Contractility as a Prerequisite for TGF-β–Induced Myofibroblast Transdifferentiation in Human Tenon Fibroblasts

PURPOSE

To assess the significance of Rho-kinase-dependent contractility in TGF-beta-induced myofibroblast transdifferentiation of human tenon fibroblasts to characterize possible pharmacological targets for the inhibition of postoperative scarring after glaucoma surgery.

METHODS

Human tenon fibroblasts (HTFs) were grown in culture and stimulated with TGF-beta1. The effect of TGF-beta on Rho-GTPase activity was assessed by GST-rhotekin binding domain pulldown assay and detected by Western blot analysis. Contractility was evaluated in a silicone substrate wrinkling assay and in fibroblast-populated collagen gels. The actin cytoskeleton and focal adhesions were visualized by immunofluorescence microscopy. alpha-SMA transcripts were measured by real-time RT-PCR. TGF-beta-induced Smad- and p38-activation and expression of alpha-SMA were detected by Western blot analysis. Nuclear translocation of Smad2/3 was determined by confocal immunofluorescence microscopy. The influence of Rho-dependent kinase (ROCK) and myosin light chain kinase (MLCK) were studied by using specific kinase inhibitors (Y-27632, HA-1077, H-1152, and ML-7).

RESULTS

Within 10 minutes of stimulation, TGF-beta induced Rho activation that was associated with an increase in cell tension and followed by actin stress fiber enhancement. ROCK inhibitors released cell tension and averted TGF-beta-induced cytoskeletal changes, p38 activation and subsequent alpha-SMA expression, whereas Smad2-phosphorylation and nuclear translocation were preserved. MLCK inhibition also blocked alpha-SMA expression. In fibroblast-populated collagen lattices, ROCK inhibitors prevented TGF-beta-induced stress fiber assembly and contraction.

CONCLUSIONS

TGF-beta induces a rapid contractile response in HTFs that precedes myofibroblast transdifferentiation. ROCK inhibitors release this contraction and block subsequent TGF-beta-induced myofibroblast transdifferentiation and may therefore serve to modulate postoperative scarring after glaucoma filtering surgery.

Systemic mediators induce fibrogenic effects in normal liver after partial bile duct ligation

BACKGROUND/AIMS

Collagen production by activated hepatic stellate cells (HSCs) is a key event in liver fibrosis, and a number of factors have been characterized that trigger HSC activation and collagen production. However, it remains unclear if these factors act locally at the site of injury or also affect HSCs distant to the site of injury.

METHODS

A model of partial bile duct ligation (PBDL) in which fibrogenesis can be compared between the injured ligated lobe and the non-ligated lobe.

RESULTS

After PBDL, HSCs showed an increased expression of procollagen type I alpha1 mRNA and collagen-reporter gene activity not only in the ligated lobe, but also in the non-ligated lobe, albeit at a lower level. In contrast, an increase in the number of desmin- and alpha-smooth muscle actin positive HSCs, and accumulation of inflammatory cells were observed only in the ligated lobe. Although transforming growth factor-beta (TGF-beta) mRNA was increased only in the ligated lobe, Smad2/3 were activated in the ligated and the non-ligated lobe. These data suggest that the systemic increase in profibrogenic mediators including TGF-beta induces collagen transcription in the uninjured liver.

CONCLUSION

Systemic profibrogenic mediators from the injury site affect the residual non-injured liver.

Vitronectin is present in epithelial cells of the intact lens and promotes epithelial mesenchymal transition in lens epithelial explants

PURPOSE

Extracellular matrix (ECM) accumulates during the development of posterior capsule opacification (PCO). Vitronectin, an ECM component that is generally prominent in wound healing, has been detected in PCO specimens. Here we set out to investigate the distribution of vitronectin in the lens and determine how it, and other ECM components, influence the lens epithelial phenotype.

METHODS

Rat lens epithelial explants were cultured on vitronectin, fibronectin, and laminin substrata. Explants were monitored for cell migration and the appearance of markers for epithelial mesenchymal transition (EMT), using phase contrast microscopy and immunohistochemistry, respectively. Explants were also monitored for evidence of Smad signaling. Vitronectin expression was analyzed in embryonic and postnatal rodent lens development by immunohistochemistry, western blotting, and in situ hybridization.

RESULTS

Vitronectin, like fibronectin and laminin, provided a good substratum for cellular attachment and migration. However, in the case of vitronectin and fibronectin, this was accompanied by a major phenotypic change. On either vitronectin or fibronectin, but not laminin, most of the cells became elongated, spindle-shaped and were strongly reactive for filamentous alpha-smooth muscle actin. In these respects this transition was typical of the well known TGFbeta-induced EMT. In explants cultured on vitronectin and fibronectin, but not laminin, cell nuclei showed prominent reactivity for Smad 2/3. Vitronectin was also shown to be expressed during embryonic and postnatal development. Initially mRNA and protein were detected in all lens cells, however as development progressed, expression became restricted to cells of the epithelium and transition zone.

CONCLUSIONS

The results clearly show that lens cell engagement with a vitronectin or a fibronectin, but not laminin, substratum has a potent EMT promoting effect and that Smad 2/3 signaling is involved. Thus when considering strategies to slow or prevent PCO, these results highlight the need to take into account ECM molecules such as vitronectin that have the capacity to promote EMT.

Activated hepatic stellate cells induce tumor progression of neoplastic hepatocytes in a TGF-beta dependent fashion

The development of hepatocellular carcinomas from malignant hepatocytes is frequently associated with intra- and peritumoral accumulation of connective tissue arising from activated hepatic stellate cells. For both tumorigenesis and hepatic fibrogenesis, transforming growth factor (TGF)-beta signaling executes key roles and therefore is considered as a hallmark of these pathological events. By employing cellular transplantation we show that the interaction of neoplastic MIM-R hepatocytes with the tumor microenvironment, containing either activated hepatic stellate cells (M1-4HSCs) or myofibroblasts derived thereof (M-HTs), induces progression in malignancy. Cotransplantation of MIM-R hepatocytes with M-HTs yielded strongest MIM-R generated tumor formation accompanied by nuclear localization of Smad2/3 as well as of beta-catenin. Genetic interference with TGF-beta signaling by gain of antagonistic Smad7 in MIM-R hepatocytes diminished epithelial dedifferentiation and tumor progression upon interaction with M1-4HSCs or M-HTs. Further analysis showed that tumors harboring disrupted Smad signaling are devoid of nuclear beta-catenin accumulation, indicating a crosstalk between TGF-beta and beta-catenin signaling. Together, these data demonstrate that activated HSCs and myofibroblasts directly govern hepatocarcinogenesis in a TGF-beta dependent fashion by inducing autocrine TGF-beta signaling and nuclear beta-catenin accumulation in neoplastic hepatocytes. These results indicate that intervention with TGF-beta signaling is highly promising in liver cancer therapy.

Mechanisms underlying TGF-beta1-induced expression of VEGF and Flk-1 in mouse macrophages and their implications for angiogenesis

TGF-beta induces vascular endothelial growth factor (VEGF), a potent angiogenic factor, at the transcriptional and protein levels in mouse macrophages. VEGF secretion in response to TGF-beta1 is enhanced by hypoxia and by overexpression of Smad3/4 and hypoxia-inducible factor-1alpha/beta (HIF-1alpha/beta). To examine the transcriptional regulation of VEGF by TGF-beta1, we constructed mouse reporters driven by the VEGF promoter. Overexpression of HIF-1alpha/beta or Smad3/4 caused a slight increase of VEGF promoter activity in the presence of TGF-beta1, whereas cotransfection of HIF-1alpha/beta and Smad3/4 had a marked effect. Smad2 was without effect on this promoter activity, whereas Smad7 markedly reduced it. Analysis of mutant promoters revealed that the one putative HIF-1 and two Smad-binding elements were critical for TGF-beta1-induced VEGF promoter activity. The relevance of these elements was confirmed by chromatin immunoprecipitation assay. p300, which has histone acetyltransferase activity, augmented transcriptional activity in response to HIF-1alpha/beta and Smad3/4, and E1A, an inhibitor of p300, inhibited it. TGF-beta1 also increased the expression of fetal liver kinase-1 (Flk-1), a major VEGF receptor, and TGF-beta1 and VEGF stimulated pro-matrix metalloproteinase 9 (MMP-9) and active-MMP-9 expression, respectively. The results from the present study indicate that TGF-beta1 can activate mouse macrophages to express angiogenic mediators such as VEGF, MMP-9, and Flk-1.

ANP signaling inhibits TGF-beta-induced Smad2 and Smad3 nuclear translocation and extracellular matrix expression in rat pulmonary arterial smooth muscle cells

Atrial natriuretic peptide (ANP) and transforming growth factor (TGF)-beta play important counterregulatory roles in pulmonary vascular adaptation to chronic hypoxia. To define the molecular mechanism of this important interaction, we tested whether ANP-cGMP-protein kinase G (PKG) signaling inhibits TGF-beta1-induced extracellular matrix (ECM) expression and defined the specific site(s) at which this molecular merging of signaling pathways occurs. Rat pulmonary arterial smooth muscle cells (PASMCs) were treated with ANP (1 muM) or cGMP (1 mM) with or without pretreatment with PKG inhibitors KT-5823 (1 muM) or Rp-8-bromo-cGMP (Rp-8-Br-cGMP 50 muM), then exposed to TGF-beta1 (1 ng/ml) for 5-360 min (for pSmad nuclear translocation and protein analysis) or 24 h (for ECM mRNA expression). Nuclear translocation of pSmad2 and pSmad3 was assessed by fluorescent confocal microscopy. ANP and cGMP inhibited TGF-beta1-induced pSmad2 and pSmad3 nuclear translocation and expression of periostin, osteopontin, and plasminogen activator inhibitor-1 mRNA and protein, but not TGF-beta1-induced phosphorylation of Smad2 and Smad3. KT-5823 and Rp-8-Br-cGMP blocked ANP/cGMP-induced activation of PKG and inhibition of TGF-beta1-stimulated nuclear translocation of pSmad2 and pSmad3 in PASMCs. These results reveal for the first time a precise site at which ANP-cGMP-PKG signaling exerts its antifibrogenic effect on the profibrogenic TGF-beta1 signaling pathway: by blocking TGF-beta1-induced pSmad2 and pSmad3 nuclear translocation and ECM expression in PASMCs. Blocking nuclear translocation and subsequent binding of pSmad2 and pSmad3 to TGF-beta-Smad response elements in ECM genes may be responsible for the inhibitory effects of ANP on TGF-beta-induced expression of ECM molecules.

Muscular atrophy of caveolin-3-deficient mice is rescued by myostatin inhibition

Caveolin-3, the muscle-specific isoform of caveolins, plays important roles in signal transduction. Dominant-negative mutations of the caveolin-3 gene cause autosomal dominant limb-girdle muscular dystrophy 1C (LGMD1C) with loss of caveolin-3. However, identification of the precise molecular mechanism leading to muscular atrophy in caveolin-3-deficient muscle has remained elusive. Myostatin, a member of the muscle-specific TGF-beta superfamily, negatively regulates skeletal muscle volume. Here we report that caveolin-3 inhibited myostatin signaling by suppressing activation of its type I receptor; this was followed by hypophosphorylation of an intracellular effector, Mad homolog 2 (Smad2), and decreased downstream transcriptional activity. Loss of caveolin-3 in P104L mutant caveolin-3 transgenic mice caused muscular atrophy with increase in phosphorylated Smad2 (p-Smad2) as well as p21 (also known as Cdkn1a), a myostatin target gene. Introduction of the myostatin prodomain, an inhibitor of myostatin, by genetic crossing or intraperitoneal administration of the soluble type II myostatin receptor, another inhibitor, ameliorated muscular atrophy of the mutant caveolin-3 transgenic mice with suppression of p-Smad2 and p21 levels. These findings suggest that caveolin-3 normally suppresses the myostatin-mediated signal, thereby preventing muscular atrophy, and that hyperactivation of myostatin signaling participates in the pathogenesis of muscular atrophy in a mouse model of LGMD1C. Myostatin inhibition may be a promising therapy for LGMD1C patients.

Small C-terminal domain phosphatases dephosphorylate the regulatory linker regions of Smad2 and Smad3 to enhance transforming growth factor-beta signaling

Transforming growth factor-beta (TGF-beta) controls a diverse set of cellular processes, and its canonical signaling is mediated via TGF-beta-induced phosphorylation of receptor-activated Smads (2 and 3) at the C-terminal SXS motif. We recently discovered that PPM1A can dephosphorylate Smad2/3 at the C-terminal SXS motif, implicating a critical role for phosphatases in regulating TGF-beta signaling. Smad2/3 activity is also regulated by phosphorylation in the linker region (and N terminus) by a variety of intracellular kinases, making it a critical platform for cross-talk between TGF-beta and other signaling pathways. Using a functional genomic approach, we identified the small C-terminal domain phosphatase 1 (SCP1) as a specific phosphatase for Smad2/3 dephosphorylation in the linker and N terminus. A catalytically inactive SCP1 mutant (dnSCP1) had no effect on Smad2/3 phosphorylation in vitro or in vivo. Of the other FCP/SCP family members SCP2 and SCP3, but not FCP1, could also dephosphorylate Smad2/3 in the linker/N terminus. Depletion of SCP1/2/3 enhanced Smad2/3 linker phosphorylation. SCP1 increased TGF-beta-induced transcriptional activity in agreement with the idea that phosphorylation in the Smad2/3 linker must be removed for a full transcriptional response. SCP1 overexpression also counteracts the inhibitory effect of epidermal growth factor on TGF-beta-induced p15 expression. Taken together, this work identifies the first example of a Smad2/3 linker phosphatase(s) and reveals an important new substrate for SCPs.

Perspectives on blockade of TGFbeta overexpression

Many approaches to blocking profibrotic TGFbeta overexpression are under way. Therapeutic targeting of TGFbeta-Smad signaling holds promise for slowing or halting progressive renal disease. In this issue, Fukasawa et al., using the unilateral ureteral obstruction model, provide a new target for therapeutic intervention by identifying loss of the Smad corepressors Ski and SnoN as a mechanism that amplifies the profibrotic actions of TGFbeta.

Smads orchestrate specific histone modifications and chromatin remodeling to activate transcription

Smads are intracellular transducers for TGF-beta superfamily ligands, but little is known about the mechanism by which complexes of receptor-phosphorylated Smad2 and Smad4 regulate transcription. Using an in vitro transcription system, we have discovered that, unlike most transcription factors that are sufficient to recruit the basal transcription machinery and therefore activate transcription on both naked DNA and chromatin templates, the Smads only activate transcription from chromatin templates. We demonstrate that Smad2-mediated transcription requires the histone acetyltransferase, p300. Smad2-recruited p300 exhibits an altered substrate specificity, specifically acetylating nucleosomal histone H3 at lysines 9 and 18, and these modifications are also detected on an endogenous Smad2-dependent promoter in a ligand-induced manner. Furthermore, we show that endogenous Smad2 interacts with the SWI/SNF ATPase, Brg1, in a TGF-beta-dependent manner, and demonstrate that Brg1 is recruited to Smad2-dependent promoters and is specifically required for TGF-beta-induced expression of endogenous Smad2 target genes. Our data indicate that the Smads define a new class of transcription factors that absolutely require chromatin to assemble the basal transcription machinery and activate transcription.

The NH2-terminal propeptide of type I procollagen acts intracellularly to modulate cell function

The function of the NH(2)-terminal propeptide of type I procollagen (N-propeptide) is poorly understood. We now show that a recombinant trimeric N-propeptide interacts with transforming growth factor-beta1 and BMP2 and exhibits functional effects in stably transfected cells. The synthesis of N-propeptide by COS-7 cells results in an increase in phosphorylation of Akt and Smad3 and is associated with a marked reduction in type I procollagen synthesis and impairment in adhesion. In C2C12 cells, N-propeptide inhibits the osteoblastic differentiation induced by BMP2. Our data suggest that these effects are mediated by the interaction of N-propeptide with an intracellular receptor in the secretory pathway, because they are not observed when recombinant N-propeptide is added to the culture medium of either COS-7 or C2C12 cells. Both the binding of N-propeptide to cytokines and its functional properties are entirely dependent on the exon 2-encoded globular domain, and a mutation that substitutes a serine for a highly conserved cysteine in exon 2 abolishes its function. Our findings suggest that N-propeptide performs an important feedback regulatory function and provides a rationale for the prominence of a homotrimeric form of type I procollagen (alpha1 trimer) during vertebrate development.

ERK contributes to the effects of Smad signaling on oxidized LDL-induced PAI-1 expression in human mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) stimulates plasminogen activator inhibitor-1 (PAI-1) expression in human mesangial cells mediated by transforming growth factor-beta (TGF-beta)/Smad signaling pathway. TGF-beta activates extracellular signal-regulated kinase (ERK) in mesangial cells, and ERK is involved in activation of Smad2/3. This study examines whether an interaction exists between Ox-LDL-induced TGF-beta/Smad signaling pathways and ERK activation leading to PAI-1 transcription in human mesangial cells. Ox-LDL (50 microg/mL) induced an acute increase in ERK activity within 15 min, which decreased to control value at 2 h. Incubation with anti-TGF-beta or SB-431542, an inhibitor of the TGF-beta type I receptor, along with Ox-LDL, inhibited the expected increase in ERK phosphorylation. Treatment with PD98059 or UO126, mitogen-activated ERK-activating kinase 1/2 inhibitors, significantly inhibited the Ox-LDL-induced increase in PAI-1 mRNA and nuclear Smad3 expression, DNA/protein complex formation, and PAI-1 promoter activity. These results suggest that phosphorylation of ERK is induced by Ox-LDL through the induction of the TGF-beta signaling pathway and that activated ERK, in turn, participates in the Ox-LDL-induced Smad3 activation and subsequent PAI-1 gene expression in mesangial cells.

Altered subcellular location of phosphorylated Smads in Alzheimer's disease

A number of growth factors and cytokines, such as transforming growth factor beta 1 (TGF-beta1), is elevated in Alzheimer's disease (AD), giving rise to activated intracellular mitogenic signaling cascades. Activated mitogenic signaling involving the mitogen-activated protein kinases (MAPKs) and other protein kinases might alter the phosphorylation states of structural proteins such as tau, resulting in hyperphosphorylated deposits. Many intracellular signaling proteins are potential targets of misregulated phosphorylation and dephosphorylation. Recently, a crosstalk between MAPKs and Smad proteins, both involved in mediating TGF-beta1 signaling, has been reported. Although TGF-beta1 has previously been shown to be involved in the pathogenesis of AD, the role of Smad proteins has not been investigated. In this study we thus analysed the subcellular distribution of phosphorylated Smad2 and Smad3 in the hippocampus of both normal and AD brains. Here we report on strong nuclear detection of phosphorylated Smad2 and Smad3 in neurons of control brains. In AD brains these phosphorylated proteins were additionally found in cytoplasmic granules in hippocampal neurons, within amyloid plaques and attached to neurofibrillary tangles. Our data suggest a critical role of Smad proteins in the pathogenesis of AD.

IN-1130, a novel transforming growth factor-β type I receptor kinase (ALK5) inhibitor, suppresses renal fibrosis in obstructive nephropathy

The transforming growth factor-beta (TGF-beta) plays a central role in the progression of renal fibrosis. TGF-beta transduces its signal through the activin receptor-like kinase (ALK)5. IN-1130, a novel small molecule ALK5 inhibitor, inhibited the purified kinase domain of ALK5-mediated Smad3 phosphorylation with an IC(50) value of 5.3 nM. IN-1130 proved to be highly selective in a panel of 27 serine/threonine and tyrosine kinases including p38alpha mitogen-activated protein kinase. We evaluated the efficacy of IN-1130 to block renal fibrogenesis induced by unilateral ureteral obstruction (UUO) in rats. Either vehicle (saline) or IN-1130 (10 and 20 mg/kg/day) was intraperitoneally administered to UUO rats for 7 and 14 days. Phosphorylated Smad2 (pSmad2) and markers of fibrosis were analyzed in kidney tissues. In UUO control kidneys, interstitial fibrosis including tubular atrophy, loss and dilation, inflammatory cell infiltration, and fibroblast cell proliferation was prominent. These morphological changes were notably reduced by IN-1130 treatment. IN-1130 decreased levels of TGF-beta1 messenger RNA (mRNA), type I collagen mRNA, and pSmad2, compared to UUO control rats. As determined by measuring the hydroxyproline content, total kidney collagen amount was increased in UUO control kidneys, but significantly reduced by IN-1130 treatment, which was comparable to results of histochemical staining for collagen. IN-1130 also suppressed the expression of alpha-smooth muscle actin (alpha-SMA) and fibronectin in UUO kidneys. Our results show that IN-1130 suppressed the fibrogenic process of UUO, further underscoring the potential clinical benefits of IN-1130 in the treatment of renal fibrosis.

Effects of rhDecorin on TGF-beta1 induced human hepatic stellate cells LX-2 activation

Decorin is a small leucine-rich extracellular matrix proteoglycan composed of a core protein with a single glycosaminoglycan (GAG) chain near the N-terminus and N-glycosylated at three potential sites. Decorin is involved in the regulation of formation and organization of collagen fibrils, modulation of the activity of growth factors such as transforming growth factor beta (TGF-beta), and exerts other effects on cell proliferation and behavior. Increasing evidences show that decorin plays an important role in fibrogenesis by regulating TGF-beta, a key stimulator of fibrosis, and by directly modulating the degradation of extracellular matrix (ECM) from activated hepatic stellate cells (HSCs). In this study, the core protein of human decorin was cloned and expressed in Escherichia coli. The purified recombinant human decorin (rhDecorin) significantly inhibited the proliferation of LX-2 cells, a human HSC cell line, stimulated by TGF-beta1. RT-PCR result showed that the expression of metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-1 (TIMP-1) were reduced by rhDecorin in LX-2 cells stimulated by TGF-beta1. Furthermore, the protein expression of smooth muscle-alpha-actin (alpha-SMA), collagen type III and phosphorylated Smad2 (p-Smad2) was significantly decreased in the presence of rhDecorin. rhDecorin also reduced fibrillogenesis of collagen type I in a dose-dependent manner. Gene expression profiles of LX-2 cells stimulated by TGF-beta1 in the presence and the absence of rhDecorin were obtained by using cDNA microarray technique and differentially expressed genes were identified to provide further insight into the molecular action mechanism of decorin on LX-2 cells.

Nuclear retention of the tumor suppressor cPML by the homeodomain protein TGIF restricts TGF-beta signaling

The homeodomain protein TGIF has been implicated in the negative regulation of TGF-beta signaling. In this study, we report an unexpected role of TGIF in the inhibition of Smad2 phosphorylation, which occurs by a mechanism independent of its association with Smad2. This inhibitory function of TGIF is executed in concert with c-Jun, which facilitates the interaction of TGIF with cPML, resulting in the nuclear sequestration of cPML and the disruption of the cPML-SARA complex. Notably, knockdown of TGIF by siRNA caused increased association of cPML with SARA and cytoplasmic accumulation of cPML. Furthermore, c-Jun(-/-) fibroblasts exhibit enhanced association of cPML with SARA. c-Jun(-/-) fibroblasts also lose their sensitivity to TGIF-mediated disruption of the cPML-SARA complex and of nuclear sequestration of cPML. We suggest that the interaction of TGIF with cPML through c-Jun may negatively regulate TGF-beta signaling through controlling the localization of cPML and, consequently, the assembly of the cPML-SARA complex.

IGF-I and IGFBP-3 augment transforming growth factor-beta actions in human renal carcinoma cells

Renal cell carcinoma (RCC) is the most prevalent cancer of the kidney. In human RCC cells, we recently showed that insulin-like growth factor I (IGF-I) has growth-promoting effects regulated by IGF-binding protein 3 (IGFBP-3). In this study, the analysis was expanded to include the interaction between the IGF and transforming growth factor-beta (TGF-beta) systems in the human RCC cells Caki-2 (from a primary tumor) and SK-RC-52 (from a metastasis). Functional effects such as cell proliferation, TGF-beta receptor (TbetaR) signaling, and IGFBP-3 levels were monitored after stimulation with various concentrations of IGF-I, TGF-beta, and IGFBP-3. In addition, human RCC tissues as well as experimental human RCC tumors were analyzed for cellular expression of phosphorylated Smad2 by immunohistochemistry. TGF-beta regulated the endogenous IGFBP-3 levels in these RCC cells as neutralizing anti-TGF-beta(1-3) antibodies strongly reduced the basal IGFBP-3 level. In addition, IGF-I increased the IGFBP-3 levels five- to eightfold with TGF-beta acting in synergy to enhance the IGFBP-3 levels 12- to 17-fold. Neutralizing TGF-beta(1-3) activity circumvented the growth inhibitory effects of IGFBP-3 seen in SK-RC-52, whereas it inhibited the growth-promoting effects of IGFBP-3 in Caki-2. Moreover, IGF-I interacted directly with TGF-beta activation of the TbetaR complex by enhancing phosphorylation and nuclear translocation of Smad2. This study demonstrates a direct interaction of the IGF and TGF-beta systems in human renal carcinoma cells. The observations that IGF-I enhances the TGF-beta signaling and that TGF-beta promotes IGFBP-3 production and thus influence the biological activity of IGF may be of importance for future therapeutic options.

Downregulation of SnoN expression in obstructive nephropathy is mediated by an enhanced ubiquitin-dependent degradation

Smad transcriptional co-repressor SnoN acts as an antagonist that tightly controls the trans-activation of TGF-beta/Smad target genes. SnoN protein is reduced progressively in the fibrotic kidney after obstructive injury, suggesting that the loss of Smad antagonist is a critical event that leads to an uncontrolled fibrogenic signaling. However, the mechanism underlying SnoN downregulation remains unknown. This study investigated the regulation and mechanism of renal SnoN expression in vivo. Whereas SnoN protein was markedly diminished, its mRNA levels remained relatively constant in the obstructed kidney after ureteral ligation. An increased ubiquitination and proteasome-dependent degradation of SnoN was found in obstructed kidney, compared with sham controls. Smad ubiquitination regulatory factor-2, an E3 ubiquitin ligase, was induced and formed a complex with SnoN in vivo. In vitro, TGF-beta1 promoted SnoN protein degradation, which was mediated by ubiquitination and a proteasome-dependent mechanism. SnoN constitutively interacted with another Smad co-repressor, Ski, and they formed ternary complex with Smad2/3 upon TGF-beta1 stimulation. However, ectopic expression of Ski did not alter the degradation rate of SnoN. Blockage of SnoN degradation by proteasome inhibitor abolished TGF-beta1-mediated alpha-smooth muscle actin and fibronectin induction, suggesting that SnoN degradation could be necessary for TGF-beta1 to exert its fibrogenic action. Furthermore, knockdown of Smad ubiquitination regulatory factor-2 expression by small interfering RNA strategy led to an increase in SnoN abundance and inhibited the TGF-beta1-mediated gene transcription. These results indicate that downregulation of SnoN expression in the obstructed kidney is mediated by an enhanced ubiquitin-dependent degradation. Preservation of SnoN by inhibiting its degradation may be a novel strategy for targeting hyperactive Smad signaling in renal fibrotic diseases.

Aldosterone promotes fibronectin production through a Smad2-dependent TGF-β1 pathway in mesangial cells

Accumulating evidence demonstrates that aldosterone can cause extra-cellular matrix (ECM) accumulation, in addition to regulating sodium and potassium homeostasis. Increased extra-cellular matrix production by renal glomerular mesangial cells has been suggested to be involved in pathogenesis of glomerular sclerosis. The present studies examine whether aldosterone is also produced in renal mesangial cells, and the effect of aldosterone on ECM accumulation in these cells. In cultured renal mesangial cells, aldosterone synthase (CYP11B2), mineralocorticoid receptor (MR), and 11beta-HSD2 mRNA expressions were detected by RT-PCR. The ability of renal mesangial cells to produce aldosterone was confirmed by directly detecting aldosterone in culture medium via radioimmunoassay. Real-time RT-PCR showed that the expression of CYP11B2 mRNA in mesangial cells was significantly enhanced by AngII (P<0.001) and by potassium (P<0.05). Exposure of the cultured mesangial cells to aldosterone significantly increased fibronectin production from 12.4+/-1.9 to 74.6+/-16.8ng/ml (P<0.05). The aldosterone induced fibronectin production was abolished by aldosterone receptor antagonist spironolactone. Aldosterone also increased the TGF-beta1 reporter luciferase activity from 0.8+/-0.1 to 1.7+/-0.1 (P<0.05). Immunoblot showed TGF-beta1 protein expression was increased following aldosterone treatment. Blocking TGF-beta1 signaling pathway by knocking down Smad2 significantly blunted the aldosterone induced fibronectin production. The present studies indicate that renal mesangial cell is a target of local aldosterone action, which promotes ECM protein fibronectin production via TGF-beta1/Smad2 signaling pathway.

Betaglycan induces TGF-β signaling in a ligand-independent manner, through activation of the p38 pathway

Betaglycan, a cell surface heparan sulphate proteoglycan, is traditionally thought to function by binding transforming growth factor type beta (TGF-beta) via its core protein and then transferring the growth factor to its signaling receptor, the type II receptor. However, there is increasing evidence that the function of betaglycan is more complex. Here, we have evaluated the role of betaglycan through adenoviral expression (Adv-BG) in myoblasts and fibroblasts and found that in Adv-BG-infected cells, the activity of p3TP-Lux and pCTGF-Luc reporter after transient transfection, as well as fibronectin synthesis, all of which are target processes for TGF-beta, were highly increased in the absence of TGF-beta. It is known that this cytokine strongly inhibits myogenin induction in myoblasts. In Adv-BG-infected myoblasts, the activity of pMyo-Luc reporter after transient transfection was strongly inhibited in the absence of TGF-beta. These effects were not precluded by applying TGF-beta-blocking antibodies, the soluble TGF-beta type II receptor, or soluble betaglycan to sequester TGF-beta present in the cell medium. Furthermore, the data suggest that the cytoplasmic domain of betaglycan is required for this TGF-beta-independent response, giving further support to a ligand-independent signaling effect for betaglycan. The process also seemed independent of Smad-2 phosphorylation, although Adv-BG infection induced p38 phosphorylation, and SB239063, an inhibitor of the p38 pathway, inhibited p3TP-Lux-driven activity. These results suggest a novel signaling mechanism for betaglycan, which is independent of the canonical TGF-beta signal pathway although it involves TGF-beta receptors and takes place through p38 pathways.

[Expressions of TGF-betaR I, Smad2, Smad3 and Smad7 in keloids]

OBJECTIVE

To investigate the expression of TGF-betaR I, Smad2, Smad3 and Smad7 in keloids, normal scars and normal skins. Discuss the significance of these proteins in the course of keloid.

METHODS

Immunohistochemistry method was used to detect the expression intensity and distribution of these proteins in above 3 kinds of different tissues in 44 cases. Statistics was used to analyze the data.

RESULTS

The expression of TGF-betaR I were much stronger in keloid than in the other two tissues. The expression of Smad7 were lower in keloids. The increase expression of Smad2,3 were not obvious, but they were found to accumulate in the nucleus.

CONCLUSIONS

The results indicate that over-expression of TGF-betaR I, low-expression of Smad7 and accumulation of Smad2,3 may be one of the etiological factors of keloids. This research may provide a new idea to prevent and treat keloids or other fibrosis diseases in the future.

Ginkgo biloba extract suppresses hypertrophy and extracellular matrix accumulation in rat mesangial cells

AIM

To observe the effects of Ginkgo biloba extract (EGb) on the hypertrophy of mesangial cells and the accumulation of extracellular matrix (ECM) in mesangial cells.

METHODS

Cultured mesangial cells were allotted into 7 groups: normal group, solvent control group, high glucose group, low dose of EGb group, moderate dose of EGb group, high dose of EGb group, and captopril group. Activities of cell antioxidases, S phase percentage and G(0)/G(1) phase percentage, collagen IV and laminin, Smad2/3 and Smad7, TGF-beta(1) mRNA were measured by different methods.

RESULTS

For EGb-treated groups, when compared with high glucose group, the cell percentage of S phase was raised and the percentage of G(0)/G(1) was lowered. The intensity of oxidative stress was weakened. The expression of Smad2/3 was greatly decreased and Smad7 was increased. Collagen IV, laminin and TGF- beta(1)mRNA were also reduced.

CONCLUSION

EGb can suppress cell hypertrophy and the accumulation of ECM in rat mesangial cells, which means it could play a vital role in the delay of glomerulosclerosis in diabetic nephropathy.

TGF-β regulates differentially the proliferation of fetal and adult human skin fibroblasts via the activation of PKA and the autocrine action of FGF-2

Transforming growth factor-beta (TGF-beta) is a potent regulator of cell proliferation; interestingly its action is clearly cell type-dependent. In particular, it inhibits epithelial and endothelial cells' proliferation, while its action on many mesenchymal cells has been reported to be stimulatory. In this direction, we have recently shown that TGF-beta regulates the proliferation of normal human skin fibroblasts according to their developmental origin: i.e. it inhibits fetal fibroblasts, while it stimulates the proliferation of adult ones. Here, we present evidence on the mechanisms underlying this differential action. Concerning fetal fibroblasts, we have found that TGF-beta activates Protein Kinase A (PKA) and induces the expression of the cyclin-dependent kinase inhibitors (CKIs) p21(CIP1/WAF1) and p15(INK4B). Moreover, the specific PKA inhibitor H-89 blocks the induction of both CKIs and annuls the TGF-beta-mediated inhibitory effect, indicating the central role of PKA in this process. In contrast, in adult cells no PKA activation is observed. Moreover, TGF-beta stimulates cell proliferation by activating the MEK-ERK pathway, as the MEK inhibitor PD98059 blocks this effect. A specific neutralizing antibody against Fibroblast Growth Factor-2 (FGF-2) inhibits both ERK activation and the mitogenic activity of TGF-beta, indicating that the latter establishes an autocrine loop, via FGF-2, leading to cell proliferation. This loop requires FGF receptor-1 (FGFR-1), as its down-regulation by siRNA approach prevents TGF-beta from stimulating ERK-1/2 activation and DNA synthesis. In conclusion, the differential proliferative response of fetal and adult normal human skin fibroblasts to TGF-beta is regulated by distinct signaling pathways and furthermore it may provide information on the bimodal effect of this factor on cell proliferation, in general.

Man1, an inner nuclear membrane protein, regulates vascular remodeling by modulating transforming growth factor beta signaling

A growing number of integral inner nuclear membrane (INM) proteins have been implicated in diverse cellular functions. Man1, an INM protein, has recently been shown to regulate transforming growth factor (Tgf) beta superfamily signaling by interacting with receptor-associated Smads. However, the in vivo roles of Man1 have not been fully characterized. Here, we show that Man1 regulates vascular remodeling by analyzing Man1-deficient embryos lacking the Smad interacting domain. Man1-deficient embryos die at midgestation because of defects in embryonic vasculature; the primary capillary plexus forms, but subsequent remodeling is perturbed. It has been proposed that the angiogenesis process is divided into two balanced phases, the activation and resolution/maturation phases, both of which are regulated by Tgfbeta1. We have demonstrated, in Man1-deficient embryos, the expression of Tgfb1 is upregulated and Smad2/3 signaling is abnormally activated, resulting in increased extracellular matrix deposition, a hallmark of the resolution phase of angiogenesis. We have also showed that the recruitment of mural cells to the vascular wall is severely disturbed in mutants, which may lead to disruption of intercellular communication between endothelial and mural cells required for proper vascular remodeling. These results have revealed a novel role for Man1 in angiogenesis and provide the first evidence that vascular remodeling can be regulated at the INM through the interaction between Man1 and Smads.

Activin A inhibits organization of sarcomeric proteins in cardiomyocytes induced by leukemia inhibitory factor

Cytokine systems are activated in heart failure, and it is believed that interaction between such systems may be important during progression of this disorder. We have previously shown that failing hearts have increased levels of the interleukin-6 related cytokine leukemia inhibitory factor (LIF) and activin A, a member of the transforming growth factor-beta family. The aim of this study was to examine the effects of activin A on cardiomyocytes and a potential interaction with LIF-mediated changes in cell signaling and growth. Cardiomyocytes were isolated from 1- to 3-day-old Wistar rats, and the cells were treated with LIF, activin A or a combination thereof. Our main findings were: (i) activin A treatment reduced the LIF-mediated increase in cardiomyocyte length, perimeter and sarcomeric organization and was accompanied by a substantially decreased alpha-skeletal actin gene expression. (ii) The activin A-mediated phosphorylation of Smad2 was markedly enhanced by LIF. (iii) Activin A markedly induced SOCS3 gene expression, while LIF potently increased the expression of Smad7 mRNA, representing inhibitors of LIF and activin A signaling pathways, respectively. (iv) Inhibiting activation of the Smad2/3 pathway abolished the effects of activin A on LIF-induced changes in cell length, perimeter and sarcomeric organization. In conclusion, activin A markedly attenuates LIF-induced changes in cardiomyocytes, reflecting a potentially important role for both activin A and the Smad2/3 pathway in regulation of myocardial remodeling.

Molecular basis of oocyte-paracrine signalling that promotes granulosa cell proliferation

Oocytes regulate follicle growth by secreting paracrine growth factors that act on neighbouring granulosa cells (GCs). Those factors identified to date are mainly members of the transforming growth factor-beta (TGFbeta) superfamily, but little is known about which specific receptor/signalling system(s) they employ. This study was conducted to determine the requisite pathways utilised by oocytes to promote GC proliferation. We used an established oocyte-secreted mitogen bioassay, where denuded mouse oocytes are co-cultured with mural GCs. Oocytes, growth differentiation factor-9 (GDF9), TGFbeta1 and activin-A all promoted GC DNA synthesis, but bone-morphogenetic protein 6 (BMP6) did not. Subsequently, we tested the capacity of various TGFbeta superfamily receptor ectodomains (ECD) to neutralise oocyte- or specific growth factor-stimulated GC proliferation. The BMP type-II receptor (BMPR-II) ECD antagonised oocyte and GDF9 bioactivity dose-dependently, but had no or minimal effect on TGFbeta1 and activin-A bioactivity, demonstrating its specificity. The TGFbetaR-II, activinR-IIA and activinR-IIB ECDs all failed to neutralise oocyte- or GDF9-stimulated GC DNA synthesis, whereas they did antagonise the activity of their respective native ligands. An activin receptor-like kinase (ALK) 4/5/7 inhibitor, SB431542, also antagonised both oocyte and GDF9 bioactivity in a dose-dependent manner. Consistent with these findings, oocytes, GDF9 and TGFbeta1 all activated SMAD2/3 reporter constructs in transfected GC, and led to phosphorylation of SMAD2 proteins in treated cells. Surprisingly, oocytes did not activate the SMAD1/5/8 pathway in transfected GCs although exogenous BMP6 did. This study indicates that oocyte paracrine factors primarily utilise a similar signalling pathway first identified for GDF9 that employs an unusual combination of TGFbeta superfamily receptors, the BMPR-II and a SMAD2/3 stimulatory ALK (4, 5 or 7), for transmitting their mitogenic actions in GC. This cell-signalling pathway may also have relevance in the hypothalamic-pituitary axis and in germ-somatic cell interactions in the testis.

p38 Mitogen-activated protein kinase affects transforming growth factor-beta/Smad signaling in human dental pulp cells

Transforming Growth Factor-beta (TGF-beta) plays an essential role in differentiation of dental pulp cells into odontoblasts during reparative dentine formation. However, the mechanism by which TGF-beta stimulates dental repair remains rather obscure. Human dental pulp cells were used as an in vitro model in the present work. We showed that TGF-beta signaled through mitogen-activated protein kinases (MAPKs), such as ERK1/2 and p38, along with Smad pathway. Distinct pathways exerted different time response. SB203580, a specific p38 MAPK inhibitor, reduced phosphorylation of Smad3, while it slightly enhanced phosphorylation of Smad2. Increased phosphorylation of ERK1/2 and p38 confirmed that SB203580 did not block activation of TGF-beta receptors. In addition, the inhibition of ERK1/2 activity with MEK1/2 inhibitor U0126 increased TGF-beta mediated phosphorylation of Smad3. Our results suggest that p38 affects the phosphorylation of Smad2 and Smad3 differentially during TGF-beta signaling in human dental pulp cells and ERK1/2 might be involved in the process.

Quantitative characterization of 15-deoxy-delta(12,14)-prostaglandin J2 in regulating EGFPSmad2 translocation in CHO cells through PPARgamma/TGFbeta/Smad2 pathway

Smad2 is an important factor in TGFbeta/Smad2 signal transduction pathway with ability for signal propagation, it could translocate from cytoplasm to nucleus after the TGFbeta receptor-mediated phosphorylation. 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2), a natural agonist of the peroxisome proliferator-activated receptor gamma (PPARgamma), is found recently to be able to function in the regulation of Smad2 activity. However, no quantification data have been yet reported, and it still keeps suspenseful whether or not 15d-PGJ2 could regulate Smad2 activity by depending on PPARgamma through PPAR gamma/TGFbeta/ Smad2 pathway. In this work, by analyzing the EGFP-Smad2 location in CHO cells according to the Nucleus Trafficking Analysis Module based on IN Cell Analyzer 1000 platform, TGFbeta stimulated EGFP-Smad2 translocation regulated by 15d-PGJ2 was quantitatively investigated. The results showed that TGFbeta could induce EGFP-Smad2 translocation from cytoplasm to nucleus by EC50 of 8.83 pM, and 15d-PGJ2 could impede the TGFbeta-stimulated Smad2 translocation by IC50 of 0.68 microM. Moreover, GW9662, a PPARgamma antagonist, could attenuate such a 15d-PGJ2 inhibitory activity by almost one order of magnitude. This result thereby implies that 15d-PGJ2 might inhibit Smad2 translocation through PPARgamma/TGFbeta/Smad2 pathway. Further investigation discovered that different from the case for 15d-PGJ2, rosiglitazone, another PPARgamma agonist, could enhance Smad2 translocation to nucleus, suggesting that rosiglitazone and 15d-PGJ(2) might take different modes in the activation of PPARgamma within the signaling pathway.

Renal bone morphogenetic protein-7 protects against diabetic nephropathy

Longstanding diabetes causes renal injury with early dropout of podocytes, albuminuria, glomerular and tubulointerstitial fibrosis, and progressive renal failure. The renal pathology seems to be driven, in part, by TGF-beta and is associated with a loss of renal bone morphogenic protein-7 (BMP-7) expression. Here, the hypothesis that maintenance of renal (especially podocyte) BMP-7 by transgenic expression reduces diabetic renal injury was tested. Diabetic mice that expressed the phosphoenolpyruvate carboxykinase promoter-driven BMP-7 transgene and nondiabetic, transgenic mice as well as diabetic and nondiabetic wild-type controls were studied for up to 1 yr. Transgenic expression of BMP-7 in glomerular podocytes and proximal tubules prevents podocyte dropout and reductions in nephrin levels in diabetic mice. Maintenance of BMP-7 also reduces glomerular fibrosis and interstitial collagen accumulation as well as collagen I and fibronectin expression. Diabetic wild-type mice develop progressive albuminuria, which is substantially reduced in transgenic mice. These effects of the BMP-7 transgene occur without changing renal TGF-beta levels. It is concluded that maintenance of renal BMP-7 during the evolution of diabetic nephropathy reduces diabetic renal injury, especially podocyte dropout. The findings also establish a role for endogenous glomerular BMP-7 as an autocrine regulator of podocyte integrity in vivo.

COMP–Angiopoietin-1 Ameliorates Renal Fibrosis in a Unilateral Ureteral Obstruction Model

Injury to the renal microvasculature may be a major factor in the progression of renal disease; therefore, protection of endothelial cells (EC) in renal vasculature may have a therapeutic role in renal fibrosis. Recently, a soluble, stable, and potent angiopoietin-1 (Ang1) variant, cartilage oligomeric matrix protein (COMP)-Ang1, was developed. The contribution of COMP-Ang1 in renal interstitial fibrosis, however, remains to be clarified. This study investigated the effects of COMP-Ang1 on peritubular capillary EC in the renal cortex and the renal fibrogenic process that is triggered by unilateral ureteral obstruction. COMP-Ang1 preserved renal platelet-EC adhesion molecule-1-and Tie2-positive EC. Morphologic examination indicated less tubular injury and tubulointerstitial fibrosis in mice that received COMP-Ang1 than vehicle-treated mice. Interstitial type I collagen and myofibroblast accumulation were significantly suppressed by COMP-Ang1 treatment. COMP-Ang1 increased Tie2 and Akt phosphorylation in ureteral obstructed kidneys. Renal surface microvasculature and renal blood flow were higher after treatment with COMP-Ang1 than with vehicle. COMP-Ang1 treatment decreased monocyte/macrophage infiltration, tissue levels of TGF-beta1, and Smad 2/3 phosphorylation and increased Smad 7 in the obstructed kidney. These results demonstrate that COMP-Ang1 treatment can decrease the progression of renal fibrosis in unilateral ureteral obstruction. COMP-Ang1 may be an endothelium-specific therapeutic modality in fibrotic renal disease.

TSAd interacts with Smad2 and Smad3

Smad-dependent signalling initiated by TGFbeta superfamily members can be modulated by a variety of interacting proteins. Using yeast two-hybrid, co-immunoprecipitation, and GST pull-down assays we identified T-cell SH2 adapter (TSAd) as a protein that interacts with Smad2 and Smad3. TSAd is an adapter protein thought to participate in many different signalling pathways. The objective of this study was to elucidate the domains important for interaction between TSAd and Smad proteins. Our results suggest a model for TSAd-Smad interaction that is facilitated by multiple TSAd domains, but primarily through the TSAd type I SH2 domain. Interestingly, we also found that both Smad2 and Smad3 interact with the Lck type I SH2 domain, but not the PI3K type III SH2 domain. This research raises the possibility that interaction between SH2-containing proteins and Smad proteins may represent another method to modulate Smad-dependent signalling.

The autocrine effect of activin A on human ovarian clear cell adenocarcinoma cells

The functions of activin, a member of TGF-beta superfamily, in ovarian clear cell adenocarcinoma remain unsolved, although we recently found that inhibin betaA-subunit, activin A, activin receptor type IA, type IB, type IIA, type IIB, Smad2, Smad3 and Smad4 were localized in tumor cells of the ovarian clear cell adenocarcinoma tissue by immunohistochemistry. In the present study, in order to investigate the role of activin concerning cell growth in ovarian clear cell adenocarcinoma cells, we determined the production of activin A and inhibin A, and the expression of activin receptors and Smads using the human ovarian clear cell adenocarcinoma cell line JHOC-5. Moreover, we examined the effects of activin A on the activation of activin signaling pathway and on the proliferation in JHOC-5 cells. We detected a measurable amount of activin A in the culture medium of JHOC-5 cells, although inhibin A was not detected. The expression of activin receptor type IA, IB, IIA, IIB, Smad2, Smad3 and Smad4 was observed in JHOC-5 cells. Activin A induced a significant increase in proliferation of JHOC-5 cells compared with the untreated control. On the other hand, activin A did not affect the growth of JHOC-5 cells and no statistically significant difference was observed in the presence of follistatin which is a specific binding protein of activin. Phosphorylated Smad2, an activated form of Smad2, was detected both in treated JHOC-5 cells and in untreated cells by activin A. Activin A significantly increased the expression of phosphorylated Smad2 in JHOC-5 cells. Therefore, it is possible that activin has autocrine roles in tumor growth of ovarian clear cell adenocarcinoma cells.

Activation of estrogen receptor-alpha reduces aortic smooth muscle differentiation

Women are at high risk of dying from unrecognized cardiovascular disease. Many differences in cardiovascular disease between men and women appear to be mediated by vascular smooth muscle cells (SMC). Because estrogen reduces the proliferation of SMC, we hypothesized that activation of estrogen receptor-alpha (ERalpha) by agonists or by growth factors altered SMC function. To determine the effect of growth factors, estrogen, and ERalpha expression on SMC differentiation, human aortic SMC were cultured in serum-free conditions for 10 days. SMC from men had lower spontaneous expression of ERalpha and higher levels of the differentiation markers calponin and smooth muscle alpha-actin than SMC from women. When SMC containing low expression of ERalpha were transduced with a lentivirus containing ERalpha, activation of the receptor by ligands or growth factors reduced differentiation markers. Conversely, inhibiting ERalpha expression by small interfering RNA (siRNA) in cells expressing high levels of ERalpha enhanced the expression of differentiation markers. ERalpha expression and activation reduced the phosphorylation of Smad2, a signaling molecule important in differentiation of SMC and initiated cell death through cleavage of caspase-3. We conclude that ERalpha activation switched SMC to a dedifferentiated phenotype and may contribute to plaque instability.

Effects of bio-active ceramic resources in cutaneous wound healing and the role of TGF-β signaling

The wound healing process is a highly orchestrated process, which includes inflammation, re-epithelialization, granulation tissue formation, matrix formation and re-modeling. In this paper, we attempt to determine if bio-active ceramic resource powder particles had an effect on cutaneous wound healing. Furthermore, we investigated its related mechanism and the expression of Smads of cutaneous wound healing, which can be accelerated by bio-active ceramic ointment. Topically applied lesions of 5%, 10% and 15% bio-active ceramic ointment (AO) showed accelerated wound closure, re-epithelialization, and the related immediate down stream of TGF-beta (p-Smad2/3 and Smad3) was suppressed. In particular, 10% and 15% AO lesions became closed faster at Days 3 and 4 of post-wound and p-Smad2/3 was also suppressed. All AO lesions showed accelerated mild wound closure at Day 6, but there were no significant difference. Several papers reported that Smad3 may mediate the signaling pathways that is inhibitory to wound healing, as the deletion of Smad3 leads to enhanced re-epithelialization and contraction of the wound area. This study showed that topical, bio-active ceramic ointment applications accelerated wound closure, re-epithelialization and the suppression of Smad proteins (p-Smad2/3, Smad3). The data revealed that the suppression of Smad3, which was induced by bio-active ceramic resources powder particles affected re-epithelialization and cutaneous wound closure. At the end of this paper, we concluded that bio-active ceramic resources affect cutaneous wound healing by accelerating the re-epithelialization of keratinocytes and that is mediated by the suppression of related protein, Smad3.

A phosphatase controls the fate of receptor-regulated Smads

In this issue of Cell, Lin et al. (2006) answer one of the long-standing questions in the TGFbeta field by identifying a phosphatase, PPM1A, that directly dephosphorylates Smad2 and Smad3 to limit their activation.

Hematopoiesis controlled by distinct TIF1gamma and Smad4 branches of the TGFbeta pathway

Tissue homeostasis in mammals relies on powerful cytostatic and differentiation signals delivered by the cytokine TGFbeta and relayed within the cell via the activation of Smad transcription factors. Formation of transcription regulatory complexes by the association of Smad4 with receptor-phosphorylated Smads 2 and 3 is a central event in the canonical TGFbeta pathway. Here we provide evidence for a branching of this pathway. The ubiquitious nuclear protein Transcriptional Intermediary Factor 1gamma (TIF1gamma) selectively binds receptor-phosphorylated Smad2/3 in competition with Smad4. Rapid and robust binding of TIF1gamma to Smad2/3 occurs in hematopoietic, mesenchymal, and epithelial cell types in response to TGFbeta. In human hematopoietic stem/progenitor cells, where TGFbeta inhibits proliferation and stimulates erythroid differentiation, TIF1gamma mediates the differentiation response while Smad4 mediates the antiproliferative response with Smad2/3 participating in both responses. Thus, Smad2/3-TIF1gamma and Smad2/3-Smad4 function as complementary effector arms in the control of hematopoietic cell fate by the TGFbeta/Smad pathway.

PPM1A functions as a Smad phosphatase to terminate TGFbeta signaling

TGFbeta signaling controls diverse normal developmental processes and pathogenesis of diseases including cancer and autoimmune and fibrotic diseases. TGFbeta responses are generally mediated through transcriptional functions of Smads. A key step in TGFbeta signaling is ligand-induced phosphorylation of receptor-activated Smads (R-Smads) catalyzed by the TGFbeta type I receptor kinase. However, the potential of Smad dephosphorylation as a regulatory mechanism of TGFbeta signaling and the identity of Smad-specific phosphatases remain elusive. Using a functional genomic approach, we have identified PPM1A/PP2Calpha as a bona fide Smad phosphatase. PPM1A dephosphorylates and promotes nuclear export of TGFbeta-activated Smad2/3. Ectopic expression of PPM1A abolishes TGFbeta-induced antiproliferative and transcriptional responses, whereas depletion of PPM1A enhances TGFbeta signaling in mammalian cells. Smad-antagonizing activity of PPM1A is also observed during Nodal-dependent early embryogenesis in zebrafish. This work demonstrates that PPM1A/PP2Calpha, through dephosphorylation of Smad2/3, plays a critical role in terminating TGFbeta signaling.

Transforming growth factor beta activation of c-Abl is independent of receptor internalization and regulated by phosphatidylinositol 3-kinase and PAK2 in mesenchymal cultures

Transforming growth factor beta (TGF-beta) modulates a number of cellular phenotypes as divergent as growth stimulation and growth inhibition. Although the Smad pathway is critical for many of these responses, recent evidence indicates that Smad-independent pathways may also have a critical role. One such protein previously shown to regulate TGF-beta action independent of the Smad proteins is the c-Abl nonreceptor tyrosine kinase. In the current study we determined that TGF-beta receptor signaling activates c-Abl kinase activity in a subset of fibroblast but not epithelial cultures. This cell type-specific response occurs in a membrane-proximal locale independent of receptor internalization and upstream of dynamin action. Although c-Abl activation by TGF-beta is independent of Smad2 or Smad3, it is prevented by inhibitors of phosphatidylinositol 3-kinase or PAK2. Thus, c-Abl represents a target downstream of phosphatidylinositol 3-kinase-activated PAK2, which differentiates TGF-beta signaling in fibroblasts and epithelial cell lines and integrates serine/threonine receptor kinases with tyrosine kinase pathways.

Smad3 is acetylated by p300/CBP to regulate its transactivation activity

Smad proteins are crucial for the intracellular signaling of transforming growth factor-beta (TGF-beta). Upon their receptor-induced activation, Smad proteins are phosphorylated and translocated to the nucleus to activate the transcription of a select set of target genes. Here, we show that the co-activator p300/CBP bound and acetylated Smad3 as well as Smad2 in vivo, and that the acetylation was stimulated by TGF-beta. A major acetylation site of Smad3 by p300/CBP is Lys-378 in the MH2 domain (Smad3C) known to be critical for the regulation of transcriptional activity. Replacement of Lys-378 with Arg decreased the transcriptional activity of GAL4-Smad3C in a luciferase assay. Moreover, p300/CBP potentiated the transcriptional activity of GAL4-Smad3C, but not the acetylation-resistant GAL4-Smad3C(K378R) mutant. These results suggest that acetylation of Smad3 by p300/CBP regulates positively its transcriptional activity.

Lack of activated Smad2 in transforming growth factor-beta signaling is an unfavorable prognostic factor in patients with esophageal squamous cell carcinoma

BACKGROUND AND OBJECTIVES

Transforming growth factor-beta (TGF-beta) regulates cell growth in various cells, and inactivation of the TGF-beta-signaling pathway contributes to tumor progression. In this study, we investigated the expression of Smad2 and Smad3, which are specific intracellular mediators of TGF-beta signaling. We also examined the relationship between the expression levels of activated Smad2 by TGF-beta and clinicopathologic characteristics of patients with esophageal squamous cell carcinoma (SCC).

METHODS

Immunohistochemical staining with anti-phosphorylated Smad2 (P-Smad2) polyclonal antibody, anti-Smad2 monoclonal antibody, and anti-Smad3 polyclonal antibody was performed on surgical specimens obtained from 80 patients with esophageal SCC.

RESULTS

Our data indicated that a low level of P-Smad2, as detected immunohistologically, correlated with lymph node metastasis (P = 0.0002), distant metastasis (P = 0.0338), pathologic stage (P = 0.0093), and poor survival rate (P = 0.0246). All patients without positive Smad2 immunostaining were included among those without positive P-Smad2 immunostaining. There was no significant correlation between expression of Smad2 or Smad3 and clinicopathologic characteristics.

CONCLUSIONS

We demonstrated that a lack of Smad2-P appears to be correlated with tumor development and poor prognosis in patients with esophageal SCC.

The cysteine-rich domain protein KCP is a suppressor of transforming growth factor beta/activin signaling in renal epithelia

The transforming growth factor beta (TGF-beta) superfamily, including the bone morphogenetic protein (BMP) and TGF-beta/activin A subfamilies, is regulated by secreted proteins able to sequester or present ligands to receptors. KCP is a secreted, cysteine-rich (CR) protein with similarity to mouse Chordin and Xenopus laevis Kielin. KCP is an enhancer of BMP signaling in vertebrates and interacts with BMPs and the BMP type I receptor to promote receptor-ligand interactions. Mice homozygous for a KCP null allele are hypersensitive to developing renal interstitial fibrosis, a disease stimulated by TGF-beta but inhibited by BMP7. In this report, the effects of KCP on TGF-beta/activin A signaling are examined. In contrast to the enhancing effect on BMPs, KCP inhibits both activin A- and TGF-beta1-mediated signaling through the Smad2/3 pathway. These inhibitory effects of KCP are mediated in a paracrine manner, suggesting that direct binding of KCP to TGF-beta1 or activin A can block the interactions with prospective receptors. Consistent with this inhibitory effect, primary renal epithelial cells from KCP mutant cells are hypersensitive to TGF-beta and exhibit increased apoptosis, dissociation of cadherin-based cell junctions, and expression of smooth muscle actin. Furthermore, KCP null animals show elevated levels of phosphorylated Smad2 after renal injury. The ability to enhance BMP signaling while suppressing TGF-beta activation indicates a critical role for KCP in modulating the responses between these anti- and profibrotic cytokines in the initiation and progression of renal interstitial fibrosis.

Corticosteroids induce the differential expression of TGFbeta isoforms, receptors and signaling in the gastric mucosa of suckling rats

Glucocorticoids inhibit the cell proliferation in the gastric epithelium, and induce differentiation, migration and death. The mechanism by which these effects are triggered and controlled is still discussed and can involve the transcription and activation of transforming growth factor beta (TGFbeta). The present study was conducted to evaluate the effect of hydrocortisone short-term treatment on tissue level and distribution of TGFbeta isoforms, receptors and signaling through Smad2/3. To achieve that, 18-day-old rats were injected with hydrocortisone (50 mg/Kg b.wt.) for 0, 1 and 3 h. The stomachs were collected and processed for immunohistochemistry and western blotting. We observed that the treatment for 3 h increased the number of labeled epithelial cells for TGFbeta1 (p < 0.05), decreased the distribution of TGFbeta2 (p < 0.05) and did not alter TGFbeta3, TbetaRI and TbetaRII status. The levels of TGFbeta1 and receptors were checked by western blotting and results corroborate the immunodetection. We also found that phosphorylation of Smad2/3 into Smad2P increased after 3 h (p < 0.05), indicating that the high level TGFbeta1 was active on the cells. We suggest that glucocorticoids differentially regulate the expression of TGFbeta isoforms, receptors and signaling, and so TGFbeta1 might be involved in the inhibitory pathway triggered by the hormone.

Deletion of exon I of SMAD7 in mice results in altered B cell responses

The members of the TGF-beta superfamily, i.e., TGF-beta isoforms, activins, and bone morphogenetic proteins, regulate growth, differentiation, and apoptosis, both during embryonic development and during postnatal life. Smad7 is induced by the TGF-beta superfamily members and negatively modulates their signaling, thus acting in a negative, autocrine feedback manner. In addition, Smad7 is induced by other stimuli. Thus, it can fine-tune and integrate TGF-beta signaling with other signaling pathways. To investigate the functional role(s) of Smad7 in vivo, we generated mice deficient in exon I of Smad7, leading to a partial loss of Smad7 function. Mutant animals are viable, but significantly smaller on the outbred CD-1 mouse strain background. Mutant B cells showed an overactive TGF-beta signaling measured as increase of phosphorylated Smad2-positive B cells compared with B cells from wild-type mice. In agreement with this expected increase in TGF-beta signaling, several changes in B cell responses were observed. Mutant B cells exhibited increased Ig class switch recombination to IgA, significantly enhanced spontaneous apoptosis in B cells, and a markedly reduced proliferative response to LPS stimulation. Interestingly, LPS treatment reverted the apoptotic phenotype in the mutant cells. Taken together, the observed phenotype highlights a prominent role for Smad7 in development and in regulating the immune system's response to TGF-beta.

Antitransforming growth factor-beta antibody 1D11 ameliorates normal tissue damage caused by high-dose radiation

PURPOSE

The aim of this study was to determine whether a neutralizing transforming growth factor-beta (TGFbeta) antibody can prevent radiation (RT) induced lung injury.

METHODS AND MATERIALS

Fractionated and sham right lung irradiation in Fischer 344 rats was delivered to assess the radioprotective effect of the antibodies. Animals were divided into the following groups: (1) control (sham RT, control antibody 13C4); (2) RT (800cGy x 5)+13C4); (3) RT + 0.1 mg/kg 1D11 anti-TGFbeta antibody; and (4) RT + 1 mg/kg 1D11 antibody. Antibodies were intraperitoneally administered immediately after the last fraction of RT. Animals were sacrificed at 6 and 26 weeks after irradiation. Lungs were assessed for histologic changes, activation of macrophages, expression/activation of TGFbeta and its signal transduction pathway.

RESULTS

At 6 weeks post-RT, there was a significant reduction in macrophage accumulation (p = 0.041), alveolar wall thickness (p = 0.0003), and TGF-beta activation (p = 0.032) in animals receiving 1.0 mg/kg 1D11 vs. in the control group. However, at 6 weeks, the low dose of 1D11 antibody (0.1 mg/kg) failed to produce any significant changes. At 6 months post-RT, radioprotection is apparent for the group receiving 1.0 mg/kg 1D11, with activated macrophages (p = 0.037), alveolar wall thickness (p = 0.0002), TGFbeta activation (p = 0.002) and its signal transduction proteins (p < 0.05) compared with the control group.

CONCLUSIONS

Administration of a single dose of 1.0 mg/kg of the anti-TGFbeta antibody 1D11 resulted in decreased morphologic changes, inflammatory response, and reduced expression and activation of TGFbeta 6 weeks and 6 months after 40 Gy to the right hemithorax. Targeting the TGFbeta pathway may be a useful strategy to prevent radiation-induced lung injury.

Pro- and antiinflammatory cytokine signaling: reciprocal antagonism regulates interferon-gamma production by human natural killer cells

Activated monocytes produce proinflammatory cytokines (monokines) such as interleukin (IL)-12, IL-15, and IL-18 for induction of interferon-gamma (IFN-gamma) by natural killer (NK) cells. NK cells provide the antiinflammatory cytokine transforming growth factor (TGF)-beta, an autocrine/negative regulator of IFN-gamma. The ability of one signaling pathway to prevail over the other is likely important in controlling IFN-gamma for the purposes of infection and autoimmunity, but the molecular mechanism(s) of how this counterregulation occurs is unknown. Here we show that in isolated human NK cells, proinflammatory monokines antagonize antiinflammatory TGF-beta signaling by downregulating the expression of the TGF-beta type II receptor, and its signaling intermediates SMAD2 and SMAD3. In contrast, TGF-beta utilizes SMAD2, SMAD3, and SMAD4 to suppress IFN-gamma and T-BET, a positive regulator of IFN-gamma. Indeed, activated NK cells from Smad3(-/-) mice produce more IFN-gamma in vivo than NK cells from wild-type mice. Collectively, our data suggest that pro- and antiinflammatory cytokine signaling reciprocally antagonize each other in an effort to prevail in the regulation of NK cell IFN-gamma production.

Protein tyrosine phosphatase 1B regulates TGFβ1-induced Smad2 activation through PI3 kinase-dependent pathway

Insulin is known to modulate transforming growth factor-beta (TGFbeta) signaling. In this report, by using the IN Cell Analyzer 1000, the fluorescence cell imaging instrument, we demonstrated that protein tyrosine phosphatase 1B (PTP1B) could regulate TGFbeta1-induced Smad2 activation in a PI3 kinase-dependent manner. By using the CHO cells stably expressing EGFP-Smad2, we showed that TGFbeta1 effectively stimulated Smad2 nuclear translocation in CHO cells. When pretreated with insulin, TGFbeta1-induced Smad2 nuclear entry was dramatically decreased. Furthermore, both the PI3K inhibitor LY294002 and the dominant negative AKT (DN-AKT) abolished the inhibitory effects of insulin, demonstrating that the inhibition of Smad2 activation by insulin was PI3K/AKT dependent. Since PTP1B negatively modulates insulin signaling, we further addressed the effects of PTP1B on insulin-mediated inhibition of Smad2 activation. Our data showed that overexpression of PTP1B effectively attenuated insulin-induced inhibition of Smad2 stimulation. Moreover, the PTP1B inhibitor, 3-(3,5-dibromo-4-hydroxy-benzoyl)-2-ethyl-benzofuran-6-sulfonicacid-(4-(thiazol-2-ylsulfamyl)-phenyl)-amide (Compound-2), recovered insulin inhibition of Smad2 activation. In conclusion, our data revealed the insulin inhibitory effects on TGFbeta1-induced Smad2 activation and the regulation role of PTP1B in the inhibition events.

Post-transcriptional Control of Cited2 by Transforming Growth Factor β

Cited2 is a transcription factor without typical DNA binding domains. Cited2 interacts with cAMP-responsive element-binding protein-binding protein (CBP)/p300, TFAP2, Lhx2, and nuclear receptors, such as peroxisome proliferator-activated receptor and estrogen receptor to function as a transcriptional modulator. Overexpression of Cited2 in Rat1 cells leads to tumor formation in nude mice, suggesting that Cited2 is a transforming gene. Through microarray analysis, Cited2 was found to be down-regulated by transforming growth factor beta1 (TGF-beta) in various cell lines. In this study, we confirmed that both mRNA and protein levels of Cited2 are down-regulated in MDA-MB-231 breast cancer cells. Overexpression of Smad7 or knockdown of Smad4 in MDA-MB-231 cells showed that the Smad pathway is involved in the down-regulation of Cited2. Based on nuclear run-on analysis and Cited2 promoter/reporter assay, Cited2 transcription was not affected by TGF-beta, supporting that down-regulation of Cited2 by TGF-beta is most likely through post-transcriptional regulation. By using transcriptional inhibitors, we demonstrated that the turnover of Cited2 transcripts appears to be accelerated during TGF-beta stimulation. Pharmacologic inhibition of translation with cycloheximide attenuated Cited2 down-regulation by TGF-beta. We examined the expression of recombinant Cited2 gene introduced into MDA-MB-231 cells by stable transfection, and we found that mRNA containing the Cited2 protein-coding region controlled by a heterologous promoter indeed responds to TGF-beta-mediated down-regulation. Study from Cited2 deletion mutants showed that the C-terminal conserved region of Cited2 coding sequence is essential for the down-regulation. This is the first demonstration that TGF-beta-mediated down-regulation of Cited2 is post-transcriptional, through the Smad pathway, and requires the presence of its coding sequence.

Endogenous Transforming Growth Factor-β Receptor-mediated Smad Signaling Complexes Analyzed by Mass Spectrometry

ASmad proteins are the central feature of the transforming growth factor-beta (TGF-beta) intracellular signaling cascade. They function by carrying signals from the cell surface to the nucleus through the formation of a series of signaling complexes. Changes in Smad proteins and their complexes upon treatment with TGF-beta were studied in mink lung epithelial (Mv1Lu) cell cultures. A time course of incubation with TGF-beta was carried out to determine the peak of appearance of phosphorylated Smad2. Immobilized monoclonal antibody against Smad2 was then used to isolate the naturally occurring complexes. Three strategies were used to identify changes in proteins partnering with Smad2: separation by one-dimensional SDS-PAGE followed by MALDI peptide mass fingerprinting, cleavable ICAT labeling of the protein mixtures analyzed by LC-MS/MS, and nano-LC followed by MALDI MS TOF/TOF. Smad2 forms complexes with many other polypeptides both in the presence and absence of TGF-beta. Some of the classes of proteins identified include: transcription regulators, proteins of the cytoskeletal scaffold and other tethering proteins, motility proteins, proteins involved in transport between the cytoplasm and nucleus, and a group of membrane adaptor proteins. Although some of these have been reported in the literature, most have not been reported previously. This work expands the repertoire of proteins known to participate in the TGF-beta signal transduction processes.

Involvement of the c-Ski oncoprotein in cell cycle arrest and transformation during nurse cell formation after Trichinella spiralis infection

The role of c-Ski, an oncoprotein encoded by the oncogene, c-ski, in Trichinella spiralis-infected muscle tissues during nurse cell formation, was investigated by following the expression kinetics and distribution of c-Ski (both protein and mRNA) in the infected muscle cell, as well as the expression kinetics of the transforming growth factor beta (TGF-beta) signaling pathway factor genes (TGF-beta, Smad2 and Smad4) which cooperate with c-Ski. Immunohistochemical analysis using an anti-c-Ski antibody indicated that in the early stages of infection (13 and 18 days post-infection (p.i.)) the increased expression of the c-Ski protein was limited to the eosinophilic cytoplasm and not the enlarged nuclei or basophilic cytoplasm. At a later stage of infection (23 and 28 days p.i.) the c-Ski protein was limited to the enlarged nuclei in the basophilic cytoplasm, rather than the eosinophilic cytoplasm. At 48 days p.i., the c-Ski protein was barely detectable. Real-time PCR analysis showed that expression of the c-ski gene increased from 13 days p.i., reached a peak at 23-28 days p.i. and then decreased to a low level by 48 days p.i. Expression kinetics for the TGF-beta signaling pathway factor genes (TGF-beta, Smad2 and Smad4) were similar to that of c-ski. These findings provide evidence that the c-Ski protein is involved in nurse cell formation through the TGF-beta signaling pathway process in the host cell nucleus.

EGF blocks NADPH oxidase activation by TGF-beta in fetal rat hepatocytes, impairing oxidative stress, and cell death

Epidermal growth factor (EGF) is a survival signal for transforming growth factor-beta (TGF-beta)-induced apoptosis in hepatocytes, phosphatidylinositol 3-kinase (PI 3-K) being involved in this effect. Here, we analyze the possible cross talks between EGF and TGF-beta signals to understand how EGF impairs the early pro-apoptotic events induced by TGF-beta. Data have indicated that neither SMAD nor c-Jun NH2 Terminal Kinase (JNK) activations are altered by EGF, which clearly interferes with events directly related to the radical oxygen species (ROS) production, impairing oxidative stress, p38 MAP kinase activation, and cell death. Activation of a NADPH-oxidase-like system, which is responsible for the early ROS production by TGF-beta, is completely inhibited by EGF, through a PI 3-K-dependent mechanism. Activity of RAC1 increases by TGF-beta, but also by EGF, and both act synergistically to get maximum effects. Fetal rat hepatocytes express nox4, in addition to nox1 and nox2, and TGF-beta clearly upregulates nox4. EGF blocks up-regulation of nox4 by TGF-beta. Interestingly, in the presence of PI 3-K inhibitors, EGF is not able to counteract the nox4 upregulation by TGF-beta. Taking together these results indicate that impairment of TGF-beta-induced NADPH oxidase activation by EGF is a RAC1-independent process and correlates with an inhibition of the mechanisms that address the increase of nox4 mRNA levels by TGF-beta.