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Role of Oncogenes and Tumor Suppressor Genes in Multistage Carcinogenesis

1994; Elsevier BV; Volume: 103; Issue: 5 Linguagem: Inglês

10.1038/jid.1994.16

1523-1747

Stuart H. Yuspa, Andrzej A. Dlugosz, Christina Cheng, Mitchell F. Denning, Tamar Tennenbaum, Adam B. Glick, Wendy C. Weinberg,

Cancer and Skin Lesions

The introduction of the techniques of molecular biology as tools to study skin carcinogenesis has provided more precise localization of biochemical pathways that regulate the tumor phenotype. This approach has identified genetic changes that are characteristic of each of the specific stages of squamous cancer pathogenesis: initiation, exogenous promotion, premalig-nant progression, and malignant conversion. Initiation can result from mutations in a single gene, and the Harvey allele of the ras gene family has been identified as a frequent site for initiating mutations. Heterozygous activating mutations in c-ras H2 are dominant, and affected keratinocytes hyperproliferate and are resistant to signals for terminal differentiation. An important pathway impacted by c-ras H2 activation is the protein kinase C (PKC) path-way, a major regulator of keratinocyte differentiation. Increased activity of PKCα and suppression of PKC δ by tyrosine phospho-rylation contribute to the phenotypic consequences of ras H2 gene activation in keratinocytes. Tumor promoters disturb epidermal homeostasis and cause selective clonal expansion of initiated cells to produce multiple benign squamous papillomas. Resistance to differentiation and enhanced growth rate of initiated cells impart a growth advantage when the epidermis is exposed to promoters. The frequency of premalignant progression varies among papillomas, and subpopulations at high risk for progression have been identified. These high-risk papillomas overexpress the α 6 β 4 integrin and are deficient in transforming growth factor β 1 and β 2 peptides, two changes associated with a very high proliferation rate in this subset of tumors. The introduction of an oncogenic ras H2 gene into epidermal cells derived from transgenic mice with a null mutation in the TGF β 1 gene have an accelerated rate of malignant progression when examined in vivo . Thus members of the TGF β gene family contribute a tumor-suppressor function in carcinogenesis. Accelerated malignant progression is also found with v- ras H2 transduced keratinocytes from skin of mice with a null mutation in the p53 gene. The similarities in risk for malignant conversion by initiated keratinocytes from TG β 1 and p53 null geneotypes suggest that a common, growth-related pathway may underly the tumor-suppressive functions of these proteins in the skin carcinogenesis model. J Invest Dermatol 103:90S-95S, 1994