HIF-2alpha downregulation in the absence of functional VHL is not sufficient for renal cell differentiation.

Michael D Hughes,Alan R Schoenfeld,Erilda Kapllani,Robert D Burk,Ashlynn E Alexander

doi:10.1186/1475-2867-7-13

Abstract

BackgroundMutational inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene has been linked to hereditary as well as sporadic clear cell renal carcinomas. The product of the VHL gene, pVHL, acts to target hypoxia-inducible factor alpha (HIF-α) subunits for ubiquitination and subsequent degradation. Using an RNA interference approach to lower levels of HIF-2α in two different renal cell lines that lack functional pVHL, we have tested the contribution of HIF-2α toward cellular pVHL activities.ResultsKnockdown of HIF-2α resulted in cell cycle arrest of renal cells that were grown on collagen I, indicating that this pVHL function is dependent on HIF-2α regulation. However, cellular morphological changes and downregulation of integrins α5 and β1, which were seen upon pVHL replacement, were not faithfully phenocopied by HIF-2α reduction. Moreover, fibronectin deposition and expression of renal cell differentiation markers were observed in cells containing replaced pVHL, but not in HIF-2α knockdown cells, indicating that these pVHL functions may occur independently of HIF-2α downregulation.ConclusionThese results indicate that HIF-2α regulation is not sufficient for pVHL-induced renal cell differentiation. We hypothesize that in addition to HIF-2α dysregulation, abrogation of additional pVHL functions is required for the initiation of renal carcinogenesis.

Highlights

Mutational inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene has been linked to hereditary as well as sporadic clear cell renal carcinomas
We report that hypoxia inducible factor (HIF)-2α regulation plays a role in certain, but not all VHL-associated cellular phenotypes. These results suggest that pVHL has other important biochemical and cellular functions in addition to the ubiquitination of HIF-α that may be important for tumor suppression
Expression of the renal marker HNF-1α was observed in 786-O cells expressing pVHL, but not in cells with reduced HIF-2α levels (Figure 6c). These results indicate that HIF-2α regulation alone does not cause renal cell differentiation and that the differentiation process in renal cells is dependent on other VHL activities

Summary

Introduction

Mutational inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene has been linked to hereditary as well as sporadic clear cell renal carcinomas. The product of the VHL gene, pVHL, acts to target hypoxia-inducible factor alpha (HIF-α) subunits for ubiquitination and subsequent degradation. Lindau (VHL) disease arises from heterozygous germline mutations in the VHL tumor suppressor gene, which resides on chromosome 3p25, and is characterized by clear cell renal carcinomas, hemangiomas, pheochromocytomas, as well as other tumor types [1,2]. The shorter form has been shown to contain full tumor suppressor function [3,5,6] Both protein products of the VHL gene (collectively called pVHL) contain an alpha and beta domain [7]. HIF-α, the alpha subunit of the heterodimeric transcription factor hypoxia inducible factor (HIF), binds to pVHL's beta domain and is the best-known substrate of the pVHL E3 ligase complex [14,15]

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