Role of the CLOCK Protein in the Mammalian Circadian Mechanism

Abstract

The mouse Clock gene encodes a bHLH-PAS protein that regulates circadian rhythms and is related to transcription factors that act as heterodimers. Potential partners of CLOCK were isolated in a two-hybrid screen, and one, BMAL1, was coexpressed with CLOCK and PER1 at known circadian clock sites in brain and retina. CLOCK-BMAL1 heterodimers activated transcription from E-box elements, a type of transcription factor-binding site, found adjacent to the mouse per1 gene and from an identical E-box known to be important for per gene expression in Drosophila. Mutant CLOCK from the dominant-negative Clock allele and BMAL1 formed heterodimers that bound DNA but failed to activate transcription. Thus, CLOCK-BMAL1 heterodimers appear to drive the positive component of per transcriptional oscillations, which are thought to underlie circadian rhythmicity.

Reciprocal regulation of carbon monoxide metabolism and the circadian clock

“…Mutagenesis of the E box to an inactive form (CACGTG to TTTAGT; described in ref. 57) was performed by site-directed mutagenesis (QuikChange Site-Directed Mutagenesis Kit; Stratagene).…”

The role of clock genes and rhythmicity in the liver

“…The hepatic oscillator is centered on a pair of transcriptional activators, BMAL1 (also named Mop3) (Bunger et al, 2000;Hogenesch et al, 1998) and CLOCK (Gekakis et al, 1998;King et al, 1997) and two classes of repressors of the Period (Per) Shearman et al, 1997;Sun et al, 1997;Tei et al, 1997) and Cryptochrome (Cry) gene families (Griffin et al, 1999;Kume et al, 1999;van der Horst et al, 1999;Vitaterna et al, 1999) (Fig. 2).…”

Clock and ATF4 transcription system regulates drug resistance in human cancer cell lines

“…No significant alteration of c-Myc and USF1 expression was observed between parental and cisplatin-resistant cells. As the Clock/BMAL1 complex regulates the expression of circadian genes (Gekakis et al, 1998), we analysed the BMAL1 expression. However, the BMAL1 expression was not upregulated in cisplatin-resistant cells (data not shown).…”

“…Interestingly, a database search revealed an E-box in the core promoter region of ATF4, and we show that the essential circadian regulator Clock binds to this E-box and is overexpressed in cisplatin-resistant cells. It has been reported previously that Clock/BMAL1 heterodimers activate transcription from E-box elements (Gekakis et al, 1998); therefore, ATF4 is thought to be regulated by circadian transcription factors. Downregulation of either Clock or ATF4 using small interfering RNAs (siRNAs) was shown to confer cell sensitivity to anticancer agents.…”