Differential Effects of SUMO1/2 on Circadian Protein PER2 Stability and Function

Posttranslational modification (PTM) of core circadian clock proteins, including Period2 (PER2), is required for proper circadian regulation. PER2 function is regulated by casein kinase 1 (CK1)-mediated phosphorylation and ubiquitination but little is known about other PER2 PTMs or their interaction with PER2 phosphorylation. We found that PER2 can be SUMOylated by both SUMO1 and SUMO2; however, SUMO1 versus SUMO2 conjugation had different effects on PER2 turnover and transcriptional suppressor function. SUMO2 conjugation facilitated PER2-β-TrCP interaction leading to PER2 proteasomal degradation. In contrast, SUMO1 conjugation, mediated by E3 SUMO-protein ligase RanBP2, enhanced CK1-mediated PER2 S662 phosphorylation and increased PER2 transcriptional suppressor function. PER2 K736 was critical for both SUMO1- and SUMO2-conjugation. A PER2 K736R mutation was sufficient to alter circadian periodicity and reduce PER2-mediated transcriptional suppression. Together, our data revealed SUMO1 versus SUMO2 conjugation acts as an upstream determinant of PER2 phosphorylation and thereby affects the circadian regulatory system and circadian periodicity.