title: Induction of thymomas by N-methyl-N-nitrosourea in AKR mice: interaction between the chemical carcinogen and endogenous murine leukaemia viruses.
abstract: AKR mice develop thymomas spontaneously when greater than 6 months old but when young AKR mice are treated with N-methyl-N-nitrosourea (MNU) they develop thymomas at 3-6 months of age. In this study the potential role of oncogene activation in the development of both the spontaneous and MNU-induced thymomas in AKR mice has been examined by DNA transfection into NIH3T3 mouse fibroblasts and by Southern analysis of tumour DNA. The results show that a high proportion of MNU-induced thymomas contain activated cellular rasK while no activated cellular ras genes were detected in spontaneous thymomas. Southern analysis of tumour DNA revealed that 2/30 spontaneous tumours and 2/52 MNU-induced tumours contained alterations in the c-myc gene while 5/29 spontaneous tumours and 6/56 MNU-induced tumours contained alterations in the Pim-1 gene. A more detailed analysis of the Pim-1 gene demonstrated that the alterations observed in most MNU-induced and spontaneous tumours resulted from proviral integration at the 3' end of this gene. Our analyses also demonstrated that the majority of MNU-induced tumours, including those containing rearrangements in the Pim-1 gene, lacked the somatically acquired recombinant MCF proviruses that are present in most spontaneous AKR lymphomas. These results provide evidence that the mechanisms of development of MNU-induced and spontaneous tumours in AKR mice are distinct and the development of thymomas that contain proviral integrations at the Pim-1 locus in the MNU-treated AKR mice involve cooperation between the chemical carcinogen and endogenous murine leukaemia viruses.
mesh_terms: D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000187:drug effects; D002472:Cell Transformation, Viral / Q000187:drug effects; D003043:Cocarcinogenesis; D004262:DNA Restriction Enzymes / Q000378:metabolism; D007700:Kinetics; D009052:Leukemia Virus, Murine; D008770:Methylnitrosourea; D051379:Mice; D013945:Thymoma / Q000139:chemically induced*; D013953:Thymus Neoplasms / Q000139:chemically induced*; D014162:Transfection
chemical_list: D008770:Methylnitrosourea; D004262:DNA Restriction Enzymes