Regulation of delta-aminolevulinic acid dehydratase by krüppel-like factor 1

The involvement of krüppel-like transcription factor 2 in megakaryocytic differentiation induction by phorbol 12-myrestrat 13-acetate

BACKGROUND

Megakaryocytic differentiation is a complicated process regulated by a series of transcription factors in a context- and stage-dependent manner. Recent studies have suggested that krüppel-like transcription factor 2 (KLF2) is involved in the control of embryonic erythroid precursor cell differentiation and maturation. However, the function and mechanism of KLF2 in regulating megakaryocytic differentiation remain unclear.

METHODS

The expression patterns of krüppel-like transcription factors (KLFs) during megakaryocytic differentiation were identified from public databases. Phorbol 12-myristate 13-acetate (PMA) treatment of the myeloid-erythroid-leukemic cell lines K562 and HEL were used as cellular megakaryocytic differentiation models. A lentiviral transduction system was utilized to achieve the goal of amplifying or reducing KLF2. The expression of KLF2 was examined using real-time PCR and western blot. The impact of KLF2 on the megakaryocytic differentiation of K562 cells was examined by flow cytometry, Giemsa staining, Phalloidin staining and western blot. RNA-sequencing (RNA-seq) and chromatin immunoprecipitation-sequencing (ChIP-seq) technologies were used to identify the KLF2-regulated targets.

RESULTS

KLF2 is increased in the maturation process of megakaryocytes. KLF2 overexpression accelerated the PMA-induced megakaryocytic differentiation, as reflected by an increased percentage of CD41/CD61 cells, an increased number of polyploid cells, and an elevated expression of P21 and P27. KLF2 knockdown exhibited the opposite results, indicating that KLF2 knockdown suppressed the megakaryocytic differentiation. Further, combination of the RNA-seq and ChIP-seq results suggested that chimerin 1 (CHN1) and potassium voltage-gated channel subfamily Q member 5 (KCNQ5) may be target genes regulated of KLF2. Both CHN1 and KCNQ5 knockdown could block the megakaryocytic differentiation to some content.

CONCLUSION

This study implicated a regulatory role of KLF2 in megakaryocytic differentiation, which may suggest KLF2 as a target for illness with abnormal megakaryocytic differentiation.

Krüppel-Like Factor 1: A Pivotal Gene Regulator in Erythropoiesis

Krüppel-like factor 1 (KLF1) plays a crucial role in erythropoiesis. In-depth studies conducted on mice and humans have highlighted its importance in erythroid lineage commitment, terminal erythropoiesis progression and the switching of globin genes from γ to β. The role of KLF1 in haemoglobin switching is exerted by the direct activation of β-globin gene and by the silencing of γ-globin through activation of BCL11A, an important γ-globin gene repressor. The link between KLF1 and γ-globin silencing identifies this transcription factor as a possible therapeutic target for β-hemoglobinopathies. Moreover, several mutations have been identified in the human genes that are responsible for various benign phenotypes and erythroid disorders. The study of the phenotype associated with each mutation has greatly contributed to the current understanding of the complex role of KLF1 in erythropoiesis. This review will focus on some of the principal functions of KLF1 on erythroid cell commitment and differentiation, spanning from primitive to definitive erythropoiesis. The fundamental role of KLF1 in haemoglobin switching will be also highlighted. Finally, an overview of the principal human mutations and relative phenotypes and disorders will be described.

Interplay between cofactors and transcription factors in hematopoiesis and hematological malignancies

Hematopoiesis requires finely tuned regulation of gene expression at each stage of development. The regulation of gene transcription involves not only individual transcription factors (TFs) but also transcription complexes (TCs) composed of transcription factor(s) and multisubunit cofactors. In their normal compositions, TCs orchestrate lineage-specific patterns of gene expression and ensure the production of the correct proportions of individual cell lineages during hematopoiesis. The integration of posttranslational and conformational modifications in the chromatin landscape, nucleosomes, histones and interacting components via the cofactor–TF interplay is critical to optimal TF activity. Mutations or translocations of cofactor genes are expected to alter cofactor–TF interactions, which may be causative for the pathogenesis of various hematologic disorders. Blocking TF oncogenic activity in hematologic disorders through targeting cofactors in aberrant complexes has been an exciting therapeutic strategy. In this review, we summarize the current knowledge regarding the models and functions of cofactor–TF interplay in physiological hematopoiesis and highlight their implications in the etiology of hematological malignancies. This review presents a deep insight into the physiological and pathological implications of transcription machinery in the blood system.

Promiscuous DNA-binding of a mutant zinc finger protein corrupts the transcriptome and diminishes cell viability

The rules of engagement between zinc finger transcription factors and DNA have been partly defined by in vitro DNA-binding and structural studies, but less is known about how these rules apply in vivo. Here, we demonstrate how a missense mutation in the second zinc finger of Krüppel-like factor-1 (KLF1) leads to degenerate DNA-binding specificity in vivo, resulting in ectopic transcription and anemia in the Nan mouse model. We employed ChIP-seq and 4sU-RNA-seq to identify aberrant DNA-binding events genome wide and ectopic transcriptional consequences of this binding. We confirmed novel sequence specificity of the mutant recombinant zinc finger domain by performing biophysical measurements of in vitro DNA-binding affinity. Together, these results shed new light on the mechanisms by which missense mutations in DNA-binding domains of transcription factors can lead to autosomal dominant diseases.

Krüppel-like factors compete for promoters and enhancers to fine-tune transcription

Krüppel-like factors (KLFs) are a family of 17 transcription factors characterized by a conserved DNA-binding domain of three zinc fingers and a variable N-terminal domain responsible for recruiting cofactors. KLFs have diverse functions in stem cell biology, embryo patterning, and tissue homoeostasis. KLF1 and related family members function as transcriptional activators via recruitment of co-activators such as EP300, whereas KLF3 and related members act as transcriptional repressors via recruitment of C-terminal Binding Proteins. KLF1 directly activates the Klf3 gene via an erythroid-specific promoter. Herein, we show KLF1 and KLF3 bind common as well as unique sites within the erythroid cell genome by ChIP-seq. We show KLF3 can displace KLF1 from key erythroid gene promoters and enhancers in vivo. Using 4sU RNA labelling and RNA-seq, we show this competition results in reciprocal transcriptional outputs for >50 important genes. Furthermore, Klf3-/- mice displayed exaggerated recovery from anemic stress and persistent cell cycling consistent with a role for KLF3 in dampening KLF1-driven proliferation. We suggest this study provides a paradigm for how KLFs work in incoherent feed-forward loops or networks to fine-tune transcription and thereby control diverse biological processes such as cell proliferation.

Krüppeling erythropoiesis: an unexpected broad spectrum of human red blood cell disorders due to KLF1 variants

Until recently our approach to analyzing human genetic diseases has been to accurately phenotype patients and sequence the genes known to be associated with those phenotypes; for example, in thalassemia, the globin loci are analyzed. Sequencing has become increasingly accessible, and thus a larger panel of genes can be analyzed and whole exome and/or whole genome sequencing can be used when no variants are found in the candidate genes. By using such approaches in patients with unexplained anemias, we have discovered that a broad range of hitherto unrelated human red cell disorders are caused by variants in KLF1, a master regulator of erythropoiesis, which were previously considered to be extremely rare causes of human genetic disease.

EKLF/KLF1, a tissue-restricted integrator of transcriptional control, chromatin remodeling, and lineage determination

Erythroid Krüppel-like factor (EKLF or KLF1) is a transcriptional regulator that plays a critical role in lineage-restricted control of gene expression. KLF1 expression and activity are tightly controlled in a temporal and differentiation stage-specific manner. The mechanisms by which KLF1 is regulated encompass a range of biological processes, including control of KLF1 RNA transcription, protein stability, localization, and posttranslational modifications. Intact KLF1 regulation is essential to correctly regulate erythroid function by gene transcription and to maintain hematopoietic lineage homeostasis by ensuring a proper balance of erythroid/megakaryocytic differentiation. In turn, KLF1 regulates erythroid biology by a wide variety of mechanisms, including gene activation and repression by regulation of chromatin configuration, transcriptional initiation and elongation, and localization of gene loci to transcription factories in the nucleus. An extensive series of biochemical, molecular, and genetic analyses has uncovered some of the secrets of its success, and recent studies are highlighted here. These reveal a multilayered set of control mechanisms that enable efficient and specific integration of transcriptional and epigenetic controls and that pave the way for proper lineage commitment and differentiation.