Preclinical Investigations on Anti-fibrotic Potential of Long-Term Oral Therapy of Sodium Astragalosidate in Animal Models of Cardiac and Renal Fibrosis

In traditional Chinese medicine, Radix Astragali has played a vital role in treating progressive fibrotic diseases. One of its main active components, astragaloside IV, is a promising anti-fibrotic treatment despite its extremely low bioavailability. Our study aimed to optimize sodium astragalosidate (SA) by salt formation to improve solubility and oral absorption for anti-fibrotic therapy in vivo. Isoproterenol-induced myocardial fibrosis rat models and obese BKS-db mice presenting diabetic kidney fibrosis were used in this study. Daily oral administration of SA (20 mg/kg) for 14 days ameliorated cardiac fibrosis by reducing collagen accumulation and fibrosis-related inflammatory signals, including TNF-α, IL-1β, and IL-6. In db/db mice, SA (5,10, and 20 mg/kg per day for 8 weeks) dose-dependently alleviated lipid metabolism impairment and renal dysfunction when administered orally. Furthermore, Western blot and immunohistochemistry analyses demonstrated that SA treatment inhibited renal fibrosis by suppressing TGF-β1/Smads signaling. Taken together, our findings provide the oral-route medication availability of SA, which thus might offer a novel lead compound in preclinical trial-enabling studies for developing a long-term therapy to treat and prevent fibrosis.

Human Skin Keratinocytes on Sustained TGF-β Stimulation Reveal Partial EMT Features and Weaken Growth Arrest Responses

Defects in wound closure can be related to the failure of keratinocytes to re-epithelize. Potential mechanisms driving this impairment comprise unbalanced cytokine signaling, including Transforming Growth Factor-β (TFG-β). Although the etiologies of chronic wound development are known, the relevant molecular events are poorly understood. This lack of insight is a consequence of ethical issues, which limit the available evidence to humans. In this work, we have used an in vitro model validated for the study of epidermal physiology and function, the HaCaT cells to provide a description of the impact of sustained exposure to TGF-β. Long term TGF-β1 treatment led to evident changes, HaCaT cells became spindle-shaped and increased in size. This phenotype change involved conformational re-arrangements for actin filaments and E-Cadherin cell-adhesion structures. Surprisingly, the signs of consolidated epithelial-to-mesenchymal transition were absent. At the molecular level, modified gene expression and altered protein contents were found. Non-canonical TGF-β pathway elements did not show relevant changes. However, R-Smads experienced alterations best characterized by decreased Smad3 levels. Functionally, HaCaT cells exposed to TGF-β1 for long periods showed cell-cycle arrest. Yet, the strength of this restraint weakens the longer the treatment, as revealed when challenged by pro-mitogenic factors. The proposed setting might offer a useful framework for future research on the mechanisms driving wound chronification.

Liuwei Dihuang pill treats diabetic nephropathy in rats by inhibiting of TGF-β/SMADS, MAPK, and NF-kB and upregulating expression of cytoglobin in renal tissues

Liuwei Dihuang pill (LDP) was assessed for its effects on renal deficiency.90 STZ induced DN rats were divided into groups (n = 22) without treatment (STZ) and LDP treated (STZ-L) (n = 23), Zhenwu decoction treated (STZ-Z) (n = 22), and valsartan treated (STZ-V) (n = 23) groups, with 16 normal control rats. Total urine protein (TP), blood urea nitrogen (BUN), and serum creatinine (Cr) were measured. Superoxide dismutase (SOD), nitric oxide synthase (NOS), and malondialdehyde (MDA) concentrations as well as expression/phosphorylation of SMAD3, SMAD2, and α-SMA, TGF-β, RI /II, P38, ERK, and NF-kB in renal tissues were determined. In vitro experiments analyzed the effect of enhanced TGF-β containing rat serums of the STZ groups on mesangial cells with and without transient transfection with a cytoglobin-containing plasmid.LDP treatment reduced the kidney coefficient, serum creatinine, blood urea nitrogen, and urine protein and prevented pathological changes. Expression of SOD and NOS in kidney tissue was increased but MDA expression reduced. LDP modulated multiple pathways, and its administration inhibited the phosphorylation of SMADS, ERK, p38, and the expression of NF-kB, α-SMA, and TGF-β RI/II, and upregulated the expression of cytoglobin. In vitro studies revealed that overexpression of cytoglobin suppressed phosphorylation of Smad2, ERK, and p38 induced by TGF-β and expression of NF-kB, α-SMA, and TGF-β RI.LDP prevented renal fibrosis and protected glomerular mesangial cells by upregulation of cytoglobin and suppression of multiple pathways involving TGF-β/SMADS, MAPK, NF-kB signaling.

Effects of tanshinone IIA on the transforming growth factor β1/Smad signaling pathway in rat cardiac fibroblasts

OBJECTIVES

This study explores the mechanism of tanshinone IIA (TSN)-mediated inhibition of myocardial fibrosis by investigating the effect of TSN on transforming growth factor β1 (TGFβ1) signal transduction in rat cardiac fibroblasts (CFs).

MATERIALS AND METHODS

CFs were isolated from neonatal Sprague-Dawley rats by trypsin digestion and differential adhesion and stimulated with 5 ng/mL TGFβ1 and TSN (10(-6), 10(-5), or 10(-4) mol/L). The expression of fibronectin (FN) mRNA in the CFs was determined using reverse transcriptase-polymerase chain reaction and the protein expression of FN and Smads in CFs was detected using Western blot. The intracellular expression and localization of Smads in the CFs were analyzed using immunocytochemistry.

RESULTS

TGFβ1 induced the expression of FN and Smads in a time-dependent manner. At the end of the culture treatment, the mRNA expression of FN and the expression of phosphorylated Smad2/3 (p-Smad2/3) increased significantly (P < 0.01). TSN pretreatment (10(-5) and 10(-4) mol/L) reduced the expression of FN and p-Smad2/3 (P < 0.01) following TGFβ1 stimulation and led to a significant decrease in the nuclear staining intensity and a positive rate of p-Smad2/3 (P < 0.05 and P < 0.01, respectively).

CONCLUSION

The inhibitory effect of TSN on myocardial fibrosis may be associated with its inhibition of TGFβ1-induced Smad2/3 phosphorylation and p-Smad2/3 nuclear translocation, which blocks the TGFβ1/Smad signaling pathway in CFs.

Fluoride promotes viability and differentiation of osteoblast-like Saos-2 cells via BMP/Smads signaling pathway

The BMP/Smad signaling pathway plays an important role in the viability and differentiation of osteoblast; however, it is not clear whether this pathway is involved in the fluoride-induced osteoblast differentiation. In this study, we investigated the role of BMP/Smad signaling pathway in fluoride-induced osteoblast-like Saos-2 cells differentiation. Cells were exposed to fluoride of different concentrations (0, 0.1, 0.2, 0.4, 0.8, and 1.6 mM), and cell proliferation was determined using WST assays. The expression of osteoblast marker genes such as osteocalcin (BGP) and bone alkaline phosphatase (BALP) were detected by qRT-PCR. We found that fluoride enhanced the proliferation of Saos-2 cells in a dose-dependent manner and 0.2 mM of fluoride resulted in a higher expression of osteoblast marker genes. In addition, immunofluorescence analysis showed that the promotion effects of 0.2 mM of fluoride on Saos-2 cells differentiation were associated with the activation of the BMP/Smad pathway. Expression of phosphorylated Smad1/5(p-Smad1/5) was higher in cells exposed to 0.2 mM of fluoride. Plasmid expression vectors encoding the short hairpin RNA (shRNA) targeting Smad4 gene were used to block the BMP/Smad pathway, which resulted in a significantly reduced expression of BGP and BALP as well as their corresponding mRNA. The mRNA levels after transfection remained low even in the presence of fluoride. The present results reveal that BMP/Smad signaling pathway was altered during the period of osteogenesis, and that the activities of p-Smad1/5 were required for Saos-2 cells viability and differentiation induced by fluoride.

Alterations in the Smad pathway in human cancers

Members of the TGF-beta superfamily exhibit various biological activities, and perturbations of their signaling are linked to certain clinical disorders including cancer. The role of TGF-beta signaling as a tumor suppressor pathway is best illustrated by the presence of inactivating mutations in genes encoding TGF-beta receptors and Smads in human carcinomas. This perspective is further supported by studies of tumor development in mouse models after modulation of receptors and Smads. TGF-beta also controls processes such as cell invasion, immune regulation, and microenvironment alterations that cancer cells may exploit to their advantage for their progression. Consequently, the output of a TGF-beta response is highly situation dependent, across different tissues, and also in cancer in general. Understanding the mechanisms of TGF-beta superfamily signaling is thus important for the development of new ways to treat various types of cancer. This review focuses on recent advances in understanding the Smad dependent TGF-beta pathway as it relates to human carcinogenesis.

PPM1A dephosphorylates RanBP3 to enable efficient nuclear export of Smad2 and Smad3

Smad2 and Smad3 (Smad2/3) are essential signal transducers and transcription factors in the canonical transforming growth factor-β (TGF-β) signalling pathway. Active Smad2/3 signalling in the nucleus is terminated by dephosphorylation and subsequent nuclear export of Smad2/3. Here we report that protein phosphatase PPM1A regulates the nuclear export of Smad2/3 through targeting nuclear exporter RanBP3. PPM1A directly interacted with and dephosphorylated RanBP3 at Ser 58 in vitro and in vivo. Consistently, RanBP3 phosphorylation was elevated in PPM1A-null mouse embryonic fibroblasts. Dephosphorylation of RanBP3 at Ser 58 promoted its ability to export Smad2/3 and terminate TGF-β responses. Our findings indicate the critical role of PPM1A in maximizing exporter activity of RanBP3 for efficient termination of canonical TGF-β signalling.

Metastatic bone disease: role of transcription factors and future targets

Progression of cancer from the earliest event of cell transformation through stages of tumor growth and metastasis at a distal site involves many complex biological processes. Underlying the numerous responses of cancer cells to the tumor microenvironment which support their survival, migration and metastasis are transcription factors that regulate the expression of genes reflecting properties of the tumor cell. A number of transcription factors have been identified that play key roles in promoting oncogenesis, tumor growth, metastasis and tissue destruction. Relevant to solid tumors and leukemias, tissue-specific transcription factors that are deregulated resulting from mutations, being silenced or aberrantly expressed, have been well characterized. These are the master transcription factors of the Runx family of genes, the focus of this review, with emphasis placed on Runx2 that is abnormally expressed at very high levels in cancer cell lines that are metastatic to bone. Recent evidence has identified a correlation of Runx2 levels in advanced stages of prostate and breast cancer and demonstrated that effective depletion of Runx2 by RNA interference inhibits migration and invasive properties of the cells prevents metastatic bone disease. This striking effect is consistent with the broad spectrum of Runx2 properties in activating many genes in tumor cells that have already been established as indicators of bone metastasis in poor prognosis. Potential strategies to translate these findings for therapeutic applications are discussed.

Bone morphogenetic protein signaling regulates gastric epithelial cell development and proliferation in mice

BACKGROUND & AIMS

We investigated the role of bone morphogenetic protein (BMP) signaling in the regulation of gastric epithelial cell growth and differentiation by generating transgenic mice that express the BMP inhibitor noggin in the stomach.

METHODS

The promoter of the mouse H+/K+-ATPase β-subunit gene, which is specifically expressed in parietal cells, was used to regulate expression of noggin in the gastric epithelium of mice. The transgenic mice were analyzed for noggin expression, tissue morphology, cellular composition of the gastric mucosa, gastric acid content, and plasma levels of gastrin. Tissues were analyzed by immunohistochemical, quantitative real-time polymerase chain reaction, immunoblot, microtitration, and radioimmunoassay analyses.

RESULTS

In the stomachs of the transgenic mice, phosphorylation of Smad 1, 5, and 8 decreased, indicating inhibition of BMP signaling. Mucosa were of increased height, with dilated glands, cystic structures, reduced numbers of parietal cells, and increased numbers of cells that coexpressed intrinsic factor, trefoil factor 2, and Griffonia (Bandeiraea) simplicifolia lectin II, compared with wild-type mice. In the transgenic mice, levels of the H+/K+-ATPase α-subunit protein and messenger RNA were reduced, whereas those of intrinsic factor increased. The transgenic mice were hypochloridric and had an increased number of Ki67- and proliferating cell nuclear antigen-positive cells; increased levels of plasma gastrin; increased expression of transforming growth factor-α, amphiregulin, and gastrin; and activation of extracellular signal-regulated kinase 2.

CONCLUSIONS

Inhibiting BMP signaling in the stomachs of mice by expression of noggin causes loss of parietal cells, development of transitional cells that express markers of mucus neck and zymogenic lineages, and activation of proliferation. BMPs are therefore important regulators of gastric epithelial cell homeostasis.

New insights into ovarian function

Infertility adversely affects many couples worldwide. Conversely, the exponential increase in world population threatens our planet and its resources. Therefore, a greater understanding of the fundamental cellular and molecular events that control the size of the primordial follicle pool and follicular development is of utmost importance to develop improved in vitro fertilization as well as to design novel approaches to regulate fertility. In this review we attempt to highlight some new advances in basic research of the mammalian ovary that have occurred in recent years focusing primarily on mouse models that have contributed to our understanding of ovarian follicle formation, development, and ovulation. We hope that these new insights into ovarian function will trigger more research and translation to clinically relevant problems.

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.

Prohibitin regulates TGF-beta induced apoptosis as a downstream effector of Smad-dependent and -independent signaling

BACKGROUND

Prohibitin (PHB), a protein located on the inner mitochondrial membrane and nuclei, is an intracellular effector of transforming growth factor-beta (TGF-beta) signaling in prostate cancer cells. This study investigated the involvement of PHB in the apoptosis and survival outcomes of human prostate cancer cell to TGF-beta. shRNA PHB loss of function in prostate cancer cells led to enhanced apoptotic response to TGF-beta via Smad-dependent mechanism.

METHOD

TGF-beta activation of Raf-Erk intracellular signaling, led to PHB phosphorylation, decreased inner mitochondrial permeability, and increased cell survival. Calcein-based immunofluorescence studies revealed the functional involvement of PHB in maintaining inner mitochondrial membrane permeability as an integral component of TGF-beta induced apoptosis in prostate cancer cells.

RESULTS

These finding indicates that induction of TGF-beta apoptosis is mediated by Smad-dependent and Smad-independent signaling (MAPK) converging at PHB as a downstream effector regulating inner mitochondrial permeability. Putative PHB associated proteins were identified by subjecting TGF-beta treated cells to immunoprecipitation with anti-PHB, and mass spectrometry. A screen for the kinase specific phosphorylation sites of PHB revealed three protein kinase (PKC) binding sites.

CONCLUSION

Our results demonstrate that TGF-beta led to upregulation of the PKC inhibitor 14-3-3 protein and promoted its association with PHB, while PHB association with PKC-delta, was inhibited by the MEK1 inhibitor, documenting a critical interdependence between the MEK-ERK signaling and prohibitin phosphorylation. These findings suggest a dual role for PHB as a downstream determinant of the cellular response to TGF-beta via Smad-dependent pathway (apoptosis) and MAPK intracellular signaling (survival).

Integration of non-SMAD and SMAD signaling in TGF-beta1-induced plasminogen activator inhibitor type-1 gene expression in vascular smooth muscle cells

Overexpression of plasminogen activator inhibitor-1 (SERPINE1, PAI-1), the major physiological inhibitor of pericellular plasmin generation, is a significant causative factor in the progression of vascular disorders (e.g. arteriosclerosis, thrombosis, perivascular fibrosis) as well as a biomarker and a predictor of cardiovascular-disease associated mortality. PAI-1 is a temporal/spatial regulator of pericellular proteolysis and ECM accumulation impacting, thereby, vascular remodeling, smooth muscle cell migration, proliferation and apoptosis. Within the specific context of TGF-beta1-initiated vascular fibrosis and neointima formation, PAI-1 is a member of the most prominently expressed subset of TGF-beta1-induced transcripts. Recent findings implicate EGFR/pp60c-src-->MEK/ERK1/2 and Rho/ROCK-->SMAD2/3 signaling in TGF-beta1-stimulated PAI-1 expression in vascular smooth muscle cells. The EGFR is a direct upstream regulator of MEK/ERK1/2 while Rho/ROCK modulate both the duration of SMAD2/3 phosphorylation and nuclear accumulation. E-box motifs (CACGTG) in the PE1/PE2 promoter regions of the human PAI-1 gene, moreover, are platforms for a MAP kinase-directed USF subtype switch (USF-1-->USF-2) in response to growth factor addition suggesting that the EGFR-->MEK/ERK axis impacts PAI-1 expression, at least partly, through USF-dependent transcriptional controls. This paper reviews recent data suggesting the essential cooperativity among the EGFR-->MAP kinase cascade, the Rho/ROCK pathway and SMADs in TGF-beta1-initiated PAI-1 expression. The continued clarification of mechanistic controls on PAI-1 transcription may lead to new targeted therapies and clinically-relevant options for the treatment of vascular diseases in which PAI-1 dysregulation is a major underlying pathogenic feature.

Molecular requirements for induction of CTGF expression by TGF-beta1 in primary osteoblasts

Connective tissue growth factor (CTGF/CCN2) is a cysteine rich, extracellular matrix protein that acts as an anabolic growth factor to regulate osteoblast differentiation and function. In osteoblasts, CTGF is induced by TGF-beta1 where it acts as a downstream mediator of TGF-beta1 induced matrix production. The molecular mechanisms that control CTGF induction by TGF-beta1 in osteoblasts are not known. To assess the role of individual Smads in mediating the induction of CTGF by TGF-beta1, we used specific Smad siRNAs to block Smad expression. These studies demonstrated that Smads 3 and 4, but not Smad 2, are required for TGF-beta1 induced CTGF promoter activity and expression in osteoblasts. Since the activation of MAPKs (Erk, Jnk and p38) by TGF-beta1 is cell type specific, we were interested in determining the role of individual MAPKs in TGF-beta1 induction of CTGF promoter activity and expression. Using dominant negative (DN) mutants for Erk, Jnk and p38, we demonstrated that the expression of DN-Erk caused a significant inhibition of TGF-beta1 induced CTGF promoter activity. In contrast, the expression of DN-p38 or DN-Jnk failed to inhibit activation of CTGF promoter activity. To confirm the vital role of Erk, we used the Erk inhibitor (PD98059) to block its activation, demonstrating that it prevented TGF-beta1 activation of the CTGF promoter and up-regulation of CTGF expression in osteoblasts. Since Src can also act as a downstream signaling effector for TGF-beta in some cell types, we determined its role in TGF-beta1 induction of CTGF in osteoblasts. Treatment of osteoblasts with a Src family kinase inhibitor, PP2, or the expression of two independent kinase-dead Src mutant constructs caused significant inhibition of TGF-beta1 induced CTGF promoter activity and expression. Additionally, blocking Src activation prevented Erk activation by TGF-beta1 demonstrating a role for Src as an upstream mediator of Erk in regulating CTGF expression in osteoblasts. To investigate the involvement of the TGF-beta1 response element (TRE) and the SMAD binding element (SBE) in CTGF induction, we cloned the rat CTGF proximal promoter (-787 to +1) containing the TRE and SBE motifs into a pGL3-Luciferase reporter construct. Using a combination of CTGF promoter deletion constructs and site-directed mutants, we demonstrated the unique requirement of both the TRE and SBE for CTGF induction by TGF-beta1 in osteoblasts. Electro-mobility shift assays using specific probes containing the TRE, SBE or both showed TGF-beta1 inducible complexes that can be ablated by mutation of the respective motif, confirming their requirement for TGF-beta1 induced CTGF promoter activity. In conclusion, these studies demonstrate that CTGF induction by TGF-beta1 in osteoblasts involves Smads 3 and 4, the Erk and Src signaling pathways, and requires both the TRE and SBE motifs in the CTGF proximal promoter.

Zfp423 controls proliferation and differentiation of neural precursors in cerebellar vermis formation

Neural stem cells and progenitors in the developing brain must choose between proliferation with renewal and differentiation. Defects in navigating this choice can result in malformations or cancers, but the genetic mechanisms that shape this choice are not fully understood. We show by positional cloning that the 30-zinc finger transcription factor Zfp423 (OAZ) is required for patterning the development of neuronal and glial precursors in the developing brain, particularly in midline structures. Mutation of Zfp423 results in loss of the corpus callosum, reduction of hippocampus, and a malformation of the cerebellum reminiscent of human Dandy-Walker patients. Within the cerebellum, Zfp423 is expressed in both ventricular and external germinal zones. Loss of Zfp423 results in diminished proliferation by granule cell precursors in the external germinal layer, especially near the midline, and abnormal differentiation and migration of ventricular zone-derived neurons and Bergmann glia.

TGF-beta inhibits muscle differentiation through functional repression of myogenic transcription factors by Smad3

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of skeletal muscle differentiation, but the molecular mechanism and signaling events that lead to this inhibition are poorly characterized. Here we show that the TGF-beta intracellular effector Smad3, but not Smad2, mediates the inhibition of myogenic differentiation in MyoD-expressing C3H10T1/2 cells and C2C12 myoblasts by repressing the activity of the MyoD family of transcriptional factors. The Smad3-mediated repression was directed at the E-box sequence motif within muscle gene enhancers and the bHLH region of MyoD, the domain required for its association with E-protein partners such as E12 and E47. The repression could be overcome by supplying an excess of E12, and covalent tethering of E47 to MyoD rendered the E-box-dependent transcriptional activity refractory to the effects of Smad3 and TGF-beta. Smad3 physically interacted with the HLH domain of MyoD, and this interaction correlated with the ability of Smad3 to interfere with MyoD/E protein heterodimerization and binding of MyoD complexes to oligomerized E-box sites. Together, these results reveal a model for how TGF-beta, through Smad3-mediated transcriptional repression, inhibits myogenic differentiation.

Interplay between bone morphogenetic proteins and cognate binding proteins in bone and cartilage development: noggin, chordin and DAN

This commentary is a concise discussion of the interactions between bone morphogenetic proteins (BMPs) and their binding proteins in bone and cartilage morphogenesis. BMPs are a family of growth and differentiation factors, and they act on mesenchymal cells to induce cartilage and bone differentiation in concentration-dependent thresholds. The BMP-BMP receptor binding leads to a cascade of signaling and transcription of BMP response genes. BMP binding proteins, noggin, chordin and DAN, act as antagonists and determine the bioavailability of BMPs for binding to cognate receptors to elicit the biological response. Noggin null mice with unrestricted action of BMPs exhibit defects in joint morphogenesis. BMPs and their binding proteins may reciprocally regulate the dynamic topography of joints, muscle, tendons and ligaments during morphogenesis of the skeleton. In addition, BMP actions may be potentiated by twisted gastrulation. BMPs and their binding proteins may play a critical role in regeneration of cartilage in osteoarthritis.

A mechanism of suppression of TGF-beta/SMAD signaling by NF-kappa B/RelA

A number of pathogenic and proinflammatory stimuli, and the transforming growth factor-beta (TGF-beta) exert opposing activities in cellular and immune responses. Here we show that the RelA subunit of nuclear factor kappaB (NF-kappaB/RelA) is necessary for the inhibition of TGF-beta-induced phosphorylation, nuclear translocation, and DNA binding of SMAD signaling complexes by tumor necrosis factor-alpha (TNF-alpha). The antagonism is mediated through up-regulation of Smad7 synthesis and induction of stable associations between ligand-activated TGF-beta receptors and inhibitory Smad7. Down-regulation of endogenous Smad7 by expression of antisense mRNA releases TGF-beta/SMAD-induced transcriptional responses from suppression by cytokine-activated NF-kappaB/RelA. Following stimulation with bacterial lipopolysaccharide (LPS), or the proinflammatory cytokines TNF-alpha and interleukin-1beta (IL-1beta, NF-kappaB/RelA induces Smad7 synthesis through activation of Smad7 gene transcription. These results suggest a mechanism of suppression of TGF-beta/SMAD signaling by opposing stimuli mediated through the activation of inhibitory Smad7 by NF-kappaB/RelA.

Synergistic cooperation of TFE3 and smad proteins in TGF-beta-induced transcription of the plasminogen activator inhibitor-1 gene

Members of the TGF-beta superfamily influence a broad range of biological activities including stimulation of wound healing and inhibition of cell growth. TGF-beta signals through type I and II receptor serine/ threonine kinases and induces transcription of many genes including plasminogen activator inhibitor-1 (PAI-1). To identify proteins that participate in TGF-beta-induced gene expression, we developed a novel retrovirus-mediated expression cloning strategy; and using this approach, we established that transcription factor microE3 (TFE3) is involved in TGF-beta-induced activation of the PAI-1 promoter. We showed that TFE3 binds to an E-box sequence in PE2, a 56-bp promoter fragment of the PAI-1 promoter, and that mutation of this sequence abolishes both TFE3 binding as well as TGF-beta-dependent activation. TFE3 and Smad3 synergistically activate the PE2 promoter and phosphorylated Smad3 and Smad4 bind to a sequence adjacent to the TFE3-binding site in this promoter. Binding of both TFE3 and the Smad proteins to their cognate sequences is indispensable for TGF-beta-inducible activation of the PE2 promoter. Hence, TFE3 is an important transcription factor in at least one TGF-beta-activated signal transduction pathway.