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

Galectin-1 (gal-1) a member of the mammalian beta-galactoside-binding prote ins recognizes preferentially Gal beta 1-4GlcNAc sequences of oligosacchari des associated with several cell surface glycoconjugates. In the present wo rk, 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 imm unoprecipitates on blots. In CD45(+) Jurkat E6.1 cells, the lectin stimulat es 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 o n [Ca2+](i) is completely inhibited by lactose at 10 mM and was absent in C D45(-) Jurkat J45.01 cells. Preincubation of Jurkat E6.1 cells with cholera toxin or with the protein tyrosine kinase inhibitor herbimycin A reduced t he gal-1 induced calcium response whereas the increase in [Ca2+](i) stimula ted by CD2 or CD3 monoclonal antibodies (mAbs) was completely inhibited. De polarization 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 wa s without effects on the lectin-mediated calcium release from intracellular stores but inhibited the gal-1 induced receptor-operated calcium influx. I n Jurkat E6.1 cells the lectin stimulates the transient generation of inosi tol-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 ind uces early events in T-cell activation comparable with that elicited by CD2 or CD3 mAbs.