A New Path to Ca 2+ Influx

Abstract

Patterson et al. have uncovered a surprising role for phospholipase C-γ (PLC-γ) isoforms in mediating Ca 2+ influx after G protein-coupled receptor (GPCR) stimulation through a mechanism independent of their catalytic activity. PLC proteins are critically involved in mobilizing receptor-mediated Ca 2+ signaling. GPCRs activate PLC-β isoforms, whereas receptor and nonreceptor tyrosine kinases activate PLC-γ. Activated PLC hydrolyzes phosphatidylinositol 4,5-bisphosphate to form inositol 1,4,5-trisphosphate, which triggers Ca 2+ release from intracellular stores, followed by Ca 2+ influx through channels in the plasma membrane. Patterson et al. showed that, when conditionally overexpressed in PC12 cells, both wild-type PLC-γ1 and mutant PLC-γ1 lacking lipase activity enhanced Ca 2+ influx after purinergic receptor stimulation, whereas mutant PLC-γ1 lacking the SH3 domain did not. Using RNA interference to deplete endogenous PLC, the authors found that depleting either PLC-γ1 or PLC-γ2 reduced Ca 2+ entry after purinergic stimulation in PC12 cells or serotonin stimulation in A7r5 cells without affecting release from internal stores. In DT40 B lymphocyte PLC-γ2 knockout cells overexpressing a muscarinic receptor, Ca 2+ entry from extracellular sources after receptor stimulation was abolished, whereas PLC-β-dependent Ca 2+ release from intracellular stores remained intact. Ca 2+ entry in the DT40 knockout cells was rescued by transfection with either PLC-γ2 or a PLC-γ2 lipase-inactive mutant. These data establish a lipase-independent role for PLC-γ in mediating Ca 2+ influx after GPCR stimulation. The inability of the SH3 domain mutant to enhance Ca 2+ influx, together with a requirement for this domain for coimmunoprecipitation of PLC-γ1 with transfected Ca 2+ channels, suggests that the effects of PLC-γ on Ca 2+ entry involve structural interactions with plasma membrane Ca 2+ channels or some protein intermediary. R. L. Patterson, D. B. van Rossum, D. L. Ford, K. J. Hurt, S. S. Bae, P.-G. Suh, T. Kurosaki, S. H. Snyder, D. L. Gill, Phospholipase C-γ is required for agonist-induced Ca 2+ entry. Cell 111 , 529-541 (2002). [Online Journal]