Circadian regulation of low density lipoprotein receptor promoter activity by CLOCK/BMAL1, Hes1 and Hes6

Abstract

Low density lipoprotein receptor (LDLR) plays an important role in the cholesterol homeostasis. We examined the possible circadian regulation of LDLR and mechanism(s) underlying it. In mice, blood glucose and plasma triglyceride, total and high density lipoprotein cholesterol varied distinctively throughout a day. In addition, LDLR mRNA oscillated in the liver in a functional clock-dependent manner. Accordingly, analysis of human LDLR promoter sequence revealed three putative E-boxes, raising the possible regulation of LDLR expression by E-box-binding transcription factors. To test this possibility, human LDLR promoter reporter constructs were transfected into HepG2 cells and the effects of CLOCK/BMAL1, Hes1, and Hes6 expression were analyzed. It was found that positive circadian transcription factor complex CLOCK/BMAL1 upregulated human LDLR promoter activity in a serum-independent manner, while Hes family members Hes1 and Hes6 downregulated it only under serum-depleted conditions. Both effects were mapped to proximal promoter region of human LDLR, where mutation or deletion of well-known sterol regulatory element (SRE) abolished only the repressive effect of Hes1. Interestingly, hes6 and hes1 mRNA oscillated in an anti-phasic manner in the wild-type but not in the per1-/-per2-/- mouse. Comparative analysis of mouse, rat and human hes6 genes revealed that three E-boxes are conserved among three species. Transfection and site-directed mutagenesis studies with hes6 reporter constructs confirmed that the third E-box in the exon IV is functionally induced by CLOCK/BMAL1. Taken together, these results suggest that LDLR expression is under circadian control involving CLOCK/BMAL1 and Hes family members Hes1 and Hes6.

Control of hair cell development by molecular pathways involving Atoh1, Hes1 and Hes5

“…Furthermore, these regulations involve another transcription factor CLOCK/BMAL1 (Lee et al, 2012). A new E-box-like clock-related element EL-box that involves in circadian regulation by BMAL1/CLOCK and HES1 was detected in 2012 (Ueshima et al, 2012).…”

“…The oscillatory expression pattern of Hes1 also leads to the circadian regulation of its downstream genes, such as LDLR (Lee et al, 2012). Furthermore, these regulations involve another transcription factor CLOCK/BMAL1 (Lee et al, 2012).…”

“…Intriguingly, under serum-depleted conditions, HES1 and HES6 both repress the expression of low density lipoprotein receptors (LDLR), which play an important role in cholesterol homeostasis (Lee et al, 2012) (Table 4). In this study, the HES1 binding site was found in the sterol regulatory element (SRE) of the LDLR promoter, which let us speculate that HES6 might bind to a site independent of SRE, but is also involved in the proximal region of the LDLR promoter.…”

Hairy and Enhancer of Split 6 (Hes6) Deficiency in Mouse Impairs Neuroblast Differentiation in Dentate Gyrus Without Affecting Cell Proliferation and Integration into Mature Neurons

“…Hes6 is indirectly related to Hes1, which functions to increase cell proliferation by sustaining the undifferentiated state (Ishibashi et al 1994;Ohtsuka et al 2001). Although we did not examine the interaction between the two molecules in the present study, Hes6 and Hes1 mRNA are known from previous work to oscillate in an anti-phasic manner during the 24 h of circadian cycle (Lee et al 2012). …”

“…Proneuronal genes such as Mash1, Math3, and Ngn2 induce Hes6 expression (Kageyama et al 2005), and their mutation blocks neuronal differentiation (Fode et al 1998;Guillemot et al 1993;Ma et al 1998). An upstream promoter region of Hes6 in mice, rats, and humans contains binding sites for Ngn1/3 and NeuroD1 (Lee et al 2012). Hes6 can also regulate the transcription of proneuronal factors, including Mash1, Ngn2, Nts, and NeuroD1 (Vias et al 2008).…”