Transcriptional Activators Differ in Their Responses to Overexpression of TATA-Box-Binding Protein

Abstract

We investigated how overexpression of human TATA-box-binding protein (TBP) affects the action of estrogen receptor (ER) and compared the response with that of other activators. When ER activates a simple promoter, consisting of a response element and either the collagenase or tk TATA box, TBP overexpression potentiates transcription. TBP potentiates only estrogen-induced and not basal transcription and does so independent of spacing between response element and TATA box. TBP overexpression also reduces autoinhibition by overexpressed ER, suggesting that one target of the autoinhibition may be TBP itself. Both AF-1 and AF-2 domains of ER are potentiated by TBP, and each domain binds TBP in vitro. Like ER, chimeric GAL4/VP16 and GAL4/Tat activators are also potentiated by TBP, as is the synergistic activation by ER and GAL4/VP16 on a complex promoter. Unlike ER, GAL4/Sp1 and GAL4/NF-I become less potent when TBP is overexpressed. Furthermore, synergy between ER and Sp1 or between ER and NF-I, whether these are supplied by transfected GAL4 fusions or by the endogenous genes, is inhibited by TBP overexpression. Thus, ER resembles VP16 in response to TBP overexpression and is different from Sp1 and NF-I, which predominate over ER in setting the response on complex promoters.The estrogen receptor (ER) is an upstream activator protein that binds an estrogen response element (ERE) on DNA and enhances transcription from nearby promoters. Two ER activation domains contribute to this process: AF-1 in the amino terminus, which is constitutive, and AF-2 in the C-terminal ligand-binding domain (LBD), which is active only when hormone is bound (13, 57). Neither of the ER domains is marked by an abundance of glutamine, proline, or acidic amino acids as has been noted for many other transcriptional activation domains.The mechanism whereby the ER domains contribute to transcriptional activation is unknown, but by analogy with betterunderstood viral activators, it is thought that interactions with target proteins within the transcriptional apparatus are important (for a review, see reference 55; see also references 11 and 27 and references therein). The TATA-box-binding protein (TBP) is one candidate target. TBP binding to the promoter is a pivotal event leading to unwinding of the DNA at the TATA box and widening of the minor groove (31,32,47). TBP binding is needed for the subsequent recruitment of TFIIB and RNA polymerase II (reviewed in reference 60). Several activators bind TBP in vitro. These include the acidic activator VP16 (26, 52), E1a (3, 24, 37), c-Rel (30, 59), and Tax 1 (7). For several of these activator mutations that decrease binding to TBP decrease transcriptional activation, suggesting that the binding is of functional significance. In higher eukaryotes, TBP is tightly associated with a class of coactivators called TBPassociated factors (TAFs). This complex, but not isolated TBP, mediates transcriptional enhancement by activator proteins in vitro (10, 14, 53, 61; reviewed in reference 55). TAFs and activators al...

Synergistic Transcriptional Activation by TATA-Binding Protein and hTAFII28 Requires Specific Amino Acids of the hTAFII28 Histone Fold

“…Our results would be consistent with the incorporation of hTAF II 28 and TBP spm3 into a TFIID complex comprising endogenous TAF II s. Indeed, we and others have previously shown that a fraction of transfected TBP spm3 and hTAF II 28 (and indeed other TAF II s) do associate with the endogenous cellular TFIID (12,22,32). Transfected hTAF II 28 may be assembled into TFIID complexes via TAF-TAF rather than TAF-TBP interactions, explaining why the mutations in TBP do not abolish functional cooperation.…”

p300 and estrogen receptor cooperatively activate transcription via differential enhancement of initiation and reinitiation

“…Because transcriptional activation by the ER occurs with chromatin but not with nonchromatin templates, we suggest that chromatin provides an environment that is conducive to multiple cycles of transcription, such as that mediated by the ER. It has also been found that ER interacts with TBP, hTAF II 30, hTAF II 28, and TFIIB (Ing et al 1992;Jacq et al 1994;Sadovsky et al 1995;Beato and Sá nchez-Pacheo 1996;May et al 1996). Thus, the results collectively suggest that there might be a complex containing ER and TFIID and/or TFIIB that remains bound at the promoter for multiple cycles of transcription and facilitates reinitiation.…”

Functional Domain and Motif Analyses of Androgen Receptor Coregulator ARA70 and Its Differential Expression in Prostate Cancer

“…Recently, it has been reported that several SRs can interact directly with components of the basal transcription machinery, such as TBP (11), TFIIB (12), TFIIF (13), and TFIIH (14). In addition, specific sets of proteins are recruited by the SRs as coregulators that may function as bridging factors between the receptors and general transcription machinery in the preinitiation complex (15,16).…”