Potentiation of CD3-induced expression of the linker for activation of T cells (LAT) by the calcineurin inhibitors cyclosporin A and FK506

The activation of blood cells, including T cells, triggers intracellular si gnals that control the expression of critical molecules, including cytokine s and cytokine receptors. We show that T-cell receptor (TCR) ligation incre ases the cellular level of the protein linker for activation of T cells (LA T), a molecule critical for T cell development and function. T-cell activat ion increased LAT messenger RNA, as determined by reverse transcription-pol ymerase chain reaction and by Northern blotting, The TCR-induced increase i n LAT expression involved the activation of the serine/threonine kinases PK C and MEK, because inhibitors of these kinases blocked the increase in LAT, Accordingly, the PKC activator phorbol myristate acetate up-regulated LAT expression. Strikingly, the calcineurin inhibitors cyclosporin A (CsA) and FK506 strongly potentiated TCR-induced LAT expression, suggesting that the activation of calcineurin following TCR ligation negatively regulates LAT e xpression. Accordingly, Ca++ ionophores, which can activate calcineurin by increasing intracellular Ca++, blocked the TCR-induced increase in cellular LAT, CsA and FK506 blocked the Ca++ ionophores' inhibitory effect on LAT e xpression. Notably, CsA and FK506 preferentially up-regulated TCR-induced L AT expression; under the same conditions, these compounds did not increase the expression of 14 other molecules that previously had been implicated in T-cell activation. These data show that TCR-induced LAT expression involve s the activation of the PKC-Erk pathway and is negatively regulated by the activation of calcineurin. Furthermore, the potentiation of TCR-induced LAT expression by CsA and FK506 suggests that the action of these agents invol ves up-regulating the cellular level of critical signaling molecules. These findings may have important therapeutic implications. (Blood, 2000;95:2733 -2741) (C) 2000 by The American Society of Hematology.