A MEDIATOR ROLE OF CERAMIDE IN THE REGULATION OF NEUROBLASTOMA NEURO2A CELL-DIFFERENTIATION

Current studies indicate that ceramide is involved in the regulation o f important cell functions, namely cell growth, differentiation, and a poptosis, In the present study, the possible role of ceramide in the d ifferentiation of neuroblastoma Neuro2a cells was investigated, The fo llowing results were obtained, (a) Ceramide content of Neuro2a cells, induced to differentiate by retinoic acid (RA) treatment rapidly incre ased after addition of RA, was maintained at high levels in RA differe ntiated cells and returned to the starting levels with removal of RA a nd reversal of differentiation; under the same conditions, the sphingo sine content remained unchanged, (b) After a short pulse with [H-3]sph ingomyelin or [H-3]sphingosine or L-[H-3]serine, the metabolic formati on of ceramide was markedly higher and more rapid in RA-differentiated than undifferentiated cells, (c) Inhibitors of ceramide biosynthesis (Fumonisin B1, beta-chloroalanine and L-cycloserine) diminished the ex tent of the differentiating effect of RA and concomitantly Cer content decreased, (d) The activity of neutral sphingomyelinase increased aft er addition of RA, maintained high levels in RA-differentiated cells, and returned to the initial levels with removal of RA, (e) Experimenta l conditions that cause an elevation of ceramide content (treatment wi th sphingosine or ceramide or C-2-ceramide or bacterial sphingomyelina se) inhibited cell proliferation and stimulated neurite outgrowth; dih ydro analogues of sphingosine, ceramide, and C-2-ceramide had no effec t on differentiation. (f) treatment with Fumonisin B1 completely inhib ited sphingosine-induced differentiation. These data suggest a specifi c bioregulatory function of ceramide in the control of Neuro2a cell gr owth and differentiation and pose the general hypothesis of a mediator role of ceramide in the differentiation of cells of neural origin.