Involvement of CD2 and CD3 in galectin-1 induced signaling in human Jurkat T-cells

Galectin-1 (gal-1) a member of the mammalian beta-galactoside-binding proteins recognizes preferentially Gal beta 1-4GlcNAc sequences of oligosaccharides associated with several cell surface glycoconjugates. In the present work, gal-1 has been identified to be a ligand for the CD3-complex as well as for CD2 as detected by affinity chromatography of Jurkat T-cell lysates on gal-1 agarose and by binding of the biotinylated lectin to CD3 and CD2 immunoprecipitates on blots. In CD45(+) Jurkat E6.1 cells, the lectin stimulates a sustained increase in the intracytoplasmic calcium concentration ([Ca2+](i)) consisting of both the release of calcium from intracellular stores and the calcium influx from the extracellular space. This effect of gal-1 on [Ca2+](i) is completely inhibited by lactose at 10 mM and was absent in CD45(-) Jurkat J45.01 cells. Preincubation of Jurkat E6.1 cells with cholera toxin or with the protein tyrosine kinase inhibitor herbimycin A reduced the gal-1 induced calcium response whereas the increase in [Ca2+](i) stimulated by CD2 or CD3 monoclonal antibodies (mAbs) was completely inhibited. Depolarization of E6.1 cells in a high-potassium buffer, a standard method to activate voltage-operated calcium channels, was without effect on [Ca2+](i). Membrane depolarization with gramicidin or by a high-potassium buffer was without effects on the lectin-mediated calcium release from intracellular stores but inhibited the gal-1 induced receptor-operated calcium influx. In Jurkat E6.1 cells the lectin stimulates the transient generation of inositol-1,4,5-trisphosphate and the tyrosine phosphorylation of phospholipase C gamma 1. The results suggest that the ligation of CD2 and CD3 by gal-1 induces early events in T-cell activation comparable with that elicited by CD2 or CD3 mAbs.