In:
American Journal of Physiology-Gastrointestinal and Liver Physiology, American Physiological Society, Vol. 297, No. 6 ( 2009-12), p. G1259-G1267
Abstract:
The cholestatic bile acid taurolithocholate (TLC) inhibits biliary secretion of organic anions and hepatic uptake of taurocholate (TC). TLC has been suggested to induce retrieval of Mrp2 from the canalicular membrane via the phosphoinositide-3-kinase (PI3K)/PKB-dependent activation of novel protein kinase Cε (nPKCε) in rat hepatocytes. The aim of the present study was to determine whether TLC-induced inhibition of TC uptake may also involve PI3K-dependent activation of PKCε in HuH7 cells stably transfected with human Na + -dependent TC-cotransporting polypeptide (NTCP) (HuH-NTCP cells). To avoid direct competition for uptake, cells were pretreated with TLC, washed, and then incubated with 3 H-TC to determine TC uptake. TLC produced time- and dose-dependent inhibition of TC uptake. TLC inhibited TC uptake competitively without affecting NTCP membrane translocation. A PI3K inhibitor failed to reverse TLC-induced TC uptake inhibition and TLC-inhibited PKB phosphorylation. TLC did activate nPKCε as evidenced by increased membrane translocation and nPKCε-Ser 729 phosphorylation. Overexpression of dominant negative-nPKCε reversed TLC-induced inhibition of PKB phosphorylation but not of TC uptake. Finally, cAMP prevented TLC-induced inhibition of TC uptake via the PI3K pathway, and the prevention is due to the sum of cAMP-induced stimulation and TLC-induced inhibition of TC uptake. Taken together, these results suggest that TLC-induced inhibition of PKB, but not of TC uptake, is mediated via nPKCε. Activation of nPKCε and inhibition of TC uptake by TLC are not mediated via the PI3K/PKB pathway.
Type of Medium:
Online Resource
ISSN:
0193-1857
,
1522-1547
DOI:
10.1152/ajpgi.00177.2009
Language:
English
Publisher:
American Physiological Society
Publication Date:
2009
detail.hit.zdb_id:
1477329-6
SSG:
12
Permalink
