title: A-to-I RNA Editing Up-regulates Human Dihydrofolate Reductase in Breast Cancer.
abstract: Dihydrofolate reductase (DHFR) plays a key role in folate metabolism and is a target molecule of methotrexate. An increase in the cellular expression level of DHFR is one of the mechanisms of tumor resistance to methotrexate. The present study investigated the possibility that adenosine-to-inosine RNA editing, which causes nucleotide conversion by adenosine deaminase acting on RNA (ADAR) enzymes, might modulate DHFR expression. In human breast adenocarcinoma-derived MCF-7 cells, 26 RNA editing sites were identified in the 3'-UTR of DHFR. Knockdown of ADAR1 decreased the RNA editing levels of DHFR and resulted in a decrease in the DHFR mRNA and protein levels, indicating that ADAR1 up-regulates DHFR expression. Using a computational analysis, miR-25-3p and miR-125a-3p were predicted to bind to the non-edited 3'-UTR of DHFR but not to the edited sequence. The decrease in DHFR expression by the knockdown of ADAR1 was restored by transfection of antisense oligonucleotides for these miRNAs, suggesting that RNA editing mediated up-regulation of DHFR requires the function of these miRNAs. Interestingly, we observed that the knockdown of ADAR1 decreased cell viability and increased the sensitivity of MCF-7 cells to methotrexate. ADAR1 expression levels and the RNA editing levels in the 3'-UTR of DHFR in breast cancer tissues were higher than those in adjacent normal tissues. Collectively, the present study demonstrated that ADAR1 positively regulates the expression of DHFR by editing the miR-25-3p and miR-125a-3p binding sites in the 3'-UTR of DHFR, enhancing cellular proliferation and resistance to methotrexate.
authors.affiliation: From the Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Nakano
authors.affiliation: From the Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
authors.forename: Tatsuki
authors.initials: T
authors.lastname: Fukami
authors.affiliation: From the Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Gotoh
authors.affiliation: From the Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan nmiki@p.kanazawa-u.ac.jp.
authors.forename: Miki
authors.initials: M
authors.lastname: Nakajima
mesh_terms: D020413:3' Untranslated Regions; D000241:Adenosine / Q000235:genetics; D000243:Adenosine Deaminase / Q000235:genetics*; D001940:Breast / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics*; D049109:Cell Proliferation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007288:Inosine / Q000235:genetics; D061986:MCF-7 Cells; D035683:MicroRNAs / Q000235:genetics; D017393:RNA Editing; D016601:RNA-Binding Proteins / Q000235:genetics*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D015854:Up-Regulation
chemical_list: D020413:3' Untranslated Regions; D035683:MicroRNAs; D016601:RNA-Binding Proteins; D007288:Inosine; D013762:Tetrahydrofolate Dehydrogenase; C000595356:ADAR protein, human; D000243:Adenosine Deaminase; D000241:Adenosine
keywords: RNA editing; anticancer drug; breast cancer; cancer biology; dihydrofolate reductase; microRNA (miRNA)