Functional Analysis of the von Hippel-Lindau Disease Tumor Suppressor Gene

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We found that, in normal human renal proximal tubule epithelial cells, the steady-state amount of VHL protein is strictly regulated by cell density. The cellular VHL content is more than 100-fold higher in dense cultures than in sparse cultures. The growth rates of renal cell cacinoma cells lacking an intact VHL gene and their derivatives with wild-type or mutant VHL expression vector do not differ significantly when they are growing in log-phase. Importantly, however, there is a difference when they reach confluency : cells lacking wild-type VHL grew continuously, while cells expressing exogenous VHL protein showed relatively limited cell growth. VHL protein functions as a growth suppressor at high cell density, and this might be the basis of the tumor suppressor function of VHL. We investigated the role of the VHL gene in CNS development using rodent CNS progenitor cells. We show that expression of the VHL protein is correlated with neuronal differentiation but not with glial differe … More ntiation in CNS progenitor cells, and we also show that VHL gene transduction induces neuronal differentiation. In addition, a VHL mRNA antisense oligonucleotide inhibits differentiation of CNS progenitor cells and up-regulates their cell cycle. The VHL protein contains two domains, alpha and beta. We report that the beta-domain interacts directly with atypical PKC isotypes, PKC zeta and PKC lambda. Further, the regulatory domain of aPKC is sufficient for this direct protein-protein interaction. To investigate the potential role of the PTEN gene in renal tumorigenesis, we searched for abnormalities of the gene in 68 primary renal-cell carcinomas (RCCs) as well as in 17 renal carcinoma-derived cell lines. Five of 68 (7.5 %) primary RCCs exhibited intragenic mutations, and 1 of 17 (5.9 %) cell lines had an insertion mutation. Four of the 5 primary tumors with PTEN mutation were high-grade, advanced clear-cell RCCs with distant metastases or renal vein tumor invasions, resulting in poor prognostic courses. PTEN mutation is observed m a subset of RCCs and that, especially in clear-cell RCCs, it occurs as a late-stage event and may contribute to the invasive and/or metastatic tumor phenotype. Less