Loss of expression of the differentially expressed in adenocarcinoma of the lung (DAL-1) protein is associated with metastasis of non-small cell lung carcinoma cells

The differentially expressed in adenocarcinoma of the lung-1 (DAL-1) protein is a member of the membrane-associated cytoskeleton protein 4.1 family. This protein was previously found to be downregulated or lost in more than half of primary non-small cell lung cancers (NSCLC). In this study, the relationship between DAL-1 expression and NSCLC metastasis was examined. DAL-1 mRNA and protein levels were measured in NSCLC cell lines and in tumor cells isolated from the pleural fluid of NSCLC patients clinically diagnosed with distant metastases to the bone or brain. The results revealed that DAL-1 expression was observed in two (GLC-82 and NCI-H460) out of seven metastatic NSCLC cell lines examined. DAL-1 expression was not observed in the cells isolated from the pleural fluid in nine out of ten patients. Overexpression of DAL-1 in A549 cells, a cell line lacking endogenous DAL-1, inhibited cell migration and invasion by approximately 38 and 48 %, respectively. In contrast, DAL-1 knockdown in NCI-H460 cells enhanced the migration and invasion potential of this cell line 4.6- and 3-fold, respectively. Furthermore, DAL-1 promoter methylation was observed in six of nine pleural fluid NSCLC cell isolates and in two cell lines (A549 and H1299), as evidenced by a lack of endogenous DAL-1. Demethylation in A549 cells successfully restored DAL-1 mRNA and protein expression levels, resulting in a parallel remarkable inhibition of migration and invasion. These results indicated that DAL-1 was pivotal in triggering NSCLC migration and invasion and that loss of DAL-1 expression was due to the epigenetic methylation.