Oxidative stress-induced phospholipase C-gamma l activation enhances cell survival

Phospholipase C-gamma1 (PLC-gamma1) is rapidly activated in response to gro wth factor stimulation and plays an important role in regulating cell proli feration and differentiation through the generation of the second messenger s diacylglycerol and inositol 1,4,5-trisphosphate, leading to the activatio n of protein kinase C (PKC) and increased levels of intracellular calcium, respectively. Given the existing overlap between signaling pathways that ar e activated in response to oxidant injury and those involved in responding to proliferative stimuli, we investigated the role of PLC-gamma1 during the cellular response to oxidative stress. Treatment of normal mouse embryonic fibroblasts (MEF) with H2O2 resulted in time- and concentration-dependent tyrosine phosphorylation of PLC-gamma1. Phosphorylation could be blocked by pharmacological inhibitors of Src family tyrosine kinases or the epidermal growth factor receptor tyrosine kinase, but not by inhibitors of the plate let-derived growth factor receptor or phosphatidylinositol 3-kinase. To inv estigate the physiologic relevance of H2O2-induced tyrosine phosphorylation of PLC-gamma1, we compared survival of normal MEF and PLC-gamma1-deficient MEF following exposure to H2O2. Treatment of PLC-gamma1-deficient MEF with H2O2 resulted in rapid cell death, whereas normal MEF were resistant to th e stress. Pretreatment of normal MEF with a selective pharmacological inhib itor of PLC-gamma1, or inhibitors of inositol trisphosphate receptors and P KC, increased their sensitivity to H2O2, whereas treatment of PLC-gamma1-de ficient MEF with agents capable of directly activating PKC and enhancing ca lcium mobilization significantly improved their survival. Finally, reconsti tution of PLC-gamma1 protein expression in PLC-gamma1-deficient MEF restore d cell survival following H2O2 treatment. These findings suggest an importa nt protective function for PLC-gamma1 activation during the cellular respon se to oxidative stress.