Molecular alterations in squamous cell carcinomas of the skin : emphasis on genes on chromosome 9q

Abstract: Skin cancer is the most common type of cancer in the western world. The incidence of melanoma and non-melanoma skin cancer is continuously increasing and, in Sweden, 2300 new cases per year are diagnosed of squamous cell carcinoma (SCC) alone. In this thesis, we have investigated genes and proteins from signal transduction pathways important for tumor development. Special emphasis has been put on chromosomal region 9q22-q31 where frequent loss of heterozygosity has been observed in non-melanoma skin cancers.Mutation analysis of the PTCH1 and XPA genes, connected to the familial cancer syndromes nevoid basal cell carcinoma syndrome and xeroderma pigmentosum, respectively, was performed. Based on lack of mutation or altered mRNA expression, we conclude that these two genes are not likely to be involved in development of sporadic SCCs. Next, we studied the correlation of the two phenotypes, anchorage independence and tumorigenicity, to the loss of chromosome 9 material in a panel of somatic cell hybrids. By microsatellite analysis, we show that the anchorage independence gene is located distal to the marker D9S155. The mapping of the gene for tumor suppression revealed three commonly deleted regions on chromosome regions 9p23-p22, 9p21-p12 and 9q31-q33. Another two candidates from the 9q22-q31 region, CORO2A and TßR-I, were investigated both at the gene and the protein level. We did not detect any alterations in the TßR-I gene or protein, but CORO2A protein was over-expressed in 4 of 40 (10%) tumors, indicating an involvement in sec carcinogenesis in a subset of tumors. In one healthy individual from the control population, we found a heterozygous germline mutation in CORO2A creating a stop codon, which results in a truncated protein. Thus, one functional allele might be sufficient to sustain a normal cellular function. When investigating occurrence of aberrant protein expression in the interconnected Wnt and Notch pathways, Notch1 was found to be expressed in only 5 of 40 (14%) of the normal epidermal cells, while strong staining was displayed in all the tumors. No altered expression of the most central protein of the Wnt pathway, ß-catenin, was observed, but the up-stream Dvl-1 protein was found to be up-regulated in 8 of 38 (21%) tumors. Dvl-1 was also detected in the nucleus in the majority of normal and tumor cases and a potential nuclear localization signal was identified in the Dvl-1 A isoform.None of the genes from the chromosomal region 9q22-q31 displayed alterations consistent with those of a tumor suppressor gene. Most likely, this gene remains to be identified.