Patients afflicted with hereditary von Hippel-Lindau disease develop retinal, cerebellar and spinal cord hemangioblastomas as well as renal carcinomas and tumors of the pancreas and epididymis due to mutations in the gene encoding von Hippel-Lindau tumor suppressor protein (pVHL). pVHL normally functions as an adapter in an E3 ubiquitin ligase complex to regulate the activity of the transcription factor, HIF-1?. When cellular oxygen levels are reduced, HIF-1? is activated and upregulates cellular proliferation factors resulting in cell growth. In the absence of functional pVHL, dysregulation of HIF-1? can lead to uncontrolled cell growth regardless of oxygen levels. Studies from the Frydman laboratory have demonstrated that proper folding and functionality of pVHL requires an interaction between pVHL and the chaperone Hsp70 and the large cytosolic heterooligomeric chaperonin TriC. Folded pVHL is then competent to form a complex with elongins B and C (herein elongin BC), a step that is required for pVHL stability. The pVHL-elongin BC complex (VBC), when incorporated into the SCF E3 ubiquitin ligase complex, directs the proteolytic degradation of HIF-1? in the presence of oxygen. Thus, proper folding and functionality of pVHL involves several protein quality control "checkpoints" mediated by chaperone and proteasomal machinery. Importantly, some of the mutants leading to VHL disease have the potential to achieve folding, but fail to do so through the action of these quality control checkpoints that result in their degradation. The mechanism of proteolytic degradation of pVHL mutants is unclear. The long-term goal of this research is to determine how cellular protein folding and degradation machinery cooperate to maintain quality control of the tumor suppressor protein pVHL. Here we propose to determine the chaperone and proteolytic degradation quality control requirements of tumor-causing mutations in the easily manipulated yeast system and then determine if these mechanisms are conserved in mammalian cells. This understanding may lead to therapeutic strategies to restore the function of these mutant proteins in affected patients. Since other pathological processes, including other cancers, are caused by mutations that affect the folding or stability of key regulatory proteins, the results obtained for VHL may provide a paradigm with broad conceptual and therapeutic implications.
Patients with hereditary von Hippel-Lindau disease have the potential to develop a variety of tumors including hemangioblastomas in retinal, cerebellar and spinal cord tissue as well as renal carcinomas and tumors of the pancreas and epididymis. The basis of tumor formation in these patients is due to mutations in the von Hippel- Lindau tumor suppressor protein (pVHL), a protein that normally functions to keep cell division in check. In this proposal, we will determine the mechanism by which the cell recognizes and processes mutant pVHL protein in an effort to identify therapies by which normal pVHL function can be restored in human cells.