Protein Kinase Cζ Phosphorylates Nuclear Factor of Activated T Cells and Regulates Its Transactivating Activity

Abstract Although several isoforms of protein kinase C (PKC) have been implicated in T lymphocyte activation events, little is known about their mode of action. To address the role of PKCζ in T cell activation, we have generated Jurkat T cell transfectants expressing either the wild type (J-PKCζ) or “kinase-dead” mutant (J-PKCζmut) versions of this protein. Expression of PKCζ but not PKCζmut increased transcriptional activation mediated by the NF-κB or nuclear factor of activated T cells (NFAT). PKCζ cooperates with calcium ionophore and with NFAT1 or NFAT2 proteins to enhance transcriptional activation of a NFAT reporter construct. However, neither NFAT nuclear translocation nor DNA binding were in J-PKCζ cells. Our results show that PKCζ enhanced transcriptional activity mediated by Gal4-NFAT1 fusion proteins containing the N-terminal transactivation domain of human NFAT1. Interestingly, PKCζ synergizes with calcineurin to induce transcriptional activation driven by the NFAT1 transactivation domain. Co-precipitation experiments showed physical interaction between PKCζ and NFAT1 or NFAT2 isoforms. Even more, PKCζ was able to phosphorylate recombinant glutathione S-transferase-NFAT1 (1–385) protein. These data reveal a new role of PKCζ in T cells through the control of NFAT function by modulating the activity of its transactivation domain.