Aberrant CpG island hypermethylation of RASSF1A in gastric cardia adenocarcinoma.

Ras-association domain family 1A (RASSF1A) gene, a candidate tumor suppressor gene, is inactivated in several human tumors, usually by hypermethylation of its promoter region. RASSF1A induces cell cycle arrest through inhibition of cyclin D1 accumulation. In this work, the promoter methylation status of the RASSF1A in 92 gastric cardia adenocarcinoma (GCA) and corresponding normal tissues were investigated using Methylation-specific PCR (MSP) approach, immunohistochemistry method and RT-PCR were used respectively to examine the protein expression and mRNA expression of RASSF1A in tumors and corresponding normal tissues. Cyclin D1 expression was examined by immunohistochemistry. RASSF1A was methylated in 54/92 (58.7%) tumor specimens, which was significantly higher than that in corresponding normal tissues (p <.001). Methylation frequencies of stage III and IV tumor tissues were significantly higher than that in stage I and II tumor tissues (p <.05). By immunostaining, 43/92 (46.7%) tumor tissues demonstrated heterogeneous, positive immunostaining of tumor tissues was significantly reduced with comparison to matched normal tissues (p <.001). mRNA expressions of RASSF1A in GCA tumor tissues were reduced significantly with comparison to the corresponding normal tissues (OD value: 0.2376 +/- 0.2315 vs 0.6874 +/- 0.2668, p <.001). RASSF1A mRNA expression in methylation group of GCA was significantly different from that in unmethylation group (p <.001). Cyclin D1 hyper-expression was found in 72/92 (78.3%) cases and correlated with RASSF1A methylation (p <.05). Our data suggested that epigenetic silencing of RASSF1A gene expression by promoter hypermethylation may play an important role in GCA.