Extracellular signal regulated kinases are key mediators of mitogenic signals in rat pancreatic stellate cells

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Abstract
Background: Pancreatic stellate cells (PSCs) have been implicated in pancreatic fibrosis as they synthesise increased amounts of extracellular matrix proteins in response to activation by profibrogenic mediators such as cytokines. Aims: The purpose of this study was to analyse cytokine receptor stimulated signalling pathways involved in PSC activation. Using a rat culture model of PSCs, we have also tested the potential of the platelet derived growth factor (PDGF) antagonist trapidil and PD98059, a specific inhibitor of extracellular signal regulated kinase (ERK) activation, to suppress PSC growth. Methods: Cultured PSCs were stimulated with PDGF, and the signal transduction pathways activated in response to the mitogen were analysed by immunoblotting, kinase assays, and electrophoretic mobility shift assays. Furthermore, comparison of signalling cascades activated in PSCs before and after completing transdifferentiation to α-smooth muscle actin expressing myofibroblasts was performed. Biological effects of PDGF, trapidil, and PD98059 were analysed by proliferation assays and correlated with molecular effects of the substances. Results: PDGF induced rapid activation of Raf-1, ERKs 1 and 2, as well as AP-1 proteins. The transforming growth factor β activated transcription factor Smad2 was found to be constitutively phosphorylated in PSCs of different transdifferentiation grades. Furthermore, the results indicate a correlation between ERK activities and induction of PSC activation. Trapidil efficiently inhibited both PDGF induced ERK activation and, in common with PD98059, PSC proliferation. Conclusions: Our data suggest that ERKs play a key role in the regulation of PSC growth and that inhibition of the ERK signalling pathway may become a strategy to prevent activation of these cells.