The relationship between DNA methylation and Reprimo gene expression in gastric cancer cells

Reprimo (RPRM) is a tumor suppressor involved in the development of a number of malignant tumors including gastric cancer which is highly related to its gene hypermethylation. However, the regulation of RPRM gene expression by DNA methylation in gastric cancer is not well understood. We examined the RPRM gene methylation in gastric cancer tissues or plasma samples by bisulfite sequencing, and investigated the relationship between DNA methylation and the RPRM gene expression by quantitative reverse transcription-PCR and Western blotting. We found that the RPRM gene promoter region is hypermethylated in gastric cancer tissues (75%, 45/60), plasma samples (86.3%, 44/51) and various cancer cell lines (75%, 3/4), which is correlated with the decrease of RPRM gene expression. The hypermethylation-induced RPRM reduction can be recovered by treating with zebularine, a demethylating agent, and by inhibition of the DNA methyltransferases via RNA interference and CRISPR/Cas9-mediated gene knockout. In addition, we generated RPRM gene-knockout cells and studied the effects of the RPRM deficiency on tumor formation by inoculating these cells in mice. The data show that the loss of RPRM can promote tumorigenesis. These data suggest that the RPRM expression is inhibited by DNA methyltransferases and the RPRM normal function can be restored by treating with DNA methylation inhibitors. The study provides important information regarding the role of RPRM and its methylation related to gastric cancer development.