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Molecular and Cellular Biology, December 2002, p. 8302-8319, Vol. 22, No. 23
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.23.8302-8319.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Inhibitors of Histone Deacetylase and DNA Methyltransferase Synergistically Activate the Methylated Metallothionein I Promoter by Activating the Transcription Factor MTF-1 and Forming an Open Chromatin Structure

Kalpana Ghoshal,* Jharna Datta, Sarmila Majumder, Shoumei Bai, Xiaocheng Dong, Mark Parthun, and Samson T. Jacob*

Department of Molecular and Cellular Biochemistry, College of Medicine, The Ohio State University, Columbus, Ohio 43210

Received 23 May 2002/ Returned for modification 5 August 2002/ Accepted 20 August 2002

Inhibitors of DNA methyltransferase (Dnmt) and histone deacetylases (HDAC) synergistically activate the methylated metallothionein I gene (MT-I) promoter in mouse lymphosarcoma cells. The cooperative effect of these two classes of inhibitors on MT-I promoter activity was robust following demethylation of only a few CpG dinucleotides by brief exposure to 5-azacytidine (5-AzaC) but persisted even after prolonged treatment with the nucleoside analog. HDAC inhibitors (trichostatin A [TSA] and depsipeptide) either alone or in combination with 5-AzaC did not facilitate demethylation of the MT-I promoter. Treatment of cells with HDAC inhibitors increased accumulation of multiply acetylated forms of H3 and H4 histones that remained unaffected after treatment with 5-AzaC. Chromatin immunoprecipitation (ChIP) assay showed increased association of acetylated histone H4 and lysine 9 (K9)-acetyl H3 with the MT-I promoter after treatment with TSA, which was not affected following treatment with 5-AzaC. In contrast, the association of K9-methyl histone H3 with the MT-I promoter decreased significantly after treatment with 5-AzaC and TSA. ChIP assay with antibodies specific for methyl-CpG binding proteins (MBDs) demonstrated that only methyl-CpG binding protein 2 (MeCP2) was associated with the MT-I promoter, which was significantly enhanced after TSA treatment. Association of histone deacetylase 1 (HDAC1) with the promoter decreased after treatment with TSA or 5-AzaC and was abolished after treatment with both inhibitors. Among the DNA methyltransferases, both Dnmt1 and Dnmt3a were associated with the MT-I promoter in the lymphosarcoma cells, and association of Dnmt1 decreased with time after treatment with 5-AzaC. Treatment of these cells with HDAC inhibitors also increased expression of the MTF-1 (metal transcription factor-1) gene as well as its DNA binding activity. In vivo genomic footprinting studies demonstrated increased occupancy of MTF-1 to metal response elements of the MT-I promoter after treatment with both inhibitors. Analysis of the promoter by mapping with restriction enzymes in vivo showed that the MT-I promoter attained a more open chromatin structure after combined treatment with 5-AzaC and TSA as opposed to treatment with either agent alone. These results implicate involvement of multifarious factors including modified histones, MBDs, and Dnmts in silencing the methylated MT-I promoter in lymphosarcoma cells. The synergistic activation of this promoter by these two types of inhibitors is due to demethylation of the promoter and altered association of different factors that leads to reorganization of the chromatin and the resultant increase in accessibility of the promoter to the activated transcription factor MTF-1.

* Corresponding author. Mailing address: Department of Molecular and Cellular Biochemistry, College of Medicine, The Ohio State University, 333 Hamilton Hall, 1645 Neil Ave., Columbus, OH 43210. Phone: (614) 688-5494. Fax: (614) 688-5600. E-mail for Samson T. Jacobi: jacob.42{at}osu.edu. E-mail for Kalpana Ghoshal: ghoshal.1{at}osu.edu.

Molecular and Cellular Biology, December 2002, p. 8302-8319, Vol. 22, No. 23
0022-538X/02/$04.00+0     DOI: 10.1128/MCB.22.23.8302-8319.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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