Cell Swelling-induced Translocation of Rat Liver Na+/Taurocholate Cotransport Polypeptide Is Mediated via the Phosphoinositide 3-Kinase Signaling Pathway

Abstract

Cell swelling stimulates phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) in hepatocytes, and the PI3K signaling pathway is involved in cAMP-mediated translocation of sinusoidal Na ؉ /taurocholate (TC) cotransporter (Ntcp) to the plasma membrane. We determined whether cell swelling also stimulates TC uptake and Ntcp translocation via the PI3K and/or MAPK signaling pathway. All studies were conducted in isolated rat hepatocytes. Hepatocyte swelling induced by hypotonic media resulted in: 1) time-and medium osmolarity-dependent increases in TC uptake, 2) an increase in the V max of Na ؉ /TC cotransport, and 3) wortmannin-sensitive increases in TC uptake and plasma membrane Ntcp mass. Hepatocyte swelling also induced wortmannin-sensitive activation of PI3K, protein kinase B, and p70 S6K . Rapamycin, an inhibitor of p70 S6K , inhibited cell swelling-induced activation of p70 S6K but failed to inhibit cell swelling-induced stimulation of TC uptake. Because PD98095, an inhibitor of MAPK, did not inhibit cell swelling-induced increases in TC uptake, it is unlikely that the effect of cell swelling on TC uptake is mediated via the MAPK signaling pathway. Taken together, these results indicate that 1) cell swelling stimulates TC uptake by translocating Ntcp to the plasma membrane, 2) this effect is mediated via the PI3K, but not MAPK, signaling pathway, and 3) protein kinase B, but not p70 S6K

Short-term feedback regulation of bile salt uptake by bile salts in rodent liver

“…50 In contrast, in isolated rat hepatocytes, inhibition of MEK1, an upstream effector of Erk1/2, failed to affect cell swelling-induced translocation of Ntcp to the plasma membrane. 20 Here, PD98059 or the p38MAPK inhibitor SB202190 had no significant effect on TCDC-dependent reduction of TC uptake, indicating that Erk1/2 and p38MAPK are not downstream effectors of TCDC. Likewise, the involvement of ROS seems unlikely.…”

“…Consequently, reduction of V max by an internalization of transport molecules may decrease uptake of TCDC at physiological concentrations. 20 This mechanism may be especially relevant for CDC derivatives, which have unfavorable effects on cell survival. 5 Apart from this, sensitivity of TCDC-induced cholestasis toward specific inhibitors points to the involvement of distinct signaling pathways stimulated by TCDC.…”

“…25 Furthermore, hepatocyte swelling stimulated rapid Ntcp insertion into the basolateral membrane and increases TC uptake in hepatocytes. 20 In perfusion experiments p38MAPKinase inhibition with SB202190 had an additive effect on TCDC-dependent inhibition of TC* secretion into bile. SB202190 significantly decreased the amount of TC* in bile in TCDC-perfused livers from 31 6 7% to 13 6 7% total TC* input.…”

“…25,48,49 Furthermore, cell swelling causes Ntcp exocytosis by way of PI3K. 20 cAMP stimulates protein phosphatase 2B-mediated dephosphorylation of NTCP and leads to an increased retention of Ntcp at the plasma membrane. 44 In contrast, NADPH-dependent ROS formation (oxidative stress) triggers cell shrinkage and cholestasis by endocytosis of Bsep/Mrp2.…”

Involvement of Integrins and Src in Insulin Signaling toward Autophagic Proteolysis in Rat Liver

“…Hypoosmotic cell swelling activates PtdIns-3-kinase signaling in isolated hepatocytes (42,43) and perfused rat liver (44). Because insulin-induced swelling depends on PtdIns-3-kinase and possibly at the same time feeds into the PtdIns-3-kinase pathway, it was hypothesized that insulin-induced swelling FIG.…”