FIH-1: a novel protein that interacts with HIF-1 alpha and VHL to mediate repression of HIF-1 transcriptional activity

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of oxygen homeosta sis that controls angiogenesis, erythropoiesis, and glycolysis via transcri ptional activation of target genes under hypoxic conditions. O-2-dependent binding of the von Hippel-Lindau (VHL) tumor suppressor protein targets the HIF-1 alpha subunit for ubiquitination and proteasomal degradation. The ac tivity of the HIF-1 alpha transactivation domains is also O-2 regulated by a previously undefined mechanism. Here, we report the identification of fac tor inhibiting HIF-1 (FIH-1), a protein that binds to HIF-1 alpha. and inhi bits its transactivation function. In addition, we demonstrate that FIH-1 b inds to VHL and that VHL also functions as a transcriptional corepressor th at inhibits HIF-1 alpha. transactivation function by recruiting histone dea cetylases. Involvement of VHL in association with FIH-1 provides a unifying mechanism for the modulation of HIF-1 alpha protein stabilization and tran scriptional activation in response to changes in cellular O-2 concentration .