DNA binding, but not interaction with Bmal1, is responsible for DEC1-mediated transcription regulation of the circadian gene mPer1.
DEC1 (differentially expressed in chondrocytes 1) and DEC2 are E-box-binding transcription factors and exhibit a circadian expression pattern. Recently, both proteins were found to repress the Clock/Bmal1-activated E-box promoters (e.g. mPer1). Yeast two-hybrid assay detected interactions between Bmal1 and DECs. It was hypothesized that DEC-mediated repression on the mPer1 promoter is achieved by binding to E-box elements and interacting with Bmal1. In the present study, we report that E-box binding rather than Bmal1 interaction is responsible for the observed repression. In the absence of Clock/Bmal1, both DEC1 and DEC2 markedly repressed the mPer1 promoter reporter; however, DNA-binding mutants showed no repressive activity. Similarly, DEC1, but not its DNA-binding mutants, repressed the Clock/Bmal1-induced activation. In addition, DEC1(R58P), a DNA-binding mutant with Bmal1 interactivity, repressed neither the mPer1 reporter directly nor the Clock/Bmal1-induced activation, providing direct evidence that DNA binding, rather than Bmal1 interactions, is responsible for the repression on the mPer1 promoter. Furthermore, disruption of the Sp1 site in the proximal promoter of mPer1 increased the repression of DEC1 proteins. Previous studies with mouse DEC2 showed that this factor interacts with Sp1. These findings suggest that DEC proteins regulate the expression of mPer1 through E-box binding and Sp1 interaction. Alterations on circadian systems are increasingly recognized as important risk factors for disease initiation and progression, and the expression of Dec genes is rapidly induced by environmental stimuli and is highly increased in tumour tissues. Therefore de-regulated expression of DEC genes probably alters normal circadian rhythms and contributes significantly to the pathogenesis of many diseases including cancer.
Li
Yuxin
Y
Department of Biomedical Sciences, University of Rhode Island, Kingston, RI 02881, USA.
Song
Xiulong
X
Ma
Yuzhong
Y
Liu
Jirong
J
Yang
Dongfang
D
Yan
Bingfang
B
D056930:ARNTL Transcription Factors; D000595:Amino Acid Sequence; D051792:Basic Helix-Loop-Helix Proteins; D001665:Binding Sites; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D002460:Cell Line; D002940:Circadian Rhythm / Q000235:genetics*; D018398:Homeodomain Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics*; D056950:Period Circadian Proteins; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology
D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D056950:Period Circadian Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C538960:BMAL1 protein, human; C538961:Bmal1 protein, mouse; C470968:Bhlhb3 protein, mouse; C491539:Bhlhe40 protein, mouse; C539022:PER1 protein, human; C539023:Per1 protein, mouse; C538943:CLOCK protein, human; C538944:Clock protein, mouse