Connective tissue growth factor induces c-fos gene activation and cell proliferation through p44/42 MAP kinase in primary rat hepatic stellate cells

Abstract

Background/Aims Connective tissue growth factor (CCN2) is expressed during activation of hepatic stellate cells (HSC) and promotes HSC proliferation, adhesion, and collagen production. The aim of the study was to investigate CCN2 signaling pathways in HSC. Methods Primary HSC were obtained by enzymatic perfusion of rat liver. DNA synthesis was evaluated by [ 3H]thymidine incorporation. Phosphorylation of Elk-1, extracellular signal-regulated kinase (ERK1/2) and focal adhesion kinase (FAK) was evaluated by Western blot. Transcriptional factor binding activity was determined by gel mobility shift assay while c-fos promoter and CCN2 promoter activity was evaluated using luciferase reporters. c-fos mRNA expression was evaluated by Northern blot. Results CCN2 stimulated DNA synthesis and phosphorylation of FAK, Elk-1 and ERK1/2, the latter of which was blocked by heparin. The serum response element binding activity and luciferase reporter activity of the c-fos promoter, together with expression of c-fos, were enhanced by CCN2. CCN2-induced c-fos gene activation, expression and cell proliferation were blocked by inhibiting ERK1/2 with PD98059. CCN2 promoter activity was enhanced by TGF-β1 or PDGF via a Smad7-dependent pathway. Conclusions CCN2-stimulated HSC DNA synthesis is associated with transient induction of c-fos gene activation and expression as well as activation of the ERK1/2 signal pathway.