TRANSACTIVATION OF THE P2 PROMOTER OF PARATHYROID HORMONE-RELATED PROTEIN BY HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-I TAX1 - EVIDENCE FOR THEINVOLVEMENT OF TRANSCRIPTION FACTOR ETS1

Expression of the parathyroid hormone-related protein (PTHrP), a prote in that plays a primary role in the development of the humoral hyperca lcemia of malignancy, is regulated by two distinct promoters, P1 and P 2. PTHrP is overexpressed in lymphocytes from adult T-cell leukemia pa tients. We now demonstrate that in the human T-cell lymphotropic virus type I-transformed cell line MT-2, RNA synthesis is initiated primari ly at the P2 promoter. Furthermore, in cotransfection experiments, Tax 1 transactivates the P2 promoter 10- to 12-fold. By using deletion and site-specific point mutations, we have identified a promoter-proximal sequence (positions -72 to -40) which is important for Tax1 transacti vation. The PTHrP promoter-proximal element contains two potential ove rlapping Ets1 binding sites, EBS I and EBS II. Gel shift analysis demo nstrated that Ets1 binds specifically to both EBS I and EBS II. Mutati on of the consensus GGAA core motif in EBS I abolished binding and Tax 1 transactivation in Jurkat lymphocytes. In Ets1-deficient cells, cotr ansfection of Tax, and Ets1 expression plasmids stimulates PTHrP promo ter activity. In the absence of Ets1, minimal transactivation of the P THrP promoter is observed. These data suggest that Ets1 binds to EBS I and cooperates with Tax, to transactivate the PTHrP P2 promoter.