Targeted TET oxidase activity through methyl-CpG-binding domain extensively suppresses cancer cell proliferation

DNA methyltransferase (DNMT) inhibitors are epigenetic drugs used to treat myelodysplastic syndrome. They not only induce DNA demethylation but also have significant cytostatic and cytotoxic effects; however, the relationships between these characteristics have not been established yet due to the lack of a method to induce only DNA demethylation. Herein, we show that a fusion protein comprised of the methyl-CpG-binding domain (MBD) and the catalytic domain of Ten-eleven translocation protein 1 (TET1-CD) globally demethylates and upregulates a number of methylated genes. These upregulated genes frequently contained CpG islands (CGIs) within ± 1000 bp of the transcription start site (TSS). Interestingly, 65% of the genes upregulated fivefold or more by MBD-TET1-CDwt were also reactivated after treatment with a DNMT inhibitor, 5-azacytidine (Aza-CR), suggesting that gene reactivation by both methods primarily shares the same mechanism, DNA demethylation. In order to examine whether DNA demethylation affects the growth of cancer cells, we have established a tetracycline inducible system that can regulate the expression of MBD-TET1-CDwt in a prostate cancer cell line, LNCaP. The induction of MBD-TET1-CDwt demethylated and upregulated glutathione S-transferase pi 1 (GSTP1), one of the hypermethylated genes in prostate cancer. In accordance with the reactivation of methylated genes, induction of MBD-TET1-CDwt extensively suppressed the growth of LNCaP cells through G1/S arrest. These results clearly indicate that TET oxidase activity recruited at methyl-CpG sites through MBD induces reactivation of hypermethylated genes by DNA demethylation and allows us to analyze the effect of only global DNA demethylation in a wide variety of cancer cells.