Brain and muscle Arnt-like protein-1 (BMAL1; also known as MOP3 or Arnt3) is a transcription factor known to regulate circadian rhythm. Here, we established its involvement in the control of adipogenesis and lipid metabolism activity in mature adipocytes. During adipose differentiation in 3T3-L1 cells, the level of BMAL1 mRNA began to increase 4 days after induction and was highly expressed in differentiated cells. In white adipose tissues isolated from C57BL͞6J mice, BMAL1 was predominantly expressed in a fraction containing adipocytes, as compared with the stromalvascular fraction. BMAL1 knockout mice embryonic fibroblast cells failed to be differentiated into adipocytes. Importantly, adding BMAL1 back by adenovirus gene transfer restored the ability of BMAL1 knockout mice embryonic fibroblast cells to differentiate. Knock-down of BMAL1 expression in 3T3-L1 cells by an RNA interference technique allowed the cells to accumulate only minimum amounts of lipid droplets in the cells. Adenovirus-mediated expression of BMAL1 in 3T3-L1 adipocytes resulted in induction of several factors involved in lipogenesis. The promoter activity of these genes was stimulated in a BMAL1-dependent manner. Interestingly, expression of these factors showed clear circadian rhythm in mice adipose tissue. Furthermore, overexpression of BMAL1 in adipocytes increased lipid synthesis activity. These results indicate that BMAL1, a master regulator of circadian rhythm, also plays important roles in the regulation of adipose differentiation and lipogenesis in mature adipocytes.circadian rhythm A dipocytes play essential metabolic roles not only serving as massive energy reserves but also secreting hormones and cytokines that regulate metabolic activities (1, 2). The link between metabolic activity in adipocytes and circadian rhythm has long been studied; e.g., glucose and lipid homeostasis are well known to exhibit circadian variation (3-6). More recently, circadian expression of adiponectin receptors in adipocytes was reported (7). Therefore, molecular clock may play important roles in the regulation of metabolic activity in adipocytes. In a previous study, we reported that white adipose tissue contains functional molecular clock and that expression of several adipocytokines, including leptin, and plasminogen activator inhibitor-1 display circadian rhythm (8). The diurnal rhythm in the level of these molecules suggests that the molecular clock is at least partly associated with the onset of metabolic syndrome.The molecular clock is composed of transcriptional feedback loops in organisms ranging from cyanobacteria to humans. Brain and muscle Arnt-like protein-1 [BMAL1; also referred to as MOP3 (9) or Arnt3 (10)] is a transcription factor playing central roles in the regulation of circadian rhythms (11). BMAL1 forms heterodimers with another basic helix-loop-helix͞PAS protein, CLOCK, which drives transcription from E-box elements found in the promoter of circadian responsive genes, including period (Per)1 and cryptochrome (Cry). After translati...

No abstract

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that possesses a basic-helix-loop-helix (bHLH)/Per-Arnt-Sim (PAS) domain and mediates a spectrum of toxic and biological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. 1,2) Unliganded AhR exists in the cytoplasm in the form of a complex with 90 kDa heat-shock protein and immunophilinrelated protein. [3][4][5][6] Upon binding to the ligand, AhR translocates to the nucleus and forms heterodimer with another bHLH/PAS protein, Ah receptor nuclear translocator (Arnt). 7)This heterodimer drives transcription from the xenobiotic responsive element (XRE) found in the promoter of xenobiotic-metabolizing enzymes, including cytochrome P450 (CYP)1A1 and CYP1A2. [8][9][10] Recent studies have shown that AhR/Arnt modulates gene expression by not only direct control of transcription but also by crosstalk with endogenous signals critical to hormone responses, cell cycle, etc.11-25) AhR/Arnt physically interacts with several effectors involved in these pathways, resulting in super activation or inhibition of the signals. Among crosstalks between AhR and signal effectors, the interactions of AhR/Arnt with estrogen receptor (ER)-a and b have been well-characterized. [11][12][13][14][15][16] ERs associate with AhR/Arnt, followed by activation of target gene transcription and estrogenic effects in the absence of estrogen. The mechanisms involve the recruitment of histone acetyltransferase (HAT) complexes such as p300 to the ER target gene. Contrary to ligand-free ER, the function of liganded ER is attenuated by AhR/Arnt. 11) Consequently, AhR plays a role as a coactivator/suppressor of other transcription factors in addition to the representative roles as a transcription factor. These multiple roles of the AhR in the regulation of gene expression may generate diverse effects of the AhR ligands.Several reports have shown constitutive activation of the AhR in the absence of an exogenous ligand, suggesting that the AhR may play an important role not only in the regulation of xenobiotic metabolism but also in the maintenance of homeostatic functions. [26][27][28] One of the possible physiological roles of the AhR is regulation of cell growth. Stable transfection of AhR cDNA into AhR-defective mouse hepatoma cells has shown that the AhR control cell-cycle progression and differentiation, and that no exogenous ligands are required for this function.29) Studies using mouse embryonic fibroblast cells (MEF) have shown that AhRϪ/Ϫ MEF proliferates more slowly than AhRϩ/ϩ MEF, presumably due to the excess production of tumor growth factor (TGF)-b in AhR null cells. 30,31) We have previously shown that overexpression of AhR, as well as AhR ligand treatment, stimulates cell proliferation of human lung cancer A549 cells.32) Activated-AhR increases the expression of several DNA synthesis regulatory factors, thus shortening the cell cycle of the late M to S phases. 32) On the other hand, Kolluri et al. have shown that AhR activation with TCD...

Topical vitamin D3 has relatively recently been introduced for the treatment of psoriasis. Synthetic vitamin D3 analogues with a high potential for inducing differentiation of cells, but with a low hypercalcemic effect have recently been developed. One such synthetic analogue of 1,25-dihydroxyvitamin D3 (calcitriol), 22-oxacalcitriol (OCT), is a novel agent for the topical treatment of psoriasis. The activity of OCT in vitro was investigated and compared with that of a series of vitamin D3 analogues as to their ability to inhibit murine T lymphocyte proliferation stimulated by con-A, to suppress IL-6 and IL-8 production by keratinocytes stimulated with IL-1alpha and TNFalpha, and to inhibit AP-1- and NFkappaB-dependent reporter gene expression. OCT inhibited the proliferation of lymphocytes and suppressed IL-8 and IL-6 production by keratinocytes to the same extent as the other vitamin D3 analogues. It also inhibited AP-1- and NFkappaB-controlled luciferase activity to the same extent as the other vitamin D3 analogues, which demonstrates its mechanism of action in the suppression of inflammatory processes.

It is known that baldness caused by androgenetic alopecia is involved with androgen and the androgen receptor. Furthermore, it has been reported that testosterone secretion follows a circadian rhythm. Therefore, we hypothesized that a relationship exists between androgen-induced alopecia and biological rhythm. The mammalian circadian rhythm is controlled by several clock genes. Brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein-1 (BMAL1), one of the clock genes, is a transcription factor that plays central roles in the regulation of circadian rhythms. In this study, we investigated the influence of BMAL1 on hair follicle functions and hair growth. Mice deficient in BMAL1 expression exhibited a delay in hair regrowth after shaving. In hair follicles of mouse vibrissa, expression of Bmal1 and other clock genes was found to be rhythmic. Knockdown of BMAL1 in human follicle dermal papilla cells resulted in modulation of expression of several hair growth-related genes. Therefore, we concluded that expression of clock genes in hair follicles is linked to the circadian rhythm and that BMAL1 can regulate hair growth.