Cytoplasmic RASSF2A is a proapoptotic mediator whose expression is epigenetically silenced in gastric cancer

Gastric cancer cells often show altered Ras signaling, though the underlying molecular mechanism is not fully understood. We examined the expression profile of eight ras-association domain family (RASSF) genes plus MST1/2 and found that RASSF2A is the most frequently downregulated in gastric cancer. RASSF2A was completely silenced in 6 of 10 gastric cancer cell lines as a result of promoter methylation, and expression was restored by treating the cells with 5-aza-2′-deoxycytidine. Introduction of RASSF2A into non-expressing cell lines suppressed colony formation and induced apoptosis. These effects were associated with the cytoplasmic localization of RASSF2A and morphological changes to the cells. Complementary DNA microarray analysis revealed that RASSF2A suppresses the expression of inflammatory cytokines, which may in turn suppress angiogenesis and invasion. In primary gastric cancers, aberrant methylation of RASSF2A was detected in 23 of 78 (29.5%) cases, and methylation correlated significantly with an absence of the lymphatic invasion, absence of venous invasion, absence of lymph node metastasis, less advanced stages, Epstein–Barr virus, absence of p53 mutations and the presence of the CpG island methylator phenotype-high. These results suggest that epigenetic inactivation of RASSF2A is required for tumorigenesis in a subset of gastric cancers

RASSF2A-mediated growth suppression and apoptosis in gastric cancer cell lines

( and ) Suppression of cell growth by RASSF2A. Growth suppression was evaluated by assaying geneticin-resistant colony formation. JRST and HSC44 cells were transfected with either pCDNA3.1 (control plasmid), RASSF2A or RASSF2A-ΔRA and incubated in RPMI 1640 medium containing 0.6 mg/ml G418. After 14 days, the plates were stained with Giemsa solution (A), and the colonies were counted (B). The bars indicate means ± SD of three independent experiments. ( and ) Flow cytometric analysis. (C) Representative flow cytometry after introduction of Ad-RASSF2A. The incidence of sub-G cells was determined 72 h after infection. (D) Quantitative analysis of sub-G cells. Percentages of sub-G cells are shown on the -axis. Error bars indicate standard error.<p><b>Copyright information:</b></p><p>Taken from "Cytoplasmic RASSF2A is a proapoptotic mediator whose expression is epigenetically silenced in gastric cancer"</p><p></p><p>Carcinogenesis 2008;29(7):1312-1318.</p><p>Published online 29 Feb 2008</p><p>PMCID:PMC2500213.</p><p></p