Benzo[a]pyrene-induced murine skin tumors exhibit frequent and characteristic G to T mutations in the p53 gene.

Abstract

Human tobacco-related cancers exhibit a high frequency of G to T transversions in the mutation hot spot region of the p53 tumor suppressor gene, possibly the result of specific mutagens in tobacco smoke, most notably benzo [a] An increasing body of molecular epidemiological evidence suggests that regions ofthe p53 gene may be a selective target of environmental carcinogens etiologically associated with specific human cancers (4-19). In this context, a high frequency of G to T transversions in the mutation hot spot regions of the p53 gene (2, 3) have been identified in human hepatocellular carcinomas and strongly correlated with the mutagenic effects of dietary aflatoxin B1 exposurf (4,(13)(14)(15).Similarly, UV-B-specific dipyrimidine G to T transitions in the p53 gene have been characterized in human squamous cell carcinomas of the skin (16,17). Unique mutations in p53 have likewise been reported in radon-associated lung cancers (18) and in human epithelial cells exposed to nickel(II) in vitro (19), providing evidence for an important molecular target for the genotoxic effects of these agents. Of particular clinical and epidemiological interest are the observations of a high frequency of G to T transversions among p53 mutations in tobacco-related human neoplasias, including small-cell and non-small-cell lung cancers (5-8), esophageal carcinomas (10-12), and squamous cell carcinomas of the head and neck (9). In several ofthese studies, the presence of p53 mutations in tumors was strongly correlated with lifetime cigarette consumption (7) or a history of heavy smoking (9).It has been suggested (4-12) that the frequent G to T transversion in the p53 gene in tobacco-related cancers may be associated with specific mutagens in tobacco smoke, most notably activated benzo [a] We have previously investigated the role of p53 alterations in the development and progression of the two-stage mouse skin tumorigenesis model induced by 7,12-dimethylbenz- (24) following hematoxylin/eosin staining. Primary explant cultures of skin tumors were prepared as described (22). Papillomas harvested for analyses were subjected to 35-38 weeks of B[a]P treatment, while carcinomas analyzed were subjected to 50 weeks of carcinogen exposure. In the complete carcinogenesis protocol with DMBA, papillomas and carcinomas used in molecular analyses were obtained from mice subjected to 34-52 weeks of carcinogen exposure. The two-stage carcinogenesis protocol using DMBA as initiator has been described (22

Induction of Invasive Mouse Skin Carcinomas in Transgenic Mice with Mutations in Both H-ras and p53

“…The majority of the skin tumors found in wild-type (p53 wt/wt Hras wt/wt ) mice were papillomas or well-differentiated SCCs, consistent with numerous previous studies (6,19). As shown in Fig.…”

“…Inactivation of several tumor suppressor genes, including p53, p15, and p16, occurs principally in late-stage tumors, such as SCCs (p53) or spindle carcinomas (p15 and p16). p53 mutations have been detected in both chemically induced and UV-induced mouse skin tumors (6,7). Loss of heterozygosity studies have been conducted to identify the regions of frequent allele loss in skin tumors of various F 1 hybrid mouse strains to localize important tumor suppressor genes (8).…”

NAD(P)H:quinone oxidoreductase 1 reduces the mutagenicity of DNA caused by NADPH:P450 reductase-activated metabolites of benzo(a)pyrene quinones

“…While BPDE resulted almost exclusively in basepair substitution mutations, BP-3,6-Q and its reductive metabolites caused both frameshift mutations, in particular deletions and base substitutions. BPDE-induced G:C -+ T:A transversions and the identification of a mutational hot spot at GI 15 of the supF tRNA gene were in agreement with previous reports (Rodriguez and Leochler, 1993;Ruggeri et al, 1993). Figure 4 Model for benzo(a)pyrene quinones mutagenicity and carcinogenicity.…”

Frequent expression of new cancer/testis gene D40/AF15q14 in lung cancers of smokers

“…Tobacco smoke contains a mixture of highly mutagenic chemicals, such as benzo(a)pyrene and 4-methylnitrosoamine-1-(3-pyridyl)-1-butanone. Benzo(a)pyrene induces point mutations such as G to T transversion (Ruggeri et al, 1993) and forms DNA adducts at the major mutational hot spots of the p53 gene in lung cancer (Denissenko et al, 1996). The mutagen 4-methylnitrosoamine-1-(3-pyridyl)-1-butanone causes epigenetic alterations of the genome through the modification of DNA methyltransferase activity (Belinsky et al, 1996).…”