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This Article Full Text Full Text (PDF) All Versions of this Article: 297/3/G532    most recent 00052.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Sarwar, Z. Articles by Alrefai, W. A. PubMed PubMed Citation Articles by Sarwar, Z. Articles by Alrefai, W. A.

MUCOSAL BIOLOGY

Modulation of ileal apical Na⁺-dependent bile acid transporter ASBT by protein kinase C

Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago and Jesse Brown Veterans Affairs Medical Center, Chicago, Illinios

Submitted 11 February 2009 ; accepted in final form 29 June 2009

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 [³H]taurocholic acid uptake in Caco-2 cells was significantly inhibited in response to 2 h incubation with 100 nM PMA compared with incubation with 4-PMA (inactive form). The inhibitory effect of PMA was blocked in the presence of 5 µM bisindolylmaleimide I (PKC inhibitor) but not 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (Ca²⁺ chelator) or LY-294002 (phosphatidylinositol 3-kinase inhibitor). PMA inhibition of ASBT function was also abrogated in the presence of myristoylated PKC pseudosubstrate peptide, indicating involvement of the atypical PKC 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 PKC-dependent pathway.

apical sodium-dependent bile acid transporter; SLC10A2; diacylglycerol; atypical protein kinase C