Proteolytic cleavage of phospholipase C-γ1 during apoptosis in Molt-4 cells

Apoptosis is a cell suicide mechanism that requires the activation of cellular death proteases for its induction. We examined whether the progress of apoptosis involves cleavage of phospholipase C-gamma 1 (PLC-gamma 1), which plays a pivotal role in mitogenic signaling pathway. Pretreatment of T leukemic Molt-4 cells with PLC inhibitors such as U-73122 or ET-18-OCH3 potentiated etoposide-induced apoptosis in these cells. PLC-gamma 1 was fragmented when Molt-4 cells were treated with several apoptotic stimuli such as etoposide, ceramides, and tumor necrosis factor alpha. Cleavage of PLC-gamma 1 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-gamma 1 in vitro and generated a cleavage product of the same size as that observed in vivo, suggesting that PLC-gamma 1 is cleaved by group II caspases in vivo. From point mutagenesis studies, Ala-Glu-Pro-Asp(770) was identified to be a cleavage site within PLC-gamma 1. Epidermal growth factor receptor (EGFR) -induced tyrosine phosphorylation of PLC-gamma 1 resulted in resistance to cleavage by caspase-3 in vitro. Furthermore, cleaved PLC-gamma 1 could not be tyrosine-phosphorylated by EGFR in vitro. In addition, tyrosine-phosphorylated PLC-gamma 1 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-gamma 1. We provide evidence for the biochemical relationship between PLC-gamma 1-mediated signal pathway and apoptotic signal pathway, indicating that the defect of PLC-gamma 1-mediated signaling pathway can facilitate an apoptotic progression.-Bae, S. S., Ferry, D. K., Oh, Y. S., Choi, J. H., Galadari, S. H., Ghayur, T., Ryu, S. H., Hannun, Y. A., Suh, P.-G. Proteolytic cleavage of phospholipase C-gamma 1 during apoptosis in Molt-4 cells.