title: Mcl-1 degradation during hepatocyte lipoapoptosis.
abstract: 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.
authors.affiliation: Division of Gastroenterology and Hepatology, College of Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Howard C
authors.initials: HC
authors.lastname: Masuoka
authors.forename: Justin
authors.initials: J
authors.lastname: Mott
authors.forename: Steven F
authors.initials: SF
authors.lastname: Bronk
authors.forename: Nathan W
authors.initials: NW
authors.lastname: Werneburg
authors.forename: Yuko
authors.initials: Y
authors.lastname: Akazawa
authors.forename: Scott H
authors.initials: SH
authors.lastname: Kaufmann
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Gores
mesh_terms: D000818:Animals; D017209:Apoptosis; D045744:Cell Line, Tumor; D005227:Fatty Acids / Q000494:pharmacology*; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010168:Palmitates / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011489:Protein Denaturation; D011493:Protein Kinase C / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D013228:Stearates / Q000494:pharmacology
chemical_list: D005227:Fatty Acids; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010168:Palmitates; D019253:Proto-Oncogene Proteins c-bcl-2; D013228:Stearates; D011493:Protein Kinase C; D046988:Proteasome Endopeptidase Complex