Mitochondrial anchoring of PKCalpha by PICK1 confers resistance to etoposide-induced apoptosis.

Various pathways, including regulation of functions of the Bcl-2 family, are implicated in the survival promotion by PKCalpha, however the molecular mechanisms are still obscure. We have previously demonstrated that PKCalpha is selectively anchored to mitochondria by PICK1 in fibroblasts NIH 3T3. In this study, we show that over-expression of PICK1 in leukemia REH confers resistance to etoposide-induced apoptosis, which requires an interaction with PKCalpha as the non-interacting mutant PICK1 loses the pro-survival activity. The PKCalpha selective inhibitor Gö6976 also abolishes the anti-apoptotic effect indicating a requirement for PKC activity. Disruption of PICK1/PKCalpha interactions by inhibitory peptides significantly increases cellular susceptibility to etoposide. Similar effects are also observed in HL60 cells, which exhibit an intrinsic resistance to etoposide. Molecular analysis shows that the wild type PICK1, but not the non-interacting mutant, prevents the loss of mitochondrial membrane potential with a coincident increase in phosphorylation of the anti-apoptotic Bcl-2(Ser70) and a decrease in dimerization of the pro-apoptotic Bax. PICK1 may provide the spatial proximity for phosphorylation of Bcl-2(Ser70) by PKCalpha which then leads to a higher survival. Taken together, our results suggest that PICK1 may mediate the pro-survival activity of PKCalpha by serving as a molecular link between PKCalpha and mitochondria.