Role of pertussis toxin-sensitive G-proteins in intracellular Ca2+ releaseand apoptosis induced by inhibiting cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels in HepG2 human hepatoblastoma cells

Previously, we have reported that inhibition of cystic fibrosis transmembra ne conductance regulator (CFTR) Cl- channels by glibenclamide induced intra cellular Ca2+ release from IP3-sensitive stores and apoptosis in HepG2 huma n hepatoblastoma cells (Kim IA, Kang YS, Lee SH, Lee EH, Yoo BH, Lee YS. 19 99. Biochem Biophys Res Commun 261:682-688). In this study we investigated the upstream signals involved in the mechanism of these actions of glibencl amide. Treatment with glibenclamide initiated production of inositol 1,4,5- trisphosphate (IP3) in a dose- and time-dependent manner. The glibenclamide -induced formation of IP3 was significantly inhibited by CFTR activators (l evamisole and bromotetramisole). The intracellular Ca2+ release and apoptos is induced by glibenclamide were significantly suppressed by treatment with phospholipase C (PLC) inhibitors (U-73122 and manoalide) or by pretreatmen t with pertussis toxin (PTx). In addition, PTx-catalyzed ADP-ribosylation o f GTP-binding proteins (G-proteins) was markedly enhanced by treatment with glibenclamide in a time-dependent manner. Taken together, these results su ggest that PTx-sensitive G-proteins coupled to PLC beta may mediate the int racellular Ca2+ release and apoptosis induced by inhibiting CFTR Cl- channe ls in HepG2 cells. These results further suggest that the PTx-sensitive G-p roteins may be a valuable target for the therapeutic intervention of human hepatomas. (C) 2001 Wiley-Liss, Inc.