Aberrant promoter methylation of human DAB2 interactive protein (hDAB2IP) gene in lung cancers

The human DOC-2/DAB2 interactive protein gene (hDAB2IP) is a novel member of the Ras GTPase-activating gene family that is known to act as a tumor suppressor gene and is inactivated by methylation in prostate and breast cancers. We established previously a methylation-specific PCR (MSP) for the promoter region (m2a and m2b regions) of hDAB2IP and examined hDAB2IP methylation status in breast cancers. We analyzed the methylation and expression status of hDAB2IP in lung cancers. The methylation status of hDAB2IP was examined in lung cancer cell lines using bisulfite sequencing and MSP. Expression was examined using conventional and real-time RT-PCR, and methylation was found to be inversely correlated with expression, confirming that the MSP can also be used to examine hDAB2IP methylation status in lung cancers. Aberrant methylation was detected at the m2a region in 19 of 47 lung cancer cell lines (40%) and 26 of 70 primary tumors (37%) and at the m2b in 16 lines (34%) and 25 of 70 tumors (36%). Gene expression was restored in methylated cell lines supplemented with 5-aza-2'-deoxycytidine, confirming that methylation was responsible for downregulation. We also examined the relationship between hDAB2IP methylation and clinico-pathological features of the lung cancers and found that hDAB2IP methylation was associated with advanced disease stage. Our results demonstrate that hDAB2IP methylation is frequently present in lung cancers and plays a key role in hDAB2IP silencing. hDAB2IP methylation could be used as a biomarker for disease stage, reflecting the degree of clinico-pathological malignancy of lung cancer.