Mechanism by which cAMP activates PI3-kinase and increases bile acid secretion in WIF-B9 cells

• Published in: American Journal of Physiology: Cell Physiology 2002-12, Vol.52 (6), p.C1655-C1666
• Main Authors: KAGAWA, Tatehiro, VARTICOVSKI, Lyuba, SAI, Yoshimichi, ARIAS, Irwin M
• Format: Article
• Language: English
• Subjects: Acids; Bile; Biological and medical sciences; Cellular biology; Fundamental and applied biological sciences. Psychology; Liver. Bile. Biliary tracts; Vertebrates: digestive system
• ISSN: 0363-6143; 1522-1563

Previous studies in rat bile canalicular membrane vesicles and WIF-B9 cells revealed that cAMP-induced trafficking of ATP-binding cassette (ABC) transporters to the canalicular membrane and their activation require phosphoinositide 3-kinase (PI3-K) products. In the present studies, canalicular secretion of fluorescein isothiocyanate-glycocholate in WIF-B9 cells was increased by cAMP and a decapeptide that enhances PI3-K activity; these effects were inhibited by wortmannin. To determine the mechanism(s) whereby cAMP activates PI3-K, we examined signal transduction pathways in WIF-B9 and COS-7 cells. cAMP activated PI3-K in both cell lines in a phosphotyrosine-independent manner. PI3-K activity increased in association with p110 in both cell lines. The effect of cAMP was KT-5720 sensitive, suggesting involvement of protein kinase A. Expression of a dominant-negative -adrenergic receptor kinase COOH terminus (-ARKct), which blocks G signaling, decreased PI3-K activation in both cell lines. cAMP increased GTP-bound Ras in COS-7 but not WIF-B9 cells. Expression of dominant-negative Ras abolished cAMP-mediated PI3-K, which suggests that the effect is downstream of Ras and G. These data indicate that cAMP activates PI3-K in a cell type-specific manner and provide insight regarding mechanisms of PI3-K activation required for bile acid secretion.