Genetic mapping of cancer susceptibility/resistance loci in the mouse

Association of KRAS polymorphisms with risk for lung adenocarcinoma accompanied by atypical adenomatous hyperplasias

The pulmonary adenoma susceptibility 1 (Pas1) gene affects susceptibility to the development of lung adenomas in mice with a subset of the adenomas progressing to adenocarcinoma (ADC). In this study, genotype distributions for 10 polymorphisms in the human counterparts for three mouse candidate Pas1 genes, KRAS, CASC1/LAS1 and LRMP, were examined in a hospital-based case-control study consisting of 364 lung ADC cases and 253 controls. All the ADC cases were subjected to lobectomy and subsequent pathological investigation of atypical adenomatous hyperplasia (AAH), a putative precursor for peripheral lung ADC, including bronchioloalveolar carcinoma, in the resected lobes. Eighty-one (22%) of the ADC cases carried at least one AAH lesion in addition to the primary ADC and 34 (9%) of them carried multiple AAH lesions. None of the 10 polymorphisms examined showed significant associations with overall lung ADC risk (P > 0.05). However, minor allele carriers for two polymorphisms in the KRAS gene, KRAS-1 and -6, showed significantly increased odds ratios (ORs) for ADC accompanied by multiple AAHs [OR = 3.0; 95% confidence interval (CI) = 1.4-6.2, P = 0.004 and OR = 2.4; 95% CI = 1.1-4.7, P = 0.02, respectively]. Minor haplotypes including the minor allele for the KRAS-6 polymorphism showed increased ORs for ADC accompanied by multiple AAHs, and KRAS transcripts from the minor allele for this polymorphism were more abundantly detected in lung tissues than those from the major allele. Thus, KRAS polymorphisms were indicated to be involved in risk for the development of AAHs that progress to ADC by causing differential KRAS oncogene expression in the lungs.

Five quantitative trait loci affecting 4-nitroquinoline 1-oxide-induced tongue cancer in the rat

In our previous study, Dark-Agouti (DA) rats were found to be highly susceptible to 4-nitroquinoline 1-oxide (4NQO)-induced tongue carcinoma (TC), whereas Wistar / Furth (WF) rats were barely susceptible. Interval mapping analysis of reciprocal backcross rats showed two quantitative trait loci (QTL) on rat chromosomes (RNO) 1 and 19. In the present study, a composite interval mapping analysis was applied to 4NQO-induced TC in 130 (DA x WF) F2 rats, demonstrating five independent QTL, Tongue squamous cell carcinoma 1 - 5 (Tscc1 - 5), responsible for phenotypic differences in the size and number of TCs in the two strains. Two of these QTL were mapped on RNO1, and the others were mapped on RNO4, 14, and 19. The DA allele at these loci consistently yielded semidominant susceptibility to TC. Out of the five loci detected in this F2 generation, Tscc1 and 2 were identical to Stc1 and Rtc1 described in our previous study, but the other three were novel. We propose a new nomenclature consistent with their function. Genome-wide screening of the F2 progeny also suggested the presence of three additional QTL on RNO5, 6, and 10. The possible roles of these loci in tongue carcinogenesis are discussed.

Predisposition to lung tumorigenesis

Mouse inbred strains with inherited predisposition and resistance to lung cancer provide an essential tool for the dissection of the genetics of this complex disease. We have previously mapped a major locus (Pulmonary adenoma susceptibility 1, Pas1) affecting inherited predisposition to lung cancer in mice on chromosome 6, near Kras2. Appropriate crosses that include susceptible mice (Pas1(s)) provide a model system for identifying loci that can modify the lung cancer predisposition phenotype caused by Pas1. Using this approach we have mapped the Pulmonary adenoma resistance 1 (Par1) locus that behaves like a modifier locus of Pas1. More recently, we mapped additional lung tumor resistance loci (Par2, and Par4), and a locus specifically involved with lung tumor progression (Papg1). The mapping of Pas1 in mice stimulated us to test the possible association of genetic markers located in the homologous human region (12p12) with risk and prognosis of lung adenocarcinomas in man. In the Italian population, we carried out an association study by genotyping lung adenocarcinoma patients and healthy controls for genetic markers located in the putative region of interest. Homozygosity of the A2 allele at a Kras2/RsaI polymorphism, and allele 2 at a VNTR polymorphism in the PTHLH gene showed borderline statistically significant associations with lung cancer risk. Furthermore, the same alleles were significantly associated with tumor prognosis. Studies on association were then performed in the Japanese and in European populations. In the Japanese population, the KRAS2/RsaI marker was significantly associated with prognosis of lung adenocarcinoma, whereas the European study did not confirm this association. Our results may provide evidence for the existence of the human PAS1 locus, suggesting that the mouse model of inherited predisposition to lung tumorigenesis is predictive of a human genetic mechanism of susceptibility to lung cancer.