Secreted Phospholipase A2‐IIA Modulates Key Regulators of Proliferation on Astrocytoma Cells

Human group IIA secreted phospholipase A2 (sPLA2‐IIA) has been characterized in numerous inflammatory and neoplastic conditions. sPLA2‐IIA can either promote or inhibit cell growth depending on the cellular type and the specific injury. We have previously demonstrated that exogenous sPLA2‐IIA, by engagement to a membrane structure, induces proliferation and activation of mitogen‐activated protein kinases cascade in human astrocytoma cells. In this study, we used human astrocytoma 1321N1 cells to investigate the key molecules mediating sPLA2‐IIA‐induced cell proliferation. We found that sPLA2‐IIA promoted reactive oxygen species (ROS) accumulation, which was abrogated in the presence of allopurinol and DPI, but not by rotenone, discarding mitochondria as a ROS source. In addition, sPLA2‐IIA triggered Ras and Raf‐1 activation, with kinetics that paralleled ERK phosphorylation, and co‐immunoprecipitation assays indicated an association between Ras, Raf‐1 and ERK. Additionally, Akt, p70 ribosomal protein S6 kinase, and S6 ribosomal protein were also phosphorylated upon sPLA2‐IIA treatment, effect that was abrogated by N‐acetylcysteine or LY294002 treatment indicating that ROS and phosphatidylinositol 3 kinase are upstream signaling regulators. As the inhibitors N‐acetylcysteine, PD98059, LY294002 or rapamycin blocked sPLA2‐IIA‐induced proliferation without activation of the apoptotic program, we suggest that inhibition of these intracellular signal transduction elements may represent a mechanism of growth arrest. Our results reveal new potential targets for therapeutic intervention in neuroinflammatory disorders and brain cancer in particular.