![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Department of Biology and Center for Research on Biological Clocks, College Station, Texas (X.Q., V.M.C., D.J.E.); Department of Integrative Biosciences, College of Veterinary Medicine, Texas A&M University, College Station, Texas (R.P.M., W.W.P.); and Department of Neurosciences and Experimental Therapeutics, Texas A&M University Health Science Center, College of Medicine, College Station, Texas (D.J.E.)
Received June 27, 2007; accepted August 22, 2007
 |
Abstract |
|---|
 Top Abstract Materials and MethodsResultsDiscussionReferences |
|---|
). The PAS domain is a multifunctional protein motif governing ligand and DNA binding as well as interactions between PAS and non-PAS proteins. Most PAS proteins function as heterodimers consisting of a sensor protein associated with a general binding partner. For example, the aryl hydrocarbon receptor (AhR) partners with the AhR nuclear translocator (Arnt) to mediate the transcriptional activation of xenobiotic-metabolizing enzymes, whereas circadian locomotor output cycles kaput (Clock) associates with brain, muscle ARNT-like protein 1 (Bmal1) to form core elements of the circadian clock mechanism in mammals. Not surprisingly, PAS protein-regulated pathways are interconnected through a variety of mechanisms, including competition for binding partners (Woods and Whitelaw, 2002), functional interference (Moffett et al., 1997), direct interaction (Hogenesch et al., 1998), and transcriptional regulation (Chilov et al., 2001). The importance of the PAS genes AhR and Arnt responding to environmental toxins such as polycyclic aromatic hydrocarbons (PAHs) is well documented. After entry into the cell, PAHs bind the AhR, which is complexed with 90-kDa heat shock proteins and the aryl hydrocarbon receptor-interacting protein. Upon ligand binding, this complex dissociates, and PAH-bound AhR translocates to the nucleus and partners with ARNT. AhR-ARNT heterodimers bind to xenobiotic response elements in target gene promoters affecting their expression. Principal targets of AhR signaling are cytochrome P450 enzymes of the A and B subfamily, including Cyp1A1, Cyp1A2, and Cyp1B1. Cytochromes P450 catalyze oxidation of PAHs to reactive metabolites suitable for conjugation by phase II detoxifying enzymes, including glutathione transferases and UDP-glucuronosyltransferases. The resulting conjugates are generally less reactive, more hydrophilic molecules that are easier to excrete. If not rendered less reactive or excreted, oxidative PAH metabolites can form DNA adducts, leading to mutations and increased cancer risk.
The PAS genes Clock, Bmal1, Period 1 (Per1), and Per2 are important components of the circadian clock mechanism in mammals. These PAS genes form interacting positive- and negative-feedback loops in which the transcription of core components is rhythmically regulated by their protein products. PER1 and PER2 form heterodimeric complexes with the protein products of the cryptochrome (Cry) genes, and after a delay, these complexes are translocated to the nucleus (Kume et al., 1999; Yagita et al., 2000). CRY proteins then inhibit the transcription of Clock and Bmal1 (Griffin et al., 1999). In turn, CLOCK and BMAL1 close the feedback loop by forming heterodimers that positively regulate the rhythmic transcription of the Per and Cry genes via the activation of E-box elements (Gekakis et al., 1998; Hogenesch et al., 1998; Jin et al., 1999). CLOCK:BMAL1 complexes also mediate the activation of clock-controlled genes that serve as outputs from the clock and function to regulate downstream rhythmic processes throughout the body.
Recent evidence suggests that molecular components of the circadian clock serve important functions in other PAS gene-regulated processes, including development, tumorigenesis, and drug metabolism. For example, Per1 and Per2 have been implicated in mammary gland development and differentiation based on changes in their expression during different stages of development and of the cell cycle. Per1 and Per2 involvement in the regulation of neoplastic growth is supported by the observations that Per2-deficient mice are more susceptible to the development of spontaneous and 
-radiation-induced tumors (Fu et al., 2002) and that PER1 and PER2 expression is down-regulated in human breast tumors relative to normal surrounding tissue (Chen et al., 2005).
Because PAHs are potent carcinogens, and PAS proteins can interact with one another, we examined whether core elements of the clock mechanism also play some role in PAH responses mediated by the PAS gene AhR. Previous studies indicate that Drosophila melanogaster PER forms dimers with AhR and ARNT via the PAS domain, and this process interferes with the DNA binding activity of AhR/ARNT heterodimers (Lindebro et al., 1995). Clock gene function in AhR signaling is also suggested by studies demonstrating that BMAL1 interacts with AhR (Hogenesch et al., 1997). Consequently, experiments were conducted to determine whether targeted disruption of the clock genes, Per1 and/or Per2, affects the activation of cytochromes P450 and other components of the AhR signaling pathway in the mammary gland by the protypical AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Our results demonstrate that disruption of the circadian clock produces hyperinduction of host responsiveness to environmental toxicants.
|
Materials and Methods |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
). Animals were maintained in the vivarium at Texas A&M University System Health Science Center (College Station, TX) under a standard 12-h light:dark cycle (lights-on at 6:00 AM) with access to food and water ad libitum. Procedures used in this study were approved by the University Laboratory Animal Care Committee at Texas A&M University.
Experiment 1: Effects of Targeted Disruption of Per1, Per2, and Per1/Per2 on TCDD-Induced Responses of the AhR Signaling Pathway in the Mouse Mammary Gland in Vivo
Responses of the AhR signaling pathway were examined in 8-week-old female mice treated with TCDD (provided by Dr. Stephen Safe, School of Veterinary Medicine, Texas A&M University) at a dose of 10 µg/kg body weight. Previous studies showed a single dose of 5 µg/kg TCDD or higher for 24 h significantly induces hepatic Cyp1A1 expression in mice (Narasimhan et al., 1994). In the current study, animals received an intraperitoneal injection of vehicle (corn oil) or TCDD approximately 6 h after lights-on in the 12-h light/dark cycles (12:00 PM; zeitgeber time [ZT] 6). Twenty-four hours after treatment, animals were sacrificed by cervical dislocation at ZT 6), and mammary gland tissues were collected in RNA Stabilization Reagent (RNAlater; QIAGEN, Valencia, CA) for later extraction of total RNA. For each tissue sample, approximately 30 mg of mammary tissue was homogenized and processed for extraction of total cellular RNA using the RNeasy Lipid Tissue Mini kit (QIAGEN). The final RNA pellet was subjected to on-column DNase digestion (QIAGEN), suspended in 100 µl of RNase-free water, and then it was stored at –80°C.
Experiment 2: Effects of Targeted Disruption of Per1, Per2, and Per1/Per2 on TCDD-Induced Responses of the AhR Signaling Pathway in Primary Cultures of the Mouse Mammary Gland
Mammary gland cells were collected from 12-to 14-week-old female mice, and primary cultures of these cells were established using methods similar to those described previously (Pullan and Streuli, 1996; Seagroves et al., 1998). For each experiment, mammary gland cultures were obtained from WT mice and compared with those from the mutant mice (Per1ldc, Per2ldc, or Per1ldc/Per2ldc) at the same age (each n = 3). In brief, cells were extracted from mouse mammary glands and cultured on serum/fetuin-coated six-well plates in Dulbecco's modified Eagle's medium/Ham's F-12 medium (Invitrogen, Carlsbad, CA) containing 5 µg/ml insulin (Sigma-Aldrich, St. Louis, MO), 1 µg/ml hydrocortisone (Sigma-Aldrich), 5 ng/ml epithelial growth factor (QED/Advanced Research Technologies, San Diego, CA), 50 µg/ml gentamicin (Invitrogen), 100 U/ml penicillin/streptomycin (Invitrogen), and 5% fetal bovine serum at 37°C in a humidified incubator with 5% CO2. Confluent cultures were treated with vehicle [n = 3; dimethyl sulfoxide (DMSO); Sigma-Aldrich] or 20 nM TCDD (n = 3) for 24 h. After treatment, cultures were collected by trypsinization, and total RNA was extracted using RNeasy Mini kit (QIAGEN). The dose and duration of TCDD treatment in these experiments were based on previous observations indicating that robust increases in Cyp1A1 and Cyp1B1 mRNA and protein levels occur within human mammary epithelial cells in vitro after exposure to TCDD for 24 h (Chen et al., 2004).
Experiment 3: Time-Dependent Effects of TCDD Treatment on the AhR Signaling Pathway in the Mouse Mammary Gland in Vivo
To determine whether TCDD-induced effects on the AhR signaling pathway in vivo vary as a function of treatment time, WT mice were injected intraperitoneally with vehicle or 10 µg of TCDD/kg of b.wt. at the midpoint of either the light phase (12:00 PM; ZT 6; n = 22) or dark phase [12:00 AM (midnight); ZT 18; n = 12], and mammary gland tissues were collected 24 h after treatment as described in experiment 1.
Quantitative Reverse Transcription-Polymerase Chain Reaction Analysis. Quantification of relative mRNA abundance was performed using SYBR Green real-time PCR technology (Applied Biosystems, Foster City, CA) as described previously (Metz et al., 2006). Total RNA (1 µg) was reverse transcribed using Superscript II (Invitrogen) and random hexamers. For each sample, the cDNA equivalent to 1.25 ng of total RNA per 12.5-µl reaction was amplified in an ABI 7500 Fast Real-Time PCR system using 9600 emulation modes. To control for differences in sample RNA content, cyclophilin A (CypA), or 
-actin was amplified from the same samples. Primer sequences for PCR amplification of target and control genes are listed in Table 1.
|
The comparative CT method was used to calculate the relative mRNA abundance for a given target gene. Using this method, the amount of target gene mRNA in each sample was normalized first to corresponding CypA or -actin mRNA levels, and then relative to a calibrator consisting of pooled cDNA from multiple samples that was analyzed on each reaction plate.
Statistical Analysis
In experiments 1 and 2, statistical analyses were first performed on the raw data using two-way analyses of variance (ANOVAs) with treatment (vehicle versus TCDD) and genotype (WT, Per1ldc, Per2ldc, and Per1ldc/Per2ldc) as two independent variables. If significant main effects of treatment were identified, planned comparisons using independent t tests were applied to compare gene expression between control and TCDD groups of the same genotype. The -fold differences in gene expression between these treatment groups were then analyzed using one-way ANOVA, and, if required, Fisher's least significant difference post hoc analyses to determine whether genotype had a significant effect on TCCD-induced changes in mRNA levels for a given gene. In experiment 3, the raw data were first analyzed using two-way ANOVAs, with treatment (vehicle versus TCDD) and time (ZT 6 versus ZT 18) as two independent variables. If significant main effects were identified, planned comparisons using independent t tests were applied to compare gene expression between control and TCDD groups at the same treatment time. For the P450 genes, the -fold differences in TCDD-induced gene expression were also analyzed using independent t tests to determine the significance of treatment time. The 
value was set at 0.05 for all statistical analyses.
|
Results |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
). Consistent with previous findings (Narasimhan et al., 1994), basal levels of Cyp1A1 mRNA expression were observed in the mammary glands of all vehicle-treated WT and mutant mice (Fig. 1A). Relative to vehicle controls, TCDD had a robust effect in inducing Cyp1A1 expression within the mammary gland. In both WT and mutant mice, mammary gland levels of Cyp1A1 mRNA were significantly greater (p < 0.05) in TCDD-treated animals than in vehicle controls. Genotype-related differences were evident in the absolute values of TCDD-induced Cyp1A1 expression in the mammary gland (Fig. 1A). In the mammary glands of Per1ldc and Per1ldc/Per2ldc mutant mice, the TCDD-induced Cyp1A1 expression was significantly (p < 0.05) and approximately 3 times higher than that found in WT animals. Analysis of the -fold difference in gene expression between the TCDD- and vehicle-treated groups for each genotype revealed further distinctions in the activation of the AhR signaling pathway among mutant mice with targeted disruptions of the Per1 and Per2 genes (Fig. 1B). The -fold differences in the TCDD-induced Cyp1A1 expression within the mammary gland were significantly greater in Per1ldc (p < 0.05) and Per1ldc/Per2ldc (p < 0.05) mutant mice than in WT animals. In fact, the inductive effects of TCDD on Cyp1A1 expression within the mammary glands of Per1ldc and Per1ldc/Per2ldc mutant mice were increased by 17.9- and 5.9-fold, respectively, relative to that found in WT mice.
|
Two major regulators of TCDD-induced responses, AhR and Arnt were also analyzed in our study. Similar levels of AhR expression were observed in mammary glands of all vehicle-treated WT and mutant mice (Fig. 2). No significant differences in mammary gland levels of AhR mRNA were evident among vehicle control and TCCD-treated mice, regardless of their genotype. Similar to AhR, Arnt mRNA expression in the mammary gland was comparable in all mice, with no major treatment-or genotype-based differences (Fig. 2).
|
-estradiol in vivo (Gorski et al., 1988; Christou et al., 1995; Prough et al., 1996) and because serum levels and the rhythmic regulation of steroid hormones are altered in Per1-deficient mice (Dallmann et al., 2006), parallel in vitro analysis was conducted to indirectly address the role of Per-mediated hormonal changes in the potentiation of TCDD-induced AhR signaling in mutant mice. Primary cultures of the mouse mammary gland were used to determine whether the observed amplification of TCDD-induced P450 expression in Per mutant mice persists in vitro in the absence of hormonal influences. Basal levels of Cyp1A1 expression were observed among all vehicle-treated mammary gland cultures derived from WT and mutant animals (Fig. 3A). Relative to vehicle controls, treatment with 20 nM TCDD for 24 h induced significant increases (p < 0.05) in Cyp1A1 expression in all mammary gland cultures. Genotype-based distinctions were evident in the -fold differences in Cyp1A1 expression between TCDD- and vehicle-treated cultures. Consistent with the results of our in vivo study, the -fold differences in the TCDD-induced Cyp1A1 expression were significantly greater in mammary gland cultures derived from Per1ldc and Per1ldc/Per2ldc (p < 0.05) mutant mice than in those from WT animals (Fig. 3B). The TCDD-mediated induction of Cyp1A1 mRNA levels was 5.7- and 4.2-fold higher in Per1ldc and Per1ldc /Per2ldc mammary cells than in WT cultures. In mammary gland cultures from Per2ldc mice, the -fold differences in the induction of Cyp1A1 expression by TCDD were reduced relative to WT cells.
|
Similar to Cyp1A1, Cyp1B1 expression was consistently low in vehicle-treated mammary cells (Fig. 3A). TCDD had a significant effect in inducing Cyp1B1 expression in all WT and mutant cultures (p < 0.05). Interactions between treatment and genotype were comparable with those observed in vivo. TCDD treatment produced increases in Cyp1B1 expression in Per1ldc and Per1ldc/Per2ldc mammary cells that were significantly greater (p < 0.05) than those found in WT cultures (Fig. 3A). Further analysis revealed that the -fold differences in TCDD-induced Cyp1B1 expression were significantly greater (p < 0.05) in Per1ldc and Per1ldc/Per2ldc mammary gland cultures than in WT cells (Fig. 3B). The -fold differences in TCDD-mediated Cyp1B1 induction in Per1ldc and Per1ldc/Per2ldc cells were 2.3 and 3.9 times higher, respectively, than that in WT cultures.
The central regulators of TCDD-induced signaling, AhR and Arnt, were differentially expressed and affected by this toxin in primary cultures of the mouse mammary gland. Among vehicle-treated mammary cells, it is interesting that AhR mRNA expression in all mutant cultures were significantly greater (p < 0.05) than WT levels. The highest levels of AhR expression in vehicle-treated cells were observed in cultures derived from Per1ldc mice. TCDD had a significant effect in reducing AhR mRNA levels in both WT and mutant mammary cells (p < 0.05) (Fig. 4). In response to TCDD exposure, AhR expression was reduced to comparable levels among WT and mutant cells, with exception of cultures derived from Per1ldc mice. After treatment, AhR mRNA levels in Per1ldc mammary gland cultures were significantly (approximately 2 times) higher (p < 0.05) than those found in WT cells exposed to TCDD. In contrast to AhR, there was no significant effect of either treatment or genotype on Arnt expression in mammary gland cultures (Fig. 4). Similar levels of Arnt mRNA were expressed by both WT and mutant cells after treatment with vehicle or TCDD.
|
). In oil-injected WT mice, Cyp1A1 mRNA levels in the mammary gland were low irrespective of treatment time (Fig. 5A). TCDD administered during the day and at night both triggered significant increases in mammary gland levels of Cyp1A1 mRNA (p < 0.05). It is noteworthy that treatment time had a significant effect (p < 0.05) on the -fold differences in the TCDD-mediated Cyp1A1 induction in the mammary gland such that the increase in the expression of this P450 gene triggered by toxin injection at ZT 18 was 8.6-fold higher than that after treatment at ZT 6 (Fig. 5B). Unlike the pattern for Cyp1A1, Cyp1B1 expression in the mammary glands of vehicle-treated animals was marked by significant variation over time (p < 0.05) with mRNA levels at ZT 6 that were substantially greater than those at ZT 18. Consequently, TCDD had no significant effects on mammary gland levels of Cyp1B1 mRNA when treatment was administered at ZT 6, but it induced significant increases (p < 0.05) in expression of this P450 gene after exposure at ZT 18 (Fig. 5A). Moreover, the -fold differences of TCDD-induced Cyp1B1 expression within the mammary gland at ZT 18 were significantly (p < 0.05) and approximately 2 times higher than those observed at ZT 6 (Fig. 5B).
|
|
|
Discussion |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
; Reppert and Weaver, 2002) in conjunction with a myriad of other physiological or behavioral disturbances, including decreased body weight, shortened life span, increased tendon calcification (McDearmon et al., 2006), premature aging, tissue hyperplasia (Fu et al., 2002; Lee, 2006), increased alcohol consumption (Spanagel et al., 2005), and altered responses to other drugs of abuse (Kondratov et al., 2007). Consistent with these observations, the present study revealed that targeted disruption of the Per genes modifies mammary gland responses to the environmental toxin TCDD. It is interesting that the inductive effects of TCDD on expression of the cytochrome P450 genes Cyp1A1 and Cyp1B1 were potentiated in mammary glands and in primary cultures of mammary cells from Per1ldc and Per1ldc/Per2ldc, but not Per2ldc, mice. Similar to primary analyses of these mutant mice indicating that the Per1 and Per2 genes influence different molecular processes but are indispensable for normal clock function (Shearman et al., 2000; Bae et al., 2001; Zheng et al., 2001), our findings suggest that Per1 plays a distinct role in modulating TCDD activation of the AhR signaling pathway.
The mechanism by which the Per genes interact with components of the AhR signaling pathway and influence its activation by TCDD is currently unknown. However, a possible explanation is that the potentiation of TCDD-induced Cyp1A1 and Cyp1B1 expression in the mammary gland is associated with the altered function of the circadian clockworks in Per1ldc and Per1ldc/Per2ldc mice. Similar to the findings of Bae et al. (2001), these mutant mice exhibited arrhythmic patterns of wheel-running activity after 1 to 2 weeks of exposure to constant darkness (data not shown). Because up to 10% of the transcriptome is clock-controlled in peripheral tissues (Duffield, 2003) and some of these genes with oscillatory profiles are essential elements of critical biochemical processes mediating drug metabolism and responses to xenobiotic agents (Gachon et al., 2006; Menger et al., 2007), the disruptive effects of the Per1 mutation on circadian clock function may extend to the rhythmic regulation of the AhR signaling pathway in Per1ldc and Per1ldc/ Per2ldc mice. This hypothesis is indirectly supported by the present observations that AhR expression and TCDD-mediated induction of P450 genes in the mammary gland are marked by diurnal variation. In the mammary glands of WT mice, AhR mRNA levels are lower and TCDD-induced Cyp1A1 and Cyp1B1 expression is greater during the night than during the day. Because the diurnal variation in the TCDD-mediated P450 induction in the mammary gland is inversely related to the temporal pattern of Per1 gene expression, in which tissue mRNA levels peak during the day and remain low throughout the night (Metz et al., 2006), the disruption of Per1 expression and rhythmicity in Per1ldc and Per1ldc/Per2ldc mice may be responsible for the potentiated activity of the AhR signaling pathway in response to this toxin. To further explore this possibility, it will be necessary to determine whether the rhythmic variation in TCDD-induced P450 gene expression in the mammary gland is also abolished in Per1ldc and Per1ldc/Per2ldc mice.
A related explanation for the present findings is that the disruption of Per1 gene expression or clock function in Per1ldc and Per1ldc/Per2ldc mice may indirectly mediate the potentiation of TCDD-induced P450 expression in the mammary gland, perhaps by altering the levels and/or circadian cycles of hormones that influence the AhR signaling pathway. The potential involvement of Per-mediated hormonal changes in the altered TCDD responses in Per1ldc and Per1ldc/Per2ldc mice is compatible with the observations that steroid hormones modulate AhR signaling in vivo (Gorski et al., 1988; Christou et al., 1995; Prough et al., 1996) and that steroid hormone levels and cycles are altered in Per1-deficient mice (Dallmann et al., 2006). However, the results of our in vitro study do not seem to support this possibility, because the potentiation of TCDD-induced Cyp1A1 and Cyp1B1 expression persists in mammary cultures from these mutant mice despite the absence of hormonal signals that occur in vivo.
On the other hand, the potentiation of TCDD-induced P450 gene expression in Per1ldc and Per1ldc/Per2ldc mice may not be associated with the disruption of the circadian clockworks but instead be related to changes in Per gene interactions with specific components of the AhR signaling pathway. Our findings raise the possibility that Per1 may directly inhibit TCDD activation of the AhR signaling pathway. This inhibition could occur via interactions between Per1 and PAS gene components of the AhR signaling pathway at several different levels. Because the function of PER1 in regulating circadian rhythmicity is distinctly mediated through its interactions with other PAS proteins in the feedback loop (Bae et al., 2001), PER1 may similarly interact with the PAS proteins AhR and ARNT and perhaps inhibit their dimerization. Per1 may also directly influence the AhR signaling pathway by inhibiting the binding of AhR:ARNT complexes to the dioxin response elements of target genes. This hypothesis is corroborated by the observation that D. melanogaster PER impedes the formation and DNA binding activity of AhR:ARNT complexes by dimerizing with AhR and ARNT via the PAS domain (Lindebro et al., 1995). Our in vitro results suggest that AhR expression is another prospective target for Per1 in down-regulating TCCD-mediated activation of the AhR signaling pathway, because AhR mRNA expression in mammary gland cells derived from Per1ldc, Per2ldc and Per1ldc/Per2ldc mutant mice was substantially higher than that found in WT cultures. Further analysis will be necessary to specifically determine whether the Per genes modulate TCDD-mediated induction of P450 gene expression by inhibiting AhR expression, the formation of AhR:ARNT heterodimers, or the binding of these complexes with DREs.
In summary, our data indicate that the targeted disruption of Per1 potentiates the inductive effects of TCDD on P450 gene expression in the mammary gland in vivo and in vitro. Because the induced expression of the P450 genes Cyp1A1 and Cyp1B1 has been associated with increased cancer risk (Schrenk, 1998), this finding may have further implications for the involvement of the Per genes in carcinogenesis. Previous studies have shown that Per2 suppresses tumor development by regulating responses to DNA damage (Fu et al., 2002). Moreover, human breast cancer tissue is distinguished by Per1 promoter methylation and associated alterations in PER1 protein levels relative to that found in adjacent normal cells (Chen et al., 2005). Together with the present evidence for diurnal fluctuations in AhR expression and TCDD-induced Cyp1A1 and Cyp1B1 expression within the mammary gland, these observations suggest that the Per genes, perhaps via their function in the circadian clockworks, may play an important role in regulating responses to environmental toxins and in modulating their carcinogenic effects.
|
Acknowledgements |
|---|
|
Footnotes |
|---|
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS: PAS, Per-Arnt-Sim (periodicity/aryl hydrocarbon receptor nuclear translocator/simple-minded); AhR, aryl hydrocarbon receptor; ARNT, aryl hydrocarbon receptor nuclear translocator; Clock, circadian locomotor output cycles kaput; Bmal1, brain, muscle ARNT-like protein 1; PAH, polycyclic aromatic hydrocarbon; Per, Period; Cry, cryptochrome; TCDD, 2,3,7,8-tetrachlorodibenzo-p-dioxin; WT, wild type; ZT, zeitgeber time; DMSO, dimethyl sulfoxide; PCR, polymerase chain reaction; ANOVA, analysis of variance.
Address correspondence to: Dr. David J. Earnest, Department of Neuroscience and Experimental Therapeutics, 238 Reynolds Medical Bldg., Texas A&M University Health Science Center, College Station, TX 77843-1114. E-mail: dearnest{at}tamu.edu
|
References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Chen ST, Choo KB, Hou MF, Yeh KT, Kuo SJ, and Chang JG (2005) Deregulated expression of the PER1, PER2 and PER3 genes in breast cancers. Carcinogenesis 26: 1241–1246.
Chen ZH, Hurh YJ, Na HK, Kim JH, Chun YJ, Kim DH, Kang KS, Cho MH, and Surh YJ (2004) Resveratrol inhibits TCDD-induced expression of CYP1A1 and CYP1B1 and catechol estrogen-mediated oxidative DNA damage in cultured human mammary epithelial cells. Carcinogenesis 25: 2005–2013.
Chilov D, Hofer T, Bauer C, Wenger RH, and Gassmann M (2001) Hypoxia affects expression of circadian genes PER1 and CLOCK in mouse brain. FASEB J 15: 2613–2622.
Christou M, Savas U, Schroeder S, Shen X, Thompson T, Gould MN, and Jefcoate CR (1995) Cytochromes CYP1A1 and CYP1B1 in the rat mammary gland: cell-specific expression and regulation by polycyclic aromatic hydrocarbons and hormones. Mol Cell Endocrinol 115: 41–50.[CrossRef][Medline]
Crews ST, Fan CM (1999) Remembrance of things PAS: regulation of development by bHLH-PAS proteins. Curr Opin Genet Dev 9: 580–587.[CrossRef][Medline]
Dallmann R, Touma C, Palme R, Albrecht U, and Steinlechner S (2006) Impaired daily glucocorticoid rhythm in Per1Brd mice. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 192: 769–775.[CrossRef][Medline]
Duffield GE (2003) DNA microarray analyses of circadian timing: the genomic basis of biological time. J Neuroendocrinol 15: 991–1002.[CrossRef][Medline]
Fu L, Pelicano H, Liu J, Huang P, and Lee C (2002) The circadian gene Period 2 plays an important role in tumor suppression and DNA damage response in vivo. Cell 111: 41–50.[CrossRef][Medline]
Gachon F, Olela FF, Schaad O, Descombes P, and Schibler U (2006) The circadian PAR-domain basic leucine zipper transcription factors DBP, TEF, and HLF modulate basal and inducible xenobiotic detoxification. Cell Metab 4: 25–36.[CrossRef][Medline]
Gekakis N, Staknis D, Nguyen HB, Davis FC, Wilsbacher LD, King DP, Takahashi JS, and Weitz CJ (1998) Role of the CLOCK protein in the mammalian circadian mechanism. Science 280: 1564–1569.
Gorski JR, Lebofsky M, and Rozman K (1988) Corticosterone decreases toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in hypophysectomized rats. J Toxicol Environ Health 25: 349–360.[Medline]
Griffin EA, Staknis D, and Weitz CJ (1999) Light-independent role of CRY1 and CRY2 in the mammalian circadian clock. Science 286: 768–771.
Hogenesch JB, Chan WK, Jackiw VH, Brown RC, Gu YZ, Pray-Grant M, Perdew GH, and Bradfield CA (1997) Characterization of a subset of the basic-helix-loop-helix-PAS superfamily that interacts with components of the dioxin signaling pathway. J Biol Chem 272: 8581–8593.
Hogenesch JB, Gu YZ, Jain S, and Bradfield CA (1998) The basic-helix-loop-helix-PAS orphan MOP3 forms transcriptionally active complexes with circadian and hypoxia factors. Proc Natl Acad SciUSA 95: 5474–5479.
Jin X, Shearman LP, Weaver DR, Zylka MJ, de Vries GJ, and Reppert SM (1999) A molecular mechanism regulating rhythmic output from the suprachiasmatic circadian clock. Cell 96: 57–68.[CrossRef][Medline]
Kondratov RV, Gorbacheva VY, and Antoch MP (2007) The role of mammalian circadian proteins in normal physiology and genotoxic stress responses. Curr Top Dev Biol 78: 173–216.[Medline]
Kume K, Zylka MJ, Sriram S, Shearman LP, Weaver DR, Jin X, Maywood ES, Hastings MH, and Reppert SM (1999) mCRY1 and mCRY2 are essential components of the negative limb of the circadian clock feedback loop. Cell 98: 193–205.[CrossRef][Medline]
Lee CC (2006) Tumor suppression by the mammalian Period genes. Cancer Causes Control 17: 525–530.[CrossRef][Medline]
Lindebro MC, Poellinger L, and Whitelaw ML (1995) Protein-protein interaction via PAS domains: role of the PAS domain in positive and negative regulation of the bHLH/PAS dioxin receptor-Arnt transcription factor complex. EMBO J 14: 3528–3539.[Medline]
McDearmon EL, Patel KN, Ko CH, Walisser JA, Schook AC, Chong JL, Wilsbacher LD, Song EJ, Hong HK, Bradfield CA, et al. (2006) Dissecting the functions of the mammalian clock protein BMAL1 by tissue-specific rescue in mice. Science 314: 1304–1308.
Menger GJ, Allen GC, Neuendorff N, Nahm SS, Thomas TL, Cassone VM, and Earnest DJ (2007) Circadian profiling of the transcriptome in NIH/3T3 fibroblasts: comparison with rhythmic gene expression in SCN2.2 cells and the rat SCN. Physiol Genomics 29: 280–289.
Metz RP, Qu X, Laffin B, Earnest D, and Porter WW (2006) Circadian clock and cell cycle gene expression in mouse mammary epithelial cells and in the developing mouse mammary gland. Dev Dyn 235: 263–271.[CrossRef][Medline]
Moffett P, Reece M, and Pelletier J (1997) The murine Sim-2 gene product inhibits transcription by active repression and functional interference. Mol Cell Biol 17: 4933–4947.[Abstract]
Narasimhan TR, Craig A, Arellano L, Harper N, Howie L, Menache M, Birnbaum L, and Safe S (1994) Relative sensitivities of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced Cyp1a-1 and Cyp1a-2 gene expression and immunotoxicity in female B6C3F1 mice. Fundam Appl Toxicol 23: 598–607.[CrossRef][Medline]
Prough RA, Linder MW, Pinaire JA, Xiao GH, and Falkner KC (1996) Hormonal regulation of hepatic enzymes involved in foreign compound metabolism. FASEB J 10: 1369–1377.[Abstract]
Pullan SE and Streuli CH (1996) The mammary gland epithelial cell, in Epithelial Cell Culture (Harris A ed) pp 97–121, Cambridge University Press, Cambridge, UK.
Reppert SM and Weaver DR (2002) Coordination of circadian timing in mammals. Nature 418: 935–941.[CrossRef][Medline]
Schrenk D (1998) Impact of dioxin-type induction of drug-metabolizing enzymes on the metabolism of endo- and xenobiotics. Biochem Pharmacol 55: 1155–1162.[CrossRef][Medline]
Seagroves TN, Krnacik S, Raught B, Gay J, Burgess-Beusse B, Darlington GJ, and Rosen JM (1998) C/EBPbeta, but not C/EBPalpha, is essential for ductal morphogenesis, lobuloalveolar proliferation, and functional differentiation in the mouse mammary gland. Genes Dev 12: 1917–1928.
Shearman LP, Sriram S, Weaver DR, Maywood ES, Chaves I, Zheng B, Kume K, Lee CC, van der Horst GT, Hastings MH, et al. (2000) Interacting molecular loops in the mammalian circadian clock. Science 288: 1013–1019.
Spanagel R, Pendyala G, Abarca C, Zghoul T, Sanchis-Segura C, Magnone MC, Lascorz J, Depner M, Holzberg D, Soyka M, et al. (2005) The clock gene Per2 influences the glutamatergic system and modulates alcohol consumption. Nat Med 11: 35–42.[CrossRef][Medline]
Woods SL and Whitelaw ML (2002) Differential activities of murine single minded 1 (SIM1) and SIM2 on a hypoxic response element. Cross-talk between basic helix-loop-helix/per-Arnt-Sim homology transcription factors. J Biol Chem 277: 10236–10243.
Yagita K, Yamaguchi S, Tamanini F, van Der Horst GT, Hoeijmakers JH, Yasui A, Loros JJ, Dunlap JC, and Okamura H (2000) Dimerization and nuclear entry of mPER proteins in mammalian cells. Genes Dev 14: 1353–1363.
Zheng B, Albrecht U, Kaasik K, Sage M, Lu W, Vaishnav S, Li Q, Sun ZS, Eichele G, Bradley A, et al. (2001) Nonredundant roles of the mPer1 and mPer2 genes in the mammalian circadian clock. Cell 105: 683–694.[CrossRef][Medline]
This article has been cited by other articles:
|
|
 |
|
  M. Mukai, T.-M. Lin, R. E. Peterson, P. S. Cooke, and S. A. Tischkau Behavioral Rhythmicity of Mice Lacking AhR and Attenuation of Light-Induced Phase Shift by 2,3,7,8-Tetrachlorodibenzo-p-Dioxin J Biol Rhythms, June 1, 2008; 23(3): 200 - 210. [Abstract] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
 |
 |
|
 |
 |
 |
, p < 0.05) mutant mice than in WT animals.
