Functional domains and DNA-binding sequences of RFLAT-1/KLF13, a Krüppel-like transcription factor of activated T lymphocytes

Evolution of a Human-Specific De Novo Open Reading Frame and Its Linked Transcriptional Silencer

In the human genome, two short open reading frames (ORFs) separated by a transcriptional silencer and a small intervening sequence stem from the gene SMIM45. The two ORFs show different translational characteristics, and they also show divergent patterns of evolutionary development. The studies presented here describe the evolution of the components of SMIM45. One ORF consists of an ultra-conserved 68 amino acid (aa) sequence, whose origins can be traced beyond the evolutionary age of divergence of the elephant shark, ~462 MYA. The silencer also has ancient origins, but it has a complex and divergent pattern of evolutionary formation, as it overlaps both at the 68 aa ORF and the intervening sequence. The other ORF consists of 107 aa. It develops during primate evolution but is found to originate de novo from an ancestral non-coding genomic region with root origins within the Afrothere clade of placental mammals, whose evolutionary age of divergence is ~99 MYA. The formation of the complete 107 aa ORF during primate evolution is outlined, whereby sequence development is found to occur through biased mutations, with disruptive random mutations that also occur but lead to a dead-end. The 107 aa ORF is of particular significance, as there is evidence to suggest it is a protein that may function in human brain development. Its evolutionary formation presents a view of a human-specific ORF and its linked silencer that were predetermined in non-primate ancestral species. The genomic position of the silencer offers interesting possibilities for the regulation of transcription of the 107 aa ORF. A hypothesis is presented with respect to possible spatiotemporal expression of the 107 aa ORF in embryonic tissues.

Krüppel-like Factor-9 and Krüppel-like Factor-13: Highly Related, Multi-Functional, Transcriptional Repressors and Activators of Oncogenesis

Specificity Proteins/Krüppel-like Factors (SP/KLF family) are a conserved family of transcriptional regulators. These proteins share three highly conserved, contiguous zinc fingers in their carboxy-terminus, requisite for binding to cis elements in DNA. Each SP/KLF protein has unique primary sequence within its amino-terminal and carboxy-terminal regions, and it is these regions which interact with co-activators, co-repressors, and chromatin-modifying proteins to support the transcriptional activation and repression of target genes. Krüppel-like Factor 9 (KLF9) and Krüppel-like Factor 13 (KLF13) are two of the smallest members of the SP/KLF family, are paralogous, emerged early in metazoan evolution, and are highly conserved. Paradoxically, while most similar in primary sequence, KLF9 and KLF13 display many distinct roles in target cells. In this article, we summarize the work that has identified the roles of KLF9 (and to a lesser degree KLF13) in tumor suppression or promotion via unique effects on differentiation, pro- and anti-inflammatory pathways, oxidative stress, and tumor immune cell infiltration. We also highlight the great diversity of miRNAs, lncRNAs, and circular RNAs which provide mechanisms for the ubiquitous tumor-specific suppression of KLF9 mRNA and protein. Elucidation of KLF9 and KLF13 in cancer biology is likely to provide new inroads to the understanding of oncogenesis and its prevention and treatments.

Repression motif in HSF1 regulated by phosphorylation

The heat shock factor 1 (HSF1) is a transcription factor that itself is a sensor for stress and integrates various intrinsic or environmental stress sensing pathways. Thus HSF1 orchestrates the heat shock response (HSR) by translating these pathways into a distinct transcriptional program that aids the cells to cope with and adapt to proteotoxic stress. Although heavily researched the regulation of HSF1 activation is still not completely understood. A conserved reaction to stress is the hyperphosphorylation of the otherwise confined constitutive phosphorylated HSF1. Therefore, this stress specific phosphorylation is believed to be involved in the regulatory mechanism and hence, was and is focus of many studies, ascribing various effects to single phosphorylation sites. To gain additional insight into effects of phosphorylation, HSF1 carrying amino acid substitutions on up to 18 amino acids were tested for their transactivation potential on an HSR reporter plasmid. A pattern of eleven phosphor-mimicking and diminishing amino acid substitutions on well-known phosphorylation sites of HSF1 were introduced to produce transcriptional active [11 M(+)] or repressed [11 M(-)] phenotypes. It could be confirmed that heat activates HSF1 regardless of phosphorylation. Distinct cellular stress, obtained by chemical HSR inducers or mimicked by a constitutively active HSF1, showed clear differences in the activation potential of HSF1-11 M(+) and 11 M(-). Further refinement to the single amino acid level identified the S303/307 double-phosphorylation motif, wherein phosphorylation of S303 was sole responsible for the repressing effect. The effect could be reproduced in different cell lines and is not entirely based on degradation. A small repression motif could be dissociated from the HSF1 context, which is still capable of repressing the background transcription of a specifically designed reporter plasmid. Taken together these results indicate, that besides already described mechanisms of pS303/307 mediated repression of HSF1 activation, an additional mechanism repressing the transcriptional output of the entire HSE containing promoter is mediated by this small repressive motif.

KLF4 transcription factor in tumorigenesis

Krüppel-like transcriptional factor is important in maintaining cellular functions. Deletion of Krüppel-like transcriptional factor usually causes abnormal embryonic development and even embryonic death. KLF4 is a prominent member of this family, and embryonic deletion of KLF4 leads to alterations in skin permeability and postnatal death. In addition to its important role in embryo development, it also plays a critical role in inflammation and malignancy. It has been investigated that KLF4 has a regulatory role in a variety of cancers, including lung, breast, prostate, colorectal, pancreatic, hepatocellular, ovarian, esophageal, bladder and brain cancer. However, the role of KLF4 in tumorigenesis is complex, which may link to its unique structure with both transcriptional activation and transcriptional repression domains, and to the regulation of its upstream and downstream signaling molecules. In this review, we will summarize the structural and functional aspects of KLF4, with a focus on KLF4 as a clinical biomarker and therapeutic target in different types of tumors.

KLF13 Loss‐of‐Function Mutations Underlying Familial Dilated Cardiomyopathy

Background

Dilated cardiomyopathy (DCM), characterized by progressive left ventricular enlargement and systolic dysfunction, is the most common type of cardiomyopathy and a leading cause of heart failure and cardiac death. Accumulating evidence underscores the critical role of genetic defects in the pathogenesis of DCM, and >250 genes have been implicated in DCM to date. However, DCM is of substantial genetic heterogeneity, and the genetic basis underpinning DCM remains elusive in most cases.

Methods and Results

By genome‐wide scan with microsatellite markers and genetic linkage analysis in a 4‐generation family inflicted with autosomal‐dominant DCM, a new locus for DCM was mapped on chromosome 15q13.1–q13.3, a 4.77‐cM (≈3.43 Mbp) interval between markers D15S1019 and D15S1010, with the largest 2‐point logarithm of odds score of 5.1175 for the marker D15S165 at recombination fraction (θ)=0.00. Whole‐exome sequencing analyses revealed that within the mapping chromosomal region, only the mutation in the KLF13 gene, c.430G>T (p.E144X), cosegregated with DCM in the family. In addition, sequencing analyses of KLF13 in another cohort of 266 unrelated patients with DCM and their available family members unveiled 2 new mutations, c.580G>T (p.E194X) and c.595T>C (p.C199R), which cosegregated with DCM in 2 families, respectively. The 3 mutations were absent from 418 healthy subjects. Functional assays demonstrated that the 3 mutants had no transactivation on the target genes ACTC1 and MYH7 (2 genes causally linked to DCM), alone or together with GATA4 (another gene contributing to DCM), and a diminished ability to bind the promoters of ACTC1 and MYH7 . Add, the E144X‐mutant KLF13 showed a defect in intracellular distribution.

Conclusions

This investigation indicates KLF13 as a new gene predisposing to DCM, which adds novel insight to the molecular pathogenesis underlying DCM, implying potential implications for prenatal prevention and precision treatment of DCM in a subset of patients.

Evolutionarily conserved transcription factors as regulators of longevity and targets for geroprotection

Aging is the single largest risk factor for many debilitating conditions, including heart diseases, stroke, cancer, diabetes, and neurodegenerative disorders. While far from understood in its full complexity, it is scientifically well-established that aging is influenced by genetic and environmental factors, and can be modulated by various interventions. One of aging's early hallmarks are aberrations in transcriptional networks, controlling for example metabolic homeostasis or the response to stress. Evidence in different model organisms abounds that a number of evolutionarily conserved transcription factors, which control such networks, can affect lifespan and healthspan across species. These transcription factors thus potentially represent conserved regulators of longevity and are emerging as important targets in the challenging quest to develop treatments to mitigate age-related diseases, and possibly even to slow aging itself. This review provides an overview of evolutionarily conserved transcription factors that impact longevity or age-related diseases in at least one multicellular model organism (nematodes, flies, or mice), and/or are tentatively linked to human aging. Discussed is the general evidence for transcriptional regulation of aging and disease, followed by a more detailed look at selected transcription factor families, the common metabolic pathways involved, and the targeting of transcription factors as a strategy for geroprotective interventions.

Genome-wide identification, evolution of Krüppel-like factors (klfs) and their expressions during GCRV challenge in grass carp (Ctenopharyngodonidella)

The Krüppel-like factors (KLFs) are a family of transcription factors containing three highly conserved tandem zinc finger structures, and each member participates in multiple physiological and pathological processes. The publication of genome sequences and the application of bioinformatics tools have led to the discovery of numerous gene families in fishes. Here, 24 klf genes were re-annotated in grass carp. Subsequently, the number of klf family members were investigated in some representative vertebrate species. Then, a series of bioinformatics analysis showed that grass carp klfs in the same subfamily had similar genome structure patterns and conserved distribution patterns of motifs, which supported their molecular evolutionary relationships. Furthermore, the mRNA expression profiles showed that 24 grass carp klfs were ubiquitously expressed in 11 different tissues, and some of them displayed tissue-enriched expression patterns. Finally, the expressions of the evolutionarily expanded klf members (klf2a, 2b, 2l, 5a, 5b, 5l, 6a, 6b, 7a, 7b, 11a, 11b, 12a, 12b, 15 and 15l) during GCRV infection were also analyzed. The results suggested that grass carp klf genes with common evolutionary sources may share functional diversity and conservation. In conclusion, this study provides preliminary clues for further researches on grass carp klf members and their underlying transcriptional regulatory mechanisms during GCRV infection.

Potential Molecular Cross Talk Among CCR5 Pathway Predicts Regorafenib Responsiveness in Metastatic Colorectal Cancer Patients

BACKGROUND

Genetic variants in the CCL5/CCR5 pathway have been shown to predict regorafenib efficacy in patients with metastatic colorectal cancer (mCRC). This study investigated the biological role of CCL4 and CCL3 gene polymorphisms in patients with refractory mCRC treated using regorafenib.

PATIENTS AND METHODS

We analyzed the genomic DNA extracted from mCRC patients receiving regorafenib. Serum factor levels at baseline, day 21, and progressive disease (PD) were measured using ELISA.

RESULTS

Decreased CCL4 levels at day 21 or increased CCL3 levels at PD were associated with better clinical outcomes. In patients with any CCL5 rs2280789 G allele, CCL3 significantly increased between BL and day 21 compared with the A/A variant (72.7% vs. 23.1%, p=0.006), but CCL4 decreased (31.8% vs. 69.2%, p=0.043).

CONCLUSION

Increased CCL3 and decreased CCL4 seen in specific genotypes may serve as potential biomarkers of regorafenib in mCRC patients.

Identification and analysis of KLF13 variants in patients with congenital heart disease

Background

The protein Kruppel-like factor 13 (KLF13) is a member of the KLF family and has been identified as a cardiac transcription factor that is involved in heart development. However, the relationship between KLF13 variants and CHDs in humans remains largely unknown. The present study aimed to screen the KLF13 variants in CHD patients and genetically analyze the functions of these variants.

Methods

KLF13 variants were sequenced in a cohort of 309 CHD patients and population-matched healthy controls (n = 200) using targeted sequencing. To investigate the effect of variants on the functional properties of the KLF13 protein, the expression and subcellular localization of the protein, as well as the transcriptional activities of downstream genes and physical interactions with other transcription factors, were assessed.

Results

Two heterozygous variants, c.487C > T (P163S) and c.467G > A (S156N), were identified in two out of 309 CHD patients with tricuspid valve atresia and transposition of the great arteries, respectively. No variants were found among healthy controls. The variant c.467G > A (S156N) had increased protein expression and enhanced functionality compared with the wild type, without affecting the subcellular localization. The other variant, c.487C > T (P163S), did not show any abnormalities in protein expression or subcellular localization; however, it inhibited the transcriptional activities of downstream target genes and physically interacted with TBX5, another cardiac transcription factor.

Conclusion

Our results show that the S156N and P163S variants may affect the transcriptional function of KLF13 and physical interaction with TBX5. These results identified KLF13 as a potential genetic risk factor for congenital heart disease.

Genetic variants in CCL5 and CCR5 genes and serum VEGF-A levels predict efficacy of bevacizumab in metastatic colorectal cancer patients

Early VEGF-A reduction (EVR) by targeting abundant VEGF-A is a potential predictive marker of bevacizumab (BEV). The CCL5/CCR5 axis modulates VEGF-A production via endothelial progenitor cells migration. We tested whether genetic polymorphisms in the CCL5/CCR5 pathway could predict efficacy of BEV in patients with metastatic colorectal cancer (mCRC) in a first-line setting. Genomic DNA was extracted from 215 samples from three independent cohorts: 61 patients receiving FOLFOX+BEV (evaluation cohort); 83 patients receiving FOLFOX (control cohort); 71 patients receiving FOLFOX/XELOX+BEV (exploratory cohort) for validation and serum biochemistry assay (n = 48). Single nucleotide polymorphisms of genes in the CCL5/CCR5 pathway were analyzed by PCR-based direct sequencing. Considering the unbalanced distribution of patient baseline characteristics between the evaluation and control cohorts, propensity score matching analysis was performed. Serum VEGF-A levels during treatment were measured using ELISA. Among the evaluation and control cohorts, patients with any CCL5 rs2280789 G allele had longer progression-free survival (PFS) and overall survival (OS) when receiving FOLFOX+BEV than FOLFOX (PFS: 19.8 vs. 11.0 months, HR 0.44, 95%CI: 0.24-0.83, p = 0.004; OS: 41.8 vs. 24.5 months, HR: 0.50, 95%CI: 0.26-0.95, p = 0.024). No significant difference was shown in patients with the A/A variant. In the exploratory cohort, CCL5 rs2280789 G alleles were associated with higher VEGF-A levels at baseline and a greater decrease in VEGF-A levels at day 14 compared to the A/A variant. CCL5 and CCR5 impact the angiogenic environment, and the genotypes in CCL5/CCR5 genes may identify specific populations who will benefit from BEV in first-line treatment for mCRC.

mGluR5 mediates post-radiotherapy fatigue development in cancer patients

Cancer-related fatigue (CRF) is a common burden in cancer patients and little is known about its underlying mechanism. The primary aim of this study was to identify gene signatures predictive of post-radiotherapy fatigue in prostate cancer patients. We employed Fisher Linear Discriminant Analysis (LDA) to identify predictive genes using whole genome microarray data from 36 men with prostate cancer. Ingenuity Pathway Analysis was used to determine functional networks of the predictive genes. Functional validation was performed using a T lymphocyte cell line, Jurkat E6.1. Cells were pretreated with metabotropic glutamate receptor 5 (mGluR5) agonist (DHPG), antagonist (MPEP), or control (PBS) for 20 min before irradiation at 8 Gy in a Mark-1 γ-irradiator. NF-κB activation was assessed using a NF-κB/Jurkat/GFP Transcriptional Reporter Cell Line. LDA achieved 83.3% accuracy in predicting post-radiotherapy fatigue. "Glutamate receptor signaling" was the most significant (p = 0.0002) pathway among the predictive genes. Functional validation using Jurkat cells revealed clustering of mGluR5 receptors as well as increased regulated on activation, normal T cell expressed and secreted (RANTES) production post irradiation in cells pretreated with DHPG, whereas inhibition of mGluR5 activity with MPEP decreased RANTES concentration after irradiation. DHPG pretreatment amplified irradiation-induced NF-κB activation suggesting a role of mGluR5 in modulating T cell activation after irradiation. These results suggest that mGluR5 signaling in T cells may play a key role in the development of chronic inflammation resulting in fatigue and contribute to individual differences in immune responses to radiation. Moreover, modulating mGluR5 provides a novel therapeutic option to treat CRF.

Gene Polymorphisms in the CCL5/CCR5 Pathway as a Genetic Biomarker for Outcome and Hand-Foot Skin Reaction in Metastatic Colorectal Cancer Patients Treated With Regorafenib

BACKGROUND

The C-C motif chemokine ligand 5/C-C motif chemokine receptor 5 (CCL5/CCR5) pathway has been shown to induce endothelial progenitor cell migration, resulting in increased vascular endothelial growth factor A expression. We hypothesized that genetic polymorphisms in the CCL5/CCR5 pathway predict efficacy and toxicity in patients with metastatic colorectal cancer (mCRC) treated with regorafenib.

PATIENTS AND METHODS

We analyzed genomic DNA extracted from 229 tumor samples from 2 different cohorts of patients who received regorafenib: an evaluation cohort of 79 Japanese patients and a validation cohort of 150 Italian patients. Single nucleotide polymorphisms of CCL5/CCR5 pathway-related genes were analyzed by PCR-based direct sequencing.

RESULTS

CCL4 rs1634517 and CCL3 rs1130371 were associated with progression-free survival in the evaluation cohort (hazard ratio [HR] 1.54, P = .043; HR 1.48, P = .064), and progression-free survival (HR 1.74, P < .001; HR 1.66, P = .002) and overall survival (HR 1.65, P = .004; HR 1.65, P = .004) in the validation cohort. The allelic frequencies of CCL5 single nucleotide polymorphisms varied between the evaluation and validation cohorts (G/G variant in rs2280789, 21.5% vs. 1.3%, P < .001; T/T variant in rs3817655, 22.8% vs. 2.7%, P < .001). In the evaluation cohort, patients with the G/G variant in rs2280789 had a higher incidence of grade 3+ hand-foot skin reaction compared to any A allele (53% vs. 27%, P = .078), and similarly to the T/T variant in rs3817655 compared to any A allele (56% vs. 26%, P = .026).

CONCLUSION

Genetic variants in the CCL5/CCR5 pathway may serve as prognostic markers and may predict severe hand-foot skin reaction in mCRC patients receiving regorafenib therapy.

Krüppel-like factors in mammalian stem cells and development

Krüppel-like factors (KLFs) are a family of zinc-finger transcription factors that are found in many species. Recent studies have shown that KLFs play a fundamental role in regulating diverse biological processes such as cell proliferation, differentiation, development and regeneration. Of note, several KLFs are also crucial for maintaining pluripotency and, hence, have been linked to reprogramming and regenerative medicine approaches. Here, we review the crucial functions of KLFs in mammalian embryogenesis, stem cell biology and regeneration, as revealed by studies of animal models. We also highlight how KLFs have been implicated in human diseases and outline potential avenues for future research.

Characterization and phylogenetic analysis of Krüppel-like transcription factor (KLF) gene family in tree shrews (Tupaia belangeri chinensis)

Krüppel-like factors (KLFs) are a family of zinc finger transcription factors regulating embryonic development and diseases. The phylogenetics of KLFs has not been studied in tree shrews, an animal lineage with a closer relationship to primates than rodents. Here, we identified 17 KLFs from Chinese tree shrew (Tupaia belangeri chinensis). KLF proteins are highly conserved among humans, monkeys, rats, mice and tree shrews compared to zebrafish and chickens. The CtBP binding site, Sin3A binding site and nuclear localization signals are largely conserved between tree shrews and human beings. Tupaia belangeri (Tb) KLF5 contains several conserved post-transcriptional modification motifs. Moreover, the mRNA and protein expression patterns of multiple tbKLFs are tissue-specific. TbKLF5, like hKLF5, significantly promotes NIH3T3 cell proliferation in vitro. These results provide insight for future studies regarding the structure and function of the tbKLF gene family.

Prophylactic Chronic Zinc Administration Increases Neuroinflammation in a Hypoxia-Ischemia Model

Acute and subacute administration of zinc exert neuroprotective effects in hypoxia-ischemia animal models; yet the effect of chronic administration of zinc still remains unknown. We addressed this issue by injecting zinc at a tolerable dose (0.5 mg/kg weight, i.p.) for 14 days before common carotid artery occlusion (CCAO) in a rat. After CCAO, the level of zinc was measured by atomic absorption spectrophotometry, nitrites were determined by Griess method, lipoperoxidation was measured by Gerard-Monnier assay, and mRNA expression of 84 genes coding for cytokines, chemokines, and their receptors was measured by qRT-PCR, whereas nitrotyrosine, chemokines, and their receptors were assessed by ELISA and histopathological changes in the temporoparietal cortex-hippocampus at different time points. Long-term memory was evaluated using Morris water maze. Following CCAO, a significant increase in nitrosative stress, inflammatory chemokines/receptors, and cell death was observed after 8 h, and a 2.5-fold increase in zinc levels was detected after 7 days. Although CXCL12 and FGF2 protein levels were significantly increased, the long-term memory was impaired 12 days after reperfusion in the Zn+CCAO group. Our data suggest that the chronic administration of zinc at tolerable doses causes nitrosative stress, toxic zinc accumulation, and neuroinflammation, which might account for the neuronal death and cerebral dysfunction after CCAO.

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.

A C2H2 zinc finger protein FEMU2 is required for fox1 expression in Chlamydomonas reinhardtii

Chlamydomonas reinhardtii fox1 gene encodes a ferroxidase that is involved in cellular Fe uptake and highly induced during Fe deficient conditions. In an effort to identify fox1 promoter regulatory elements, an insertional library was generated in a transgenic Chlamydomonas strain (2A38) harboring an arylsulfatase (ARS) reporter gene driven by the fox1 promoter. Mutants with a defective response to low iron conditions were selected for further study. Among these, a strain containing a disrupted femu2 gene was identified. Activation of the fox1 promoter by the femu2 gene product was confirmed by silencing the femu2 gene using RNA interference. In three femu2 RNAi transgenic lines (IR3, IR6, and IR7), ARS reporter gene activities declined by 84.3%, 86.4%, and 88.8%, respectively under Fe deficient conditions. Furthermore, RT-PCR analysis of both the femu2 mutant and the RNAi transgenic lines showed significantly decreased transcript abundance of the endogenous fox1 gene under Fe deficient conditions. Amino acid sequence analysis of the femu2 gene product identified three potential C2H2 zinc finger (ZF) motifs and a nuclear localization study suggests that FEMU2 is localized to the nucleus. In addition, a potential FEMU2 binding site ((G/T)TTGG(G/T)(G/T)T) was identified using PCR-mediated random binding site selection. Taken together, this evidence suggests that FEMU2 is involved in up-regulation of the fox1 gene in Fe deficient cells.

The Fli-1 transcription factor regulates the expression of CCL5/RANTES

The friend leukemia insertion site 1 (Fli-1) transcription factor, an Ets family member, is implicated in the pathogenesis of systemic lupus erythematosus in human patients and murine models of lupus. Lupus-prone mice with reduced Fli-1 expression have significantly less nephritis, prolonged survival, and decreased infiltrating inflammatory cells into the kidney. Inflammatory chemokines, including CCL5, are critical for attracting inflammatory cells. In this study, decreased CCL5 mRNA expression was observed in kidneys of lupus-prone NZM2410 mice with reduced Fli-1 expression. CCL5 protein expression was significantly decreased in endothelial cells transfected with Fli-1-specific small interfering RNA compared with controls. Fli-1 binds to endogenous Ets binding sites in the distal region of the CCL5 promoter. Transient transfection assays demonstrate that Fli-1 drives transcription from the CCL5 promoter in a dose-dependent manner. Both Ets1, another Ets family member, and Fli-1 drive transcription from the CCL5 promoter, although Fli-1 transactivation was significantly stronger. Ets1 acts as a dominant-negative transcription factor for Fli-1, indicating that they may have at least one DNA binding site in common. Systematic deletion of DNA binding sites demonstrates the importance of the sites located within a 225-bp region of the promoter. Mutation of the Fli-1 DNA binding domain significantly reduces transactivation of the CCL5 promoter by Fli-1. We identified a novel regulator of transcription for CCL5. These results suggest that Fli-1 is a novel and critical regulator of proinflammatory chemokines and affects the pathogenesis of disease through the regulation of factors that recruit inflammatory cells to sites of inflammation.

KLF13 cooperates with c-Maf to regulate IL-4 expression in CD4+ T cells

Kruppel-like factor (KLF) 13 is a transcription factor that positively regulates expression of the chemokine RANTES 3-5 d after activation of T cells. In this study, we document a key role for KLF13 in the expression of IL-4 in CD4(+) T cells. Gene expression analysis in activated T cells from Klf13(-/-) mice showed that IL-4, along with other Th2 cytokine genes, was downregulated when compared with cells from wild-type mice. The decreased levels of IL-4 were not associated with changes in expression of the Th2-inducing transcription factors GATA3 or c-Maf. Additional analysis revealed that KLF13 directly binds to IL-4 promoter regions and synergizes with c-Maf to positively regulate IL-4 expression. These results indicate that KLF13 is a positive regulator for differentiation of Th2 cells, as part of the transcriptional machinery that regulates IL-4 production in Th2 cells.

VIP contribution to the decidualization program: regulatory T cell recruitment

During early pregnancy, the human uterus undergoes profound tissue remodeling characterized by leukocyte invasion and production of proinflammatory cytokines, followed by tissue repair and tolerance maintenance induction. Vasoactive intestinal peptide (VIP) is produced by trophoblast cells and modulates the maternal immune response toward a tolerogenic profile. Here, we evaluated the contribution of the VIP/VPAC to endometrial renewal, inducing decidualization and the recruitment of induced regulatory T cells (iTregs) that accompany the implantation period. For that purpose, we used an in vitro model of decidualization with a human endometrial stromal cell line (HESC) stimulated with progesterone (P4) and lipopolysaccharide (LPS) simulating the inflammatory response during implantation and human iTregs (CD4(+)CD25(+)FOXP3(+)) differentiated from naïve T cells obtained from peripheral blood mononuclear cells of fertile women. We observed that VIP and its receptor VPAC1 are constitutively expressed in HESCs and that P4 increased VIP expression. Moreover, in HESC VIP induced expression of RANTES (CCL5), one of the main chemokines involved in T cell recruitment, and this effect is enhanced by the presence of P4 and LPS. Finally, assays of the migration of iTregs toward conditioned media from HESCs revealed that endogenous VIP production induced by P4 and LPS and RANTES production were involved, as anti-RANTES neutralizing Ab or VIP antagonist prevented their migration. We conclude that VIP may have an active role in the decidualization process, thus contributing to recruitment of iTregs toward endometrial stromal cells by increasing RANTES expression in a P4-dependent manner.

Polycomb antagonizes p300/CREB-binding protein-associated factor to silence FOXP3 in a Kruppel-like factor-dependent manner

Inducible gene expression underlies the epigenetically inherited differentiation program of most immune cells. We report that the promoter of the FOXP3 gene possesses two distinct functional states: an "off state" mediated by the polycomb histone methyltransferase complex and a histone acetyltransferase-dependent "on state." Regulating these states is the presence of a Kruppel-like factor (KLF)-containing Polycomb response element. In the KLF10(-/-) mouse, the FOXP3 promoter is epigenetically silenced by EZH2 (Enhancer of Zeste 2)-mediated trimethylation of Histone 3 K27; thus, impaired FOXP3 induction and inappropriate adaptive T regulatory cell differentiation results in vitro and in vivo. The epigenetic transmittance of adaptive T regulatory cell deficiency is demonstrated throughout more than 40 generations of mice. These results provide insight into chromatin remodeling events key to phenotypic features of distinct T cell populations.

KLF13 sustains thymic memory-like CD8(+) T cells in BALB/c mice by regulating IL-4-generating invariant natural killer T cells

Transcription factor KLF13 regulates the elevated numbers of iNKT cells in the BALB/c versus C57BL/6 thymus that results in production of sufficient levels of IL-4 to generate memory-like CD8+ T cells.

“Memory-like T cells” are a subset of thymic cells that acquire effector function through the maturation process rather than interaction with specific antigen. Disruption of genes encoding T cell signaling proteins or transcription factors have provided insights into the differentiation of such cells. In this study, we show that in BALB/c, but not C57BL/6, mice, a large portion of thymic CD4^-CD8⁺ T cells exhibit a memory-like phenotype. In BALB/c mice, IL-4 secreted by invariant natural killer T (iNKT) cells is both essential and sufficient for the generation of memory-like T cells. In C57BL/6 mice, iNKT cells are less abundant, producing IL-4 that is insufficient to induce thymic memory-like CD8⁺ T cells. BALB/c mice deficient in the transcription factor Kruppel-like factor (KLF) 13 have comparable numbers of iNKT cells to C57BL/6 mice and extremely low levels of thymic memory-like CD8⁺ T cells. This work documents the impact of a small number of KLF13-dependent iNKT cells on the generation of memory-like CD8⁺ T cells.

GKLF transfection inhibits the growth of xenograft tumors derived from human gastric carcinoma cell line SGC-7901 in nude mice

AIM: To investigate the effects of transfection of the gut-enriched Krüppel-like factor (GKLF) gene on the growth of xenograft tumors derived from human gastric carcinoma cell line SGC-7901 in nude mice and to explore the potential role of the GKLF gene in gastric carcinogenesis.

METHODS: A recombinant plasmid carrying the GKLF gene (pcDNA3.1-GKLF) was transfected into SGC-7901 cells by lipofectin-mediated method. Cells stably expressing the GKLF gene were selected using G418. SGC-7901 cells untransfected and those transfected with empty pcDNA3.1 plasmid were used as controls. A xenograft tumor model was then established. Tumor growth was monitored. Tumor histopathological changes were determined by hematoxylin and eosin (HE) staining. The expression of GKLF and Ki-67 proteins in xenograft tissue was detected by immunohistochemistry.

RESULTS: Compared with the SGC7901-pcDNA3.1 and SGC-7901 groups, the period of latency was significantly lengthened in the SGC7901-pcDNA3.1-GKLF group (14.67 d ± 3.08 d vs 8.33 d ± 1.03 d, 8.67 d ± 1.03 d, both P < 0.05). The weight of xenograft tumors in the SGC7901-pcDNA3.1-GKLF group was significantly lower than that in the SGC7901-pcDNA3.1 and SGC-7901 groups (4.46 g ± 0.92 g vs 8.05 g ± 1.66 g, 7.82 g ± 1.14 g, both P < 0.05). The degree of tumor differentiation in the SGC7901-pcDNA3.1-GKLF group was better than that in the other two groups. Furthermore, the positive proportion of GKLF protein expression in xenograft tissue was increased while that of Ki-67 protein expression was decreased in the SGC7901-pcDNA3.1-GKLF group when compared with the other two groups (4/6 vs 2/6, 2/6; 1/6 vs 4/6, 4/6).

CONCLUSION: Transfection of the GKLF gene inhibits the growth of subcutaneous xenograft tumors derived from SGC-7901 cell line in nude mice by down-regulating the expression of Ki-67. The GKLF gene is a potential target for gene therapy of gastric carcinoma.

Mammalian Krüppel-like factors in health and diseases

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, growth, development, survival, and responses to external stress. Seventeen mammalian KLFs have been identified, and numerous studies have been published that describe their basic biology and contribution to human diseases. KLF proteins have received much attention because of their involvement in the development and homeostasis of numerous organ systems. KLFs are critical regulators of physiological systems that include the cardiovascular, digestive, respiratory, hematological, and immune systems and are involved in disorders such as obesity, cardiovascular disease, cancer, and inflammatory conditions. Furthermore, KLFs play an important role in reprogramming somatic cells into induced pluripotent stem (iPS) cells and maintaining the pluripotent state of embryonic stem cells. As research on KLF proteins progresses, additional KLF functions and associations with disease are likely to be discovered. Here, we review the current knowledge of KLF proteins and describe common attributes of their biochemical and physiological functions and their pathophysiological roles.

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.

Putative tumor-suppressive function of Kruppel-like factor 4 in primary lung carcinoma

PURPOSE

Krüppel-like factor 4 (KLF4) is a zinc-finger protein that plays important roles in stem cells and the development of gastric cancers. However, the role of KLF4 in primary lung cancer is unknown. The purpose of this study is to determine possible roles of KLF4 in lung cancer.

EXPERIMENTAL DESIGN

The KLF4 expression in primary lung cancer tissues and case-matched normal lung tissues were determined by protein and mRNA analyses. The effects of KLF4 on cell proliferation, clonogenic formation, and cell cycle progression were determined in cultured lung cancer cells or bronchial epithelial cells after enforced KLF4 overexpression or small interfering RNA knockdown. The in vivo antitumor activity of KLF4 was evaluated by using stably transfected lung cancer cells and by adenovector-mediated gene delivery. The effect of KLF4 in regulating p21 and cyclin D1 was also evaluated.

RESULTS

KLF4 protein and mRNA levels were dramatically decreased in most primary lung tumors compared with in case-matched normal lung tissues. Enforced expression of KLF4 resulted in marked inhibition of cell growth and clonogenic formation. The tumor-suppressive effect of KLF4 was associated with its role in up-regulating p21 and down-regulating cyclin D1, leading to cell cycle arrest at the G(1)-S checkpoint. Knockdown of KLF4 promoted cell growth in immortalized human bronchial epithelial cells. The enforced expression of KLF4 gene to lung cancer cells by ex vivo transfection or adenovector-mediated gene transfer suppressed tumor growth in vivo.

CONCLUSIONS

Our results suggest that KLF4 plays an important role in suppressing the growth of lung carcinoma.

Characterization of Snail nuclear import pathways as representatives of C2H2 zinc finger transcription factors

Snail proteins are C(2)H(2) class zinc finger transcription factors involved in different processes during embryonic development, as well as in several adult pathologies including cancer and organ fibrosis. The expression of Snail transcription factors is tightly regulated at the transcriptional level and their activity is modulated by their subcellular localization. Given the importance of this gene family in physiology and pathology, it is essential to understand the mechanisms by which Snail proteins are imported into or exported out of the nucleus. Here we show that several importins mediate the nuclear import of the human Snail proteins and we identify a unique nuclear localization signal (NLS), recognized by all the importins, that has been conserved during the evolution of the Snail family. This NLS is characterized by the presence of basic residues at defined positions in at least three consecutive zinc fingers. Interestingly, the consensus residues for importin-binding are also involved in DNA binding, suggesting that importins could prevent non-specific binding of these transcription factors to cytoplasmic polyanions. Importantly, the identified basic residues are also conserved in other families of C(2)H(2) transcription factors whose nuclear localization requires the zinc finger region.

Hepatocyte nuclear factor 4alpha contributes to thyroid hormone homeostasis by cooperatively regulating the type 1 iodothyronine deiodinase gene with GATA4 and Kruppel-like transcription factor 9

Type 1 iodothyronine deiodinase (Dio1), a selenoenzyme catalyzing the bioactivation of thyroid hormone, is highly expressed in the liver. Dio1 mRNA and enzyme activity levels are markedly reduced in the livers of hepatocyte nuclear factor 4alpha (HNF4alpha)-null mice, thus accounting for its liver-specific expression. Consistent with this deficiency, serum T4 and rT3 concentrations are elevated in these mice compared with those in HNF4alpha-floxed control littermates; however, serum T3 levels are unchanged. Promoter analysis of the mouse Dio1 gene demonstrated that HNF4alpha plays a key role in the transactivation of the mouse Dio1 gene. Deletion and substitution mutation analyses demonstrated that a proximal HNF4alpha site (direct repeat 1 [TGGACAAAGGTGC]; HNF4alpha-RE) is crucial for transactivation of the mouse Dio1 gene by HNF4alpha. Mouse Dio1 is also stimulated by thyroid hormone signaling, but a direct role for thyroid hormone receptor action has not been reported. We also showed that thyroid hormone-inducible Krüppel-like factor 9 (KLF9) stimulates the mouse Dio1 promoter very efficiently through two CACCC sequences that are located on either side of HNF4alpha-RE. Furthermore, KLF9 functions together with HNF4alpha and GATA4 to synergistically activate the mouse Dio1 promoter, suggesting that Dio1 is regulated by thyroid hormone in the mouse through an indirect mechanism requiring prior KLF9 induction. In addition, we showed that physical interactions between the C-terminal zinc finger domain (Cf) of GATA4 and activation function 2 of HNF4alpha and between the basic domain adjacent to Cf of GATA4 and a C-terminal domain of KLF9 are both required for this synergistic response. Taken together, these results suggest that HNF4alpha regulates thyroid hormone homeostasis through transcriptional regulation of the mouse Dio1 gene with GATA4 and KLF9.

Interaction of PRP4 with Kruppel-like factor 13 regulates CCL5 transcription

Activation of resting T lymphocytes initiates differentiation into mature effector cells over 3-7 days. The chemokine CCL5 (RANTES) and its major transcriptional regulator, Krüppel-like factor 13 (KLF13), are expressed late (3-5 days) after activation in T lymphocytes. Using yeast two-hybrid screening of a human thymus cDNA library, PRP4, a serine/threonine protein kinase, was identified as a KLF13-binding protein. Specific interaction of KLF13 and PRP4 was confirmed by reciprocal coimmunoprecipitation. PRP4 is expressed in PHA-stimulated human T lymphocytes from days 1 and 7 with a peak at day 3. Using an in vitro kinase assay, it was found that PRP4 phosphorylates KLF13. Furthermore, although phosphorylation of KLF13 by PRP4 results in lower binding affinity to the A/B site of the CCL5 promoter, coexpression of PRP4 and KLF13 increases nuclear localization of KLF13 and CCL5 transcription. Finally, knock-down of PRP4 by small interfering RNA markedly decreases CCL5 expression in T lymphocytes. Thus, PRP4-mediated phosphorylation of KLF13 plays a role in the regulation of CCL5 expression in T lymphocytes.

Kruppel-like transcription factor 13 regulates T lymphocyte survival in vivo

Krüppel-like transcription factor (KLF)13, previously shown to regulate RANTES expression in vitro, is a member of the Krüppel- like family of transcription factors that controls many growth and developmental processes. To ascertain the function of KLF13 in vivo, Klf13-deficient mice were generated by gene targeting. As expected, activated T lymphocytes from Klf13(-/-) mice show decreased RANTES expression. However, these mice also exhibit enlarged thymi and spleens. TUNEL, as well as spontaneous and activation-induced death assays, demonstrated that prolonged survival of Klf13(-/-) thymocytes was due to decreased apoptosis. Microarray analysis suggests that protection from apoptosis-inducing stimuli in Klf13(-/-) thymocytes is due in part to increased expression of BCL-X(L), a potent antiapoptotic factor. This finding was confirmed in splenocytes and total thymocytes by real-time quantitative PCR and Western blot as well as in CD4+CD8- single-positive thymocytes by real-time quantitative PCR. Furthermore, EMSA and luciferase reporter assays demonstrated that KLF13 binds to multiple sites within the Bcl-X(L) promoter and results in decreased Bcl-X(L) promoter activity, making KLF13 a negative regulator of BCL-X(L).

Functional domains of the TGF-β-inducible transcription factor Tieg3 and detection of two putative nuclear localization signals within the zinc finger DNA-binding domain

The recently identified TGF-beta-inducible early gene 3 (Tieg3) belongs to the gene family of Sp1/Klf-like transcription factors and is upregulated immediately after TGF-beta treatment. To explore the molecular mechanisms of Tieg3-mediated transcriptional control, GAL4-based luciferase assays were performed in order to determine regulatory domains within the Tieg3 protein. Using EGFP-fusion proteins, we monitored the intracellular localization and mapped putative nuclear localization signals (NLS). We provide evidence that the amino-terminus of Tieg3 is essential to repress the transcription and that the loss of the mSin3A interacting domain (SID) disrupts the repressive effects of Tieg3 in the oligodendroglial cell line OLI-neu. Herein we also demonstrate that the zinc finger containing DNA-binding domain (DBD) alone is able to activate the transcription of a reporter gene. Sequence analysis of the zinc finger region revealed no similarities to known activation domains. Analysis of the subcellular localization disclosed Tieg3 as a nuclear protein. Further, we identified the DBD as being essential for the nuclear localization of Tieg3. We detected two closely located putative bipartite NLS within the second and third zinc finger, which are conserved among the members of the Tieg family of proteins. Together these results may help to increase the understanding of Tieg3-mediated transcriptional control and to characterize this TGF-beta-induced Sp1/Klf-like transcription factor.

Dynamic interplay of transcriptional machinery and chromatin regulates "late" expression of the chemokine RANTES in T lymphocytes

The chemokine RANTES (regulated upon activation normal T cell expressed and secreted) is expressed "late" (3 to 5 days) after activation in T lymphocytes. In order to understand the molecular events that accompany changes in gene expression, a detailed analysis of the interplay between transcriptional machinery and chromatin on the RANTES promoter over time was undertaken. Krüppel-like factor 13 (KLF13), a sequence-specific DNA binding transcription factor, orchestrates the induction of RANTES expression in T lymphocytes by ordered recruitment of effector molecules, including Nemo-like kinase, p300/cyclic AMP response element binding protein (CBP), p300/CBP-associated factor, and Brahma-related gene 1, that initiate sequential changes in phosphorylation and acetylation of histones and ATP-dependent chromatin remodeling near the TATA box of the RANTES promoter. These events recruit RNA polymerase II to the RANTES promoter and are responsible for late expression of RANTES in T lymphocytes. Therefore, KLF13 is a key regulator of late RANTES expression in T lymphocytes.

The Kruppel-like transcription factor KLF13 is a novel regulator of heart development

In humans, congenital heart defects occur in 1-2% of live birth, but the molecular mechanisms and causative genes remain unidentified in the majority of cases. We have uncovered a novel transcription pathway important for heart morphogenesis. We report that KLF13, a member of the Krüppel-like family of zinc-finger proteins, is expressed predominantly in the heart, binds evolutionarily conserved regulatory elements on cardiac promoters and activates cardiac transcription. KLF13 is conserved across species and knockdown of KLF13 in Xenopus embryos leads to atrial septal defects and hypotrabeculation similar to those observed in humans or mice with hypomorphic GATA-4 alleles. Physical and functional interaction with GATA-4, a dosage-sensitive cardiac regulator, provides a mechanistic explanation for KLF13 action in the heart. The data demonstrate that KLF13 is an important component of the transcription network required for heart development and suggest that KLF13 is a GATA-4 modifier; by analogy to other GATA-4 collaborators, mutations in KLF13 may be causative for congenital human heart disease.

Key role of Krüppel-like factor proteins in pancreatic cancer and other gastrointestinal neoplasias

PURPOSE OF REVIEW

To describe recent studies on Krüppel-like factor transcription factors and their relationship with gastrointestinal neoplasias, in particular pancreatic cancer.

RECENT FINDINGS

Krüppel-like factor proteins are a subfamily of transcription factors 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 including cell growth and differentiation. Recently, a number of publications have provided evidence of the implication of Krüppel-like factor proteins in gastrointestinal carcinogenesis.

SUMMARY

This article will focus on the results of studies in the field published in the last year.

Human KLF17 is a new member of the Sp/KLF family of transcription factors

The Sp/KLF transcription factors perform a variety of biological functions, but are related in that they bind GC-box and CACCC-box sequences in DNA via a highly conserved DNA-binding domain. A database homology search, using the zinc finger DNA-binding domain characteristic of the family, has identified human KLF17 as a new family member that is most closely related to KLFs 1-8 and 12. KLF17 appears to be the human orthologue of the previously reported mouse gene, zinc finger protein 393 (Zfp393), although it has diverged significantly. The DNA-binding domain is the most conserved region, suggesting that both the murine and the human forms recognize the same binding sites in DNA and may retain similar functions. We show that human KLF17 can bind G/C-rich sites via its zinc fingers and is able to activate transcription from CACCC-box elements. This is the first report of the DNA-binding characteristics and transactivation activity of human KLF17, which, together with the homology it displays to other KLF proteins, put it in the Sp/KLF family.

DNA Binding Domains and Nuclear Localization Signal of LEDGF: Contribution of two Helix-Turn-Helix (HTH)-like Domains and a Stretch of 58 Amino Acids of the N-terminal to the Trans-activation Potential of LEDGF

Lens epithelium derived growth factor (LEDGF), a nuclear protein, plays a role in regulating the transcription of stress-associated genes such as heat shock proteins by binding to consensus core DNA sequences nAGGn or nGAAn or their repeats, and in doing so helps to provide cyto-protection. However, additional information is required to identify the specific structural features of LEDGF involved in gene transcription. Here we have investigated the functional domains activating and repressing DNA-binding modules, by using a DNA binding assay and trans-activation experiments performed by analyzing proteins prepared from deletion constructs. The results disclosed the DNA-binding domain of N-terminal LEDGF mapped between amino acid residues 5 and 62, a 58 amino acid residue stretch PWWP domain which binds to stress response elements (STRE; A/TGGGGA/T). C-terminal LEDGF contains activation domains, an extensive loop-region (aa 418-530) with two helix-turn-helix (HTH)-like domains, and binds to a heat shock element (HSE; nGAAn). A trans-activation assay using Hsp27 promoter revealed that both HTH domains contribute in a cooperative manner to the trans-activation potential of LEDGF. Interestingly, removal of N-terminal LEDGF (aa 1-187) significantly enhances the gene activation potential of C-terminal LEDGF (aa 199-530); thus the N-terminal domain (aa 5-62), exhibits auto-transcriptional repression activity. It appears that this domain is involved in stabilizing the LEDGF-DNA binding complex. Collectively, our results demonstrate that LEDGF contains three DNA-binding domains, which regulate gene expression depending on cellular microenvironment and thus modify the physiology of cells to maintain cellular homeostasis.

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.

Analysis of transcription factor expression during discrete stages of postnatal thymocyte differentiation

Postnatal T lymphocyte differentiation in the thymus is a multistage process involving serial waves of lineage specification, proliferative expansion, and survival/cell death decisions. Although these are believed to originate from signals derived from various thymic stromal cells, the ultimate consequence of these signals is to induce the transcriptional changes that are definitive of each step. To help to characterize this process, high density microarrays were used to analyze transcription factor gene expression in RNA derived from progenitors at each stage of T lymphopoietic differentiation, and the results were validated by a number of appropriate methods. We find a large number of transcription factors to be expressed in developing T lymphocytes, including many with known roles in the control of differentiation, proliferation, or cell survival/death decisions in other cell types. Some of these are expressed throughout the developmental process, whereas others change substantially at specific developmental transitions. The latter are particularly interesting, because stage-specific changes make it increasingly likely that the corresponding transcription factors may be involved in stage-specific processes. Overall, the data presented here represent a large resource for gene discovery and for confirmation of results obtained through other methods.

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Activation of mouse RAG-2 promoter by Myc-associated zinc finger protein

Recombination activating gene-1 (RAG-1) and RAG-2 are expressed specifically in lymphocytes undergoing the antigen receptor gene rearrangement during the lymphocyte development. Our previous study showed that the -41 to -17 nucleotides (nt) 5' -upstream region of mouse RAG-2 were pre-requisite for the core promoter activity and that Pax-5/c-Myb/LEF-1 protein-protein complex was responsible for its activity in immature B cells. In this study, we show that the -65/-42 sequence, the non-conserved sequence between human and mouse RAG-2 promoter, is necessary for the full promoter activity for mouse RAG-2. Electrophoresis mobility shift assay revealed that Myc-associated zinc finger protein (MAZ) as well as SP1/3 binds a GA box in this region. Using chromatin immunoprecipitation, we show that MAZ binds the RAG-2 promoter region in pre-B cells. Furthermore, we show that MAZ synergistically activates the murine RAG-2 promoter with Pax-5/c-Myb/LEF-1 complex. These results first demonstrate that MAZ participates in activation of mouse RAG-2 promoter.

Signals and receptors for the nuclear transport of TFIIIA in Xenopus oocytes

The transcription factor IIIA (TFIIIA) is a zinc finger protein that binds to both 5S genes and 5S ribosomal RNA. In Xenopus oocytes it is predominantly associated with 5S rRNA and retained as storage particle (7S RNP) in the cytoplasm. In this study, we have mapped the nuclear localization signal (NLS) activity in TFIIIA both in vivo and in vitro. Two independent nuclear import signals localize to the zinc finger region of TFIIIA, which is in direct contact with 5S rRNA in the context of the 7S RNP. A systematic analysis of importin alpha variants in Xenopus reveals that only importin alpha1 and importin alpha2 are expressed in a pattern similar to TFIIIA during Xenopus embryogenesis; the same two import adaptors interact specifically with TFIIIA in vitro. On the basis of these and our previous findings, we therefore propose that the massive amounts of TFIIIA which are produced in early stages of oogenesis are imported into the nucleus via interaction with importin alpha1 and alpha2. TFIIIA-induced synthesis of 5S rRNA then allows for the formation and nuclear export of the 7S RNP; the 7S RNP is retained in the cytoplasm due to NLS masking via 5S rRNA binding.

Selective modulation of the SM22alpha promoter by the binding of BTEB3 (basal transcription element-binding protein 3) to TGGG repeats

We have previously identified a C2H2 zinc-finger transcription factor [BTEB3 (basal transcription element-binding protein 3)/KLF13 (Krüppel-like factor 13)] that activates the minimal promoter for the smooth muscle-specific SM22alpha gene in other types of cell. We show that recombinant BTEB3 binds to three TGGG motifs in the minimal SM22alpha promoter. By mutation analysis, only one of these boxes is required for BTEB3-dependent promoter activation in P19 cells and BTEB3 activates or inhibits reporter gene expression depending on the TGGG box to which it binds. Transient transfection experiments show that BTEB3 also activates reporter gene expression from the SM22alpha promoter in VSMCs (vascular smooth muscle cells). Similar studies showed that BTEB3 did not activate expression from the promoter regions of the smooth muscle myosin heavy chain or smooth muscle alpha-actin promoters, which contain similar sequences, implying that promoter activation by BTEB3 is selective. The expression of BTEB3 is readily detectable in VSMCs in vitro and is modulated in response to injury in vivo.

Subcellular localization of feline immunodeficiency virus integrase and mapping of its karyophilic determinant

Feline immunodeficiency virus (FIV), like other members of the lentivirus subfamily, such as human immunodeficiency virus type 1 (HIV-1), can infect nondividing and terminally differentiated cells. The transport of the preintegration complex into the nucleus is cell cycle-independent, but the mechanism is not well understood. Integrase is a key component of the complex and has been suggested to play a role in nuclear import during HIV-1 replication. To determine its karyophilic property, FIV integrase fused with glutathione S-transferase and enhanced green fluorescent protein was expressed in various feline and human cells and the subcellular localization was visualized by fluorescence microscopy. Wild-type FIV integrase was karyophilic in all cell lines tested and capable of targeting the fusion protein to the nuclei of transfected cells. Analysis of deletion and point mutation variants of FIV integrase failed to reveal any canonical nuclear localization signal, and the karyophilic determinant was mapped to the highly conserved N-terminal zinc-binding HHCC motif. A region near the C-terminal domain enriched with basic amino acid residues also affected the nuclear import of integrase. However, the role of this region is only modulatory in comparison to that of the zinc-binding domain. The N-terminal zinc-binding domain does not bind DNA and instead is essential in integrase multimerization. We therefore postulate that the karyophilic property of FIV integrase requires subunit multimerization promoted by the HHCC motif. Alternatively, the HHCC motif may directly promote interaction between FIV integrase and cellular proteins involved in nuclear import.

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.