The coactivator CBP stimulates human T-cell lymphotrophic virus type I Tax transactivation in vitro.
Tax interacts with the cellular cyclic AMP-responsive element binding protein (CREB) and facilitates the binding of the coactivator CREB binding protein (CBP), forming a multimeric complex on the cyclic AMP-responsive element (CRE)-like sites in the human T-cell lymphotrophic virus type I (HTLV-I) promoter. The trimeric complex is believed to recruit additional regulatory proteins to the HTLV-I long terminal repeat, but there has been no direct evidence that CBP is required for Tax-mediated transactivation. We present evidence that Tax and CBP activate transcription from the HTLV-I 21 base pair repeats on naked DNA templates. Transcriptional activation of the HTLV-I sequences required both Tax and CBP and could be mediated by either the N-terminal activation domain of CBP or the full-length protein. Fluorescence polarization binding assays indicated that CBP does not markedly enhance the affinity of Tax for the trimeric complex. Transcription analyses suggest that CBP activates Tax-dependent transcription by promoting transcriptional initiation and reinitiation. The ability of CBP to activate the HTLV-I promoter does not involve the stabilization of Tax binding, but rather depends upon gene activation properties of the co-activator that function in the context of a naked DNA template.
Kashanchi
F
F
Laboratory of Receptor Biology and Gene Expression, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Duvall
J F
JF
Kwok
R P
RP
Lundblad
J R
JR
Goodman
R H
RH
Brady
J N
JN
D000123:Acetyltransferases / Q000378:metabolism; D000818:Animals; D050882:CREB-Binding Protein; D002460:Cell Line; D003001:Cloning, Molecular; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D016356:Gene Products, tax / Q000235:genetics / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000235:genetics*; D006801:Humans; D007700:Kinetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D018411:Spodoptera; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
D017362:Cyclic AMP Response Element-Binding Protein; D016356:Gene Products, tax; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D000123:Acetyltransferases; D050882:CREB-Binding Protein; C494363:CREBBP protein, human