The von Hippel-Lindau tumor suppressor protein mediates ubiquitination of activated atypical protein kinase C

The von Hippel-Lindau tumor-suppressor protein (pVHL) forms a protein complex (VCB-Cul2) with elongin C, elongin B, Cul-2, and Rbx1, which functions as a ubiquitin-protein ligase (EU The a-subunits of the bypoxia-inducible factors have been identified as targets for the VCB-Cul2 ubiquitin ligase. However, a variety of cellular defects caused by the depletion of pVHL cannot be explained solely by the ubiquitin-mediated degradation of hypoxia-inducible factor-a. We show here that a member of the atypical protein kinase C (PKC) group, PKC lambda, is ubiquitinated by the pVHL-containing E3 enzyme. An active PKC lambda mutant is ubiquitinated more extensively than wild-type PKC lambda in HEK293 cells, and the ubiquitination is further enhanced by the overexpression of pVHL. The activation of wild-type PKC lambda by serum stimulation of cells enhances the ubiquitination of the protein, supporting the notion that active PKC lambda is preferentially ubiquitinated by VCB-Cul2 ubiquitin ligase. Furthermore, we show that PKC lambda can be ubiquitinated in vitro in a cell-free ubiquitination assay using purified recombinant components including VCB-Cul2. Given the known function of aPKC in the regulation of cell polarity and cell growth, PKC lambda may be a target of pVHL in its function as a tumor suppressor.