Refined-mapping of the Novel TSG Within the 17q24.3 Chromosomal Region in Non-small Cell Lung Cancer Samples

Lung cancer is a leading cause of cancer mortality in Taiwan. It has been previously demonstrated that alterations to tumor suppressor genes (TSGs) are involved in the multi-step carcinogenesis process that results in the development of human cancer, including lung cancer. Both copies of the TSG must be inactivated for their function to be lost. As a result, it is important to search for the genomic regions that potentially contain TSGs and to investigate the etiological association of lung cancer with the allelic deletion of various candidate TSGs. Previous genome-wide loss of heterozygosity (LOH) data has demonstrated that the chromosome region at 17q24.3 was a novel and frequent LOH region that was associated with non-small-cell lung cancer (NSCLC). In the present study, refined mapping using 9 additional microsatellite markers was performed targeting chromosome 17q24.3 by polymerase chain reaction (PCR)-LOH analysis. The allelic loss pattern across 48 available tumors indicates that the minimal deletion region was located between markers D17S1882 and D17S2193 and spanned a distance of approximately 2.7 Mb, reaching 65% LOH at locus D17S1816. A putative gene, LOC51321 (), was postulated to be the deletion target on 17q24.3 based on the findings from these NSCLC samples. Reverse transcription-PCR (RT-PCR) expression analysis indicated reduced expression of LOC51321 in 54% (7/13) of the NSCLC cell lines tested and 36% (19/53) of the NSCLC tumor tissue samples analyzed. In CL1-5-F4 cells, low mRNA and protein expression of LOC51321 were associated with the promoter hypermethylation, as determined by RT-PCR, western blotting and methylation-specific PCR assays. In addition, treatment with 5-Aza-deoxycytosine successfully restored mRNA expression by de-methylating the putative promoter region in CL1-5-F4 cells that lacked LOC51321 expression, but did harbor the relevant methylated promoter. These findings indicate that LOC51321 may be involved in lung tumorigenesis.