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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 phospho‐lipase C‐γΙ (PLC‐γΙ), which plays a pivotal role in mitogenic signaling pathway. Pretreatment of T leu‐kemic Molt‐4 cells with PLC inhibitors such as U‐73122 or ET‐18‐OCH₃ potentiated etoposide‐in‐duced apoptosis in these cells. PLC‐γΙ was fragmented when Molt‐4 cells were treated with several apoptotic stimuli such as etoposide, ceramides, and tumor necrosis factor a. Cleavage of PLC‐γΙ 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‐γΙ in vitro and generated a cleavage product of the same size as that observed in vivo, suggesting that PLC‐γΙ is cleaved by group II caspases in …