Molecular Interactions Involved in the Transactivation of the Human T-Cell Leukemia Virus Type 1 Promoter Mediated by Tax and CREB-2 (ATF-4)

Abstract

The human T-cell leukemia virus type 1 (HTLV-1) Tax protein activates viral transcription through three 21-bp repeats located in the U3 region of the HTLV-1 long terminal repeat and called Tax-responsive elements (TxREs). Each TxRE contains nucleotide sequences corresponding to imperfect cyclic AMP response elements (CRE). In this study, we demonstrate that the bZIP transcriptional factor CREB-2 is able to bind in vitro to the TxREs and that CREB-2 binding to each of the 21-bp motifs is enhanced by Tax. We also demonstrate that Tax can weakly interact with CREB-2 bound to a cellular palindromic CRE motif such as that found in the somatostatin promoter. Mutagenesis of Tax and CREB-2 demonstrates that both N- and C-terminal domains of Tax and the C-terminal region of CREB-2 are required for direct interaction between the two proteins. In addition, the Tax mutant M47, defective for HTLV-1 activation, is unable to form in vitro a ternary complex with CREB-2 and TxRE. In agreement with recent results suggesting that Tax can recruit the coactivator CREB-binding protein (CBP) on the HTLV-1 promoter, we provide evidence that Tax, CREB-2, and CBP are capable of cooperating to stimulate viral transcription. Taken together, our data highlight the major role played by CREB-2 in Tax-mediated transactivation.

ACKNOWLEDGMENTS

This work was supported by institutional grants from the Centre National de la Recherche Scientifique (CNRS) and a grant to J.-M.M. from the Association pour la Recherche sur le Cancer (ARC no. 9515). A.P., F.G., and S.T. are fellows of, respectively, the Fondation pour la Recherche Médicale (FRM), the Ministère de l'Education Nationale, de la Recherche et de la Technologie (MENRT), and the CNRS (Bourse Docteur Ingénieur).

We thank W. C. Greene for the kind gift of the mutants Tax M22 and M47, C.-Z. Giam for pCMV-K88A, J. M. Leiden for pCDM7-CREB-2_262-351, R. H. Goodman for GST-KIX and pRSV-CBP, and J. Nyborg for the plasmids pminLUC-viral TxRE, pminLUC-cellular CRE, and pRSV-KIX. Anti-Tax was obtained through the AIDS Research and Reference Reagent Program, Division of AIDS, NIAID, NIH. HTLV-1 Tax hybridoma 168A51-42 (Tab176) was from B. Langton.