title: Transforming growth factor-beta and platelet-derived growth factor signal via c-Jun N-terminal kinase-dependent Smad2/3 phosphorylation in rat hepatic stellate cells after acute liver injury.
abstract: After liver injury, transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF) regulate the activation of hepatic stellate cells (HSCs) and tissue remodeling. Mechanisms of PDGF signaling in the TGF-beta-triggered cascade are not completely understood. TGF-beta signaling involves phosphorylation of Smad2 and Smad3 at linker and C-terminal regions. Using antibodies to distinguish Smad2/3 phosphorylated at linker regions from those phosphorylated at C-terminal regions, we investigated Smad2/3-mediated signaling in rat liver injured by CCl(4) administration and in cultured HSCs. In acute liver injury, Smad2/3 were transiently phosphorylated at both regions. Although linker-phosphorylated Smad2 remained in the cytoplasm of alpha-smooth muscle actin-immunoreactive mesenchymal cells adjacent to necrotic hepatocytes in centrilobular areas, linker-phosphorylated Smad3 accumulated in the nuclei. c-Jun N-terminal kinase (JNK) in the activated HSCs directly phosphorylated Smad2/3 at linker regions. Co-treatment of primary cultured HSCs with TGF-beta and PDGF activated the JNK pathway, subsequently inducing endogenous linker phosphorylation of Smad2/3. The JNK pathway may be involved in migration of resident HSCs within the space of Disse to the sites of tissue damage because the JNK inhibitor SP600125 inhibited HSC migration induced by TGF-beta and PDGF signals. Moreover, treatment of HSCs with both TGF-beta and PDGF increased transcriptional activity of plasminogen activator inhibitor-1 through linker phosphorylation of Smad3. In conclusion, TGF-beta and PDGF activate HSCs by transmitting their signals through JNK-mediated Smad2/3 phosphorylation at linker regions, both in vivo and in vitro.
authors.affiliation: Third Department of Internal Medicine, Kansai Medical University, 10-15 Fumizonocho, Moriguchi, Osaka 570-8507, Japan.
authors.forename: Katsunori
authors.initials: K
authors.lastname: Yoshida
authors.forename: Koichi
authors.initials: K
authors.lastname: Matsuzaki
authors.forename: Shigeo
authors.initials: S
authors.lastname: Mori
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Tahashi
authors.forename: Hideo
authors.initials: H
authors.lastname: Yamagata
authors.forename: Fukiko
authors.initials: F
authors.lastname: Furukawa
authors.forename: Toshihito
authors.initials: T
authors.lastname: Seki
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishizawa
authors.forename: Junichi
authors.initials: J
authors.lastname: Fujisawa
authors.forename: Kazuichi
authors.initials: K
authors.lastname: Okazaki
mesh_terms: D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D006133:Growth Substances / Q000494:pharmacology*; D015151:Immunoblotting; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D048031:JNK Mitogen-Activated Protein Kinases / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000187:drug effects* / Q000293:injuries / Q000378:metabolism; D008297:Male; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D051785:Smad Proteins; D015534:Trans-Activators / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology
chemical_list: D004268:DNA-Binding Proteins; D006133:Growth Substances; D010982:Platelet-Derived Growth Factor; D051785:Smad Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D048031:JNK Mitogen-Activated Protein Kinases