RRAD, one of the small Ras-related GTPases, is highly expressed in human skeletal muscle, lung, and heart. Although the loss of expression in breast cancer cells has been reported and RRAD may act as an oncogene, the mechanism of silencing was unknown. To clarify the role of RRAD in cancer pathogenesis, we examined mRNA expression of RRAD in lung and breast cancer cell lines using RT-PCR. Loss of RRAD expression was found in 14 of 20 (70%) NSCLC cell lines, 11 of 11 (100%) SCLC cell lines, and 8 of 10 (80%) breast cancer cell lines compared with normal bronchial and mammary epithelial cells. Treatment of 23 expression negative cell lines with a demethylating agent restored expression in all cases. We developed a MSP assay from the analysis of bisulfite sequencing of 5’ region of RRAD in expression negative and positive cell lines, and the assay showed good concordance between methylation and expression. Primary lung and breast cancers showed hypermethylation in 98 of 232 (42%) and 39 of 63 (62%) of cases respectively. RRAD hypermethylation correlated with smoking history and poorer prognosis in lung adenocarcinomas. These results suggest that epigenetic silencing of RRAD is a frequent event in lung and breast cancers and may provide novel opportunities as a molecular tool for prognosis and therapy of these cancers.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]