Upregulation of TET2 and Resistance to DNA Methyltransferase (DNMT) Inhibitors in DNMT1 -Deleted Cancer Cells

Ten-eleven-translocation (TET) 2 is a member of the TET family of proteins (TET1-3). gene deletion confers resistance to DNA methyltransferase (DNMT) inhibitors in colorectal, breast, and ovarian cancer cells. Currently, the effect of gene status on TET2 phenotype following DNMT inhibitor treatment is unclear in human malignancies. Human colorectal carcinoma HCT116 cells ( ) and their isogenic DNMT1 knockout ( ) counterpart were treated with DNMT inhibitors. Expression of TET2 and tumor suppressor (p16 and p15 ) proteins were examined by Western blot. Apoptosis and promoter demethylation following drug treatment were detected by Annexin-V apoptosis assay and methylation-specific PCR. TET2 expression was robustly increased in cells by 0.5 µM and 5 µM decitabine and azacitidine treatment. Augmentation of TET2 expression was accompanied by re-expression of p16 and p15 proteins and promoter demethylation. TET2 upregulation and tumor suppressor re-expression were associated with resistance conferred by deletion. Treatment with 5-aza-4'-thio-2'-deoxycytidine at a low 0.5 µM dose only upregulated TET2 and reduced promoter methylation, and re-expression of p16 in cells. DNMT inhibitors showed minimal effects on TET2 upregulation and re-expression of tumor suppressor proteins in cells with intact . gene deletion made cancer cells prone to TET2 upregulation and activation of tumor suppressor expression upon DNMT inhibitor challenge. TET2 augmentation is concomitant with resistance to DNMT inhibitors in a -deleted state.