Establishment and characterization of a rat lung adenocarcinoma cell line with low malignant potential

Multi-step lung carcinogenesis model induced by oral administration of N-nitrosobis(2-hydroxypropyl)amine in rats

N-Nitrosobis(2-hydroxypropyl)amine (BHP) was first synthesized by Krüger et al. (1974), and has been shown to primarily induce pancreatic duct adenocarcinomas by a subcutaneous injection in Syrian hamsters. By contrast, the carcinogenic effect of BHP has been indicated at the different target organs in rats, namely the lung. When rats are received by an oral administration of BHP in drinking water for 25 weeks, a high incidence of lung carcinomas are induced, which include adenocarcinomas, squamous cell carcinomas and combined squamous cell and adenocarcinomas. So many similarities are observed in terms of not only histological appearances but also gene alterations between human and BHP-induced rat lung cancers. Moreover, the step by step development of lung lesions, from preneoplastic lesions to cancers in rat lung carcinogenesis by BHP offers a good model to investigate the mechanisms underlying the pathogenesis of lung cancers. Because data for genetic and epigenetic alterations have indeed been accumulated during the BHP-induced rat lung carcinogenesis, we will introduce them in this review and hence demonstrate that this lung carcinogenesis model provides a useful opportunity for the research on the pathogenesis of lung cancers of both humans and rats.

Loss of lysophosphatidic acid receptor-3 enhances cell migration in rat lung tumor cells

Lysophosphatidic acid (LPA) indicates several biological effects, such as cell proliferation, differentiation and migration. LPA interacts with G protein-coupled transmembrane LPA receptors. In our previous report, we detected that loss of the LPA receptor-1 (Lpar1) expression is due to its aberrant DNA methylation in rat tumor cell lines. In this study, to assess an involvement of the other LPA receptor, Lpar3, in the pathogenesis of rat lung tumor cells, we measured the expression levels of the Lpar3 gene and its DNA methylation status by reverse transcription (RT)-polymerase chain reaction (PCR) and bisulfite sequencing analyses, respectively. RLCNR lung adenocarcinoma cells showed reduced expression of the Lpar3, compared with normal lung tissues. In the 5' upstream region of the Lpar3, normal lung tissues were unmethylated. By contrast, RLCNR cells were highly methylated, correlating with reduced expressions of the Lpar3. Based on these results, we generated the Lpar3-expressing RLCNR-a3 cells and measured the cell migration ability. Interestingly, the cell migration of RLCNR-a3 cells was significantly lower than that of RLCNR cells. This study suggests that loss of the Lpar3 due to aberrant DNA methylation may be involved in the progression of rat lung tumor cells.

Implication of p16 inactivation in tumorigenic activity of respiratory epithelial cell lines and adenocarcinoma cell line established from plutonium-induced lung tumor in rat

To investigate whether p16 inactivation is involved in the development of rat pulmonary tumors, we compared the p16 status and tumorigenicity of cell lines which indicated different p16 status. The tumor cell line (PuD2) was established from lung adenocarcinoma induced in plutonium dioxide-inhaled rat in this study. The virus-immortalized SV40T2 cells, benzo[a]pyrene-induced BP cells, BP-derived BP(P)Tu cells, and gamma ray-transformed RTiv3 cells were utilized as the respiratory epithelial cell lines. A tumorigenicity assay-inoculating cells into nude mice revealed that PuD2, BP, and BP(P)Tu cells were tumorigenic, but SV40T2 and RTiv3 cells were not. Methylation-specific PCR of the p16 promoter region revealed that SV40T2 cells were unmethylated, BP cells displayed heterogeneous methylation, and BP(P)Tu and RTiv3 cells were completely methylated. Methylation-specific PCR and PCR of genomic DNA in the p16 region did not amplify product in PuD2 cells, indicating deletion of p16. Banded karyotypes prepared from PuD2 cells exhibited trisomy of chromosome 4, inversion in chromosome 11, and partial deletion of chromosomes 4 and 5. The demethylating agent 5Aza2dC partially demethylated the p16 promoter region of BP(P)Tu, BP and RTiv3 cells, increasing expression of the p16 transcript and decreasing growth of the cells. These results indicate that hypermethylation of the p16 promoter region occurs early in neoplastic transformation before acquisition of tumorigenicity in rat respiratory epithelium. Loss of genes located on chromosomes 4 and 5 may be important for tumor progression and acquisition of high tumorigenic activity in the Pu-induced rat lung tumor.