EVIDENCE FOR THE ROLE OF PROTEIN-KINASE-C IN ASTROCYTE-INDUCED PROLIFERATION OF RAT CEREBROMICROVASCULAR ENDOTHELIAL-CELLS

The proliferation of cerebral endothelial cells is a crucial step in n eural angiogenesis and is a process responsive to changes in the surro unding environment. Serum-free medium conditioned by rat cortical astr ocytes was found to accelerate DNA synthesis, induce transient activat ion of protein kinase C (PKC), and increase the endogenous phosphoryla tion of the PKC-specific substrate, the 85 kDa MARCKS protein, in rat cerebromicrovascular endothelial cells (RCEC). The stimulatory factor( s) in astrocyte conditioned media (ACM) were heat- and trypsin-sensiti ve and found to have an apparent molecular weight greater than 10 kDa. The potent PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA) , also stimulated RCEC proliferation, whereas the inhibition of PKC by staurosporine caused a concomitant loss in ACM-induced PKC translocat ion, MARCKS protein phosphorylation and DNA synthesis. These findings implicate PKC activation as a critical early event in cerebral endothe lial cell proliferation triggered by astrocyte-derived mitogen(s).