Overexpression of cytosolic group IVA phospholipase A2 protects cells from Ca2+-dependent death.

The calcium ionophore ionomycin induces apoptosis-like events in the human embryonic kidney cell line at early times. Plasma membrane blebbing, mitochondrial depolarization, externalization of phosphatidylserine, and nuclear permeability changes can all be observed within 15 min of treatment. However, there is no activation of caspases or chromatin condensation. Expression of a fusion protein containing the enhanced green fluorescent protein (EGFP) and human cytosolic Group IVA phospholipase A(2)alpha (EGFP-cPLA(2)alpha) in these cells prevents ionomycin-induced phosphatidylserine externalization and death. Cells expressing the cPLA(2)alpha mutant D43N, which does not bind calcium, retain their susceptibility to ionomycin-induced cell death. Both nonexpressing and EGFP-D43N-cPLA(2)alpha-expressing human embryonic kidney cells can be spared from ionomycin-induced cell death by pretreating them with exogenous arachidonic acid. Moreover, during calcium overload, mitochondrial depolarization is significantly lower in the EGFP-cPLA(2)alpha-expressing cells than in cells expressing normal amounts of cPLA(2)alpha. These results suggest that early cell death events promoted by an overload of calcium can be prevented by the presence of high levels of arachidonic acid.