Cytosolic and calcium-independent phospholipase A(2) mediate glioma-enhanced proangiogenic activity of brain endothelial cells

Abstract

Glioma is characterized by an active production of proangiogenic molecules. We observed that conditioned medium (CM) from C6 glioma significantly enhanced proliferation and migration of immortalized rat brain GP8.3 endothelial cells (ECs) and primary bovine brain microvascular ECs. The glioma CM effect was significantly reduced by cytosolic (cPLA(2)) and Ca(++)-independent (iPLA(2)) phospholipase A(2), cyclooxygenase-2, and protein kinase inhibitors. In GP8.3 ECs, cPLA(2) and iPLA(2) enzyme activities and phosphorylation of cPLA(2), significantly stimulated after 24h CM co-incubation, were attenuated by PLA(2), PI3-K, MEK-1, and ERK1/2 inhibitors. By confocal microscopy, in glioma CM-stimulated ECs, enhancement of fluorescence signals for phospho-cPLA(2), phospho-ERK1/2, phospho-PKCα, COX-2, and iPLA(2) was in parallel observed. Electroporation of anti-iPLA(2) and cPLA(2) antibodies and siRNAs directed against iPLA(2) and cPLA(2) significantly inhibited cell proliferation and migration. Incubation of CM- or VEGF peptide-stimulated ECs with antibodies against VEGF or VEGFR-1/-2 receptors strongly reduced mitotic rate, cell migration, and phospho-cPLA(2) and iPLA(2) protein levels. The findings suggest that PLA(2) activities are involved in stimulating EC migration and proliferation in the presence of glioma CM and that cPLA(2) is positively regulated upstream by PI3-K, PKCα, and ERK1/2 signal cascades. Our work provides new insights in understanding EC metabolism and signaling during tumor angiogenesis.