[8-(diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl], the inhibitor of intracellular calcium mobilization, blocked mitogen-induced T cell proliferation by interfering with the sustained phase of protein kinase C activation

The physiological role of IP3-dependent Ca2+ release in T cell activation w as in question due to the contradictory findings that [8-(Diethylamino)octy l-3,4,5-trimethoxybenzoate, HCl] (TMB-8), an inhibitor of intracellular Ca2 + mobilization, blocked T cell proliferation, curtailing specifically the l evel of released Ca2+ did not affect T cell activation and T cell line lack ing IP3 receptor was defective in IL-2 production in response to TCR/CD3 li gand. In the present study we found that TMB-8 inhibited Concanavalin A (Co n A)- but not PMA/lonomycin-induced T cell proliferation in a reversible an d dose-dependent manner. The kinetic study revealed that TMB-8 exerted the inhibitory effect at a very early step of T cell activation. The Ca2+ ionop hore ionomycin augmented instead of overcoming the inhibitory effect of TMB -8, although the same doses of ionomycin alone had no effect on Con A-induc ed T cell proliferation. PMA the metabolically stable, but not diacylglycer ol (DAG) the metabolically labile, activator of protein Kinase C (PKC) comp letely overcome the antiproliferative effect of TMB-8. A specific DAC lipas e inhibitor RHC80267 also overcome the effect of TMB-8. Taken together, the se results showed that the process of Ca2+ release through IP3 receptor, no t the released Ca2+, is essential for the sustained phase of PKC activation during T cell proliferation. (C) 2000 Wiley-Liss, Inc.