MAP kinase activation by cyclosporine A.

Short treatment of HeLa cells with cyclosporine A led to the activation in the crude cell extracts of a MAP kinase-like activity. Fractionation by chromatography on a Mono Q column allowed the separation of two activities co-eluting with the MAP kinases ERK1 and ERK2. The activation of these two MAP kinases was demonstrated in Western Blotting by the appearance, after CsA treatment, of two new slowly migrating forms on SDS electrophoretic gels. A similar activation was also obtained in renal epithelial BSC-1 cells and 3T3 fibroblasts. MAP kinase activation might result from a perturbation of calcium homeostasis induced by CsA treatment.