title: Human T-cell lymphotropic virus type I (HTLV-I) transcriptional activator, Tax, enhances CREB binding to HTLV-I 21-base-pair repeats by protein-protein interaction.
abstract: HTLV-I Tax protein activates transcription from three 21-base-pair (bp) repeat sequences in the viral enhancer. The HTLV-I 21-bp repeat contains a TGACGT motif that is homologous to the cAMP-responsive element (CRE) and crucial for tax transactivation. Tax exhibits marginal affinity for DNA but rather interacts with cellular CRE-binding proteins to enhance their affinity for the HTLV-I 21-bp repeats. Using the HTLV-I 21-bp repeat and Jurkat T-lymphocyte nuclear extract in a gel electrophoretic mobility-shift assay, we previously detected three protein-DNA complexes that are specific for the CRE in the 21-bp repeat (complexes I, II, and IV). Complexes I and II but not IV interacted with Tax. We now show that complexes I, II, and IV are composed of CREB (CRE binding protein) homodimer, CREB/ATF-1 (activating transcription factor 1) heterodimer, and ATF-1 homodimer, respectively. Tax stabilizes complexes I and II via a direct interaction with the CREB moiety. In the absence of DNA, CREB and Tax continue to form a complex that can be immunoprecipitated by a Tax-specific antibody. These results suggest that one mechanism by which Tax activates transcription may be mediated through the direct interaction with CREB homodimer and/or CREB/ATF-1 heterodimer to stabilize their assembly on the Tax-responsive CRE motifs in the HTLV-I enhancer.
authors.affiliation: Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH 44106.
authors.forename: L J
authors.initials: LJ
authors.lastname: Zhao
authors.forename: C Z
authors.initials: CZ
authors.lastname: Giam
mesh_terms: D000595:Amino Acid Sequence; D000906:Antibodies; D001482:Base Composition; D001665:Binding Sites; D002467:Cell Nucleus / Q000502:physiology; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D004926:Escherichia coli / Q000235:genetics; D016356:Gene Products, tax / Q000378:metabolism*; D006367:HeLa Cells; D015368:Human T-lymphotropic virus 1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D010766:Phosphorylation; D011485:Protein Binding; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping
chemical_list: D000906:Antibodies; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D010455:Peptides; D011994:Recombinant Proteins