sEH (soluble epoxide hydrolase), which is encoded by the EPHX2 gene, regulates the actions of bioactive lipids, EETs (epoxyeicosatrienoic acids). Previously, we found that high-glucose-induced oxidative stress suppressed sEH levels in a hepatocarcinoma cell line (Hep3B) and sEH was decreased in streptozotocin-induced diabetic mice in vivo. In the present study, we investigated the regulatory mechanisms underlying EPHX2 transcriptional suppression under high-glucose conditions. The decrease in sEH was prevented by an Sp1 (specificity protein 1) inhibitor, mithramycin A, and overexpression or knockdown of Sp1 revealed that Sp1 suppressively regulated sEH expression, in contrast with the general role of Sp1 on transcriptional activation. In addition, we found that AP2α (activating protein 2α) promoted EPHX2 transcription. The nuclear transport of Sp1, but not that of AP2α, was increased under high glucose concomitantly with the decrease in sEH. Within the EPHX2 promoter −56/+32, five Sp1-binding sites were identified, and the mutation of each of these sites showed that the first one (SP1_1) was important in both suppression by Sp1 and activation by AP2α. Furthermore, overexpression of Sp1 diminished the binding of AP2α by DNA-affinity precipitation assay and ChIP, suggesting competition between Sp1 and AP2α on the EPHX2 promoter. These findings provide novel insights into the role of Sp1 in transcriptional suppression, which may be applicable to the transcriptional regulation of other genes.
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Research Article|
September 04 2015
Down-regulation of EPHX2 gene transcription by Sp1 under high-glucose conditions
Ami Oguro;
Ami Oguro
*Research Center for Environmental Bioscience and Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan
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Shoko Oida;
Shoko Oida
*Research Center for Environmental Bioscience and Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan
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Susumu Imaoka
Susumu Imaoka
1
*Research Center for Environmental Bioscience and Department of Bioscience, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan
1To whom correspondence should be addressed (email [email protected]).
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Publisher: Portland Press Ltd
Received:
March 30 2015
Revision Received:
July 09 2015
Accepted:
July 15 2015
Accepted Manuscript online:
July 15 2015
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 2015 Authors; published by Portland Press Limited
2015
Biochem J (2015) 470 (3): 281–291.
Article history
Received:
March 30 2015
Revision Received:
July 09 2015
Accepted:
July 15 2015
Accepted Manuscript online:
July 15 2015
Citation
Ami Oguro, Shoko Oida, Susumu Imaoka; Down-regulation of EPHX2 gene transcription by Sp1 under high-glucose conditions. Biochem J 15 September 2015; 470 (3): 281–291. doi: https://doi.org/10.1042/BJ20150397
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