Copyright ©) 1994, American Society for Microbiology Involvement of the Cyclic AMP-Responsive Element Binding Protein in Bovine Leukemia Virus Expression In Vivo

The TAR element (Tax-responsive element; also called TxRE) is a major determinant of the regulation of bovine leukemia virus (BLV) expression. In order to gain insight into the mechanisms of viral expression, complexes formed between proteins and the TAR enhancer DNA were analyzed by gel retardation assays. We report here that nuclear lysates from ex vivo-isolated B lymphocytes contain proteins that specifically bind to TAR. An antibody directed toward the cyclic AMP-responsive element binding (CREB) protein supershifted a complex (Cl) present only in BLV-infected B lymphocytes. The CREB protein thus appears to be a major transcription factor involved in BLV expression in vivo. Bovine leukemia virus (BLV) is a naturally occurring, exog-enous, oncogenic retrovirus associated with persistent lympho-cytosis (PL) and lymphosarcoma in cattle (6, 11, 32). PL is characterized by a marked increase in the percentage of BLV-infected B lymphocytes in the blood (22). On the basis of studies of well-characterized cattle populations, less than 10% of BLV-infected cattle develop lymphosarcoma and about 30 % develop PL (13). Thus, a large majority of BLV-infecte