Abstract
von Hippel-Lindau (VHL) hereditary cancer syndrome is caused by mutations in the VHL tumor suppressor gene and is characterized by a predisposition to form various types of tumors, including renal cell carcinomas, hemangioblastomas, and pheochromocytomas. The protein products of the VHL gene, pVHL, are part of an ubiquitin ligase complex that tags hypoxia inducible factor alpha (HIF-α) for proteosomal degradation. pVHL has also been reported to bind to atypical protein kinase C (aPKC).
To better understand the relationship between pVHL and aPKC, the PKC iota (PKCι) isoform of aPKC was knocked out in renal carcinoma cells, both pVHL-negative and those with replaced pVHL. Cellular properties associated with pVHL function were assayed. Knockout of PKCι in pVHL-expressing cells led to greater downregulation of HIF-α than seen with pVHL alone, suggesting that the presence of PKCι opposes complete regulation of HIF-α by pVHL. In contrast, absence of either pVHL or PKCι disrupted tight junction formation and led to upregulated levels of α5 integrin, both of which were phenocopied by lysosomal inhibition. LAMP1 (lysosome associated membrane protein 1), a marker for lysosomes, showed dysregulated localization and altered electrophoretic gel migration in the absence of pVHL. While the upregulated α5 integrin seen in the absence of either pVHL or PKCι loss was associated with increased cell adhesion, loss of pVHL caused increased cell motility whereas loss of PKCι decreased motility.
These data are consistent with a known role of PKCι in endocytosis of α5 integrin and suggest a subsequent novel role of pVHL in targeting a pool of endocytosed α5 integrin for lysosomal degradation.