Transcriptional activation of human TR3/nur77 gene expression by human T-lymphotropic virus type I Tax protein through two AP-1-like elements

The Tax transactivator of human T-lymphotropic virus type I (HTLV-I) is cap able of inducing expression of the human immediate-early TR3/nur77 gene. De letion and mutation analyses of the TR3/nur77 promoter demonstrated that mu ltiple transcription elements in the 121 bp sequence proximal to the transc ription start site are required for full Tax transactivation. Mutations of CArG-like, Ets and RCE motifs in this region severely decreased Tax transac tivation. Mutation of either of the two identical AP-1-like elements (NAP 1 and 2) immediately upstream of the TATA box caused around 80% reduction of Tax transactivation. Mutation of both NAP elements blocked Tax-mediated ac tivation totally. These two NAP elements could confer Tax-responsiveness on a heterologous basal promoter. Furthermore, the specific NAP-binding compl ex was only observed in HTLV-1-infected cells. Formation of this specific N AP-binding complex was correlated directly with Tax expression, as demonstr ated in JPX-9 cells upon induction of Tax expression. The specific NAP bind ing could be competed for by consensus AP-1 and CREB elements, indicating t hat the NAP-binding proteins probably belong to the AP-1 and CREB/ATF trans cription factor families. Supershift analysis with antibodies to both the A P-1 and CREB/ATF transcription factor families revealed that only anti-JunD antibody could partially shift this NAP-binding complex, indicating that J unD is a component of the NAP complex. This work suggests that JunD is invo lved in Tax-regulated TR3/nur77 expression.