Proteolytic cleavage of phospholipase C-γ1 during apoptosis

다국어 초록 (Multilingual Abstract)

Apoptosis is a cell suicide mechanism that requires the activation of cellular death proteases for the execution of cell death. We examined if the progress of apoptosis involves cleavage of phospholiapase C(PLC)-γ1 that plays a pivotal role in mitogenic signaling pathway. PLC-γ1 was fragmented in Molt-4 cells, T-cell leukemia cell, when treated with etoposide which induces apoptosis of the cells. Other apoptotic stimuli such as ceramides and tumor necrosis factor-α(TNF-α) also induced cleavage of PLC-γ1. Pretreatment of Molt-4 cells with a PLC inhibitor such as U-73122 or ET-18-OCH3, potentiated etoposide-induced apoptosis. Cleavage of PLC-γ1 was blocked by overexpression of Bcl-2 and by specific inhibitors of caspases such as Z-DEVD-CH2F and YVAD-cmk. Purified caspase-3 and caspase-7, group Ⅱ caspases, cleaved PLC-γ1 in vitro and generated a cleavage product that has the same size as that observed in vivo, suggesting that PLC-γ1 is cleaved by group Ⅱ caspases in vivo. From point mutagenesis studies, Ala-Glu-Pro-Asp770 was identified to be a cleavage site within PLC-γ1. Epidermal growth factor receptor-induced tyrosine phosphorylation of PLC-γ1 resulted in resistance to cleavage by caspase-3 in vitro. In addition, tyrosine-phosphorylated PLC-γ1 was not significantly cleaved during etoposide-induced apoptosis in Molt-4 cells. This suggests that the growth factor-induced tyrosine phosphorylation may suppress apoptosis-induced fragmentation of PLC-γ1. Taken together, we provide evidences for the biochemical relationship between PLC-γ1-mediated signal pathway and apoptotic signal pathway