HIF alpha expression in VHL-deficient renal cancer cells is dependent on phospholipase D

Loss of the von Hippel-Lindau (VHL) tumor suppressor gene contributes to proliferative disorders including renal cell carcinoma. The consequence of VHL loss is increased levels of hypoxia-inducible factor-alpha (HIFalpha), which is targeted for proteolytic degradation by the VHL gene product pVHL. HIF is a transcription factor that increases the expression of factors critical for tumorigenesis in renal cell carcinoma. We report here another regulatory component of HIFalpha expression in renal cancer cells. Phospholipase D (PLD), which is commonly elevated in renal and other cancers, is required for elevated levels of both HIF1alpha and HIF2alpha in VHL-deficient renal cancer cells. The induction of both HIF1alpha and HIF2alpha by hypoxic mimetic conditions was also dependent on PLD in renal cancer cells with restored pVHL expression. The effect of PLD activity upon HIFalpha expression was at the level of translation. PLD activity also provides a survival signal that suppresses apoptosis induced by serum deprivation in the renal cancer cells. Suppression of HIF2alpha has been shown to reverse tumorigenesis with renal cancer cells. The finding here that HIF2alpha expression is dependent on PLD in renal cancer cells suggests that targeting PLD signals may represent an alternative therapeutic strategy for targeting HIF2alpha in renal cancers where HIF2alpha is critical for tumorigenesis and elevated PLD activity is common.