Transcriptional regulation of Smad2 is required for enhancement of TGF?/Smad signaling by TGF? inducible early gene

Roles of SP/KLF transcription factors in odontoblast differentiation: From development to diseases

OBJECTIVES

A zinc-finger transcription factor family comprising specificity proteins (SPs) and Krüppel-like factor proteins (KLFs) plays an important role in dentin development and regeneration. However, a systematic regulatory network involving SPs/KLFs in odontoblast differentiation has not yet been described. This review examined the expression patterns of SP/KLF gene family members and their current known functions and mechanisms in odontoblast differentiation, and discussed prospective research directions for further exploration of mechanisms involving the SP/KLF gene family in dentin development.

MATERIALS AND METHODS

Relevant literature on SP/KLF gene family members and dentin development was acquired from PubMed and Web of Science.

RESULTS

We discuss the expression patterns, functions, and related mechanisms of eight members of the SP/KLF gene family in dentin development and genetic disorders with dental problems. We also summarize current knowledge about their complementary or synergistic actions. Finally, we propose future research directions for investigating the mechanisms of dentin development.

CONCLUSIONS

The SP/KLF gene family plays a vital role in tooth development. Studying the complex complementary or synergistic interactions between SPs/KLFs is helpful for understanding the process of odontoblast differentiation. Applications of single-cell and spatial multi-omics may provide a more complete investigation of the mechanism involved in dentin development.

New Insights into the Role of KLF10 in Tissue Fibrosis

Fibrosis, characterized by excessive extracellular matrix accumulation, disrupts normal tissue architecture, causes organ dysfunction, and contributes to numerous chronic diseases. This review focuses on Krüppel-like factor 10 (KLF10), a transcription factor significantly induced by transforming growth factor-β (TGF-β), and its role in fibrosis pathogenesis and progression across various tissues. KLF10, initially identified as TGF-β-inducible early gene-1 (TIEG1), is involved in key biological processes including cell proliferation, differentiation, apoptosis, and immune responses. Our analysis investigated KLF10 gene and protein structures, interaction partners, and context-dependent functions in fibrotic diseases. This review highlights recent findings that underscore KLF10 interaction with pivotal signaling pathways, such as TGF-β, and the modulation of gene expression in fibrotic tissues. We examined the dual role of KLF10 in promoting and inhibiting fibrosis depending on tissue type and fibrotic context. This review also discusses the therapeutic potential of targeting KLF10 in fibrotic diseases, based on its regulatory role in key pathogenic mechanisms. By consolidating current research, this review aims to enhance the understanding of the multifaceted role of KLF10 in fibrosis and stimulate further research into its potential as a therapeutic target in combating fibrotic diseases.

Loss of Krüppel-like factor-10 facilitates the development of chemical-induced liver cancer in mice

BACKGROUND

Krüppel-like factor 10 (KLF10) is involved in a positive feedback loop that regulates transforming growth factor β (TGFβ) signaling, and TGFβ plays an important role in the pathogenesis of liver disease. Here, we investigated whether KLF10 deletion affects the development of liver fibrosis and hepatocellular carcinoma (HCC).

METHODS

We induced KLF10 deletion in C57BL/6 mice. Liver fibrosis was induced by feeding a diet high in fat and sucrose (high-fat diet [HFD]), whereas HCC was produced by intraperitoneal administration of N-diethylnitrosamine (DEN). An in vitro experiment was performed to evaluate the role of KLF10 in the cancer microenvironment using Hep3B and LX2 cells. An immunohistochemical study of KLF10 expression was performed using human HCC samples from 60 patients who had undergone liver resection.

RESULTS

KLF10 deletion resulted in an increased DEN-induced HCC burden with significant upregulation of SMAD2, although loss of KLF10 did not alter HFD-induced liver fibrosis. DEN-treated mice with KLF10 deletion exhibited increased levels of mesenchymal markers (N-cadherin and SNAI2) and tumor metastasis markers (matrix metalloproteinases 2 and 9). KLF10 depletion in Hep3B and LX2 cells using siRNA was associated with increased invasiveness. Compared with co-culture of KLF10-preserved Hep3B cells and KLF10-intact LX2 cells, co-culture of KLF10-preserved Hep3B cells and KLF10-depleted LX2 cells resulted in significantly enhanced invasion. Low KLF10 expression in resected human HCC specimens was associated with poor survival.

CONCLUSION

The results of this study suggest that loss of KLF10 facilitates liver cancer development with alteration in TGFβ signaling.

Kruppel-like Factors in Skeletal Physiology and Pathologies

Kruppel-like factors (KLFs) belong to a large group of zinc finger-containing transcription factors with amino acid sequences resembling the Drosophila gap gene Krüppel. Since the first report of molecular cloning of the KLF family gene, the number of KLFs has increased rapidly. Currently, 17 murine and human KLFs are known to play crucial roles in the regulation of transcription, cell proliferation, cellular differentiation, stem cell maintenance, and tissue and organ pathogenesis. Recent evidence has shown that many KLF family molecules affect skeletal cells and regulate their differentiation and function. This review summarizes the current understanding of the unique roles of each KLF in skeletal cells during normal development and skeletal pathologies.

Krüppel-like factors in bone biology

The krüppel-like factor (KLF) family is a group of zinc finger transcription factors and contributes to different cellular processes such as differentiation, proliferation, migration, and apoptosis. While different studies show the roles of this family in skeletal development-specifically in chondrocyte and osteocyte development and bone homeostasis-there are few reviews summarizing their importance. To fill this gap, this review discusses current knowledge on different functions of the KLF family during skeletal development, including their roles in stem cell maintenance and differentiation, cell apoptosis, and cell cycle. To understand the importance of the KLF family, we also review genotype-phenotype correlations in different animal models. We also discuss how KLF proteins function through different signaling pathways and display their paramount importance in skeletal development. To highlight their roles in cartilage- or bone-related cells, we also use single-cell RNA sequencing publicly available data on mouse hindlimb. We also challenge our knowledge of how the KLF family is epigenetically regulated-e.g., using DNA methylation, histone modifications, and noncoding RNAs-during chondrocyte and osteocyte development.

Krüppel like factor 10 prevents intervertebral disc degeneration via TGF-β signaling pathway both in vitro and in vivo

Background

Krüppel like factor 10 (KLF10), which is also known as TGF-β Inducible Early Gene-1 (TIEG1), plays a crucial role in regulating cell proliferation, cell apoptosis and inflammatory reaction in human carcinoma cells. Moreover, KLF10 knockout in mice leads to severe defects associated with muscle, skeleton and heart etc. However, the function of KLF10 in intervertebral disc degeneration (IVDD) has not been reported yet.

Methods

The relationship between KLF10 and IVDD were investigated in nucleus pulposus (NP) tissues from human and rats. The role of KLF10 in NP cells was explored via loss or gain of function experiments. IVDD rat models were constructed through needle puncture and the effects of KLF10 in IVDD model of rats were investigated via intradiscal injection of KLF10.

Results

We first found that KLF10 was lowly expressed in degenerative NP tissues and the level of KLF10 showed negative correlation with the disc grades of IVDD patients. Loss or gain of function experiments demonstrated that KLF10 could inhibit apoptosis and enhance migration and proliferation of IL-1β induced NP cells. And KLF10 overexpression reduced extracellular matrix (ECM) degeneration and enhanced ECM synthesis, whereas knockdown of KLF10 resulted in adverse effects. These positive effects of KLF10 could be reversed by the inhibition of TGF-β signaling pathway. In vivo, KLF10 overexpression alleviated IVDD.

Conclusions

This is the first study to reveal that KLF10 was dysregulated in IVDD and overexpressed KLF10 could alleviate IVDD by regulating TGF-β signaling pathway both in vitro and in vivo, which were involved in prohibiting apoptosis, promoting proliferation and migration of NP cells.The translational potential of this article: Overexpression of KLF10 might be an effective therapeutic strategy in the treatment of IVDD.

The Krüppel-like factor Cabut has cell cycle regulatory properties similar to E2F1

Using a gain-of-function screen in Drosophila, we identified the Krüppel-like factor Cabut (Cbt) as a positive regulator of cell cycle gene expression and cell proliferation. Enforced cbt expression is sufficient to induce an extra cell division in the differentiating fly wing or eye, and also promotes intestinal stem cell divisions in the adult gut. Although inappropriate cell proliferation also results from forced expression of the E2f1 transcription factor or its target, Cyclin E, Cbt does not increase E2F1 or Cyclin E activity. Instead, Cbt regulates a large set of E2F1 target genes independently of E2F1, and our data suggest that Cbt acts via distinct binding sites in target gene promoters. Although Cbt was not required for cell proliferation during wing or eye development, Cbt is required for normal intestinal stem cell divisions in the midgut, which expresses E2F1 at relatively low levels. The E2F1-like functions of Cbt identify a distinct mechanism for cell cycle regulation that may be important in certain normal cell cycles, or in cells that cycle inappropriately, such as cancer cells.

KLF10 is a modulatory factor of chondrocyte hypertrophy in developing skeleton

To define the functional role of Krüppel-like factor (KLF) 10 as a modulator of chondrocyte hypertrophy in developing skeleton, the developmental features in the long bone of KLF10 knockout (KO) mice were investigated and the mesenchymal stem cells (MSCs) from KLF10 KO mice were characterized regarding chondrogenesis and osteogenesis. Delayed long bone growth and delayed formation of primary ossification center were observed in an early embryonic stage in KLF10 KO mouse along with very low Indian hedgehog expression in epiphyseal plate. While the chondrogenic potential of mouse MSCs from KLF10 KO mice appeared normal or slight decreased, hypertrophy and osteogenesis were extensively suppressed. These findings suggest that KLF10 is a mediator of chondrocyte hypertrophy in developing skeleton, and that suppression of KLF10 may be employed as a new strategy for preventing hypertrophy in cartilage regeneration using MSCs.

Novel role of Tieg1 in muscle metabolism and mitochondrial oxidative capacities

AIM

Tieg1 is involved in multiple signalling pathways, human diseases, and is highly expressed in muscle where its functions are poorly understood.

METHODS

We have utilized Tieg1 knockout (KO) mice to identify novel and important roles for this transcription factor in regulating muscle ultrastructure, metabolism and mitochondrial functions in the soleus and extensor digitorum longus (EDL) muscles. RNA sequencing, immunoblotting, transmission electron microscopy, MRI, NMR, histochemical and mitochondrial function assays were performed.

RESULTS

Loss of Tieg1 expression resulted in altered sarcomere organization and a significant decrease in mitochondrial number. Histochemical analyses demonstrated an absence of succinate dehydrogenase staining and a decrease in cytochrome c oxidase (COX) enzyme activity in KO soleus with similar, but diminished, effects in the EDL. Decreased complex I, COX and citrate synthase (CS) activities were detected in the soleus muscle of KO mice indicating altered mitochondrial function. Complex I activity was also diminished in KO EDL. Significant decreases in CS and respiratory chain complex activities were identified in KO soleus. ¹ H-NMR spectra revealed no significant metabolic difference between wild-type and KO muscles. However, ³¹ P spectra revealed a significant decrease in phosphocreatine and ATPγ. Altered expression of 279 genes, many of which play roles in mitochondrial and muscle function, were identified in KO soleus muscle. Ultimately, all of these changes resulted in an exercise intolerance phenotype in Tieg1 KO mice.

CONCLUSION

Our findings have implicated novel roles for Tieg1 in muscle including regulation of gene expression, metabolic activity and organization of tissue ultrastructure. This muscle phenotype resembles diseases associated with exercise intolerance and myopathies of unknown consequence.

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.

Feedback regulation of TGF-β signaling

Transforming growth factor beta (TGF-β) is a multi-functional polypeptide that plays a critical role in regulating a broad range of cellular functions and physiological processes. Signaling is initiated when TGF-β ligands bind to two types of cell membrane receptors with intrinsic Ser/Thr kinase activity and transmitted by the intracellular Smad proteins, which act as transcription factors to regulate gene expression in the nucleus. Although it is relatively simple and straight-forward, this TGF-β/Smad pathway is regulated by various feedback loops at different levels, including the ligand, the receptor, Smads and transcription, and is thus fine-tuned in terms of signaling robustness, duration, specificity, and plasticity. The precise control gives rise to versatile and context-dependent pathophysiological functions. In this review, we firstly give an overview of TGF-β signaling, and then discuss how each step of TGF-β signaling is finely controlled by distinct modes of feedback mechanisms, involving both protein regulators and miRNAs.

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 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 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.

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.

Synergistic effects of overexpression of BMP‑2 and TGF‑β3 on osteogenic differentiation of bone marrow mesenchymal stem cells

Bone morphogenetic protein 2 (BMP-2) and transforming growth factor β (TGF-β) isoforms are important in advancing bone regeneration. The aim of the present study was to investigate the positive and reciprocal effect of TGF-β3, one of the three TGF-β isoforms, on BMP-2 in promoting osteogenic differentiation. Exogenous BMP-2 and TGF-β3 genes were separately, and in combination, overexpressed in rabbit bone marrow-derived mesenchymal stem cells (rBMSCs). Expression levels of BMP-2 and TGF-β3 were evaluated using reverse-transcription-polymerase chain reaction (RT-PCR) and Western blotting assays. Furthermore, the osteogenic differentiation capacities of BMSCs were assessed by measuring Alizarin Red S staining, an alkaline phosphatase activity assay, and quantification of the osteogenic-specific genes, Runt-related transcription factor 2 (Runx2) and Osterix (Osx). Using lentiviral-mediated transfection, robust co-transfection efficiency of >90% was achieved. RT-PCR and immunoblotting results indicated a marked elevated expression of BMP-2 and TGF-β3 in rBMSCs undergoing co-transfection, compared with transfection with BMP-2 or TGF-β3 alone, indicating that BMP-2 and TGF-β3 are synergistically expressed in rBMSCs. Furthermore, enhanced osteogenic differentiation was observed in rBMSCs co-transfected with BMP-2/TGF-β3. The present study successfully delivered BMP-2 together with TGF-β3 into rBMSCs with high efficiency for the first time. Furthermore, TGF-β3 overexpression was demonstrated to enhance the osteogenic efficacy of BMP-2 in rBMSCs, and vice versa. This provides a potential clinical therapeutic approach for regenerating the function of osseous tissue, and may present a promising strategy for bone defect healing.

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.

Targeting the SIN3A-PF1 interaction inhibits epithelial to mesenchymal transition and maintenance of a stem cell phenotype in triple negative breast cancer

Triple negative breast cancer (TNBC) is characterized by a poorly differentiated phenotype and limited treatment options. Aberrant epigenetics in this subtype represent a potential therapeutic opportunity, but a better understanding of the mechanisms contributing to the TNBC pathogenesis is required. The SIN3 molecular scaffold performs a critical role in multiple cellular processes, including epigenetic regulation, and has been identified as a potential therapeutic target. Using a competitive peptide corresponding to the SIN3 interaction domain of MAD (Tat-SID), we investigated the functional consequences of selectively blocking the paired amphipathic α-helix (PAH2) domain of SIN3. Here, we report the identification of the SID-containing adaptor PF1 as a factor required for maintenance of the TNBC stem cell phenotype and epithelial-to-mesenchymal transition (EMT). Tat-SID peptide blocked the interaction between SIN3A and PF1, leading to epigenetic modulation and transcriptional downregulation of TNBC stem cell and EMT markers. Importantly, Tat-SID treatment also led to a reduction in primary tumor growth and disseminated metastatic disease in vivo. In support of these findings, knockdown of PF1 expression phenocopied treatment with Tat-SID both in vitro and in vivo. These results demonstrate a critical role for a complex containing SIN3A and PF1 in TNBC and provide a rational for its therapeutic targeting.

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.

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.

Selective Inhibition of SIN3 Corepressor with Avermectins as a Novel Therapeutic Strategy in Triple-Negative Breast Cancer

Triple-negative breast cancers (TNBC) lacking estrogen, progesterone, and HER2 receptors account for 10% to 20% of breast cancer and are indicative of poor prognosis. The development of effective treatment strategies therefore represents a pressing unmet clinical need. We previously identified a molecularly targeted approach to target aberrant epigenetics of TNBC using a peptide corresponding to the SIN3 interaction domain (SID) of MAD. SID peptide selectively blocked binding of SID-containing proteins to the paired α-helix (PAH2) domain of SIN3, resulting in epigenetic and transcriptional modulation of genes associated with epithelial-mesenchymal transition (EMT). To find small molecule inhibitor (SMI) mimetics of SID peptide, we performed an in silico screen for PAH2 domain-binding compounds. This led to the identification of the avermectin macrocyclic lactone derivatives selamectin and ivermectin (Mectizan) as candidate compounds. Both selamectin and ivermectin phenocopied the effects of SID peptide to block SIN3-PAH2 interaction with MAD, induce expression of CDH1 and ESR1, and restore tamoxifen sensitivity in MDA-MB-231 human and MMTV-Myc mouse TNBC cells in vitro. Treatment with selamectin or ivermectin led to transcriptional modulation of genes associated with EMT and maintenance of a cancer stem cell phenotype in TNBC cells. This resulted in impairment of clonogenic self-renewal in vitro and inhibition of tumor growth and metastasis in vivo. Underlining the potential of avermectins in TNBC, pathway analysis revealed that selamectin also modulated the expression of therapeutically targetable genes. Consistent with this, an unbiased drug screen in TNBC cells identified selamectin-induced sensitization to a number of drugs, including those targeting modulated genes.

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.

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.

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.

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.

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.

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-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.

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.

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.

Histone demethylase JARID1B/KDM5B is a corepressor of TIEG1/KLF10

JARID1B/KDM5B (jumonji AT-rich interactive domain 1B/lysine-specific demethylase 5B) is an enzyme that efficiently removes methyl residues from trimethylated lysine 4 on histone H3, a pivotal mark for active chromatin. TIEG1/KLF10 (transforming growth factor-β inducible early gene-1/Krüppel-like transcription factor 10) is a zinc-finger transcription factor that is involved in bone metabolism and exerts antiproliferative activity. Here, we found that TIEG1 interacts with JARID1B. In particular, the repression domains of TIEG1 bind to the C-terminus of JARID1B. Moreover, overexpression of JARID1B augments TIEG1 to repress transcription of Smad7, an inhibitor of the TGF-β (transforming growth factor-β) signaling pathway. Conversely, JARID1B knock-down leads to increased Smad7 mRNA levels. Thus, TIEG1 and JARID1B may cooperate to suppress tumorigenesis by enhancing TGF-β signaling. Notably, both TIEG1 and JARID1B are downregulated in melanomas, suggesting that they indeed cooperate physiologically. In conclusion, JARID1B is the first TIEG1 corepressor identified, explaining how TIEG1 represses transcription through inducing histone H3 lysine 4 demethylation, which may be important for TIEG1 function in both normal and cancer cells.

Dynamic transcriptional changes of TIEG1 and TIEG2 during mouse tissue development

TGF-beta-inducible early-response gene (TIEG) is a family of primary response genes induced by TGF-beta, which are well recognized in regulating cellular proliferation and apoptosis. However, their expression profile has never been investigated during embryogenesis in different organs. In this study, we aimed to investigate the transcriptional level of both TIEG1 and TIEG2 during development in various mice organs, including the brain cortex, cerebellum and stem, brain striatum, muscle, heart, liver, kidney, and lung. Quantitative real-time PCR was used to profile the change of transcriptional level of the two TIEG members in the mice tissues at six developmental stages. Taken together, the expression of TIEG1 and TIEG2 was specific in different organs yet varied with different developmental time points. Their dynamic changes were moderately consistent in most organs including the brain cortex, striatum, liver, kidney, and lung. However, their mRNA expression in both the heart and muscle was significantly different at all developmental stages, which might propose a compensation of functions in the TIEG family. Nevertheless, our data indicate that both the TIEG genes are essential in regulating the normal organ development and functioning in murine model, as their expressions were ubiquitous and tissue specific at various developmental stages.

Functional role of KLF10 in multiple disease processes

Since the discovery by this laboratory of the zinc finger transcription factor, KLF10, a member of the Krüppel-like family of transcription factors, there have been multiple publications regarding its functions and its immediate family members, in numerous cell types. KLF10 has been shown to be rapidly induced by TGFbeta1, 2, 3, E(2), epidermal growth factor, and bone morphogenetic protein-2. TGFbeta inducible early gene-1 activates the TGFbeta-Smad signaling pathway via repression of Smad 7 expression and activation of Smad 2 expression and activity. Overall, KLF10 has been implicated in cell differentiation, as a target gene for a variety of signaling pathways, and in serving as a potential marker for human diseases such as breast cancer, cardiac hypertrophy, and osteoporosis. Like other KLF members, KLF10 is expressed in specific cell types in numerous tissues and is known to be involved in repressing cell proliferation and inflammation as well as inducing apoptosis similar to that of TGFbeta. KLF10 binds to Sp-1-GC rich DNA sequences and can activate or repress the transcription of a number of genes. Overall, KLF10 has been shown to play a major role in the TGFbeta inhibition of cell proliferation and inflammation and induction of apoptosis, and its overexpression in human osteoblasts and pancreatic carcinoma cells mimics the actions of TGFbeta.

TIEG-null mice display an osteopenic gender-specific phenotype

TGFbeta inducible early gene-1 (TIEG) was originally cloned from human osteoblasts (OB) and has been shown to play an important role in TGFbeta/Smad signaling, regulation of gene expression and OB growth and differentiation. To better understand the biological role of TIEG in the skeleton, we have generated congenic TIEG-null (TIEG(-/-)) mice in a pure C57BL/6 background. Through the use of DXA and pQCT analysis, we have demonstrated that the femurs and tibias of two-month-old female TIEG(-/-) mice display significant decreases in total bone mineral content, density, and area relative to wild-type (WT) littermates. However, no differences were observed for any of these bone parameters in male mice. Further characterization of the bone phenotype of female TIEG(-/-) mice involved mechanical 3-point bending tests, micro-CT, and histomorphometric analyses of bone. The 3-point bending tests revealed that the femurs of female TIEG(-/-) mice have reduced strength with increased flexibility compared to WT littermates. Micro-CT analysis of femurs of two-month-old female TIEG(-/-) mice revealed significant decreases in cortical bone parameters compared to WT littermates. Histomorphometric evaluation of the distal femur revealed that female TIEG(-/-) mice also display a 31% decrease in cancellous bone area, which is primarily due to a decrease in trabecular number. At the cellular level, female TIEG(-/-) mice exhibit a 42% reduction in bone formation rate which is almost entirely due to a reduction in double labeled perimeter. Differences in mineral apposition rate were not detected between WT and TIEG(-/-) mice. Taken together, these findings suggest that female TIEG(-/-) mice are osteopenic mainly due to a decrease in the total number of functional/mature OBs.

Estrogen-TGFbeta cross-talk in bone and other cell types: role of TIEG, Runx2, and other transcription factors

It is well established that E(2) and TGFbeta have major biological effects in multiple tissues, including bone. The signaling pathways through which these two factors elicit their effects are well documented. However, the interaction between these two pathways and the potential consequences of cross-talk between E(2) and TGFbeta continue to be elucidated. In this prospectus, we present known and potential roles of TIEG, Runx2, and other transcription factors as important mediators of signaling between these two pathways.

Chronic fluoxetine treatment induces brain region-specific upregulation of genes associated with BDNF-induced long-term potentiation

Several lines of evidence implicate BDNF in the pathogenesis of stress-induced depression and the delayed efficacy of antidepressant drugs. Antidepressant-induced upregulation of BDNF signaling is thought to promote adaptive neuronal plasticity through effects on gene expression, but the effector genes downstream of BDNF has not been identified. Local infusion of BDNF into the dentate gyrus induces a long-term potentiation (BDNF-LTP) of synaptic transmission that requires upregulation of the immediate early gene Arc. Recently, we identified five genes (neuritin, Narp, TIEG1, Carp, and Arl4d) that are coupregulated with Arc during BDNF-LTP. Here, we examined the expression of these genes in the dentate gyrus, hippocampus proper, and prefrontal cortex after antidepressant treatment. We show that chronic, but not acute, fluoxetine administration leads to upregulation of these BDNF-LTP-associated genes in a brain region-specific pattern. These findings link chronic effects of antidepressant treatment to molecular mechanisms underlying BDNF-induced synaptic plasticity.

Role of TIEG1 in biological processes and disease states

A novel TGFbeta Inducible Early Gene-1 (TIEG1) was discovered in human osteoblast (OB) cells by our laboratory. Over the past decade, a handful of laboratories have revealed a multitude of organismic, cellular, and molecular functions of this gene. TIEG1 is now classified as a member of the 3 zinc finger family of Krüppel-like transcription factors (KLF10). Other closely related factors [TIEG2 (KLF11) and TIEG3/TIEG2b] have been reported and are briefly compared. As described in this review, TIEG1 is shown to play a role in regulating estrogen and TGFbeta actions, the latter through the Smad signaling pathway. In both cases, TIEG1 acts as an inducer or repressor of gene transcription to enhance the TGFbeta/Smad pathway, as well at other signaling pathways, to regulate cell proliferation, differentiation, and apoptosis. This review outlines TIEG1's molecular functions and roles in skeletal disease (osteopenia/osteoporosis), heart disease (hypertrophic cardiomyopathy), and cancer (breast and prostate).

Different regulatory elements are required for response of hepcidin to interleukin-6 and bone morphogenetic proteins 4 and 9

Hepcidin is a major regulator of iron homeostasis. Hepcidin expression is upregulated by inflammatory cytokines, particularly interleukin (IL)-6 and even more potently by the bone morphogenetic proteins 2, 4 and 9 (BMP-2, BMP-4 and BMP-9). This study showed that the regulation of hepcidin expression by IL-6 and BMPs occurs through distinct regulatory elements. The induction of hepcidin by BMPs requires at least two regions of the Hamp1 promoter, one between 140-260 bp and the other between 1.6-2.0 kb upstream of the start of translation. Reporter constructs including 1.6-2.0 kb of the Hamp1 promoter were induced >16-fold by BMPs whereas a 260 bp reporter Hamp1 promoter construct was induced only two- to threefold. The distal 1.6-2.0 kb region appeared to contain several different BMP-responsive elements, as incremental lengthening of the promoter construct in this region produced gradual escalation of BMP-responsiveness. In contrast, the IL-6 response required only the proximal 260 bp Hamp1 promoter region. Furthermore, there were no regulatory elements located in the non-coding or coding regions of Hamp1 and activation of the Hamp1 promoter was absent or markedly reduced in cells of non-hepatic origin.

The role of STAT, AP-1, E-box and TIEG motifs in the regulation of hepcidin by IL-6 and BMP-9: lessons from human HAMP and murine Hamp1 and Hamp2 gene promoters

Hepcidin, the principal regulator of the iron metabolism, is up-regulated in response to inflammatory stimuli, bone morphogenic proteins (BMPs) and iron excess. There are two murine hepcidin genes: hepcidin-1 (Hamp1) and hepcidin-2 (Hamp2). Hamp1 gene responds to both IL-6 and BMPs while Hamp2 responds to neither. We replaced the putative functional regulatory motifs of the Hamp1 promoter with the corresponding putative "non-functional" Hamp2 motifs and vice versa in reporter constructs. Conversion of the Hamp1 STAT site into the Hamp2 site reduced the basal level of reporter expression but did not affect IL-6 and BMP responsiveness; replacing Hamp2 site with the Hamp1 site only resulted in partial responsiveness. These data are in contrast to the role of the STAT site in the human hepcidin promoter which is important in both basal level and IL-6 inducible promoter activity. The murine AP1, E-box and TIEG motifs were found to neither influence the basal level of expression of Hamp1 and HAMP promoters nor play a critical role in the IL-6 and BMP-9 induced response. Our data suggest that the STAT site (nt -148 to -130) is important for the regulation of basal level expression of Hamp1 but there are additional regions that are responsible for the IL-6 and BMP-9 responsiveness within the Hamp1 promoter.

Interleukin-10 regulates transforming growth factor-beta signaling in cultured human bronchial epithelial cells

BACKGROUND

The basic pathological features of bronchial asthma can be explained on the basis of chronic airway inflammation, involving inflammatory cells such as T cells (particularly type 2 helper T, Th2, cells) and mast cells, and airway remodeling. Many aspects of airway remodeling remain unclear at the molecular level. Recent attention has focused on the role of transforming growth factor (TGF)-beta, a fibrogenic cytokine, in airway remodeling. Currently available evidence suggests that airway remodeling is caused by an imbalance in regulatory mechanisms mediated by Smads, a family of signal-transducing molecules.

OBJECTIVES

We studied the effects of the Th2 cytokines interleukin (IL)-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF), and the regulatory cytokine IL-10 on the expression of inhibitory Smad7 protein in bronchial epithelial cells.

METHODS

Real-time reverse-transcriptase polymerase chain reaction was employed.

RESULTS

Stimulation with IL-10 upregulated the expression of Smad7 compared with control. Neither IL-5 nor GM-CSF induced Smad7 expression. Smad7 expression was upregulated by IL-10 plus either IL-5 or GM-CSF. IL-10 inhibited the expression of TGF-beta-inducible early gene, which is known to downregulate Smad7 expression.

CONCLUSIONS

Our results suggest that IL-10 acts as a regulatory cytokine in the inhibition of airway inflammation.

TGFbeta inducible early gene-1 (TIEG1) and cardiac hypertrophy: Discovery and characterization of a novel signaling pathway

Cellular mechanisms causing cardiac hypertrophy are currently under intense investigation. We report a novel finding in the TGFbeta inducible early gene (TIEG) null mouse implicating TIEG1 in cardiac hypertrophy. The TIEG(-/-) knock-out mouse was studied. Male mice age 4-16 months were characterized (N = 86 total) using echocardiography, transcript profiling by gene microarray, and immunohistochemistry localized upregulated genes for determination of cellular mechanism. The female mice (N = 40) did not develop hypertrophy or fibrosis. The TIEG(-/-) knock-out mouse developed features of cardiac hypertrophy including asymmetric septal hypertrophy, an increase in ventricular size at age 16 months, an increase (214%) in mouse heart/weight body weight ratio TIEG(-/-), and an increase in wall thickness in TIEG(-/-) mice of (1.85 +/- 0.21 mm), compared to the control (1.13 +/- 0.15 mm, P < 0.04). Masson Trichrome staining demonstrated evidence of myocyte disarray and myofibroblast fibrosis. Microarray analysis of the left ventricles demonstrated that TIEG(-/-) heart tissues expressed a 13.81-fold increase in pituitary tumor-transforming gene-1 (Pttg1). An increase in Pttg1 and histone H3 protein levels were confirmed in the TIEG(-/-) mice hearts tissues. We present evidence implicating TIEG and possibly its target gene, Pttg1, in the development of cardiac hypertrophy in the TIEG null mouse.

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.