The Human T-cell Leukemia Virus-1 Transcriptional Activator Tax Enhances cAMP-responsive Element-binding Protein (CREB) Binding Activity through Interactions with the DNA Minor Groove

• Published in: The Journal of biological chemistry Vol. 273; no. 30; pp. 19251 - 19259
• Main Authors: Lundblad, J R, Kwok, R P, Laurance, M E, Huang, M S, Richards, J P, Brennan, R G, Goodman, R H
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 24-07-1998
• Subjects: Cyclic AMP Response Element-Binding Protein - metabolism; Cytosine - metabolism; Dimerization; DNA - metabolism; DNA Footprinting; Gene Products, tax - metabolism; Human T-lymphotropic virus 1; Humans; Inosine - metabolism; Kinetics; Models, Molecular; Oligonucleotides - metabolism; Phenanthrolines - metabolism; Repetitive Sequences, Nucleic Acid; Spectrometry, Fluorescence
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.30.19251

Tax-1, the transcriptional activation protein of human T-cell leukemia virus-1, increases transcription from the human T-cell
leukemia virus-1 long terminal repeat and specific cellular promoters through interactions with cellular DNA-binding proteins.
The Tax response elements (TxREs) of the long terminal repeat resemble cAMP response elements (CREs), the target of cAMP-responsive
element-binding protein (CREB). CREB binds the TxRE with reduced affinity; however, the interaction is specifically enhanced
by Tax. Using a fluorescence quenching method, we determined that CREB dimerizes in the absence of DNA, and that Tax does
not enhance dimerization. DNA footprinting of the TxRE with 1,10-phenanthroline-copper complex demonstrates that Tax contacts
DNA and extends the footprint of CREB to GC-rich sequences flanking the core CRE-like element. The minor groove-binding drug
chromomycin A 3 , but not distamycin A, disrupted Tax-enhanced CREB binding to the TxRE. Substitution of the guanine-rich sequences flanking
the core of the TxRE with inosine residues also blocked the Tax effect. Finally, the IC-substituted TxRE binds CREB with increased
affinity, suggesting flanking DNA influences the binding of CREB to the core CRE-like element. These data indicate that Tax
does not regulate DNA binding of CREB by altering dimerization, but rather enhances DNA binding by additionally interacting
with the minor groove of flanking DNA sequences.