The Journal of biological chemistry
The mechanisms of free fatty acid-induced lipoapoptosis are incompletely understood. Here we demonstrate that Mcl-1, an anti-apoptotic member of the Bcl-2 family, was rapidly degraded in hepatocytes in response to palmitate and stearate by a proteasome-dependent pathway. Overexpression of a ubiquitin-resistant Mcl-1 mutant in Huh-7 cells attenuated palmitate-mediated Mcl-1 loss and lipoapoptosis; conversely, short hairpin RNA-targeted knockdown of Mcl-1 sensitized these cells to lipoapoptosis. Palmitate-induced Mcl-1 degradation was attenuated by the novel protein kinase C (PKC) inhibitor rottlerin. Of the two human novel PKC isozymes, PKCdelta and PKC, only activation of PKC was observed by phospho-immunoblot analysis. As compared with Jurkat cells, a smaller PKC polypeptide and mRNA were expressed in hepatocytes consistent with an alternative splice variant. Short hairpin RNA-mediated knockdown of PKC reduced Mcl-1 degradation and lipoapoptosis. Likewise, genetic deletion of Pkc also attenuated Mcl-1 degradation and cytotoxicity by palmitate in primary hepatocytes. During treatment with palmitate, rottlerin inhibited phosphorylation of Mcl-1 at Ser(159), a phosphorylation site previously implicated in Mcl-1 turnover. Consistent with these results, an Mcl-1 S159A mutant was resistant to degradation and improved cell survival during palmitate treatment. Collectively, these results implicate PKC-dependent destabilization of Mcl-1 as a mechanism contributing to hepatocyte lipoapoptosis.
Animals, Apoptosis, Cell Line, Tumor, Fatty Acids, Hepatocytes, Humans, Jurkat Cells, Mice, Myeloid Cell Leukemia Sequence 1 Protein, Palmitates, Proteasome Endopeptidase Complex, Protein Denaturation, Protein Kinase C, Proto-Oncogene Proteins c-bcl-2, Stearates
Masuoka, Howard C.; Mott, Justin L.; Bronk, Steven F.; Werneburg, Nathan W.; Akazawa, Yuko; Kaufmann, Scott H.; and Gores, Gregory J., "Mcl-1 degradation during hepatocyte lipoapoptosis." (2009). Journal Articles: Biochemistry & Molecular Biology. 15.