title: Regulation of transforming growth factor-β1-dependent integrin β6 expression by p38 mitogen-activated protein kinase in bile duct epithelial cells.
abstract: Bile duct epithelial cells (BDECs) contribute to liver fibrosis by expressing αVβ6 integrin, a critical activator of latent transforming growth factor β (TGF-β). β6 integrin (Itgβ6) mRNA induction and αVβ6 integrin expression in BDECs are partially TGF-β-dependent. However, the signaling pathways required for TGF-β-dependent Itgβ6 mRNA induction in BDECs are not known. We tested the hypothesis that the p38 mitogen-activated protein kinase (MAPK) signaling pathway contributes to TGF-β1 induction of Itgβ6 mRNA by activating SMAD and activator protein 1 (AP-1) transcription factors. Pretreatment of transformed human BDECs (MMNK-1 cells) with two different p38 MAPK inhibitors, but not a control compound, inhibited TGF-β1 induction of Itgβ6 mRNA. Inhibition of p38 also reduced TGF-β1 activation of a SMAD-dependent reporter construct. Expression of a dominant-negative SMAD3 (SMAD3ΔC) significantly reduced TGF-β1-induced Itgβ6 mRNA expression. Expression of JunB mRNA, but not other AP-1 proteins, increased in TGF-β1-treated MMNK-1 cells, and induction of JunB expression was p38-dependent. Consistent with a requirement for de novo induction of JunB protein, cycloheximide pretreatment inhibited TGF-β1 induction of Itgβ6 mRNA. Expression of a dominant-negative AP-1 mutant (TAM67) also inhibited TGF-β1 induction of Itgβ6 mRNA. Overall, the results suggest that p38 contributes to TGF-β1-induced Itgβ6 mRNA expression in MMNK-1 cells by regulating activation of both SMAD and AP-1 transcription factors.
authors.affiliation: Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Blvd, MS-1018, Kansas City, KS 66160, USA.
authors.forename: Bradley P
authors.initials: BP
authors.lastname: Sullivan
authors.forename: Karen M
authors.initials: KM
authors.lastname: Kassel
authors.forename: Sharon
authors.initials: S
authors.lastname: Manley
authors.forename: Alyson K
authors.initials: AK
authors.lastname: Baker
authors.forename: James P
authors.initials: JP
authors.lastname: Luyendyk
mesh_terms: D001652:Bile Ducts / Q000166:cytology / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D003720:Densitometry; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D039641:Integrin beta Chains / Q000096:biosynthesis*; D008156:Luciferases / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D051900:Smad3 Protein / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D039641:Integrin beta Chains; D034741:RNA, Small Interfering; D051900:Smad3 Protein; D018808:Transcription Factor AP-1; D053773:Transforming Growth Factor beta1; C072170:integrin beta6; D012313:RNA; D008156:Luciferases; D048051:p38 Mitogen-Activated Protein Kinases