A study on DNA methylation modifying natural compounds identified EGCG for induction of IFI16 gene expression related to the innate immune response in cancer cells

Innate immune sensor IFN-induced protein 16 (IFI16) exhibits anti-inflammatory effects via IFNβ and IFN-stimulated gene (ISG)15 induction in cancer cells. Epigallocatechin gallate (EGCG) is a potent natural DNA methyltransferase inhibitor (DNMTi). Previous studies revealed that conventional DNMTis, such as 5-azacytidine (5-aza-dc), induce IFI16 expression and EGCG decreases DNMT mRNA expression and global methylation (5mC) level via promoter demethylation of tumor suppressor genes in cancer cell lines. To the best of our knowledge, however, EGCG-mediated IFI16 promoter methylation status has been overlooked. Here, initial screening was performed to determine IFI16 expression and its correlation with DNMTs in cancer cell lines from various databases. Following treatment of breast cancer cell lines with 5-aza-dc, vitamin C and EGCG, expression levels of IFI16 and its downstream transcription targets IFNβ1 and ISG15 were assessed using RT-qPCR, and the 5mC level was assessed using ELISA. In silico molecular docking simulation was performed for all DNMTs to predict the mode of ligands binding with proteins. Finally, promoter methylation level in IFI16 gene was assessed following EGCG treatment. EGCG treatment induced IFI16 expression, interacted with certain amino acids residues in DNMT proteins and decreased 5mC level and promoter methylation of IFI16. The present results may provide a basis for targeting IFI16 expression as a therapeutic option in breast cancer cell lines.