Inhibition of neurite outgrowth in neuroblastoma cells by sphingosine

Mouse neuroblastoma NS-20Y cells were induced to grow neurites by removal of serum from the medium. The percentage of cells with neurites reached about 50-60% after 24 h, whereas in medium containing 10% serum only a few cells (1-3%) were bearing neurites. Sphingosine inhibited the neuritogenesis in serum-free medium in a dose-dependent manner; a maximal effect was observed at 1-2 microM. Sphingosine also caused retraction of neurites which had been induced to extend in serum-free medium. N,N-Dimethylsphingosine was 10 times more potent in preventing neurite outgrowth, and N-acetylsphingosine was 10 times less effective compared to sphingosine. However, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) did not inhibit the extension of neurites. Neurite outgrowth in serum-free medium and its inhibition by sphingosine were still observed in the cells made protein kinase C-deficient by prolonged treatment with phorbol ester. These results suggest that the effect of sphingosine is not mediated by inhibition of protein kinase C.