Pancreatic stellate cells (PSCs) play a major role in promoting pancreatic fibrosis. Transforming growth factor-β1 (TGF-β1) regulates PSC activation and proliferation in an autocrine manner. The intracellular signaling pathways of the regulation were examined in this study. Immunoprecipitation and immunocytochemistry revealed that Smad2, Smad3, and Smad4 were functionally expressed in PSCs. Adenovirus-mediated expression of Smad2, Smad3, or dominant-negative Smad2/3 did not alter TGF-β1 mRNA expression level or the amount of autocrine TGF-β1 peptide. However, expression of dominant-negative Smad2/3 inhibited PSC activation and enhanced their proliferation. Co-expression of Smad2 with dominant-negative Smad2/3 restored PSC activation inhibited by dominant-negative Smad2/3 expression without changing their proliferation. By contrast, co-expression of Smad3 with dominant-negative Smad2/3 attenuated PSC proliferation enhanced by dominant-negative Smad2/3 expression without altering their activation. Exogenous TGF-β1 increased TGFβ1 mRNA expression in PSCs. However, PD98059, a specific inhibitor of mitogen-activated protein kinase kinase (MEK1), inhibited ERK activation by TGF-β1, and consequently attenuated TGF-β1 enhancement of its own mRNA expression in PSCs. We propose that TGF-β1 differentially regulates PSC activation, proliferation, and TGF-β1 mRNA expression through Smad2-, Smad3-, and ERK-dependent pathways, respectively.
This work was supported by grants-in-aid from the ministry of Education, Culture, Sports, Science and Technology of Japan. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
