INHIBITORS OF CALCINEURIN BLOCK EXPRESSION OF CYCLIN-A AND CYCLIN-E INDUCED BY FIBROBLAST GROWTH-FACTOR IN SWISS 3T3 FIBROBLASTS

In Swiss 3T3 fibroblasts, growth factor-stimulated progression from G1 to S phase involves activation of the Ca2+/calmodulin-dependent serin e/threonine-specific protein phosphatase 2B (calcineurin). Here we rep ort that both cobalt and the calcium chelator EGTA, inhibitors of calc ium uptake, as well as cyclosporin A and FK-506, specific inhibitors o f calcineurin function, abolished fibroblast growth factor (FGF)-induc ed ex pression of cyclins A and E, but not cyclin D-1. At 0.1 mu M con centration cyclosporin A completely blocked FGI-induced expression of cyclins E and A and it inhibited FGF-stimulated DNA synthesis by 40%; full inhibition of DNA synthesis required 10 mu M cyclosporin A. PD 98 059, an inhibitor of mitogen-activated protein (MAP) kinase kinase, an d hemicholinium-3, an inhibitor of FGF-induced MAP kinase activity, di d not inhibit the stimulatory effect of FGF on the expression of cycli n E. On the other hand, the inhibitory effect of 0.1 mu M cyclosporin A on FGF-stimulated DNA synthesis was additive with that of hemicholin ium-3, suggesting that the two inhibitors acted by different mechanism s. The inhibitors of calcineurin and calcium uptake also completely bl ocked the stimulatory effects of lysophosphatidic acid on the expressi on of cyclins E and A, but not cyclin D-1. The results suggest that FG F-or lysophosphatidic acid-induced transcription of cyclin A and cycli n E genes is mediated by calcineurin involving a MAP kinase-independen t mechanism and that increased expression of cyclins A and E is requir ed for the maximal stimulatory effects of these mitogens on DNA synthe sis. (C) 1998 Academic Press.