In vitro aging of rat lung cells. Downregulation of telomerase activity and continuous decrease of telomere length are not incompatible with malignant transformation

Cytogenetic and molecular characterization of plutonium-induced rat osteosarcomas

The association between ionizing radiation and the subsequent development of osteosarcoma has been well described, but little is known about the cytogenetic and molecular events, which could be involved in the formation of radiation-induced osteosarcomas. Here, we performed comparative genomic hybridization (CGH) to detect chromosomal copy number changes in a series of 16 rat osteosarcomas induced by injection of plutonium-238. Recurrent gains/amplifications were observed at chromosomal regions 3p12-q12, 3q41-qter, 4q41-qter, 6q12-q16, 7q22-q34, 8q11-q23, 9q11-q22, 10q32.1-qter, and 12q, whereas recurrent losses were observed at 1p, 1q, 3q23-q35, 5q21-q33, 8q24-q31, 10q22-q25, 15p, 15q, and 18q. The gained region at 7q22-q34 was homologous to human chromosome bands 12q13-q15/8q24/22q11-q13, including the loci of Mdm2, Cdk4, c-Myc and Pdgf-b genes. The lost regions at 5q21-q33, 10q22-q25 and 15q contained tumor suppressor genes such as p16INK4a/p19ARF, Tp53 and Rb1. To identify potential target gene(s) for the chromosomal aberrations, we compared the expression levels of several candidate genes, located within the regions of frequent chromosomal aberrations, between the tumors and normal osteoblasts by using quantitative RT-PCR analysis. The Cdk4, c-Myc, Pdgf-b and p57KIP2 genes were thought to be possible target genes for the frequent chromosomal gain at 7q22-34 and loss at 1q in the tumors, respectively. In addition, mutations of the Tp53 gene were found in 27% (4 of 15) osteosarcomas. Our data may contribute to further understanding of the molecular mechanisms underlying osteosarcomas induced by ionizing radiation in human.

Molecular analysis of a multistep lung cancer model induced by chronic inflammation reveals epigenetic regulation of p16 and activation of the DNA damage response pathway

The molecular hallmarks of inflammation-mediated lung carcinogenesis have not been fully clarified, mainly due to the scarcity of appropriate animal models. We have used a silica-induced multistep lung carcinogenesis model driven by chronic inflammation to study the evolution of molecular markers and genetic alterations. We analyzed markers of DNA damage response (DDR), proliferative stress, and telomeric stress: gamma-H2AX, p16, p53, and TERT. Lung cancer-related epigenetic and genetic alterations, including promoter hypermethylation status of p16(CDKN2A), APC, CDH13, Rassf1, and Nore1A, as well as mutations of Tp53, epidermal growth factor receptor, K-ras, N-ras, and c-H-ras, have been also studied. Our results showed DDR pathway activation in preneoplastic lesions, in association with inducible nitric oxide synthase and p53 induction. p16 was also induced in early tumorigenic progression and was inactivated in bronchiolar dysplasias and tumors. Remarkably, lack of mutations of Ras and epidermal growth factor receptor, and a very low frequency of Tp53 mutations suggest that they are not required for tumorigenesis in this model. In contrast, epigenetic alterations in p16(CDKN2A), CDH13, and APC, but not in Rassf1 and Nore1A, were clearly observed. These data suggest the existence of a specific molecular signature of inflammation-driven lung carcinogenesis that shares some, but not all, of the molecular landmarks of chemically induced lung cancer.

Telomerase regulation and progressive telomere shortening of rat hepatic stem-like epithelial cells during in vitro aging

Rat hepatic stem-like epithelial cells, LE/2, LE/6, and WB-F344, share some phenotypic properties with oval cells, observed in the early stages of hepatocarcinogenesis. Here, we describe regulations of telomerase and telomere length during in vitro aging of LEs and WB-F344. These cells displayed no apparent aging phenotypes for over 140 passages. Telomerase activity and telomere length of these cells progressively decreased with the passages, and at the late passages, telomere shortening appeared to be reduced as telomerase activity increased. Regulation of TERT and TR, key components of telomerase, was similar to that of the telomerase activity. LEs possessed weak telomerase activity with a slow rate of proliferation compared to WB-F344, and were not tumorigenic, whereas WB-F344 was transformed in vitro from intermediate passage. In conclusion, LEs and WB-F344 have different biochemical properties, and telomerase activation and short telomeres are unlikely necessary for the transformation of WB-F344. TERT and TR seem to be the regulators of the telomerase activity. The relationship between telomere length and telomerase activity suggests that telomerase contributes to the regulation of telomere length in these cells. Our findings provide a better understanding of mechanisms in neoplastic transformation of rat hepatic stem-like epithelial cells.