title: PKB/Akt activation inhibits p53-mediated HIF1A degradation that is independent of MDM2.
abstract: Cross-talk between the two transcription factors, p53 and hypoxia inducible factor 1alpha (HIF1A), is important in different pathophysiological conditions (Hammond and Giaccia, 2006, Clin Cancer Res 12:5007-5009) such as in the transition from myocardial hypertrophy to cardiac dilatation and heart failure. In that context, p53 induces HIF1A degradation which in turn provokes the transition from compensatory hypertrophy to myocardial thinning and chamber dilatation (Sano et al., 2007, Nature 446:444-448). In order to investigate the mechanism of p53-induced HIF1A degradation, we used the established in vitro model of deferroxamine (DFX)-induced HIF1A accumulation in H9c2 cardiac cells (Sano et al., 2007, Nature 446:444-448). Here, we report that opposite to HIF1A accumulation following exposure to DFX, prolonged DFX-induced p53 activation and HIF1A protein decrease, without any change in Hif1a mRNA. HIF1A protein decrease accompanied upregulated HIF1A ubiquitination. MDM2, an ubiquitin E3 ligase target gene of p53, was upregulated following prolonged DFX, but using p53/Mdm2 double-null mouse embryonic fibroblasts, we found that p53 upregulated HIF1A ubiquitination and degradation independently of MDM2. Moreover, with prolonged DFX treatment, an enhanced interaction between MDM2 and HIF1A was lacking. Instead, phospho-Akt(ser473) was decreased during the phase coinciding with HIF1A degradation, and inhibition of PKB/Akt phosphorylation using PI3K inhibitor (LY294002) upregulated HIF1A ubiquitination. In summary, we propose that p53-induced HIF1A degradation is not exclusively MDM2-mediated, but reversible by PKB/Akt phosphorylation.
authors: Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 20QQ, UK.
authors: Mun-Kit
authors: MK
authors: Choy
authors: Mehregan
authors: M
authors: Movassagh
authors: Martin R
authors: MR
authors: Bennett
authors: Roger S-Y
authors: RS
authors: Foo
mesh_terms: D000818:Animals; D006332:Cardiomegaly / Q000201:enzymology* / Q000473:pathology; D002460:Cell Line; D048429:Cell Size; D002867:Chromones / Q000494:pharmacology; D003676:Deferoxamine / Q000494:pharmacology; D004195:Disease Models, Animal; D005347:Fibroblasts / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D032386:Myoblasts, Cardiac / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012694:Serine; D013997:Time Factors; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D002867:Chromones; D003676:Deferoxamine; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D046988:Proteasome Endopeptidase Complex; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D051736:Proto-Oncogene Proteins c-mdm2; D012333:RNA, Messenger; D012694:Serine; D016159:Tumor Suppressor Protein p53; C497443:Hif1a protein, mouse; C497444:Hif1a protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C497207:Mdm2 protein, mouse; C497208:Mdm2 protein, rat