Circadian transcription of the cholesterol 7 alpha hydroxylase gene may involve the liver-enriched bZIP protein DBP.

Abstract

The liver-enriched transcription factor DBP is expressed with a stringent circadian rhythm. We present evidence that DBP is a regulator of the circadian expression of the rat gene encoding cholesterol 7a hydroxylase (C7aH), the rate-limiting enzyme in the conversion of cholesterol to bile acids. As with DBP, C7aH mRNA reaches peak levels in the evening, and its cycling is independent of daily food and light cues. As predicted for a DBP target gene, the primary level of C7otH circadian expression is at the transcriptional level. DBP can activate the C7aH promoter in cotransfection assays through a cognate DNA site centered around -225. In nuclear extracts prepared by a novel method that, in contrast to conventional techniques, yields near-quantitative recovery of DBP and other non-histone proteins, the DNA site required for DBP activation is the predominant site of occupancy by nuclear factors on the C7otH promoter. At this site, the predominant binding activity is an evening-specific complex of which DBP is a component. These data suggest that DBP may play an important role in cholesterol homeostasis through circadian transcriptional regulation of cholesterol 7a hydroxylase.

Cholesterol 7?-hydroxylase (CYP7A): Patterns of messenger RNA expression during rat liver development

“…DBP has been proposed to be a regulator of the circadian expression of C7␣H. 15,35 It is induced 3 to 4 weeks after birth, 35 thus, it is unlikely to play a role in C7␣H regulation before that time. Other possible transcription factors that may be involved include LXR␣, which has been proposed to modulate oxysterol-mediated C7␣H transcription.…”

“…11-13 It exhibits a diurnal rhythm, with maximum activity in the dark phase and minimum during the light phase in rats. [13][14][15] The expression of C7␣H in adult rats is tightly regulated spatially along the liver cell plate; the enzymatic activity 16 and mRNA level 17,18 are not distributed uniformly among parenchymal cells; rather, C7␣H is predominantly found in a subgroup of hepatocytes localized around the central vein.Liver cell heterogeneity is considered to be a major determinant for proper execution and regulation of most liver functions. 19,20 It reflects differentiation of hepatocytes within the liver plate, which is established during development.…”

“…[11][12][13] It exhibits a diurnal rhythm, with maximum activity in the dark phase and minimum during the light phase in rats. [13][14][15] The expression of C7␣H in adult rats is tightly regulated spatially along the liver cell plate; the enzymatic activity 16 and mRNA level 17,18 are not distributed uniformly among parenchymal cells; rather, C7␣H is predominantly found in a subgroup of hepatocytes localized around the central vein.…”

The Activity of the Highly Inducible Mouse Phenylalanine Hydroxylase Gene Promoter Is Dependent upon a Tissue-Specific, Hormone-Inducible Enhancer

“…Nuclei of cultured cells were prepared as described elsewhere (9). Nuclear extracts used for in vitro footprinting assays were obtained as described previously (31), and extracts used in gel mobility shift experiments were prepared essentially as indicated in reference 9, except that (NH 4 ) 2 SO 4 precipitation and dialysis were omitted. The protein concentrations were determined by the method of Bradford (6).…”

The avian transcription factor c-Rel is induced and translocates into the nucleus of thymocytes undergoing apoptosis

“…The supernatants containing cytoplasmic proteins were stored in aliquots at 7808C. The pellets of nuclei were resuspended in nine volumes of NUN 1.16 buffer (1.1 M Urea, 0.33 M NaCl, 1.1% Nonidet P40, 0.27 M Hepes pH 7.6), incubated for 15 min on ice, and centrifuged 15 min at 10,000 g at 48C (Schibler et al, 1993;Lavery and Schibler, 1993). The supernatants containing nuclear proteins were stored in aliquots at 7808C.…”