Regulatory roles of cell surface sialylation in susceptibility to sphingomyelinase in human diffuse large B cell lymphoma.

Sphingolipid metabolites are important regulators of cell growth and apoptosis. To clarify the biological roles of cell surface sialylation in the effects of sphingomyelinase (SM) treatment on cell viability, the human diffuse large B cell lymphoma cell line, HBL-2 with or without treatment with Vibrio cholerae neuraminidase, was incubated with exogenous bacterial SM which is a key enzyme of ceramide production from sphingolipids in cell membranes. SM treatment enhanced viability of HBL-2 cells compared to non-treatment after 6 h of incubation. On the other hand, viability of HBL-2 cells was decreased by SM treatment with neuraminidase pre-treatment after 6 and 24 h of incubation, and ceramide production on cell surfaces of SM treated cells was enhanced by neuraminidase treatment as shown by flow cytometric analysis. Furthermore, treatment with D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, an inhibitor which specifically reduces the activity of UDP-glucose:ceramide glucosyltransferase in combination with SM treatment, causes the viability of HBL-2 cells to be decreased more with neuraminidase pre-treatment than without it. Exogenous C6-ceramide induced HBL-2 cell death, and there was no difference in the effects of C6-ceramide after 6 h of incubation between treatment and non-treatment with neuraminidase. Together these data suggest that alteration in susceptibility of HBL-2 cells to SM by neuraminidase treatment may precede the process of ceramide production, and that cell death through the activation of SM, which induces ceramide production, is regulated by cell surface sialylation in DLBCL.