The development of human cancer proceeds in a multistep fashion involving both the loss of tumor suppressor gene function and the activation of oncogenes. While greater than one hundred oncogenes have been identified, only a modest number of tumor suppressor genes have been isolated. The discovery of most tumor suppressor genes has relied on the knowledge of their physical location on a particular chromosome; few functional assays for these genes exist. We have used the technique of microcell hybridization to map the location of tumor suppressor genes for adult and pediatric cancers. Demonstration of tumor suppression by transferring a single normal human chromosome into a human tumor cell line maps tumor suppressor gene(s) to that genetic unit. This method provides a powerful tool for identifying these genes in malignancies where extensive chromosome rearrangements and deletions mask their locale. Using this approach, we have mapped a functional tumor suppressor gene for a human squamous cell carcinoma (SCC) cell line to chromosome 11. By using a translocated chromosome T(X;11), we have localized the gene to the region between 11q13 to 11qter. We and others have also demonstrated tumor suppressor gene activity for renal cell carcinoma, lung carcinoma and cervical carcinoma on this same chromosome. Thus, our results may indicate that many types of epithelial malignancies result from the inactivation of the same tumor suppressor gene. In this grant application, we plan to localize the side of the tumor suppressor information to an approximately 1 mb region on chromosome 11. A. We have switched to the use of an in vitro raft assay which significantly decreases the time required for determination of tumor suppressor gene activity. B. We will begin to identify candidate tumor suppressor genes from this region. The availability of epidemiology data for these samples will allow us to gauge the relative importance of this tumor suppressor gene in the process of squamous cell carcinoma development. Squamous cell carcinomas appear to develop from a complex interaction of genetic, epigenetic and environmental factors. Exposure of environmental agents including alcohol, tobacco and food carcinogens may especially impact the development of oral squamous cell carcinomas. Identification and characterization of tumor suppressor genes affected by these events will allow investigators to determine the relative importance of each of them in the process of carcinogenesis. Recent reports linking other tumor suppressor genes with a genetic susceptibility to cancer emphasize the importance of these proposed studies.
