LFA-1-dependent Ca2+ entry following suboptimal T cell receptor triggering proceeds without mobilization of intracellular Ca2+.
A surge in cytosolic calcium ion concentration by entry of extracellular Ca2+ is a hallmark of T cell activation. According to store-operated Ca2+ entry mechanism, the Ca2+ entry is preceded by activation of phospholipase C-gamma1 (PLC-gamma1) and the consequent mobilization of intracellular Ca2+. Using membrane vesicles expressing the mouse class I major histocompatibility complex, i.e. Ld plus costimulatory ligands, i.e. B7-1 and intercellular adhesion molecule-1 along with 2C T cell receptor transgenic T cells, we investigated the roles of CD28 and LFA-1 (lymphocyte function-associated antigen-1) in the activation of PLC-gamma1 and Ca2+ signaling. Both CD28 and LFA-1 made significant and comparable contributions to the activation of PLC-gamma1 as gauged by the level of its phosphorylation at tyrosine 783. In contrast, their roles in Ca2+ signaling were quite distinct so that LFA-1/intercellular adhesion molecule-1 interaction exerted a determining role, whereas CD28/B7-1 interaction played only a minimal role. In particular, when the T cells were activated by suboptimal T cell receptor stimulation, LFA-1 played an indispensable role in the Ca2+ signaling. Further experiments using Ca2+-free medium demonstrated that the entry of extracellular Ca2+ was not always accompanied by mobilization of intracellular Ca2+. Thus, intracellular Ca2+ mobilization was hardly detected under the condition that LFA-1 played the indispensable role in the entry of extracellular Ca2+, while a distinct level of intracellular Ca2+ mobilization was readily detected under the condition that LFA-1 played only the supporting role. These results ensure the unique role of LFA-1 in T cell Ca2+ signaling and reveal that LFA-1-dependent Ca2+ entry proceeds via a mechanism separate from store-operated Ca2+ entry.
Kim
Kwangmi
K
Department of Chemistry and Chemical Biology, The Scripps Research Institute, La Jolla, California 92037.
Wang
Lin
L
Department of Chemistry and Chemical Biology, The Scripps Research Institute, La Jolla, California 92037.
Hwang
Inkyu
I
Department of Chemistry and Chemical Biology, The Scripps Research Institute, La Jolla, California 92037.
D000818:Animals; D018106:CD28 Antigens / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D051966:Phospholipase C gamma / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism; D013997:Time Factors
D018106:CD28 Antigens; D015395:Histocompatibility Antigens Class I; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D011948:Receptors, Antigen, T-Cell; D051966:Phospholipase C gamma; D002118:Calcium