Resumo

CARAMELO, Carlos et al. Response to hypoxia: A systemic mechanism based on the control of gene expression. Medicina (B. Aires) [online]. 2006, vol.66, n.2, pp.155-164. ISSN 0025-7680.

New, critically important data have been recently generated about the response to hypoxia. This response can be schematized in three main systems or functions, ie, detectional or oxygen sensing, regulatory, which controls gene expression and effector. The principal organizer of the regulatory branch is a specific transcription factor, the hypoxia-inducible factor 1 (HIF-1). In the presence of oxygen, the a subunit of HIF-1 (HIF-1a) is modified by hydroxylases, that represent the central point of the oxygen sensing mechanism. This type of hydroxylation induces HIF-1a catabolism by the proteosome. On the contrary, in hypoxia, or in the presence of certain growth factors that increase HIF-1a synthesis, HIF-1a translocates to the nucleus, where it binds HIF-1b, and thence acts on transcription of genes carrying hypoxia responsive elements (HRE) on their promoters. These genes regulate the synthesis of an ample series of proteins, which span from respiratory enzymes and transporters to hormones regulating circulation and erythropoiesis. The role of HIF-1a is not restricted to the mere induction of adaptation to decreased oxygen: instead, it significantly participates in cell repairing mechanisms. A simple list of some of the stimulatory or inhibitory alterations of pathophysiological importance involving the HIF-1 system, would include: chronic lung disease, smoking adaptation, anemia/hemorrhage, ischemia/reperfusion, growth, vascularization and cell resistance of tumors, preeclampsia and intrauterine growth retardation, retinal hyper o hypovascularization, drug intoxications, bowel inflammatory disease and wound repair. This list illustrates by itself the importance of the mechanism herein reviewed.

Palavras-chave : hypoxia; HIF-1; oxygen sensor; VEGF; erythropoietin.

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