| Summary: | 博士 === 國立陽明大學 === 生物化學研究所 === 93 === Protein kinase C (PKC) is a family of serine / threonine kinases consisting of 11 isozymes. Upon activation, each isozyme translocates to particular intracellular compartments and thus exerts distinct functions in response to external signals. The translocation is mediated, at least in part, by isozyme-specific anchoring proteins. PICK1 is initially cloned as a PKCα-binding protein. In this study, it is demonstrated that PICK1 localizes in mitochondria through its PDZ domain. Upon serum stimulation, PICK1 displays a dynamic redistribution from cytosol to peri-nuclear region where it still associates with mitochondria. PKCα, but not the non-interacting C terminal-deleted mutant, co-translocates with PICK1 to mitochondria upon serum stimulation. The results suggest that PICK1 targets PKCα to mitochondria through a direct protein-protein interaction. In addition to intracellular targeting, PICK1 also modulates the activity of PKCα toward a selective substrate. These results demonstrate that PICK1 is a specific anchoring protein of PKCα. To investigate the cellular significance of targeting of PKCα to mitochondria by PICK1, REH cells clones stably expressing heterologous wild type and the non-interacting mutant PICK1 are selected. Over-expression of PICK1 renders cells more resistant to etoposide-induced apoptosis which is associated with enhanced phosphorylation of Bcl-2 at Ser70, a known phosphorylation site of PKCα, reduced dimerization of Bax proteins and stabilized mitochondrial membrane potential. In addition, resistance to etoposide-induced apoptosis requires an interaction between PICK1 and PKC��. These results indicate that PICK1 may exert its anti-apoptotic activity by anchoring PKC�� to mitochondria which thus leads to enhanced phosphorylation of Bcl-2 and stabilized mitochondrial membrane potential. Enhanced PKC�� activity is associated with a variety of tumors. This study has unveiled a new avenue for the development of anti-cancer therapy by increasing drug sensitivity targeting PICK1 / PKC�� interactions.
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