Role of Clara Cells and Type II Cells in the Development of Pulmonary Tumors in Rats and Mice Following Exposure to a Tobacco-Specific Nitrosamine

Abstract

The role of the Clara and type II cell in the development of pulmonary tumors in the A/J mouse and Fischer rat was investigated by determining the relationship of DNA methylation and repair in pulmonary cells to oncogene activation and by characterizing the morphology of pulmonary tumors induced by treatment with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Marked differences in the formation of the promutagenic adduct O6-methylguanine (O6MG) were observed in pulmonary cells following treatment of rats with NNK. Concentrations of this adduct in Clara cells greatly exceeded (3- to 30-fold) those detected in type II cells and whole lung with doses of NNK ranging from 0.1 to 50 mg/kg. In addition, very low rates of repair of this adduct were detected in Clara cells, whereas efficient adduct removal occurred in type II cells. The importance of this adduct and the role of cell specificity was suggested by the fact that a strong correlation was observed between the concentration of O6MG in Clara cells and tumor incidence in the Fischer rat with doses of NNK ranging from 0.03-50 mg/kg. In contrast, no differences in adduct concentration between type II and Clara cells from A/J mice were observed under conditions resulting in pulmonary tumor formation. Activation of the K-ras gene was detected in lung tumors from A/J mice. This gene was activated by a mutation in codon 12 involving a GC to AT transition (GGT to GAT) and is consistent with base mispairing produced by the formation of O6MG. Activation of this gene was not associated with lung tumor formation in the Fischer rat. DNA from rat lung tumors did induce tumors in the nude mouse carcinogenicity assay. In addition, rat repetitive sequences were detected in DNA isolated from these nude mouse tumors. In spite of the cell selectivity for DNA methylation in Clara cells from rat and the relationship between O6MG formation and tumorigenicity, early proliferative lesions observed in both mice and rats involved the alveolar areas. Ultrastructural examination of these lesions and adenomas revealed morphologic features characteristic of the type II cell. Thus the lack of agreement between biochemical and morphological findings makes it difficult to hypothesize a cell of origin for the pulmonary neoplasms induced by NNK. However, these studies indicate that the concentration of O6MG in Clara cells is an excellent indicator of the carcinogenic potency of NNK in the rat.(ABSTRACT TRUNCATED AT 400 WORDS)

Roles of the Pas1 and Par2 genes in determination of the unique, intermediate susceptibility of BALB/cByJ mice to urethane-induction of lung carcinogenesis: Differential effects on tumor multiplicity, size and Kras2 mutations

“…Although the Hras1 mutation frequency of mouse liver tumors has been reported to positively correlate with genetic susceptibility to hepatocarcinogenesis (Dragani et al, 1991b;Buchmann et al, 1991), this is not necessarily the case for Kras2 in lung carcinogenesis. For example, it has been shown that almost all dimethylnitrosamine (DMN) or 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumors developing in C3H as well as A/J mice possess an activated Kras2 with a speci®c G to A transition at the second position of codon 12 (Belinsky et al, 1989;Devereux et al, 1991;Chen et al, 1993;Matzinger et al, 1994). This appears to be in contradiction with our data.…”

“…Activating point mutations of the Kras2 gene are commonly seen in both mouse (Belinsky et al, 1989;You et al, 1989) and human (Suzuki et al, 1990) lung tumors. In fact, a series of studies by You and his coworkers has provided evidence that the two genes, Pas1 and Kras2 could be identical.…”

p53 polymorphisms associated with mutations in and loss of heterozygosity of the p53 gene in male oral squamous cell carcinomas in Taiwan

“…The most prevalent types of p53 mutation found in Taiwanese OSCCs were G:C to A:T transitions and G:C to T:A transversions. Studies have demonstrated that these types of mutations are the most common mutations observed in animals treated with NNK or other tobacco nitrosamines (Belinsky et al, 1991;Oreffo et al, 1993;Ronai et al, 1993;Chang et al, 1996). Evidence from the literature also indicates that NNK-associated DNA adducts, in addition to being repaired by the nucleotide excision repair pathway, are also repaired by base excision repair (Cloutier and Castonguay, 1998).…”

Mice defective in the DNA mismatch gene PMS2 are hypersensitive to MNU induced thymic lymphoma and are partially protected by transgenic expression of human MGMT

“…Unless repaired, O 6 -mG preferentially pairs with thymine (T) instead of cytosine (C) during DNA replication, resulting in a G:C to A:T transition mutation. Some of these mutations may result in activation of proto-oncogenes and cause malignant transformation, since G:C to A:T transition mutations have typically been detected at the second guanine of codon 12 (GGT) of the K-ras or Hras oncogenes in rodent tumors induced by N-nitroso carcinogens (Belinsky et al, 1989;Sakumar et al, 1983;Wang et al, 1990). Carcinogenic N-alkyl-N-nitrosoureas are known to induce tumors preferentially in tissues with low AGT activity (Gerson et al, 1986;Thomale et al, 1990), indicating that repair of O 6 -alkylguanine protects cell from malignant conversion.…”

“…For K-ras mutation analysis, activating G to A point mutations in codon 12 of K-ras, the most common site of activated ras mutations in this model system (Belinsky et al, 1989;Sakumar et al, 1983;Wang et al, 1990), were investigated using PCR-RFLP as previously described (Zaidi et al, 1995). A modi®cation was introduced by changing a primer for the second PCR ampli®cation, which makes the G to A point mutation at the second position in codon 12 of K-ras recognized by the restriction enzyme, Fok-I, as shown in Figure 4.…”