Cell calcium signaling via GM1 cell surface gangliosides in the human Jurkat T cell line

The cell surface ganglioside GM1 is the specific receptor for the B subunit of cholera toxin. We show here that in the human Jurkat T cell line an increase in intracellular free Ca2+ concentration can be elicited by using B subunits to ligate GM1 molecules. This Ca2+ signaling effect is clearly mediated through GM1 because it can be observed after direct insertion of exogenous GM1 in a Jurkat cell variant deficient in GM1 expression. The observed Ca2+ response clearly involves both the release of Ca2+ from intracellular stores and a Ca2+ influx from extracellular spaces. It is sustained in the presence of 1 mM extracellular Ca2+, whereas it becomes transient in Ca(2+)-free medium. We show that the GM1-mediated stimulation partially empties the CD3-dependent and inositol 1,4,5-trisphosphate-sensitive intracellular Ca2+ pool suggesting a dependence of the Ca2+ response from activation of phospholipase C (PLC) metabolism. Accordingly, tyrosine phosphorylation of PLC gamma-1 can be evidenced but only in Jurkat cells highly expressing GM1. GM1 stimulation results in an IL-2 production comparable to that obtained after CD3 activation. Finally, the GM1-linked cell Ca2+ activation pathway is also observed in a Jurkat cell clone lacking Ag-specific receptor expression suggesting that the presence of functional CD3/TCR molecules is not essential for GM1-induced cell Ca2+ response. Altogether, these data show that cell surface gangliosides GM1 may act as a signaling molecule in Jurkat T cells possibly by a new pathway, a finding of importance when considering a possible function for ubiquitous membrane carbohydrate structures in T cell recognition systems.