PHOSPHOLIPASE C A New Path to Ca²⁺ Influx

Patterson et al. have uncovered a surprising role for phospholipase C- (PLC-) isoforms in mediating Ca²⁺ 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 Ca²⁺ signaling. GPCRs activate PLC-ß isoforms, whereas receptor and nonreceptor tyrosine kinases activate PLC-. Activated PLC hydrolyzes phosphatidylinositol 4,5-bisphosphate to form inositol 1,4,5-trisphosphate, which triggers Ca²⁺ release from intracellular stores, followed by Ca²⁺ influx through channels in the plasma membrane. Patterson et al. showed that, when conditionally overexpressed in PC12 cells, both wild-type PLC-1 and mutant PLC-1 lacking lipase activity enhanced Ca²⁺ influx after purinergic receptor stimulation, whereas mutant PLC-1 lacking the SH3 domain did not. Using RNA interference to deplete endogenous PLC, the authors found that depleting either PLC-1 or PLC-2 reduced Ca²⁺ entry after purinergic stimulation in PC12 cells or serotonin stimulation in A7r5 cells without affecting release from internal stores. In DT40 B lymphocyte PLC-2 knockout cells overexpressing a muscarinic receptor, Ca²⁺ entry from extracellular sources after receptor stimulation was abolished, whereas PLC-ß-dependent Ca²⁺ release from intracellular stores remained intact. Ca²⁺ entry in the DT40 knockout cells was rescued by transfection with either PLC-2 or a PLC-2 lipase-inactive mutant. These data establish a lipase-independent role for PLC- in mediating Ca²⁺ influx after GPCR stimulation. The inability of the SH3 domain mutant to enhance Ca²⁺ influx, together with a requirement for this domain for coimmunoprecipitation of PLC-1 with transfected Ca²⁺ channels, suggests that the effects of PLC- on Ca²⁺ entry involve structural interactions with plasma membrane Ca²⁺ 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- is required for agonist-induced Ca²⁺ entry. Cell 111, 529-541 (2002). [Online Journal]