VHL is a tumor suppressor gene whose germline loss results in Von Hippel-Lindau disease, a hereditary cancer syndrome in which affected individuals have an increased rate of renal clear cell carcinoma, hemangioblastoma, and pheochromocytoma. Lee et al. (2005) showed that suppression of the VHL protein (pVHL) confers a survival advantage to nerve growth factor (NGF)-deprived sympathetic- neuron-like pheochromocytoma cells (PCI 2 cells). This and other evidence led to the hypothesis that loss of VHL in developing sympathoadrenal cells leads to an escape from normal programmed cell death, which may contribute to pheochromocytoma. A prerequisite for this hypothesis is that pVHL functions normally to regulate programmed cell death in cells of the sympathoadrenal lineage. The overall goal of this proposal is to examine the role of pVHL in developmental apoptosis in sympathetic neurons. Extensive cell death occurs as developing sympathetic neurons innverate their targets. Sympathetic neurons that successfully receive trophic support in the form of NGF survive, and those that do not undergo apoptosis. Here, we propose a novel function for pVHL based upon the following rationale: we have found that pVHL overexpression promotes death in sympathetic neurons, and preliminary data suggests that loss of pVHL delays death in sympathetic neurons after NGF deprivation. pVHL is a multifunctional protein best characterized for regulating the stability of hypoxia inducible factor (HIF) via ubiquitination, and we have recently found that HIF2alpha is a survival-promoting factor in these neurons. Further evidence suggests that pVHL may also regulate c-Jun and BIM-EL, both of which are known mediators of cell death after NGF deprivation. We hypothesize that pVHL regulates these specific pro-survival and pro-death factors (HIF, c-Jun, and/or BIM-EL), and that this regulation is required for apoptosis after NGF deprivation in sympathetic neurons. We propose two specific aims to determine the role of pVHL in cell death after NGF deprivation in sympathetic neurons:-1) we will use VHL loxP/loxP conditional knockout mice to test the hypothesis that pVHL loss in vitro will result in inhibition of apoptosis after NGF deprivation, and we will determine if this protection proceeds from changes in HIF, c-Jun, or BIM-EL and 2) we will use loxP/loxP Wntl-CRE mice to determine the effects of loss of pVHL in vivo in the developing sympathoadrenal lineage. This proposal will elucidate signaling events important for NGF deprivation and may describe functions of pVHL that, when lost could contribute to pheochromocytoma.
