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1.  Molecular Pathways: Targeting MYC-induced Metabolic Reprogramming and Oncogenic Stress in Cancer 
MYC is a multi-functional transcription factor that is deregulated in many human cancers. MYC impacts a collaborative genetic program that orchestrates cell proliferation, metabolism, and stress responses. Although the progression of MYC-amplified tumors shows robust dependence on MYC activity, directly targeting MYC as a therapeutic method has proven to be technically difficult. Therefore, alternative approaches are currently under development with a focus on interference with MYC-mediated downstream effects. To fuel rapid cell growth, MYC reprograms cancer cell metabolism in a way that is substantially different from normal cells. The MYC-induced metabolic signature is characterized by enhanced glucose and glutamine uptake, increased lactate production, and altered amino acid metabolism. Targeting MYC-reprogrammed cancer cell metabolism is considered to be promising based on multiple preclinical studies. In addition, the increased biosynthetic demand of MYC-driven tumors coupled with limited nutrient access within tumor microenvironments create multiple levels of oncogenic stress, which can also be utilized as tumor-specific targets for pharmacological intervention. Presumably, the best therapeutic strategy for treating MYC-amplified tumors is combined targeting of multiple MYC-mediated pathways, especially those involved in regulating cell proliferation, metabolism, and oncogenic stress.
doi:10.1158/1078-0432.CCR-12-3629
PMCID: PMC3818456  PMID: 23897900
2.  Nutrient-sensing pathways and metabolic regulation in stem cells 
The Journal of Cell Biology  2013;203(1):23-33.
Stem cells exert precise regulation to maintain a balance of self-renewal and differentiation programs to sustain tissue homeostasis throughout the life of an organism. Recent evidence suggests that this regulation is modulated, in part, via metabolic changes and modifications of nutrient-sensing pathways such as mTOR and AMPK. It is becoming increasingly clear that stem cells inhibit oxidative phosphorylation in favor of aerobic glycolysis for energy production. Recent progress has detailed the molecular mechanisms of this metabolic phenotype and has offered insight into new metabolic pathways that may be involved in stem cell homeostasis.
doi:10.1083/jcb.201303110
PMCID: PMC3798256  PMID: 24127214
3.  MYC Degradation under Low O2 Tension Promotes Survival by Evading Hypoxia-Induced Cell Death 
Molecular and Cellular Biology  2013;33(17):3494-3504.
Cells encounter oxygen deprivation (hypoxia) in various physiological and pathological contexts. Adaptation to hypoxic stress occurs in part by suppressing MYC, a key regulator of cellular metabolism, proliferation, and survival. Hypoxia has been reported to inhibit MYC through multiple means, including disruption of MYC transcriptional complexes and decreased MYC protein abundance. Here we identify enhanced proteasomal degradation and cathepsin-mediated proteolysis as important mechanisms for hypoxic MYC inhibition in human colon carcinoma cells. MYC protein levels were similarly reduced in hypoxic primary keratinocytes. Increased MYC turnover at low O2 tension was dependent on the E3 ubiquitin ligases FBXW7 and DDB1, as well as hypoxic induction of cathepsins D and S. Reduced MYC protein levels coincided with hypoxic inhibition of RNA polymerase III-dependent MYC target genes, which MYC regulates independently of its binding partner MAX. Finally, MYC overexpression in hypoxic cells promoted cell cycle progression but also enhanced cell death via increased expression of the proapoptotic genes NOXA and PUMA. Collectively, these results indicate that hypoxic cells promote MYC degradation as an adaptive strategy to reduce proliferation, suppress biosynthetic processes, and promote cell survival under low O2 tension.
doi:10.1128/MCB.00853-12
PMCID: PMC3753854  PMID: 23816886
4.  Restricted expression of miR-30c-2-3p and miR-30a-3p in Clear Cell Renal Carcinomas enhances HIF2α activity 
Cancer discovery  2013;4(1):53-60.
Inactivation of the von-Hippel Lindau (VHL) tumor suppressor gene occurs in 90% of human clear cell renal cell carcinomas (ccRCC), and leads to the stable expression of the hypoxia inducible factors HIF1α and HIF2α. The constitutive expression of HIF1α in a majority of VHL-deficient tumors is counterintuitive, given that HIF1α functions as a tumor suppressor in ccRCC, whereas HIF2α clearly enhances tumor growth. We demonstrate here that miR-30c-2-3p and miR-30a-3p specifically bind and inhibit expression of HIF2α transcripts, and that the locus encoding miR-30c-2-3p and miR-30a-3p is selectively repressed in “H1H2” VHL-deficient tumors expressing both HIF1α and HIF2α proteins. Inhibiting miR-30a-3p expression increases HIF2α levels in H1H2 ccRCC cells, and promotes cellular proliferation, angiogenesis, and xenograft tumor growth. Our results indicate that miR-30c-2-3p and miR-30a-3p repression enhances HIF2α expression, and suggest a mechanism whereby the tumor suppressive effects of constitutive HIF1α expression are attenuated in VHL-deficient H1H2 tumors.
doi:10.1158/2159-8290.CD-13-0291
PMCID: PMC3947282  PMID: 24189146
5.  Hypoxia-Induced Angiogenesis 
Genes & Cancer  2011;2(12):1117-1133.
The vascular network delivers oxygen (O2) and nutrients to all cells within the body. It is therefore not surprising that O2 availability serves as a primary regulator of this complex organ. Most transcriptional responses to low O2 are mediated by hypoxia-inducible factors (HIFs), highly conserved transcription factors that control the expression of numerous angiogenic, metabolic, and cell cycle genes. Accordingly, the HIF pathway is currently viewed as a master regulator of angiogenesis. HIF modulation could provide therapeutic benefit for a wide array of pathologies, including cancer, ischemic heart disease, peripheral artery disease, wound healing, and neovascular eye diseases. Hypoxia promotes vessel growth by upregulating multiple pro-angiogenic pathways that mediate key aspects of endothelial, stromal, and vascular support cell biology. Interestingly, recent studies show that hypoxia influences additional aspects of angiogenesis, including vessel patterning, maturation, and function. Through extensive research, the integral role of hypoxia and HIF signaling in human disease is becoming increasingly clear. Consequently, a thorough understanding of how hypoxia regulates angiogenesis through an ever-expanding number of pathways in multiple cell types will be essential for the identification of new therapeutic targets and modalities.
doi:10.1177/1947601911423654
PMCID: PMC3411127  PMID: 22866203
angiogenesis; hypoxia; HIFs; vascular diseases; cancer; anti-angiogenic therapies
6.  HIF and c-Myc: sibling rivals for control of cancer cell metabolism and proliferation 
Cancer cell  2007;12(2):108-113.
O2 deprivation (hypoxia) and cellular proliferation engage opposite cellular pathways, yet often coexist during tumor growth. The ability of cells to grow during hypoxia results in part from crosstalk between hypoxia inducible factors (HIFs) and the proto-oncogene c-Myc. Acting alone, HIF and c-Myc partially regulate complex adaptations undertaken by tumor cells growing in low O2. However, acting in concert, these transcription factors reprogram metabolism, protein synthesis and cell cycle progression, to “fine tune” adaptive responses to hypoxic environments.
doi:10.1016/j.ccr.2007.07.006
PMCID: PMC3215289  PMID: 17692803
7.  Hypoxia Inducible Factors: Central Regulators of the Tumor Phenotype 
Low oxygen levels are a defining characteristic of solid tumors, and responses to hypoxia contribute substantially to the malignant phenotype. Hypoxia-induced gene transcription promotes characteristic tumor behaviors including angiogenesis, invasion, metastasis, de-differentiation and enhanced glycolytic metabolism. These effects are mediated, at least in part, by targets of the Hypoxia Inducible Factors (HIFs). The HIFs function as heterodimers, made up of an oxygen-labile α-subunit and a stable (β-subunit, also referred to as ARNT. HIF-1α and HIF-2α stimulate the expression of overlapping as well as unique transcriptional targets, and their induction can have distinct biological effects. New targets and novel mechanisms of dysregulation place the HIFs in an ever more central role in tumor biology, and have led to development of pharmacological inhibitors of their activity.
doi:10.1016/j.gde.2006.12.006
PMCID: PMC3215290  PMID: 17208433
8.  Novel insights into the molecular origins and treatment of lung cancer 
Cell Cycle  2010;9(20):4098-4105.
Lung cancer is the most common and most deadly cancer worldwide. Because of the aggressive and metastatic nature of many forms of the disease, it is frequently diagnosed late and responds poorly to the therapies currently available. Although our understanding of the molecular origins and evolution of lung cancer is still incomplete, recent research has yielded several developments that may offer opportunities for new, targeted and effective therapy. In this review we first discuss the prevalence and origins of lung cancer, with emphasis on non-small-cell lung cancer and adenocarcinoma, together with current treatments and their efficacy. We then look at a selection of recent papers which between them shed new light on possible therapeutic opportunities, including a novel synthetic interaction with the Kras gene and genomic or proteomic profiling studies that may pave the way for personalized treatment for lung cancer based on specific “signatures” of protein and gene expression.
Lung cancer remains the foremost cause of cancer deaths worldwide. Despite advances in both detection and treatment, diagnosis is often late and the prognosis for patients poor. Our understanding of the molecular basis and progression of lung cancer remains incomplete, hampering the design and development of more effective diagnostic tools and therapies for this devastating disease. However, the last twelve months have witnessed the publication of several studies that represent significant advances in our knowledge of lung cancer, and may represent important steps on the road to effective new therapies. In this review we aim to summarize these recent developments, and give our perspectives on the therapeutic possibilities they may offer in the future.
doi:10.4161/cc.9.20.13588
PMCID: PMC3055194  PMID: 20962595
lung cancer; adenocarcinoma; egfr; kras; chemotherapy; synthetic lethal; genomic profiling; customized therapy; cancer stem cells; hypoxia-inducible factor
9.  Hypoxia Induced Energy Stress Regulates mRNA Translation and Cell Growth 
Molecular cell  2006;21(4):521-531.
Oxygen deprivation, or hypoxia, has profound effects on cell metabolism and growth. Cells can adapt to low O2 in part through activation of hypoxia-inducible factor (HIF). We report here that hypoxia inhibits mRNA translation by suppressing multiple key regulators including eIF2α, eEF2, and the mTOR effectors 4EBP1, p70S6K, and rpS6, independent of HIF. Hypoxia results in energy starvation and activation of the AMPK/TSC2/Rheb/mTOR pathway. Hypoxic AMPK activation also leads to eEF2 inhibition. Moreover, hypoxic effects on cellular bioenergetics and mTOR inhibition increase over time. Mutation of the TSC2 tumor suppressor gene confers a growth advantage to cells by repressing hypoxic mTOR inhibition and hypoxia-induced G1 arrest. Together, eIF2α, eEF2 and mTOR inhibition represent important HIF-independent mechanisms of energy conservation which promote survival under low O2 conditions.
doi:10.1016/j.molcel.2006.01.010
PMCID: PMC3153113  PMID: 16483933
Hypoxia; mTOR; eIF2; eEF2; AMPK; TSC2; Rheb
10.  Hypoxia inducible factor-2α: a critical mediator of aggressive tumor phenotypes 
Intra-tumoral hypoxia (low oxygen [O2] level) is an independent indicator of unfavorable patient diagnosis, and increasing evidence demonstrates that hypoxia contributes to a more aggressive tumor phenotype. Adaptation to hypoxia is predominantly regulated by two structurally related hypoxia inducible factors, HIF-1α and HIF-2α, which activate the expression of genes involved in proliferation, metabolism, angiogenesis, and metastasis. While highly homologous, HIF-1α and HIF-2α have been shown to have different roles in tumorigenesis dependent on specific tumor microenvironments. Here we summarize recent studies on HIF-2α and discuss the potential mechanisms whereby it contributes to tumor aggressiveness.
doi:10.1016/j.gde.2008.12.001
PMCID: PMC3146034  PMID: 19167211
11.  HIF –dependent hematopoietic factors regulate the development of the embryonic vasculature 
Developmental cell  2006;11(1):81-92.
SUMMARY
Hypoxia Inducible Factors (HIFs) regulate adaptive responses to changes in oxygen (O2) tension during embryogenesis, tissue ischemia, and tumorigenesis. Because HIF deficient embryos exhibit a number of developmental defects, the precise role of HIF in early vascular morphogenesis has been uncertain. Using para-aortic splanchnopleural (P-Sp) explant cultures we show that deletion of the HIF-β subunit (ARNT) results in defective hematopoiesis and the inhibition of both vasculogenesis and angiogenesis. These defects are rescued upon the addition of wild type Sca-1+ hematopoietic cells or recombinant VEGF. Arnt−/− embryos exhibit reduced levels of VEGF protein and increased numbers of apoptotic hematopoietic cells. These results suggest that HIF coordinates early endothelial cell emergence and vessel development by promoting hematopoietic cell survival and paracrine growth factor production.
doi:10.1016/j.devcel.2006.04.018
PMCID: PMC3145415  PMID: 16824955
HIF; ARNT; hypoxia; splanchnopleural; endothelial cells; hematopoiesis; vasculogenesis; angiogenesis; VEGF
12.  Hypoxia-inducible factors as essential regulators of inflammation 
Myeloid cells provide important functions in low oxygen (O2) environments created by pathophysiological conditions, including sites of infection, inflammation, tissue injury and solid tumors. Hypoxia-inducible factors (HIFs) are principle regulators of hypoxic adaptation, regulating gene expression involved in glycolysis, erythropoiesis, angiogenesis, proliferation and stem cell function under low O2. Interestingly, increasing evidence accumulated over recent years suggests an additional important regulatory role for HIFs in inflammation. In macrophages, HIFs not only regulate glycolytic energy generation, but also optimize innate immunity, control pro-inflammatory gene expression, mediate bacterial killing and influence cell migration. In neutrophils, HIF-1α promotes survival under O2-deprived conditions and mediates blood vessel extravasation by modulating β2 integrin expression. Additionally, HIFs contribute to inflammatory functions in various other components of innate immunity, such as dendritic cells, mast cells and epithelial cells. This review will dissect the role of each HIF isoform in myeloid cell function and discuss their impact on acute and chronic inflammatory disorders. Currently, intensive studies are being conducted to illustrate the connection between inflammation and tumorigenesis. Detailed investigation revealing interaction between microenvironmental factors such as hypoxia and immune cells is needed. We will also discuss how hypoxia and HIFs control properties of tumor-associated macrophages and their relationship to tumor formation and progression.
doi:10.1007/82_2010_74
PMCID: PMC3144567  PMID: 20517715
13.  Hypoxia inducible factors and the response to hypoxic stress 
Molecular cell  2010;40(2):294-309.
Oxygen (O2) is an essential nutrient that serves as a key substrate in cellular metabolism and bioenergetics. In a variety of physiological and pathological states, organisms encounter insufficient O2 availability, or hypoxia. In order to cope with this stress, evolutionarily conserved responses are engaged. In mammals, the primary transcriptional response to hypoxic stress is mediated by the Hypoxia-inducible factors (HIFs). While canonically regulated by prolyl hydroxylase domain-containing enzymes (PHDs), the HIFα subunits are intricately responsive to numerous other factors including Factor Inhibiting HIF-1α (FIH1), sirtuins, and metabolites. These transcription factors function in normal tissue homeostasis and impinge on critical aspects of disease progression and recovery. Insights from basic HIF biology are being translated into pharmaceuticals targeting the HIF pathway.
doi:10.1016/j.molcel.2010.09.022
PMCID: PMC3143508  PMID: 20965423
15.  The role of MXI1 in VHL deficient tumorigenesis 
Cancer biology & therapy  2008;7(10):1628-1629.
PMCID: PMC3141207  PMID: 18836305
MXI1; c-MYC; MAX; HIF-1α; HIF-2α; VHL; renal cell carcinoma
16.  The impact of O2 availability on human cancer 
Nature reviews. Cancer  2008;8(12):967-975.
During the last century, it has been established that regions within solid tumors experience mild to severe oxygen deprivation, due to aberrant vascular function. These hypoxic regions are associated with altered cellular metabolism, as well as increased resistance to radiation and chemotherapy. As discussed in this Timeline, over the past decade, work from many laboratories has elucidated the mechanisms by which hypoxia-inducible factors (HIFs) modulate tumor cell metabolism, angiogenesis, growth, and metastasis. The central role played by intra-tumoral hypoxia and HTF in these processes has made them attractive therapeutic targets in the treatment of multiple human malignancies.
doi:10.1038/nrc2540
PMCID: PMC3140692  PMID: 18987634
17.  EPAS1 Is Required for Spermatogenesis in the Postnatal Mouse Testis1 
Biology of Reproduction  2010;82(6):1227-1236.
Spermatogenesis, a process involving the differentiation of spermatogonial stem cells into mature spermatozoa, takes place throughout masculine life. A complex system in the testis, including endocrine signaling, physical interactions between germ and somatic cells, spermatocyte meiosis, and timely release of spermatozoa, controls this cycle. We demonstrate herein that decreased O2 levels and Epas1 activation are critical components of spermatogenesis. Postnatal Epas1 ablation leads to male infertility, with reduced testis size and weight. While immature spermatogonia and spermatocytes are present in Epas1Delta/Delta testes, spermatid and spermatozoan numbers are dramatically reduced. This is not due to germ cell-intrinsic defects. Rather, EpasDelta/Delta Sertoli cells exhibit decreased ability to form tight junctions, thereby disrupting the blood-testis barrier necessary for proper spermatogenesis. Reduced numbers of tight junction complexes are due to decreased expression of multiple genes encoding tight junction proteins, including TJP1 (ZO1), TJP2 (ZO2), and occludin. Furthermore, Epas1Delta/Delta testes exhibit disrupted basement membranes surrounding the seminiferous tubules, causing the premature release of incompletely differentiated germ cells. We conclude that low O2 levels in the male gonad regulate germ cell homeostasis in this organ via EPAS1.
Postnatal deletion of Epas1 in the mouse testis impairs the integrity of the blood-testis barrier required for proper spermatogenesis.
doi:10.1095/biolreprod.109.079202
PMCID: PMC2874504  PMID: 20181618
developmental biology; hypoxia; Sertoli cells; signal transduction; sperm; spermatogenesis; testis; tight junctions
18.  A liver HIF-2α/IRS2 pathway sensitizes hepatic insulin signaling and is modulated by VEGF inhibition 
Nature medicine  2013;19(10):1331-1337.
Insulin initiates diverse hepatic metabolic responses, including gluconeogenic suppression and induction of glycogen synthesis and lipogenesis1,2. The liver possesses a rich sinusoidal capillary network with increased hypoxia and decreased gluconeogenesis in the perivenous zone3. Here, diverse vascular endothelial growth factor (VEGF) inhibitors improved glucose tolerance in normal or diabetic db/db mice, potentiating hepatic insulin signaling, decreasing gluconeogenic gene expression, increasing glycogen storage and suppressing hepatic glucose production (HGP). VEGF inhibition induced hepatic hypoxia via sinusoidal vascular regression and sensitized liver insulin signaling through hypoxia inducible factor-2α (HIF-2α) stabilization. Notably, liver-specific constitutive activation of HIF-2α, but not HIF-1α, was sufficient to augment hepatic insulin signaling via direct and indirect induction of insulin receptor substrate 2 (IRS2), an essential insulin receptor adaptor protein4–6. Further, liver IRS2 was both necessary and sufficient to mediate HIF-2α and VEGF inhibition effects on glucose tolerance and hepatic insulin signaling. These results demonstrate an unsuspected intersection between HIF-2α–mediated hypoxic signaling and hepatic insulin action via IRS2 induction, which can be co-opted by VEGF inhibitors to modulate glucose metabolism. These studies also indicate distinct roles in hepatic metabolism for HIF-1α, which promotes glycolysis7–9, versus HIF-2α, which suppresses gluconeogenesis, and suggest novel treatment approaches for type 2 diabetes mellitus.
doi:10.1038/nm.3295
PMCID: PMC3795838  PMID: 24037094
19.  Biology of Hypoxia-Inducible Factor-2α in Development and Disease 
Cell death and differentiation  2008;15(4):628-634.
The transcriptional response to hypoxia is primarily mediated by two hypoxia-inducible factors – HIF-1α and HIF-2α. While these proteins are highly homologous, increasing evidence suggests they have unique transcriptional targets and differential impact on tumor growth. Furthermore, non-transcriptional effects of the HIF-α subunits, including effects on the Notch and c-Myc pathways, contribute to their distinct functions. HIF-2α transcriptional targets include genes involved in erythropoiesis, angiogenesis, metastasis, and proliferation. Therefore, HIF-2α contributes significantly to both normal physiology as well as tumorigenesis. Here we summarize the function of HIF-2α during development as well as its contribution to pathologic conditions such as tumors and vascular disease.
doi:10.1038/cdd.2008.17
PMCID: PMC2882207  PMID: 18259197
hypoxia; erythropoiesis; development; renal carcinoma; neuroblastoma
20.  The role of oxygen availability in embryonic development and stem cell function 
Low levels of oxygen (O2) occur naturally in developing embryos. Cells respond to their hypoxic microenvironment by stimulating several hypoxia-inducible factors (and other molecules that mediate O2 homeostasis), which then coordinate the development of the blood, vasculature, placenta, nervous system, and other organs. Furthermore, embryonic stem and progenitor cells frequently occupy hypoxic ‘niches’ and low O2 regulates their differentiation. Recent work has revealed an important link between factors involved in regulating stem/progenitor cell behaviour and hypoxia-inducible factors, which provides a molecular framework for hypoxic control of differentiation and cell fate. These findings have important implications for the development of therapies for tissue regeneration and disease.
doi:10.1038/nrm2354
PMCID: PMC2876333  PMID: 18285802
21.  Hypoxia-Inducible Factors in Stem cells and Cancer 
Journal of cellular and molecular medicine  2009;13(11-12):4319-4328.
Cellular properties are influenced by complex factors inherent to their microenvironments. While oxygen deprivation (hypoxia) occurs in tumors due to rapid cell proliferation and aberrant blood vessel formation, embryonic cells develop in a naturally occurring hypoxic environment. Cells respond to hypoxia by stabilizing hypoxia-inducible factors (HIFs), which are traditionally viewed to function by altering cellular metabolism and blood vessel architecture. Recently, HIFs have been shown to modulate specific stem cell effectors, such as Notch, Wnt, and Oct4, that control stem cell proliferation, differentiation and pluripotency. Direct molecular links have also been established between HIFs and critical cell signalling pathways such as cMyc and p53. These novel links suggest a new role for HIFs in stem cell and tumor regulation.
doi:10.1111/j.1582-4934.2009.00963.x
PMCID: PMC2874971  PMID: 19900215
Hypoxia-inducible factors (HIF-1, HIF-2); stem cell signalling; cancer pathways
22.  Reactive Oxygen Species and Cellular Oxygen Sensing 
Free radical biology & medicine  2007;43(9):1219-1225.
Many organisms activate adaptive transcriptional programs to help them cope with decreased oxygen levels, or hypoxia, in their environment. These responses are triggered by various oxygen sensing systems in bacteria, yeast and metazoans. In metazoans, the hypoxia inducible factors (HIFs) mediate the adaptive transcriptional response to hypoxia by upregulating genes involved in maintaining bioenergetic homeostasis. The HIFs in turn are regulated by HIF-specific prolyl hydroxlase activity, which is sensitive to cellular oxygen levels and other factors such as tricarboxylic acid cycle metabolites and reactive oxygen species (ROS). Establishing a role for ROS in cellular oxygen sensing has been challenging since ROS are intrinsically unstable and difficult to measure. However, recent advances in fluorescence energy transfer resonance (FRET)-based methods for measuring ROS are alleviating some of the previous difficulties associated with dyes and luminescent chemicals. In addition, new genetic models have demonstrated that functional mitochondrial electron transport and associated ROS production during hypoxia are required for HIF stabilization in mammalian cells. Current efforts are directed at how ROS mediate prolyl hydroxylase activity and hypoxic HIF stabilization. Progress in understanding this process has been enhanced by the development of the FRET-based ROS probe, an vivo prolyl hydroxylase reporter and various genetic models harboring mutations in components of the mitochondrial electron transport chain.
doi:10.1016/j.freeradbiomed.2007.07.001
PMCID: PMC2696222  PMID: 17893032
reactive oxygen species; prolyl hydroxylase; mitochondria; cellular oxygen sensing; hypoxia; hypoxia inducible factor
23.  The N-Terminal Transactivation Domain Confers Target Gene Specificity of Hypoxia-inducible Factors HIF-1α and HIF-2α 
Molecular Biology of the Cell  2007;18(11):4528-4542.
The basic helix-loop-helix-Per-ARNT-Sim–proteins hypoxia-inducible factor (HIF)-1α and HIF-2α are the principal regulators of the hypoxic transcriptional response. Although highly related, they can activate distinct target genes. In this study, the protein domain and molecular mechanism important for HIF target gene specificity are determined. We demonstrate that although HIF-2α is unable to activate multiple endogenous HIF-1α–specific target genes (e.g., glycolytic enzymes), HIF-2α still binds to their promoters in vivo and activates reporter genes derived from such targets. In addition, comparative analysis of the N-terminal DNA binding and dimerization domains of HIF-1α and HIF-2α does not reveal any significant differences between the two proteins. Importantly, replacement of the N-terminal transactivation domain (N-TAD) (but not the DNA binding domain, dimerization domain, or C-terminal transactivation domain [C-TAD]) of HIF-2α with the analogous region of HIF-1α is sufficient to convert HIF-2α into a protein with HIF-1α functional specificity. Nevertheless, both the N-TAD and C-TAD are important for optimal HIF transcriptional activity. Additional experiments indicate that the ETS transcription factor ELK is required for HIF-2α to activate specific target genes such as Cited-2, EPO, and PAI-1. These results demonstrate that the HIF-α TADs, particularly the N-TADs, confer HIF target gene specificity, by interacting with additional transcriptional cofactors.
doi:10.1091/mbc.E06-05-0419
PMCID: PMC2043574  PMID: 17804822
24.  Taking aim at translation for tumor therapy 
The Journal of Clinical Investigation  2007;117(9):2385-2388.
Increased cap-dependent mRNA translation rates are frequently observed in human cancers. Mechanistically, many human tumors often overexpress the cap binding protein eukaryotic translation initiation factor 4E (eIF4E), leading to enhanced translation of numerous tumor-promoting genes. In this issue of the JCI, Graff and colleagues describe potent antitumor effects using second-generation antisense oligonucleotides for eIF4E (see the related article beginning on page 2638). If their results are recapitulated in a clinical setting, this strategy will provide a promising antitumor therapy with broad-reaching applications.
doi:10.1172/JCI33107
PMCID: PMC1952643  PMID: 17786234
25.  Overcoming evasive resistance from vascular endothelial growth factor A inhibition in sarcomas by genetic or pharmacologic targeting of hypoxia inducible factor 1α 
Increased levels of hypoxia and hypoxia inducible factor 1 (HIF-1α) in human sarcomas correlate with tumor progression and radiation resistance. Prolonged anti-angiogenic therapy of tumors can delay tumor growth but may also increase hypoxia and HIF-1α activity. In our recent clinical trial, treatment with the anti-vascular endothelial growth factor A (VEGF-A) antibody, bevacizumab, followed by a combination of bevacizumab and radiation led to near complete necrosis in nearly half of sarcomas. Gene set enrichment analysis of microarrays from pre-treatment biopsies found the Gene Ontology category “Response to hypoxia” was upregulated in poor responders, and hierarchical clustering based on 140 hypoxia-responsive genes reliably separated poor responders from good responders. The most commonly used chemotherapeutic drug for sarcomas, doxorubicin (Dox), was recently found to block HIF-1α binding to DNA at low metronomic doses. In 4 sarcoma cell lines, HIF-1 shRNA or Dox at low concentrations blocked HIF-1α induction of VEGF-A by 84–97%, and carbonic anhydrase 9 by 83–93%. HT1080 sarcoma xenografts had increased hypoxia and/or HIF-1α activity with increasing tumor size and with anti-VEGF receptor antibody (DC101) treatment. Combining DC101 with HIF-1α shRNA or metronomic Dox had a synergistic effect in suppressing growth of HT1080 xenografts, at least in part via induction of tumor endothelial cell apoptosis. In conclusion, sarcomas respond to increased hypoxia by expressing HIF-1α-target genes which may promote resistance to anti-angiogenic and other therapies. Adding HIF-1α inhibition blocks resistance and augments destruction of the tumor vasculature.
doi:10.1002/ijc.27666
PMCID: PMC3677782  PMID: 22684860

Results 1-25 (81)