Distinct modes of gene regulation by a cell-specific transcriptional activator

Abstract

The architectural layout of a eukaryotic RNA polymerase II core promoter plays a role in general transcriptional activation. However, its role in tissue-specific expression is not known. For example, differing modes of its recognition by general transcription machinery can provide an additional layer of control within which a single tissue-restricted transcription factor may operate. Erythroid Kruppel-like factor (EKLF) is a hematopoietic-specific transcription factor that is critical for the activation of subset of erythroid genes. We find that EKLF interacts with TATA binding protein-associated factor 9 (TAF9), which leads to important consequences for expression of adult ␤-globin. First, TAF9 functionally supports EKLF activity by enhancing its ability to activate the ␤-globin gene. Second, TAF9 interacts with a conserved ␤-globin downstream promoter element, and ablation of this interaction by ␤-thalassemia-causing mutations decreases its promoter activity and disables superactivation. Third, depletion of EKLF prevents recruitment of TAF9 to the ␤-globin promoter, whereas depletion of TAF9 drastically impairs ␤-promoter activity. However, a TAF9-independent mode of EKLF transcriptional activation is exhibited by the ␣-hemoglobin-stabilizing protein (AHSP) gene, which does not contain a discernable downstream promoter element. In this case, TAF9 does not enhance EKLF activity and depletion of TAF9 has no effect on AHSP promoter activation. These studies demonstrate that EKLF directs different modes of tissue-specific transcriptional activation depending on the architecture of its target core promoter.

Structural and functional characterization of an atypical activation domain in erythroid Krüppel-like factor (EKLF)

“…However, like other acidic TADs, it is thought that EKLFTAD participates in interactions with transcriptional regulatory factors such as general transcription factors, chromatin remodeling complexes, and HATs (12)(13)(14)16). In this article, we demonstrate that EKLFTAD displays sequence homology to the p53TAD and contains two functional subdomains (EKLF-TAD1 and EKLFTAD2).…”

“…Like the DBD, the TAD plays an important role in EKLF's ability to activate β-globin expression (16)(17)(18). Initial experiments demonstrated that the first 100 residues constituted the minimal TAD of EKLF (EKLFTAD) (17).…”

“…EKLF specifically binds to CAACC elements (1,3) and either the absence of EKLF or mutations in the β-globin CAACC element leads to severe β-thalassemia (5,6,10). In addition, EKLF plays a role in generating an open chromatin structure on the adult β-globin gene through interactions with transcriptional regulatory factors (11)(12)(13)(14)(15)(16).…”

Promoting developmental transcription

“…Finally, enhancer-bound transcription factors can activate the transcription of natural target genes that have different core promoter elements and depend on different basal transcription factors. For example, the mouse hematopoietic-specific transcription factor EKLF (erythroid Krupple-like factor, or KLF1) activates the transcription of both the adult -globin gene and the Ahsp (-hemoglobin-stabilizing protein) gene, but -globin transcription depends on its core promoter DCE and on a particular basal transcription factor (the TFIID subunit TAF9, as discussed below), whereas the Ahsp core promoter lacks a DCE and its transcription is TAF9 independent (Sengupta et al, 2009). Thus, enhancer elements and transcription factors are often compatible with multiple core promoter elements and basal transcription factors.…”

Transcription factor EKLF (KLF1) recruitment of the histone chaperone HIRA is essential for β-globin gene expression

“…S5). The β-globin and BKLF promoters share some similarities in their promoter architecture (e.g., INI and DPE elements), unlike the AHSP promoter (46). In addition, EKLF/TAF9 interactions are critical for β-globin but not AHSP promoter activity.…”