Modulation of ileal apical Na+-dependent bile acid transporter ASBT by protein kinase C.
Ileal apical Na(+)-dependent bile acid transporter (ASBT) is responsible for reabsorbing the majority of bile acids from the intestinal lumen. Rapid adaptation of ASBT function in response to physiological and pathophysiological stimuli is essential for the maintenance of bile acid homeostasis. However, not much is known about molecular mechanisms responsible for acute posttranscriptional regulation of ileal ASBT. The protein kinase C (PKC)-dependent pathway represents a major cell signaling mechanism influencing intestinal epithelial functions. The present studies were, therefore, undertaken to investigate ASBT regulation in intestinal Caco-2 monolayers by the well-known PKC activator phorbol 12-myristate 13-acetate (PMA). Our results showed that Na(+)-dependent [(3)H]taurocholic acid uptake in Caco-2 cells was significantly inhibited in response to 2 h incubation with 100 nM PMA compared with incubation with 4alpha-PMA (inactive form). The inhibitory effect of PMA was blocked in the presence of 5 microM bisindolylmaleimide I (PKC inhibitor) but not 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (Ca(2+) chelator) or LY-294002 (phosphatidylinositol 3-kinase inhibitor). PMA inhibition of ASBT function was also abrogated in the presence of myristoylated PKCzeta pseudosubstrate peptide, indicating involvement of the atypical PKCzeta isoform. The inhibition by PMA was associated with a significant decrease in the maximal velocity of the transporter and a reduction in ASBT plasma membrane content, suggesting a modulation by vesicular recycling. Our novel findings demonstrate a posttranscriptional modulation of ileal ASBT function and membrane expression by phorbol ester via a PKCzeta-dependent pathway.
Sarwar
Zaheer
Z
Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago and Jesse Brown Veterans Affairs Medical Center, Chicago, Illinios 60612, USA.
Annaba
Fadi
F
Dwivedi
Alka
A
Saksena
Seema
S
Gill
Ravinder K
RK
Alrefai
Waddah A
WA
D001647:Bile Acids and Salts / Q000378:metabolism*; D018938:Caco-2 Cells; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D002614:Chelating Agents / Q000494:pharmacology; D002867:Chromones / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D020536:Enzyme Activators / Q000494:pharmacology; D006801:Humans; D007082:Ileum / Q000187:drug effects / Q000201:enzymology*; D007211:Indoles / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000187:drug effects / Q000201:enzymology*; D007700:Kinetics; D008301:Maleimides / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D029363:Organic Anion Transporters, Sodium-Dependent / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D000099221:Protein Kinase C zeta
D001647:Bile Acids and Salts; D002118:Calcium; D002614:Chelating Agents; D002867:Chromones; D004533:Egtazic Acid; D020536:Enzyme Activators; D007211:Indoles; D008301:Maleimides; D009025:Morpholines; D029363:Organic Anion Transporters, Sodium-Dependent; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D047428:Protein Kinase Inhibitors; D027981:Symporters; D013755:Tetradecanoylphorbol Acetate; D000099221:Protein Kinase C zeta; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; C071908:sodium-bile acid cotransporter; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C070515:bisindolylmaleimide I