Histone Acetyltransferase Domain Research Articles

Characterization of Human Activating Transcription Factor 4, a Transcriptional Activator That Interacts with Multiple Domains of cAMP-responsive Element-binding Protein (CREB)-binding Protein (CBP)

We demonstrate that human activating transcription factor 4 (hATF4), a member of the activating transcription factor/cAMP-responsive element-binding protein (ATF/CREB) family of transcription factors, is a potent transcriptional activator in both mammalian cells and yeast. The N-terminal 113 amino acids of hATF4 activate transcription efficiently, and unexpectedly, the C-terminal bZip DNA binding domain of hATF4 also activates transcription, albeit weakly. Our results indicate that hATF4 interacts with several general transcription factors: TATA-binding protein, TFIIB, and the RAP30 subunit of TFIIF. In addition, hATF4 interacts with the coactivator CREB-binding protein (CBP) at four regions: 1) the KIX domain, 2) a region that contains the third zinc finger and the E1A-interacting domain, 3) a C-terminal region that contains the p160/SRC-1-interacting domain, and 4) the recently identified histone acetyltransferase domain. Interestingly, both the N-terminal and C-terminal regions of hATF4 interact with the above general transcription factors and CBP, providing a mechanistic explanation for their ability to activate transcription. Consistent with its role as a coactivator, CBP potentiates the ability of hATF4 to activate transcription. The potential significance of the interaction between hATF4 and multiple factors is discussed.

Two tandem and independent sub-activation domains in the amino terminus of p53 require the adaptor complex for activity.

The ability of p53 to function as a tumor suppressor is linked to its function as a transcriptional activator, since p53 mutants that do not transactivate are unable to suppress tumor cell growth. Previous studies identified an activation domain in the amino terminal 40 residues of the protein, a region that binds to several general transcription factors and to some oncogene products. For example, mdm-2, a cellular oncoprotein, binds to this region and represses p53 transactivation. Here we describe a new activation domain within the amino terminus of p53 that maps between amino acids 40-83, and whose residues trp-53 and phe-54 are critical for function both in yeast and in mammalian cells. In vivo studies in yeast show that the new activation subdomain, unlike the previously described, is mdm-2 independent. Both p53 activation subdomains (1-40 and 40-83) require the yeast adaptor complex ADA2/ADA3/GCN5 for transcriptional activation. Moreover, since activation by p53 requires GCN5's enzymatic histone acetyltransferase domain, p53 may regulate gene expression by influencing chromatin modification.

MLL is fused to CBP, a histone acetyltransferase, in therapy-related acute myeloid leukemia with a t(11;16)(q23;p13.3).

The recurring translocation t(11;16)(q23;p13.3) has been documented only in cases of acute leukemia or myelodysplasia secondary to therapy with drugs targeting DNA topoisomerase II. We show that the MLL gene is fused to the gene that codes for CBP (CREB-binding protein), the protein that binds specifically to the DNA-binding protein CREB (cAMP response element-binding protein) in this translocation. MLL is fused in-frame to a different exon of CBP in two patients producing chimeric proteins containing the AT-hooks, methyltransferase homology domain, and transcriptional repression domain of MLL fused to the CREB binding domain or to the bromodomain of CBP. Both fusion products retain the histone acetyltransferase domain of CBP and may lead to leukemia by promoting histone acetylation of genomic regions targeted by the MLL AT-hooks, leading to transcriptional deregulation via aberrant chromatin organization. CBP is the first partner gene of MLL containing well defined structural and functional motifs that provide unique insights into the potential mechanisms by which these translocations contribute to leukemogenesis.

Histone acetyltransferase activity and interaction with ADA2 are critical for GCN5 function in vivo.

Yeast GCN5 is one component of a putative adaptor complex that includes ADA2 and ADA3 and functionally connects DNA-bound transcriptional activators with general transcription factors. GCN5 possesses histone acetyltransferase (HAT) activity, conceptually linking transcriptional activation with enzymatic modification at chromatin. We have identified the minimal catalytic domain within GCN5 necessary to confer HAT activity and have shown that in vivo activity of GCN5 requires this domain. However, complementation of growth and transcriptional activation in gcn5- cells required not only the HAT domain of GCN5, but also interaction with ADA2. The bromodomain in GCN5 was dispensable for HAT activity and for transcriptional activation by strong activators; however, it was required for full complementation in other assays. Fusion of GCN5 to the bacterial lexA DNA binding domain activated transcription in vivo, and required both the HAT domain and the ADA2 interaction domain. These results suggest that both functions of GCN5, HAT activity and interaction with ADA2, are necessary for targeting and acetylation of nucleosomal histones.

Histone Acetyltransferase Activity Is Conserved between Yeast and Human GCN5 and Is Required for Complementation of Growth and Transcriptional Activation

Yeast and human ADA2 and GCN5 (y- and hADA2 and y- and hGCN5, respectively) have been shown to potentiate transcription in vivo and may function as adaptors to bridge physical interactions between DNA-bound activators and the basal transcriptional machinery. Recently it was shown that yGCN5 is a histone acetyltransferase (HAT), suggesting a link between enzymatic modification of nucleosomes and transcriptional activation. In this report, we demonstrate that hGCN5 is also an HAT and has the same substrate specificity as yGCN5. Since hGCN5 does not complement functional defects caused by deletion of yGCN5, we constructed a series of hGCN5-yGCN5 chimeras to identify human regions capable of activity in yeast. Interestingly, only the putative HAT domain of hGCN5, when fused to the remainder of yGCN5, complemented gcn5- cells for growth and transcriptional activation. Moreover, an amino acid substitution mutation within the HAT domain reduced both HAT activity in vitro and transcription in vivo. These findings directly link enzymatic histone acetylation and transcriptional activation and show evolutionary conservation of this potentially crucial pathway in gene regulation.

The CBP co-activator is a histone acetyltransferase.

The CBP protein acts as a transcriptional adaptor for many different transcription factors by directly contacting DNA-bound activators. One mechanism by which CBP is thought to stimulate transcription is by recruiting the histone acetyltransferase (HAT) P/CAF to the promoter. Here we show that CBP has intrinsic HAT activity. The HAT domain of CBP is adjacent to the binding site for the transcriptional activator E1A. Although E1A displaces P/CAF from CBP, it does not disrupt the CBP-associated HAT activity. Thus E1A carries HAT activity when complexed with CBP. Targeting CBP-associated HAT activity to specific promoters may therefore be a mechanism by which E1A acts as a transcriptional activator.