Cyclooxygenase 2 promotes cell survival by stimulation of dynein light chain expression and inhibition of neuronal nitric oxide synthase activity

Cyclooxygenase 2 (COX-2) inhibits nerve growth factor (NGF) withdrawal apop tosis in differentiated PC12 cells. The inhibition of apoptosis by COX-2 wa s concomitant with prevention of caspase 3 activation. To understand how CO X-2 prevents apoptosis, we used cDNA expression arrays to determine whether COX-2 regulates differential expression of apoptosis-related genes. The ex pression of dynein light chain (DLC) (also known as protein inhibitor of ne uronal nitric oxide synthase [PIN]) was significantly stimulated in PC12 ce lls overexpressing COX-2. The COX-2-dependent stimulation of DLC expression was, at least in part, mediated by prostaglandin E-2. Overexpression of DL C also inhibited NGF withdrawal apoptosis in differentiated PC12 cells. Sti mulation of DLC expression resulted in an increased association of DLC/PIN with neuronal nitric oxide synthase (nNOS), thereby reducing nNOS activity. Furthermore, nNOS expression and activity were significantly increased in differentiated PC12 cells after NGF withdrawal. This increased nNOS activit y as well as increased nNOS dimer after NGF withdrawal were inhibited by CO X-2 or DLC/PIN overexpression. An nNOS inhibitor or a membrane-permeable su peroxide dismutase (SOD) mimetic protected differentiated PC12 cells from N GF withdrawal apoptosis. In contrast, NO donors induced apoptosis in differ entiated PC12 cells and potentiated apoptosis induced by NGF withdrawal. Th e protective effects of COX-2 on apoptosis induced by NGF withdrawal were a lso overcome by NO donors. These findings suggest that COX-2 promotes cell survival by a mechanism linking increased expression of prosurvival genes c oupled to inhibition of NO- and superoxide-mediated apoptosis.