Erythroid Krüppel-Like Factor Directly Activates the Basic Krüppel-Like Factor Gene in Erythroid Cells

Abstract

The Sp/Krüppel-like factor (Sp/Klf) family is comprised of around 25 zinc finger transcription factors that recognize CACCC boxes and GC-rich elements. We have investigated basic Krüppel-like factor (Bklf/Klf3) and show that in erythroid tissues its expression is highly dependent on another family member, erythroid Krüppel-like factor (Eklf/Klf1). We observe that Bklf mRNA is significantly reduced in erythroid tissues from Eklf-null murine embryos. We find that Bklf is driven primarily by two promoters, a ubiquitously active GC-rich upstream promoter, 1a, and an erythroid downstream promoter, 1b. Transcripts from the two promoters encode identical proteins. Interestingly, both the ubiquitous and the erythroid promoter are dependent on Eklf in erythroid cells. Eklf also activates both promoters in transient assays. Experiments utilizing an inducible form of Eklf demonstrate activation of the endogenous Bklf gene in the presence of an inhibitor of protein synthesis. The kinetics of activation are also consistent with Bklf being a direct Eklf target. Chromatin immunoprecipitation assays confirm that Eklf associates with both Bklf promoters. Eklf is typically an activator of transcription, whereas Bklf is noted as a repressor. Our results support the hypothesis that feedback cross-regulation occurs within the Sp/Klf family in vivo.

Non-random subcellular distribution of variant EKLF in erythroid cells

“…Recent studies more directly show that there are other targets, including some in the primitive cell, that are also negatively affected by the absence of EKLF [17][18][19][20]. In the case of Band 4.9 and AHSP expression, this effect is as dramatic in the primitive cell as for β-globin in the definitive cell [17].…”

“…EKLF protein can interact with coactivators such as p300/CBP histone acetyltransferases as well as chromatin remodelers such as SWI/SNF to maximally transactivate the β-globin gene [15,16]. EKLF also activates protein-stabilizing, heme biosynthetic pathway, and red cell membrane protein genes in both primitive and definitive cells [17][18][19][20]. Although EKLF predominantly serves as a transcriptional activator, protein-protein interactions between EKLF and corepressors, such as mSin3A and HDAC1 [21], can result in the stage-specific repression of EKLF target genes [22].…”

The mammalian zinc finger transcription factor Krüppel‐like factor 3 (KLF3/BKLF)

“…Mice with targeted deletion of KLF1 die in utero from lethal b-thalassemia, and KLF1 has been defined as a master regulator of erythropoiesis (40,41). Like KLF1, KLF3 is also highly expressed in red blood cells, both in cell lines and throughout mouse development in primary erythroid tissue (4,8,9). In support of an erythroid role for KLF3, it was noted that KLF3 expression is dramatically reduced in the KLF1 knockout mouse.…”

“…In addition to the interaction with CtBP, full repression activity is dependent on sumoylation (6). Recent progress has begun to define the biology of KLF3, suggesting widespread roles in differentiation, including erythropoiesis, lymphopoiesis, and adipogenesis (7)(8)(9)(10). This review will describe the molecular structure of KLF3 in the context of the KLF family, the molecular mechanisms by which it regulates expression of its target genes and also the biological functions that have been recently attributed to this protein.…”

Kruppel-like Factors (KLFs) in muscle biology

“…These data raise the intriguing possibility that KLF15 may function as a postnatal repressor, in part, via antagonism of KLF13 at critical promoters and that this crosstalk may involve competition for GATA4 binding. Furthermore, the possibility that KLFs directly regulate the expression of each other in the heart is another important area on inquiry as such regulation has been demonstrated in other tissues [62]. In fact, the broad aspects of regulation of the KLF expression in the myocardium is poorly understood and will provide invaluable insights into their tissue-specific functions.…”