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 Ca(2+)-dependent cPKCalpha and Ca(2+)-independent PKCepsilon 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 PKCepsilon 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 micromol/liter) and Gö6976 (0.2 micromol/liter), a selective inhibitor of Ca(2+)-dependent PKC isoforms, diminished the PMA effect by 50 and 60%, respectively. Thymeleatoxin (Ttx,) a selective activator of Ca(2+)-dependent cPKCs, did not translocate rat PKCepsilon-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 Ca(2+)-dependent PKC isoforms as inducers of cholestasis. This is mainly due to inhibition of taurocholate excretion involving transporter retrieval from the canalicular membrane.
Authors	Ralf Kubitz, Nirmalendu Saha, Thomas Kühlkamp, Supiya Dutta, Stephan vom Dahl, Matthias Wettstein, Dieter Häussinger
Journal	The Journal of biological chemistry (J Biol Chem) Vol. 279 Issue 11 Pg. 10323-30 (Mar 12 2004) ISSN: 0021-9258 [Print] United States
PMID	14679204 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References	Bacterial Proteins Carbazoles Detergents Indoles Luminescent Proteins Maleimides Phorbol Esters Protein Isoforms yellow fluorescent protein, Bacteria Go 6976 Taurocholic Acid thymeleatoxin Prkce protein, rat PRKCA protein, human PRKCE protein, human Protein Kinase C Protein Kinase C-alpha Protein Kinase C-epsilon bisindolylmaleimide I Tetradecanoylphorbol Acetate Calcium
Topics	Animals Bacterial Proteins (chemistry) Bile (metabolism) Biological Transport Blotting, Western Calcium (metabolism) Carbazoles (pharmacology) Cell Line Cell Membrane (metabolism) Cells, Cultured Cholestasis (etiology) Cloning, Molecular Densitometry Detergents (pharmacology) Dose-Response Relationship, Drug Enzyme Activation Hepatocytes (metabolism) Humans Indoles (pharmacology) Liver (metabolism, pathology) Luminescent Proteins (chemistry) Male Maleimides (pharmacology) Microscopy, Confocal Models, Biological Perfusion Phorbol Esters (pharmacology) Polymerase Chain Reaction Protein Isoforms Protein Kinase C (chemistry, metabolism) Protein Kinase C-alpha Protein Kinase C-epsilon Protein Transport Rats Rats, Wistar Signal Transduction Taurocholic Acid (pharmacology) Tetradecanoylphorbol Acetate Time Factors Transfection

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