GENES INVOLVED IN PRENEOPLASTIC PROGRESSION

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The aim of this research is to identify and characterize two classes of genes involved in multistage carcinogenesis. The first class includes genes associated with susceptibility to tumor promoter-induced neoplastic transformation. The second class includes genes that specify expression of tumor cell phenotype. Mouse JB6 promotion-resistant (P-), promotion-sensitive (P+), and tumorigenic (Tx) JB6-derived epidermal cell lines have been found to differ in the expression of several genes described in the accompanying project ZOICPO5383-08 LVC, "Membrane Signal Transduction in Tumor Promotion." The changes in expression of these genes during the progression from P- to P+ to Tx phenotypes appear to be genetically controlled in these stable variant cell lines. We have recently discovered a stable change in a response to tumor promoters by a JB6-derived tumorigenic cell line. The change involves acquisition of a cell-killing response to activators of protein kinase C. The treated cells show the type of DNA damage that characterizes apoptosis (programmed cell death). A novel transformation-associated sequence unrelated to any known oncogene has been cloned from human nasopharyngeal carcinoma (NPC) cells by human Alu screening of an NPC/JB6 transfectant genomic library. A hybridizing mRNA of 1.7 Kilobase is observed in NPC cells but not in mouse recipient cells. A recently isolated NPC cDNA clone is being analyzed. In addition, two independent NPC cell lines show the same expressed mutation in one of the "hot spots" of the tumor suppressor gene, p53, thus appearing to activate it to an oncogene. Additional NPC samples from Taiwanese patients are being provided to us for examination of both the newly cloned NPC transformationassociated gene and the p53 gene for transformation-relevant mutations. Finally, we have learned that JB6 P+ cells can be transformed to a tumor phenotype by overexpression of activated v-H-ras, v-raf, or src, but not by any of several other oncogenes. The profiles of gene expression in these JB6/oncogene transfectant cell lines are being examined to increase our understanding of transformation pathways in the JB6_ model.