p38 MAPK mediates fibrogenic signal through Smad3 phosphorylation in rat myofibroblasts

Abstract

Mikio Ni~hizawa,~ Hepatic stellate cells (HSCs) spontaneously transdifferentiate into myofibroblast (MFB) -phenotype on plastic dishes. This response recapitulates the features of activation in viva Transforming growth &tor P (TGF-P) plays a prominent role in stimulating liver fibrogenesis by MFBs. In quiescent HSCs, TGF-P signaling involves TGF-P type I receptor (TPRI)-mediated phosphorylation of serine residues within the conserved SSXS motif at the C-terminus of Smad2 and Smad3. The middle linker regions of Smad2 and Smad3 also are phosphorylated by mitogenactivated protein b a s e (MAPK). This study elucidates the change of Smad3-mediated signals during the transdifferentiation process. By using antibodies highly specific to the phosphorylated C-terminal region and the phosphorylated linker region of Smad3, we found that TGF-& dependent Smad3 phosphorylation at the C-terminal region decreased, but that the phosphorylation at the linker region increased in the process of transdifferentiation. TGF-P activated the p38 MAPK pathway, further leading to Smad3 phosphorylation at the linker region in the cultured MFBs, irrespective of Smad2. The phosphorylation promoted hetero-complex formation and nuclear translocation of Smad3 and Smad4. Once combined with TPRI-phosphorylated Smad2, the Smad3 and Smad4 complex bound to plasminogen activator inhibitor-type I promoter could enhance the transcription. In addition, Smad3 phosphorylation mediated by the activated TPRI was impaired severely in MFBs during chronic liver injury, whereas Smad3 phosphorylation at the linker region was remarkably induced by p38 MAPK pathway. In conclusion, p38 MAPK-dependent Smad3 phosphorylation promoted extracellular matrix production in MFBs both in vitro and in viva (HEPATOLOGY 2003 age as well as after their prolonged culture on plastic dishes.' This process involves changes in the cell morphology and gene expression and is characterized by the gradual loss in the retinoid content and the synthesis of a large amount of extracellular matrix (ECM) components.Transforming growth factor P (TGF-P) is an important mediator of ECM accumulation and is involved in a variety of physiologic and pathologic processes.2 In particular, the expression of TGF-/3 at high steady-state levels associated with the accelerated ECM accumulation in MFBs is a common finding in human chronic liver disease of different etiologies.3 Uncontrolled ECM accumulation mediated by TGF-P is thought to be essential for the development of liver fibrosis. However, the change of TGF-P signals during the transdifferentiation process of HSCs remains unclear.O n the other hand, recent studies over the past several years have elucidated how TGF-P initiates its response. TGF-/3 transduces the signal from its receptor to nucleus through Smads.4 The activated TGF-P type I receptor (TPRI) phosphorylates such receptor-regulated Smads 879

TGFβ pathobiology in the eye

“…[33][34][35][36] Thus, ligands capable of activating MAPKs potentially modulate Smad signaling induced by TGFb. It has recently been demonstrated that p38MAPK activate phosphorylation of Smad3 in the middle linker region, which enhances Smad3/4 complex formation and nuclear translocation, 37 consistent with our finding of diminished Smad3/4 reporter gene activity in the presence of a p38MAPK inhibitor. Such phosphorylation by MAPKs in the Smad3 linker region is reportedly required for the full activation of Smad signaling.…”

Nicotine inhibits myofibroblast differentiation in human gingival fibroblasts

“…It has been shown that p38 MAPK was activated by TGF-β1 in hepatic stellate cells, and p38 MAPK phosphorylated Smad3 and promoted the nuclear translocation of Smad3/Smad4 [Furukawa et al, 2003]. In addition, inhibition of p38 MAPK by SB203580 and SB 202190 decreased α-SMA expression in pancreatic stellate cells [Masamune et al, 2003].…”

Chronic inflammation associated with hepatitis C virus infection perturbs hepatic transforming growth factor β signaling, promoting cirrhosis and hepatocellular carcinoma

“…10,11 Although several studies of EMT have suggested that the process involves Smad-independent pathways, 12 recent studies using Smad3 knockout mice have indicated that signaling through the Smad3-dependent pathway is required for injury-dependent multistage transition of an epithelial cell to a mesenchymal phenotype. 13 We therefore have focused on Smad3 signaling, 14,15 and have recently reported different roles of Smad3 phosphoisoform-mediated signaling in epithelial cells and mesenchymal cells. 16,17 Thus, TGF-␤ activates not only TGF-␤ type I receptor (T␤RI) but also c-Jun N-terminal kinase (JNK), converting Smad3 into two distinctive phosphoisoforms: C-terminally phosphorylated Smad3 (pSmad3C) and linker-phosphorylated Smad3 (pSmad3L).…”