Secretory group IIA phospholipase A(2) generates anti-apoptotic survival signals in kidney fibroblasts

Mammalian group IIA phospholipase A(2) (PLA(2)) is believed to play importa nt roles in inflammation, cell injury, and tumor resistance. However, the c ellular site of action has not been clearly defined as it has long been rec ognized that group IIA PLA(2) is both a secretory and mitochondrial protein . The purpose of this study was to determine the subcellular target of the group IIA PLA(2) and its role in apoptosis stimulated by growth factor with drawal. Cloning of the rat liver group IIA PLA(2) demonstrated a typical se cretory signal and no alternative splicing of the primary transcript. When a sequence including the signal peptide and first 8 residues in the mature enzyme or the entire PLA(2) (including the signal peptide) was fused to enh anced green fluorescent protein, the fusion protein was directed to the sec retory pathway rather than mitochondria in baby hamster kidney (BHK) cells. To examine the role of group IIA PLA(2) in cell injury, wild type (wt) rat group IIA PLA(2) and a mutant group IIA PLA(2) containing a His-47 --> Gln mutation (at the catalytic center) were transfected into BHK cells and cel ls stably expressing these constructs were isolated. After deprivation of g rowth factors, both normal BHK cells and BHK cells expressing mutant PLA(2) underwent massive apoptosis, while BHK cells expressing wt PLA(2) showed c onsiderable resistance to growth factor withdrawal-induced apoptosis, The s ecretory PLA(2) inhibitors 12-epi-scalaradial and aristolochic acid abrogat ed resistance to apoptosis in the wt PLA(2) expressing cells. These two inh ibitors did not induce cell death in the presence of fetal bovine serum, su ggesting that they induce cell death by blocking PLA(2) generated survival signals. This study demonstrates that group IIA PLA(2) generates anti-apopt otic survival signals in BHK cells targeting the secretory pathway, and sug gests that high levels of group HA PLA(2) accumulated at inflammatory sites may not only regulate inflammation, but also may protect cells from unnece ssary death induced by pro-inflammatory agents.