Potentiation of okadaic acid-induced ceramide elevation but not apoptosis by inhibition of glucosylceramide synthase in human neuroepithelioma cells

Caspase-dependent apoptosis induced by okadaic acid (OA) in CHP-100 neuroep ithelioma cells has previously been shown to associate with a rapid and sus tained elevation in intracellular ceramide concentration. We now report tha t treatment of CHP-100 cells with OA also evoked a rapid elevation in gluco sylceramide levels that was maintained at steady state as cells underwent a poptosis; moreover, as observed for ceramide, OA-induced glucosylceramide a ccumulation was not blocked by fumonisin B-1. Remarkably, when cell death w as prevented by caspase inhibition, glucosylceramide accumulation was poten tiated and ceramide elevation reduced, thus suggesting that, during apoptos is completion, accumulation of ceramide was partly driven by impairment of its glucosylation through a caspase-dependent mechanism. We studied whether ceramide glucosylation provided a mechanism for negative modulation of OA- induced apoptosis. We observed that the blocking of glucosylceramide synthe sis markedly potentiated OA-induced ceramide elevation, but neither acceler ated apoptosis onset nor potentiated the apoptotic response. These results indicate that modulation of ceramide glucosylation does not affect the apop totic response to okadaic acid and suggest that caution must be exercised c oncerning the possibility that ceramide plays a key role in apoptosis induc tion. (C) 2001 Elsevier Science Inc. All rights reserved.