Frantz, Betsy

Abstract The Ca2+-dependent phosphatase calcineurin, a target of FK506 and CsA, synergizes with PKC-induced activation of nuclear factor (NF)-kappa B in T cell lines. We have investigated whether this synergy is present in other cell types and the mechanism(s) by which these two pathways lead to NF-kappa B activation. While this synergy is present in other cell types, in the monocytic cell line U937 calcineurin is also sufficient to activate NF-kappa B. Having previously shown that Ca2+- and PKC-dependent pathways synergize by accelerating the degradation of IkB α, we focused on the regulation of IkB α phosphorylation. While PKC-dependent pathways sequentially result in the phosphorylation and in an incomplete degradation of IkB α in T cell lines, co-activation of Ca2+-dependent pathways accelerates the rate of IkB α phosphorylation and results in its complete degradation. Activation of Ca2+-dependent pathways alone do not result in the phosphorylation and/or degradation of IkB α in Jurkat T or in U937 cells. Treatment of T cells with the selective PKC inhibitor GF109203X abrogates the PMA-induced IkB α phosphorylation/degradation irrespective of activation of Ca2+-dependent pathways, but not the phosphorylation and degradation of IkB α induced by TNF-α, a PKC-independent stimulus. Contrary to the interaction with PKC, Ca2+-dependent pathways synergize with TNF-α not at the level of IkB α phosphorylation, but at the level of its degradation. These results indicate that Ca2+-dependent pathways, including the phosphatase calcineurin, participate in the regulation of NF-kappa B in a cell specific fashion and synergize with PKC-dependent and -independent pathways at the level of IkB α phosphorylation and degradation.