c-Jun and p53 activity is modulated by SUMO-1 modification

The ubiquitin-related SUMO-1 molecule has been shown recently to modify cov alently a number of cellular proteins including I kappa B alpha. SUMO-1 mod ification was found to antagonize I kappa B alpha ubiquitination and protec t it from degradation. Here we identify the transcription factors c-Jun and p53, two well known, targets of ubiquitin, as new substrates for SUMO-1 bo th in vitro and in vivo. In contrast to ubiquitin, SUMO-1 preferentially ta rgets a single lysine residue in c-Jun (Lys-229), and the abrogation of SUM O-1 modification does not compromise its ubiquitination, Activation of Jun NH2-terminal kinases, which induces a reduction in c-Jun ubiquitination, si milarly decreases SUMO-1 modification. Accordingly, loss of the two major J un NH2-terminal kinase phosphorylation sites in c-Jun, Ser-63 and Ser-73, g reatly enhances conjugation by SUMO-1. A SUMO-1-deficient c-JunK229R mutant shows an increased transactivation potential on an AP-1-containing promote r compared with wild-type c-Jun, suggesting that SUMO-1 negatively regulate s c-Jun activity. As with c-Jun, SUMO-1 modification of p53 is abrogated by phosphorylation but remains unaltered upon chemical damage to DNA or Mdm2- mediated ubiquitination. The SUMO-1 attachment site in p53 (Lys-386) reside s within a region known to regulate the DNA binding activity of the protein . A p53 mutant, defective for SUMO-1 conjugation, shows unaltered ubiquitin ation but has a slightly impaired apoptotic activity, indicating that modif ication by SUMO-1 might be important for the full biological activity of p5 3, Taken together, these data provide a first link between the SUMO-1 conju gation pathway and the regulation of transcription factors.