ADP-ribosylation is a reversible posttranslational modification mediated by poly-ADP-ribose polymerase (PARP). The results of recent studies demonstrate that ADP-ribosylation contributes to transcription regulation. Here, we report that transcription factor NFAT binds to and is ADP-ribosylated by PARP-1 in an activation-dependent manner. Mechanistically, ADP-ribosylation increases NFAT DNA binding. Functionally, NFAT-mediated interleukin-2 (IL-2) expression was reduced in T cells upon genetic ablation or pharmacological inhibition of PARP-1. Parp-1 / T cells also exhibit reduced expression of other NFAT-dependent cytokines, such as IL-4. Together, these results demonstrate that ADP-ribosylation mediated by PARP-1 provides a molecular switch to positively regulate NFAT-dependent cytokine gene transcription. These results also imply that, similar to the effect of calcineurin inhibition, PARP-1 inhibition may be beneficial in modulating immune functions. ADP-ribosylation is a reversible posttranslational modification that transfers ADP-ribose from NAD to Glu, Asp, and/or Arg amino acids of target proteins (18). Similar to ubiquitination, ADP-ribosylation modifies target proteins to various masses due to the assorted chain lengths of the ADPribose. ADP-ribosylation is inhibited by the NAD analog 3-aminobenzamide and, more specifically, by PJ-34 (45). PolyADP-ribose polymerase-1 (PARP-1) is a nuclear enzyme that accounts for the bulk of ADP-ribosylation in vivo (43). Indeed, only 10% of PARP activity remains in Parp-1 / cells upon DNA damage. In addition to its role in DNA damage repair
