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Heme oxygenase-1 induction by NRF2 requires inactivation of the transcriptional repressor BACH1.

Reichard JF, Motz GT, Puga A - Nucleic Acids Res. (2007)

Bottom Line: In contrast, thioredoxin reductase 1 (TXNRD1) is regulated by NRF2 but not by BACH1.By comparing the expression levels of HMOX1 with TXNRD1, we show that nuclear accumulation of NRF2 is not necessary for HMOX1 induction; rather, BACH1 inactivation permits NRF2 already present in the nucleus at low basal levels to bind the HMOX1 promoter and elicit HMOX1 induction.Thus, BACH1 confers an additional level of regulation to ARE-dependent genes that reveals a new dimension to the oxidative stress response.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, Cincinnati, OH 45267-0056, USA. john.reichard@childrens.harvard.edu

ABSTRACT
Oxidative stress activates the transcription factor NRF2, which in turn binds cis-acting antioxidant response element (ARE) enhancers and induces expression of protective antioxidant genes. In contrast, the transcriptional repressor BACH1 binds ARE-like enhancers in cells naïve to oxidative stress and antagonizes NRF2 binding until it becomes inactivated by pro-oxidants. Here, we describe the dynamic roles of BACH1 and NRF2 in the transcription of the heme oxygenase-1 (HMOX1) gene. HMOX1 induction, elicited by arsenite-mediated oxidative stress, follows inactivation of BACH1 and precedes activation of NRF2. BACH1 repression is dominant over NRF2-mediated HMOX1 transcription and inactivation of BACH1 is a prerequisite for HMOX1 induction. In contrast, thioredoxin reductase 1 (TXNRD1) is regulated by NRF2 but not by BACH1. By comparing the expression levels of HMOX1 with TXNRD1, we show that nuclear accumulation of NRF2 is not necessary for HMOX1 induction; rather, BACH1 inactivation permits NRF2 already present in the nucleus at low basal levels to bind the HMOX1 promoter and elicit HMOX1 induction. Thus, BACH1 confers an additional level of regulation to ARE-dependent genes that reveals a new dimension to the oxidative stress response.

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Association of NRF2 and BACH1 DNA binding with transcriptional activation. Time course of DNA binding by BACH1 (A) NRF2 (B) and RNA polymerase II (C) following treatment with 25 μM arsenite, 5 μM MG132 or 25 μM hemin. ChIP-enriched DNA was quantified using qRT–PCR with primers flanking the HMOX1 ARE motifs at positions −3992 (NRF2 and BACH1) and −148 (RNA Pol II) and is expressed as the value for each treatment normalized to its corresponding input and expressed as fold enrichment relative to untreated control. Figures represent the results of two independent experiments performed in triplicate ± SEM.
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Figure 4: Association of NRF2 and BACH1 DNA binding with transcriptional activation. Time course of DNA binding by BACH1 (A) NRF2 (B) and RNA polymerase II (C) following treatment with 25 μM arsenite, 5 μM MG132 or 25 μM hemin. ChIP-enriched DNA was quantified using qRT–PCR with primers flanking the HMOX1 ARE motifs at positions −3992 (NRF2 and BACH1) and −148 (RNA Pol II) and is expressed as the value for each treatment normalized to its corresponding input and expressed as fold enrichment relative to untreated control. Figures represent the results of two independent experiments performed in triplicate ± SEM.

Mentions: The observation that expression of HMOX1 is associated with nuclear efflux of BACH1 rather than with NRF2 activation, suggests that BACH1 removal is the dominant event regulating HMOX1 induction. To test this hypothesis we followed the temporal dynamics of HMOX1 transcriptional initiation by ChIP analysis. The time course of BACH1 and NRF2 binding to the E1 (Figure 4) and E2 (data not shown) enhancer regions of HMOX1, as well as RNA pol II binding at the proximal promoter (−148), were quantified after treatments with arsenite, hemin or MG132. These treatments induced very similar interactions of NRF2 and BACH1 at both of these enhancer regions, of which the observed interactions at E1 are representative. As anticipated, arsenite treatment produces a significant loss of BACH1 binding that is clearly detected 30 min after treatment and reaches minimal level by 60 min (Figure 4A). Conversely, arsenite triggers a prominent increase in NRF2 binding (Figure 4B), but this increase is delayed by at least 60 min relative to the BACH1 decrease, and is maximal at 150 min after treatment. Arsenite also produces a large increase in RNA pol II binding (Figure 4C) that temporally follows the loss of BACH1 but precedes NRF2 binding by at least 60 min and this coincides with the relatively low level of NRF2 binding during the period between 60 and 120 min.Figure 4.


Heme oxygenase-1 induction by NRF2 requires inactivation of the transcriptional repressor BACH1.

Reichard JF, Motz GT, Puga A - Nucleic Acids Res. (2007)

Association of NRF2 and BACH1 DNA binding with transcriptional activation. Time course of DNA binding by BACH1 (A) NRF2 (B) and RNA polymerase II (C) following treatment with 25 μM arsenite, 5 μM MG132 or 25 μM hemin. ChIP-enriched DNA was quantified using qRT–PCR with primers flanking the HMOX1 ARE motifs at positions −3992 (NRF2 and BACH1) and −148 (RNA Pol II) and is expressed as the value for each treatment normalized to its corresponding input and expressed as fold enrichment relative to untreated control. Figures represent the results of two independent experiments performed in triplicate ± SEM.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2175339&req=5

Figure 4: Association of NRF2 and BACH1 DNA binding with transcriptional activation. Time course of DNA binding by BACH1 (A) NRF2 (B) and RNA polymerase II (C) following treatment with 25 μM arsenite, 5 μM MG132 or 25 μM hemin. ChIP-enriched DNA was quantified using qRT–PCR with primers flanking the HMOX1 ARE motifs at positions −3992 (NRF2 and BACH1) and −148 (RNA Pol II) and is expressed as the value for each treatment normalized to its corresponding input and expressed as fold enrichment relative to untreated control. Figures represent the results of two independent experiments performed in triplicate ± SEM.
Mentions: The observation that expression of HMOX1 is associated with nuclear efflux of BACH1 rather than with NRF2 activation, suggests that BACH1 removal is the dominant event regulating HMOX1 induction. To test this hypothesis we followed the temporal dynamics of HMOX1 transcriptional initiation by ChIP analysis. The time course of BACH1 and NRF2 binding to the E1 (Figure 4) and E2 (data not shown) enhancer regions of HMOX1, as well as RNA pol II binding at the proximal promoter (−148), were quantified after treatments with arsenite, hemin or MG132. These treatments induced very similar interactions of NRF2 and BACH1 at both of these enhancer regions, of which the observed interactions at E1 are representative. As anticipated, arsenite treatment produces a significant loss of BACH1 binding that is clearly detected 30 min after treatment and reaches minimal level by 60 min (Figure 4A). Conversely, arsenite triggers a prominent increase in NRF2 binding (Figure 4B), but this increase is delayed by at least 60 min relative to the BACH1 decrease, and is maximal at 150 min after treatment. Arsenite also produces a large increase in RNA pol II binding (Figure 4C) that temporally follows the loss of BACH1 but precedes NRF2 binding by at least 60 min and this coincides with the relatively low level of NRF2 binding during the period between 60 and 120 min.Figure 4.

Bottom Line: In contrast, thioredoxin reductase 1 (TXNRD1) is regulated by NRF2 but not by BACH1.By comparing the expression levels of HMOX1 with TXNRD1, we show that nuclear accumulation of NRF2 is not necessary for HMOX1 induction; rather, BACH1 inactivation permits NRF2 already present in the nucleus at low basal levels to bind the HMOX1 promoter and elicit HMOX1 induction.Thus, BACH1 confers an additional level of regulation to ARE-dependent genes that reveals a new dimension to the oxidative stress response.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, Cincinnati, OH 45267-0056, USA. john.reichard@childrens.harvard.edu

ABSTRACT
Oxidative stress activates the transcription factor NRF2, which in turn binds cis-acting antioxidant response element (ARE) enhancers and induces expression of protective antioxidant genes. In contrast, the transcriptional repressor BACH1 binds ARE-like enhancers in cells naïve to oxidative stress and antagonizes NRF2 binding until it becomes inactivated by pro-oxidants. Here, we describe the dynamic roles of BACH1 and NRF2 in the transcription of the heme oxygenase-1 (HMOX1) gene. HMOX1 induction, elicited by arsenite-mediated oxidative stress, follows inactivation of BACH1 and precedes activation of NRF2. BACH1 repression is dominant over NRF2-mediated HMOX1 transcription and inactivation of BACH1 is a prerequisite for HMOX1 induction. In contrast, thioredoxin reductase 1 (TXNRD1) is regulated by NRF2 but not by BACH1. By comparing the expression levels of HMOX1 with TXNRD1, we show that nuclear accumulation of NRF2 is not necessary for HMOX1 induction; rather, BACH1 inactivation permits NRF2 already present in the nucleus at low basal levels to bind the HMOX1 promoter and elicit HMOX1 induction. Thus, BACH1 confers an additional level of regulation to ARE-dependent genes that reveals a new dimension to the oxidative stress response.

Show MeSH
Related in: MedlinePlus