FK506 inhibits antigen receptor-mediated induction of c-rel in B and T lymphoid cells

Stimulation of B and T cells via the antigen receptor, by phorbol ester or by phorbol ester and ionomycin, leads to nuclear translocation of the inducible transcription factor NF-κB, comprising the p50 and p65 rel- related polypeptides. In this report we show that c-rel is a component of the antigen receptor-induced κB binding proteins in both B and T cells. Whereas NF-κB can be induced by phorbol ester alone, optimal induction of c-rel requires stimulation by both phorbol ester and ionomycin, the dual signal that is necessary for proliferation of untransformed lymphocytes. Furthermore, c-rel induction is blocked by the immunosuppressive drug FK506 that is known to inhibit B and T cell activation. c-rel-dependent transactivation of the interleukin-2 receptor α chain (IL-2Rα) promoter is augmented by coexpression of calcineurin, suggesting the involvement of a calcineurin-dependent intracellular pathway. Our results identify c-rel as a target of immunosuppressive agents and illustrate the similarity of activation pathways in both B and T cells.