title: Bile acids inhibit Mcl-1 protein turnover via an epidermal growth factor receptor/Raf-1-dependent mechanism.
abstract: Bile acids have been implicated in biliary tract carcinogenesis, in part, by activating the epidermal growth factor receptor (EGFR). Overexpression of Mcl-1, a potent antiapoptotic protein of the Bcl-2 family, has also been reported in cholangiocarcinomas. Because receptor tyrosine kinases like EGFR may modulate antiapoptotic protein expression, we examined the hypothesis that bile acids modulate Mcl-1 expression levels via EGFR. Deoxycholate increased cellular Mcl-1 protein in a concentration-dependent manner. The deoxycholate-mediated increase of cellular Mcl-1 protein was blocked equally by EGFR tyrosine kinase inhibitors or an EGFR-neutralizing antibody. Although inhibition of mitogen-activated protein kinases did not attenuate the deoxycholate-associated increase in Mcl-1 protein, the Raf-1 inhibitor, BAY 37-9751, effectively blocked the cellular increase of this protein. Neither Mcl-1 transcriptional activity nor its mRNA stability was altered by deoxycholate treatment. However, Mcl-1 protein stability was increased by bile acid treatment, an effect duplicated by proteasome inhibition. Deoxycholate prolongation of Mcl-1 turnover was blocked by either EGFR inhibitors or the Raf-1 inhibitor. Whereas the deoxycholate-induced increase in Mcl-1 reduced Fas-mediated apoptosis, the Raf-1 inhibitor potentiated Fas apoptosis. Our results demonstrate that bile acids block Mcl-1 protein degradation via activation of an EGFR/Raf-1 cascade resulting in its cellular accumulation. Raf-1 inhibitors block this increase of Mcl-1 and render the cells more susceptible to apoptosis, a potential therapeutic strategy for cholangiocarcinomas.
authors.affiliation: Division of Gastroenterology and Hepatology, Mayo Medical School, Clinic, and Foundation, Rochester, Minnesota 55905, USA.
authors.forename: Jung-Hwan
authors.initials: JH
authors.lastname: Yoon
authors.forename: Nathan W
authors.initials: NW
authors.lastname: Werneburg
authors.forename: Hajime
authors.initials: H
authors.lastname: Higuchi
authors.forename: Ali E
authors.initials: AE
authors.lastname: Canbay
authors.forename: Scott H
authors.initials: SH
authors.lastname: Kaufmann
authors.forename: Cahit
authors.initials: C
authors.lastname: Akgul
authors.forename: Steven W
authors.initials: SW
authors.lastname: Edwards
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Gores
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D018281:Cholangiocarcinoma / Q000378:metabolism; D003840:Deoxycholic Acid / Q000494:pharmacology*; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000502:physiology*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D003840:Deoxycholic Acid; D066246:ErbB Receptors; D019908:Proto-Oncogene Proteins c-raf