SMAD and p38 MAPK signaling pathways independently regulate alpha1(I) collagen gene expression in unstimulated and transforming growth factor-beta-stimulated hepatic stellate cells.
The hepatic stellate cell (HSC) is the predominant cell type responsible for excess collagen deposition during liver fibrosis. Both transforming growth factor-beta (TGF-beta), the most potent fibrogenic cytokine for HSCs, which classically activates Smad signaling, and p38 MAPK signaling have been shown to influence collagen gene expression; however, the relative contribution and mechanisms that these two signaling pathways have in regulating collagen gene expression have not been investigated. The aim of this study was to investigate the relative roles and mechanisms of both Smad and p38 MAPK signaling in alpha1(I) collagen gene expression in HSCs. Inhibiting either p38 MAPK or Smad signaling reduced alpha1(I) collagen mRNA expression in untreated or TGF-beta-treated HSCs, and when both signaling pathways were simultaneously inhibited, alpha1(I) collagen gene expression was essentially blocked. Both signaling pathways were found to independently and additively increase alpha1(I) collagen gene expression by transcriptional mechanisms. TGF-beta treatment increased alpha1(I) collagen mRNA half-life, mediated by increased stability of alpha1(I) collagen mRNA through p38 MAPK signaling but not through Smad signaling. In conclusion, both p38 MAPK and Smad signaling independently and additively regulate alpha1(I) collagen gene expression by transcriptional activation, whereas p38 MAPK and not Smad signaling increased alpha1(I) collagen mRNA stability.
Tsukada
Shigeki
S
Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Westwick
John K
JK
Ikejima
Kenichi
K
Sato
Nobuhiro
N
Rippe
Richard A
RA
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D024042:Collagen Type I / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005786:Gene Expression Regulation; D015971:Gene Expression Regulation, Enzymologic; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D008099:Liver / Q000166:cytology*; D048371:MAP Kinase Kinase 3 / Q000378:metabolism; D048669:MAP Kinase Kinase 6 / Q000378:metabolism; D008297:Male; D009130:Muscle, Smooth / Q000166:cytology; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012260:Ribonucleases / Q000378:metabolism; D015398:Signal Transduction; D051785:Smad Proteins; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D001616:beta-Galactosidase / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D024042:Collagen Type I; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D011725:Pyridines; D012333:RNA, Messenger; D051785:Smad Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D049452:Green Fluorescent Proteins; D003094:Collagen; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D012260:Ribonucleases; D001616:beta-Galactosidase; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one