Basic Krüppel-like factor functions within a network of interacting haematopoietic transcription factors

Erythroid Krüppel-Like Factor (KLF1): A Surprisingly Versatile Regulator of Erythroid Differentiation

Erythroid Krüppel-like factor (KLF1), first discovered in 1992, is an erythroid-restricted transcription factor (TF) that is essential for terminal differentiation of erythroid progenitors. At face value, KLF1 is a rather inconspicuous member of the 26-strong SP/KLF TF family. However, 30 years of research have revealed that KLF1 is a jack of all trades in the molecular control of erythropoiesis. Initially described as a one-trick pony required for high-level transcription of the adult HBB gene, we now know that it orchestrates the entire erythroid differentiation program. It does so not only as an activator but also as a repressor. In addition, KLF1 was the first TF shown to be directly involved in enhancer/promoter loop formation. KLF1 variants underlie a wide range of erythroid phenotypes in the human population, varying from very mild conditions such as hereditary persistence of fetal hemoglobin and the In(Lu) blood type in the case of haploinsufficiency, to much more serious non-spherocytic hemolytic anemias in the case of compound heterozygosity, to dominant congenital dyserythropoietic anemia type IV invariably caused by a de novo variant in a highly conserved amino acid in the KLF1 DNA-binding domain. In this chapter, we present an overview of the past and present of KLF1 research and discuss the significance of human KLF1 variants.

An integrated workflow for quantitative analysis of the newly synthesized proteome

The analysis of proteins that are newly synthesized upon a cellular perturbation can provide detailed insight into the proteomic response that is elicited by specific cues. This can be investigated by pulse-labeling of cells with clickable and stable-isotope-coded amino acids for the enrichment and mass spectrometric characterization of newly synthesized proteins (NSPs), however convoluted protocols prohibit their routine application. Here we report the optimization of multiple steps in sample preparation, mass spectrometry and data analysis, and we integrate them into a semi-automated workflow for the quantitative analysis of the newly synthesized proteome (QuaNPA). Reduced input requirements and data-independent acquisition (DIA) enable the analysis of triple-SILAC-labeled NSP samples, with enhanced throughput while featuring high quantitative accuracy. We apply QuaNPA to investigate the time-resolved cellular response to interferon-gamma (IFNg), observing rapid induction of targets 2 h after IFNg treatment. QuaNPA provides a powerful approach for large-scale investigation of NSPs to gain insight into complex cellular processes.

The balance between protective and pathogenic immune responses to pneumonia in the neonatal lung is enforced by gut microbiota

Although modern clinical practices such as cesarean sections and perinatal antibiotics have improved infant survival, treatment with broad-spectrum antibiotics alters intestinal microbiota and causes dysbiosis. Infants exposed to perinatal antibiotics have an increased likelihood of life-threatening infections, including pneumonia. Here, we investigated how the gut microbiota sculpt pulmonary immune responses, promoting recovery and resolution of infection in newborn rhesus macaques. Early-life antibiotic exposure interrupted the maturation of intestinal commensal bacteria and disrupted the developmental trajectory of the pulmonary immune system, as assessed by single-cell proteomic and transcriptomic analyses. Early-life antibiotic exposure rendered newborn macaques more susceptible to bacterial pneumonia, concurrent with increases in neutrophil senescence and hyperinflammation, broad inflammatory cytokine signaling, and macrophage dysfunction. This pathogenic reprogramming of pulmonary immunity was further reflected by a hyperinflammatory signature in all pulmonary immune cell subsets coupled with a global loss of tissue-protective, homeostatic pathways in the lungs of dysbiotic newborns. Fecal microbiota transfer was associated with partial correction of the broad immune maladaptations and protection against severe pneumonia. These data demonstrate the importance of intestinal microbiota in programming pulmonary immunity and support the idea that gut microbiota promote the balance between pathways driving tissue repair and inflammatory responses associated with clinical recovery from infection in infants. Our results highlight a potential role for microbial transfer for immune support in these at-risk infants.

C2H2-Type Zinc Finger Proteins: Evolutionarily Old and New Partners of the Nuclear Hormone Receptors

Nuclear hormone receptors (NRs) are evolutionarily conserved ligand-dependent transcription factors. They are essential for human life, mediating the actions of lipophilic molecules, such as steroid hormones and metabolites of fatty acid, cholesterol, and external toxic compounds. The C2H2-type zinc finger proteins (ZNFs) form the largest family of the transcription factors in humans and are characterized by multiple, tandemly arranged zinc fingers. Many of the C2H2-type ZNFs are conserved throughout evolution, suggesting their involvement in preserved biological activities, such as general transcriptional regulation and development/differentiation of organs/tissues observed in the early embryonic phase. However, some C2H2-type ZNFs, such as those with the Krüppel-associated box (KRAB) domain, appeared relatively late in evolution and have significantly increased family members in mammals including humans, possibly modulating their complicated transcriptional network and/or supporting the morphological development/functions specific to them. Such evolutional characteristics of the C2H2-type ZNFs indicate that these molecules influence the NR functions conserved through evolution, whereas some also adjust them to meet with specific needs of higher organisms. We review the interaction between NRs and C2H2-type ZNFs by focusing on some of the latter molecules.

KLF10 as a Tumor Suppressor Gene and Its TGF-β Signaling

Krüppel-like factor 10 (KLF10), originally named TGF-β (Transforming growth factor beta) inducible early gene 1 (TIEG1), is a DNA-binding transcriptional regulator containing a triple C2H2 zinc finger domain. By binding to Sp1 (specificity protein 1) sites on the DNA and interactions with other regulatory transcription factors, KLF10 encourages and suppresses the expression of multiple genes in many cell types. Many studies have investigated its signaling cascade, but other than the TGF-β/Smad signaling pathway, these are still not clear. KLF10 plays a role in proliferation, differentiation as well as apoptosis, just like other members of the SP (specificity proteins)/KLF (Krüppel-like Factors). Recently, several studies reported that KLF10 KO (Knock out) is associated with defects in cell and organs such as osteopenia, abnormal tendon or cardiac hypertrophy. Since KLF10 was first discovered, several studies have defined its role in cancer as a tumor suppressor. KLF10 demonstrate anti-proliferative effects and induce apoptosis in various carcinoma cells including pancreatic cancer, leukemia, and osteoporosis. Collectively, these data indicate that KLF10 plays a significant role in various biological processes and diseases, but its role in cancer is still unclear. Therefore, this review was conducted to describe and discuss the role and function of KLF10 in diseases, including cancer, with a special emphasis on its signaling with TGF-β.

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.

Epigenetic silencing of Kruppel like factor-3 increases expression of pro-metastatic miR-182

Accumulating evidence indicates that microRNAs (miRs) regulate cancer metastasis. We have shown that miR-182 drives sarcoma metastasis in vivo by coordinated regulation of multiple genes. Recently, we also demonstrated that in a subset of primary sarcomas that metastasize to the lung, miR-182 expression is elevated through binding of MyoD1 to the miR-182 promoter. However, it is not known if there are also transcription factors that inhibit miR-182 expression. Defining negative regulators of miR-182 expression may help explain why some sarcomas do not metastasize and may also identify pathways that can modulate miR-182 for therapeutic benefit. Here, we use an in silico screen, chromatin-immunoprecipitation, and luciferase reporter assays to discover that Kruppel like factor-3 (Klf-3) is a novel transcriptional repressor of miR-182. Knockdown of Klf-3 increases miR-182 expression, and stable overexpression of Klf-3, but not a DNA-binding mutant Klf-3, decreases miR-182 levels. Klf-3 expression is downregulated in both primary mouse and human metastatic sarcomas, and Klf-3 levels negatively correlate with miR-182 expression. Interestingly, Klf-3 also negatively regulates MyoD1, suggesting an alternative mechanism for Klf-3 to repress miR-182 expression in addition to direct binding of the miR-182 promoter. Using Methylation Specific PCR (MSP) and pyrosequencing assays, we found that Klf-3 is epigenetically silenced by DNA hypermethylation both in mouse and human sarcoma cells. Finally, we show the DNA methylation inhibitor 5'Azacytidine (Aza) restores Klf-3 expression while reducing miR-182 levels. Thus, our findings suggest that demethylating agents could potentially be used to modulate miR-182 levels as a therapeutic strategy.

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.

KLF1-null neonates display hydrops fetalis and a deranged erythroid transcriptome

We describe a case of severe neonatal anemia with kernicterus caused by compound heterozygosity for null mutations in KLF1, each inherited from asymptomatic parents. One of the mutations is novel. This is the first described case of a KLF1-null human. The phenotype of severe nonspherocytic hemolytic anemia, jaundice, hepatosplenomegaly, and marked erythroblastosis is more severe than that present in congenital dyserythropoietic anemia type IV as a result of dominant mutations in the second zinc-finger of KLF1. There was a very high level of HbF expression into childhood (>70%), consistent with a key role for KLF1 in human hemoglobin switching. We performed RNA-seq on circulating erythroblasts and found that human KLF1 acts like mouse Klf1 to coordinate expression of many genes required to build a red cell including those encoding globins, cytoskeletal components, AHSP, heme synthesis enzymes, cell-cycle regulators, and blood group antigens. We identify novel KLF1 target genes including KIF23 and KIF11 which are required for proper cytokinesis. We also identify new roles for KLF1 in autophagy, global transcriptional control, and RNA splicing. We suggest loss of KLF1 should be considered in otherwise unexplained cases of severe neonatal NSHA or hydrops fetalis.

Regulation of an inflammatory disease: Krüppel-like factors and atherosclerosis

This invited review summarizes work presented in the Russell Ross lecture delivered at the 2012 proceedings of the American Heart Association. We begin with a brief overview of the structural, cellular, and molecular biology of Krüppel-like factors. We then focus on discoveries during the past decade, implicating Krüppel-like factors as key determinants of vascular cell function in atherosclerotic vascular disease.

Novel excitation-contraction coupling related genes reveal aspects of muscle weakness beyond atrophy-new hopes for treatment of musculoskeletal diseases

Research over the last decade strengthened the understanding that skeletal muscles are not only the major tissue in the body from a volume point of view but also function as a master regulator contributing to optimal organismal health. These new contributions to the available body of knowledge triggered great interest in the roles of skeletal muscle beyond contraction. The World Health Organization, through its Global Burden of Disease (GBD) report, recently raised further awareness about the key importance of skeletal muscles as the GDB reported musculoskeletal (MSK) diseases have become the second greatest cause of disability, with more than 1.7 billion people in the globe affected by a diversity of MSK conditions. Besides their role in MSK disorders, skeletal muscles are also seen as principal metabolic organs with essential contributions to metabolic disorders, especially those linked to physical inactivity. In this review, we have focused on the unique function of new genes/proteins (i.e., MTMR14, MG29, sarcalumenin, KLF15) that during the last few years have helped provide novel insights about muscle function in health and disease, muscle fatigue, muscle metabolism, and muscle aging. Next, we provide an in depth discussion of how these genes/proteins converge into a common function of acting as regulators of intracellular calcium homeostasis. A clear link between dysfunctional calcium homeostasis is established and the special role of store-operated calcium entry is analyzed. The new knowledge that has been generated by the understanding of the roles of previously unknown modulatory genes of the skeletal muscle excitation-contraction coupling (ECC) process brings exciting new possibilities for treatment of MSK diseases, muscle regeneration, and skeletal muscle tissue engineering. The next decade of skeletal muscle and MSK research is bound to bring to fruition applied knowledge that will hopefully offset the current heavy and sad burden of MSK diseases on the planet.

Decreased Kruppel-like factor 4 (KLF4) expression may correlate with poor survival in gastric adenocarcinoma

Kruppel-like factors (KLFs) play either anti- or pro-proliferation roles in different human cancers. Here, we investigated the expression of KLF4 in gastric cancers and its correlation with clinicopathological parameters and overall survival. KLF4 expression was measured in 118 surgical specimens by immunohistochemical microarray assay. No association of cytoplasmic KLF4 expression with gender, TNM status, stage, survival, and pathological type was found. Using Kaplan-Meier analysis, significantly higher overall survival rate was observed in patients with high cytoplasmic KLF4 expression compared to low cytoplasmic KLF4 expression. Univariate analysis revealed that cytoplasmic KLF4 expression, grade, histological type, lymph node metastasis, and stages were correlated to longer overall survival. Our results suggest that KLF4 may play an anti-oncogenic role in gastric tumorigenesis.

Krüppel-like factors in cancer

Krüppel-like factors (KLFs) are a family of DNA-binding transcriptional regulators with diverse and essential functions in a multitude of cellular processes, including proliferation, differentiation, migration, inflammation and pluripotency. In this Review, we discuss the roles and regulation of the 17 known KLFs in various cancer-relevant processes. Importantly, the functions of KLFs are context dependent, with some KLFs having different roles in normal cells and cancer, during cancer development and progression and in different cancer types. We also identify key questions for the field that are likely to lead to important new translational research and discoveries in cancer biology.

A feedback loop consisting of microRNA 23a/27a and the β-like globin suppressors KLF3 and SP1 regulates globin gene expression

The developmental stage-specific expression of the human β-like globin genes has been studied for decades, and many transcriptional factors as well as other important cis elements have been identified. However, little is known about the microRNAs that potentially regulate β-like globin gene expression directly or indirectly during erythropoiesis. In this study, we show that microRNA 23a (miR-23a) and miR-27a promote β-like globin gene expression in K562 cells and primary erythroid cells through targeting of the transcription factors KLF3 and SP1. Intriguingly, miR-23a and miR-27a further enhance the transcription of β-like globin genes through repression of KLF3 and SP1 binding to the β-like globin gene locus during erythroid differentiation. Moreover, KLF3 can bind to the promoter of the miR-23a∼27a∼24-2 cluster and suppress this microRNA cluster expression. Hence, a positive feedback loop comprised of KLF3 and miR-23a promotes the expression of β-like globin genes and the miR-23a∼27a∼24-2 cluster during erythropoiesis.

Microarray characterization of gene expression changes in blood during acute ethanol exposure

Background

As part of the civil aviation safety program to define the adverse effects of ethanol on flying performance, we performed a DNA microarray analysis of human whole blood samples from a five-time point study of subjects administered ethanol orally, followed by breathalyzer analysis, to monitor blood alcohol concentration (BAC) to discover significant gene expression changes in response to the ethanol exposure.

Methods

Subjects were administered either orange juice or orange juice with ethanol. Blood samples were taken based on BAC and total RNA was isolated from PaxGene™ blood tubes. The amplified cDNA was used in microarray and quantitative real-time polymerase chain reaction (RT-qPCR) analyses to evaluate differential gene expression. Microarray data was analyzed in a pipeline fashion to summarize and normalize and the results evaluated for relative expression across time points with multiple methods. Candidate genes showing distinctive expression patterns in response to ethanol were clustered by pattern and further analyzed for related function, pathway membership and common transcription factor binding within and across clusters. RT-qPCR was used with representative genes to confirm relative transcript levels across time to those detected in microarrays.

Results

Microarray analysis of samples representing 0%, 0.04%, 0.08%, return to 0.04%, and 0.02% wt/vol BAC showed that changes in gene expression could be detected across the time course. The expression changes were verified by qRT-PCR.

The candidate genes of interest (GOI) identified from the microarray analysis and clustered by expression pattern across the five BAC points showed seven coordinately expressed groups. Analysis showed function-based networks, shared transcription factor binding sites and signaling pathways for members of the clusters. These include hematological functions, innate immunity and inflammation functions, metabolic functions expected of ethanol metabolism, and pancreatic and hepatic function. Five of the seven clusters showed links to the p38 MAPK pathway.

Conclusions

The results of this study provide a first look at changing gene expression patterns in human blood during an acute rise in blood ethanol concentration and its depletion because of metabolism and excretion, and demonstrate that it is possible to detect changes in gene expression using total RNA isolated from whole blood. The analysis approach for this study serves as a workflow to investigate the biology linked to expression changes across a time course and from these changes, to identify target genes that could serve as biomarkers linked to pilot performance.

Role of kruppel-like transcription factors in adipogenesis

The zinc-finger transcription factors of the kruppel-like factor family (KLF) are critical in many physiological and pathological processes including cell proliferation, differentiation, inflammation, and apoptosis. Recently, there is increasing evidence that suggests these KLFs have an important role in fat biology. This review summarizes the role of KLFs in lipid metabolism, especially in adipogenesis, and reveals the relationship networks among members of KLF family in differentiation.

Partner in fat metabolism: role of KLFs in fat burning and reproductive behavior

The abnormalities caused by excess fat accumulation can result in pathological conditions which are linked to several interrelated diseases, such as cardiovascular disease and obesity. This set of conditions, known as metabolic syndrome, is a global pandemic of enormous medical, economic, and social concern affecting a significant portion of the world’s population. Although genetics, physiology and environmental components play a major role in the onset of disease caused by excessive fat accumulation, little is known about how or to what extent each of these factors contributes to it. The worm, Caenorhabditis elegans offers an opportunity to study disease related to metabolic disorder in a developmental system that provides anatomical and genomic simplicity relative to the vertebrate animals and is an excellent eukaryotic genetic model which enable us to answer the questions concerning fat accumulation which remain unresolved. The stored triglycerides (TG) provide the primary source of energy during periods of food deficiency. In nature, lipid stored as TGs are hydrolyzed into fatty acids which are broken down through β-oxidation to yield acetyl-CoA. Our recent study suggests that a member of C. elegans Krüppel-like factor, klf-3 regulates lipid metabolism by promoting FA β-oxidation and in parallel may contribute in normal reproduction and fecundity. Genetic and epigenetic factors that influence this pathway may have considerable impact on fat related diseases in human. Increasing number of studies suggest the role of mammalian KLFs in adipogenesis. This functional conservation should guide our further effort to explore C. elegans as a legitimate model system for studying the role of KLFs in many pathway components of lipid metabolism.

"Go with the flow": how Krüppel-like factor 2 regulates the vasoprotective effects of shear stress

Laminar shear stress is known to confer potent anti-inflammatory, antithrombotic, and antiadhesive effects by differentially regulating endothelial gene expression. The identification of Krüppel-like factor 2 as a flow-responsive molecule has greatly advanced our understanding of molecular mechanisms governing vascular homeostasis. This review summarizes the current understanding of Krüppel-like factor 2 action in endothelial gene expression and function.

Krüppel-like transcription factors in the nervous system: novel players in neurite outgrowth and axon regeneration

The Krüppel-like family of transcription factors (KLFs) have been widely studied in proliferating cells, though very little is known about their role in post-mitotic cells, such as neurons. We have recently found that the KLFs play a role in regulating intrinsic axon growth ability in retinal ganglion cells (RGCs), a type of central nervous system (CNS) neuron. Previous KLF studies in other cell types suggest that there may be cell-type specific KLF expression patterns, and that their relative expression allows them to compete for binding sites, or to act redundantly to compensate for another's function. With at least 15 of 17 KLF family members expressed in neurons, it will be important for us to determine how this complex family functions to regulate the intricate gene programs of axon growth and regeneration. By further characterizing the mechanisms of the KLF family in the nervous system, we may better understand how they regulate neurite growth and axon regeneration.

Deregulated expression of Kruppel-like factors in acute myeloid leukemia

The known participation of Kruppel-like transcription factors (KLF) in cellular differentiation prompted us to investigate their expression in acute myeloid leukemia (AML) blast cells that are typically blocked in their differentiation. We determined the expression patterns of KLFs with a putative role in myeloid differentiation in a large cohort of primary AML patient samples, CD34+ progenitor cells and granulocytes from healthy donors. We found that KLF2, KLF3, KLF5 and KLF6 are significantly lower expressed in AML blast and CD34+ progenitor cells as compared to normal granulocytes. Moreover, we found markedly increased KLF levels in acute promyelocytic leukemia patients who received oral ATRA. Accordingly, we observed a strong induction of KLF5/6 upon ATRA-treatment in NB4 and HT93 APL but not in ATRA-resistant NB4-R cells. Lastly, knocking down KLF5 or KLF6 in NB4 cells significantly attenuated neutrophil differentiation. In conclusion, we found a significant repression of KLF transcription factors in primary AML samples as compared to mature neutrophils and further show that KLF5 and KLF6 are functionally involved in neutrophil differentiation of APL cells.

Role of Kruppel-like factors in leukocyte development, function, and disease

The Krüppel-like transcription factor (KLF) family participates in diverse aspects of cellular growth, development, differentiation, and activation. Recently, several groups have identified new connections between the function of these factors and leukocyte responses in health and disease. Gene targeting of individual KLFs in mice has uncovered novel and unexpected physiologic roles among myeloid and lymphocyte cell lineage maturation, particularly in the bone marrow niche and blood. In addition, several KLF family members are downstream targets of stimuli and signaling pathways critical to T-cell trafficking, T regulatory cell differentiation or suppressor function, monocyte/macrophage activation or renewal, and B memory cell maturation or activation. Indeed, KLFs have been implicated in subtypes of leukemia, lymphoma, autoimmunity, and in acute and chronic inflammatory disease states, such as atherosclerosis, diabetes, and airway inflammation, raising the possibility that KLFs and their upstream signals are of therapeutic interest. This review focuses on the relevant literature of Krüppel-like factors in leukocyte biology and their implications in clinical settings.

Effects of Astragalus polysaccharide on the erythroid lineage and microarray analysis in K562 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus polysaccharide (APS), obtained from Astragalus membranaceus, displays a range of activities in many systems, including the promotion of immune responses, anti-inflammation, and the protection of vessels. It possesses potent pharmacological activity on differentiation to the erythroid lineage.

AIM OF THE STUDY

To investigate the effects of APS on the erythroid differentiation and the mechanism of action by microarray analysis in K562 cells.

MATERIALS AND METHODS

Benzidine staining, semi-quantitative RT-PCR, Western blot and microarray methods were used to survey the effects of APS on inducing erythroid differentiation and the changes of gene expression profile in K562 cells.

RESULTS

Of the 13.2% positive cells detected by benzidine staining, the induction was the highest with 200 microg/ml APS on 72h. Ggamma-mRNA expression and fetal hemoglobin synthesis were significantly up-regulated. Microarray analysis showed that 31 genes were up-regulated and 108 genes were down-regulated. These differential expression genes generally regulate protein binding, cellular metabolic process, the cell proliferation, and transcriptional activator activity. The gamma-globin gene was up-regulated, the genes related with erythroid differentiation such as LMO2, Runx1 and GTF2I were up-regulated, while Bklf, Eklf, EPHB4 and Sp1 were down-regulated.

CONCLUSIONS

Our studies indicate that APS indicate potent activities on the erythroid differentiation by modulating genes of LMO2, Klf1, Klf3, Runx1, EphB4 and Sp1, increasing gamma-globin mRNA expression and fetal hemoglobin synthesis in K562 cells.

C-terminal binding proteins (CtBPs) attenuate KLF4-mediated transcriptional activation

We aimed to examine the physical interaction between CtBPs and KLF4 and the potential importance of this interaction. Co-immunoprecipitation indicated that CtBP1 indeed interacted with KLF4. This was supported by the co-localization of both KLF4 and CtBP1 in the promoter regions of KLF4 downstream target genes. In addition, overexpression of CtBP1 significantly decreased KLF4-mediated transcriptional activation in both an artificial (pGL5) and genuine (IAP and Keratin-4) reporter system. Mutations in the potential CtBP binding motif in KLF4 were accompanied by loss of the inhibitory effect of CtBP1 in the reporter assay and of the physical interaction with CtBP1. Overall, our results suggest that CtBPs attenuate KLF4-mediated transcriptional activation through the physical interaction with KLF4.

Kruppel-like factor 2 cooperates with the ETS family protein ERG to activate Flk1 expression during vascular development

The VEGF receptor, FLK1, is essential for differentiation of the endothelial lineage and for embryonic vascular development. Using comparative genomics, we have identified conserved ETS and Krüppel-like factor (KLF) binding sites within the Flk1 enhancer. In transgenic studies, mutation of either site results in dramatic reduction of Flk1 reporter expression. Overexpression of KLF2 or the ETS transcription factor ERG is sufficient to induce ectopic Flk1 expression in the Xenopus embryo. Inhibition of KLF2 function in the Xenopus embryo results in a dramatic reduction in Flk1 transcript levels. Furthermore, we show that KLF2 and ERG associate in a physical complex and that the two proteins synergistically activate transcription of Flk1. Since the ETS and KLF protein families have independently been recognized as important regulators of endothelial gene expression, cooperation between the two families has broad implications for gene regulation during development, normal physiology and vascular disease.

Distinct genetic loci control plasma HIV-RNA and cellular HIV-DNA levels in HIV-1 infection: the ANRS Genome Wide Association 01 study

Previous studies of the HIV-1 disease have shown that HLA and Chemokine receptor genetic variants influence disease progression and early viral load. We performed a Genome Wide Association study in a cohort of 605 HIV-1-infected seroconverters for detection of novel genetic factors that influence plasma HIV-RNA and cellular HIV-DNA levels. Most of the SNPs strongly associated with HIV-RNA levels were localised in the 6p21 major histocompatibility complex (MHC) region and were in the vicinity of class I and III genes. Moreover, protective alleles for four disease-associated SNPs in the MHC locus (rs2395029, rs13199524, rs12198173 and rs3093662) were strikingly over-represented among forty-five Long Term HIV controllers. Furthermore, we show that the HIV-DNA levels (reflecting the HIV reservoir) are associated with the same four SNPs, but also with two additional SNPs on chromosome 17 (rs6503919; intergenic region flanked by the DDX40 and YPEL2 genes) and chromosome 8 (rs2575735; within the Syndecan 2 gene). Our data provide evidence that the MHC controls both HIV replication and HIV reservoir. They also indicate that two additional genomic loci may influence the HIV reservoir.

Macrophage responses to silica nanoparticles are highly conserved across particle sizes

Concerns about the potential adverse health effects of engineered nanoparticles stems in part from the possibility that some materials display unique chemical and physical properties at nanoscales which could exacerbate their biological activity. However, studies that have assessed the effect of particle size across a comprehensive set of biological responses have not been reported. Using a macrophage cell model, we demonstrate that the ability of unopsonized amorphous silica particles to stimulate inflammatory protein secretion and induce macrophage cytotoxicity scales closely with the total administered particle surface area across a wide range of particle diameters (7-500 nm). Whole genome microarray analysis of the early gene expression changes induced by 10- and 500-nm particles showed that the magnitude of change for the majority of genes affected correlated more tightly with particle surface area than either particle mass or number. Gene expression changes that were particle size-specific were also identified. However, the overall biological processes represented by all gene expression changes were nearly identical, irrespective of particle diameter. Direct comparison of the cell processes represented in the 10- and 500-nm particle gene sets using gene set enrichment analysis revealed that among 1009 total biological processes, none were statistically enriched in one particle size group over the other. The key mechanisms involved in silica nanoparticle-mediated gene regulation and cytotoxicity have yet to be established. However, our results suggest that on an equivalent nominal surface area basis, common biological modes of action are expected for nano- and supranano-sized silica particles.

Defining a transcriptional fingerprint of murine splenic B-cell development

B-cell development occurs in a stepwise fashion that can be followed by the expression of B cell-specific surface markers. In this study, we wished to identify proteins that could contribute to the changes in expression of such markers. By using RNA from freshly isolated B220+ cells, we hoped to reduce the effect of artifacts that occur during the isolation and amplification steps necessary to use flow cytometry analysis-sorted subsets in microarray experiments. Analyses comparing expression patterns from B220+ 2-week bone marrow (pro-B, pre-B, immature B cells), 2-week spleen (predominantly transitional cells) and 8-week spleen (mainly mature B cells) yielded hundreds of genes. We also examined the B cell-activating factor (BAFF)-dependent effects on immature splenic B cells by comparing expression patterns in the spleen between 2-week A/J vs 2-week A/WySnJ mice, which lack functional BAFF receptor signaling. Genes that showed the expression differences between spleen and bone marrow samples were then analyzed through quantitative PCR on B-cell subsets isolated using two different sorting protocols. A comparison of the results from our study with the results from other analyses showed not only some overlap of preferentially expressed genes but also an expansion of other genes potentially involved in B-cell development.

A global role for zebrafish klf4 in embryonic erythropoiesis

There are two waves of erythropoiesis, known as primitive and definitive waves in mammals and lower vertebrates including zebrafish. The founding member of the Kruppel-like factor (KLF) family of CACCC-box binding proteins, EKLF/Klf1, is essential for definitive erythropoiesis in mammals but only plays a minor role in primitive erythropoiesis. Morpholino knockdown experiments have shown a role for zebrafish klf4 in primitive erythropoiesis and hatching gland formation. In order to generate a global understanding of how klf4 might influence gene expression and differentiation, we have performed expression profiling of klf4 morphants, and then performed validation of many putative target genes by qRT-PCR and whole mount in situ hybridization. We found a critical role for klf4 in embryonic globin, heme synthesis and hatching gland gene expression. In contrast, there was an increase in expression of definitive hematopoietic specific genes such as larval globin genes, runx1 and c-myb from 24 hpf, suggesting a selective role for klf4 in primitive rather than definitive erythropoiesis. In addition, we show klf4 preferentially binds CACCC box elements in the primitive zebrafish beta-like globin gene promoters. These results have global implications for primitive erythroid gene regulation by KLF-CACCC box interactions.

Role of Krüppel-Like Transcription Factors in Endothelial Biology

Krüppel-like factors are members of the zinc finger family of transcription factors that have been implicated as playing key roles in regulating cellular differentiation and tissue development. Studies over the past several years support an important role for this family of factors in vascular biology. This review summarizes the role of Krüppel-like factors in endothelial cell biology.

Kruppel-like Factors (KLFs) in muscle biology

The Kruppel-like Factor (KLF) family of zinc-finger transcription factors are critical regulators of cell differentiation, phenotypic modulation and physiologic function. An emerging body of evidence implicates an important role for these factors in cardiovascular biology, however, the role of KLFs in muscle biology is only beginning to be understood. This article reviews the published data describing the role of KLFs in the heart, smooth muscle, and skeletal muscle and highlights the importance of these factors in cardiovascular development, physiology and disease pathobiology.

KLF4 suppresses transformation of pre-B cells by ABL oncogenes

Genes that are strongly repressed after B-cell activation are candidates for being inactivated, mutated, or repressed in B-cell malignancies. Krüppel-like factor 4 (Klf4), a gene down-regulated in activated murine B cells, is expressed at low levels in several types of human B-cell lineage lymphomas and leukemias. The human KLF4 gene has been identified as a tumor suppressor gene in colon and gastric cancer; in concordance with this, overexpression of KLF4 can suppress proliferation in several epithelial cell types. Here we investigate the effects of KLF4 on pro/pre-B-cell transformation by v-Abl and BCR-ABL, oncogenes that cause leukemia in mice and humans. We show that overexpression of KLF4 induces arrest and apoptosis in the G1 phase of the cell cycle. KLF4-mediated death, but not cell-cycle arrest, can be rescued by Bcl-XL overexpression. Transformed pro/pre-B cells expressing KLF4 display increased expression of p21CIP and decreased expression of c-Myc and cyclin D2. Tetracycline-inducible expression of KLF4 in B-cell progenitors of transgenic mice blocks transformation by BCR-ABL and depletes leukemic pre-B cells in vivo. Collectively, our work identifies KLF4 as a putative tumor suppressor in B-cell malignancies.

The family feud: turning off Sp1 by Sp1-like KLF proteins

Sp1 is one of the best characterized transcriptional activators. The biological importance of Sp1 is underscored by the fact that several hundreds of genes are thought to be regulated by this protein. However, during the last 5 years, a more extended family of Sp1-like transcription factors has been identified and characterized by the presence of a conserved DNA-binding domain comprising three Krüppel-like zinc fingers. Each distinct family member differs in its ability to regulate transcription, and, as a consequence, to influence cellular processes. Specific activation and repression domains located within the N-terminal regions of these proteins are responsible for these differences by facilitating interactions with various co-activators and co-repressors. The present review primarily focuses on discussing the structural, biochemical and biological functions of the repressor members of this family of transcription factors. The existence of these transcriptional repressors provides a tightly regulated mechanism for silencing a large number of genes that are already known to be activated by Sp1.

Hepatic expression of the tumor necrosis factor family member lymphotoxin-beta is regulated by interleukin (IL)-6 and IL-1beta: transcriptional control mechanisms in oval cells and hepatoma cell lines

BACKGROUND

Lymphotoxin-beta (LT-beta) plays an important role in inflammation and its promoter contains a functional nuclear factor-kappaB (NF-kappaB) element, rendering it a likely target of pro-inflammatory cytokines. Inflammatory cytokines play a central role in liver regeneration resulting from acute or chronic liver injury, with interleukin (IL)-6 signaling essential for liver regeneration induced by partial hepatectomy. In hepatic oval cells observed following chronic liver injury, LT-beta levels are upregulated, suggesting a link between LT-beta and liver regeneration.

RESULTS

The expression of LT-beta in hepatic oval cell and hepatocellular carcinoma cell lines was further investigated, along with its responsiveness to IL-6 and IL-1beta. Key regulatory cis-acting elements of the LT-beta promoter that mediate IL-6 responsiveness (Sp/BKLF, Ets, NF-kappaB and Egr-1/Sp1) and IL-1beta responsiveness (NF-kappaB and Ets) of hepatic LT-beta expression were identified. The novel binding of basic Kruppel-like factor (BKLF) proteins to an apparent composite Sp/BKLF site of the LT-beta promoter was shown to mediate IL-6 responsiveness. Binding of NF-kappaB p65/p50 heterodimers and Ets-related transcription factors to their respective sites mediates responsiveness to IL-1beta.

CONCLUSION

The identification of IL-6 and IL-1beta as activators of LT-beta supports their involvement in LT-beta signaling in liver regeneration associated with chronic liver damage.

Proviral integration of an Abelson-murine leukemia virus deregulates BKLF-expression in the hypermutating pre-B cell line 18-81

The transcription factor BKLF (basic Krüppel-like factor, KLF3) is a member of the Krüppel-like factors (KLF) family. KLF members harbor a characteristic C-terminal zinc-finger DNA-binding domain and bind preferentially to CACCC-motifs. BKLF is highly expressed in haematopoietic and erythoid cells and works either as repressor or activator of transcription in various genes. BKLF-deficient mice display myeloproliferative disorders and abnormalities in haematopoiesis. Other members of the KLF-family such as GKLF and BCL11A have been implicated in tumorigenesis, however, for BKLF such association has not yet been demonstrated. We report here that a single Abelson-murine leukemia virus (A-MuLV) provirus is present in the genome of the hypermutating murine pre-B cell line 18-81. The provirus has integrated into the locus of the transcription factor BKLF. In contrast to other A-MuLV transformed pre-B cell lines, BKLF is highly transcribed in cell line 18-81. BKLF transcripts originate from the retroviral long terminal repeats (LTRs) and BKLF protein can be detected by gel shift retardation assay. We hypothesize on a potential role of BKLF deregulation in tumorigenesis and/or in the induction of somatic hypermutation in cell line 18-81.

Predictive screening for regulators of conserved functional gene modules (gene batteries) in mammals

Background

The expression of gene batteries, genomic units of functionally linked genes which are activated by similar sets of cis- and trans-acting regulators, has been proposed as a major determinant of cell specialization in metazoans. We developed a predictive procedure to screen the mouse and human genomes and transcriptomes for cases of gene-battery-like regulation.

Results

In a screen that covered ~40 per cent of all annotated protein-coding genes, we identified 21 co-expressed gene clusters with statistically supported sharing of cis-regulatory sequence elements. 66 predicted cases of over-represented transcription factor binding motifs were validated against the literature and fell into three categories: (i) previously described cases of gene battery-like regulation, (ii) previously unreported cases of gene battery-like regulation with some support in a limited number of genes, and (iii) predicted cases that currently lack experimental support. The novel predictions include for example Sox 17 and RFX transcription factor binding sites that were detected in ~10% of all testis specific genes, and HNF-1 and 4 binding sites that were detected in ~30% of all kidney specific genes respectively. The results are publicly available at .

Conclusion

21 co-expressed gene clusters were enriched for a total of 66 shared cis-regulatory sequence elements. A majority of these predictions represent novel cases of potential co-regulation of functionally coupled proteins. Critical technical parameters were evaluated, and the results and the methods provide a valuable resource for future experimental design.

Important roles of reversible acetylation in the function of hematopoietic transcription factors

Hematopoiesis is a very complex process whose proper functioning requires the regulated action of a number of transcription factors. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) play significant roles in the regulation of hematopoietic transcription factors activity. Transcription factors such as GATA-1, EKLF, NF-E2, GATA-1, PU.1 recruit HATs and HDACs to chromatin, leading to histone acetylation and deacetylation, that affect chromatin structure and result in gene expression changes. On the other hand, transcription factors themselves can be acetylated and deacetylated by HATs and HDACs, respectively. Consequently, some important functions of these transcription factors are influenced, including DNA binding, transcription activation, repressor activity and proteinprotein interactions. The regulation of hematopoietic transcription factors activity by HATs and HDACs may serve as a good model for studying how tissue-specific and lineage-specific gene expression is controlled through acetylation/ deacetylation of histone/nonhistone proteins.

An emerging role for Krüppel-like factors in vascular biology

The Krüppel-like family of transcription factors play diverse roles regulating cellular differentiation and tissue development. Accumulating evidence supports an important role for these factors in vascular biology. This review examines the current knowledge of this gene family's role in key cell types that critically regulate vessel biology under physiologic and pathologic states.

Identification and characterization of mechanistically distinct inducers of γ-globin transcription

Inhibition of HbS polymerization is a major target for therapeutic approaches in sickle cell anemia. Toward this goal, initial efforts at pharmacological elevation of fetal hemoglobin (HbF) has shown therapeutic efficacy. In order to identify well-tolerated, novel agents that induce HbF in patients, we developed a high-throughput screening approach based on induction of gamma-globin gene expression in erythroid cells. We measured gamma-globin transcription in K562 cells transfected with either gamma promoter elements fused with the locus control region hypersensitivity site 2 and luciferase reporter gene (HS2 gamma) or a beta-yeast artificial chromosome in which the luciferase reporter gene was recombined into the gamma-globin coding sequences (gamma YAC). Corresponding pharmacological increases in HbF protein were confirmed in both K562 cells and in human primary erythroid progenitor cells. Approximately 186,000 defined chemicals and fungal extracts were evaluated for their ability to increase gamma gene transcription in either HS2 gamma or gamma YAC models. Eleven distinct classes of compounds were identified, the majority of which were active within 24-48 hr. The short chain hydroxamate-containing class generally exhibited delayed maximal activity, which continued to increase transcription up to 120 hr. The cyclic tetrapeptide OSI-2040 and the hydroxamates were shown to have histone deacetylase inhibitory activity. In primary hematopoietic progenitor cell cultures, OSI-2040 increased HbF by 4.5-fold at a concentration of only 40 nM, comparable to the effects of hydroxyurea at 100 microM. This screening methodology successfully identifies active compounds for further mechanistic and preclinical evaluation as potential therapeutic agents for sickle cell anemia.

Impaired hematopoiesis in mice lacking the transcription factor Sp3

As the zinc-finger transcription factor specificity protein 3 (Sp3) has been implicated in the regulation of many hematopoietic-specific genes, we analyzed the role of Sp3 in hematopoiesis. At embryonic day 18.5 (E18.5), Sp3-/- mice exhibit a partial arrest of T-cell development in the thymus and B-cell numbers are reduced in liver and spleen. However, pre-B-cell proliferation and differentiation into immunoglobulin M-positive (IgM+) B cells in vitro are not affected. At E14.5 and E16.5, Sp3-/- mice exhibit a significant delay in the appearance of definitive erythrocytes in the blood, paralleled by a defect in the progression of differentiation of definitive erythroid cells in vitro. Perinatal death of the null mutants precludes the analysis of adult hematopoiesis in Sp3-/- mice. We therefore investigated the ability of E12.5 Sp3-/- liver cells to contribute to the hematopoietic compartment in an in vivo transplantation assay. Sp3-/- cells were able to repopulate the B- and T-lymphoid compartment, albeit with reduced efficiency. In contrast, Sp3-/- cells showed no significant engraftment in the erythroid and myeloid lineages. Thus, the absence of Sp3 results in cell-autonomous hematopoietic defects, affecting in particular the erythroid and myeloid cell lineages.

The LIM protein FHL3 binds basic Krüppel-like factor/Krüppel-like factor 3 and its co-repressor C-terminal-binding protein 2

The ability of DNA-binding transcription factors to recruit specific cofactors is central to the mechanism by which they regulate gene expression. BKLF/KLF3, a member of the Krüppel-like factor family of zinc finger proteins, is a potent transcriptional repressor that recruits a CtBP co-repressor. We show here that BKLF also recruits the four and a half LIM domain protein FHL3. Different but closely linked regions of BKLF mediate contact with CtBP2 and FHL3. We present evidence that CtBP2 also interacts with FHL3 and demonstrate that the three proteins co-elute in gel filtration experiments. CtBP and FHL proteins have been implicated in both nuclear and cytoplasmic functions, but expression of BKLF promotes the nuclear accumulation of both FHL3 and CtBP2. FHL proteins have been shown to act predominantly as co-activators of transcription. However, we find FHL3 can repress transcription. We suggest that LIM proteins like FHL3 are important in assembling specific repression or activation complexes, depending on conditions such as cofactor availability and promoter context.

Sp1- and Krüppel-like transcription factors

Sp1-like proteins and Krüppel-like factors (KLFs) are highly related zinc-finger proteins that are important components of the eukaryotic cellular transcriptional machinery. By regulating the expression of a large number of genes that have GC-rich promoters, Sp1-like/KLF transcription regulators may take part in virtually all facets of cellular function, including cell proliferation, apoptosis, differentiation, and neoplastic transformation. Individual members of the Sp1-like/KLF family can function as activators or repressors depending on which promoter they bind and the coregulators with which they interact. A long-standing research aim has been to define the mechanisms by which Sp1-like factors and KLFs regulate gene expression and cellular function in a cell- and promoter-specific manner. Most members of this family have been identified in mammals, with at least 21 Sp1-like/KLF proteins encoded in the human genome, and members are also found in frogs, worms and flies. Sp1-like/KLF proteins have highly conserved carboxy-terminal zinc-finger domains that function in DNA binding. The amino terminus, containing the transcription activation domain, can vary significantly between family members.

Cloning and characterization of the 5'-flanking region of the canine growth hormone gene

The growth hormone (GH) gene is expressed in a variety of tissues outside the pituitary, including the mammary gland. GH expression in the mammary gland is stimulated by progestins. The local synthesis of mammary GH may provide a highly proliferative environment within the mammary gland that may contribute to the development or progression of mammary tumours. To elucidate the mechanism regulating mammary GH expression, we cloned the 5'-flanking region of the canine GH gene using inverse polymerase chain reaction. Gel-shift experiments showed that several sequences in the 5'-flanking region of the GH gene bind mammary nuclear proteins and may be involved in basal and progesterone-induced mammary GH expression. Sequence analysis and comparison with the GH promoters of human, rat, and mouse genes revealed a number of shared binding sites for transcription factors such as Pit-1, which is involved in pituitary GH expression, and for factors involved in the differentiation of lymphoid cells. Moreover, a putative binding site for the progesterone receptor (PR) was identified in all promoters, indicating that the progestin-induced expression of GH in mammary tissue is most probably a direct effect of activated PRs on the GH gene promoter and that this may occur in various species.

Detection and visualization of compositionally similar cis-regulatory element clusters in orthologous and coordinately controlled genes

Evolutionarily conserved noncoding genomic sequences represent a potentially rich source for the discovery of gene regulatory regions. However, detecting and visualizing compositionally similar cis-element clusters in the context of conserved sequences is challenging. We have explored potential solutions and developed an algorithm and visualization method that combines the results of conserved sequence analyses (BLASTZ) with those of transcription factor binding site analyses (MatInspector) (http://trafac.chmcc.org). We define hits as the density of co-occurring cis-element transcription factor (TF)-binding sites measured within a 200-bp moving average window through phylogenetically conserved regions. The results are depicted as a Regulogram, in which the hit count is plotted as a function of position within each of the two genomic regions of the aligned orthologs. Within a high-scoring region, the relative arrangement of shared cis-elements within compositionally similar TF-binding site clusters is depicted in a Trafacgram. On the basis of analyses of several training data sets, the approach also allows for the detection of similarities in composition and relative arrangement of cis-element clusters within nonorthologous genes, promoters, and enhancers that exhibit coordinate regulatory properties. Known functional regulatory regions of nonorthologous and less-conserved orthologous genes frequently showed cis-element shuffling, demonstrating that compositional similarity can be more sensitive than sequence similarity. These results show that combining sequence similarity with cis-element compositional similarity provides a powerful aid for the identification of potential control regions.

Sp/Krüppel-like transcription factors are essential for the expression of mitochondrial glycerol phosphate dehydrogenase promoter B

The human mitochondrial glycerol phosphate dehydrogenase (hmGPD) is abundant in the normal pancreatic insulin cell and its level is lowered to 50% by high glucose and diabetes. Using Drosophila and INS-1 cells, we have analysed the hmGPD gene promoter B to characterize cis-elements and trans-acting factors that affect its regulation. We identified ten efficient Sp/Krüppel-like transcription-factor-binding sites in the promoter sequence. These sites include four GC-boxes (CCCGCCC at -227, -68, -46 and GGGCGAG at -382), three GT-boxes (CCCCACCC at -350, CCCACACCC at -257, and CACCCGCCC at -48), and three CT/GA-boxes (TCCCTCCC at -262, GGGAGGGAG at -129, and GGGAGGAGGA at -107). Transfection of Drosophila SL2 cells, which lack Sp/Krüppel-like factors, with constructs encoding either Sp1, Sp3, Sp4 or erythroid Krüppel-like factor (EKLF) specifically activates the hmGPD promoter B up to 50-fold. Promoter activation requires the Sp1 activation and the DNA binding domains. Co-transfected EKLF was synergistic with either Sp1 or Sp3. On the other hand, the basic Krüppel-like factor (BKLF) inhibited Sp1-and EKLF-mediated promoter activation. Similarly, constructs encoding either GA-binding protein (GABP) or PU.1 inhibited Sp1-mediated promoter activation. Oligonucleotide 'decoys' with potential transcription factor binding sites decreased promoter activity in both INS-1 and Drosophila cells. Significant loss of Sp- and EKLF-mediated activation was observed with some internal as well as sequential 5' deletions of the promoter DNA. The level of Sp1 protein was reduced by 50% in INS-1 cells chronically exposed to a high concentration of glucose. The results demonstrate that Sp/Krüppel-like factors are essential for mGPD gene expression.

Transcriptional regulation of erythropoiesis. Fine tuning of combinatorial multi-domain elements

Haematopoiesis, the differentiation of haematopoietic stem cells and progenitors into various lineages, involves complex interactions of transcription factors that modulate the expression of downstream genes and mediate proliferation and differentiation signals. Commitment of pluripotent haematopoietic stem cells to the erythroid lineage induces erythropoiesis, the production of red blood cells. This process involves a concerted progression through an erythroid burst forming unit (BFU-E), an erythroid colony forming unit (CFU-E), proerythroblast and an erythroblast. The terminally differentiated erythrocytes, in mammals, lose their nucleus yet function several more months. A well-coordinated cohort of transcription factors regulates the formation, survival, proliferation and differentiation of multipotent progenitor into the erythroid lineage. Here, we discuss broad-spectrum factors essential for self-renewal and/or differentiation of multipotent cells as well as specific factors required for proper erythroid development. These factors may operate solely or as part of transcriptional complexes, and exert activation or repression. Sequence comparisons reveal evolutionarily conserved modular composition for these factors; X-ray crystallography demonstrates that they include multidomain elements (e.g. HLH or zinc finger motifs), consistent with their complex interactions with other proteins. Finally, transfections and genomic studies show that the timing of each factor's expression during the hematopoietic process, the cell lineages affected and the existing combination of other factors determine the erythroid cell fate.

Sp1 and krüppel-like factor family of transcription factors in cell growth regulation and cancer

The Sp/KLF family contains at least twenty identified members which include Sp1-4 and numerous krüppel-like factors. Members of the family bind with varying affinities to sequences designated as 'Sp1 sites' (e.g., GC-boxes, CACCC-boxes, and basic transcription elements). Family members have different transcriptional properties and can modulate each other's activity by a variety of mechanisms. Since cells can express multiple family members, Sp/KLF factors are likely to make up a transcriptional network through which gene expression can be fine-tuned. 'Sp1 site'-dependent transcription can be growth-regulated, and the activity, expression, and/or post-translational modification of multiple family members is altered with cell growth. Furthermore, Sp/KLF factors are involved in many growth-related signal transduction pathways and their overexpression can have positive or negative effects on proliferation. In addition to growth control, Sp/KLF factors have been implicated in apoptosis and angiogenesis; thus, the family is involved in several aspects of tumorigenesis. Consistent with a role in cancer, Sp/KLF factors interact with oncogenes and tumor suppressors, they can be oncogenic themselves, and altered expression of family members has been detected in tumors. Effects of changes in Sp/KLF factors are context-dependent and can appear contradictory. Since these factors act within a network, this diversity of effects may arise from differences in the expression profile of family members in various cells. Thus, it is likely that the properties of the overall network of Sp/KLF factors play a determining role in regulation of cell growth and tumor progression.