Expression of fibronectin and HIF-1alpha in renal cell carcinomas: relationship to von Hippel-Lindau gene inactivation

The von Hippel-Lindau (VHL) tumor suppressor gene (TSG) at 3p25 is mutated in approximately 50% of conventional (clear cell) renal cell carcinomas (cRCC). VHL normally regulates the ubiquitin-mediated proteolysis of hypoxia-inducible factor 1alpha (HIF-1alpha), and VHL inactivation results in increased cellular HIF-1alpha expression. VHL protein (pVHL) also interacts with fibronectin (Fn) and VHL inactivation results in defective Fn extracellular matrix assembly. The present study investigated the immunohistochemical (IHC) staining for Fn and HIF-1alpha in 11 cRCC and the relationship of the staining to VHL inactivation by gene deletion, mutation, or hypermethylation. Evidence for VHL inactivation by 3p deletions and VHL mutations were found in six tumors. Fn-positive IHC staining of tumor cells and negative to weak staining of extracellular stroma was found in five cases having exon 1 or exon 2 mutations. In contrast, Fn staining was absent in tumor cells and positive in the stroma of five tumors without VHL inactivation and in one tumor with a C-terminal exon 3 mutation. HIF-1alpha tumor cell staining was present in the cRCC with VHL inactivation but was also present in two tumors having 3p deletions but neither mutation nor hypermethylation of VHL. These two cRCC showed a tumor cell-negative and stroma-positive pattern of Fn staining. The findings indicate that VHL inactivation plays a role in the development of some cRCC by altering Fn cell--stroma relationships. They also suggest that some C-terminal mutations may not interfere with Fn assembly and that a 3p TSG in addition to VHL influences HIF-1alpha degradation.