pVHL acts as an adaptor to promote the inhibitory phosphorylation of the NF-κB agonist Card9 by CK2

The VHL tumor suppressor protein (pVHL) is part of an E3 ubiquitin ligase that targets HIF for destruction. pVHL-defective renal carcinoma cells exhibit increased NF-B-K activity but the mechanism is unclear. NF-KB affects tumorigenesis and therapeutic resistance in some settings. We found that pVHL associates with the NF-KB agonist Card9 but does not target Card9 for destruction. Instead, pVHL serves as an adaptor that promotes the phosphorylation of the Card9 C terminus by CK2. Elimination of these sites markedly enhanced Card9's ability to activate NF-B-K in VHL+/+ cells, and Card9 siRNA normalized NF-B-K activity in VHL-/- cells and restored their sensitivity to cytokine-induced apoptosis. Furthermore, downregulation of Card9 in VHL-/- cancer cells reduced their tumorigenic potential. Therefore pVHL can serve as an adaptor for both a ubiquitin conjugating enzyme and a kinase. The latter activity, which promotes Card9 phosphorylation, links pVHL to control of NF-B-K activity and tumorigenesis.