The Role of Phosphoinositide 3-Kinase in Taurocholate-induced Trafficking of ATP-dependent Canalicular Transporters in Rat Liver*
- From the Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111 and the ¶Department of Biomedical Research, St. Elizabeth’s Medical Center, Boston, Massachusetts 02135
Abstract
Recent studies indicate that wortmannin, a potent inhibitor of phosphatidylinositol (PI) 3-kinase, interferes with bile acid secretion in rat liver; taurocholate induces recruitment of ATP-dependent transporters to the bile canalicular membrane, and PI 3-kinase products are important in intracellular trafficking.
We investigated the role of PI 3-kinase in bile acid secretion by studying the in vivo effect of taurocholate, colchicine, and wortmannin on bile acid secretion, kinase activity, and protein levels in canalicular membrane vesicle (CMV) and sinusoidal membrane vesicle (SMV) fractions from rat liver. Treatment of rats or perfusion of isolated liver with taurocholate significantly increased PI 3-kinase activity in both membrane fractions. Taurocholate increased protein content of ATP-dependent transporters, which were detected only in CMVs, whereas increased levels of p85 and a cell adhesion molecule, cCAM 105, were observed in both fractions.
Colchicine prevented taurocholate-induced changes in all proteins studied, as well as the increase in PI 3-kinase activity in CMVs, but it resulted in further accumulation of PI 3-kinase activity, p85, and cCAM 105 in SMVs. These results indicate that taurocholate-mediated changes involve a microtubular system.
Wortmannin blocked taurocholate-induced bile acid secretion. The effect was more profound when wortmannin was administered prior to treatment with taurocholate. When wortmannin was given after taurocholate, the protein levels of each ATP-dependent transporter were maintained in CMVs, whereas the levels of p85 and cCAM decreased in both membrane fractions. Perfusion of liver with wortmannin before taurocholate administration blocked accumulation of all proteins studied in CMVs and SMVs.
These results indicate that PI 3-kinase is required for intracellular trafficking of itself, as well as of ATP-dependent canalicular transporters.
Footnotes
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↵* This work was supported by National Institutes of Health Grants DK35652 (NIDDK) (to I. M. A.), 30DK34928 (Digestive Disease Center, NIDDK), and CA 94536 (NCI) (to L.V.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ These authors contributed to the same degree in this research.
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↵§ To whom correspondence should be addressed: Dept. of Physiology, Tufts School of Medicine, 136 Harrison Ave., Boston, MA 02111. Tel.: 617-636-6739; Fax: 617-636-0445.
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↵2 A. Nies, Y. Sai, and H. Kipp, personal communication.
- Abbreviations:
- CMV
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canalicular membrane vesicle
- SMV
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sinusoidal membrane vesicle
- mdr
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multidrug resistance protein
- mrp
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multidrug resistance-associated protein
- cCAM 105
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canalicular cell adhesion molecule
- spgp
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sister of P-glycoprotein
- PI
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phosphatidylinositol.
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- Received May 21, 1998.
- Revision received July 15, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
