ABSTRACT
Human group IIA secreted phospholipase A(2) (sPLA(2)-IIA) has been characterized in numerous inflammatory and neoplastic conditions. sPLA(2)-IIA can either promote or inhibit cell growth depending on the cellular type and the specific injury. We have previously demonstrated that exogenous sPLA(2)-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 sPLA(2)-IIA-induced cell proliferation. We found that sPLA(2)-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, sPLA(2)-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 sPLA(2)-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 sPLA(2)-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.
