Ca2+-induced p38/SAPK signalling inhibited by the immunosuppressant cyclosporin A in human peripheral blood mononuclear cells

To understand the effects of the immunosuppressant cyclosporin A (CsA) on C a2+-mediated intracellular signalling pathways in human peripheral blood mo nonuclear cells (PBMCs), we investigated its effects on the activity profil es of mitogen-activated protein kinase (MAPK) cascades. PBMCs, or subpopula tions thereof, were simultaneously stimulated with a phorbol ester and the calcium ionophore ionomycin, in the presence or absence of therapeutic conc entrations of CsA. In these primary human cells, CsA significantly inhibite d PMA/ionomycin-mediated and ionomycin-mediated activation of the MAPK kina se MKK6, as well as its downstream kinases SAPK2a (p38 alpha a) and MAPKAP- K2. PMA/ionomycin treatment also mediated activation of SAPK1 (JNKs) which was inhibited by CsA. Treatment with ionomycin alone also resulted in CsA-s ensitive activation of SAPK1. With regard to transcription factors targeted by the Ca2+-induced MAPK signalling network, we found CsA to inhibit the i onomycin-mediated phosphorylation of ATF2 at Thr71. We identified the heter odimeric transcription factor ATF2/CREB as constitutively binding to the es sential cAMP response element (CRE) site within the Ca2+-regulated DNA poly merase beta promoter and contributing to the activation of this promoter. O ur data implicate ATF2 phosphorylation status as a nuclear sensor within PB MCs that monitors converging intracellular Ca2+-signalling pathways.