Ca2+-dependent protein kinase C isoforms are critical to estradiol 17β-D-glucuronide-induced cholestasis in the rat

Abstract

The endogenous estradiol metabolite estradiol 17β-D-glucuronide (E217G) induces an acute cholestasis in rat liver coincident with retrieval of the canalicular transporters bile salt export pump (Bsep, Abcc11) and multidrug resistance-associated protein 2 (Mrp2, Abcc2) and their associated loss of function. We assessed the participation of Ca2+-dependent protein kinase C isoforms (cPKC) in the cholestatic manifestations of E217G in perfused rat liver (PRL) and in isolated rat hepatocyte couplets (IRHCs). In PRL, E217G (2 μmol/liver; intraportal, single injection) maximally decreased bile flow, total glutathione, and [3H] taurocholate excretion by 61%, 62%, and 79%, respectively; incorporation of the specific cPKC inhibitor Gö6976 (500 nM) in the perfusate almost totally prevented these decreases. In dose-response studies using IRHC, E217G (3.75-800 μM) decreased the canalicular vacuolar accumulation of the Bsep substrate cholyl-lysylfluorescein with an IC50 of 54.9±7.9 μM. Gö6976 (1 μM) increased the IC50 to 178.4 ± 23.1 μM, and similarly prevented the decrease in the canalicular vacuolar accumulation of the Mrp2 substrate, glutathione methylfluorescein. Prevention of these changes by Gö6976 coincided with complete protection against E217G-induced retrieval of Bsep and Mrp2 from the canalicular membrane, as detected both in the PRL and IRHC. E217G also increased paracellular permeability in IRHC, which was only partially prevented by Gö6976. The cPKC isoform PKCα, but not the Ca2+-independent PKC isoform, PKCε, translocated to the plasma membrane after E217G administration in primary cultured rat hepatocytes; Gö6976 completely prevented this translocation, thus indicating specific activation of cPKC. This is consistent with increased autophosphorylation of cPKC by E217G, as detected via western blotting. Conclusion: Our finndings support a central role for cPKC isoforms in E217G-induced cholestasis, by inducing both transporter retrieval from the canalicular membrane and opening of the paracellular route. Copyright © 2008 by the American Association for the Study of Liver Diseases.