cAMP stimulates the secretory and proliferative capacity of the rat intrahepatic biliary epithelium through changes in the PKA/Src/MEK/ERK1/2 pathway

Background/Aims: To evaluate if increased cholangiocyte cAMP levels alone are sufficient to enhance cholangiocyte proliferation and secretion. Methods: Normal rats were treated in vivo with forskolin for two weeks. Cholangiocyte apoptosis, proliferation and secretion were evaluated. Purified cholangiocytes from normal rats were treated in vitro with forskolin in the absence or presence of Rp-cAMPs (a PKA inhibitor), PP2 (an Src inhibitor) or PD98059 (a MEK inhibitor). Subsequently, we evaluated cholangiocyte proliferation by determination of proliferating cellular nuclear antigen (PCNA) protein expression by immunoblots. We evaluated if the effects of forskolin on cholangiocyte functions are associated with changes in the cAMP/PKA/Src/MEK/ERK1/2 pathway. Results: Chronic administration of forskolin to normal rats increased the number of ducts, cAMP levels, and secretin-induced choleresis compared to controls. Forskolin-induced increases in cholangiocyte proliferation and secretion were devoid of cholangiocyte necrosis, inflammation and apoptosis. In vitro, in pure isolated cholangiocytes, forskolin increased cholangiocyte proliferation, which was ablated by Rp-cAMPs, PP2 and PD98059. The effects of forskolin on cholangiocyte proliferation were associated with increased activity of PKA, Src Tyrosine 139 (Tyr 139) and ERK1/2. Conclusions: Modulation of the PKA/Src/MEK/ERK1/2 pathway may be important in the regulation of cholangiocyte growth and secretion observed in cholestatic liver diseases. (C) 2004 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.