Effects of ARA-C on neutral sphingomyelinase and mitogen- and stress-activated protein kinases in T-lymphocyte cell lines

Neutral sphingomyelinase (SMase)(1) can be activated by extracellular signals to produce ceramide, which may affect mitogen-activated protein kinase (MAPK) activities. Neutral SMase activity was assessed in membranes from Jurkat, a human T-cell line, and EL4, a murine T-cell line. Ara-C activated SMase within 10 minutes in both Jurkat and ELA cells, while phorbol ester (PMA) had no effect. PMA, but not Ara-C or ceramides, activated ERK MAPKs in Jurkat and EL4. PMA acted synergistically with ionomycin to activate JNK MAPKs in Turkat and EL4 within 10 minutes. Ara-C activated JNKs only after prolonged incubation (90-120 minutes). Thus, ceramide is not a positive signal for ERK activation in T-cell lines. The effects of Ara-C on JNK activity may be mediated through secondary response pathways.