Pellino-1, an adaptor protein of interleukin-1 receptor/toll-like receptor signaling, is sumoylated by Ubc9

Covalent modifications of the Pellino-1 protein are essential for transmitting innate immune response signals downstream, as the phosphorylation and polyubiquitination of Pellino-1 mediated by the IRAK proteins appear to have roles in regulating Pellino-1 function. In this study, we demonstrate that the Pellino-1 protein is post-translationally modified by small-ubiquitin-related modifier-1 (SUMO-1). Sumoylation assays with Pellino-1 and SUMO-1 expression plasmids reveal that the Pellino-1 protein is sumoylated in vitro and in vivo. Treatment of SUMO-1 specific protease 1 (SENP1) inhibited the sumoylation of the Pellino-1 protein and a GST pull-down assay as well as a yeast two hybrid assay showed that Pellino-1 binds to the SUMO-conjugating enzyme, Ubc9. Furthermore, we identified the five lysine residues of the Pellino-1 protein where SUMO-1 covalently attaches. Some of the sumoylated sites overlap with previously identified ubiquitination sites, suggesting competition between sumoylation and ubiquitination, as well as suggesting that the sumoylated Pellino-1 protein may have a cellular function distinct from previously identified functions.