title: Prolyl hydroxylase domain 2 protein suppresses hypoxia-induced endothelial cell proliferation.
abstract: Prolyl hydroxylase domain 2 protein (PHD2) signals the degradation of hypoxia-inducible factor (HIF)-1alpha by hydroxylating specific prolyl residues located within oxygen-dependent degradation domains. As expected, endothelial cells (ECs) overexpressing PHD2 had reduced HIF-1alpha and vascular endothelial growth factor-A expression and failed to accelerate their proliferation in response to hypoxia. Surprisingly, although these cells displayed further reductions in HIF-1alpha and vascular endothelial growth factor-A expression when cultured under normoxia, there was no further reduction in EC proliferation. Thus, there seemed to be no consistent correlation between PHD2 hydroxylase-mediated suppression of HIF-1alpha expression and inhibition of EC growth. Indeed, overexpression of a mutant PHD2 lacking hydroxylase activity also greatly diminished EC response to hypoxia-induced increase in proliferation, in spite of the fact that hypoxia-induced HIF-1alpha accumulation was not affected by mutant PHD2. These data strongly suggest the existence of a hydroxylase-independent mechanism for PHD2-mediated inhibition of EC proliferation under hypoxia. In support of a physiological relevance of PHD2 overexpression, we found that endogenous PHD2 expression was significantly upregulated by hypoxia and that silencing of the Phd2 gene by RNA interference significantly enhanced hypoxia-induced EC proliferation. In conclusion, this study demonstrates that PHD2 may act as a negative feedback regulator to antagonize hypoxia-induced EC proliferation.
authors.affiliation: Center for Vascular Biology, University of Connecticut Health Center, 263 Farmington Ave, Farmington, CT 06030-3501, USA.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Takeda
authors.forename: Guo-Hua
authors.initials: GH
authors.lastname: Fong
mesh_terms: D002460:Cell Line; D049109:Cell Proliferation; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D042783:Endothelial Cells / Q000378:metabolism* / Q000473:pathology*; D025461:Feedback, Physiological; D020868:Gene Silencing; D006900:Hydroxylation; D000860:Hypoxia / Q000378:metabolism* / Q000473:pathology*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011393:Procollagen-Proline Dioxygenase; D014162:Transfection; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism / Q000494:pharmacology
chemical_list: D004268:DNA-Binding Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017874:Immediate-Early Proteins; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; D011393:Procollagen-Proline Dioxygenase; C490189:Egln1 protein, mouse; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases