[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

Abstract

The physiological role of IP3-dependent Ca2+ release in T cell activation was in question due to the contradictory findings that [8- (Diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl] (TMB-8), an inhibitor of intracellular Ca2+ mobilization, blocked T cell proliferation, curtailing specifically the level of released Ca2+ did not affect T cell activation and T cell line lacking IP3 receptor was defective in IL-2 production in response to TCR/CD3 ligand. In the present study we found that TMB-8 inhibited Concanavalin A (con A), but not PMA/ionomycin-induced T cell proliferation in a reversible and 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+ ionophore ionomycin augmented instead of overcoming the inhibitory effect of TMB-8, although the same doses of ionomycin alone had no effect on Con A-induced T cell proliferation. PMA the metabolically stable, but not diacylglycerol (DAG) the metabolically labile, activator of protein Kinase C (PKC) completely overcome the antiproliferative effect of TMB-8. A specific DAG lipase inhibitor RHC80267 also overcome the effect of TMB-8. Taken together, these results showed that the process of Ca2+ release through IP3 receptor, not the released Ca2+, is essential for the sustained phase of PKC activation during T cell proliferation. (C) 2000 Wiley-Liss, Inc.