Mcl-1 degradation during hepatocyte lipoapoptosis

Howard C. Masuoka, Justin Mott, Steven F. Bronk, Nathan W. Werneburg, Yuko Akazawa, Scott H. Kaufmann, Gregory J. Gores

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32 Scopus citations

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, PKCδ and PKCθ, only activation of PKCθ was observed by phospho-immunoblot analysis. As compared with Jurkat cells, a smaller PKCθ polypeptide and mRNA were expressed in hepatocytes consistent with an alternative splice variant. Short hairpin RNA-mediated knockdown of PKCθ reduced Mcl-1 degradation and lipoapoptosis. Likewise, genetic deletion of Pkcθ also attenuated Mcl-1 degradation and cytotoxicity by palmitate in primary hepatocytes. During treatment with palmitate, rottlerin inhibited phosphorylation of Mcl-1 at Ser159, 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 PKCθ-dependent destabilization of Mcl-1 as a mechanism contributing to hepatocyte lipoapoptosis.

Original languageEnglish (US)
Pages (from-to)30039-30048
Number of pages10
JournalJournal of Biological Chemistry
Volume284
Issue number44
DOIs
StatePublished - Oct 30 2009

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

Masuoka, H. C., Mott, J., Bronk, S. F., Werneburg, N. W., Akazawa, Y., Kaufmann, S. H., & Gores, G. J. (2009). Mcl-1 degradation during hepatocyte lipoapoptosis. Journal of Biological Chemistry, 284(44), 30039-30048. https://doi.org/10.1074/jbc.M109.039545