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Description

HIF is a transcriptional complex that plays a central role in mammalian oxygen homeostasis, the posttranslational modification by prolyl hydroxylation as a key regulatory event that targets HIF-alpha subunits for proteasomal destruction via the von Hippel-Lindau ubiquitylation complex. The transcriptional complex is composed of an alpha-beta heterodimer, HIF-beta being a constitutive nuclear protein that dimerises with oxygen regulated HIF-alpha subunits. In normoxia, 4-hydroxylation of human HIF-alpha at Pro402 or Pro564 by a set of HIF prolyl hydroxylase isoenzymes (PHD 1-3) mediates HIF1-alpha recognition by von Hippel-Lindau ubiquitin ligase complex leading to its proteasomal destruction. In hypoxia (deprivation of oxygen), lack of hydroxylase activity enables HIF-alpha subunits to escape destruction and become transcriptionally active. Thus HIF hydroxylases provide a focus for understanding cellular responses to hypoxia and target for therapeutic manipulation. There are several HIF factors, which include HIF 1-alpha, HIF 1-beta, HIF 2-alpha. HIF 1-alpha is an 812 a.a. protein in rat and 836 a.a. long in mouse and human. A master transcriptional regulator of the adaptive response to hypoxia. Under hypoxic conditions activates the transcription of over 40 genes, including, erythropoietin, glucose transporters, glycolytic enzymes, vascular endothelial growth factor, and other genes whose protein products increase oxygen delivery or facilitate metabolic adaptation to hypoxia. Plays an essential role in embryonic vascularization, tumor angiogenesis and pathophysiology of ischemic disease. It is ubiquitous in expression as cytoplasmic in normoxia, nuclear translocation in response to hypoxia.