The Virtual Free Radical School Hypoxia Inducible Factor
The Virtual Free Radical School Hypoxia Inducible Factor 1 (HIF-1): A High Impact Factor Min Wang Free Radical & Radiation Biology College of Medicine The University of Iowa E-mail: [email protected] Phone: (319)335-6749; Fax: (319)335-8039 HIF-1 5/2003 SFRBM Education Program Wang, Min 1 A. What is HIF-1? HIF-1: Hypoxia Inducible Factor - 1
The studies of hypoxia response element of the erythropoietin gene leads to the discovery of HIF-1 by Semenza and Wang in 1992. Semenza GL & Wang GL. (1992). Mol. Cell. Biol. 12: 54475454. HIF-1 is a protein with DNA binding activity. It is composed of two subunits: HIF-1 and HIF-1. HIF-1 5/2003 SFRBM Education Program Wang, Min 2 HIF-1 is constitutively made and degraded via VHL. Proline residue 402 & 564 in HIF-1 can be hydroxylated by prolyl hydroxylase. The hydroxylation of proline causes the binding of
von Hippel-Lindau tumor suppressor (VHL). The binding of VHL leads to the ubiquitinylation of HIF-1. Ubiquitinylation of HIF-1 results in degradation by proteasome. Bruick RK. (2002) Science. 295:807-808. HIF-1 5/2003 SFRBM Education Program Wang, Min 3 Prolyl hydroxylase is O2-dependent The activation of prolyl hydroxylase depends on several co-factors such as O2, Fe2+, -ketoglutarate and ascorbate. Under hypoxia, prolyl hydroxylase cannot be activated. Thus, HIF-1 accumulates and translocates into nucleus. In the nucleus, it binds to HIF-1
forming HIF-1. 5/2003 SFRBM Education ProgramCBP/p300 and Wang, HIF-1 binds to co-activators is Min 4 HIF-1 HIF-1 is a heterodimer hypoxia HIF-1 Pol II CBP/p300 complex HIF-1 HIF-1 Angiogenesis HIF-1
5/2003 Glucose Cell metabolism proliferation SFRBM Education Program Wang, Min 5 Human HIF1A and HIF1B gene structures NLS-N NLS-C HIF-1A b HLH A
PAS HIF-1B ARNT b HLH A PAS B B TAD ID N TAD C
826 aa 774/789 aa Both bHLH and PAS are essential for dimerization and DNA-binding. bHLH: basic helix-loop-helix domain; PAS: domain with A and B repeats, amino-terminal (N) and carboxyl-terminal (C) nuclear localization signal (NLS); TAD: transactivation domain; ID: transcriptional inhibitory domain. Iyer NV (1998). Genomics. 52:159-165. HIF-1 5/2003 SFRBM Education Program Wang, Min 6 B. Where is HIF-1? Ubiquitous Expression
mRNA: brain, heart, kidney, lung, liver, pancreas, plancenta, skeletal muscle and all human tissues checked so far. BLAST Search: Bone, fetal and adult brain, pancreatic islets, retina, uterus and white blood cells. Wiener CM (1996). Biochem Biophys Res Commun. 225: 485-488. HIF-1 5/2003 SFRBM Education Program Wang, Min 7 C. What does HIF-1 do? 1. Helps normal tissues as well as tumors to survive under hypoxic conditions 2. HIF-1 is a transcription factor that turns on genes needed for survival under hypoxic conditions. 3. So far, more than 40 target genes have been found to be regulated by HIF-1. 4. These genes can be classified into 3 main groups:
HIF-1 5/2003 SFRBM Education Program Wang, Min 8 HIF-1 Target Genes Erythropoeitin (EPO) Nitric oxide synthase 2 (NOS2) Transferrin Transferrin receptor Vascular endothelial growth factor (VEGF) Group 1: O2 Delivery
VEGF receptor FLT-1 HIF-1 5/2003 SFRBM Education Program Wang, Min 9 Aldolase A Aldolase C Enolase 1 (ENO1) Glucose transporter 1 Glyceraldehyde phosphate dehydrogenase Hexokinase 1 Hexokinase 2 Lactate dehydrogenase A Phosphofructokinase L Phosphoglycerate kinase 1 Pyruvate kinase M HIF-1
5/2003 SFRBM Education Program Group 2: Glucose /Energy Metabolism Wang, Min 10 Insulin-like growth factor 2 (IGF-2) IGF binding protein 1 IGF binding protein 3 p21 p35srj HIF-1 5/2003
Group 3: Cell Proliferation /Viability SFRBM Education Program Wang, Min 11 D. How does HIF-1 do the job? Protein Expression as a Function of [O ] Relative HIF-1 Expression 2 HIF-1 expression increases exponentially when O2 concentration decreases. The curve shows a point of inflection around 4-5% O2, which is the O2
concentration in normal human tissues. Oxygen Concentration HIF-1 5/2003 Semenza GL. (1997) Kidney Int. 51:553-555 SFRBM Education Program Wang, Min 12 Hypoxia is widespread in tumors Tumor blood vessels are highly irregular and disorganized. Most human solid tumors have pO2 values lower than their normal tissues of origin. Severe hypoxia can rarely be found in normal tissues, but these regions always exist in tumors. HIF-1
5/2003 SFRBM Education Program Wang, Min 13 So, tumor cells are living in a low oxygen and low nutrient environment. But tumor cells are usually proliferating faster than normal cells. Therefore, the ability of tumor cells to sense and adapt to low oxygen (hypoxia) is essential for tumor growth. HIF-1 5/2003 SFRBM Education Program
Wang, Min 14 Among the first responses at the onset of hypoxia is an increase in the protein levels of hypoxia-inducible factor-1 (HIF-1) HIF-1 The oxygen and nutrients display a gradient away from the necrotic center gradient O2, glucose, growth factors An idealized diagram of a tumor cross section HIF-1 5/2003
SFRBM Education Program Wang, Min 15 HIF-1 Correlates with Tumor Vascularity Low oxygen tension is associated with increased metastasis and decreased survival of patients The expression of HIF-1 is positively correlated with tumor vascularity. Zagzag D. (2000) Cancer. 88:2606 HIF-1 5/2003 SFRBM Education Program Wang, Min 16
Summary HIF-1 is a transcription factor that is composed of HIF-1 and HIF-1 subunits. More than 40 target genes have been found to be regulated by HIF-1. HIF-1 expression is positively correlated with tumor vascularity, indicating HIF-1 plays a crucial role in tumor angiogenesis progression. HIF-1 is degraded by proteasome via VHL. HIF-1 5/2003 SFRBM Education Program Wang, Min 17 Finally Thank you for stopping by. HIF-1
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