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Results for “Smad7 Protein”

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At least 19 recordsLinked to original sources

PubMed1997

The MAD-related protein Smad7 associates with the TGFbeta receptor and functions as an antagonist of TGFbeta signaling.

TGFbeta signaling is initiated when the type I receptor phosphorylates the MAD-related protein, Smad2, on C-terminal serine residues. This leads to Smad2 association with Smad4, translocation to the nucleus, and regulation of transcriptional responses. Here we demonstrate that Smad7 is an inhibitor of TGFbeta signaling. Smad7 prevents TGFbeta-dependent formation of Smad2/Smad4 complexes and inhibits the nuclear accumulation of Smad2. Smad7 interacts stably with the activated TGFbeta type I receptor, thereby blocking the association, phosphorylation, and activation of Smad2. Furthermore, mutations in Smad7 that interfere with receptor binding disrupt its inhibitory activity. These studies thus define a novel function for MAD-related proteins as intracellular antagonists of the type I kinase domain of TGFbeta family receptors.

Amino Acid Sequence↗

PubMed2005

Smad7 abrogates transforming growth factor-beta1-mediated growth inhibition in COLO-357 cells through functional inactivation of the retinoblastoma protein.

Smad7 is overexpressed in 50% of human pancreatic cancers. COLO-357 pancreatic cancer cells engineered to overexpress Smad7 are resistant to the actions of transforming growth factor-beta1 (TGF-beta1) with respect to growth inhibition and cisplatin-induced apoptosis but not with respect to modulation of gene expression. To delineate the mechanisms underlying these divergent consequences of Smad7 overexpression, we studied the effects of Smad7 on TGF-beta1-dependent signaling pathways and cell cycle regulating proteins. TGF-beta1 induced the phosphorylation of MAPK, p38 MAPK, and AKT2 irrespective of the levels of Smad7, and inhibitors of these pathways did not alter TGF-beta1 actions on cell growth. By contrast, Smad7 overexpression interfered with TGF-beta1-mediated attenuation of cyclin A and B levels, inhibition of cdc2 dephosphorylation and CDK2 inactivation, up-regulation of p27, and the maintenance of the retinoblastoma protein (RB) in a hypophosphorylated state. Smad7 also suppressed TGF-beta1-mediated inhibition of E2F activity but did not alter TGF-beta1-mediated phosphorylation of Smad2, the nuclear translocation of Smad2/3/4, or DNA binding of the Smad2/3/4 complex. Although Smad7 did not associate with the type I TGF-beta receptor (TbetaRI), SB-431542, an inhibitor of the kinase activity of this receptor, blocked TGF-beta1-mediated effects on Smad-2 phosphorylation. These findings point toward a novel paradigm whereby Smad7 acts to functionally inactivate RB and de-repress E2F without blocking the activation of TbetaRI and the nuclear translocation of Smad2/3, thereby allowing for TGF-beta1 to exert effects in a cancer cell that is resistant to TGF-beta1-mediated growth inhibition.

Active Transport, Cell Nucleus↗

PubMed2003

Gonadotropin releasing hormone analogue (GnRHa) alters the expression and activation of Smad in human endometrial epithelial and stromal cells.

Gonadotropin releasing hormone analogues (GnRHa) are often used to regress endometriosis implants and prevent premature luteinizing hormone surges in women undergoing controlled ovarian stimulation. In addition to GnRH central action, the expression of GnRH and receptors in the endometrium implies an autocrine/paracrine role for GnRH and an additional site of action for GnRHa. To further examine the direct action of GnRH (Leuprolide acetate) in the endometrium, we determined the effect of GnRH on endometrial stromal (ESC) and endometrial surface epithelial (HES) cells expression and activation of Smads (Smad3, -4 and -7), intracellular signals activated by transforming growth factor beta (TGF-beta), a key cytokine expressed in the endometrium. The results show that GnRH (0.1 microM) increased the expression of inhibitory Smad7 mRNA in HES with a limited effect on ESC, while moderately increasing the common Smad4 and Smad7 protein levels in these cells (P < 0.05). GnRH in a dose--(0.01 to 10 microM) and time--(5 to 30 min) dependent manner decreased the rate of Smad3 activation (phospho-Smad3, pSmad3), and altered Smad3 cellular distribution in both cell types. Pretreatment with Antide (GnRH antagonist) resulted in further suppression of Smad3 induced by GnRH, with Antide inhibition of pSmad3 in ESC. Furthermore, co-treatment of the cells with GnRH + TGF-beta, or pretreatment with TGF-beta type II receptor antisense to block TGF-beta autocrine/paracrine action, in part inhibited TGF-beta activated Smad3. In conclusion, the results indicate that GnRH acts directly on the endometrial cells altering the expression and activation of Smads, a mechanism that could lead to interruption of TGF-beta receptor signaling mediated through this pathway in the endometrium.

Adult↗

PubMed2004

[Functional study on TGF-beta/Smads signaling pathway in human ovarian cancer cells].

Resistance to the growth inhibitory effects of transforming growth factor-beta (TGF-beta) is a characteristic of many transformed cells. The purpose of this study was to determine the response of ovarian cancer cells to TGF-beta1 and to investigate the roles of components of the TGF-beta/Smads signaling pathway in carcinogenesis of ovarian cancer. Three ovarian cancer cell lines, HO-8910, HO-8910PM and SKOV3, were treated with TGF-beta1 and assayed for growth response by MTT assay. Furthermore, expression and subcellular localization of the components of TGF-beta/Smads signaling pathway in these cell lines in the absence or presence of TGF-beta1 were determined by RT-PCR and immunofluorescence analysis. We found that proliferation of SKOV3 cell was not significantly inhibited by TGF-beta1 while it expressed all components of the TGF-beta/Smads signaling pathway. After exposure to TGF-beta1, Smad7 protein in SKOV3 increased transiently and translocated to cytoplasm from nucleus while P-Smad2 translocated into nucleus from cytoplasm. Taken together, the results suggested that the TGF-beta/Smads signaling pathway remained functional in human ovarian cancer cells, HO-8910, HO-8910PM and SKOV3, and the abnormalities of the downstream effectors of Smads proteins might contribute to the resistance of SKOV3 cell to TGF-beta1.

Cell Line, Tumor↗

PubMed2006

Smad7 and protein phosphatase 1alpha are critical determinants in the duration of TGF-beta/ALK1 signaling in endothelial cells.

BACKGROUND: In endothelial cells (EC), transforming growth factor-beta (TGF-beta) can bind to and transduce signals through ALK1 and ALK5. The TGF-beta/ALK5 and TGF-beta/ALK1 pathways have opposite effects on EC behaviour. Besides differential receptor binding, the duration of TGF-beta signaling is an important specificity determinant for signaling responses. TGF-beta/ALK1-induced Smad1/5 phosphorylation in ECs occurs transiently. RESULTS: The temporal activation of TGF-beta-induced Smad1/5 phosphorylation in ECs was found to be affected by de novo protein synthesis, and ALK1 and Smad5 expression levels determined signal strength of TGF-beta/ALK1 signaling pathway. Smad7 and protein phosphatase 1alpha (PP1alpha) mRNA expression levels were found to be specifically upregulated by TGF-beta/ALK1. Ectopic expression of Smad7 or PP1alpha potently inhibited TGF-beta/ALK1-induced Smad1/5 phosphorylation in ECs. Conversely, siRNA-mediated knockdown of Smad7 or PP1alpha enhanced TGF-beta/ALK1-induced signaling responses. PP1alpha interacted with ALK1 and this association was further potentiated by Smad7. Dephosphorylation of the ALK1, immunoprecipitated from cell lysates, was attenuated by a specific PP1 inhibitor. CONCLUSION: Our results suggest that upon its induction by the TGF-beta/ALK1 pathway, Smad7 may recruit PP1alpha to ALK1, and thereby control TGF-beta/ALK1-induced Smad1/5 phosphorylation.

Activin Receptors↗

PubMed2000

Smad7 is induced by CD40 and protects WEHI 231 B-lymphocytes from transforming growth factor-beta -induced growth inhibition and apoptosis.

Transforming growth factor-beta (TGF-beta) is a potent inducer of apoptosis in B-lymphocytes and is essential for immune regulation and maintenance of self-tolerance. Here we show that concomitant signaling through CD40 sustains proliferation and rescues the premature B cell line WEHI 231 from both TGF-beta-induced and anti-IgM-induced apoptosis. The anti-apoptotic effect of CD40 is associated with the transcriptional activation of the inhibitory Smad7 protein. The transactivation of Smad7 by CD40 is NFkappaB-dependent in that pharmacological inhibitors of this pathway, N-tosyl-l-phenylalanine chloromethyl ketone and pyrrolidine dithiocarbamate, abrogate CD40-induced Smad7 expression. Ectopic overexpression of Smad7 inhibited Smad2 activation, TGF-beta-mediated growth inhibition, and apoptosis in WEHI 231 cells. Consistent with this result, dominant negative interference with Smad2 and Smad3 function also inhibited TGF-beta-induced apoptosis. The inhibitory effects of Smad7 overexpression were specific to TGF-beta-induced apoptosis and were without effect on anti-IgM-induced cell death. These results suggest a mechanism of suppression of TGF-beta-induced apoptosis by CD40, mediated through activation of NF-kappaB and, consequently, induction of Smad7 expression.

Antigens, CD↗

PubMedDate not supplied

Liver fibrogenesis due to cholestasis is associated with increased Smad7 expression and Smad3 signaling.

BACKGROUND/AIMS: Profibrogenic TGF-beta signaling in hepatic stellate cells is modulated during transdifferentiation. Strategies to abrogate TGF-beta effects provide promising antifibrotic results, however, in vivo data regarding Smad activation during fibrogenesis are scarce. METHODS: Here, liver fibrosis was assessed subsequent to bile duct ligation by determining liver enzymes in serum and collagen deposition in liver tissue. Activated hepatic stellate cells were identified by immunohistochemistry and immunoblots for alpha smooth muscle actin. Cellular localization of Smad3 and Smad7 proteins was demonstrated by immunohistochemistry. RTPCR for Smad4 and Smad7 was conducted with total RNA and Northern blot analysis for Smad7 with mRNA. Whole liver lysates were prepared to detect Smad2/3/4 and phospho- Smad2/3 by Western blotting. RESULTS: Cholestasis induces TGF-beta signaling via Smad3 in vivo, whereas Smad2 phosphorylation was only marginally increased. Smad4 expression levels were unchanged. Smad7 expression was continuously increasing with duration of cholestasis. Hepatocytes of fibrotic lesions exhibited nuclear staining Smad3. In contrast to this, Smad7 expression was localized to activated hepatic stellate cells. CONCLUSIONS: Hepatocytes of damaged liver tissue display increased TGF-beta signaling via Smad3. Further, negative feedback regulation of TGF-beta signaling by increased Smad7 expression in activated hepatic stellate cells occurs, however does not interfere with fibrogenesis.

Animals↗

PubMed2002

TGFbeta inducible early gene enhances TGFbeta/Smad-dependent transcriptional responses.

TGFbeta inducible early gene (TIEG) encodes a three zinc-finger Krüppel-like transcription factor whose overexpression has been shown to mimic the effects of TGFbeta in human osteosarcoma and pancreatic carcinoma cells. In order to investigate a potential role of TIEG in the TGFbeta signal transduction pathway, we studied its impact on a Smad binding element (SBE) reporter which is known to be regulated by TGFbeta through the R-Smad proteins. We demonstrate that TIEG overexpression enhances TGFbeta induction of SBE reporter activity. TIEG overexpression also enhances induction of the endogenous TGFbeta regulated genes p21 and PAI-1. The ability of TIEG to enhance TGFbeta actions is Smad dependent since TIEG has no effect on SBE transcription in the absence of Smad4 expression or when an inhibitory Smad protein, Smad7, is overexpressed. Furthermore, TIEG overexpression enhances TGFbeta induced Smad2 phosphorylation. Lastly, TIEG appears to function by binding to and thereby repressing a specific element in the proximal promoter of the inhibitory Smad7 gene. In conclusion, these results describe a novel mechanism for the potentiation of TGFbeta/Smad signaling via repression of the inhibitory Smad7 gene by TIEG.

Cyclin-Dependent Kinase Inhibitor p21↗

PubMed2006

Gene transfer of Smad7 modulates injury-induced conjunctival wound healing in mice.

PURPOSE: Smad7 is a molecule that blocks the Smad2/3 signal. Herein, we examined the effects of Smad7 gene introduction on post-injury conjunctival wound healing in mice. Its effects on the cultured human subconjunctival fibroblasts (SCFs) were also investigated. METHODS: A circumferential incision was made in the equatorial conjunctiva by using scissors in the right eye of fully anesthetized adult C57BL/6 mice (n=72). Smad7 cDNA-expressing adenoviral vector was topically applied. The control eye received nonfunctioning adenoviral vector. After 2, 5, 7, and 30 days the eyes were processed for histological or immunohistochemical examination to evaluate wound healing of conjunctiva. The expressions of type-I collagen and growth factors were evaluated by real time-reverse transcriptase-polymerase chain reaction. The effects of Smad7 gene introduction on the cultured human SCFs were also studied. RESULTS: Marked Smad7 protein expression was detected in the vector-treated conjunctival epithelium and fibroblasts that coincided with green fluorescein protein expression, whereas faint endogenous Smad7 expression was observed in the control tissue. In vivo Smad7 gene introduction blocked Smad2/3 nuclear translocation with suppression of alpha-smooth muscle actin (alphaSMA) and vascular endothelial growth factor (VEGF) in fibroblasts and invasion of macrophages. Smad7 gene transfer suppressed mRNA expressions of connective tissue growth factor (CTGF), VEGF, and monocyte chemoattractant protein-1 in vivo and those of type-I collagen, alphaSMA, and CTGF in vitro. CONCLUSIONS: Smad7 gene transfer modulates injury-induced wound healing of conjunctival tissue in mice, suggesting that this strategy may be effective in preventing excessive scarring following filtration surgery. The mechanism might include suppression of activation of fibroblasts and reduction of macrophage invasion.

Actins↗

PubMed2004

Smad3 as a mediator of the fibrotic response.

Transforming growth factor-beta (TGF-beta) plays a central role in fibrosis, contributing to the influx and activation of inflammatory cells, the epithelial to mesenchymal transdifferentiation (EMT) of cells and the influx of fibroblasts and their subsequent elaboration of extracellular matrix. TGF-beta signals through transmembrane receptor serine/threonine kinases to activate novel signalling intermediates called Smad proteins, which modulate the transcription of target genes. The use of mice with a targeted deletion of Smad3, one of the two homologous proteins which signals from TGF-beta/activin, shows that most of the pro-fibrotic activities of TGF-beta are mediated by Smad3. Smad3 null inflammatory cells and fibroblasts do not respond to the chemotactic effects of TGF-beta and do not autoinduce TGF-beta. The loss of Smad3 also interferes with TGF-beta-mediated induction of EMT and genes for collagens, plasminogen activator inhibitor-1 and the tissue inhibitor of metalloprotease-1. Smad3 null mice are resistant to radiation-induced cutaneous fibrosis, bleomycin-induced pulmonary fibrosis, carbon tetrachloride-induced hepatic fibrosis as well as glomerular fibrosis induced by induction of type 1 diabetes with streptozotocin. In fibrotic conditions that are induced by EMT, such as proliferative vitreoretinopathy, ocular capsule injury and glomerulosclerosis resulting from unilateral ureteral obstruction, Smad3 null mice also show an abrogated fibrotic response. Animal models of scleroderma, cystic fibrosis and cirrhosis implicate involvement of Smad3 in the observed fibrosis. Additionally, inhibition of Smad3 by overexpression of the inhibitory Smad7 protein or by treatment with the small molecule, halofuginone, dramatically reduces responses in animal models of kidney, lung, liver and radiation-induced fibrosis. Small moleucule inhibitors of Smad3 may have tremendous clinical potential in the treatment of pathological fibrotic diseases.

Animals↗

PubMed2003

GATA- and Smad1-dependent enhancers in the Smad7 gene differentially interpret bone morphogenetic protein concentrations.

Smad7, an inhibitor of transforming growth factor beta superfamily signaling, is induced by bone morphogenetic protein (BMP) in an inhibitory feedback loop. Here, we identify multiple BMP response elements (BREs) in the Smad7 gene and demonstrate that they function differentially to interpret BMP signals in a cell type-specific manner. Two BREs (BRE-1 and -2) reside in the promoter region. One of these contains several conserved Smad1 and Smad4 binding sites that cooperate to mediate BMP-dependent induction, most likely in the absence of DNA binding partners. The third BRE (I-BRE) resides in the first intron and contains GATA factor binding sites. GATA-1, -5, or -6 is required for strong activation of I-BRE, and we show that they assemble with Smad1 on the I-BRE in living cells. Activation of the I-BRE is mediated by a specific region in GATA-5 and -6 but does not require direct physical interaction with Smad1. Comparison of I-BRE to BRE-1 showed that I-BRE is more responsive to low BMP concentrations. Moreover, analysis by chromatin immunoprecipitation experiments demonstrates that the endogenous I-BRE is occupied more robustly by endogenous Smad1 than is BRE-1. This correlates with regulation of the Smad7 gene, which is induced at lower BMP concentrations in GATA-expressing cell lines compared to non-GATA-expressing lines. These data thus define how cooperative and noncooperative Smad-dependent transcriptional regulation can function to interpret different BMP concentrations.

Animals↗

PubMed2002

[Influence of TGF beta(1) on expression of Smad7 mRNA and protein in rat liver cells].

OBJECTIVE: To investigate the influence of exogenous transforming growth factor beta 1 (TGFbeta1) on growth and signal inhibitor Smad7 protein and its mRNA in BRL cells (rat liver cell line). METHODS: BRL cells were incubated with TGFbeta1 and divided into 0 minute group, 90 minute group and 24 hour group according to the time of incubation with TGFbeta1. Morphologic changes were observed. The expression of Smad7 mRNA and protein was investigated by reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immnuohistrochemistry. RESULTS: Growth stagnancy and morphologic change of cells was not seen among the three groups. The expression levels of Smad7 mRNA was the highest in 90-minute group and the lowest in 0-minute group, and the 24-hour group took the second place. Most of the Smad7 immune positive granules were observed in cytoplasm. CONCLUSION: TGFbeta1 does not induce growth stagnancy in BRL cells during the period of 90 minutes to 24 hours. There is a relation of effectiveness for a given period of time between the level of Smad7 and TGFbeta1 stimulation.

Animals↗

PubMed1998

Smad7 is an activin-inducible inhibitor of activin-induced growth arrest and apoptosis in mouse B cells.

Members of the transforming growth factor-beta (TGF-beta) family, which includes the activins, relay signals from serine/threonine kinase receptors in membrane to nucleus via intracellular Sma- and Mad-related (Smad) proteins. Inhibitory Smad proteins were found to prevent the interaction between the serine/threonine kinase receptors and pathway-restricted Smad proteins. Smad7 was identified as a TGF-beta-inducible antagonist of TGF-beta signaling, and it may participate in a negative feedback loop to control TGF-beta signaling. Here we demonstrate that the mRNA expression of Smad7 is induced by activin A in mouse B cell hybridoma HS-72 cells, which undergo growth arrest and apoptosis upon exposure to activin A. The ectopic expression of mouse Smad7 in HS-72 cells suppressed the activin A-induced cell cycle arrest in the G1 phase by abolishing the activin A-induced expression of p21(CIP1/WAF1) and hypophosphorylation of retinoblastoma protein. Furthermore, Smad7 expression suppressed activin A-induced apoptosis in HS-72 cells. Thus, our data indicate that Smad7 is an activin A-inducible antagonist of activin A-induced growth arrest and apoptosis of B lineage cells.

Activins↗

PubMed2001

Smurf1 interacts with transforming growth factor-beta type I receptor through Smad7 and induces receptor degradation.

Smad7 is an inhibitory Smad that acts as a negative regulator of signaling by the transforming growth factor-beta (TGF-beta) superfamily proteins. Smad7 is induced by TGF-beta, stably interacts with activated TGF-beta type I receptor (TbetaR-I), and interferes with the phosphorylation of receptor-regulated Smads. Here we show that Smurf1, an E3 ubiquitin ligase for bone morphogenetic protein-specific Smads, also interacts with Smad7 and induces Smad7 ubiquitination and translocation into the cytoplasm. In addition, Smurf1 associates with TbetaR-I via Smad7, with subsequent enhancement of turnover of TbetaR-I and Smad7. These results thus reveal a novel function of Smad7, i.e. induction of degradation of TbetaR-I through recruitment of an E3 ligase to the receptor.

Activin Receptors, Type I↗

PubMed2005

Regulation of Smurf2 ubiquitin ligase activity by anchoring the E2 to the HECT domain.

The conjugation of ubiquitin to proteins involves a cascade of activating (E1), conjugating (E2), and ubiquitin-ligating (E3) type enzymes that commonly signal protein destruction. In TGFbeta signaling the inhibitory protein Smad7 recruits Smurf2, an E3 of the C2-WW-HECT domain class, to the TGFbeta receptor complex to facilitate receptor degradation. Here, we demonstrate that the amino-terminal domain (NTD) of Smad7 stimulates Smurf activity by recruiting the E2, UbcH7, to the HECT domain. A 2.1 A resolution X-ray crystal structure of the Smurf2 HECT domain reveals that it has a suboptimal E2 binding pocket that could be optimized by mutagenesis to generate a HECT domain that functions independently of Smad7 and potently inhibits TGFbeta signaling. Thus, E2 enzyme recognition by an E3 HECT enzyme is not constitutively competent and provides a point of control for regulating the ubiquitin ligase activity through the action of auxiliary proteins.

Amino Acid Motifs↗

PubMed2006

IFN-gamma abrogates profibrogenic TGF-beta signaling in liver by targeting expression of inhibitory and receptor Smads.

BACKGROUND/AIMS: In a randomized open-labeled multicenter trial with patients suffering from chronic HBV infection, we recently identified a benefit of 9-month IFN-gamma treatment resulting in decreased fibrosis scores and a reduced number of alpha-smooth muscle actin-positive hepatic stellate cells (HSCs). Approaches opposing profibrogenic activities of TGF-beta may be amenable in chronic liver disease. According to experimental models, IFN-gamma counteracts several TGF-beta effects. METHODS: The crosstalk of IFN-gamma and TGF-beta signaling relevant for fibrogenesis was investigated in primary cultured rat HSCs and a cell line representing activated HSCs. RESULTS: In vitro studies with HSCs demonstrate that TGF-beta-dependent activation of (CAGA)9-MLP-Luc, a Smad3/4 responsive reporter construct, was significantly decreased by IFN-gamma, indicating a TGF-beta antagonizing function. IFN-gamma induced the activity of the Smad7 promoter and Smad7 protein expression via STAT-1 signaling. In contrast to TGF-beta, IFN-gamma was able to induce Smad7 expression in activated HSCs providing increased protein levels for at least 12h. In addition, expression of Smad2/3 was reduced by IFN-gamma and activation of Smads2/3 was abrogated. CONCLUSIONS: IFN-gamma displays antifibrotic effects in liver cells via STAT-1 phosphorylation, upregulation of Smad7 expression and impaired TGF-beta signaling.

Actins↗

PubMed2003

Growth differentiation factor-9 induces Smad2 activation and inhibin B production in cultured human granulosa-luteal cells.

The TGF beta family member growth differentiation factor-9 (GDF-9) is an oocyte-derived factor that is essential for mammalian ovarian folliculogenesis. GDF-9 mRNAs have been shown to be expressed in the human ovarian follicle from the primary follicle stage onward, and recombinant GDF-9 has been shown to promote human ovarian follicle growth in vitro. In this study with primary cultures of human granulosa-luteal (hGL) cells, we investigated whether recombinant GDF-9 activates components of the Smad signaling pathways known to be differentially activated by TGF beta and the bone morphogenetic proteins (BMPs). As with TGF beta, GDF-9 treatment caused the phosphorylation of endogenous 53-kDa proteins detected in Western blots with antiphospho-Smad2 antibodies (alpha PS2). However, unlike BMP-2, GDF-9 did not activate the phosphorylation of antiphospho-Smad1 antibody (alphaPS1)-immunoreactive proteins in hGL cells. Infection of hGL cells with an adenovirus expressing Smad2 (Ad-Smad2) confirmed that GDF-9 activates specifically phosphorylation of the Smad2 protein. Infection of hGL cells with Ad-Smad7, which expresses the inhibitory Smad7 protein, suppressed the levels of both GDF-9-induced endogenous and adenoviral alpha PS2-reactive proteins. Furthermore, GDF-9 increased the steady state levels of inhibin beta(B)-subunit mRNAs in hGL cells and strongly stimulated the secretion of dimeric inhibin B. Again, Ad-Smad7 blocked GDF-9-stimulated inhibin B production in a concentration-dependent manner. We identify here for the first time distinct molecular components of the GDF-9 signaling pathway in the human ovary. Our data suggest that GDF-9 mediates its effect through the pathway commonly activated by TGF beta and activin, but not that activated by many BMPs. The results are also consistent with the suggestion that in addition to endocrine control of inhibin production by gonadotropins, a local paracrine control of inhibin production is likely to occur via oocyte-derived factors in the human ovary.

Adenoviridae↗

PubMed2006

Imbalance of receptor-regulated and inhibitory Smads in lung fibroblasts from bleomycin-exposed rats.

Transforming growth factor (TGF)-beta plays a central role in lung fibrosis, stimulating extracellular matrix deposition. Intracellular signaling of TGF-beta is mediated by Smad proteins. We questioned whether the expression and activation of Smads would be altered in lung fibroblasts from rats exposed to bleomycin, an agent used to provoke an experimental model of lung fibrosis. Fibroblasts were isolated from rat lungs 14 d after intratracheal instillation of bleomycin (BLF) or saline (NLF), and cell cultures established. Whole cell lysates were obtained at baseline, and after stimulation with TGF-beta1 (10 ng/ml). Western blot analysis was performed to measure levels of phosphorylated Smad3 (p-Smad3) and Smad7. Real-time PCR was used to determine changes in Smad7 mRNA after TGF-beta stimulation. We found increased baseline levels of p-Smad3 in BLF versus NLF (P < 0.05). In contrast, baseline levels of Smad7 were comparable. The ratio of stimulatory to inhibitory Smads was increased in BLF compared with NLF (P < 0.05). After stimulation with TGF-beta, levels of p-Smad3 were increased in both groups, with maximal responses at 30 min (P < 0.01). While Smad7 mRNA levels were significantly upregulated (at 1 h) after TGF-beta in both groups, the increase in Smad7 protein was significant in NLF only. We conclude there is sustained activation of Smad signaling in lung fibroblasts isolated from bleomycin-exposed rats, with an imbalance between the levels of p-Smad3 and Smad7. Insufficient levels of the inhibitory Smad7 at baseline, and inadequate response to TGF-beta, may contribute to the fibrotic phenotype characteristic of BLF.

Animals↗