Hypermethylation downregulates Runx3 gene expression and its restoration suppresses gastric epithelial cell growth by inducing p27 and caspase3 in human gastric cancer

Background and Aims: Runx family transcription factors are integral components of transforming growth factor‐β signaling pathways and have been implicated in cell cycle regulation, differentiation, apoptosis, and malignant transformation. The silencing of tumor suppressor genes by aberrant hypermethylation occurs frequently in human cancer. It has been noted previously that Runx3 is regarded as an important tumor suppressor gene. Methods: Reverse transcription polymerase chain reaction was used to measure Runx3 and the DNA methyltransferase 1 (Dnmt1) messenger RNA (mRNA) expression level of paired samples of primary gastric cancer and corresponding non‐cancerous gastric mucosae, which were obtained from surgically resected specimens of 70 patients. Western blot was used to detect the expression of Runx3 at protein levels. The promoter methylation status was measured by using methylation‐specific polymerase chain reaction. We used Annexin V‐FITC/PI assay to detect cell apoptosis, and the cell cycle was also analyzed. In order to examine the cell cycle and/or apoptosis, we determined p27 and caspase 3 expression by immunohistological analysis. Results: Our results demonstrate a loss or substantial decrease of Runx3 expression in 70 cases of gastric tumors as compared with that in normal gastric mucosa (0.5749 ± 0.3580 vs 1.7252 ± 0.4085, P