Contribution of DNA methylation and EZH2 in SRBC down-regulation in gastric cancer.

Gastric cancer (GC), a high mortality malignancy, is induced by genetic and epigenetic factors. DNA and histone methylation play critical roles in tumor suppressor genes inactivation. SRBC (serum deprivation response factor-related gene product that binds to the c-kinase), suggested as a tumor suppressor gene, participates in apoptosis, tumor chemoresistance and DNA damage response and is repressed in various cancers. Inspecting the mechanisms underlying SRBC suppression is important for cancer treatments. We investigated SRBC promoter DNA methylation status and expression of SRBC and EZH2 histone methyltrasferase in gastric cancer. Also, we surveyed SRBC expression after 5-azacitidine and UNC1999 treatments of AGS cell line. In current work, we used gastric adenocarcinoma tissues, marginal samples and normal gastric biopsies. DNA methylation was detected by Methylation- Specific PCR and mRNA expression was measured by Real-Time PCR. SRBC promoter methylation analysis, showed fully and partial methylated versions that were associated with patient's age (p = 0.001). SRBC expression significantly decreased in GC compare with marginal and normal samples (p-value < 0.001). EZH2 showed remarkable up-regulation in GC than controls and demonstrated a strong inverse correlation with SRBC expression (r = - 0.69). Restoration of SRBC expression was observed after 5-azacitidine and UNC1999 applications with a remarkable increase by combinational treatment. We showed that EZH2 plays role in SRBC silencing in addition to DNA methylation. Our study, suggests that DNA methylation and EZH2 are involved in SRBC silencing and their inhibitors can be considered in cancer treatment investigations to overcome chemoresistance induced by SRBC inactivation.