Liver cells contain constitutive DNase I-hypersensitive sites at the xenobiotic response elements 1 and 2 (XRE1 and -2) of the rat cytochrome P-450IA1 gene and a constitutive, nuclear XRE-binding factor that is distinct from the dioxin receptor.

Hapgood, Janet P.; Cuthill, Scott; Söderkvist, Peter; Wilhelmsson, Anna; Pongratz, Ingemar; Tukey, Robert H.; Johnson, Eric F.; Gustafsson, Jan‐Åke; Poellinger, Lorenz

doi:10.1128/mcb.11.9.4314

Cited by 26 publications

(11 citation statements)

References 49 publications

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“…At the cyplal promoter, TCDD induces (via the Ah receptor) a rapid and actinomycin D-insensitive change in chromatin structure and nucleosome positioning that is temporally associated with the onset of transcription. This change is consistent with the observation of an inducible DNase I-hypersensitive site at the cyplal transcriptional promoter in rat liver (24).…”

Section: Itors Of Transcriptional Initiation (19-21)supporting

confidence: 91%

Transcription-dependent and transcription-independent nucleosome disruption induced by dioxin.

Morgan

Whitlock

1992

Proc. Natl. Acad. Sci. U.S.A.

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In mouse hepatoma cells, both the regulatory and the transcribed regions of the cyplal gene assume a nuceosomal configuration when the gene is silent; two nucleosomes occupy specific sites at the transcriptional promoter. Activation of transcription by 2,3,7,8-tetrachlorodibenzo-pdioxin is accompanied by changes in chromatin sucture, which depend upon a functional aromatic hydrocarbon (Ah) receptor. In the transcribed region of the gene, nucleosome disruption occurs as a consequence of RNA elongation. In contrast, at the promoter, loss of positioned nucleosomes is independent of transcription and represents an event in the mechanism by which the liganded Ah receptor enhances transcriptional initiation.2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, dioxin) is the prototype for a class of halogenated aromatic hydrocarbons that are widespread environmental contaminants (1). TCDD elicits numerous toxic effects in animals, of which birth defects and neoplasia are ofparticular concern (2, 3). The risk that dioxin poses to human health is uncertain (4). TCDDresponsive cells contain an intracellular protein [the aromatic hydrocarbon (Ah) receptor], which binds dioxin saturably and with high affinity and which mediates its biological effects (2, 3, 5). The liganded receptor is thought to act by altering the expression of dioxin-responsive genes in tissuespecific fashion (6).We have studied the induction of cytochrome P4501A1 in mouse hepatoma cells as a model response for analyzing the mechanism of dioxin action. TCDD induces the P4501A1 enzyme by increasing the transcription of the corresponding cyplal gene. The response requires the Ah receptor because it does not occur in receptor-defective cells. The liganded receptor activates transcription by binding to a specific DNA recognition sequence, several copies of which are present within a dioxin-responsive enhancer centered =1000 base pairs (bp) upstream of the cyplal transcription start site (for review, see ref. 6). The receptor-enhancer interaction increases the nuclease susceptibility of the cyplal regulatory region, suggesting that a change in chromatin structure contributes to the activation of cyplal transcription by TCDD (7).The dioxin-responsive enhancer functions in concert with the cyplal promoter; transfection experiments indicate that neither the enhancer nor the promoter, individually, is sufficient to mediate a transcriptional response to TCDD (8). In intact uninduced cells, the cyplal promoter is inaccessible to transcription factors that are constitutively present; in TCDD-induced cells, the receptor-enhancer interaction increases the accessibility of the promoter, allowing proteins to bind and transcription to occur (9). These findings imply that the chromatin structure of the promoter plays a particularly important role in the response of the cyplal gene to dioxin. Preparation of Nuclei. All procedures were at 0-40C unless otherwise indicated. All solutions contained 0.5 mM phenylmethylsulfonyl fluoride, added shortly before use from a 50 mM st...

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Section: Itors Of Transcriptional Initiation (19-21)supporting

confidence: 91%

Transcription-dependent and transcription-independent nucleosome disruption induced by dioxin.

Morgan

Whitlock

1992

Proc. Natl. Acad. Sci. U.S.A.

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“…3) Gel retardation analyses reveal that uninduced cells contain proteins that bind to naked enhancer DNA in vitro; the structure and possible function of these proteins are unknown (21,23,39,40). Our analyses reveal no evidence for the corresponding protein-DNA interactions at the inactive enhancer in vivo.…”

Section: Discussionmentioning

confidence: 69%

“…1) The paucity of protein-DNA interactions suggests that the inactive enhancer is relatively inaccessible to DNA-binding proteins. For example, mouse hepatoma cells constitutively express a protein(s) at binds to naked, G-rich DNA in vitro (39). However, such binding does not occur at the CYPIAI promoter in vivo, unless the gene has been activated by TCDD.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of dioxin action: receptor-enhancer interactions in intact cells

Whitlock

1993

Nucl Acids Res

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We have used a ligation-mediated polymerase chain reaction technique to analyze protein-DNA interactions at a dioxin-responsive enhancer upstream of the CYP1A1 gene in intact mouse hepatoma cells. In its inactive state, the enhancer binds few, if any, proteins within the major DNA groove in vivo. Thus, the inactive enhancer is relatively inaccessible to DNA-binding proteins. Exposure of cells to 2,3,7,8-tetrachlorodibenzo-p-dioxin leads to the binding of the liganded Ah receptor at six sites within the major DNA groove of the enhancer. The receptor-enhancer interactions occur rapidly and do not require ongoing transcription, consistent with their role in regulating CYP1A1 gene expression. The liganded receptor, which is a heteromer composed of at least two basic helix-loop-helix proteins, is probably the only DNA-binding transcription factor necessary to activate the enhancer in vivo. The small size and irregular distribution of receptor binding sites suggest that chromatin structure imposes substantial steric constraints upon the function of the receptor-enhancer system in intact cells.

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“…In vitro footprinting and gel shift experiments have also shown that, subsequent to binding aryl hydrocarbons, the AH receptor is activated to a form that binds specifically to XREs (12)(13)(14)(15)(16)(17). Information regarding the in vivo DNA-protein interactions important in regulating CYPlAl transcription has been provided through both lowresolution studies, employing DNase I (18), exonuclease mII (19), and restriction enzymes (20), and, recently, through highresolution in vivo footprinting studies (21)(22)(23)(24).…”

Section: Introductionmentioning

confidence: 99%

Aryl hydrocarbon-induced interactions at multiple DNA elements of diverse sequence—a multicomponent mechanism for activation of cytochrome P4501A1 (CYP1A1) gene transcription

et al. 1994

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In vivo footprinting experiments, augmented with gel shift and transfection analyses suggest that activation of the CYP1A1 gene by aryl hydrocarbons may be a multicomponent process. During the first 30 minutes of exposure to aryl hydrocarbon carcinogens and environmental contaminants, in vivo footprints appear at nine distinct sites within a 281 bp region centered 950 bp upstream of the CYP1A1 transcription start site. Six of these sites are unrelated in sequence to the three xenobiotic response elements (XREs) within this region, at which the aryl hydrocarbon (AH) receptor is known to bind. These six display a variety of footprint patterns, are diverse in sequence and range in G-C content from 60 to 75%. This diversity suggests that multiple nuclear factors may be responsible for these six in vivo footprints. These observations are consistent with competition gel shift experiments showing that the nuclear factors binding at two of these sites are different from each other, as well as from the AH receptor. Gel shifts also indicate that the sequence-specific factors binding at these sites are expressed constitutively. This is consistent with a model in which in vivo footprints are induced at these six sites, not through direct activation or de novo synthesis of DNA-binding factors, but through a two phase mechanism in which binding of the nuclear AH receptor complex to XREs facilitates the binding of constitutive factors at these sites. This facilitation could be mediated either through specific protein-protein interactions or through alterations in chromatin structure that make these sites accessible to constitutive nuclear factors. A function for the sequences at which aryl hydrocarbons induce in vivo footprints is suggested by transfection experiments showing that one of these sequences cooperates with a weak XRE to confer on a reporter gene responsiveness to aryl hydrocarbons.

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Liver cells contain constitutive DNase I-hypersensitive sites at the xenobiotic response elements 1 and 2 (XRE1 and -2) of the rat cytochrome P-450IA1 gene and a constitutive, nuclear XRE-binding factor that is distinct from the dioxin receptor.

Cited by 26 publications

References 49 publications

Transcription-dependent and transcription-independent nucleosome disruption induced by dioxin.

Transcription-dependent and transcription-independent nucleosome disruption induced by dioxin.

Mechanism of dioxin action: receptor-enhancer interactions in intact cells

Aryl hydrocarbon-induced interactions at multiple DNA elements of diverse sequence—a multicomponent mechanism for activation of cytochrome P4501A1 (CYP1A1) gene transcription

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