title: Mechanism by which cAMP activates PI3-kinase and increases bile acid secretion in WIF-B9 cells.
abstract: 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 beta in both cell lines. The effect of cAMP was KT-5720 sensitive, suggesting involvement of protein kinase A. Expression of a dominant-negative beta-adrenergic receptor kinase COOH terminus (beta-ARKct), which blocks G beta gamma 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 beta gamma. 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.
authors.affiliation: Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
authors.forename: Tatehiro
authors.initials: T
authors.lastname: Kagawa
authors.forename: Lyuba
authors.initials: L
authors.lastname: Varticovski
authors.forename: Yoshimichi
authors.initials: Y
authors.lastname: Sai
authors.forename: Irwin M
authors.initials: IM
authors.lastname: Arias
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001648:Bile Canaliculi / Q000378:metabolism; D019556:COS Cells; D002227:Carbazoles; D002460:Cell Line; D000242:Cyclic AMP / Q000008:administration & dosage / Q000494:pharmacology / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D019000:Phosphotyrosine / Q000502:physiology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011758:Pyrroles / Q000494:pharmacology; D051381:Rats; D013997:Time Factors; D000077191:Wortmannin; D018631:ras Proteins / Q000502:physiology
chemical_list: D000730:Androstadienes; D001647:Bile Acids and Salts; D002227:Carbazoles; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D007211:Indoles; D007527:Isoenzymes; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D019000:Phosphotyrosine; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011758:Pyrroles; D000077191:Wortmannin; D018631:ras Proteins; C057416:KT 5720