Abstract
Mitogen-activated protein kinase (MAPK) pathway-dependent linker phosphorylation of Smad2/3 and subsequent formation of Smad2/3/4 complex and its nuclear translocation are crucial for dysregulated transforming growth factor beta (TGF)-β/Smad signaling in liver fibrosis. Abrogation of this critical step of TGF-β/Smad signaling leading to liver fibrosis could provide new insights for future therapy, but the mechanisms remain incompletely understood. In pursuit, we investigated the subcellular expression and nuclear trafficking of the rate limiting Smad2/3/4 complex in exogenous TGF-β1-stimulated myofibroblasts (MFBs) using three MAPK-specific inhibitors. Our results showed that exogenous TGF-β1 stimulation of MFBs produced both increased protein expression and nuclear translocation of phosphorylated (p)-Smad2C/L, oncogenic pSmad3L, Smad4, importin7/8 (Imp7/8), and plasminogen activator inhibitor (PAI)-1 (Protein and mRNA), while decreased Smad7 protein expression. However, the MAPK-specific inhibitors differentially reversed these observations; for instance, ERK-specific inhibitor blocked the expression and nuclear translocation of pSmad2C/L, while both JNK and p38-specific inhibitors blocked the expression and nuclear translocation of pSmad2C/L and oncogenic pSmad3L. The MAPK-specific inhibitors had no significant effect on the total protein expression of Smad4, but rather significantly blocked its nuclear translocation. All the MAPK-specific inhibitors restored Smad7 expression and also decreased Imp7/8 and PAI-1 (Protein and mRNA) expression. Evidently, the MAPK-specific inhibitors blocked Smad2/3/4 complex formation via restoration of inhibitory Smad7 expression and blockade of Smad3L phosphorylation, while they blocked nuclear translocation of Smad2/3/4 complex through inhibition of Imp7/8 leading to decreased PAI-1 (Protein and mRNA) expression.
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Acknowledgments
We thank Prof. K Matsuzaki (Department of Gastroenterology and Hepatology, Kansai Medical University, Osaka, Japan) for providing us with the following Abs: Anti-pSmad2L and Anti-pSmad3L. Also, this work was supported by the National Natural Science Foundation of China (No. 81073098, No. 81374012).
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Yufeng Jiang and Chao Wu have been contributed equally to this work.
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Jiang, Y., Wu, C., Boye, A. et al. MAPK inhibitors modulate Smad2/3/4 complex cyto-nuclear translocation in myofibroblasts via Imp7/8 mediation. Mol Cell Biochem 406, 255–262 (2015). https://doi.org/10.1007/s11010-015-2443-x
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DOI: https://doi.org/10.1007/s11010-015-2443-x