junction integrity by integrin signaling and disruption of intercellular VE-cadherin and claudin-5 clusters . Blood , 2011 . 118 ( 14 ): 3990 - 4002 . 21841165 DOI: 10.1182/blood-2011-01-328716 http://doi.org/10.1182/blood-2011-01-328716 . ANGPTL4 modulates vascular junction integrity by integrin signaling and disruption of intercellular VE-cadherin and claudin-5 clusters HJ Hugo , L Pereira , R Suryadinata , 等 . Direct repression of MYB by ZEB1 suppresses proliferation and epithelial gene expression during epithelial-to-mesenchymal transition of breast cancer cells . Breast Cancer Res , 2013 . 15 ( 6 ): R113 24283570 DOI: 10.1186/bcr3580 http://doi.org/10.1186/bcr3580 . Direct repression of MYB by ZEB1 suppresses proliferation and epithelial gene expression during epithelial-to-mesenchymal transition of breast cancer cells WW Hwang-Verslues , PH Chang , PC Wei , 等 . miR-495 is upregulated by E12/E47 in breast cancer stem cells, and promotes oncogenesis and hypoxia resistance via downregulation of E-cadherin and REDD1 . Oncogene , 2011 . 30 ( 21 ): 2463 - 2474 . 21258409 DOI: 10.1038/onc.2010.618 http://doi.org/10.1038/onc.2010.618 . miR-495 is upregulated by E12/E47 in breast cancer stem cells, and promotes oncogenesis and hypoxia resistance via downregulation of E-cadherin and REDD1 L Incorvaia , G Badalamenti , G Rini , 等 . MMP-2, MMP-9 and activin A blood levels in patients with breast cancer or prostate cancer metastatic to the bone . Anticancer Res , 2007 . 27 ( 3B ): 1519 - 1525 . 17595770 . MMP-2, MMP-9 and activin A blood levels in patients with breast cancer or prostate cancer metastatic to the bone A Jemal , F Bray , MM Center , 等 . Global cancer statistics . CA Cancer J Clin , 2011 . 61 ( 2 ): 69 - 90 . 21296855 DOI: 10.3322/caac.20107 http://doi.org/10.3322/caac.20107 . Global cancer statistics FY Jin , U Brockmeier , F Otterbach , 等 . New insight into the SDF-1/CXCR4 axis in a breast carcinoma model: hypoxia-induced endothelial SDF-1 and tumor cell CXCR4 are required for tumor cell intravasation . Mol Cancer Res , 2012 . 10 ( 8 ): 1021 - 1031 . 22767589 DOI: 10.1158/1541-7786.MCR-11-0498 http://doi.org/10.1158/1541-7786.MCR-11-0498 . New insight into the SDF-1/CXCR4 axis in a breast carcinoma model: hypoxia-induced endothelial SDF-1 and tumor cell CXCR4 are required for tumor cell intravasation M Jo , RD Lester , V Montel , 等 . Reversibility of epithelial-mesenchymal transition (EMT) induced in breast cancer cells by activation of urokinase receptor-dependent cell signaling . J Biol Chem , 2009 . 284 ( 34 ): 22825 - 22833 . 19546228 DOI: 10.1074/jbc.M109.023960 http://doi.org/10.1074/jbc.M109.023960 . Reversibility of epithelial-mesenchymal transition (EMT) induced in breast cancer cells by activation of urokinase receptor-dependent cell signaling R Kalluri , RA Weinberg . The basics of epithelial-mesenchymal transition . J Clin Invest , 2009 . 119 ( 6 ): 1420 - 1428 . 19487818 DOI: 10.1172/JCI39104 http://doi.org/10.1172/JCI39104 . The basics of epithelial-mesenchymal transition HG Kaplan , JA Malmgren , M Atwood . Tumor size, age and stage in patient detected breast cancer . J Clin Oncol , 2005 . 23 ( 16 ): 716 . Tumor size, age and stage in patient detected breast cancer K Kasuno , S Takabuchi , K Fukuda , 等 . Nitric oxide induces hypoxia-inducible factor 1 activation that is dependent on MAPK and phosphatidylinositol 3-kinase signaling . J Biol Chem , 2004 . 279 ( 4 ): 2550 - 2558 . 14600153 DOI: 10.1074/jbc.M308197200 http://doi.org/10.1074/jbc.M308197200 . Nitric oxide induces hypoxia-inducible factor 1 activation that is dependent on MAPK and phosphatidylinositol 3-kinase signaling I Keklikoglou , C Koerner , C Schmidt , 等 . MicroRNA-520/373 family functions as a tumor suppressor in estrogen receptor negative breast cancer by targeting NF-κB and TGF-β signaling pathways . Oncogene , 2012 . 31 ( 37 ): 4150 - 4163 . 22158050 DOI: 10.1038/onc.2011.571 http://doi.org/10.1038/onc.2011.571 . MicroRNA-520/373 family functions as a tumor suppressor in estrogen receptor negative breast cancer by targeting NF-κB and TGF-β signaling pathways JW Kim , I Tchernyshyov , GL Semenza , 等 . HIF-1-mediated expression of pyruvate dehydrogenase kinase: a metabolic switch required for cellular adaptation to hypoxia . Cell Metab , 2006 . 3 ( 3 ): 177 - 185 . 16517405 DOI: 10.1016/j.cmet.2006.02.002 http://doi.org/10.1016/j.cmet.2006.02.002 . HIF-1-mediated expression of pyruvate dehydrogenase kinase: a metabolic switch required for cellular adaptation to hypoxia M Krieg , R Haas , H Brauch , 等 . Up-regulation of hypoxia-inducible factors HIF-1α and HIF-2α under normoxic conditions in renal carcinoma cells by von Hippel-Lindau tumor suppressor gene loss of function . Oncogene , 2000 . 19 ( 48 ): 5435 - 5443 . 11114720 DOI: 10.1038/sj.onc.1203938 http://doi.org/10.1038/sj.onc.1203938 . Up-regulation of hypoxia-inducible factors HIF-1α and HIF-2α under normoxic conditions in renal carcinoma cells by von Hippel-Lindau tumor suppressor gene loss of function B Krishnamachary , D Zagzag , H Nagasawa , 等 . Hypoxia-inducible factor-1-dependent repression of E-cadherin in von Hippel-Lindau tumor suppressor-null renal cell carcinoma mediated by TCF3, ZFHX1A, and ZFHX1B . Cancer Res , 2006 . 66 ( 5 ): 2725 - 2731 . 16510593 DOI: 10.1158/0008-5472.CAN-05-3719 http://doi.org/10.1158/0008-5472.CAN-05-3719 . Hypoxia-inducible factor-1-dependent repression of E-cadherin in von Hippel-Lindau tumor suppressor-null renal cell carcinoma mediated by TCF3, ZFHX1A, and ZFHX1B R Kulshreshtha , M Ferracin , SE Wojcik , 等 . A microRNA signature of hypoxia . Mol Cell Biol , 2007 . 27 ( 5 ): 1859 - 1867 . 17194750 DOI: 10.1128/MCB.01395-06 http://doi.org/10.1128/MCB.01395-06 . A microRNA signature of hypoxia D Lando , DJ Peet , DA Whelan , 等 . Asparagine hydroxylation of the HIF transactivation domain: a hypoxic switch . Science , 2002 . 295 ( 5556 ): 858 - 861 . 11823643 DOI: 10.1126/science.1068592 http://doi.org/10.1126/science.1068592 . Asparagine hydroxylation of the HIF transactivation domain: a hypoxic switch E Laughner , P Taghavi , K Chiles , 等 . Her2 (neu) signaling increases the rate of hypoxia-inducible factor 1 alpha (HIF-1α) synthesis: novel mechanism for HIF-1-mediated vascular endothelial growth factor expression . Mol Cell Biol , 2001 . 21 ( 12 ): 3995 - 4004 . 11359907 DOI: 10.1128/MCB.21.12.3995-4004.2001 http://doi.org/10.1128/MCB.21.12.3995-4004.2001 . Her2 (neu) signaling increases the rate of hypoxia-inducible factor 1 alpha (HIF-1α) synthesis: novel mechanism for HIF-1-mediated vascular endothelial growth factor expression R Lech , O Przemyslaw . Epidemiological models for breast cancer risk estimation . Ginekol Pol , 2011 . 82 ( 6 ): 451 - 454 . 21853936 . Epidemiological models for breast cancer risk estimation HS Lee , EY Seo , NE Kang , 等 . [6]-Gingerol inhibits metastasis of MDA-MB-231 human breast cancer cells . J Nutr Biochem , 2008 . 19 ( 5 ): 313 - 319 . 17683926 DOI: 10.1016/j.jnutbio.2007.05.008 http://doi.org/10.1016/j.jnutbio.2007.05.008 . [6]-Gingerol inhibits metastasis of MDA-MB-231 human breast cancer cells JY Li , Y Zhang , WH Zhang , 等 . Differential distribution of miR-20a and miR-20b may underly metastatic heterogeneity of breast cancers . Asian Pac J Cancer Prev , 2012 . 13 ( 5 ): 1901 - 1906 . 22901144 DOI: 10.7314/APJCP.2012.13.5.1901 http://doi.org/10.7314/APJCP.2012.13.5.1901 . Differential distribution of miR-20a and miR-20b may underly metastatic heterogeneity of breast cancers X Li , X Liu , W Xu , 等 . c-MYC-regulated miR-23a/24-2/27a cluster promotes mammary carcinoma cell invasion and hepatic metastasis by targeting Sprouty2 . J Biol Chem , 2013 . 288 ( 25 ): 18121 - 18133 . 23649631 DOI: 10.1074/jbc.M113.478560 http://doi.org/10.1074/jbc.M113.478560 . c-MYC-regulated miR-23a/24-2/27a cluster promotes mammary carcinoma cell invasion and hepatic metastasis by targeting Sprouty2 H Ling , M Fabbri , GA Calin . MicroRNAs and other non-coding RNAs as targets for anticancer drug development . Nat Rev Drug Disc , 2013 . 12 ( 11 ): 847 - 865 . DOI: 10.1038/nrd4140 http://doi.org/10.1038/nrd4140 . MicroRNAs and other non-coding RNAs as targets for anticancer drug development XH Liu , A Kirschenbaum , M Lu , 等 . Prostaglandin E 2 induces hypoxia-inducible factor-1α stabilization and nuclear localization in a human prostate cancer cell line . J Biol Chem , 2002 . 277 ( 51 ): 50081 - 50086 . 12401798 DOI: 10.1074/jbc.M201095200 http://doi.org/10.1074/jbc.M201095200 . Prostaglandin E2 induces hypoxia-inducible factor-1α stabilization and nuclear localization in a human prostate cancer cell line F Loayza-Puch , Y Yoshida , T Matsuzaki , 等 . Hypoxia and RAS-signaling pathways converge on, and cooperatively downregulate, the RECK tumor-suppressor protein through microRNAs . Oncogene , 2010 . 29 ( 18 ): 2638 - 2648 . 20154725 DOI: 10.1038/onc.2010.23 http://doi.org/10.1038/onc.2010.23 . Hypoxia and RAS-signaling pathways converge on, and cooperatively downregulate, the RECK tumor-suppressor protein through microRNAs FE Lock , PC Mcdonald , Y Lou , 等 . Targeting carbonic anhydrase IX depletes breast cancer stem cells within the hypoxic niche . Oncogene , 2013 . 32 ( 44 ): 5210 - 5219 . 23208505 DOI: 10.1038/onc.2012.550 http://doi.org/10.1038/onc.2012.550 . Targeting carbonic anhydrase IX depletes breast cancer stem cells within the hypoxic niche K Lundgren , C Holm , G Landberg . Hypoxia and breast cancer: prognostic and therapeutic implications . Cell Mol Life Sci , 2007 . 64 ( 24 ): 3233 - 3247 . 17957335 DOI: 10.1007/s00018-007-7390-6 http://doi.org/10.1007/s00018-007-7390-6 . Hypoxia and breast cancer: prognostic and therapeutic implications L Ma , J Teruya-Feldstein , RA Weinberg . Tumour invasion and metastasis initiated by microRNA-10b in breast cancer . Nature , 2007 . 449 ( 7163 ): 682 - 688 . 17898713 DOI: 10.1038/nature06174 http://doi.org/10.1038/nature06174 . Tumour invasion and metastasis initiated by microRNA-10b in breast cancer L Ma , F Reinhardt , E Pan , 等 . Therapeutic silencing of miR-10b inhibits metastasis in a mouse mammary tumor model . Nat Biotechnol , 2010 . 28 ( 4 ): 341 - 347 . 20351690 DOI: 10.1038/nbt.1618 http://doi.org/10.1038/nbt.1618 . Therapeutic silencing of miR-10b inhibits metastasis in a mouse mammary tumor model E Maglione , LS Ferreira , G Cattapan . Asymptotic properties of bound states in coupled quantum wave guides . J Phys A Math General , 2006 . 39 ( 5 ): 1207 - 1228 . DOI: 10.1088/0305-4470/39/5/013 http://doi.org/10.1088/0305-4470/39/5/013 . Asymptotic properties of bound states in coupled quantum wave guides PC Mahon , K Hirota , GL Semenza . FIH-1: a novel protein that interacts with HIF-1α and VHL to mediate repression of HIF-1 transcriptional activity . Genes Devel , 2001 . 15 ( 20 ): 2675 - 2686 . 11641274 DOI: 10.1101/gad.924501 http://doi.org/10.1101/gad.924501 . FIH-1: a novel protein that interacts with HIF-1α and VHL to mediate repression of HIF-1 transcriptional activity IJ Matouk , N Degroot , S Mezan , 等 . The H19 non-coding RNA is essential for human tumor growth . PLoS ONE , 2007 . 2 ( 9 ): e845 17786216 DOI: 10.1371/journal.pone.0000845 http://doi.org/10.1371/journal.pone.0000845 . The H19 non-coding RNA is essential for human tumor growth IJ Matouk , S Mezan , A Mizrahi , 等 . The oncofetal H19 RNA connection: hypoxia, p53 and cancer . BBA Mol Cell Res , 2010 . 1803 ( 4 ): 443 - 451 . DOI: 10.1016/j.bbamcr.2010.01.010 http://doi.org/10.1016/j.bbamcr.2010.01.010 . The oncofetal H19 RNA connection: hypoxia, p53 and cancer IJ Matouk , E Raveh , R Abu-Lail , 等 . Oncofetal H19 RNA promotes tumor metastasis . BBA Mol Cell Res , 2014 . 1843 ( 7 ): 1414 - 1426 . DOI: 10.1016/j.bbamcr.2014.03.023 http://doi.org/10.1016/j.bbamcr.2014.03.023 . Oncofetal H19 RNA promotes tumor metastasis CD May , N Sphyris , KW Evans , 等 . Epithelial-mesenchymal transition and cancer stem cells: a dangerously dynamic duo in breast cancer progression . Breast Cancer Res , 2011 . 13 ( 1 ): 202 21392411 DOI: 10.1186/bcr2789 http://doi.org/10.1186/bcr2789 . Epithelial-mesenchymal transition and cancer stem cells: a dangerously dynamic duo in breast cancer progression G Mees , R Dierckx , C Vangestel , 等 . Molecular imaging of hypoxia with radiolabelled agents . Eur J Nucl Med Mol Imag , 2009 . 36 ( 10 ): 1674 - 1686 . DOI: 10.1007/s00259-009-1195-9 http://doi.org/10.1007/s00259-009-1195-9 . Molecular imaging of hypoxia with radiolabelled agents G Moreno-Bueno , F Portillo , A Cano . Transcriptional regulation of cell polarity in EMT and cancer . Oncogene , 2008 . 27 ( 55 ): 6958 - 6969 . 19029937 DOI: 10.1038/onc.2008.346 http://doi.org/10.1038/onc.2008.346 . Transcriptional regulation of cell polarity in EMT and cancer UM Munoz-Najar , KM Neurath , F Vumbaca , 等 . Hypoxia stimulates breast carcinoma cell invasion through MT1-MMP and MMP-2 activation . Oncogene , 2006 . 25 ( 16 ): 2379 - 2392 . 16369494 DOI: 10.1038/sj.onc.1209273 http://doi.org/10.1038/sj.onc.1209273 . Hypoxia stimulates breast carcinoma cell invasion through MT1-MMP and MMP-2 activation D Padua , XHF Zhang , QQ Wang , 等 . TGF-β primes breast tumors for lung metastasis seeding through angiopoietin-like 4 . Cell , 2008 . 133 ( 1 ): 66 - 77 . 18394990 DOI: 10.1016/j.cell.2008.01.046 http://doi.org/10.1016/j.cell.2008.01.046 . TGF-β primes breast tumors for lung metastasis seeding through angiopoietin-like 4 B Philip , K Ito , R Moreno-Sanchez , 等 . HIF expression and the role of hypoxic microenvironments within primary tumours as protective sites driving cancer stem cell renewal and metastatic progression . Carcinogenesis , 2013 . 34 ( 8 ): 1699 - 1707 . 23740838 DOI: 10.1093/carcin/bgt209 http://doi.org/10.1093/carcin/bgt209 . HIF expression and the role of hypoxic microenvironments within primary tumours as protective sites driving cancer stem cell renewal and metastatic progression SC Pritchard , MC Nicolson , C Lloret , 等 . Expression of matrix metalloproteinases 1, 2, 9 and their tissue inhibitors in stage II non-small cell lung cancer: implications for MMP inhibition therapy . Oncol Rep , 2001 . 8 ( 2 ): 421 - 424 . 11182067 . Expression of matrix metalloproteinases 1, 2, 9 and their tissue inhibitors in stage II non-small cell lung cancer: implications for MMP inhibition therapy PP Provenzano , KW Eliceiri , JM Campbell , 等 . Collagen reorganization at the tumor-stromal interface facilitates local invasion . BMC Med , 2006 . 4 ( 1 ): 38 17190588 DOI: 10.1186/1741-7015-4-38 http://doi.org/10.1186/1741-7015-4-38 . Collagen reorganization at the tumor-stromal interface facilitates local invasion M Quintero , PA Brennan , GJ Thomas , 等 . Nitric oxide is a factor in the stabilization of hypoxia-inducible factor-1α in cancer: role of free radical formation . Cancer Res , 2006 . 66 ( 2 ): 770 - 774 . 16424008 DOI: 10.1158/0008-5472.CAN-05-0333 http://doi.org/10.1158/0008-5472.CAN-05-0333 . Nitric oxide is a factor in the stabilization of hypoxia-inducible factor-1α in cancer: role of free radical formation D Ravi , K Ramadas , BS Mathew , 等 . Apoptosis, angiogenesis and proliferation: trifunctional measure of tumour response to radiotherapy for oral cancer . Oral Oncol , 2001 . 37 ( 2 ): 164 - 171 . 11167144 DOI: 10.1016/S1368-8375(00)00082-8 http://doi.org/10.1016/S1368-8375(00)00082-8 . Apoptosis, angiogenesis and proliferation: trifunctional measure of tumour response to radiotherapy for oral cancer C Rose , O Vtoraya , A Pluzanska , 等 . An open randomised trial of second-line endocrine therapy in advanced breast cancer. Comparison of the aromatase inhibitors letrozole and anastrozole . Eur J Cancer , 2003 . 39 ( 16 ): 2318 - 2327 . 14556923 DOI: 10.1016/S0959-8049(03)00630-0 http://doi.org/10.1016/S0959-8049(03)00630-0 . An open randomised trial of second-line endocrine therapy in advanced breast cancer. Comparison of the aromatase inhibitors letrozole and anastrozole F Rothé , M Ignatiadis , C Chaboteaux , 等 . Global microRNA expression profiling identifies miR-210 associated with tumor proliferation, invasion and poor clinical outcome in breast cancer . PLoS ONE , 2011 . 6 ( 6 ): e20980 21738599 DOI: 10.1371/journal.pone.0020980 http://doi.org/10.1371/journal.pone.0020980 . Global microRNA expression profiling identifies miR-210 associated with tumor proliferation, invasion and poor clinical outcome in breast cancer J Sceneay , MT Chow , A Chen , 等 . Primary tumor hypoxia recruits CD11b + /Ly6C med /Ly6G + immune suppressor cells and compromises NK cell cytotoxicity in the premetastatic niche . Cancer Res , 2012 . 72 ( 16 ): 3906 - 3911 . 22751463 DOI: 10.1158/0008-5472.CAN-11-3873 http://doi.org/10.1158/0008-5472.CAN-11-3873 . Primary tumor hypoxia recruits CD11b+/Ly6Cmed/Ly6G+ immune suppressor cells and compromises NK cell cytotoxicity in the premetastatic niche L Schito , S Rey , M Tafani , 等 . Hypoxia-inducible factor 1-dependent expression of platelet-derived growth factor b promotes lymphatic metastasis of hypoxic breast cancer cells . PNAS , 2012 . 109 ( 40 ): E2707 - E2716 . 23012449 DOI: 10.1073/pnas.1214019109 http://doi.org/10.1073/pnas.1214019109 . Hypoxia-inducible factor 1-dependent expression of platelet-derived growth factor b promotes lymphatic metastasis of hypoxic breast cancer cells GL Semenza . Targeting HIF-1 for cancer therapy . Nat Rev Cancer , 2003 . 3 ( 10 ): 721 - 732 . 13130303 DOI: 10.1038/nrc1187 http://doi.org/10.1038/nrc1187 . Targeting HIF-1 for cancer therapy GL Semenza . Oxygen sensing, homeostasis, and disease reply . N Engl J Med , 2011 . 365 ( 19 ): 537 - 547 . 21830968 DOI: 10.1056/NEJMra1011165 http://doi.org/10.1056/NEJMra1011165 . Oxygen sensing, homeostasis, and disease reply GL Semenza . Hypoxia-inducible factors: mediators of cancer progression and targets for cancer therapy . Trends Pharmacol Sci , 2012 . 33 ( 4 ): 207 - 214 . 22398146 DOI: 10.1016/j.tips.2012.01.005 http://doi.org/10.1016/j.tips.2012.01.005 . Hypoxia-inducible factors: mediators of cancer progression and targets for cancer therapy A Singh , J Settleman . EMT, cancer stem cells and drug resistance: an emerging axis of evil in the war on cancer . Oncogene , 2010 . 29 ( 34 ): 4741 - 4751 . 20531305 DOI: 10.1038/onc.2010.215 http://doi.org/10.1038/onc.2010.215 . EMT, cancer stem cells and drug resistance: an emerging axis of evil in the war on cancer K Takahashi , IK Yan , H Haga , 等 . The hypoxia-induced long non-coding RNA linc-RoR modulates tumor cell resistance to hypoxia by an extra-cellular vesicle mediated regulation of hypoxia-signaling pathways in hepatocellular cancer . Hepatology , 2013 . 58 1067A . The hypoxia-induced long non-coding RNA linc-RoR modulates tumor cell resistance to hypoxia by an extra-cellular vesicle mediated regulation of hypoxia-signaling pathways in hepatocellular cancer KL Talks , H Turley , KC Gatter , 等 . The expression and distribution of the hypoxia-inducible factors HIF-1α and HIF-2α in normal human tissues, cancers, and tumor-associated macrophages . Am J Pathol , 2000 . 157 ( 2 ): 411 - 421 . 10934146 DOI: 10.1016/S0002-9440(10)64554-3 http://doi.org/10.1016/S0002-9440(10)64554-3 . The expression and distribution of the hypoxia-inducible factors HIF-1α and HIF-2α in normal human tissues, cancers, and tumor-associated macrophages JP Thiery . Epithelial-mesenchymal transitions in tumour progression . Nat Rev Cancer , 2002 . 2 ( 6 ): 442 - 454 . 12189386 DOI: 10.1038/nrc822 http://doi.org/10.1038/nrc822 . Epithelial-mesenchymal transitions in tumour progression S Valastyan , RA Weinberg . Tumor metastasis: molecular insights and evolving paradigms . Cell , 2011 . 147 ( 2 ): 275 - 292 . 22000009 DOI: 10.1016/j.cell.2011.09.024 http://doi.org/10.1016/j.cell.2011.09.024 . Tumor metastasis: molecular insights and evolving paradigms P Vaupel , K Schlenger , C Knoop , 等 . Oxygenation of human tumors: evaluation of tissue oxygen distribution in breast cancers by computerized O 2 tension measurements . Cancer Res , 1991 . 51 ( 12 ): 3316 - 3322 . 2040005 . Oxygenation of human tumors: evaluation of tissue oxygen distribution in breast cancers by computerized O2 tension measurements P Vaupel , A Mayer , M Hockel . Tumor hypoxia and malignant progression . Meth Enzymol , 2004 . 381 335 - 354 . 15063685 DOI: 10.1016/S0076-6879(04)81023-1 http://doi.org/10.1016/S0076-6879(04)81023-1 . Tumor hypoxia and malignant progression P Vaupel , M Hockel , A Mayer . Detection and characterization of tumor hypoxia using pO 2 histography . Antioxid Redox Signal , 2007 . 9 ( 8 ): 1221 - 1235 . 17536958 DOI: 10.1089/ars.2007.1628 http://doi.org/10.1089/ars.2007.1628 . Detection and characterization of tumor hypoxia using pO2 histography S Volinia , M Galasso , ME Sana , 等 . Breast cancer signatures for invasiveness and prognosis defined by deep sequencing of microRNA . PNAS , 2012 . 109 ( 8 ): 3024 - 3029 . 22315424 DOI: 10.1073/pnas.1200010109 http://doi.org/10.1073/pnas.1200010109 . Breast cancer signatures for invasiveness and prognosis defined by deep sequencing of microRNA GL Wang , BH Jiang , EA Rue , 等 . Hypoxia-inducible factor-1 is a basic-helix-loop-helix-pas heterodimer regulated by cellular O 2 tension . PNAS , 1995 . 92 ( 12 ): 5510 - 5514 . 7539918 DOI: 10.1073/pnas.92.12.5510 http://doi.org/10.1073/pnas.92.12.5510 . Hypoxia-inducible factor-1 is a basic-helix-loop-helix-pas heterodimer regulated by cellular O2 tension B Weigelt , JL Peterse , LJ van't Veer . Breast cancer metastasis: markers and models . Nat Rev Cancer , 2005 . 5 ( 8 ): 591 - 602 . 16056258 DOI: 10.1038/nrc1670 http://doi.org/10.1038/nrc1670 . Breast cancer metastasis: markers and models CCL Wong , DM Gilkes , HF Zhang , 等 . Hypoxia-inducible factor 1 is a master regulator of breast cancer metastatic niche formation . PNAS , 2011 . 108 ( 39 ): 16369 - 16374 . 21911388 DOI: 10.1073/pnas.1113483108 http://doi.org/10.1073/pnas.1113483108 . Hypoxia-inducible factor 1 is a master regulator of breast cancer metastatic niche formation CCL Wong , H Zhang , DM Gilkes , 等 . Inhibitors of hypoxia-inducible factor 1 block breast cancer metastatic niche formation and lung metastasis . J Mol Med , 2012 . 90 ( 7 ): 803 - 815 . 22231744 DOI: 10.1007/s00109-011-0855-y http://doi.org/10.1007/s00109-011-0855-y . Inhibitors of hypoxia-inducible factor 1 block breast cancer metastatic niche formation and lung metastasis F Xing , H Okuda , M Watabe , 等 . Hypoxia-induced Jagged2 promotes breast cancer metastasis and self-renewal of cancer stem-like cells . Oncogene , 2011 . 30 ( 39 ): 4075 - 4086 . 21499308 DOI: 10.1038/onc.2011.122 http://doi.org/10.1038/onc.2011.122 . Hypoxia-induced Jagged2 promotes breast cancer metastasis and self-renewal of cancer stem-like cells M Xue , X Li , Z Li , 等 . Urothelial carcinoma associated 1 is a hypoxia-inducible factor-1α-targeted long noncoding RNA that enhances hypoxic bladder cancer cell proliferation, migration, and invasion . Tumour Biol , 2014 . 35 ( 7 ): 6901 - 6912 . 24737584 DOI: 10.1007/s13277-014-1925-x http://doi.org/10.1007/s13277-014-1925-x . Urothelial carcinoma associated 1 is a hypoxia-inducible factor-1α-targeted long noncoding RNA that enhances hypoxic bladder cancer cell proliferation, migration, and invasion H Zhang , P Gao , R Fukuda , 等 . HIF-1 inhibits mitochondrial biogenesis and cellular respiration in VHL-deficient renal cell carcinoma by repression of C-MYC activity . Cancer Cell , 2007 . 11 ( 5 ): 407 - 420 . 17482131 DOI: 10.1016/j.ccr.2007.04.001 http://doi.org/10.1016/j.ccr.2007.04.001 . HIF-1 inhibits mitochondrial biogenesis and cellular respiration in VHL-deficient renal cell carcinoma by repression of C-MYC activity H Zhang , DZ Qian , YS Tan , 等 . Digoxin and other cardiac glycosides inhibit HIF-1α synthesis and block tumor growth . PNAS , 2008 . 105 ( 50 ): 19579 - 19586 . 19020076 DOI: 10.1073/pnas.0809763105 http://doi.org/10.1073/pnas.0809763105 . Digoxin and other cardiac glycosides inhibit HIF-1α synthesis and block tumor growth H Zhang , CCL Wong , H Wei , 等 . HIF-1-dependent expression of angiopoietin-like 4 and L1CAM mediates vascular metastasis of hypoxic breast cancer cells to the lungs . Oncogene , 2012 . 31 ( 14 ): 1757 - 1770 . 21860410 DOI: 10.1038/onc.2011.365 http://doi.org/10.1038/onc.2011.365 . HIF-1-dependent expression of angiopoietin-like 4 and L1CAM mediates vascular metastasis of hypoxic breast cancer cells to the lungs H Zhong , AM de Marzo , E Laughner , 等 . Overexpression of hypoxia-inducible factor 1α in common human cancers and their metastases . Cancer Res , 1999 . 59 ( 22 ): 5830 - 5835 . 10582706 . Overexpression of hypoxia-inducible factor 1α in common human cancers and their metastases H Zhong , K Chiles , D Feldser , 等 . Modulation of hypoxia-inducible factor 1α expression by the epidermal growth factor/phosphatidylinositol 3-kinase/PTEN/AKT/FRAP pathway in human prostate cancer cells: implications for tumor angiogenesis and therapeutics . Cancer Res , 2000 . 60 ( 6 ): 1541 - 1545 . 10749120 . Modulation of hypoxia-inducible factor 1α expression by the epidermal growth factor/phosphatidylinositol 3-kinase/PTEN/AKT/FRAP pathway in human prostate cancer cells: implications for tumor angiogenesis and therapeutics W Zundel , C Schindler , D Haas-Kogan , 等 . Loss of PTEN facilitates HIF-1-mediated gene expression . Gene Devel , 2000 . 14 ( 4 ): 391 - 396 . . Loss of PTEN facilitates HIF-1-mediated gene expression Compliance with ethics guidelines Zhao-ji LIU, Gregg L. SEMENZA, and Hua-feng ZHANG declare that they have no conflict of interest. This article does not contain any studies with human or animal subjects performed by any of the authors. 10.1631/jzus.B1400221 Project supported partially by the National Basic Research Program (973) of China (Nos. 2014CB910604 and 2012CB910104), the National Natural Science Foundation of China (Nos. 31171358 and 31371429), the Research Fund for the Doctoral Program of Higher Education of China (No. 20133402110020), the Fundamental Research Funds for the Central Universities in China, and the ‘1000 Youth Talent Program’ by the Chinese Government for Hua-feng ZHANG 2014-08-11 2014-12-18 2014-11-06 2022-01-05 Copyright © Zhejiang University and Springer-Verlag Berlin Heidelberg 2015 2015 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 01 16