HORMONE REGULATION OF BOVINE LEUKEMIA-VIRUS VIA THE LONG TERMINAL REPEAT

The hormone regulation of viruses has been of great interest since the discovery of glucocorticoid stimulation of mouse mammary tumor virus via a hormone response element in the viral long terminal repeat (LTR) promoter region. This report describes the investigation of the hormo ne responsiveness of bovine leukemia virus (BLV), an oncogenic retrovi rus that infects dairy and beef cattle worldwide. It is a member of th e human T cell leukemia (HTLV)/BLV group of retroviruses, which encode a protein, Tax, that is essential for regulating transcription of the ir own proviruses and for transforming host cells. We investigated the responsiveness of BLV to the hormones 17 beta-estradiol, progesterone , prolactin, insulin, and dexamethasone, a potent glucocorticoid. Only dexamethasone, in combination with insulin or insulin/prolactin, cons istently stimulated BLV expression, as measured by reverse transcripta se activity, RNA blot hybridization (Northern blots), and CAT (chloram phenicol acetyltransferase) reporter assays of cell lines transiently or stably transfected with the BLV LTR. This effect required the prese nce of glucocorticoid receptors and Tax. This is the first report of h ormone responsiveness in a virus of the HTLV/BLV group. (C) 1997 Acade mic Press.