Inhibition of NF-AT signal transduction events by a dominant-negative form of calcineurin

An inhibitory, 'dominant-negative,' form of the calcineurin catalytic (A) subunit was prepared, which lacks the calmodulin-binding domain, autoinhibitory domain and most of its catalytic core but possesses die regulatory (B) subunit binding domain. When tested for its ability to block calcineurin-dependent signaling in Jurkat cells, expression of this 'B-subunit knock-out' (BKO) construct suppressed reporter gene activity driven by NF-AT, the pivotal promoter element for interleukin (IL)-2 gene induction. Immunoprecipitation of epitope-labeled BKO demonstrated for the formation of a tight complex with endogenous B subunit in Jurkat cells, consistent with an inhibitory mechanism that involves the sequestration of the B subunit. Furthermore, the sharply reduced NF-AT activity produced by co-transfecting BKO could be 'rescued' by overexpression of transfected B subunit, suggesting that depletion of this subunit was responsible for the inhibition. These data suggest the potential utility of agents that disrupt calcineurin-mediated signal transduction pathways by blocking formation of the catalytically active dimer of calcineurin A and B subunits.