Hypoxia-inducible factor 1 (HIF-1) activates the transcription of genes that are involved in crucial aspects of cancer biology, including angiogenesis, cell survival, glucose metabolism and invasion. Intratumoral hypoxia and genetic alterations can lead to HIF-1alpha overexpression, which has been associated with increased patient mortality in several cancer types. In preclinical studies, inhibition of HIF-1 activity has marked effects on tumour growth. Efforts are underway to identify inhibitors of HIF-1 and to test their efficacy as anticancer therapeutics.

Targeting HIF-1 for cancer therapy

Cells undergo a variety of biological responses when placed in hypoxic conditions, including activation of signalling pathways that regulate proliferation, angiogenesis and death. Cancer cells have adapted these pathways, allowing tumours to survive and even grow under hypoxic conditions, and tumour hypoxia is associated with poor prognosis and resistance to radiation therapy. Many elements of the hypoxia-response pathway are therefore good candidates for therapeutic targeting.

Hypoxia — a key regulatory factor in tumour growth

Hypoxia-Inducible Factors in Physiology and Medicine

Hypoxia is an essential developmental and physiological stimulus that plays a key role in the pathophysiology of cancer, heart attack, stroke, and other major causes of mortality. Hypoxia-inducible factor 1 (HIF-1) is the only known mammalian transcription factor expressed uniquely in response to physiologically relevant levels of hypoxia. We now report that in Hif1a-/- embryonic stem cells that did not express the O2-regulated HIF-1alpha subunit, levels of mRNAs encoding glucose transporters and glycolytic enzymes were reduced, and cellular proliferation was impaired. Vascular endothelial growth factor mRNA expression was also markedly decreased in hypoxic Hif1a-/- embryonic stem cells and cystic embryoid bodies. Complete deficiency of HIF-1alpha resulted in developmental arrest and lethality by E11 of Hif1a-/- embryos that manifested neural tube defects, cardiovascular malformations, and marked cell death within the cephalic mesenchyme. In Hif1a+/+ embryos, HIF-1alpha expression increased between E8.5 and E9.5, coincident with the onset of developmental defects and cell death in Hif1a-/- embryos. These results demonstrate that HIF-1alpha is a master regulator of cellular and developmental O2 homeostasis.

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Cellular and developmental control of O2 homeostasis by hypoxia-inducible factor 1α

Neovascularization and increased glycolysis, two universal characteristics of solid tumors, represent adaptations to a hypoxic microenvironment that are correlated with tumor invasion, metastasis, and lethality. Hypoxia-inducible factor 1 (HIF-1) activates transcription of genes encoding glucose transporters, glycolytic enzymes, and vascular endothelial growth factor. HIF-1 transcriptional activity is determined by regulated expression of the HIF-1α subunit. In this study, HIF-1α expression was analyzed by immunohistochemistry in 179 tumor specimens. HIF-1α was overexpressed in 13 of 19 tumor types compared with the respective normal tissues, including colon, breast, gastric, lung, skin, ovarian, pancreatic, prostate, and renal carcinomas. HIF-1α expression was correlated with aberrant p53 accumulation and cell proliferation. Preneoplastic lesions in breast, colon, and prostate overexpressed HIF-1α, whereas benign tumors in breast and uterus did not. HIF-1α overexpression was detected in only 29% of primary breast cancers but in 69% of breast cancer metastases. In brain tumors, HIF-1α immunohistochemistry demarcated areas of angiogenesis. These results provide the first clinical data indicating that HIF-1α may play an important role in human cancer progression.

https://cancerres.aacrjournals.org/content/canres/59/22/5830.full.pdf

Overexpression of Hypoxia-inducible Factor 1α in Common Human Cancers and Their Metastases

Here we describe the cloning and characterization of a PAS domain transcription factor termed endothelial PAS-1 (EPAS1). This protein shares 48% sequence identity with hypoxia inducible factor (HIF-1alpha) and lesser similarity with other members of the basic helix-loop-helix/PAS domain family of transcription factors. Like HIF-1alpha, EPAS1 binds to and activates transcription from a DNA element originally isolated from the erythropoietin gene and containing the sequence 5'-GCCCTACGTGCTGTCTCA-3'. Activation by both HIF-1alpha and EPAS1 is stimulated by hypoxic conditions. EPAS1 forms a heterodimeric complex with the aryl hydrocarbon nuclear transporter prior to transcriptional activation of target genes. EPAS1 expression is limited to the endothelium of mouse embryos and, in agreement with its cell type-specific expression pattern, is capable of specifically activating the transcription of the endothelial tyrosine kinase gene Tie-2. These observations raise the possibility that EPAS1 may represent an important regulator of vascularization, perhaps involving the regulation of endothelial cell gene expression in response to hypoxia.

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Endothelial PAS domain protein 1 (EPAS1), a transcription factor selectively expressed in endothelial cells.

Mice lacking the hypoxia-inducible transcription factor EPAS1 die at mid-gestation. Despite normal morphological development of the circulatory system, EPAS1-deficient mice display pronounced bradycardia. In addition to the vascular endothelium, EPAS1 is expressed intensively in the organ of Zuckerkandl (OZ), the principle source of catecholamine production in mammalian embryos. EPAS1-deficient embryos contained substantially reduced catecholamine levels. Mid-gestational lethality was rescued by administration of the catecholamine precursor DOPS to pregnant females. We hypothesize that EPAS1 expressed in the OZ senses hypoxia during mid-gestational development and translates this signal into an altered pattern of gene expression, leading to increases in circulating catecholamine levels and proper cardiac function.

/pdf/the-hypoxia-responsive-transcription-factor-epas1-is-2mw8nw6p95.pdf

The hypoxia-responsive transcription factor EPAS1 is essential for catecholamine homeostasis and protection against heart failure during embryonic development

Here we describe two mammalian transcription factors selectively expressed in the central nervous system. Both proteins, neuronal PAS domain protein (NPAS) 1 and NPAS2, are members of the basic helix–loop–helix-PAS family of transcription factors. cDNAs encoding mouse and human forms of NPAS1 and NPAS2 have been isolated and sequenced. RNA blotting assays demonstrated the selective presence of NPAS1 and NPAS2 mRNAs in brain and spinal cord tissues of adult mice. NPAS1 mRNA was first detected at embryonic day 15 of mouse development, shortly after early organogenesis of the brain. NPAS2 mRNA was first detected during early postnatal development of the mouse brain. In situ hybridization assays using brain tissue of postnatal mice revealed an exclusively neuronal pattern of expression for NPAS1 and NPAS2 mRNAs. The human NPAS1 gene was mapped to chromosome 19q13.2–q13.3, and the mouse Npas1 gene to chromosome 7 at 2 centimorgans. Similarly, the human NPAS2 gene was assigned to chromosome 2p11.2–2q13, and the mouse Npas2 gene to chromosome 1 at 21–22 centimorgans. The chromosomal regions to which human NPAS1 and NPAS2 map are syntenic with those containing the mouse Npas1 and Npas2 genes, indicating that the mouse and human genes are true homologs.

https://www.pnas.org/content/pnas/94/2/713.full.pdf

Molecular characterization of two mammalian bHLH-PAS domain proteins selectively expressed in the central nervous system

Two androgens, testosterone and dihydrotestosterone, are required for the development of the male urogenital tract in the rat. Testosterone is secreted by the fetal testes and is thought to elicit differentiation of the Wolffian ducts into seminal vesicles, vas deferens, and epididymides. Testosterone is converted into dihydrotestosterone by steroid 5 alpha-reductase in the urogenital tract, and this conversion is necessary for the differentiation of the prostate and external genitalia. Genes encoding two 5 alpha-reductase isozymes, designated type 1 and type 2, have been identified. We examined the expression and regulation of these genes on days 17-21 in the urogenital tracts of male and female fetuses. Expression of the type 1 gene predominated in epithelial cells, whereas type 2 gene expression was limited to mesenchymal cells. Surprisingly, this expression pattern was detected in both testosterone-dependent and dihydrotestosterone-dependent anlagen of the urogenital tract and was the same in both mal...

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Expression and regulation of steroid 5 alpha-reductase in the urogenital tract of the fetal rat.

The invention provides methods and compositions relating to endothelial PAS domain protein 1 (EPAS1) and related nucleic acids. The proteins may be produced recombinantly from transformed host cells from the disclosed EPAS1 encoding nucleic acids or purified from human cells. The invention provides isolated EPAS1 hybridization probes and primers capable of specifically hybridizing with the disclosed EPAS1 gene, EPAS1-specific binding agents such as specific antibodies, and methods of making and using the subject compositions in diagnosis, therapy and in the biopharmaceutical industry.

Hui Tian

Papers

Endothelial PAS domain protein 1 (EPAS1), a transcription factor selectively expressed in endothelial cells.

The hypoxia-responsive transcription factor EPAS1 is essential for catecholamine homeostasis and protection against heart failure during embryonic development

Molecular characterization of two mammalian bHLH-PAS domain proteins selectively expressed in the central nervous system

Expression and regulation of steroid 5 alpha-reductase in the urogenital tract of the fetal rat.

Endothelial pas domain protein