The VHL gene was first identified in 1993 as the gene responsible for a rare inherited cancer syndrome called von Hippel-Lindau disease. Inheritance of a single defective VHL gene results in the predisposition to the development of a variety of cancers including clear cell renal carcinoma, pheochromocytoma, and CNS hemangioblastoma. Subsequently, it was shown that the majority of tumors derived from patients with sporadic clear cell renal carcinoma also contained both loss of heterozygosity of the VHL locus and failure of expression and/or mutations in the remaining VHL allele. The goal of this project is to understand the biochemistry and cell biology of the VHL gene product and thereby to elucidate its role in cell transformation. Our previous studies include the completion of the cloning and sequencing of the human and rat VHL gene, the biochemical characterization of the gene product and its intracellular localization. The identification and cloning of gene products that VHL interacts with has illuminated an unexpected new area of gene control--the regulation of transcriptional elongation. We have continued our characterization of the interaction between the VHL proteins and other cellular components. In order to identify new potential interacting proteins we utilized recombinant VHL-elongin B/C complexes to affinity purify additional cellular interacting proteins. One of the proteins has been recently identified as a homolog of the newly recognized cullin family of proteins. We now know that VHL exists in the cell as a stable complex containing elongin B, elongin C, and Hs-CUL-2. The cullins are homologs of the yeast protein Cdc53 which is involved in cell cycle regulation via the targeting of specific proteins for ubiquitin mediated degradation. We have recently established that VHL expression in renal cell carcinoma lines is essential for the ability to sense serum signals and in determining whether the cells leave the cell cycle and quiesce. Wild-type VHL is essential for the ability of the cells to quiesce in response to the removal of growth factors. This quiescence is associated with an inhibition of the degradation of the cycline dependent kinase inhibitor p27. Current studies are aimed at understanding how VHL links growth factors to the control of the critical decision that cells make to either cycle or not.
