A network of Krüppel-like Factors (Klfs). Klf8 is repressed by Klf3 and activated by Klf1 in vivo

The kruppel-like factor (KLF) family, diseases, and physiological events

The Kruppel-Like Factor family of regulatory proteins, which has 18 members, is transcription factors. This family contains zinc finger proteins, regulates the activation and suppression of transcription, and binds to DNA, RNA, and proteins. Klfs related to the immune system are Klf1, Klf2, Klf3, Klf4, Klf6, and Klf14. Klfs related to adipose tissue development and/or glucose metabolism are Klf3, Klf7, Klf9, Klf10, Klf11, Klf14, Klf15, and Klf16. Klfs related to cancer are Klf3, Klf4, Klf5, Klf6, Klf7, Klf8, Klf9, Klf10, Klf11, Klf12, Klf13, Klf14, Klf16, and Klf17. Klfs related to the cardiovascular system are Klf4, Klf5, Klf10, Klf13, Klf14, and Klf15. Klfs related to the nervous system are Klf4, Klf7, Klf8, and Klf9. Klfs are associated with diseases such as carcinogenesis, oxidative stress, diabetes, liver fibrosis, thalassemia, and the metabolic syndrome. The aim of this review is to provide information about the relationship of Klfs with some diseases and physiological events and to guide future studies.

Krüppel-like factors family regulation of adipogenic markers genes in bovine cattle adipogenesis

Intramuscular fat (IMF) content is a crucial determinant of meat quality traits in livestock. A network of transcription factors act in concert to regulate adipocyte formation and differentiation, which in turn influences intramuscular fat. Several genes and associated transcription factors have been reported to influence lipogenesis and adipogenesis during fetal and subsequent growth stage. Specifically in cattle, Krüppel-like factors (KLFs), which represents a family of transcription factors, have been reported to be involved in adipogenic differentiation and development. KLFs are a relatively large group of zinc-finger transcription factors that have a variety of functions in addition to adipogenesis. In mammals, the participation of KLFs in cell development and differentiation is well known. Specifically in the context of adipogenesis, KLFs function either as positive (KLF4, KLF5, KLF6, KLF8, KLF9, KLF10, KLF11, KLF12, KLF13, KLF14 and KLF15) or negative organizers (KLF2, KLF3 and KLF7), by a variety of different mechanisms such as crosstalk with C/EBP and PPARγ. In this review, we aim to summarize the potential functions of KLFs in regulating adipogenesis and associated pathways in cattle. Furthermore, the function of known bovine adipogenic marker genes, and associated transcription factors that regulate the expression of these marker genes is also summarized. Overall, this review will provide an overview of marker genes known to influence bovine adipogenesis and regulation of expression of these genes, to provide insights into leveraging these genes and transcription factors to enhance breeding programs, especially in the context of IMF deposition and meat quality.

Krüppel-like factor 15 integrated autophagy and gluconeogenesis to maintain glucose homeostasis under 20-hydroxyecdysone regulation

The regulation of glycometabolism homeostasis is vital to maintain health and development of animal and humans; however, the molecular mechanisms by which organisms regulate the glucose metabolism homeostasis from a feeding state switching to a non-feeding state are not fully understood. Using the holometabolous lepidopteran insect Helicoverpa armigera, cotton bollworm, as a model, we revealed that the steroid hormone 20-hydroxyecdysone (20E) upregulated the expression of transcription factor Krüppel-like factor (identified as Klf15) to promote macroautophagy/autophagy, apoptosis and gluconeogenesis during metamorphosis. 20E via its nuclear receptor EcR upregulated Klf15 transcription in the fat body during metamorphosis. Knockdown of Klf15 using RNA interference delayed pupation and repressed autophagy and apoptosis of larval fat body during metamorphosis. KLF15 promoted autophagic flux and transiting to apoptosis. KLF15 bound to the KLF binding site (KLF bs) in the promoter of Atg8 (autophagy-related gene 8/LC3) to upregulate Atg8 expression. Knockdown Atg8 reduced free fatty acids (FFAs), glycerol, free amino acids (FAAs) and glucose levels. However, knockdown of Klf15 accumulated FFAs, glycerol, and FAAs. Glycolysis was switched to gluconeogenesis, trehalose and glycogen synthesis were changed to degradation during metamorphosis, which were accompanied by the variation of the related genes expression. KLF15 upregulated phosphoenolpyruvate carboxykinase (Pepck) expression by binding to KLF bs in the Pepck promoter for gluconeogenesis, which utilised FFAs, glycerol, and FAAs directly or indirectly to increase glucose in the hemolymph. Taken together, 20E via KLF15 integrated autophagy and gluconeogenesis by promoting autophagy-related and gluconeogenesis-related genes expression.

Glucose is the direct substrate for energy production in animal and humans. Autophagy and gluconeogenesis are known to help organisms maintaining energy substrates; however, the mechanism of integration of autophagy and gluconeogenesis is unclear. Holometabolous insects stop feeding during metamorphosis under steroid hormone 20-hydroxyecdysone (20E) regulation, providing a good model for the study. Using lepidopteran insect Helicoverpa armigera, cotton bollworm, as a model, we revealed that Krüppel-like factor 15 (KLF15) integrated autophagy and gluconeogenesis to maintain glucose homeostasis under 20E regulation. 20E increased Klf15 expression, and KLF15 in turn promoted autophagy-related and gluconeogenesis-related genes expression during metamorphosis. Autophagy and apoptosis of the fat body provided substrates for gluconeogenesis. This work clarified the important functions and mechanisms of KLF15 in autophagy and glycometabolism reprogramming for glucose homeostasis after feeding stop during insect metamorphosis.

Loss-of-function variants in KLF4 underlie autosomal dominant palmoplantar keratoderma

PURPOSE

Palmoplantar keratodermas (PPKs) form a group of disorders characterized by thickening of palm and sole skin. Over the past 2 decades, many types of inherited PPKs have been found to result from abnormal expression, processing, or function of adhesion proteins.

METHODS

We used exome and direct sequencing to detect causative pathogenic variants. Functional analysis of these variants was conducted using reverse transcription quantitative polymerase chain reaction, immunofluorescence confocal microscopy, immunoblotting, a promoter reporter assay, and chromatin immunoprecipitation.

RESULTS

We identified 2 heterozygous variants (c.1226A>G and c.633_634dupGT) in KLF4 in 3 individuals from 2 different unrelated families affected by a dominant form of PPK. Immunofluorescence staining for a number of functional markers revealed reduced epidermal DSG1 expression in patients harboring heterozygous KLF4 variants. Accordingly, human keratinocytes either transfected with constructs expressing these variants or downregulated for KLF4 displayed reduced DSG1 expression, which in turn has previously been found to be associated with PPK. A chromatin immunoprecipitation assay confirmed direct binding of KLF4 to the DSG1 promoter region. The ability of mutant KLF4 to transactivate the DSG1 promoter was significantly decreased when compared with wild-type KLF4.

CONCLUSION

Loss-of-function variants in KLF4 cause a novel form of dominant PPK and show its importance in the regulation of epidermal differentiation.

Transcriptional Control of Gene Expression and the Heterogeneous Cellular Identity of Erythroblastic Island Macrophages

During definitive erythropoiesis, maturation of erythroid progenitors into enucleated reticulocytes requires the erythroblastic island (EBI) niche comprising a central macrophage attached to differentiating erythroid progenitors. Normally, the macrophage provides a nurturing environment for maturation of erythroid cells. Its critical physiologic importance entails aiding in recovery from anemic insults, such as systemic stress or acquired disease. Considerable interest in characterizing the central macrophage of the island niche led to the identification of putative cell surface markers enriched in island macrophages, enabling isolation and characterization. Recent studies focus on bulk and single cell transcriptomics of the island macrophage during adult steady-state erythropoiesis and embryonic erythropoiesis. They reveal that the island macrophage is a distinct cell type but with widespread cellular heterogeneity, likely suggesting distinct developmental origins and biological function. These studies have also uncovered transcriptional programs that drive gene expression in the island macrophage. Strikingly, the master erythroid regulator EKLF/Klf1 seems to also play a major role in specifying gene expression in island macrophages, including a putative EKLF/Klf1-dependent transcription circuit. Our present review and analysis of mouse single cell genetic patterns suggest novel expression characteristics that will enable a clear enrichment of EBI subtypes and resolution of island macrophage heterogeneity. Specifically, the discovery of markers such as Epor, and specific features for EKLF/Klf1-expressing island macrophages such as Sptb and Add2, or for SpiC-expressing island macrophage such as Timd4, or for Maf/Nr1h3-expressing island macrophage such as Vcam1, opens exciting possibilities for further characterization of these unique macrophage cell types in the context of their critical developmental function.

KLF4 Inhibits the Differentiation of Goat Intramuscular Preadipocytes Through Targeting C/EBPβ Directly

Intramuscular fat (IMF) deposition is a complicated process, and most of the underlying regulators of this biological process are unknown. Here, we cloned the intact CDS of KLF4 gene, investigated the role of KLF4 by gaining or losing function in vitro and further explored the pathways of KLF4 regulating differentiation of intramuscular preadipocytes in goat. Our results show that goat KLF4 gene consists of 1,536 bp encoding a protein of 486 amino acids. The expression of KLF4 is higher in the lung while lower in the heart and muscle in goat. Knockdown of KLF4 mediated by siRNA technique significantly promotes intramuscular preadipocyte lipid accumulation and upregulates mRNA expression of adipogenic related genes including C/EBPα, C/EBPβ, and PPARγ in vivo cultured cells. Consistently, overexpression of KLF4 inhibits intramuscular adipocyte lipid accumulation and significantly downregulation gene expression of C/EBPβ, PPARγ, aP2, and Pref-1. Further, we found that other members of KLFs were upregulated or downregulated after interference or overexpression of KLF4, including KLF2 and KLF5-7. We also found that C/EBPβ was a potential target of KLF4, because it had an opposite expression pattern with KLF4 during the differentiation of intramuscular preadipocytes and had putative binding sites of KLF4. The dual-luciferase reporter assay indicated that overexpression of KLF4 inhibited the transcriptional activity of C/EBPβ. These results demonstrate that KLF4 inhibits the differentiation of intramuscular preadipocytes in goat by targeting C/EBPβ.

Overexpression of Krueppel like factor 3 promotes subcutaneous adipocytes differentiation in goat Capra hircus

Previous research reported that KLF3 plays different roles in the regulation of adipose deposition across species. However, the exact function of KLF3 in goat subcutaneous adipocyte remains unknown. Here, the goat KLF3 gene was firstly cloned and showed that the mRNA sequence of the goat KLF3 gene was 1,264 bp (GenBank accession number: KU041753.1) and its coding sequence was 1,037 bp, encoding 345 amino acids with three classic zinc finger domains of KLFs family at its C-terminus. The alignment of the amino acid sequence of KLF3 among various species demonstrated that goat had the highest homology to that of sheep, presenting 99.4% similarity, while the homology similarity to that of mice presented only 93.62% in contrast. Furthermore, KLF3 had highest mRNA level in fat tissue and lowest level in the heart in comparison. Additionally, the mRNA level of KLF3 gradually tended to increase during adipogenesis. Interestingly, overexpression of KLF3 increased lipid accumulation. In line with this, the gain-of-function of KLF3 dramatically elevated the mRNA levels of TG synthetic genes and adipogenic maker genes (p < .01) . Moreover, overexpression of KLF3 upregulated all the potential target genes, except for C/EBPα. These results suggested that KLF3 is a positive regulator for subcutaneous adipocyte differentiation in goats.

Genome-Wide SNP Analysis for Milk Performance Traits in Indigenous Sheep: A Case Study in the Egyptian Barki Sheep

Simple Summary

The Barki sheep is one of the three main breeds in Egypt, which is spread mainly throughout the northwestern coastal zone, which has harsh conditions. Considering the harsh, semi-arid habitat of this breed, milk performance traits such as milk yield and milk composition have a very important role in the feeding of newborn lambs and affect their growth during the early stage of life. In this study, rare milk performance data and genomic information of Barki sheep were used to uncover diversified genomic regions that could explain the variability of milk yield and milk quality traits in the studied population of Barki ewes. Genome-wide analysis identified genomic regions harboring interesting candidate genes such as SLC5A8, NUB1, TBC1D1, KLF3 and ABHD5 for milk yield and PPARA and FBLN1 genes for milk quality traits. The findings offer valuable information for obtaining a better understanding of the genetics of milk performance traits and contribute to the genetic improvement of these traits in Barki sheep.

Abstract

Sheep milk yield and milk composition traits play an important role in supplying newborn lambs with essential components such as amino acids, energy, vitamins and immune antibodies and are also of interest in terms of the nutritional value of the milk for human consumption. The aim of this study was to identify genomic regions and candidate genes for milk yield and milk composition traits through genome-wide SNP analyses between high and low performing ewes of the Egyptian Barki sheep breed, which is well adapted to the harsh conditions of North-East Africa. Therefore, out of a herd of 111 ewes of the Egyptian Barki sheep breed (IBD = 0.08), ewes representing extremes in milk yield and milk quality traits (n = 25 for each group of animals) were genotyped using the Illumina OvineSNP50 V2 BeadChip. The fixation index (F_ST) for each SNP was calculated between the diversified groups. F_ST values were Z-transformed and used to identify putative SNPs for further analysis (Z(F_ST) > 10). Genome-wide SNP analysis revealed genomic regions covering promising candidate genes related to milk performance traits such as SLC5A8, NUB1, TBC1D1, KLF3 and ABHD5 for milk yield and PPARA and FBLN1 genes for milk quality trait. The results of this study may contribute to the genetic improvement of milk performance traits in Barki sheep breed and to the general understanding of the genetic contribution to variability in milk yield and quality traits.

miR-21-5p Regulates the Proliferation and Differentiation of Skeletal Muscle Satellite Cells by Targeting KLF3 in Chicken

The proliferation and differentiation of skeletal muscle satellite cells (SMSCs) play an important role in the development of skeletal muscle. Our previous sequencing data showed that miR-21-5p is one of the most abundant miRNAs in chicken skeletal muscle. Therefore, in this study, the spatiotemporal expression of miR-21-5p and its effects on skeletal muscle development of chickens were explored using in vitro cultured SMSCs as a model. The results in this study showed that miR-21-5p was highly expressed in the skeletal muscle of chickens. The overexpression of miR-21-5p promoted the proliferation of SMSCs as evidenced by increased cell viability, increased cell number in the proliferative phase, and increased mRNA and protein expression of proliferation markers including PCNA, CDK2, and CCND1. Moreover, it was revealed that miR-21-5p promotes the formation of myotubes by modulating the expression of myogenic markers including MyoG, MyoD, and MyHC, whereas knockdown of miR-21-5p showed the opposite result. Gene prediction and dual fluorescence analysis confirmed that KLF3 was one of the direct target genes of miR-21-5p. We confirmed that, contrary to the function of miR-21-5p, KLF3 plays a negative role in the proliferation and differentiation of SMSCs. Si-KLF3 promotes cell number and proliferation activity, as well as the cell differentiation processes. Our results demonstrated that miR-21-5p promotes the proliferation and differentiation of SMSCs by targeting KLF3. Collectively, the results obtained in this study laid a foundation for exploring the mechanism through which miR-21-5p regulates SMSCs.

Hemoglobin switching in mice carrying the Klf1Nan variant

Haploinsufficiency for transcription factor KLF1 causes a variety of human erythroid phenotypes, such as the In(Lu) blood type, increased HbA2 levels, and hereditary persistence of fetal hemoglobin. Severe dominant congenital dyserythropoietic anemia IV (OMIM 613673) is associated with the KLF1 p.E325K variant. CDA-IV patients display ineffective erythropoiesis and hemolysis resulting in anemia, accompanied by persistent high levels of embryonic and fetal hemoglobin. The mouse Nan strain carries a variant in the orthologous residue, KLF1 p.E339D. Klf1Nan causes dominant hemolytic anemia with many similarities to CDA-IV. Here we investigated the impact of Klf1Nan on the developmental expression patterns of the endogenous beta-like and alpha-like globins, and the human beta-like globins carried on a HBB locus transgene. We observe that the switch from primitive, yolk sac-derived, erythropoiesis to definitive, fetal liver-derived, erythropoiesis is delayed in Klf1wt/Nan embryos. This is reflected in globin expression patterns measured between E12.5 and E14.5. Cultured Klf1wt/Nan E12.5 fetal liver cells display growth- and differentiation defects. These defects likely contribute to the delayed appearance of definitive erythrocytes in the circulation of Klf1wt/Nan embryos. After E14.5, expression of the embryonic/fetal globin genes is silenced rapidly. In adult Klf1wt/Nan animals, silencing of the embryonic/fetal globin genes is impeded, but only minute amounts are expressed. Thus, in contrast to human KLF1 p.E325K, mouse KLF1 p.E339D does not lead to persistent high levels of embryonic/fetal globins. Our results support the notion that KLF1 affects gene expression in a variant-specific manner, highlighting the necessity to characterize KLF1 variant-specific phenotypes of patients in detail.

New insights of Krüppel-like transcription factors in adipogenesis and the role of their regulatory neighbors

Obesity is a serious public health problem associated with predisposition to develop metabolic diseases. Over the past decade, several studies in vitro and in vivo have shown that the activity of Krüppel-like factors (KLFs) regulates adipogenesis, adipose tissue function and metabolism. Comprehension of both the origin and development of adipocytes and of adipose tissue could provide new insights into therapeutic strategies to contend against obesity and related metabolic diseases. This review focus on the transcriptional role that KLF family members play during adipocyte differentiation, describes their main interactions and the mechanisms involved in this fine-tuned developmental process. We also summarize new findings of the involvement of several effectors that modulate KLFs expression during adipogenesis, including growth factors, circadian clock proteins, interleukins, nuclear receptors, protein kinases and importantly, microRNAs. Thus, KLFs regulation by these factors and emerging molecules might constitute a potential therapeutic target for anti-obesity intervention.

Krüppel-Like Factors 9 and 13 Block Axon Growth by Transcriptional Repression of Key Components of the cAMP Signaling Pathway

Krüppel-like factors (KLFs) are zinc finger transcription factors implicated in diverse biological processes, including differentiation of neural cells. The ability of mammalian neurons to elongate axons decreases during postnatal development in parallel with a decrease in cAMP, and increase in expression of several Klf genes. The paralogous KLFs 9 and 13 inhibit neurite outgrowth, and we hypothesized that their actions are mediated through repression of cAMP signaling. To test this we used the adult mouse hippocampus-derived cell line HT22 engineered to control expression of Klf9 or Klf13 with doxycycline, or made deficient for these Klfs by CRISPR/Cas9 genome editing. We also used primary hippocampal cells isolated from wild type, Klf9^–/– and Klf13^–/– mice. Forced expression of Klf9 or Klf13 in HT22 changed the mRNA levels of several genes involved with cAMP signaling; the predominant action was gene repression, and KLF13 influenced ∼4 times more genes than KLF9. KLF9 and KLF13 repressed promoter activity of the protein kinase a catalytic subunit alpha gene in transfection-reporter assays; KLF13, but not KLF9 repressed the calmodulin 3 promoter. Forskolin activation of a cAMP-dependent promoter was reduced after forced expression of Klf9 or Klf13, but was enhanced in Klf gene knockout cells. Forced expression of Klf9 or Klf13 blocked cAMP-dependent neurite outgrowth in HT22 cells, and axon growth in primary hippocampal neurons, while Klf gene knockout enhanced the effect of elevated cAMP. Taken together, our findings show that KLF9 and KLF13 inhibit neurite/axon growth in hippocampal neurons, in part, by inhibiting the cAMP signaling pathway.

Transcriptional regulation of adipogenic marker genes for the improvement of intramuscular fat in Qinchuan beef cattle

The intramuscular fat content plays a crucial role in meat quality traits. Increasing the degree of adipogenesis in beef cattle leads to an increase in the content of intramuscular fat. Adipogenesis a complex biochemical process which is under firm genetic control. Over the last three decades, the Qinchuan beef cattle have been extensively studied for the improvement of meat production and quality traits. In this study, we reviewed the literature regarding adipogenesis and intramuscular fat deposition. Then, we summarized the research conducted on the transcriptional regulation of key adipogenic marker genes, and also reviewed the roles of adipogenic marker genes in adipogenesis of Qinchuan beef cattle. This review will elaborate our understanding regarding transcriptional regulation which is a vital physiological process regulated by a cascade of transcription factors (TFs), key target marker genes, and regulatory proteins. This synergistic action of TFs and target genes ensures the accurate and diverse transmission of the genetic information for the accomplishment of central physiological processes. This information will provide an insight into the transcriptional regulation of the adipogenic marker genes and its role in bovine adipogenesis for the breed improvement programs especially for the trait of intramuscular fat deposition.

Circular RNA MTO1 Inhibits the Proliferation and Invasion of Ovarian Cancer Cells Through the miR-182-5p/KLF15 Axis

Circular RNAs (circRNAs) are a novel class of endogenous noncoding RNAs and have been shown to play important roles in a variety of physiological processes. Recently, dysregulation of circRNAs has been identified in many types of cancers. In this study, we analyzed the expression profile and biological functions of circMTO1 in ovarian cancer. We demonstrated that circMTO1 was downregulated in ovarian cancer tissues and cell lines. Upregulation of circMTO1 inhibited proliferation and invasion of ovarian cancer cells while downregulation of circMTO1 promoted these processes. Mechanistically, we showed that circMTO1 sponged miR-182-5p to support KLF15 expression, eventually leading to inhibition of ovarian cancer progression. In conclusion, our study suggested circMTO1 as a novel biomarker and therapeutic target for ovarian cancer treatment.

KLF3 Mediates Epidermal Differentiation through the Epigenomic Writer CBP

Impairments in the differentiation process can lead to skin diseases that can afflict ∼20% of the population. Thus, it is of utmost importance to understand the factors that promote the differentiation process. Here we identify the transcription factor KLF3 as a regulator of epidermal differentiation. Knockdown of KLF3 results in reduced differentiation gene expression and increased cell cycle gene expression. Over half of KLF3's genomic binding sites occur at active enhancers. KLF3 binds to active enhancers proximal to differentiation genes that are dependent upon KLF3 for expression. KLF3's genomic binding sites also highly overlaps with CBP, a histone acetyltransferase necessary for activating enhancers. Depletion of KLF3 causes reduced CBP localization at enhancers proximal to differentiation gene clusters, which leads to loss of enhancer activation but not priming. Our results suggest that KLF3 is necessary to recruit CBP to activate enhancers and drive epidermal differentiation gene expression.

Molecular Mechanisms for Krüppel-Like Factor 13 Actions in Hippocampal Neurons

Krüppel-like factors (KLFs) play key roles in nervous system development and function. Several KLFs are known to promote, and then maintain neural cell differentiation. Our previous work focused on the actions of KLF9 in mouse hippocampal neurons. Here we investigated genomic targets and functions of KLF9's paralog KLF13, with the goal of understanding how these two closely related transcription factors influence hippocampal cell function, proliferation, survival, and regeneration. We engineered the adult mouse hippocampus-derived cell line HT22 to control Klf13 expression with doxycycline. We also generated HT22 Klf13 knock out cells, and we analyzed primary hippocampal cells from wild type and Klf13^-/- mice. RNA sequencing showed that KLF13, like KLF9, acts predominantly as a transcriptional repressor in hippocampal neurons and can regulate other Klf genes. Pathway analysis revealed that genes regulated by KLF13 are involved in cell cycle, cell survival, cytoarchitecture regulation, among others. Chromatin-streptavidin sequencing conducted on chromatin isolated from HT22 cells expressing biotinylated KLF13 identified 9506 genomic targets; 79% were located within 1-kb upstream of transcription start sites. Transfection-reporter assays confirmed that KLF13 can directly regulate transcriptional activity of its target genes. Comparison of the target genes of KLF9 and KLF13 found that they share some functions that were likely present in their common ancestor, but they have also acquired distinct functions during evolution. Flow cytometry showed that KLF13 promotes cell cycle progression, and it protects cells from glutamate-induced excitotoxic damage. Taken together, our findings establish novel roles and molecular mechanisms for KLF13 actions in mammalian hippocampal neurons.

Eosinophil function in adipose tissue is regulated by Krüppel-like factor 3 (KLF3)

The conversion of white adipocytes to thermogenic beige adipocytes represents a potential mechanism to treat obesity and related metabolic disorders. However, the mechanisms involved in converting white to beige adipose tissue remain incompletely understood. Here we show profound beiging in a genetic mouse model lacking the transcriptional repressor Krüppel-like factor 3 (KLF3). Bone marrow transplants from these animals confer the beige phenotype on wild type recipients. Analysis of the cellular and molecular changes reveal an accumulation of eosinophils in adipose tissue. We examine the transcriptomic profile of adipose-resident eosinophils and posit that KLF3 regulates adipose tissue function via transcriptional control of secreted molecules linked to beiging. Furthermore, we provide evidence that eosinophils may directly act on adipocytes to drive beiging and highlight the critical role of these little-understood immune cells in thermogenesis.

Immune cells are important regulators of adipose tissue function, including adaptive thermogenesis. Here the authors show that mice with Krüppel-like factor 3 (KLF3) deficiency in bone marrow-derived cells have increased adipose tissue beiging which may at least in part be due to altered eosinophil paracrine signaling.

Knockdown of KLF9 promotes the differentiation of both intramuscular and subcutaneous preadipocytes in goat

KLF9 is reported to promote adipocyte differentiation in 3T3-L1 cells and pigs. However, the roles of KLF9 in adipocytes differentiation of goat remain unknown. In this study, the expression profiles of KLF9 were different between subcutaneous and intramuscular preadipocytes of goat during differentiation process. After silencing KLF9 gene, the lipid droplets were increased in both two types of adipocytes. In subcutaneous preadipocyte with silencing KLF9, the expressions of C/EBPβ, PPARγ, LPL, KLF1-2, KLF5, and KLF17 genes were up-regulated, while KLF12, KLF4, and KLF13 genes were down-regulated in expression level. In intramuscular preadipocyte, aP2, C/EBPα, KLF2-3, KLF5, and KLF7 gene were up-regulated, and Pref-1 gene was down-regulated. In addition, the binding sites of KLF9 existed in the promoters of aP2, C/EBPα, C/EBPβ, LPL and Pref-1. Taken together, KLF9 play a negative role in the differentiation of both intramuscular and subcutaneous preadipocytes in goats, but the functional mechanism may be different.

Krüppel-like factor 3 (KLF3) suppresses NF-κB-driven inflammation in mice

Bacterial products such as lipopolysaccharides (or endotoxin) cause systemic inflammation, resulting in a substantial global health burden. The onset, progression, and resolution of the inflammatory response to endotoxin are usually tightly controlled to avoid chronic inflammation. Members of the NF-κB family of transcription factors are key drivers of inflammation that activate sets of genes in response to inflammatory signals. Such responses are typically short-lived and can be suppressed by proteins that act post-translationally, such as the SOCS (suppressor of cytokine signaling) family. Less is known about direct transcriptional regulation of these responses, however. Here, using a combination of in vitro approaches and in vivo animal models, we show that endotoxin treatment induced expression of the well-characterized transcriptional repressor Krüppel-like factor 3 (KLF3), which, in turn, directly repressed the expression of the NF-κB family member RELA/p65. We also observed that KLF3-deficient mice were hypersensitive to endotoxin and exhibited elevated levels of circulating Ly6C⁺ monocytes and macrophage-derived inflammatory cytokines. These findings reveal that KLF3 is a fundamental suppressor that operates as a feedback inhibitor of RELA/p65 and may be important in facilitating the resolution of inflammation.

Fibroblast growth factor 21 regulates lipid accumulation and adipogenesis in goat intramuscular adipocyte

Fibroblast growth factor 21 (FGF21) plays a critical role in the regulation of lipid metabolism; however, its function in goat intramuscular fat (IMF) deposition remains unknown. To explore the role of FGF21 for goat IMF deposition, we performed gain and loss function of FGF21 in intramuscular adipocyte. Our results showed that overexpression of FGF21 mediated by adenovirus inhibits lipid accumulation of goat intramuscular adipocyte, accompanied by down-regulating the mRNA levels of peroxisome proliferator activated receptor γ (PPARγ), adipocyte fatty acid-binding protein 2 (aP2) and sterol regulatory element-binding protein 1 (SREBP1), but up-regulating counterpart of preadipocyte factor1 (Pref1). Conversely, siRNAs knocking down FGF21 promotes the expression of PPARγ and CCAAT/enhancer binding protein-α (C/EBPα) but suppressed that of lipoprotein lipase (LPL) and Pref1. Meanwhile, we found that FGF21 regulates the expression of many KLFs transcription factors, such as KLF3, 7, 9, 11, 14, and 16. These findings demonstrate a key role of FGF21 as a negative factor in the regulation of adipogenic differentiation in goat intramuscular preadipocyte.

Fibroblast growth factor 10 (FGF10) promotes the adipogenesis of intramuscular preadipocytes in goat

Fibroblast growth factor 10 (FGF10) is an adipokine that is found to participate in the regulation of adipogenesis. However, its function remains to be elucidated in intramuscular fat (IMF) deposition of goat. The purpose of this study was to explore the role of FGF10 in goat IMF deposition. Here, we investigated the expression of FGF10 in goat intramuscular adipocytes inducing 0, 2, 4, 6 and 8 days. Effect of FGF10 on adipogenesis was investigated by gaining and losing function of FGF10 in vitro. And then, we examined several lipid metabolism-related genes, including peroxisome proliferator activated receptor γ (PPARγ), sterol regulatory element binding protein 1 (SREBP1), preadipocyte factor-1 (Pref-1), CCAAT/enhancer binding protein-α (C/EBPα) and CCAAT/enhancer binding protein-β (C/EBPβ), as well as, Krüppel-like factor (KLF) family. We found that the sharp expression of FGF10 appeared at 2 days. Overexpression of FGF10 mediated by adenovirus promotes lipid accumulation, accompanied by up-regulating of LPL and C/EBPα with the down-regulating of C/EBPβ. Conversely, the expression of LPL, C/EBPα and SREBP1 was significantly decreased by the siRNAs of FGF10. Meanwhile, we showed that FGF10 regulated the expression of many KLFs members and interacted synergistically or antagonistically with them. Thus, our results demonstrated a key role of FGF10 as a positively factor in the regulation of adipogenic differentiation of intramuscular preadipocyte in goat.

Krüppel-like factors: Crippling and un-crippling metabolic pathways

Krüppel-like factors (KLFs) are DNA-binding transcriptional factors that regulate various pathways that control metabolism and other cellular mechanisms. Various KLF isoforms have been associated with cellular, organ or systemic metabolism. Altered expression or activation of KLFs has been linked to metabolic abnormalities, such as obesity and diabetes, as well as with heart failure. In this review article we summarize the metabolic functions of KLFs, as well as the networks of different KLF isoforms that jointly regulate metabolism in health and disease.

RNA sequencing analysis reveals protective role of kruppel-like factor 3 in colorectal cancer

The Kruppel-like factor (KLF) family of transcription factors plays an important role in embryonic formation and cancer progression. This study was performed to determine the clinical importance of the KLF family in colorectal cancer (CRC). In total, 361 patients with CRC from The Cancer Genome Atlas (TCGA) cohort were used to comprehensively study the role of the KLF family in CRC. The results were then further validated using an in-house cohort (n=194). Univariate and multivariate Cox proportional hazards models were used to assess the risk factors for survival. In the TCGA cohort, KLF3 (hazard ratio [HR], 0.501; 95% confidence interval [CI], 0.272-0.920; P=0.025), KLF14 (HR, 1.454; 95% CI, 1.059-1.995; P=0.020), and KLF17 (HR, 1.241; 95% CI, 1.030-1.494, P=0.023) were identified as potential biomarkers in the univariate analysis, but after Cox proportional hazards analysis, only KLF3 (HR, 0.473; 95% CI, 0.230-0.831; P=0.012) was shown to be independently predictive of overall survival in patients with CRC. This finding was validated in our in-house cohort, which demonstrated that KLF3 expression was an independent predictor of both overall survival (HR, 0.628; 95% CI, 0.342-0.922; P=0.035) and disease-free survival (HR, 0.421; 95% CI, 0.317-0.697, P=0.016). KLF3 expression was inversely correlated with the N stage (P=0.015) and lymphovascular invasion (P=0.020). Collectively, loss of KLF3 was correlated with aggressive phenotypes and poor survival outcomes. KLF3 might be a potential new predictor and therapeutic target for CRC. Further study is needed for a more detailed understanding of the role of KLF3 in CRC.

KLF9 and JNK3 Interact to Suppress Axon Regeneration in the Adult CNS

Neurons in the adult mammalian CNS decrease in intrinsic axon growth capacity during development in concert with changes in Krüppel-like transcription factors (KLFs). KLFs regulate axon growth in CNS neurons including retinal ganglion cells (RGCs). Here, we found that knock-down of KLF9, an axon growth suppressor that is normally upregulated 250-fold in RGC development, promotes long-distance optic nerve regeneration in adult rats of both sexes. We identified a novel binding partner, MAPK10/JNK3 kinase, and found that JNK3 (c-Jun N-terminal kinase 3) is critical for KLF9's axon-growth-suppressive activity. Interfering with a JNK3-binding domain or mutating two newly discovered serine phosphorylation acceptor sites, Ser106 and Ser110, effectively abolished KLF9's neurite growth suppression in vitro and promoted axon regeneration in vivo These findings demonstrate a novel, physiologic role for the interaction of KLF9 and JNK3 in regenerative failure in the optic nerve and suggest new therapeutic strategies to promote axon regeneration in the adult CNS.SIGNIFICANCE STATEMENT Injured CNS nerves fail to regenerate spontaneously. Promoting intrinsic axon growth capacity has been a major challenge in the field. Here, we demonstrate that knocking down Krüppel-like transcription factor 9 (KLF9) via shRNA promotes long-distance axon regeneration after optic nerve injury and uncover a novel and important KLF9-JNK3 interaction that contributes to axon growth suppression in vitro and regenerative failure in vivo These studies suggest potential therapeutic approaches to promote axon regeneration in injury and other degenerative diseases in the adult CNS.

Expression of Kruppel-like factor 8 and Ki67 in lung adenocarcinoma and prognosis

Kruppel-like factor 8 (KLF8) belongs to the KLF family and has various roles in the regulation of the cell cycle, proliferation and tumor genesis. KLF8 is overexpressed in gastric, ovarian, breast and renal cancer. Additionally, KLF8 may affect invasion and metastasis of tumors. However, whether KLF8 also acts as an ontogeny in lung adenocarcinoma (LAC) remains unknown. The aim of the present study was to determine the association between KLF8 expression and various clinical and pathological parameters. Western blot assays and immune histochemistry analyses revealed that KLF8 level in LAC tissues was higher than that in the normal lung tissues and KLF8 expression was significantly associated with clinical variables (P<0.05). Kaplan-Meier curves revealed that high expression of KLF8 was related to poor prognosis in patients with LAC. The present study also demonstrated that KLF8 was involved in the progression of lung adenocarcinoma. This data suggested that KLF8 may act as a prognostic factor in lung adenocarcinoma progression.

KLF2 inhibits cell growth via regulating HIF-1α/Notch-1 signal pathway in human colorectal cancer HCT116 cells

The transcription factor Krüppel-like factor 2 (KLF2) has been shown to function as a tumor suppressor and regulate biological processes of cancer cells, such as cell growth, cell apoptosis and angiogenesis. However, the function and mechanism of KLF2 in colorectal cancer (CRC) is still unknown. In the present study, we show that the expression of KLF2 is diminished in a cohort of CRC cell lines. Also, KLF2 overexpression remarkably inhibits HCT116 and SW480 cell survival and proliferation. Moreover, cell death detection ELISA plus assay showed that KLF2 overexpression increased HCT116 cell proliferation. Caspase-3/7 activity also increased in HCT116 cells transfected with PcDNA3.1-KLF2. Further studies showed that KLF2 significantly suppresses the expression of Notch-1 and is dependent on the decline of the HIF-1α level. Most importantly, silencing Notch-1 expression or HIF-1α level both impair the action of KLF2 overexpression in CRC cells. Collectively, we demonstrated that KLF2 mediates CRC cell biological processes including cell growth and apoptosis via regulating the HIF-1α/Notch-1 signal pathway. These results indicated that KLF2 plays an important role in CRC and provided novel insight on the function of KLF2 in tumor progression.

Krüppel-like Factor 3 (KLF3/BKLF) Is Required for Widespread Repression of the Inflammatory Modulator Galectin-3 (Lgals3)

The Lgals3 gene encodes a multifunctional β-galactoside-binding protein, galectin-3. Galectin-3 has been implicated in a broad range of biological processes from chemotaxis and inflammation to fibrosis and apoptosis. The role of galectin-3 as a modulator of inflammation has been studied intensively, and recent evidence suggests that it may serve as a protective factor in obesity and other metabolic disorders. Despite considerable interest in galectin-3, little is known about its physiological regulation at the transcriptional level. Here, using knockout mice, chromatin immunoprecipitations, and cellular and molecular analyses, we show that the zinc finger transcription factor Krüppel-like factor 3 (KLF3) directly represses galectin-3 transcription. We find that galectin-3 is broadly up-regulated in KLF3-deficient mouse tissues, that KLF3 occupies regulatory regions of the Lgals3 gene, and that KLF3 directly binds its cognate elements (CACCC boxes) in the galectin-3 promoter and represses its activation in cellular assays. We also provide mechanistic insights into the regulation of Lgals3, demonstrating that C-terminal binding protein (CtBP) is required to drive optimal KLF3-mediated silencing. These findings help to enhance our understanding of how expression of the inflammatory modulator galectin-3 is controlled, opening up avenues for potential therapeutic interventions in the future.

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.

Emerging roles of Krüppel-like factor 4 in cancer and cancer stem cells

Cancer stem cells (CSCs) are rare subpopulations within tumors which are recognized as culprits in cancer recurrence, drug resistance and metastasis. However, the molecular mechanisms of how CSCs are regulated remain elusive. Kruppel-like factors (KLFs) are evolutionarily conserved zinc finger-containing transcription factors with diverse functions in cell differentiation, proliferation, embryogenesis and pluripotency. Recent progress has highlighted the significance of KLFs, especially KLF4, in cancer and CSCs. Therefore, for better therapeutics of cancer disease, it is crucial to develop a deeper understanding of the mechanisms of how KLF4 regulate CSC functions. Herein we summarized the current understanding of the transcriptional regulation of KLF4 in CSCs, and discussed the functional implications of targeting CSCs for potential cancer therapeutics.

Irf6 directly regulates Klf17 in zebrafish periderm and Klf4 in murine oral epithelium, and dominant-negative KLF4 variants are present in patients with cleft lip and palate

Non-syndromic (NS) cleft lip with or without cleft palate (CL/P) is a common disorder with a strong genetic underpinning. Genome-wide association studies have detected common variants associated with this disorder, but a large portion of the genetic risk for NSCL/P is conferred by unidentified rare sequence variants. Mutations in IRF6 (Interferon Regulatory Factor 6) and GRHL3 (Grainyhead-like 3) cause Van der Woude syndrome, which includes CL/P. Both genes encode members of a regulatory network governing periderm differentiation in model organisms. Here, we report that Krüppel-like factor 17 (Klf17), like Grhl3, acts downstream of Irf6 in this network in zebrafish periderm. Although Klf17 expression is absent from mammalian oral epithelium, a close homologue, Klf4, is expressed in this tissue and is required for the differentiation of epidermis. Chromosome configuration capture and reporter assays indicated that IRF6 directly regulates an oral-epithelium enhancer of KLF4. To test whether rare missense variants of KLF4 contribute risk for NSCL/P, we sequenced KLF4 in approximately 1000 NSCL/P cases and 300 controls. By one statistical test, missense variants of KLF4 as a group were enriched in cases versus controls. Moreover, two patient-derived KLF4 variants disrupted periderm differentiation upon forced expression in zebrafish embryos, suggesting that they have dominant-negative effect. These results indicate that rare NSCL/P risk variants can be found in members of the gene regulatory network governing periderm differentiation.

KLF2 exerts antifibrotic and vasoprotective effects in cirrhotic rat livers: behind the molecular mechanisms of statins

OBJECTIVE

In the liver, the transcription factor, Kruppel-like factor 2 (KLF2), is induced early during progression of cirrhosis to lessen the development of vascular dysfunction; nevertheless, its endogenous expression results insufficient to attenuate establishment of portal hypertension and aggravation of cirrhosis. Herein, we aimed to explore the effects and the underlying mechanisms of hepatic KLF2 overexpression in in vitro and in vivo models of liver cirrhosis.

DESIGN

Activation phenotype was evaluated in human and rat cirrhotic hepatic stellate cells (HSC) treated with the pharmacological inductor of KLF2 simvastatin, with adenovirus codifying for this transcription factor (Ad-KLF2), or vehicle, in presence/absence of inhibitors of KLF2. Possible paracrine interactions between parenchymal and non-parenchymal cells overexpressing KLF2 were studied. Effects of in vivo hepatic KLF2 overexpression on liver fibrosis and systemic and hepatic haemodynamics were assessed in cirrhotic rats.

RESULTS

KLF2 upregulation profoundly ameliorated HSC phenotype (reduced α-smooth muscle actin, procollagen I and oxidative stress) partly via the activation of the nuclear factor (NF)-E2-related factor 2 (Nrf2). Coculture experiments showed that improvement in HSC phenotype paracrinally ameliorated liver sinusoidal endothelial cells probably through a vascular endothelial growth factor-mediated mechanism. No paracrine interactions between hepatocytes and HSC were observed. Cirrhotic rats treated with simvastatin or Ad-KLF2 showed hepatic upregulation in the KLF2-Nrf2 pathway, deactivation of HSC and prominent reduction in liver fibrosis. Hepatic KLF2 overexpression was associated with lower portal pressure (-15%) due to both attenuations in the increased portal blood flow and hepatic vascular resistance, together with a significant improvement in hepatic endothelial dysfunction.

CONCLUSIONS

Exogenous hepatic KLF2 upregulation improves liver fibrosis, endothelial dysfunction and portal hypertension in cirrhosis.

Krüppel-like transcription factor 8 (Klf8) is expressed and active in the neurons of the mouse brain

Krüppel-like transcription factor 8 (KLF8) is a transcription factor suggested to be involved in various cellular events, including malignant cell transformation, still its expression in the adult rodent brain remained unknown. To analyze Klf8 in the mouse brain and to identify cell types expressing it, a specific transgenic Klf8(Gt1Gaj) mouse was used. The resulting Klf8 gene-driven β-galactosidase activity was visualized by X-gal histochemical staining of the brain sections. The obtained results were complemented by in situ RNA hybridization and immunohistochemistry. Klf8 was highly expressed throughout the adult mouse brain gray matter including the cerebral cortex, hippocampus, olfactory bulb, hypothalamus, pallidum, and striatum, but not in the cerebellum. Immunofluorescent double-labeling revealed that KLF8-immunoreactive cells were neurons, and the staining was located in their nucleus. This was the first study showing that Klf8 was highly expressed in various regions of the mouse brain and in particular in the neurons, where it was localized in the cell nuclei.

Genome-wide analysis of the zebrafish Klf family identifies two genes important for erythroid maturation

Krüppel-like transcription factors (Klfs), each of which contains a CACCC-box binding domain, have been investigated in a variety of developmental processes, such as angiogenesis, neurogenesis and somatic-cell reprogramming. However, the function and molecular mechanism by which the Klf family acts during developmental hematopoiesis remain elusive. Here, we report identification of 24 Klf family genes in zebrafish using bioinformatics. Gene expression profiling shows that 6 of these genes are expressed in blood and/or vascular endothelial cells during embryogenesis. Loss of function of 2 factors (klf3 or klf6a) leads to a decreased number of mature erythrocytes. Molecular studies indicate that both Klf3 and Klf6a are essential for erythroid cell differentiation and maturation but that these two proteins function in distinct manners. We find that Klf3 inhibits the expression of ferric-chelate reductase 1b (frrs1b), thereby promoting the maturation of erythroid cells, whereas Klf6a controls the erythroid cell cycle by negatively regulating cdkn1a expression to determine the rate of red blood cell proliferation. Taken together, our study provides a global view of the Klf family members that contribute to hematopoiesis in zebrafish and sheds new light on the function and molecular mechanism by which Klf3 and Klf6a act during erythropoiesis in vertebrates.

Krüpple-like factors in the central nervous system: novel mediators in stroke

Transcription factors play an important role in the pathophysiology of many neurological disorders, including stroke. In the past three decades, an increasing number of transcription factors and their related gene signaling networks have been identified, and have become a research focus in the stroke field. Krüppel-like factors (KLFs) are members of the zinc finger family of transcription factors with diverse regulatory functions in cell growth, differentiation, proliferation, migration, apoptosis, metabolism, and inflammation. KLFs are also abundantly expressed in the brain where they serve as critical regulators of neuronal development and regeneration to maintain normal brain function. Dysregulation of KLFs has been linked to various neurological disorders. Recently, there is emerging evidence that suggests KLFs have an important role in the pathogenesis of stroke and provide endogenous vaso-or neuro-protection in the brain's response to ischemic stimuli. In this review, we summarize the basic knowledge and advancement of these transcriptional mediators in the central nervous system, highlighting the novel roles of KLFs in stroke.

The Krüppel-like factors in female reproductive system pathologies

Female reproductive tract pathologies arise largely from dysregulation of estrogen and progesterone receptor signaling, leading to aberrant cell proliferation, survival, and differentiation. The signaling pathways orchestrated by these nuclear receptors are complex, require the participation of many nuclear proteins serving as key binding partners or targets, and involve a range of paracrine and autocrine regulatory circuits. The members of the Krüppel-like factor (KLF) family of transcription factors are ubiquitously expressed in reproductive tissues and have been increasingly implicated as critical co-regulators and integrators of steroid hormone actions. Herein, we explore the involvement of KLF family members in uterine pathology, describe their currently known molecular mechanisms, and discuss their potential as targets for therapeutic intervention.

Phosphorylation of Krüppel-like factor 3 (KLF3/BKLF) and C-terminal binding protein 2 (CtBP2) by homeodomain-interacting protein kinase 2 (HIPK2) modulates KLF3 DNA binding and activity

Krüppel-like factor 3 (KLF3/BKLF), a member of the Krüppel-like factor (KLF) family of transcription factors, is a widely expressed transcriptional repressor with diverse biological roles. Although there is considerable understanding of the molecular mechanisms that allow KLF3 to silence the activity of its target genes, less is known about the signal transduction pathways and post-translational modifications that modulate KLF3 activity in response to physiological stimuli. We observed that KLF3 is modified in a range of different tissues and found that the serine/threonine kinase homeodomain-interacting protein kinase 2 (HIPK2) can both bind and phosphorylate KLF3. Mass spectrometry identified serine 249 as the primary phosphorylation site. Mutation of this site reduces the ability of KLF3 to bind DNA and repress transcription. Furthermore, we also determined that HIPK2 can phosphorylate the KLF3 co-repressor C-terminal binding protein 2 (CtBP2) at serine 428. Finally, we found that phosphorylation of KLF3 and CtBP2 by HIPK2 strengthens the interaction between these two factors and increases transcriptional repression by KLF3. Taken together, our results indicate that HIPK2 potentiates the activity of KLF3.

Krüppel-like factors in cancer progression: three fingers on the steering wheel

Krüppel-like factors (KLFs) comprise a highly conserved family of zinc finger transcription factors, that are involved in a plethora of cellular processes, ranging from proliferation and apoptosis to differentiation, migration and pluripotency. During the last few years, evidence on their role and deregulation in different human cancers has been emerging. This review will discuss current knowledge on Krüppel-like transcription in the epithelial-mesenchymal transition (EMT), invasion and metastasis, with a focus on epithelial cancer biology and the extensive interface with pluripotency. Furthermore, as KLFs are able to mediate different outcomes, important influences of the cellular and microenvironmental context will be highlighted. Finally, we attempt to integrate diverse findings on KLF functions in EMT and stem cell biology to ft in the current model of cellular plasticity as a tool for successful metastatic dissemination.

Krüppel-like factor 5 as potential molecular marker in cervical cancer and the KLF family profile expression

Cervical cancer (CC) as other cancer types, presents molecular deregulations, such as the alterations of transcription factors. Krüppel-like factors (KLF) are a family of transcriptional regulators. They are involved in diverse cellular processes, such as proliferation, apoptosis, and angiogenesis among others. Here, we analyzed the expression of all 17 KLF members at messenger RNA (mRNA) level, and protein expression of the two most commonly altered KLF5 and KLF6 in cervical tissues. Fifty-nine cervical tissues ranging from normal tissue to CC were evaluated for KLF1-17 mRNA expression by end-point RT-PCR and KLF5 by qRT-PCR. For KLF5 and KLF6 protein analysis, a tissue microarray was constructed containing the 59 cases and subjected for immunohistochemistry assay and KLF6 IVS1-27G>A single nucleotide polymorphism by direct DNA sequencing. KLF2-16 expressions were present in normal tissue, whereas all 17 were present in Low-Grade Squamous Intraepithelial Lesion, High-Grade-SIL and CC, unrelated to presence of human papillomavirus (HPV). KLF5 mRNA expression gradually increased throughout the subgroups and overexpressed in CC (p=0.01). KLF5 and KLF6 proteins were immunodetected in all samples. For the KLF6 SNP analysis, 80% of the CC population analyzed presented GG genotype and the remaining 20% presented GA genotype (p=0.491). Our present data show that KLFs expression could not be related to HPV presence, at least at transcriptional level, and KLF5 mRNA overexpression could represent a potential molecular marker for CC; KLF6 SNP has no relation to increased risk of CC.

Optimization of culture condition of human bone marrow stromal cells in terms of purification, proliferation, and pluripotency

Human bone marrow stromal cells (hBMSCs) possess multilineage differentiation potential and play an important role in modern tissue engineering. However, the development of culture media to maintain hBMSCs in an undifferentiated, self-renewing state during their robust proliferation remains a challenge. We developed and tested modified growth medium [medium 1: epidermal growth factor (EGF), platelet-derived growth factor (PDGF), low glucose, 2% fetal calf serum (FCS)] on hBMSCs by comparing primary cell isolation, multipassage expansion, culture morphology, proliferation, and cellular phenotype, and performing an expression analysis of intrinsic-regulated genes to other two media. Cell morphology, proliferation, and phenotype varied among the media, while cells cultured in medium 1 displayed small, spindle-shaped morphology with the highest rate of growth capacities and the expected phenotype. RT-PCR analysis showed that medium 1 displayed the lowest expression levels of osteogenic genes, chondrogenic genes (osteonectin, runt-related transcription factor 2, cartilage oligo matrix protein, and SOX9), and adipogenic genes (lipoprotein lipase). The expression of another adipogenic gene, peroxisome proliferator-activator receptor-γ2, was higher in medium 1 but did not reach significance. In addition, hBMSCs expanded in medium 1 showed the highest expression ratio of self-renewing-related genes Krüppel-like factor 2 (KLF2) and KLF5. In conclusion, medium 1 allows for better expansion and pluripotency maintenance of hBMSCs and serves as a preferred alternative to traditional serum-containing media for research applications and future clinical use.

Differential regulation of the α-globin locus by Krüppel-like Factor 3 in erythroid and non-erythroid cells

Background

Krüppel-like Factor 3 (KLF3) is a broadly expressed zinc-finger transcriptional repressor with diverse biological roles. During erythropoiesis, KLF3 acts as a feedback repressor of a set of genes that are activated by Krüppel-like Factor 1 (KLF1). Noting that KLF1 binds α-globin gene regulatory sequences during erythroid maturation, we sought to determine whether KLF3 also interacts with the α-globin locus to regulate transcription.

Results

We found that expression of a human transgenic α-globin reporter gene is markedly up-regulated in fetal and adult erythroid cells of Klf3^−/− mice. Inspection of the mouse and human α-globin promoters revealed a number of canonical KLF-binding sites, and indeed, KLF3 was shown to bind to these regions both in vitro and in vivo. Despite these observations, we did not detect an increase in endogenous murine α-globin expression in Klf3^−/− erythroid tissue. However, examination of murine embryonic fibroblasts lacking KLF3 revealed significant de-repression of α-globin gene expression. This suggests that KLF3 may contribute to the silencing of the α-globin locus in non-erythroid tissue. Moreover, ChIP-Seq analysis of murine fibroblasts demonstrated that across the locus, KLF3 does not occupy the promoter regions of the α-globin genes in these cells, but rather, binds to upstream, DNase hypersensitive regulatory regions.

Conclusions

These findings reveal that the occupancy profile of KLF3 at the α-globin locus differs in erythroid and non-erythroid cells. In erythroid cells, KLF3 primarily binds to the promoters of the adult α-globin genes, but appears dispensable for normal transcriptional regulation. In non-erythroid cells, KLF3 distinctly binds to the HS-12 and HS-26 elements and plays a non-redundant, albeit modest, role in the silencing of α-globin expression.

Repression of chimeric transcripts emanating from endogenous retrotransposons by a sequence-specific transcription factor

Background

Retroviral elements are pervasively transcribed and dynamically regulated during development. While multiple histone- and DNA-modifying enzymes have broadly been associated with their global silencing, little is known about how the many diverse retroviral families are each selectively recognized.

Results

Here we show that the zinc finger protein Krüppel-like Factor 3 (KLF3) specifically silences transcription from the ORR1A0 long terminal repeat in murine fetal and adult erythroid cells. In the absence of KLF3, we detect widespread transcription from ORR1A0 elements driven by the master erythroid regulator KLF1. In several instances these aberrant transcripts are spliced to downstream genic exons. One such chimeric transcript produces a novel, dominant negative isoform of PU.1 that can induce erythroid differentiation.

Conclusions

We propose that KLF3 ensures the integrity of the murine erythroid transcriptome through the selective repression of a particular retroelement and is likely one of multiple sequence-specific factors that cooperate to achieve global silencing.

KLF8 knockdown suppresses proliferation and invasion in human osteosarcoma cells

Krüppel-like factor 8 (KLF8) is a transcription factor that is important in the regulation of the cell cycle and has a critical role in oncogenic transformation and epithelial to mesenchymal transition (EMT). EMT is a key process in tumor metastasis. Although overexpression of KLF8 has been observed in a variety of human tumor types, the role of KLF8 in human osteosarcoma is yet to be elucidated. The present study aimed to investigate the biological impact of KLF8 on Saos-2 osteosarcoma cells. KLF8 gene expression was knocked down in vitro using a lentivirus-mediated small interfering (si)RNA method. Cell proliferation and cell cycle distribution were evaluated using 3-(4,5)-dimethylthiahiazo(-z-yl)-3,5-di-phenytetrazoliumromide and colony formation assays, and flow cytometry, respectively. Cell invasion was analyzed using a Transwell® invasion assay. Knockdown of KLF8 was found to significantly inhibit proliferation and invasion in osteosarcoma cells. These data suggest that KLF8 may exhibit an important role in osteosarcoma tumorigenesis and that KLF8 may be a potential therapeutic target for the treatment of osteosarcoma.

Emerging roles of zinc finger proteins in regulating adipogenesis

Proteins containing the zinc finger domain(s) are named zinc finger proteins (ZFPs), one of the largest classes of transcription factors in eukaryotic genomes. A large number of ZFPs have been studied and many of them were found to be involved in regulating normal growth and development of cells and tissues through diverse signal transduction pathways. Recent studies revealed that a small but increasing number of ZFPs could function as key transcriptional regulators involved in adipogenesis. Due to the prevalence of obesity and metabolic disorders, the investigation of molecular regulatory mechanisms of adipocyte development must be more completely understood in order to develop novel and long-term impact strategies for ameliorating obesity. In this review, we discuss recent work that has documented that ZFPs are important functional contributors to the regulation of adipogenesis. Taken together, these data lead to the conclusion that ZFPs may become promising targets to combat human obesity.

Regions outside the DNA-binding domain are critical for proper in vivo specificity of an archetypal zinc finger transcription factor

Transcription factors (TFs) are often regarded as being composed of a DNA-binding domain (DBD) and a functional domain. The two domains are considered separable and autonomous, with the DBD directing the factor to its target genes and the functional domain imparting transcriptional regulation. We examined an archetypal zinc finger (ZF) TF, Krüppel-like factor 3 with an N-terminal domain that binds the corepressor CtBP and a DBD composed of three ZFs at its C-terminus. We established a system to compare the genomic occupancy profile of wild-type Krüppel-like factor 3 with two mutants affecting the N-terminal functional domain: a mutant unable to contact the cofactor CtBP and a mutant lacking the entire N-terminal domain, but retaining the ZFs intact. Chromatin immunoprecipitation followed by sequencing was used to assess binding across the genome in murine embryonic fibroblasts. Unexpectedly, we observe that mutations in the N-terminal domain generally reduced binding, but there were also instances where binding was retained or even increased. These results provide a clear demonstration that the correct localization of TFs to their target genes is not solely dependent on their DNA-contact domains. This informs our understanding of how TFs operate and is of relevance to the design of artificial ZF proteins.

Three fingers on the switch: Krüppel-like factor 1 regulation of γ-globin to β-globin gene switching

PURPOSE OF REVIEW

Krüppel-like factor 1 (KLF1) regulates most aspects of erythropoiesis. Many years ago, transgenic mouse studies implicated KLF1 in the control of the human γ-globin to β-globin switch. In this review, we will integrate these initial studies with recent developments in human genetics to discuss our present understanding of how KLF1 and its target genes direct the switch.

RECENT FINDINGS

Recent studies have shown that human mutations in KLF1 are common and mostly asymptomatic, but lead to significant increases in levels of fetal hemoglobin (HbF) (α2γ2) and adult HbA2 (α2δ2). Genome-wide association studies (GWAS) have demonstrated that three primary loci are associated with increased HbF levels in the population: the β-globin locus itself, the BCL11A locus, and a site between MYB and HBS1L. We discuss evidence that KLF1 directly regulates BCL11A, MYB and other genes, which are involved directly or indirectly in γ-globin silencing, thus providing a link between GWAS and KLF1 in hemoglobin switching.

SUMMARY

KLF1 regulates the γ-globin to β-globin genetic switch by many mechanisms. Firstly, it facilitates formation of an active chromatin hub (ACH) at the β-globin gene cluster. Specifically, KLF1 conscripts the adult-stage β-globin gene to replace the γ-globin gene within the ACH in a stage-specific manner. Secondly, KLF1 acts as a direct activator of genes that encode repressors of γ-globin gene expression. Finally, KLF1 is a regulator of many components of the cell cycle machinery. We suggest that dysregulation of these genes leads to cell cycle perturbation and 'erythropoietic stress' leading to indirect upregulation of HbF.

Krüppel-like factor 8 promotes tumorigenic mammary stem cell induction by targeting miR-146a

The properties of stem cells can be induced during the epithelial to mesenchymal transition (EMT). The responsible molecular mechanisms, however, remain largely undefined. Here we report the identification of the microRNA-146a (miR-146a) as a common target of Krüppel-like factor 8 (KLF8) and TGF-β, both of which are known EMT-inducers. Upon KLF8 overexpression or TGF-β treatment, a significant portion of the MCF-10A cells gained stem cell traits as demonstrated by an increased expression of CD44(high)/CD24low, activity of aldehyde dehydrogenase (ALDH), mammosphere formation and chemoresistance. Along with this change, the expression of miR-146a was highly upregulated in the cells. Importantly, we found that miR-146a was aberrantly co-overexpressed with KLF8 in a panel of invasive human breast cancer cell lines. Ectopic expression of KLF8 failed to induce the stem cell traits in the MCF-10A cells if the cells were pre-treated with miR-146a inhibitor, whereas overexpression of miR-146a in the MCF-10A cells alone was sufficient to induce the stem cell traits. Co-staining and luciferase reporter analyses indicated that miR-146a targets the 3'-UTR of the Notch signaling inhibitor NUMB for translational inhibition. Overexpression of KLF8 dramatically potentiated the tumorigenecity of MCF-10A cells expressing the H-Ras oncogene, which was accompanied by a loss of NUMB expression in the tumors. Taken together, this study identifies a novel role and mechanism for KLF8 in inducing pro-tumorigenic mammary stem cells via miR-146a potentially by activating Notch signaling. This mechanism could be exploited as a therapeutic target against drug resistance of breast cancer.

Loss of Krüppel-like factor 3 (KLF3/BKLF) leads to upregulation of the insulin-sensitizing factor adipolin (FAM132A/CTRP12/C1qdc2)

Krüppel-like factor 3 (KLF3) is a transcriptional regulator that we have shown to be involved in the regulation of adipogenesis in vitro. Here, we report that KLF3-null mice are lean and protected from diet-induced obesity and glucose intolerance. On a chow diet, plasma levels of leptin are decreased, and adiponectin is increased. Despite significant reductions in body weight and adiposity, wild-type and knockout animals show equivalent energy intake, expenditure, and excretion. To investigate the molecular events underlying these observations, we used microarray analysis to compare gene expression in Klf3(+/+) and Klf3(-/-) tissues. We found that mRNA expression of Fam132a, which encodes a newly identified insulin-sensitizing adipokine, adipolin, is significantly upregulated in the absence of KLF3. We confirmed that KLF3 binds the Fam132a promoter in vitro and in vivo and that this leads to repression of promoter activity. Further, plasma adipolin levels were significantly increased in Klf3(-/-) mice compared with wild-type littermates. Boosting levels of adipolin via targeting of KLF3 offers a novel potential therapeutic strategy for the treatment of insulin resistance.

Diagnostic yield of array comparative genomic hybridization in adults with autism spectrum disorders

PURPOSE

Array comparative genomic hybridization is available for the evaluation of autism spectrum disorders. The diagnostic yield of testing is 5-18% in children with developmental disabilities, including autism spectrum disorders and multiple congenital anomalies. The yield of array comparative genomic hybridization in the adult autism spectrum disorder population is unknown.

METHODS

We performed a retrospective chart review for 40 consecutive patients referred for genetic evaluation of autism from July 2009 through April 2012. Four pediatric patients were excluded. Medical history and prior testing were reviewed. Clinical genetic evaluation and testing were offered to all patients.

RESULTS

The study population comprised 36 patients (age range 18-45, mean 25.3 years). An autism spectrum disorder diagnosis was confirmed in 34 of 36 patients by medical record review. One patient had had an abnormal karyotype; none had prior array comparative genomic hybridization testing. Of the 23 patients with autism who underwent array comparative genomic hybridization, 2 of 23 (8.7%) had pathogenic or presumed pathogenic abnormalities and 2 of 23 (8.7%) had likely pathogenic copy-number variants. An additional 5 of 23 (22%) of autism patients had variants of uncertain significance without subclassification.

CONCLUSION

Including one patient newly diagnosed with fragile X syndrome, our data showed abnormal or likely pathogenic findings in 5 of 24 (21%) adult autism patients. Genetic reevaluation in adult autism patients is warranted.