Regulation of human apolipoprotein A-I gene expression by equine estrogens
Estrogen replacement therapies, such as conjugated equine estrogen (CEE, Premarin®), reduce the risk of coronary heart disease among postmenopausal women. In the present study, a HepG2 stable cell line (HepG2/S) that harbors a luciferase reporter gene cassette with the human apolipoprotein A-I (apoA...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Elsevier
2001-11-01
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| Series: | Journal of Lipid Research |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S0022227520315054 |
| _version_ | 1818657231553429504 |
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| author | Xia Zhang Jei-Jun Jiao Bhagu R. Bhavnani Shui-Pang Tam |
| author_facet | Xia Zhang Jei-Jun Jiao Bhagu R. Bhavnani Shui-Pang Tam |
| author_sort | Xia Zhang |
| collection | DOAJ |
| description | Estrogen replacement therapies, such as conjugated equine estrogen (CEE, Premarin®), reduce the risk of coronary heart disease among postmenopausal women. In the present study, a HepG2 stable cell line (HepG2/S) that harbors a luciferase reporter gene cassette with the human apolipoprotein A-I (apoA-I) promoter region was used to examine the activity of CEE components in modulating human apoA-I promoter activity. A number of estrogens modulated apoA-I promoter activity, with equilenin (Eqn) being the most potent. Eqn produced a 3-fold increase in apoA-I promoter activity and a similar increase in apoA-I mRNA without affecting its degradation rate. Nuclear runoff assays indicated that the transcription rate of the apoA-I gene was increased 2.5-fold in Eqn-treated cells. When HepG2/S cells were exposed to Eqn, apoA-I protein secretion increased by 80%, whereas the level of secreted apoA-II remained unchanged. Transient transfection studies with human apoA-I promoter constructs derived from pGL3-luciferase reporter plasmid were used to identify the cis-acting element involved in Eqn-mediated induction. The results demonstrated that the apoA-I electrophile/antioxidant response element (EpRE/ARE) might be responsible for the increase in apoA-I promoter activity by Eqn. Cotransfection experiments using estrogen receptor (ERα and/or ERβ) expression vectors have indicated that neither receptor can potentiate the Eqn-mediated induction of apoA-I promoter activity. In addition, mobility shift analysis using antibody against either ERα or ERβ cannot detect the presence of these receptors in the DNA-protein complex. The data indicate that Eqn can induce the promoter activity of the human apoA-I gene, leading to an increase in apoA-I mRNA levels and apoA-I protein secretion through an ER-independent pathway involving apoA-I EpRE/ARE.—Zhang, X., J-J. Jiao, B. R. Bhavnani, and S-P. Tam. Regulation of human apolipoprotein A-I gene expression by equine estrogens. |
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| institution | Directory Open Access Journal |
| issn | 0022-2275 |
| language | English |
| last_indexed | 2024-12-17T03:38:12Z |
| publishDate | 2001-11-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Journal of Lipid Research |
| spelling | doaj.art-ad13c940f72a4ab9be19c58948b4ae262022-12-21T22:05:04ZengElsevierJournal of Lipid Research0022-22752001-11-01421117891800Regulation of human apolipoprotein A-I gene expression by equine estrogensXia Zhang0Jei-Jun Jiao1Bhagu R. Bhavnani2Shui-Pang Tam3Department of Biochemistry, Queen's University, Kingston, Ontario, Canada; Cancer Research Laboratories, Queen's University, Kingston, Ontario, CanadaCancer Research Laboratories, Queen's University, Kingston, Ontario, CanadaDepartment of Obstetrics and Gynecology, Institute of Medical Sciences, University of Toronto and St. Michael's Hospital, Toronto, Ontario, CanadaDepartment of Biochemistry, Queen's University, Kingston, Ontario, Canada; Cancer Research Laboratories, Queen's University, Kingston, Ontario, Canada; To whom correspondence should be addressed at Department of Biochemistry, Cancer Research Laboratories, Third Floor, Botterell Hall Queens University, Kingston, Ontario, Canada K7L 3N6. e-mail:Estrogen replacement therapies, such as conjugated equine estrogen (CEE, Premarin®), reduce the risk of coronary heart disease among postmenopausal women. In the present study, a HepG2 stable cell line (HepG2/S) that harbors a luciferase reporter gene cassette with the human apolipoprotein A-I (apoA-I) promoter region was used to examine the activity of CEE components in modulating human apoA-I promoter activity. A number of estrogens modulated apoA-I promoter activity, with equilenin (Eqn) being the most potent. Eqn produced a 3-fold increase in apoA-I promoter activity and a similar increase in apoA-I mRNA without affecting its degradation rate. Nuclear runoff assays indicated that the transcription rate of the apoA-I gene was increased 2.5-fold in Eqn-treated cells. When HepG2/S cells were exposed to Eqn, apoA-I protein secretion increased by 80%, whereas the level of secreted apoA-II remained unchanged. Transient transfection studies with human apoA-I promoter constructs derived from pGL3-luciferase reporter plasmid were used to identify the cis-acting element involved in Eqn-mediated induction. The results demonstrated that the apoA-I electrophile/antioxidant response element (EpRE/ARE) might be responsible for the increase in apoA-I promoter activity by Eqn. Cotransfection experiments using estrogen receptor (ERα and/or ERβ) expression vectors have indicated that neither receptor can potentiate the Eqn-mediated induction of apoA-I promoter activity. In addition, mobility shift analysis using antibody against either ERα or ERβ cannot detect the presence of these receptors in the DNA-protein complex. The data indicate that Eqn can induce the promoter activity of the human apoA-I gene, leading to an increase in apoA-I mRNA levels and apoA-I protein secretion through an ER-independent pathway involving apoA-I EpRE/ARE.—Zhang, X., J-J. Jiao, B. R. Bhavnani, and S-P. Tam. Regulation of human apolipoprotein A-I gene expression by equine estrogens.http://www.sciencedirect.com/science/article/pii/S0022227520315054apolipoprotein A-Iestrogen replacement therapygene regulationHDL |
| spellingShingle | Xia Zhang Jei-Jun Jiao Bhagu R. Bhavnani Shui-Pang Tam Regulation of human apolipoprotein A-I gene expression by equine estrogens Journal of Lipid Research apolipoprotein A-I estrogen replacement therapy gene regulation HDL |
| title | Regulation of human apolipoprotein A-I gene expression by equine estrogens |
| title_full | Regulation of human apolipoprotein A-I gene expression by equine estrogens |
| title_fullStr | Regulation of human apolipoprotein A-I gene expression by equine estrogens |
| title_full_unstemmed | Regulation of human apolipoprotein A-I gene expression by equine estrogens |
| title_short | Regulation of human apolipoprotein A-I gene expression by equine estrogens |
| title_sort | regulation of human apolipoprotein a i gene expression by equine estrogens |
| topic | apolipoprotein A-I estrogen replacement therapy gene regulation HDL |
| url | http://www.sciencedirect.com/science/article/pii/S0022227520315054 |
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