Cyclin D1 overexpression combined with N-nitrosomethylbenzylamine increases dysplasia and cellular proliferation in murine esophageal squamous epithelium

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Abstract
We previosuly described the oral-esophageal tissue-specific expression of cyclin D1 with the Epstein – Barr virus ED-L2 promoter in transgenic mice, and resulting dysplasia. Given the evidence for an interplay between environmental and genetic factors in esophageal squamous carcinogenesis, the aim of this study was to determine the potential cooperation of the nitrosamine compound N-nitrosomethylbenzylamine (NMBA), an esophageal specific carcinogen, in the cyclin D1 transgenic mice. NMBA was first demonstrated to induce dysplasia in two strains of inbred mice, C57BL/6 and FVB/N. Subcutaneous NMBA was then administrated to wild type and transgenic mice beginning at 4 weeks of age. Mice were monitered for the duration of the study for general appearance, activity and weight, and were euthanized at 12 and 15 months. Histopathologic analysis revealed increased severity of dysplasia in cyclin D1 mice treated with NMBA compared with treated age-matched wild-type mice and untreated mice. There was also increased proliferating cell nuclear antigen (PCNA) expression in the esophagi of NMBA treated cyclin D1 mice. Taken together, these findings suggest that a genetic alteration, specifically cyclin D1 overexpression and a chemical carinogen, NMBA, may cooperate to increase the severity of esophageal squamous dysplasia, a prominent precursor to carcinoma.

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