VIRAL-PROTEINS OF BOVINE PAPILLOMAVIRUS TYPE-4 DURING THE DEVELOPMENTOF ALIMENTARY CANAL TUMORS

In cattle infection of the upper alimentary canal mucosa by bovine pap illomavirus type 4 (BPV-4) results in the development of papillomas wh ich can progress to cancer in animals fed on bracken fern. This paper describes a study of the cellular and subcellular distribution of a nu mber of different BPV-4 products in experimentally-induced BPV-4 tumou rs. E8 and E4 proteins were detected solely as cytoplasmic antigens in the undifferentiated and differentiated layers of the papilloma, resp ectively; L2 was detected solely as a nuclear antigen in the different iated layers, whereas E7 was present in either the nucleus or the cyto plasm depending on the differentiation stage of the keratinocyte. Repl icative forms of viral DNA were detected from the spinous to the squam ous layers. Viral antigens were not detected during papilloma regressi on or in carcinomas. E8 was most prominent in early developmental stag es, while E4 and L2 were most abundant in mature papillomas, E7 was pr esent in large amounts in both early and mature stages, declining at l ater stages. These results suggest a temporal and spatial requirement for the expression and function of the viral proteins.