Expansion of CREB's DNA recognition specificity by Tax results from interaction with Ala-Ala-Arg at positions 282-284 near the conserved DNA-binding domain of CREB.

Abstract

The transactivator protein of human T-lymphotropic virus type I (HTLV-I), Tax, forms multiprotein complexes with the ubiquitous transcription factor CREB and the CREB/ATF-1 heterodimer. The interaction between Tax and CREB is highly specific and results in increased binding of the Tax/CREB complexes to the HTLY-I 21-bp repeats. Despite the extensive sequence similarities between CREB and ATF-1, Tax interacts with ATF-1 only marginally. Compared with CREB, Tax/CREB exhibits greatly increased DNA recognition specificity and preferentially assembles on a consensus binding site, GGGGG(T/A)TGACG(T/C)(A/C)TA(T/C)C-CCCC, homologous to the HTLV-I 21-bp repeats. Here we report that Tax affects CREB binding to the Tax-inducible DNA elements by interacting with the basic-eucine zipper (bZip) domain of CREB. We show by domain switching that the basic region in CREB bZip can confer on c-Jun and ATF-1 leucine zippers the ability to interact with Tax in vitro. Mutational analyses further demonstrate that the amino acid residues of CREB critical for Tax/CREB interaction are Ala-AlaArg at positions 282-284 (AAR"), immediate upstream of the higly conserved DNA-binding domain (R/K)XX(R/K) N(R/K)XAAXX(S/C)RX(R/K)(K/R) characteristic of all bZip proteins. Specific amino acid substitutions in AAR2" of CREB weakened or abolished Tax/CREB interaction, whereas reciprocal changes in ATF-1 allowed It to interact with Tax. These results support a model in which the specific interaction between Tax and the AAR284 residues near the DNA-binding domain of CREB results in a multiprotein complex with altered DNA recognition property. This protein complex assembles selectively on the viral Tax-responsive 21-bp repeats to augment transcription.Tax is a 40-kDa nuclear protein encoded by the 3' region of the genome of human T-lymphotropic virus type I (HTLV-I). It stimulates HTLV-I transcription via three imperfect 21-bp repeats in the proviral long terminal repeat (1-3). cAMP response element (CRE)-like motifs in the repeats are crucial for Tax transactivation (3). We previously detected three cellular protein factors in Jurkat T cells and HeLa cells that bound specifically to the CRE in the HTLV-I 21-bp repeats. Two ofthese factors interacted with Tax directly (4,5). These three cellular factors were identified to be CREB homodimer, CREB/ATF-1 heterodimer, and ATF-1 homodimer (5). Tax interacts directly with the CREB subunits in CREB homodimer and CREB/ATF-1 heterodimer and stabilizes their binding to the HTLV-I 21-bp repeats (5). Both CREB and ATF-1 are members of the basic-leucine zipper (bZip) family of transcription factors and are highly similar in primary amino acid sequences (6-8). The interaction between Tax and CREB is highly specific. Despite the extensive amino acid similarities shared between ATF-1 and CREB, Tax interacts marginally with ATF-1 (5). By selecting for preferred Tax/CREB or CREB binding sites in vitro, the Tax/ CREB complex was found to exhibit greatly altered DNA recognition specificity compared with CREB (9). The...

Comparative biology of human T-cell lymphotropic virus type 1 (HTLV-1) and HTLV-2

“…HTLV Tax is expressed early after infection and is a transactivator of viral gene expression. Tax increases transcription of the viral promoter by exploiting the cyclic-AMP-response element (CRE) and activating transcription factor (ATF) binding proteins (CREB/ATF) family of transcription factors (Zhao and Giam, 1992;Wagner and Green, 1993;Adya et al, 1994;Anderson and Dynan, 1994;Bantignies et al, 1996;Yin et al, 1995b). Tax facilitates the binding of these proteins to the nonpalindromic consensus cAMP response element (CRE) sequences contained within the 21 bp repeats in the HTLV promoter (Adya et al, 1994;Yin et al, 1995a).…”

“…Tax increases transcription of the viral promoter by exploiting the cyclic-AMP-response element (CRE) and activating transcription factor (ATF) binding proteins (CREB/ATF) family of transcription factors (Zhao and Giam, 1992;Wagner and Green, 1993;Adya et al, 1994;Anderson and Dynan, 1994;Bantignies et al, 1996;Yin et al, 1995b). Tax facilitates the binding of these proteins to the nonpalindromic consensus cAMP response element (CRE) sequences contained within the 21 bp repeats in the HTLV promoter (Adya et al, 1994;Yin et al, 1995a). Formation of the Tax/CREB/ promoter bound ternary complex appears to be critical for the recruitment of the multifunctional CBP/p300 coactivators and their associated cellular coactivator PCAF, which physically interacts with Tax, ultimately resulting in efficient viral transcription.…”

Binding of the human T-cell leukemia virus Tax protein to the coactivator CBP interferes with CBP-mediated transcriptional control

“…The transcriptional control region of HTLV-I carries three 21 bp repeats, called viral CREs, that serve as binding sites for members of the basic-leucine zipper (bZIP) family of cellular transcription factors (Beimling and Moelling, 1992;Franklin et al, 1993;Adya and Giam, 1995;Baranger et al, 1995;Brauweiler et al, 1995;Yin et al, 1995;Yin and Gaynor, 1996;Lenzmeier et al, 1998). Tax speci®cally interacts with the bZIP domain of the transcription factor CREB, as well as with nucleotides which immediately¯ank the CREB binding site in the viral CRE (Franklin et al, 1993;Adya et al, 1994;Baranger et al, 1995;Brauweiler et al, 1995;Yin et al, 1995;Anderson and Dynan, 1994;Perini et al, 1995;Lenzmeier et al, 1998;Kimzey and Dynan, 1998). These interactions by Tax lead to the formation of a stable ternary complex on the HTLV-I promoter that serves as a high anity binding site for the recruitment of the multifunctional cellular coactivator CREB binding protein (CBP) (Kwok et al, 1996;Giebler et al, 1997).…”

p300 and p300/cAMP-responsive Element-binding Protein Associated Factor Interact with Human T-cell Lymphotropic Virus Type-1 Tax in a Multi-histone Acetyltransferase/Activator-Enhancer Complex

“…Numerous cellular transcription factors, including NF-B, SRF, AP-1, and CREB/ATF-1 family members, are aberrantly affected by Tax (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22); effects on cell-cycle regulatory molecules and certain tumor suppressors have also been observed (23)(24)(25)(26)(27)(28)(29). HTLV-1 LTR trans-activation requires the assembly of the 40-kDa trans-activator Tax and CREB/ATF-1 transcription factors on three, 21-bp repeat enhancers located in the U3 region (22, 30 -34).…”

“…HTLV-1 LTR trans-activation requires the assembly of the 40-kDa trans-activator Tax and CREB/ATF-1 transcription factors on three, 21-bp repeat enhancers located in the U3 region (22, 30 -34). Tax is known to directly interact with the basic domain leucine zipper (bZip) of CREB/ATF-1, which binds the core cyclic AMP-responsive element (CRE) in each 21-bp repeat (7,13,21,35). Recent data suggest that, upon binding to the basic domain of CREB bZip, Tax makes additional contacts with the G/C-rich sequences that flank the CRE; thus achieving the exquisite DNA sequence specificity of Tax-mediated LTR trans-activation (35)(36)(37)(38).…”