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 O 2 -regulated HIF-1␣ 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-1␣ 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-1␣ 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-1␣ is a master regulator of cellular and developmental O 2 homeostasis.

Although it was known for a long time that oxygen deprivation leads to the transcriptional induction of the gene encoding erythropoietin, the molecular mechanisms behind this process remained enigmatic. The cloning of the hypoxia-inducible factors (HIFs), the finding that HIF-1 regulates the expression of many more genes apart from erythropoietin, and the elucidation of the oxygen-dependent mechanisms degrading the HIF alpha subunits recently led to the spectacular discovery of the molecular principles of oxygen sensing. This review aims to summarize our current knowledge of oxygen-regulated gene expression..

Integration of oxygen signaling at the consensus HRE Wenger, R H; Stiehl, D P; Camenisch, G Wenger, R H; Stiehl, D P; Camenisch, G. Integration of oxygen signaling at the consensus HRE. Sci. STKE 2005STKE , 2005 Integration of oxygen signaling at the consensus HRE AbstractThe hypoxia-inducible factor 1 (HIF-1) was initially identified as a transcription factor that regulated erythropoietin gene expression in response to a decrease in oxygen availability in kidney tissue. Subsequently, a family of oxygen-dependent protein hydroxylases was found to regulate the abundance and activity of three oxygen-sensitive HIFalpha subunits, which, as part of the HIF heterodimer, regulated the transcription of at least 70 different effector genes. In addition to responding to a decrease in tissue oxygenation, HIF is proactively induced, even under normoxic conditions, in response to stimuli that lead to cell growth, ultimately leading to higher oxygen consumption. The growing cell thus profits from an anticipatory increase in HIF-dependent target gene expression. Growth stimuli-activated signaling pathways that influence the abundance and activity of HIFs include pathways in which kinases are activated and pathways in which reactive oxygen species are liberated. These pathways signal to the HIF protein hydroxylases, as well as to HIF itself, by means of covalent or redox modifications and protein-protein interactions. The final point of integration of all of these pathways is the hypoxia-response element (HRE) of effector genes. Here, we provide comprehensive compilations of the known growth stimuli that promote increases in HIF abundance, of protein-protein interactions involving HIF, and of the known HIF effector genes. The consensus HRE derived from a comparison of the HREs of these HIF effectors will be useful for identification of novel HIF target genes, design of oxygen-regulated gene therapy, and prediction of effects of future drugs targeting the HIF system. GlossOxygen availability regulates many physiological and pathophysiological processes, including embryonic development, high-altitude adaptation, wound healing, inflammation, ischemic diseases and cancer. Central to the understanding of these processes is the elucidation of the molecular mechanisms by which cells react and adapt to insufficient oxygen supply (hypoxia). The last few years brought a wealth of novel insights into these processes. Four oxygen-sensing protein hydroxylases have been discovered which regulate the abundance and activity of three hypoxia-inducible transcription factors (HIFs) and thereby the activity of at least 70 effector genes involved in hypoxic adaptation. In addition to its reactive nature in response to a decrease in tissue oxygenation, it became evident that HIFs are also proactively induced, even under normoxic conditions, in response to growth stimuli which ultimately lead to higher oxygen consumption. The growing cell thus profits from an anticipatory increase in HIF-dependent target gene expression. Growth stimuli-activated s...

Adaptation to hypoxia is regulated by hypoxia-inducible factor 1 (HIF-1), a heterodimeric transcription factor consisting of an oxygen-regulated alpha subunit and a constitutively expressed beta subunit. Although HIF-1 is regulated mainly by oxygen tension through the oxygen-dependent degradation of its alpha subunit, in vitro it can also be modulated by cytokines, hormones and genetic alterations. To investigate HIF-1 activation in vivo, we determined the spatial and temporal distribution of HIF-1 in healthy mice subjected to varying fractions of inspiratory oxygen. Immunohistochemical examination of brain, kidney, liver, heart, and skeletal muscle revealed that HIF-1alpha is present in mice kept under normoxic conditions and is further increased in response to systemic hypoxia. Moreover, immunoblot analysis showed that the kinetics of HIF-1alpha expression varies among different organs. In liver and kidney, HIF-1alpha reaches maximal levels after 1 h and gradually decreases to baseline levels after 4 h of continuous hypoxia. In the brain, however, HIF-1alpha is maximally expressed after 5 h and declines to basal levels by 12 h. Whereas HIF-1beta is constitutively expressed in brain and kidney nuclear extracts, its hepatic expression increases concomitantly with HIF-1alpha. Overall, HIF-1alpha expression in normoxic mice suggests that HIF-1 has an important role in tissue homeostasis.