Tumor Suppressor Gene On Chromosome 11

In an analysis of 79 nonsmall cell lung carcinomas, Iizuka et al. (1995) identified a 5-cM region on chromosome 11q23 that is commonly deleted. In addition to this identification by loss of heterozygosity (LOH), the presence of a tumor suppressor gene on 11q in NSCLCs was also demonstrated by use of a functional assay. A549, a human NSCLC-derived cell line, shows complete loss of one copy of chromosome 11. When a chromosome 11 from a non-NSCLC cell line was introduced into A549 cells by microcell-mediated chromosome transfer, the transformed phenotype was lost as measured by several growth parameters and suppression of tumorigenicity in nude mice (Satoh et al., 1993). Although this assay clearly implicated chromosome 11, it did not provide the information on the precise chromosomal localization of the tumor suppressor gene. LOH had indicated the location as 11q23. Murakami et al. (1998) modified 3 YAC clones spanning the minimal loss of heterozygosity region, and used spheroplast fusion to transfer them into human A549 NSCLC or murine Lewis lung cancer (LLC) cell lines. Injection of parental A549 cells into athymic (nu/nu) mice resulted in tumor formation in 27 of 28 injection sites. In contrast, 2 independent cell lines containing the DNA segment from 11q23 formed tumors at only 3 of 20 injection sites. Cells containing the same transferred segment also suppressed tumor formation by LLC NSCLC cells in nude mice. Further localization of tumor suppression activity was accomplished by introduction of defined fragmentation derivatives into A549 cells and by analysis of YACs that were broken on transfer into LLC cells. The complementation approach localized tumor suppression activity to the central 700 kb of the critical clone and provided a functional assay for positional cloning of this tumor suppressor gene.