Protein kinase C-mediated down-regulation of MDR3 mRNA expression in Changliver cells

MDR3 is a phospholipid translocator homologous to MDR1 P-glycoprotein. MDR3 localizes to the canalicular membrane and contributes to the secretion of bile. To elucidate the role of protein kinase C in the regulation of MDR3 g ene expression, we investigated the effect of phorbol 12-myristate 13-aceta te (PMA) on the level of MDR3 mRNA in human Chang liver cells by a reverse transcription-polymerase chain reaction method. The steady-state expression of MDR3 mRNA was decreased by PMA after treatment for 8 -20 hr and at conc entrations of 1-100 nM. PMA also decreased the doxorubicin-induced expressi on of MDR3 mRNA, 4 alpha -Phorbol 12,13-didecanoate, a negative control com pound, did not decrease the expression at these concentrations. The down-re gulatory effect of PMA was partially suppressed by the protein kinase C inh ibitors 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleim ide (GF109203X) and calphostin C. Furthermore, cycloheximide, a protein syn thesis inhibitor, antagonized the effect of PMA. From these results, it was suggested that the level of MDR3 mRNA was negatively regulated by a protei n kinase C- and protein synthesis-dependent system and that the system regu lated both the stable and inducible expression of MDR3 mRNA. (C) 2001 Elsev ier Science Inc. All rights reserved.