CALCIUM-DEPENDENT ACTIVATION OF THE NF-AT TRANSCRIPTION FACTOR BY P59FYN

A reporter gene under the control of a T-cell antigen receptor respons e element was activated in Jurkat cells by antigen receptor triggering or by a combination of phorbol myristate acetate, which activates pro tein kinase C, and a calcium ionophore. Both these signals were necess ary for expression of the reporter gene. When co-transfected with a co nstruct capable of overexpressing the tyrosine kinase p59fyn, the repo rter gene was activated by PMA alone. Thus p59fyn could replace the ca lcium ionophore but not activation of protein kinase C. The activation by p59fyn plus PMA was blocked by EGTA and by the immunosuppressant d rug cyclosporin A.