Identification of a novel TGF-beta-regulated gene encoding a putative zinc finger protein in human osteoblasts

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.

KLF10 Gene Expression Modulates Fibrosis in Dystrophic Skeletal Muscle

Dystrophic skeletal muscle is characterized by fibrotic accumulation of extracellular matrix components that compromise muscle structure, function, and capacity for regeneration. Tissue fibrosis is often initiated and sustained through transforming growth factor-β (TGF-β) signaling, and Krüppel-like factor 10 (KLF10) is an immediate early gene that is transcriptionally activated in response to TGF-β signaling. It encodes a transcriptional regulator that mediates the effects of TGF-β signaling in a variety of cell types. This report presents results of investigation of the effects of loss of KLF10 gene expression in wild-type and dystrophic (mdx) skeletal muscle. On the basis of RT-PCR, Western blot, and histological analyses of mouse tibialis anterior and diaphragm muscles, collagen type I (Col1a1) and fibronectin gene expression and protein deposition were increased in KLF10^-/- mice, contributing to increased fibrosis. KLF10^-/- mice displayed increased expression of genes encoding SMAD2, SMAD3, and SMAD7, particularly in diaphragm muscle. SMAD4 gene expression was unchanged. Expression of the extracellular matrix remodeling genes, MMP2 and TIMP1, was also increased in KLF10-deficient mouse muscle. Histological analyses and assays of hydroxyproline content indicated that the loss of KLF10 increased fibrosis. Dystrophic KLF10-null mice also had reduced grip strength. The effects of loss of KLF10 gene expression were most pronounced in dystrophic diaphragm muscle, suggesting that KLF10 moderates the fibrotic effects of TGF-β signaling in chronically damaged regenerating muscle.

Impaired epidermal Langerhans cell maturation in TGFβ-inducible early gene 1 (TIEG1) knockout mice

TGF-β-inducible early gene 1 (TIEG1), also known as Krüppel-like factor 10 (Klf10), represents a major downstream transcription factor of transforming growth factor-β1 (TGF-β1) signaling. Epidermal Langerhans cells (LCs), a unique subpopulation of dendritic cells (DC), essentially mediates immune surveillance and tolerance. TGF-β1 plays a pivotal role in LC maintenance and function after birth, although the underpinning mechanisms remain elusive. Here, we hypothesized that TIEG1 might be involved in TGF-β1-mediated LC homeostasis and function. Utilizing TIEG1 null mice, we discovered that TIEG1 deficiency did not alter LC homeostasis at the steady state and LC repopulation at inflamed-state, as well as their antigen-uptake capacity, but significantly impaired their maturation ability, which was opposite to the fact that loss of TGF-β1 induced spontaneous LC maturation. Moreover, the ablation of TIEG1 enhanced skin contact hypersensitivity response. Our results suggested that TIEG1 is not a key molecule involved in TGF-β1-mediated homeostasis, while TIEG1-related signaling pathways regulate LC maturation and their function.

Transcriptome profiling analysis of senescent gingival fibroblasts in response to Fusobacterium nucleatum infection

Periodontal disease is caused by dental plaque biofilms. Fusobacterium nucleatum is an important periodontal pathogen involved in the development of bacterial complexity in dental plaque biofilms. Human gingival fibroblasts (GFs) act as the first line of defense against oral microorganisms and locally orchestrate immune responses by triggering the production of reactive oxygen species and pro-inflammatory cytokines (IL-6 and IL-8). The frequency and severity of periodontal diseases is known to increase in elderly subjects. However, despite several studies exploring the effects of aging in periodontal disease, the underlying mechanisms through which aging affects the interaction between F. nucleatum and human GFs remain unclear. To identify genes affected by infection, aging, or both, we performed an RNA-Seq analysis using GFs isolated from a single healthy donor that were passaged for a short period of time (P4) 'young GFs' or for longer period of time (P22) 'old GFs', and infected or not with F. nucleatum. Comparing F. nucleatum-infected and uninfected GF(P4) cells the differentially expressed genes (DEGs) were involved in host defense mechanisms (i.e., immune responses and defense responses), whereas comparing F. nucleatum-infected and uninfected GF(P22) cells the DEGs were involved in cell maintenance (i.e., TGF-β signaling, skeletal development). Most DEGs in F. nucleatum-infected GF(P22) cells were downregulated (85%) and were significantly associated with host defense responses such as inflammatory responses, when compared to the DEGs in F. nucleatum-infected GF(P4) cells. Five genes (GADD45b, KLF10, CSRNP1, ID1, and TM4SF1) were upregulated in response to F. nucleatum infection; however, this effect was only seen in GF(P22) cells. The genes identified here appear to interact with each other in a network associated with free radical scavenging, cell cycle, and cancer; therefore, they could be potential candidates involved in the aged GF's response to F. nucleatum infection. Further studies are needed to confirm these observations.

TIEG and estrogen modulate SOST expression in the murine skeleton

TIEG knockout (KO) mice exhibit a female-specific osteopenic phenotype and altered expression of TIEG in humans is associated with osteoporosis. Gene expression profiling studies identified sclerostin as one of the most highly up-regulated transcripts in the long bones of TIEG KO mice relative to WT littermates suggesting that TIEG may regulate SOST expression. TIEG was shown to substantially suppress SOST promoter activity and the regulatory elements through which TIEG functions were identified using promoter deletion and chromatin immunoprecipitation assays. Knockdown of TIEG in IDG-SW3 osteocyte cells using shRNA and CRISPR-Cas9 technology resulted in increased SOST expression and delayed mineralization, mimicking the results obtained from TIEG KO mouse bones. Given that TIEG is an estrogen regulated gene, and as changes in the hormonal milieu affect SOST expression, we performed ovariectomy (OVX) and estrogen replacement therapy (ERT) studies in WT and TIEG KO mice followed by miRNA and mRNA sequencing of cortical and trabecular compartments of femurs. SOST expression levels were considerably higher in cortical bone compared to trabecular bone. In cortical bone, SOST expression was increased following OVX only in WT mice and was suppressed following ERT in both genotypes. In contrast, SOST expression in trabecular bone was decreased following OVX and significantly increased following ERT. Interestingly, a number of miRNAs that are predicted to target sclerostin exhibited inverse expression levels in response to OVX and ERT. These data implicate important roles for TIEG and estrogen-regulated miRNAs in modulating SOST expression in bone.

TIEG1 modulates β-catenin sub-cellular localization and enhances Wnt signaling in bone

We have previously demonstrated that TGFβ Inducible Early Gene-1 (TIEG1), also known as KLF10, plays important roles in mediating skeletal development and homeostasis in mice. TIEG1 has also been identified in clinical studies as one of a handful of genes whose altered expression levels or allelic variations are associated with decreased bone mass and osteoporosis in humans. Here, we provide evidence for the first time that TIEG1 is involved in regulating the canonical Wnt signaling pathway in bone through multiple mechanisms of action. Decreased Wnt signaling in the absence of TIEG1 expression is shown to be in part due to impaired β-catenin nuclear localization resulting from alterations in the activity of AKT and GSK-3β. We also provide evidence that TIEG1 interacts with, and serves as a transcriptional co-activator for, Lef1 and β-catenin. Changes in Wnt signaling in the setting of altered TIEG1 expression and/or activity may in part explain the observed osteopenic phenotype of TIEG1 KO mice as well as the known links between TIEG1 expression levels/allelic variations and patients with osteoporosis.

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.

KLF10 loss in the pancreas provokes activation of SDF-1 and induces distant metastases of pancreatic ductal adenocarcinoma in the KrasG12D p53flox/flox model

Krüppel-like transcription factor 10 (KLF10), also named as TIEG1, plays essential roles in mediating transforming growth factor beta (TGFβ) signaling and has been shown to function as a tumor suppressor in multiple cancer types. However, its roles in mediating cancer progression in vivo have yet to be fully characterized. Here, we have employed two well-characterized Pdx-1CreLSL-Kras^G12D and Pdx-1CreLSL-Kras^G12Dp53^L/L pancreatic cancer models to ablate KLF10 expression and determine the impact of KLF10 deletion on tumor development and progression. We show that loss of KLF10 cooperates with Kras^G12D leading to an invasive and widely metastatic phenotype of pancreatic ductal adenocarcinoma (PDAC). Mechanistically, loss of KLF10 in PDAC is shown to increase distant metastases and cancer stemness through activation of SDF-1/CXCR4 and AP-1 pathways. Furthermore, we demonstrate that targeting the SDF-1/CXCR4 pathway in the context of KLF10 deletion substantially suppresses PDAC progression suggesting that inhibition of this pathway represents a novel therapeutic strategy for PDAC treatment.

Krüppel-like Transcription Factor KLF10 Suppresses TGFβ-Induced Epithelial-to-Mesenchymal Transition via a Negative Feedback Mechanism

TGFβ-SMAD signaling exerts a contextual effect that suppresses malignant growth early in epithelial tumorigenesis but promotes metastasis at later stages. Longstanding challenges in resolving this functional dichotomy may uncover new strategies to treat advanced carcinomas. The Krüppel-like transcription factor, KLF10, is a pivotal effector of TGFβ/SMAD signaling that mediates antiproliferative effects of TGFβ. In this study, we show how KLF10 opposes the prometastatic effects of TGFβ by limiting its ability to induce epithelial-to-mesenchymal transition (EMT). KLF10 depletion accentuated induction of EMT as assessed by multiple metrics. KLF10 occupied GC-rich sequences in the promoter region of the EMT-promoting transcription factor SLUG/SNAI2, repressing its transcription by recruiting HDAC1 and licensing the removal of activating histone acetylation marks. In clinical specimens of lung adenocarcinoma, low KLF10 expression associated with decreased patient survival, consistent with a pivotal role for KLF10 in distinguishing the antiproliferative versus prometastatic functions of TGFβ. Our results establish that KLF10 functions to suppress TGFβ-induced EMT, establishing a molecular basis for the dichotomy of TGFβ function during tumor progression. Cancer Res; 77(9); 2387-400. ©2017 AACR.

TIEG1 deficiency confers enhanced myocardial protection in the infarcted heart by mediating the Pten/Akt signalling pathway

The transforming growth factor (TGF)-β-inducible early gene-1 (TIEG1) plays a crucial role in modulating cell apoptosis and proliferation in a number of diseases, including pancreatic cancer, leukaemia and osteoporosis. However, the functional role of TIEG1 in the heart has not been fully defined. In this study, we first investigated the role of TIEG1 in ischaemic heart disease. For in vitro experiments, cardiomyocytes were isolated from both TIEG1 knockout (KO) and wile-type (WT) mice, and the apoptotic ratios were evaluated after a 48-h ischaemic insult. A cell proliferation assay was performed after 7 days of incubation under normoxic conditions. In addition, the angiogenic capacity of endothelial cells was determined by tube formation assay. For in vivo experiments, a model of myocardial infarction (MI) was established using both TIEG1 KO and WT mice. Echocardiography was performed at 3 and 28 days post-MI, whereas the haemodynamics test was performed 28 days post-MI. Histological analyses of apoptosis, proliferation, angiogenesis and infarct zone assessments were performed using terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling (TUNEL) staining, BrdU immunostaining, α-smooth muscle actin (α-SMA)/CD31 immunostaining and Masson's trichrome staining, respectively. Changes in the expression of related proteins caused by TIEG1 deficiency were confirmed using both reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. Our results demonstrated that the absence of TIEG1 prevented cardiomyocytes from undergoing apoptosis and promoted higher proliferation; it stimulated the proliferation of endothelial cells in vitro and in vivo. Improved cardiac function and less scar formation were observed in TIEG1 KO mice, and we also observed the altered expression of phosphatase and tensin homolog (Pten), Akt and Bcl-2/Bax, as well as vascular endothelial growth factor (VEGF). On the whole, our findings indicate that the absence of TIEG1 plays a cardioprotective role in ischaemic heart disease by promoting changes in Pten/Akt signalling.

TIEG1 Represses Smad7-Mediated Activation of TGF-β1/Smad Signaling in Keloid Pathogenesis

Transforming growth factor-β (TGF-β)/Smad signaling plays a key role in excessive fibrosis and keloid formations. Smad7 is a negative feedback regulator that prevents activation of TGF-β/Smad signaling. However, the regulatory mechanism for Smad7 in the keloid pathogenic process remains elusive. Here, we show that expression of TIEG1 is markedly higher in keloid fibroblasts, whereas protein, mRNA, and promoter activity levels of Smad7 are decreased. When TIEG1 was knocked down with small interfering RNA, both the promoter activity and protein expression of Smad7 were increased, whereas collagen production and the proliferation, migration, and invasion of keloid fibroblasts were decreased. In contrast, TIEG1 overexpression led to a decrease in Smad7 expression and Smad7 promoter activity. Upon TGF-β1 stimulation, TIEG1 promoted Smad2 phosphorylation by down-regulating Smad7. Luciferase reporter assays and chromatin immunoprecipitation assays further showed that TIEG1 can directly bind a GC-box/Sp1 site located between nucleotides -1392 and -1382 in the Smad7 promoter to repress Smad7 promoter activity. Taken together, these findings show that TIEG1 is highly expressed in human keloids and that it directly binds and represses Smad7 promoter-mediated activation of TGF-β/Smad2 signaling, thus providing clues for development of TIEG1 blocking strategies for therapy or prophylaxis of keloids.

Krüpple-like factor 10 regulates radio-sensitivity of pancreatic cancer via UV radiation resistance-associated gene

BACKGROUND AND PURPOSE

Krüpple-like factor 10 (Klf10), an early response gene of TGFβ, was reported to be a prognostic biomarker for pancreatic cancer survival. The role of Klf10 in predicting tumor response to cancer treatment is unknown.

MATERIALS AND METHODS

Genetically manipulated MiaPaCa and Panc-1 cells were established to evaluate clonogenic survival, autophagy, apoptosis and DNA repair after radiation. The interaction between Klf10 and UV radiation resistance-associated gene (UVRAG) was demonstrated by ChiP-PCR and luciferase reporter assay. Orthotopic murine tumor model and clinical specimens were used to evaluate radio-sensitivity of pancreatic cancer.

RESULTS

We found Klf10 silencing correlates with enhanced pancreatic cancer clonogenic survival and murine tumor growth after radiation. UVRAG was an essential down-stream mediator transcriptionally suppressed by Klf10. Silencing UVRAG mRNA in Klf10 depleted Panc-1 cells reversed the radio-resistant phenotypes including decreased apoptosis and enhanced DNA repair as well as autophagy. Metformin, an anti-diabetic agent, was found to increase Klf10 and suppress UVRAG expression to improve radiation cytotoxicity in pancreatic cancer. The predictive value of Klf10 in radiation response and the inverse correlation with UVRAG were confirmed in cohorts of pancreatic cancer patients.

CONCLUSIONS

Klf10 is a potential biomarker in predicting and sensitizing radiation effect in pancreatic cancer.

Impact of TIEG1 on the structural properties of fast- and slow-twitch skeletal muscle

INTRODUCTION

Transforming growth factor-beta (TGF-β)-inducible early gene-1 (TIEG1) is a transcription factor that is highly expressed in skeletal muscle. The purpose of this study was to characterize the structural properties of both fast-twitch (EDL) and slow-twitch (soleus) muscles in the hindlimb of TIEG1-deficient (TIEG1^-/- ) mice.

METHODS

Ten slow and 10 fast muscles were analyzed from TIEG1^-/- and wild-type (WT) mice using MRI texture (MRI-TA) and histological analyses.

RESULTS

MRI-TA could discriminate between WT slow and fast muscles. Deletion of the TIEG1 gene led to changes in the texture profile within both muscle types. Specifically, muscle isolated from TIEG1^-/- mice displayed hypertrophy, hyperplasia, and a modification of fiber area distribution.

CONCLUSIONS

We demonstrated that TIEG1 plays an important role in the structural properties of skeletal muscle. This study further implicates important roles for TIEG1 in the development of skeletal muscle and suggests that defects in TIEG1 expression and/or function may be associated with muscle disease. Muscle Nerve 55: 410-416, 2017.

Impact of TIEG1 Deletion on the Passive Mechanical Properties of Fast and Slow Twitch Skeletal Muscles in Female Mice

As transforming growth factor (TGF)-β inducible early gene-1 is highly expressed in skeletal muscle, the effect of TIEG1 gene deletion on the passive mechanical properties of slow and fast twitch muscle fibers was analyzed. Twenty five muscle fibers were harvested from soleus (Sol) and extensor digitorum longus (EDL) muscles from TIEG1^-/^- (N = 5) and control (N = 5) mice. Mechanical tests were performed on fibers and the dynamic and static stresses were measured. A viscoelastic Hill model of 3rd order was used to fit the experimental relaxation test data. In parallel, immunohistochemical analyses were performed on three serial transverse sections to detect the myosin isoforms within the slow and fast muscles. The percentage and the mean cross sectional area of each fiber type were calculated. These tests revealed a significant increase in the mechanical stress properties for the TIEG1^-/^- Sol fibers while a significant decrease appeared for the TIEG1^-/^- EDL fibers. Hill model tracked the shape of the experimental relaxation curve for both genotypes and both fiber types. Immunohistochemical results showed hypertrophy of all fiber types for TIEG1^-/^- muscles with an increase in the percentage of glycolytic fibers (IIX, and IIB) and a decrease of oxidative fibers (I, and IIA). This study has provided new insights into the role of TIEG1, known as KLF10, in the functional (Sol_typeI: more resistant, EDL_typeIIB: less resistant) and morphological (glycolytic hypertrophy) properties of fast and slow twitch skeletal muscles. Further investigation at the cellular level will better reveal the role of the TIEG1 gene in skeletal muscle tissue.

Imposed Optical Defocus Induces Isoform-Specific Up-Regulation of TGFβ Gene Expression in Chick Retinal Pigment Epithelium and Choroid but Not Neural Retina

PURPOSE

This study investigated the gene expression of TGFβ isoforms and their receptors in chick retina, retinal pigment epithelium (RPE), and choroid and the effects of short-term imposed optical defocus.

METHODS

The expression of TGFβ isoforms (TGF-β1, 2, 3) and TGFβ receptors (TGFBR1, 2, 3) was examined in the retina, RPE, and choroid of young White-Leghorn untreated chicks (19 days-old). The effects on the expression of the same genes of monocular +10 and -10 D defocusing lenses, worn for either 2 or 48 h by age-matched chicks, were also examined by comparing expression in treated and untreated fellow eyes. RNA was purified, characterized and then reverse transcribed to cDNA. Differential gene expression was quantified using real-time PCR.

RESULTS

All 3 isoforms of TGFβ and all 3 receptor subtypes were found to be expressed in all 3 ocular tissues, with apparent tissue-dependent differences in expression profiles. Data are reported as mean normalized expression relative to GAPDH. Sign-dependent optical defocus effects were also observed. Optical defocus did not affect retinal gene expression but in the RPE, TGF-β2 expression was significantly up-regulated with +10 D lenses, worn for either 2 h (349% increase ± 88%, p < 0.01) or 48 h (752% increase ± 166%, p < 0.001), and in the choroid, the expression of TGF-β3 was up-regulated with -10 D lenses, worn for 48 h (147% increase ± 9%, p < 0.01).

CONCLUSIONS

The effects of short term exposure to optical defocus on TGFβ gene expression in the RPE and choroid, which were sign-dependent and isoform specific, provide further supporting evidence for important roles of members of the TGFβ family and these two tissues in local signal cascades regulating ocular growth.

TIEG1 enhances Osterix expression and mediates its induction by TGFβ and BMP2 in osteoblasts

Deletion of TIEG1/KLF10 in mice results in an osteopenic skeletal phenotype with significant decreases in both bone mineral density and content throughout the skeleton. Calvarial osteoblasts isolated from TIEG1 knockout (KO) mice display numerous changes in gene expression and exhibit significant delays in their mineralization rates relative to wild-type (WT) controls. Here, we demonstrate that loss of TIEG1 expression in osteoblasts results in decreased levels of Osterix mRNA. Suppression of TIEG1 expression in WT osteoblasts leads to decreased Osterix expression while restoration of TIEG1 expression in TIEG1 KO osteoblasts results in increased levels of Osterix. Transient transfection and chromatin immunoprecipitation assays reveal that TIEG1 directly binds to and activates the Osterix promoter and demonstrate that the zinc finger-containing DNA binding domain of TIEG1 is necessary for this regulation. Furthermore, we reveal that TIEG1 expression is essential for the induction of Osterix expression by important bone-related cytokines such as TGFβ and BMP2 in osteoblast cells. Taken together, these data implicate an important role for TIEG1 in regulating the expression of Osterix, a master regulator of osteoblast differentiation and bone formation, and suggest that decreased expression of Osterix, as well as impaired TGFβ and BMP2 signaling, contribute to the observed osteopenic bone phenotype of TIEG1 KO mice.

Krüppel-like factor KLF10 deficiency predisposes to colitis through colonic macrophage dysregulation

Krüppel-like factor (KLF)-10 is an important transcriptional regulator of TGF-β1 signaling in both CD8(+) and CD4(+) T lymphocytes. In the present study, we demonstrate a novel role for KLF10 in the regulation of TGFβRII expression with functional relevance in macrophage differentiation and activation. We first show that transfer of KLF10(-/-) bone marrow-derived macrophages into wild-type (WT) mice leads to exacerbation of experimental colitis. At the cell biological level, using two phenotypic strategies, we show that KLF10-deficient mice have an altered colonic macrophage phenotype with higher frequency of proinflammatory LyC6(+)MHCII(+) cells and a reciprocal decrease of the anti-inflammatory LyC6(-)MHCII(+) subset. Additionally, the anti-inflammatory CD11b(+)CX3CR1(hi) subset of colonic macrophages is significantly decreased in KLF10(-/-) compared with WT mice under inflammatory conditions. Molecularly, CD11b(+) colonic macrophages from KLF10(-/-) mice exhibit a proinflammatory cytokine profile with increased production of TNF-α and lower production of IL-10 in response to LPS stimulation. Because KLF10 is a transcription factor, we explored how this protein may regulate macrophage function. Consequently, we analyzed the expression of TGFβRII expression in colonic macrophages and found that, in the absence of KLF10, macrophages express lower levels of TGFβRII and display an attenuated Smad-2 phosphorylation following TGF-β1 stimulation. We further show that KLF10 directly binds to the TGFβRII promoter in macrophages, leading to enhanced gene expression through histone H3 acetylation. Collectively, our data reveal a critical role for KLF10 in the epigenetic regulation of TGFβRII expression in macrophages and the acquisition of a "regulatory" phenotype that contributes to intestinal mucosal homeostasis.

Klf10 regulates odontoblast differentiation and mineralization via promoting expression of dentin matrix protein 1 and dentin sialophosphoprotein genes

Klf10, a member of the Krüppel-like family of transcription factors, is critical for osteoblast differentiation, bone formation and mineralization. However, whether Klf10 is involved in odontoblastic differentiation and tooth development has not been determined. In this study, we investigate the expression patterns of Klf10 during murine tooth development in vivo and its role in odontoblastic differentiation in vitro. Klf10 protein was expressed in the enamel organ and the underlying mesenchyme, ameloblasts and odontoblasts at early and later stages of murine molar formation. Furthermore, the expression of Klf10, Dmp1, Dspp and Runx2 was significantly elevated during the process of mouse dental papilla mesenchymal differentiation and mineralization. The overexpression of Klf10 induced dental papilla mesenchymal cell differentiation and mineralization as detected by alkaline phosphatase staining and alizarin red S assay. Klf10 additionally up-regulated the expression of odontoblastic differentiation marker genes Dmp1, Dspp and Runx2 in mouse dental papilla mesenchymal cells. The molecular mechanism of Klf10 in controlling Dmp1 and Dspp expression is thus to activate their regulatory regions in a dosage-dependent manner. Our results suggest that Klf10 is involved in tooth development and promotes odontoblastic differentiation via the up-regulation of Dmp1 and Dspp transcription.

Cabut/dTIEG associates with the transcription factor Yorkie for growth control

The Drosophila transcription factor Cabut/dTIEG (Cbt) is a growth regulator, whose expression is modulated by different stimuli. Here, we determine Cbt association with chromatin and identify Yorkie (Yki), the transcriptional co-activator of the Hippo (Hpo) pathway as its partner. Cbt and Yki co-localize on common gene promoters, and the expression of target genes varies according to changes in Cbt levels. Down-regulation of Cbt suppresses the overgrowth phenotypes caused by mutations in expanded (ex) and yki overexpression, whereas its up-regulation promotes cell proliferation. Our results imply that Cbt is a novel partner of Yki that is required as a transcriptional co-activator in growth control.

TGFβ2 regulates hypothalamic Trh expression through the TGFβ inducible early gene-1 (TIEG1) during fetal development

The hypothalamus regulates the homeostasis of the organism by controlling hormone secretion from the pituitary. The molecular mechanisms that regulate the differentiation of the hypothalamic thyrotropin-releasing hormone (TRH) phenotype are poorly understood. We have previously shown that Klf10 or TGFβ inducible early gene-1 (TIEG1) is enriched in fetal hypothalamic TRH neurons. Here, we show that expression of TGFβ isoforms (1-3) and both TGFβ receptors (TβRI and II) occurs in the hypothalamus concomitantly with the establishment of TRH neurons during late embryonic development. TGFβ2 induces Trh expression via a TIEG1 dependent mechanism. TIEG1 regulates Trh expression through an evolutionary conserved GC rich sequence on the Trh promoter. Finally, in mice deficient in TIEG1, Trh expression is lower than in wild type animals at embryonic day 17. These results indicate that TGFβ signaling, through the upregulation of TIEG1, plays an important role in the establishment of Trh expression in the embryonic hypothalamus.

Krüppel-like factor KLF10 regulates transforming growth factor receptor II expression and TGF-β signaling in CD8+ T lymphocytes

KLF10 has recently elicited significant attention as a transcriptional regulator of transforming growth factor-β1 (TGF-β1) signaling in CD4(+) T cells. In the current study, we demonstrate a novel role for KLF10 in the regulation of TGF-β receptor II (TGF-βRII) expression with functional relevance in antiviral immune response. Specifically, we show that KLF10-deficient mice have an increased number of effector/memory CD8(+) T cells, display higher levels of the T helper type 1 cell-associated transcription factor T-bet, and produce more IFN-γ following in vitro stimulation. In addition, KLF10(-/-) CD8(+) T cells show enhanced proliferation in vitro and homeostatic proliferation in vivo. Freshly isolated CD8(+) T cells from the spleen of adult mice express lower levels of surface TGF-βRII (TβRII). Congruently, in vitro activation of KLF10-deficient CD8(+) T cells upregulate TGF-βRII to a lesser extent compared with wild-type (WT) CD8(+) T cells, which results in attenuated Smad2 phosphorylation following TGF-β1 stimulation compared with WT CD8(+) T cells. Moreover, we demonstrate that KLF10 directly binds to the TGF-βRII promoter in T cells, leading to enhanced gene expression. In vivo viral infection with Daniel's strain Theiler's murine encephalomyelitis virus (TMEV) also led to lower expression of TGF-βRII among viral-specific KLF10(-/-) CD8(+) T cells and a higher percentage of IFN-γ-producing CD8(+) T cells in the spleen. Collectively, our data reveal a critical role for KLF10 in the transcriptional activation of TGF-βRII in CD8(+) T cells. Thus, KLF10 regulation of TGF-βRII in this cell subset may likely play a critical role in viral and tumor immune responses for which the integrity of the TGF-β1/TGF-βRII signaling pathway is crucial.

Kruppel-like factors in muscle health and disease

Kruppel-like factors (KLF) are zinc-finger DNA-binding transcription factors that are critical regulators of tissue homeostasis. Emerging evidence suggests that KLFs are critical regulators of muscle biology in the context of cardiovascular health and disease. The focus of this review is to provide an overview of the current state of knowledge regarding the physiologic and pathologic roles of KLFs in the three lineages of muscle: cardiac, smooth, and skeletal.

Progression of diet induced nonalcoholic steatohepatitis is accompanied by increased expression of Kruppel-like-factor 10 in mice

BACKGROUND

Kruppel-like-factor (KLF) 10 is identified as transforming growth factor (TGF) β inducible early gene and is reported to suppress lipogenic genes. Although previous studies report that TGFβ plays an important role in progression of nonalcoholic steatohepatitis (NASH) by regulating liver fibrosis, the association of KLF10 and NASH has never been explored. Thus we evaluated expressions and changes of KLF10 in diet induced NASH and in NASH which was alleviated by ursodeoxycholic acid (UDCA). We also assessed KLF10 in quiescent and activated hepatic stellate cells (HSCs).

METHODS

C57BL/6 mice were given high fat, sucrose diet (HFSD) at least for 12 weeks up to 48 weeks and sacrificed at 12, 24 and 48 weeks thereafter. In other groups, either standard diet (SD) or HFSD was given for 24 weeks at which point mice fed with HFSD were divided into two groups, and were given either UDCA in combination with HFSD or vehicle with HFSD. Mice under SD were given vehicle. HSCs were isolated from C57BL/6 mice in order to evaluated KLF10 expression in activated HSCs.

RESULTS

The mice were found to acquire liver steatosis and inflammation starting from week 12 of HFSD feeding, although significant liver fibrosis was noticed by week 24. Increased TGFβ and collagen α1(I) (Col1α(I)) expression was also apparent from week 24. However, expression of KLF10 mRNA started to increase from week 12, earlier than TGFβ gene. Up-regulation of KLF10 was accompanied by suppressed carbohydrate response element-binding protein (ChREBP) that is known to be protective against insulin resistance. The mice fed with HFSD and UDCA had decreased Colα(I) mRNA that was coincided with reduced TGFβ and KLF10 expression. Expression of ChREBP was also recovered by UDCA administration. Enhanced KLF10 was noticed in activated HSCs when quiescent cell showed minimal expression.

CONCLUSIONS

Our study demonstrated that KLF10 expression was significantly increased in diet induced NASH and collagen producing activated HSCs. We also noticed that this up-regulation of KLF10 was accompanied by increased TGFβ signaling genes and suppressed ChREBP expression. These observations suggest possible association of KLF10 and NASH progression.

Microarray meta-analysis identifies evolutionarily conserved BMP signaling targets in developing long bones

In vertebrates, BMP signaling has been demonstrated to be sufficient for bone formation in several tissue contexts. This suggests that genes necessary for bone formation are expressed in a BMP signaling dependent manner. However, till date no gene has been reported to be expressed in a BMP signaling dependent manner in bone. Our aim was to identify such genes. On searching the literature we found that several microarray experiments have been conducted where the transcriptome of osteogenic cells in absence and presence of BMP signaling activation have been compared. However, till date, there is no evidence to suggest that any of the genes found to be upregulated in presence of BMP signaling in these microarray analyses is indeed a target of BMP signaling in bone. We wanted to utilize this publicly available information to identify candidate BMP signaling target genes in vivo. We performed a meta-analysis of six such comparable microarray datasets. This analysis and subsequent experiments led to the identification of five targets of BMP signaling in bone that are conserved both in mouse and chick. Of these Lox, Klf10 and Gpr97 are likely to be direct transcriptional targets of BMP signaling pathway. Dpysl3, is a novel BMP signaling target identified in our study. Our data demonstrate that Dpysl3 is important for osteogenic differentiation of mesenchymal cells and is involved in cell secretion. We have demonstrated that the expression of Dpysl3 is co-operatively regulated by BMP signaling and Runx2. Based on our experimental data, in silico analysis of the putative promoter-enhancer regions of Bmp target genes and existing literature, we hypothesize that BMP signaling collaborates with multiple signaling pathways to regulate the expression of a unique set of genes involved in endochondral ossification.

Hunting complex differential gene interaction patterns across molecular contexts

Heterogeneity in genetic networks across different signaling molecular contexts can suggest molecular regulatory mechanisms. Here we describe a comparative chi-square analysis (CPχ²) method, considerably more flexible and effective than other alternatives, to screen large gene expression data sets for conserved and differential interactions. CPχ² decomposes interactions across conditions to assess homogeneity and heterogeneity. Theoretically, we prove an asymptotic chi-square null distribution for the interaction heterogeneity statistic. Empirically, on synthetic yeast cell cycle data, CPχ² achieved much higher statistical power in detecting differential networks than alternative approaches. We applied CPχ² to Drosophila melanogaster wing gene expression arrays collected under normal conditions, and conditions with overexpressed E2F and Cabut, two transcription factor complexes that promote ectopic cell cycling. The resulting differential networks suggest a mechanism by which E2F and Cabut regulate distinct gene interactions, while still sharing a small core network. Thus, CPχ² is sensitive in detecting network rewiring, useful in comparing related biological systems.

TGFβ inducible early gene-1 plays an important role in mediating estrogen signaling in the skeleton

TGFβ Inducible Early Gene-1 (TIEG1) knockout (KO) mice display a sex-specific osteopenic phenotype characterized by low bone mineral density, bone mineral content, and overall loss of bone strength in female mice. We, therefore, speculated that loss of TIEG1 expression would impair the actions of estrogen on bone in female mice. To test this hypothesis, we employed an ovariectomy (OVX) and estrogen replacement model system to comprehensively analyze the role of TIEG1 in mediating estrogen signaling in bone at the tissue, cell, and biochemical level. Dual-energy X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and micro-CT analyses revealed that loss of TIEG1 expression diminished the effects of estrogen throughout the skeleton and within multiple bone compartments. Estrogen exposure also led to reductions in bone formation rates and mineralizing perimeter in wild-type mice with little to no effects on these parameters in TIEG1 KO mice. Osteoclast perimeter per bone perimeter and resorptive activity as determined by serum levels of CTX-1 were differentially regulated after estrogen treatment in TIEG1 KO mice compared with wild-type littermates. No significant differences were detected in serum levels of P1NP between wild-type and TIEG1 KO mice. Taken together, these data implicate an important role for TIEG1 in mediating estrogen signaling throughout the mouse skeleton and suggest that defects in this pathway are likely to contribute to the sex-specific osteopenic phenotype observed in female TIEG1 KO mice.

Destabilization of KLF10, a tumor suppressor, relies on thr93 phosphorylation and isomerase association

KLF10 is now classified as a member of the Krüppel-like transcription factor family and acts as a tumor suppressor. Although KLF10 is originally named as TGF-β-inducible early gene-1 and mimicking the anti-proliferative effect of TGF-β in various carcinoma cells, the transcriptional upregulatory function of KLF10 has been described for a variety of cytokines and in many diseases. Through in vivo and in vitro phosphorylation assays, we identified that KLF10 is a phosphorylated protein in cells. Using yeast-two hybrid screening and site direct mutagenesis, we also identified PIN1 as a novel KLF10 associated protein. PIN1 is a peptidyl-prolyl isomerase enzyme belonging to the parvulin family, which specifically recognizes phosphorylated Ser/Thr-Pro containing substrates. Through protein-protein interaction assays, we showed that the Pro-directed Ser/Thr-Pro motif at Thr-93 in the KLF10 N-terminal region is essential for the interaction between KLF10 and PIN1. More importantly, PIN1 interacts with KLF10 in a phosphorylation-dependent manner and this interaction promotes KLF10 protein degradation in cells. Therefore, KLF10 shows shorter protein stability compared with mutant KLF10 that lacks PIN1 binding ability after cycloheximide treatments. The reversely correlated expression profile between KLF10 and PIN1 as observed in cell lines was also shown in clinic pancreatic cancer specimen. Using in vitro kinase assays and depletion assays, we were able to show that RAF-1 phosphorylates the Thr-93 of KLF10 and affects the KLF10 expression level in cells. Thus these findings as a whole indicate that RAF-1 phosphorylation and PIN1 isomerization together regulate KLF10 stability and further affect the role of KLF10 in tumor progression.

Thalidomide corrects impaired mesenchymal stem cell function in inducing tolerogenic DCs in patients with immune thrombocytopenia

Thalidomide (THD) is an immunomodulatory agent used to treat immune-mediated diseases. Immune thrombocytopenia (ITP) is an autoimmune disorder in which impaired mesenchymal stem cells (MSCs) are potentially involved. We demonstrated that MSCs in ITP patients had reduced proliferative capacity and lost their immunosuppressive function, which could be corrected with THD treatment. According to the gene profile, the downregulation of caspase-8 and caspase-10, and upregulation of oct3/4 and tgf-β1, may be associated with THD modulation. Dendritic cells (DCs) played an important role in mediating the inhibitory activity of MSCs. To study the functional alteration of DCs elicited by MSCs, we sorted DCs after incubation with MSCs and performed T-lymphocyte reaction assays. The THD-modulated MSCs from ITP patients induced mature DCs to become tolerogenic DCs, whereas unmodulated MSCs had no effect. The induction of tolerogenicity in DCs by MSCs was dependent on the expression of TIEG1 in DCs. The study reveals the inability of MSCs from ITP patients to induce tolerogenic ability in DCs. THD could restore the regulatory effect of MSCs on DCs. These findings will help us understand the pathogenesis of ITP, and with appropriate safeguards, THD may benefit patients with ITP.

Repression of myoblast proliferation and fibroblast growth factor receptor 1 promoter activity by KLF10 protein

BACKGROUND

FGFR1 gene expression regulates myoblast proliferation and differentiation, and its expression is controlled by Krüppel-like transcription factors.

RESULTS

KLF10 interacts with the FGFR1 promoter, repressing its activity and cell proliferation.

CONCLUSION

KLF10 represses FGFR1 promoter activity and thereby myoblast proliferation.

SIGNIFICANCE

A model of transcriptional control of chicken FGFR1 gene regulation during myogenesis is presented. Skeletal muscle development is controlled by regulation of myoblast proliferation and differentiation into muscle fibers. Growth factors such as fibroblast growth factors (FGFs) and their receptors (FGFRs) regulate cell proliferation and differentiation in numerous tissues, including skeletal muscle. Transcriptional regulation of FGFR1 gene expression is developmentally regulated by the Sp1 transcription factor, a member of the Krüppel-like factor (KLF) family of transcriptional regulators. Here, we show that another KLF transcription factor, KLF10, also regulates myoblast proliferation and FGFR1 promoter activity. Expression of KLF10 reduced myoblast proliferation by 86%. KLF10 expression also significantly reduced FGFR1 promoter activity in myoblasts and Sp1-mediated FGFR1 promoter activity in Drosophila SL2 cells. Southwestern blot, electromobility shift, and chromatin immunoprecipitation assays demonstrated that KLF10 bound to the proximal Sp factor binding site of the FGFR1 promoter and reduced Sp1 complex formation with the FGFR1 promoter at that site. These results indicate that KLF10 is an effective repressor of myoblast proliferation and represses FGFR1 promoter activity in these cells via an Sp1 binding site.

Clinical significance of expression of TGF-β1, TIEG1 and stathmin proteins in esophageal squamous cell carcinoma

AIM: To analyze the clinical significance of expression of transforming growth factor-β1 (TGF-β1), transforming growth factor β-inducible early gene 1 (TIEG1) and stathmin in esophageal squamous cell carcinoma (ESCC).

METHODS: Immunohistochemistry was used to detect the expression of TGF-β1, TIEG1 and stathmin in 62 cases of ESCC, 31 cases of tumor-adjacent atypical hyperplasia epithelium and 62 cases of normal esophageal epithelium.

RESULTS: The positive rates of TGF-β1 and TIEG1 proteins in normal esophageal epithelium were significantly higher than those in tumor-adjacent atypical hyperplasia epithelium and ESCC [TGF-β1: 62 (100.0) vs 22 (71.0), 41 (66.1), P < 0.05]. The expression of stathmin was also noted in ESCC and tumor-adjacent atypical hyperplasia epithelium, but its expression was not as wide as that of TGF-β1 and TIEG1. In normal esophageal epithelium, the expression of stathmin was not detected. Expression of stathmin in ESCC had a negative correlation with TGF-β1 and TIEG1 expression (r = -0.609, -0.459, both P < 0.05)). The expression of TGF-β1, TIEG1 and stathmin proteins was closely correlated with clinical grade and lymph node metastasis in ESCC (all P < 0.05).

CONCLUSION: TGF-β1 and TIEG1 may bind to stathmin, down-regulate stathmin expression and inhibit the metastasis of ESCC.

Klf10 inhibits IL-12p40 production in macrophage colony-stimulating factor-induced mouse bone marrow-derived macrophages

Bone marrow-derived macrophages (BMMs) treated with granulocyte-macrophage colony-stimulating factor (GM-CSF) or macrophage colony-stimulating factor (M-CSF), differentiate into GM-CSF-induced mouse bone marrow-derived macrophages (GM-BMMs) or M-CSF-induced mouse bone marrow-derived macrophages (M-BMMs), which have an M1 or M2 profile, respectively. GM-BMMs produce large amounts of proinflammatory cytokines and mediate resistance to pathogens, whereas M-BMMs produce antiinflammatory cytokines that contribute to tissue repair and remodeling. M-BMMs stimulated with lipopolysaccharide (LPS) are in an antiinflammatory state, with an IL-12(low) IL-10(high) phenotype. However, the regulation of this process remains unclear. Klf10 belongs to the family of Krüppel-like transcription factors and was initially described as a TGF-β inducible early gene 1. IL-12p40 is upregulated in LPS-stimulated M-BMMs from Klf10-deficient mice, but downregulated during Klf10 overexpression. Klf11, another member of the Krüppel-like factor family, can also repress the production of IL-12p40. Furthermore, Klf10 binds to the CACCC element of the IL-12p40 promoter and inhibits its transcription. We have therefore identified Klf10 as a transcription factor that regulates the expression of IL-12p40 in M-BMMs.

Human Krüppel-like factor 11 differentially regulates human insulin promoter activity in β-cells and non-β-cells via p300 and PDX1 through the regulatory sites A3 and CACCC box

Human Krüppel-like factor 11 (hKLF11) has been characterised to both activate and inhibit human insulin promoter (hInsP) activity. Since KLF11 is capable to differentially regulate genes dependent on recruited cofactors, we investigated the effects of hKLF11 on cotransfected hInsP in both β-cells and non-β-cells. hKLF11 protein interacts with hp300 but not with hPDX1. Overexpressed hKLF11 stimulates PDX1-transactivation of hInsP in HEK293 non-β-cells, but confers inhibition in INS-1E β-cells. Both hKLF11 functions can be neutralised by the p300 inhibitor E1A, increased hp300 levels (INS-1E), dominant negative (DN)-PDX1 and by mutation of the PDX1 binding site A3 or the CACCC box. In summary, hKLF11 differentially regulates hInsP activity depending on the molecular context via modulation of p300:PDX1 interactions with the A3 element and CACCC box. We postulate that KLF11 has a role in fine-tuning insulin transcription in certain cellular situations rather than representing a major transcriptional activator or repressor of the insulin gene.

TGFβ-inducible early gene-1 (TIEG1) mutations in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common heritable cardiovascular disease. A recent study showed that male KLF10-encoded TGFβ Inducible Early Gene-1 knock-out mice (TIEG-/-) develop HCM with 13-fold up-regulation of PTTG1-encoded pituitary tumor-transforming gene 1. We hypothesized TIEG1 could be a novel candidate gene in the pathogenesis of genotype negative HCM in humans, possibly through a loss of its repression on PTTG1 expression. A cohort of 923 unrelated patients from two independent HCM centers was analyzed for mutations in TIEG's four translated exons using DHPLC and direct DNA-sequencing. Site directed mutagenesis was performed to clone novel variants. The effect of TIEG1 mutations on SMAD7 and PTTG1 promoters was studied using transient transfection and luciferase-assays. Altered expression of PTTG1 in cardiac tissue was studied by immunohistochemistry (IHC) to determine levels of PTTG1 protein in hypertrophic diseases. Six novel TIEG1 missense mutations were discovered in six patients (two males/four females, mean age at diagnosis 56.2±23 years, MLVWT 20.8±4 mm). Compared to WT TIEG1, five TIEG1 mutants significantly increased PTTG1 promoter function similar to TIEG1-/--mice. By IHC, PTTG1-protein expression was significantly increased in multiple models of hypertrophic cardiac disease, including TIEG1-mutation positive HCM compared to normal hearts. This is the first article to associate mutations in TIEG1 to human disease with the discovery of six novel, HCM-associated variants. Functional assays suggest a role for PTTG1 in the pathogenesis of TIEG1-mediated HCM. Up-regulation of PTTG1 seems to be a common pathway in hypertrophic heart disease, including TIEG1-mediated HCM.

Impaired cutaneous wound healing in transforming growth factor-β inducible early gene1 knockout mice

Transforming growth factor-β inducible early gene (TIEG) is induced by transforming growth factor-β (TGF-β) and acts as the primary response gene in the TGF-β/Smad pathway. TGF-β is a multifunctional growth factor that affects dermal wound healing; however, the mechanism of how TGF-β affects wound healing is still not well understood because of the complexity of its function and signaling pathways. We hypothesize that TIEG may play a role in dermal wound healing, with involvement in wound closure, contraction, and reepithelialization. In this study, we have shown that TIEG1 knockout (TIEG1-/-) mice have a delay in wound closure related to an impairment in wound contraction, granulation tissue formation, collagen synthesis, and reepithelialization. We also found that Smad7 was increased in the wounds and appeared to play a role in this wound healing model in TIEG1-/- mice.

Transcriptional activity and nuclear localization of Cabut, the Drosophila ortholog of vertebrate TGF-β-inducible early-response gene (TIEG) proteins

Background

Cabut (Cbt) is a C₂H₂-class zinc finger transcription factor involved in embryonic dorsal closure, epithelial regeneration and other developmental processes in Drosophila melanogaster. Cbt orthologs have been identified in other Drosophila species and insects as well as in vertebrates. Indeed, Cbt is the Drosophila ortholog of the group of vertebrate proteins encoded by the TGF-ß-inducible early-response genes (TIEGs), which belong to Sp1-like/Krüppel-like family of transcription factors. Several functional domains involved in transcriptional control and subcellular localization have been identified in the vertebrate TIEGs. However, little is known of whether these domains and functions are also conserved in the Cbt protein.

Methodology/Principal Findings

To determine the transcriptional regulatory activity of the Drosophila Cbt protein, we performed Gal4-based luciferase assays in S2 cells and showed that Cbt is a transcriptional repressor and able to regulate its own expression. Truncated forms of Cbt were then generated to identify its functional domains. This analysis revealed a sequence similar to the mSin3A-interacting repressor domain found in vertebrate TIEGs, although located in a different part of the Cbt protein. Using β-Galactosidase and eGFP fusion proteins, we also showed that Cbt contains the bipartite nuclear localization signal (NLS) previously identified in TIEG proteins, although it is non-functional in insect cells. Instead, a monopartite NLS, located at the amino terminus of the protein and conserved across insects, is functional in Drosophila S2 and Spodoptera exigua Sec301 cells. Last but not least, genetic interaction and immunohistochemical assays suggested that Cbt nuclear import is mediated by Importin-α2.

Conclusions/Significance

Our results constitute the first characterization of the molecular mechanisms of Cbt-mediated transcriptional control as well as of Cbt nuclear import, and demonstrate the existence of similarities and differences in both aspects of Cbt function between the insect and the vertebrate TIEG proteins.

KLF10, transforming growth factor-β-inducible early gene 1, acts as a tumor suppressor

Krüppel-like factor 10 (KLF10) has been suggested to be a putative tumor suppressor. In the present study, we generated KLF10 deficient mice to explore this hypothesis in vivo. KLF10 deficient mice exhibited increased predisposition to skin tumorigenesis and markedly accelerated papilloma development after DMBA/TPA treatment. On the other hand, KLF10 deficient keratinocytes showed increased proliferation and apoptosis. In colony formation assays after oncogenic H-Ras transfection, KLF10 deficient mouse embryonic fibroblasts (MEFs) yielded more colonies than wild-type MEFs. Furthermore, KLF10 dose-dependently activated p21(WAF1/CIP1) transcription, which was independent of p53 and Sp1 binding sites in p21(WAF1/CIP1) promoter. This study demonstrates that KLF10 is a tumor suppressor and that it targets p21(WAF1/CIP1) transcription.

WOUND-HEALING PROPERTIES OF TRANSFORMING GROWTH FACTOR β (TGF-β) INDUCIBLE EARLY GENE 1 (TIEG1) KNOCKOUT MICE

Transforming growth factor beta (TGF-β) has a broad effect on wound healing, but many questions remain about the regulation of TGF-β during the healing process. TGF-β inducible early gene 1 (TIEG1) is a primary response gene for TGF-β that controls the activities of the TGF-β/Smad pathway, the primary TGF-β signaling pathway. The purpose of this study was to investigate the role of TIEG1 in cutaneous wound healing using TIEG1 knockout mice. The wound healing in TIEG1 knockout mice and wild-type controls was evaluated by wound breaking strength, Western blot, and histology at postoperative days 3, 7, and 14. Although re-epithelialization of both groups was similarly complete at day 7, the TIEG1 knockout mice had a significantly lower wound breaking strength than the controls at postoperative day 14. These results suggest that TIEG1 expression may be an important factor involved in the initiation and support of normal cutaneous wound healing.

TIEG1-NULL OSTEOCYTES DISPLAY DEFECTS IN THEIR MORPHOLOGY, DENSITY AND SURROUNDING BONE MATRIX

Through the development of TGFβ-inducible early gene-1 (TIEG1) knockout (KO) mice, we have demonstrated that TIEG1 plays an important role in osteoblast-mediated bone mineralization, and in bone resistance to mechanical strain. To further investigate the influence of TIEG1 in skeletal maintenance, osteocytes were analyzed by transmission electron microscopy using TIEG1 KO and wild-type mouse femurs at one, three and eight months of age. The results revealed an age-dependent change in osteocyte surface and density, suggesting a role for TIEG1 in osteocyte development. Moreover, there was a decrease in the amount of hypomineralized bone matrix surrounding the osteocytes in TIEG1 KO mice relative to wild-type controls. While little is known about the function or importance of this hypomineralized bone matrix immediately adjacent to osteocytes, this study reveals significant differences in this bone microenvironment and suggests that osteocyte function may be compromised in the absence of TIEG1 expression.

Social Defeat during Adolescence and Adulthood Differentially Induce BDNF-Regulated Immediate Early Genes

Stressful life events generally enhance the vulnerability for the development of human psychopathologies such as anxiety disorders and depression. The incidence rates of adult mental disorders steeply rises during adolescence in parallel with a structural and functional reorganization of the neural circuitry underlying stress reactivity. However, the mechanisms underlying susceptibility to stress and manifestation of mental disorders during adolescence are little understood. We hypothesized that heightened sensitivity to stress during adolescence reflects age-dependent differences in the expression of activity-dependent genes involved in synaptic plasticity. Therefore, we compared the effect of social stress during adolescence with social stress in adulthood on the expression of a panel of genes linked to induction of long-term potentiation (LTP) and brain-derived neurotrophic factor (BDNF) signaling. We show that social defeat during adolescence and adulthood differentially regulates expression of the immediate early genes BDNF, Arc, Carp, and Tieg1, as measured by qPCR in tissue lysates from prefrontal cortex, nucleus accumbens, and hippocampus. In the hippocampus, mRNA levels for all four genes were robustly elevated following social defeat in adolescence, whereas none were induced by defeat in adulthood. The relationship to coping style was also examined using adult reactive and proactive coping rats. Gene expression levels of reactive and proactive animals were similar in the prefrontal cortex and hippocampus. However, a trend toward a differential expression of BDNF and Arc mRNA in the nucleus accumbens was detected. BDNF mRNA was increased in the nucleus accumbens of proactive defeated animals, whereas the expression level in reactive defeated animals was comparable to control animals. The results demonstrate striking differences in immediate early gene expression in response to social defeat in adolescent and adult rats.

TIEG1 inhibits breast cancer invasion and metastasis by inhibition of epidermal growth factor receptor (EGFR) transcription and the EGFR signaling pathway

TIEG1 can induce apoptosis of cancer cells, but its role in inhibiting invasion and metastasis has not been reported and is unclear. In this study, we find that decreased TIEG1 expression is associated with increased human epidermal growth factor receptor (EGFR) expression in breast cancer tissues and cell lines. TIEG1 plays an important role in suppressing transcription of EGFR by directly binding to the EGFR promoter. While overexpression of TIEG1 attenuates EGFR expression, knockdown of TIEG1 stimulates EGFR expression. Furthermore, TIEG1 and HDAC1 form a complex, which binds to Sp1 sites on the EGFR promoter and inhibits its transcription by suppressing histone acetylation. TIEG1 significantly inhibits breast cancer cell invasion, suppresses mammary tumorigenesis in xenografts in mice, and decreases lung metastasis by inhibition of EGFR gene transcription and the EGFR signaling pathway. Therefore, TIEG1 is an antimetastasis gene product; regulation of EGFR expression by TIEG1 may be part of an integral signaling pathway that determines and explains breast cancer invasion and metastasis.

Lentivirus-mediated overexpression of TGF-β inducible early gene 1 inhibits SW1990 pancreatic cancer cell growth

TIEG1 (TGF-β inducible early gene 1) plays a significant role in regulating cell proliferation and apoptosis in various cell types. Previous studies have shown a close relationship between the expression level of TIEG1 and various cancers, including breast, prostate, colorectal and pancreatic cancer. In this study, we up-regulated the gene expression of TIEG1 in SW1990 pancreatic cancer cell line by a lentivirus transfection system and investigated its potential as a therapeutic target for pancreatic cancer. The results showed that lentivirus-mediated overexpression of TIEG1 gene inhibited human pancreatic cancer SW1990 cell proliferation and caused the cell cycle arrest at the G1-phase in vitro. SW1990 cells transduced with lenti-TIEG1 showed significant inhibition of colony formation and cancer cell growth in 3-D culture model. Moreover, overexpression of TIEG1 gene significantly slowed the growth of SW1990 xenografts in nude mice. Taken together, these data provided evidence that overexpression of TIEG1 gene by a lentivirus transfection system led to suppressed human pancreatic cancer cell growth and might therefore be a feasible approach in the clinical management of pancreatic cancer.

TIEG1-null tenocytes display age-dependent differences in their gene expression, adhesion, spreading and proliferation properties

The remodeling of extracellular matrix is a crucial mechanism in tendon development and the proliferation of fibroblasts is a key factor in this process. The purpose of this study was to further elucidate the role of TIEG1 in mediating important tenocyte properties throughout the aging process. Wildtype and TIEG1 knockout tenocytes adhesion, spreading and proliferation were characterized on different substrates (fibronectin, collagen type I, gelatin and laminin) and the expression levels of various genes known to be involved with tendon development were analyzed by RT-PCR. The experiments revealed age-dependent and substrate-dependent properties for both wildtype and TIEG1 knockout tenocytes. Taken together, our results indicate an important role for TIEG1 in regulating tenocytes adhesion, spreading, and proliferation throughout the aging process. Understanding the basic mechanisms of TIEG1 in tenocytes may provide valuable information for treating multiple tendon disorders.

Klf10 and Klf11 as mediators of TGF-beta superfamily signaling

Klf10 and Klf11 belong to the family of Sp1/Krüppel-like zinc finger transcription factors that play important roles in a variety of cell types and tissues. Although Klf10 and Klf11 were initially introduced as transforming growth factor-beta (TGF-beta)-inducible genes, several studies have described their upregulation by a plethora of growth factors, cytokines and hormones. Here, we review the current knowledge of the inductive cues for Klf10 and Klf11 and focus on their transcriptional regulation by members of the TGF-beta superfamily. We further summarize their involvement in the regulation of the TGF-beta signaling pathway and discuss their possible role as molecules mediating crosstalk between various signaling pathways. Finally, we provide an overview of the pro-apoptotic and anti-proliferative functions of Klf10 and Klf11.

Tapping the brake on cardiac growth-endogenous repressors of hypertrophic signaling

Cardiac hypertrophy is considered an early hallmark during the clinical course of heart failure and an important risk factor for cardiac morbidity and mortality. Although hypertrophy of individual cardiomyocytes in response to pathological stimuli has traditionally been considered as an adaptive response required to sustain cardiac output, accumulating evidence from studies in patients and animal models suggests that in most instances hypertrophy of the heart also harbors maladaptive aspects. Major strides have been made in our understanding of the pathways that convey pro-hypertrophic signals from the outside of the cell to the nucleus. In recent years it also has become increasingly evident that the heart possesses a variety of endogenous feedback mechanisms to counterbalance this growth response. These repressive mechanisms are of particular interest since they may provide valuable therapeutic options. In this review we summarize currently known endogenous repressors of pathological cardiac growth as they have been studied by gene targeting in mice. Many of the repressors that function in signal transduction appear to regulate calcineurin (e.g. PICOT, calsarcin, RCAN) and JNK signaling (e.g. CDC42, MKP-1) and some will be described in greater detail in this review. In addition, we will focus on factors such as Kruppel-like factors (KLF4, KLF15 and KLF10) and histone deacetylases (HDACs), which constitute a relevant group of nuclear proteins that repress transcription of the hypertrophic gene program in cardiomyocytes.

TIEG1/KLF10 modulates Runx2 expression and activity in osteoblasts

Deletion of TIEG1/KLF10 in mice results in a gender specific osteopenic skeletal phenotype with significant defects in both cortical and trabecular bone, which are observed only in female animals. Calvarial osteoblasts isolated from TIEG1 knockout (KO) mice display reduced expression levels of multiple bone related genes, including Runx2, and exhibit significant delays in their mineralization rates relative to wildtype controls. These data suggest that TIEG1 plays an important role in regulating Runx2 expression in bone and that decreased Runx2 expression in TIEG1 KO mice is in part responsible for the observed osteopenic phenotype. In this manuscript, data is presented demonstrating that over-expression of TIEG1 results in increased expression of Runx2 while repression of TIEG1 results in suppression of Runx2. Transient transfection and chromatin immunoprecipitation assays reveal that TIEG1 directly binds to and activates the Runx2 promoter. The zinc finger containing domain of TIEG1 is necessary for this regulation supporting that activation occurs through direct DNA binding. A role for the ubiquitin/proteasome pathway in fine tuning the regulation of Runx2 expression by TIEG1 is also implicated in this study. Additionally, the regulation of Runx2 expression by cytokines such as TGFβ1 and BMP2 is shown to be inhibited in the absence of TIEG1. Co-immunoprecipitation and co-localization assays indicate that TIEG1 protein associates with Runx2 protein resulting in co-activation of Runx2 transcriptional activity. Lastly, Runx2 adenoviral infection of TIEG1 KO calvarial osteoblasts leads to increased expression of Runx2 and enhancement of their ability to differentiate and mineralize in culture. Taken together, these data implicate an important role for TIEG1 in regulating the expression and activity of Runx2 in osteoblasts and suggest that decreased expression of Runx2 in TIEG1 KO mice contributes to the observed osteopenic bone phenotype.

Analysis of gene expression profile of periodontal ligament cells subjected to cyclic compressive force

Cyclic compressive force is an important mechanical stimulus on periodontal ligament (PDL). The differential expression of genes in PDL cells is thought to be involved in the remodeling of periodontal tissues subjected to mechanical stress. However, little is known about differentially expressed genes in PDL cells under cyclic compressive force. In our study, human PDL cells were subjected to 4000 μ strain compressive stress loading at 0.5 Hz for 2 h. The effect of mechanical stress on PDL cells proliferation was observed by flow cytometry. Microarray analysis was used to investigate the mechano-induced differential gene profile in PDL cells. Differential expression was confirmed by quantitative real-time polymerase chain reaction (RT-PCR) analysis on genes of interest and explored at two more force loading times (6 h, 12 h). After mechanical loading, cell proliferation was repressed. The microarray data showed that 217 out of 35,000 genes were differentially expressed; among the 217 genes, 207 were up-regulated whereas 10 were down-regulated (p < 0.05). Gene ontology analysis suggested that majority of differentially expressed genes were located in the nucleus and functioned as transcription factors involved in a variety of biological processes. Five genes of interest (IL6, IL8, ETS1, KLF10, and DLC1) were found to be closely related to negative regulation of cell proliferation. The PCR results showed increased expression after 2 h loading, then a decline with extended loading time. The signaling pathways involved were also identified. These findings expand understanding of molecular regulation in the mechano-response of PDL cells.

Drosophila TIEG is a modulator of different signalling pathways involved in wing patterning and cell proliferation

Acquisition of a final shape and size during organ development requires a regulated program of growth and patterning controlled by a complex genetic network of signalling molecules that must be coordinated to provide positional information to each cell within the corresponding organ or tissue. The mechanism by which all these signals are coordinated to yield a final response is not well understood. Here, I have characterized the Drosophila ortholog of the human TGF-β Inducible Early Gene 1 (dTIEG). TIEG are zinc-finger proteins that belong to the Krüppel-like factor (KLF) family and were initially identified in human osteoblasts and pancreatic tumor cells for the ability to enhance TGF-β response. Using the developing wing of Drosophila as “in vivo” model, the dTIEG function has been studied in the control of cell proliferation and patterning. These results show that dTIEG can modulate Dpp signalling. Furthermore, dTIEG also regulates the activity of JAK/STAT pathway suggesting a conserved role of TIEG proteins as positive regulators of TGF-β signalling and as mediators of the crosstalk between signalling pathways acting in a same cellular context.