Failure to prolyl hydroxylate hypoxia-inducible factor α phenocopies VHL inactivation in vivo

Many functions have been assigned to the von Hippel-Lindau tumor suppressor gene product (pVHL), including targeting the alpha subunits of the heterodimeric transcription factor HIF (hypoxia-inducible factor) for destruction. The binding of pVHL to HIF alpha requires that HIFa be hydroxylated on one of two prolyl residues. We introduced HIF1 alpha and HIF2 alpha variants that cannot be hydroxylated on these sites into the ubiquitously expressed ROSA26 locus along with a Lox-stop-Lox cassette that renders their expression Cre-dependent. Expression of the HIF2a variant in the skin and liver induced changes that were highly similar to those seen when pVHL is lost in these organs. Dual expression of the HIF1a and HIF2a variants in liver, however, more closely phenocopied the changes seen after pVHL inactivation than did the HIF2a variant alone. Moreover, gene expression profiling confirmed that the genes regulated by HIF1a and HIF2a in the liver are overlapping but non- identical. Therefore, the pathological changes caused by pVHL inactivation in skin and liver are due largely to dysregulation of HIF target genes.