title: Sumoylation of Hes6 Regulates Protein Degradation and Hes1-Mediated Transcription.
abstract: BACKGROUND
  Hes6 is a transcriptional regulator that induces transcriptional activation by binding to transcription repressor Hes1 and suppressing its activity. Hes6 is controlled by the ubiquitin-proteosome-mediated degradation system. Here we investigated the sumoylation of Hes6 and its functional role in its rhythmic expression.
  
  
  METHODS
  Hes6, SUMO, and ubiquitin were transfected into HeLa cells and the expression pattern was observed by Western blot and immunoprecipitation. To confirm the effect of sumoylation on the rhythmic expression of Hes6, we generated mouse Hes6 promoter-driven GFP-Hes6 fusion constructs and expressed these constructs in NIH 3T3 cells.
  
  
  RESULTS
  Overexpression of SUMO led to sumoylation of Hes6 at both lysine 27 and 30. Protein stability of Hes6 was decreased by sumoylation. Moreover, expression of a Hes6 sumoylation-defective mutant, the 2KR (K27/30R) mutant, or co-expression of SUMO protease SUSP1 with native Hes6, strongly reduced ubiquitination. In addition, sumoylation was associated with both the rhythmic expression and transcriptional regulation of Hes6. Wild type Hes6 showed oscillatory expression with about 2-hour periodicity, whereas the 2KR mutant displayed a longer period. Furthermore, sumoylation of Hes6 derepressed Hes1-induced transcriptional repression.
  
  
  CONCLUSIONS
  Hes6 sumoylation plays an important role in the regulation of its stability and Hes1-mediated transcription. These results suggest that sumoylation may be crucial for rhythmic expression of Hes6 and downstream target genes.
authors.affiliation: Department of Brain and Cognitive Sciences, Seoul National University School of Biological Sciences, Seoul, Korea.
authors.forename: Jiwon
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Brain and Cognitive Sciences, Seoul National University School of Biological Sciences, Seoul, Korea.
authors.forename: Sung Kook
authors.initials: SK
authors.lastname: Chun
authors.affiliation: Department of Legal Medicine, Korea University College of Medicine, Seoul, Korea.
authors.forename: Gi Hoon
authors.initials: GH
authors.lastname: Son
authors.affiliation: Department of Brain and Cognitive Sciences, Seoul National University School of Biological Sciences, Seoul, Korea. kyungjin@dgist.ac.kr.
authors.forename: Kyungjin
authors.initials: K
authors.lastname: Kim
keywords: Degradation; Hes6; Rhythmic expression; Sumoylation; Ubiquitination