Ca2+-dependent gene expression mediated by MEF2 transcription factors

Ca2+ induction of a subset of cellular and viral immediate-early activation genes in lymphocytes has been previously mapped to response elements recognized by the MEF2 family of transcription factors. Here, we demonstrate that Ca2+ activation of MEF2 response elements in T lymphocytes is mediated in synergy by two Ca2+/calmodulin-dependent enzymes, the phosphatase calcineurin, and the kinase type IV/Gr (CaMKIV/Gr), which promote transcription by the MEF2 family members MEF2A and MEF2D. Calcineurin up-regulates the activity of both factors by an NFAT-dependent mechanism, while CaMKIV/Gr selectively and independently activates MEF2D. These results identify MEF2 proteins as effecters of a pathway of gene induction in T lymphocytes which integrates diverse Ca2+ activation signals and may be broadly operative in several tissues.