Subtractive screening of genes involved in cellular senescence

We attempted to identify the genes involved in cellular senescence, telomere maintenance and telomerase regulation through subtractive screening of cDNA libraries prepared from a human lung adenocarcinoma cell line A549 and its sublines named A5DC7, CK and AST-9. Cell phenotypes of A5DC7, CK and AST-9 are normal cell-like, cancer cell-like and intermediate, respectively. These cell lines have different phenotypes in terms of telomerase activity and telomere maintenance, and thus are thought to be useful for identifying the genes involved in cellular senescence and telomerase regulation. In this study, we identified 86 independent cDNA clones by subtractive screening. Among these cDNA clones, subtracting A5DC7 cDNAs from A549 cDNAs and CK cDNAs gave 7 and 3 cDNA clones which highly and specifically expressed in tester cell lines. Genes corresponding to these 10 cDNA clones might participate in maintaining cancer-cell phenotypes. As a result of database searching, each four of A549 specific cDNA clones are found to correspond to known cDNAs. Each two of A549 specific and two of CK specific cDNA clones have high homology to independent ESTs. Sequences having homology to each one of A549 specific and one of CK specific cDNA clones have not been deposited in the Genbank database, indicating that these two cDNA clones are part of novel genes. We anticipate that their involvement in telomerase regulation and/or senescence program can be clarified by functional analysis using each full-length cDNA.