Phosphoinositide 3-kinase lipid products regulate ATP-dependent transport by sister of P-glycoprotein and multidrug resistance associated protein 2 in bile canalicular membrane vesicles

Bile acid transport and secretion in hepatocytes require phosphatidylinosit ol (PI) 3-kinase-dependent recruitment of ATP-dependent transporters to the bile canalicular membrane and are accompanied by increased canalicular PI 3-kinase activity. We report here that the lipid products of PI 3-kinase al so regulate ATP-dependent transport of taurocholate and dinitrophenyl-gluta thione directly in canalicular membranes. ATP-dependent transport of tauroc holate and dinitrophenyl-glutathione in isolated canalicular vesicles from rat liver was reduced 50-70% by PI 3-kinase inhibitors, wortmannin, and LY2 94002, at concentrations that are specific for Type I PI 3-kinase, Inhibiti on was reversed by addition of lipid products of PI 3-kinase (PI 3,4-bispho sphate and, to a lesser extent, PI 3-phosphate and PI 3,4,5-trisphosphate) but not by PI 4,5-bisphosphate. A membrane-permeant synthetic 10-mer peptid e that binds polyphosphoinositides and leads to activation of PI 3-kinase i n macrophages doubled PI 3-kinase activity in canalicular membrane vesicles and enhanced taurocholate and dinitrophenylglutathione transport in canali cular membrane vesicles above maximal ATP-dependent transport. The effect o f the peptide was blocked by wortmannin and LY294002. PI 3-kinase activity was also necessary for function of the transporters in vivo. ATP-dependent transport of taurocholate and PI 3-kinase activity were reduced in canalicu lar membrane vesicles isolated from rat liver that had been perfused with t aurocholate and wortmannin. PI 3,4-bisphosphate enhanced ATP-dependent tran sport of taurocholate in these vesicles above control levels. Our results i ndicate that PI 3-kinase lipid products are necessary in vivo and in vitro for maximal ATP-dependent transport of bile acid and nonbile acid organic a nions across the canalicular membrane. Our results demonstrate regulation o f membrane ATP binding cassette transporters by PI 3-kinase lipid products.