RASSF10 is an epigenetically silenced tumor suppressor in gastric cancer

To better understand the role of the N-Terminal Ras association domain family (RASSF) genes in the development of gastric cancer, we examined the expression of RASSF7 and RASSF10 and RASSF10 methylation in gastric cancer. We found that RASSF10 expression was lost in six gastric cancer cell lines, and was rescued by a DNA demethylating agent and a histone deacetylase inhibitor. However, RASSF7 expression was strong in four cancer cell lines as well as in 87% of primary gastric cancer tissues. In contrast, RASSF7 expression was moderate in the GES-1 cell line and negative in 33.3% of the corresponding non-cancerous tissues. Analysis of RASSF10 methylation by methylation-specific PCR (MSP) and sequencing revealed that the methylation frequency in primary gastric carcinoma tissues was significantly higher compared to that in adjacent non-carcinoma tissues (61.6 vs. 38.4%; p<0.01). The methylation frequency in the tumor with invasion depth at T3 and T4 was significantly higher compared to that with invasion depth at T1 and T2 (67.1 vs. 37.5%; p<0.05). Hypermethylation of RASSF10 was found in the patients with lymph node metastasis, compared to those with unaffected lymph nodes (68.8 vs. 40.9%; p<0.05). Among the 4 gross types of the Borrmann classification, i.e. EGC, Borrmann Ⅰ, Borrmann Ⅱ, Borrmann Ⅲ and Borrmann Ⅳ, the last one was more frequently methylated (85.7 vs. 56.9%; p<0.05). The present study revealed that RASSF10 is an epigenetically silenced gene involved in tumor invasion and metastasis in gastric cancer, suggesting that the methylation status of RASSF10 may be a useful indicator to predict the malignant degree of gastric cancer.