The von Hippel-Lindau gene product inhibits vascular permeability factor/vascular endothelial growth factor expression in renal cell carcinoma by blocking protein kinase C pathways.

Mutation or loss of function of the von Hippel-Lindau (VHL) tumor suppressor gene is regularly found in sporadic renal cell carcinomas (RCC), well vascularized malignant tumors that characteristically overexpress vascular permeability factor/vascular endothelial growth factor (VPF/VEGF). The wild-type VHL (wt-VHL) gene product acts to suppress VPF/VEGF expression, which is overexpressed when wt-VHL is inactive. The present study investigated the pathways by which VHL regulates VPF/VEGF expression. We found that inhibition of protein kinase C (PKC) represses VPF/VEGF expression in RCC cells that regularly overexpress VPF/VEGF. The wt-VHL expressed by stably transfected RCC cells forms cytoplasmic complexes with two specific PKC isoforms, zeta and delta, and prevents their translocation to the cell membrane where they otherwise would engage in signaling steps that lead to VPF/VEGF overexpression. Other experiments implicated mitogen-activated protein kinase (MAPK) phosphorylation as a downstream step in PKC regulation of VPF/VEGF expression. Taken together, these data demonstrate that wt-VHL, by neutralizing PKC isoforms zeta and delta and thereby inhibiting MAPK activation, plays an important role in preventing aberrant VPF/VEGF overexpression and the angiogenesis that results from such overexpression.