P53 INHIBITS HYPOXIA-INDUCIBLE FACTOR-STIMULATED TRANSCRIPTION

p53 is required for hypoxia-induced apoptosis in vivo, although the me chanism by which this occurs is not known. Conversely, induction of th e hypoxia-inducible factor-1 (HIF-1) transactivator stimulates transcr iption of a number of genes crucial to survival of the hypoxic state. Here we demonstrate that p53 represses HIF-1-stimulated transcription. Although higher levels of p53 are required to inhibit HIF than are ne cessary to transcriptionally activate p53 target genes, these levels o f p53 are similar to those that stimulate cleavage of poly(ADP-ribose) polymerase, an early event in apoptosis, Transfection of full-length p300 stimulates both p53-dependent and HIF-dependent transcription but does not relieve p53-mediated inhibition of HIF. In contrast, a p300 fragment, which binds to p53 but not to HIF-1, prevents p53-dependent repression of HIF activity. Transcriptionally inactive p53, mutated in its DNA binding domain, retains the ability to block HIF transactivat ing activity, whereas a transcriptionally inactive double point mutant defective for p300 binding does not inhibit HIF. Finally, depletion o f doxorubicin-induced endogenous p53 by E6 protein attenuates doxorubi cin-stimulated inhibition of HIF, suggesting that a p53 level sufficie nt for HIF inhibition can be achieved in vivo. These data support a mo del in which stoichiometric binding of p53 to a HIF/p300 transcription al complex mediates inhibition of HIF activity.