Tauroursodeoxycholic acid activates protein kinase C in isolated rat hepatocytes.
OBJECTIVE
Ursodeoxycholic acid (UDCA) improves liver function in patients with chronic cholestatic liver diseases by an unknown mechanism. UDCA is conjugated to taurine in vivo, and tauroursodeoxycholic acid (TUDCA) is a potent hepatocellular Ca2+ agonist and stimulates biliary exocytosis and hepatocellular Ca2+ influx, both of which are defective in experimental cholestasis. Protein kinase C (PKC) mediates stimulation of exocytosis in the liver. The aim of this study was to determine the effects of TUDCA on PKC in isolated hepatocytes.


METHODS
The effect of TUDCA on the distribution of PKC isoenzymes within the hepatocyte was studied using immunoblotting and immunofluorescence techniques. In addition, the effect of TUDCA on the accummulation of sn-1,2-diacylglycerol (DAG), the intracellular activator of PKC, and hepatocellular PKC activity was studied using radioenzymatic techniques.


RESULTS
Immunoblotting studies showed the presence of four isoenzymes (alpha, delta, epsilon, and zeta). The phorbol ester phorbol 12-myristate 13-acetate (1 mumol/L) induced translocation of alpha-PKC, delta-PKC, and epsilon-PKC from cytosol to a particulate membrane fraction, a key step for activation of PKC. TUDCA, but not taurocholic acid, selectively induced translocation of the alpha-PKC isoenzyme from cytosol to the membranes. In addition, TUDCA induced a significant increase in hepatocellular DAG mass and stimulated membrane-associated PKC activity.


CONCLUSIONS
TUDCA might stimulate Ca(2+)-dependent hepatocellular exocytosis into bile in part by activation of alpha-PKC.
Beuers
U
U
Department of Internal Medicne, Yale University School of Medicine, New Haven Connecticut, USA.
Throckmorton
D C
DC
Anderson
M S
MS
Isales
C M
CM
Thasler
W
W
Kullak-Ublick
G A
GA
Sauter
G
G
Koebe
H G
HG
Paumgartner
G
G
Boyer
J L
JL
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D002756:Cholagogues and Choleretics / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004075:Diglycerides / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013655:Taurochenodeoxycholic Acid / Q000494:pharmacology*; D013656:Taurocholic Acid / Q000494:pharmacology
D002756:Cholagogues and Choleretics; D004075:Diglycerides; D007527:Isoenzymes; D013655:Taurochenodeoxycholic Acid; D013656:Taurocholic Acid; C031655:ursodoxicoltaurine; D011493:Protein Kinase C