SERUM DEPRIVATION AND PROTEIN-SYNTHESIS INHIBITION INDUCE 2 DIFFERENTAPOPTOTIC PROCESSES IN N18 NEUROBLASTOMA-CELLS

N18 are murine neuroblastoma cells that underwent cell death upon seru m deprivation or inhibition of protein synthesis by means of cyclohexi mide (CHX), In both cases, an ultrastructural morphology and an intern ucleosomal pattern of DNA fragmentation typical of apoptosis were foun d. However, electron microscopy revealed abundant lipid vesicles in th e cytoplasm of CHX-treated cells that were not found in their serum-de prived counterparts. In addition, when both types of apoptotic cells w ere compared by means of flow cytometry and chromatin staining with pr opidium iodide, the former showed consistently less fluorescence than the latter. Therefore, in N18 cells, both apoptotic processes seemed t o differ at a structural level. At a functional level, we found that a poptosis was blocked by the protease inhibitor TLCK in CHX-treated but not in serum-deprived cells. On the other hand, we generated N18 clon es that overexpressed Bcl-2 protein. After a period of 48 h we found t hat identical levels of Bcl-2 protein were able to block apoptosis in serum-deprived but not in CHX-treated cells, In conclusion, two differ ent biochemical pathways leading to apoptosis seem to coexist in N18 n euroblastoma cells, (C) 1998 Academic Press.