Oxidative stress-induced activation of Lyn recruits sphingomyelinase and is requisite for its stimulation by Ara-C

Induction of apoptosis is considered to be the underlying mechanism that accounts for the efficiency of chemotherapeutic drugs. The identification of ceramide as a key mediator of apoptosis has made it possible to identify cellular entities that regulate drug-induced sphingomyelinase activation. Using human leukemia cell lines, we demonstrate that 1-beta-D-arabinofuranosylcytosine (Ara-C) stimulated ceramide generation, which was dependent on reactive oxygen species (ROS). Co-immunoprecipitation studies revealed that Ara-C-generated ROS activated the scr kinase p53/p56 Lyn, which then recruited neutral sphingomyelinase and was responsible for its activation. These effects were blocked by herbimycin A and Lyn antisense oligonucleotides. In conclusion, this study establishes a series of events in which early ROS generated by Ara-C leads to Lyn-dependent neutral sphingomyelinase activation, JNK phosphorylation, and apoptosis.