Ca2+-dependent Protein Kinase C Isoforms Induce Cholestasis in Rat Liver

Abstract

Bile secretion is regulated by different signaling transduction pathways including protein kinase C (PKC). However, the role of different PKC isoforms for bile formation is still controversial. This study investigates the effects of PKC isoform selective activators and inhibitors on PKC translocation, bile secretion, bile acid uptake, and subcellular transporter localization in rat liver, isolated rat hepatocytes and in HepG2 cells. In rat liver activation of Ca2+-dependent cPKCα and Ca2+-independent PKCε by phorbol 12-myristate 13-acetate (PMA, 10nmol/liter) is associated with their translocation to the plasma membrane. PMA also induced translocation of the cloned rat PKCε fused to a yellow fluorescent protein (YFP), which was transfected into HepG2 cells. In the perfused liver, PMA induced marked cholestasis. The PKC inhibitors Gö6850 (1 μmol/liter) and Gö6976 (0.2 μmol/liter), a selective inhibitor of Ca2+-dependent PKC isoforms, diminished the PMA effect by 50 and 60%, respectively. Thymeleatoxin (Ttx,) a selective activator of Ca2+-dependent cPKCs, did not translocate rat PKCε-YFP transfected in HepG2 cells. However, Ttx (0.5-10 nmol/liter) induced cholestasis similar to PMA and led to a retrieval of Bsep from the canalicular membrane in rat liver while taurocholate-uptake in isolated hepatocytes was not affected. Gö6976 completely blocked the cholestatic effect of Ttx but had no effect on tauroursodeoxycholate-induced choleresis. The data identify Ca2+-dependent PKC isoforms as inducers of cholestasis. This is mainly due to inhibition of taurocholate excretion involving transporter retrieval from the canalicular membrane.