Inhibition of neurite outgrowth in murine neuroblastoma NS-20Y cells by calmodulin inhibitors.

The roles of protein kinases and calmodulin in regulating neurite outgrowth in murine neuroblastoma NS-20Y cells were investigated by testing the effect of various inhibitors on the neuritogenesis induced by serum deprivation. The percentage of cells with neurites was low (1-3%) in medium containing 10% serum, but reached about 50-60% when the cells were cultured for 24 h in serum-free medium. W-7 (10 microM), calmidazolium (0.3 microM), and trifluoperazine (0.1 microM), drugs reported to inhibit calmodulin-dependent events, reduced neurite outgrowth. On the other hand, H-7 (inhibitor of protein kinase C and cyclic AMP-dependent protein kinase) and H-89 (inhibitor of cyclic AMP-dependent protein kinase) were ineffective. Genistein (inhibitor of protein tyrosine kinase) and wortmannin (inhibitor of phosphatidylinositol 3-kinase) did not affect the number of cells with neurites. Activation of protein kinases, which is blocked by these inhibitors, does not appear to be essential to the extension and maintenance of neurites. KN-62 and KN-93 (inhibitors of Ca2+/calmodulin-dependent protein kinase II) were also tested but did not inhibit neurite outgrowth. These results suggest that a calmodulin-dependent process, other than the activation of Ca2+/calmodulin-dependent protein kinase II, is involved in the neuritogenesis in murine neuroblastoma NS-20Y cells in serum-free medium.