Transcription factor AP-1 modulates the activity of the human foamy virus long terminal repeat.

The human foamy virus (HFV) contains within the U3 region of its long terminal repeat (LTR) three perfect consensus sequences for the binding of the inducible transcription factor AP-1. Results of DNase I footprint protection and gel retardation assays demonstrated that proteins in extracts of HeLa and BHK-21 cells as well as bacterially expressed Jun and Fos proteins bind to these AP-1 sites. By conducting transient expression assays using chloramphenicol acetyltransferase plasmids carrying LTR sequences with point-mutated AP-1 sites, it was found that the three AP-1 sites contribute to the optimal activity of the HFV promoter. It is shown that induction of the HFV LTR by 12-O-tetradecanoylphorbol-13-acetate (TPA) and serum factors is mediated through the AP-1 sites.