Co-expression of bovine papillomavirus E5 and E7 oncoproteins in naturally occurring carcinomas of the urinary bladder in cattle.

The aetiopathogenesis of urinary bladder tumours in cattle involves prolonged ingestion of bracken fern and infection by bovine papillomavirus (BPV). The aim of the present study was to determine whether there was co-expression of BPV oncoproteins E5 and E7 in such urothelial carcinomas. Fifteen samples were shown by immunohistochemistry to express E7 with labelling of both the cytoplasm and nucleus, in addition to labelling of the urothelial cell membrane. Three of these samples were subsequently investigated by dual-labelling immunofluorescence and co-expression of E5 and E7 was demonstrated. This is the first report of co-expression of these two oncoproteins in bovine urinary bladder carcinomas. The results suggest that the E7 oncogene has a role in urothelial carcinogenesis.