Quercetin induces structural chromosomal aberrations and uncommon rearrangements in bovine cells transformed by the E7 protein of bovine papillomavirus type 4 A. M. Leal 1 , O. P. Ferraz 1 , C. Carvalho 2 , A. C. Freitas 1 , R. G. Beniston 3 , W. Bec ¸ak 1 , M. S. Campo 3 and R. C. Stocco dos Santos 1 1 Laborato ´ rio de Gene ´tica, Instituto Butantan, Sa ˜o Paulo, Brazil 2 Departamento de Biologia, Universidade de Taubate ´, Taubate ´, Brazil 3 Institute of Comparative Medicine, Department of Veterinary Pathology, Glasgow University Veterinary School, Glasgow, UK Abstract Bovine papillomavirus type 4 (BPV-4) and bracken fern are cofactors in the carcinogenesis of the upper gastrointestinal (GI) tract of cattle. An experimental in vitro model system has been developed to analyse the co-operation between the viral transforming protein E7, the cellular ras oncogene and quercetin, one of the mutagens of bracken fern, during neoplastic progression of primary bovine cells. We now report cytogenetic studies of these cells at different stages of malignant transformation: parental primary non-transformed PalF cells; E7R cells transformed by BPV-4 E7 and activated ras but not tumorigenic, and tumorigenic E7Q cells derived from E7R cells after treatment with quercetin. All cell lines presented increased numbers of aneuploid cells. The rate of structural chromosomal aberrations observed was increased in transformed cells. In addition, E7Q cells showed chromosomes with peculiar rearrangements, which resulted in metacentric and submetacentric marker chromosomes, with an increase in the mean chromosome arm number. These markers were the products of possible centric fusions. These aberrations and rearrangements were distributed throughout the karyotype, no specific chromosome was involved and the het- erochromatic centromeric regions appeared to be preserved. Keywords cell transformation, chromosomal rearrangements, E7, papillomavirus, quercetin Introduction Bovine papillomavirus type 4 (BPV-4) and bracken fern (Pteridium aquilinum) in the pasture are cofactors in the carcinogenesis of the upper gastrointestinal (GI) tract of cattle (Jarrett et al., 1978; Campo et al., 1994). Bracken fern contains immunosuppressants that inhibit the ability of the animal to mount an immune response against the virus or the infected cells, and mutagens that induce damage to the cell DNA (Jackson et al., 1993). As a result of the immunosuppression, BPV-4 papillomas persist and expand, providing an enlarged target for the plant mutagens. The viral proteins induce unscheduled cell proliferation, thus expanding genetically damaged cells. The ª 2003 Blackwell Publishing Ltd 15 Correspondence address: M. S. Campo Institute of Comparative Medicine Department of Veterinary Pathology Glasgow University Veterinary School Glasgow G61 1QH UK e-mail: s.campo@vet.gla.ac.uk Original Article