ABSTRACT
Posttranslational modifications play a crucial role in the proper control of c-Myc protein stability and activity. c-Myc can be modified by small ubiquitin-like modifier (SUMO). However, how SUMOylation regulates c-Myc stability and activity remains to be elucidated. The deSUMOylation enzyme, SENP1, has recently been shown to have a prooncogenic role in cancer; however, mechanistic understanding of this is limited. Here we show that SENP1 is a c-Myc deSUMOylating enzyme. SENP1 interacts with and deSUMOylates c-Myc in cells and in vitro. Overexpression of wild-type SENP1, but not its catalytically inactive C603S mutant, markedly stabilizes c-Myc and increases its levels and activity. Knockdown of SENP1 reduces c-Myc levels, induces cell cycle arrest, and drastically suppresses cell proliferation. We further show that c-Myc can be comodified by both ubiquitination and SUMOylation. SENP1-mediated deSUMOylation reduces c-Myc polyubiquitination, suggesting that SUMOylation promotes c-Myc degradation through the proteasome system. Interestingly, SENP1-mediated deSUMOylation promotes the accumulation of monoubiquitinated c-Myc and its phosphorylation at serine 62 and threonine 58. SENP1 is frequently overexpressed, correlating with the high expression of c-Myc, in breast cancer tissues. Together, these results reveal that SENP1 is a crucial c-Myc deSUMOylating enzyme that positively regulates c-Myc's stability and activity.
