Potent Inhibition of Ca2+ Release-activated Ca2+ Channels and T-lymphocyte Activation by the Pyrazole Derivative BTP2

Ca2+ entry through store-operated Ca2+release-activated Ca2+ (CRAC) channels is essential for T-cell activation and proliferation. Recently, it has been shown that 3,5-bistrifluoromethyl pyrazole (BTP) derivatives are specific inhibitors of Ca2+-dependent transcriptional activity in T-cells (Trevillyan, J. M., Chiou, X. G., Chen, Y. W., Ballaron, S. J., Sheets, M. P., Smith, M. L., Wiedeman, P. E., Warrior, U., Wilkins, J., Gubbins, E. J., Gagne, G. D., Fagerland, J., Carter, G. W., Luly, J. R., Mollison, K. W., and Djuric, S. W. (2001) J. Biol. Chem. 276, 48118-48126). Whereas inhibition of Ca2+ signals was reported for BTP2 (Ishikawa, J., Ohga, K., Yoshino, T., Takezawa, R., Ichikawa, A., Kubota, H., and Yamada, T. (2003) J. Immunol. 170, 4441-4449), it was not found for BTP3 (Chen, Y., Smith, M. L., Chiou, G. X., Ballaron, S., Sheets, M. P., Gubbins, E., Warrior, U., Wilkins, J., Surowy, C., Nakane, M., Carter, G. W., Trevillyan, J. M., Mollison, K., and Djuric, S. W. (2002) Cell. Immunol. 220, 134-142). We show that BTP2 specifically inhibits CRAC channels in T-cells with an IC(50) of approximately 10 nm. It does not interfere with other mechanisms important for Ca2+ signals in T-cells, including Ca2+ pumps, mitochondrial Ca2+ signaling, endoplasmic reticulum Ca2+ release, and K+ channels. BTP2 inhibits Ca2+ signals in peripheral blood T-lymphocytes (in particular in CD4+ T-cells) and in human Jurkat T-cells. Inhibition of Ca2+ signals is independent of the stimulation method as Ca2+ entry was blocked following stimulation with anti-CD3, which activates the T-cell receptor, and also following stimulation with thapsigargin or inositol 1,4,5-trisphosphate. BTP2 also inhibited Ca2+-dependent gene expression (interleukins 2 and 5 and interferon gamma) and proliferation of T-lymphocytes with similar IC(50) values. BTP2 is the first potent and specific inhibitor of CRAC channels in primary T-lymphocytes. The inhibition of CRAC channels as well as Ca2+-dependent signal transduction with similar IC(50) values in T-lymphocytes emphasizes the importance of CRAC channel activity during T-cell activation. Furthermore, BTP2 could prove to be a tool to finally unmask the molecular identity of CRAC channels.