CLOCK is involved in the circadian transactivation of peroxisome-proliferator-activated receptor alpha (PPARalpha) in mice.
PPARalpha (peroxisome-proliferator-activated receptor alpha) is a member of the nuclear receptor superfamily of ligand-activated transcription factors that regulate the expression of genes associated with lipid metabolism. In the present study, we show that circadian expression of mouse PPARalpha mRNA requires the basic helix-loop-helix PAS (Per-Arnt-Sim) protein CLOCK, a core component of the negative-feedback loop that drives circadian oscillators in mammals. The circadian expression of PPARalpha mRNA was abolished in the liver of homozygous Clock mutant mice. Using wild-type and Clock-deficient fibroblasts derived from homozygous Clock mutant mice, we showed that the circadian expression of PPARalpha mRNA is regulated by the peripheral oscillators in a CLOCK-dependent manner. Transient transfection and EMSAs (electrophoretic mobility-shift assays) revealed that the CLOCK-BMAL1 (brain and muscle Arnt-like protein 1) heterodimer transactivates the PPARalpha gene via an E-box-rich region located in the second intron. This region contained two perfect E-boxes and four E-box-like motifs within 90 bases. ChIP (chromatin immunoprecipitation) also showed that CLOCK associates with this E-box-rich region in vivo. Circadian expression of PPARalpha mRNA was intact in the liver of insulin-dependent diabetic and of adrenalectomized mice, suggesting that endogenous insulin and glucocorticoids are not essential for the rhythmic expression of the PPARalpha gene. These results suggested that CLOCK plays an important role in lipid homoeostasis by regulating the transcription of a key protein, PPARalpha.
Oishi
Katsutaka
K
Clock Cell Biology Research Group, Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology, Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
Shirai
Hidenori
H
Ishida
Norio
N
D056930:ARNTL Transcription Factors; D000315:Adrenalectomy; D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D047369:Chromatin Immunoprecipitation; D002940:Circadian Rhythm / Q000235:genetics*; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism; D019281:Dimerization; D005347:Fibroblasts; D006801:Humans; D007438:Introns / Q000235:genetics; D008099:Liver / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D047493:PPAR alpha / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation / Q000235:genetics*
D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D056926:CLOCK Proteins; D047493:PPAR alpha; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; C538960:BMAL1 protein, human; C538961:Bmal1 protein, mouse; C538943:CLOCK protein, human; C538944:Clock protein, mouse