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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Runx2 is required for osteoblast differentiation but is expressed in certain nonosteoblastic cells without activating the differentiation process, suggesting that its activity is suppressed through a lineage-specific mechanism. Here we report that primary mouse dermal fibroblasts lacking Smad3 can acquire an osteoblast-like phenotype, including activation of Runx2 activity, expression of osteoblast-specific genes, and calcium deposition. We further show that negative regulation of Runx2 activity by Smad3 in dermal fibroblasts is likely mediated by controlling the expression of Msx2, an antagonist of Runx2 in this cellular context. These data support the presence of a novel mechanism for controlling cell fate determination of mesenchymal lineages by preventing differentiation toward the osteoblastic lineage via negative regulation of Runx2 activity.
Mol Cell Biol 2005 Nov
PMID:Loss of Smad3-mediated negative regulation of Runx2 activity leads to an alteration in cell fate determination. 1622 96

Members of the Smad protein family function as signal transducers of the transforming growth factor (TGF-beta) superfamily proteins. The human Smad5 protein, a signal transducer downstream of TGF-beta/BMP receptors, is composed of N-terminal DNA binding domain (MH1) and C-terminal protein-protein interaction domain (MH2) connected together by a linker motif. We used homology-modeling techniques to generate a reliable molecular model of the Smad5 MH1 domain based on the crystal structure of Smad3 MH1 domain. Our study presents the structural features of a BMP-regulated, R-Smad subfamily member (consisting of Smad1, Smad5 and Smad8) for the first time. This model provides a structural basis for explaining both functional similarities and differences between Smad3 and Smad5. Also, the structural model of this molecular target would be useful for structure-based inhibitor design because of its high accuracy. The results of our study provide important insights into understanding the structure-function relationship of the members of the Smad protein family and can serve to guide future genetic and biochemical experiments in this area.
J Mol Graph Model 2006 Jan
PMID:Homology modeling of the DNA-binding domain of human Smad5: a molecular model for inhibitor design. 1624 55

This is the first report that characterizes specific inhibitor of Smad3 (SIS3) as a potent and selective inhibitor of Smad3 function. In the reporter assay, the increased luciferase activity of p3TP-lux by the overexpression of constitutively active form of ALK-5 was abrogated by the treatment with SIS3 in a dose-dependent manner. Immunoprecipitation revealed that SIS3 attenuated the transforming growth factor (TGF)-beta1-induced phosphorylation of Smad3 and interaction of Smad3 with Smad4. On the other hand, this reagent did not affect the phosphorylation of Smad2. Thereafter, we evaluated the ability of SIS3 in the suppression of the TGF-beta1-induced type I procollagen up-regulation in human dermal fibroblasts. We found that the addition of SIS3 attenuated the effects of TGF-beta1 by reducing the transcriptional activity. SIS3 also inhibited the myofibroblast differentiation of fibroblasts by TGF-beta1. Moreover, we demonstrated that SIS3 completely diminished the constitutive phosphorylation of Smad3 as well as the up-regulated type I collagen expression in scleroderma fibroblasts. Together, our study suggested that SIS3 is a useful tool to evaluate the TGF-beta-regulated cellular mechanisms via selective inhibition of Smad3.
Mol Pharmacol 2006 Feb
PMID:Characterization of SIS3, a novel specific inhibitor of Smad3, and its effect on transforming growth factor-beta1-induced extracellular matrix expression. 1628 83

Transforming growth factor beta (TGF-beta) was originally identified by virtue of its ability to induce transformation of the AKR-2B and NRK fibroblasts but was later found to be a potent inhibitor of the growth of epithelial, endothelial, and lymphoid cells. Although the growth-inhibitory pathway of TGF-beta mediated by the Smad proteins is well studied, the signaling pathway leading to the transforming activity of TGF-beta in fibroblasts is not well understood. Here we show that SnoN, a member of the Ski family of oncoproteins, is required for TGF-beta-induced proliferation and transformation of AKR-2B and NRK fibroblasts. TGF-beta induces upregulation of snoN expression in both epithelial cells and fibroblasts through a common Smad-dependent mechanism. However, a strong and prolonged activation of snoN transcription that lasts for 8 to 24 h is detected only in these two fibroblast lines. This prolonged induction is mediated by Smad2 and appears to play an important role in the transformation of both AKR-2B and NRK cells. Reduction of snoN expression by small interfering RNA or shortening of the duration of snoN induction by a pharmacological inhibitor impaired TGF-beta-induced anchorage-independent growth of AKR-2B cells. Interestingly, Smad2 and Smad3 play opposite roles in regulating snoN expression in both fibroblasts and epithelial cells. The Smad2/Smad4 complex activates snoN transcription by direct binding to the TGF-beta-responsive element in the snoN promoter, while the Smad3/Smad4 complex inhibits it through a novel Smad inhibitory site. Mutations of Smad4 that render it defective in heterodimerization with Smad3, which are found in many human cancers, convert the activity of Smad3 on the snoN promoter from inhibitory to stimulatory, resulting in increased snoN expression in cancer cells. Thus, we demonstrate a novel role of SnoN in the transforming activity of TGF-beta in fibroblasts and also uncovered a mechanism for the elevated SnoN expression in some human cancer cells.
Mol Cell Biol 2005 Dec
PMID:Requirement for the SnoN oncoprotein in transforming growth factor beta-induced oncogenic transformation of fibroblast cells. 1631 99

Smad family proteins Smad2 and Smad3 are activated by transforming growth factor beta (TGF-beta)/activin/nodal receptors and mediate transcriptional regulation. Although differential functional roles of Smad2 and Smad3 are apparent in mammalian development, the relative functional roles of Smad2 and Smad3 in postnatal systems remain unclear. We used Cre/loxP-mediated gene targeting for hepatocyte-specific deletion of Smad2 (S2HeKO) in adult mice and generated hepatocyte-selective Smad2/Smad3 double knockouts by intercrossing AlbCre/Smad2(f/f) (S2HeKO) and Smad3-deficient Smad3ex8/ex8 (S3KO) mice. All strains were viable and had normal adult liver. However, necrogenic CCL4-induced hepatocyte proliferation was significantly increased in S2HeKO compared to Ctrl and S3KO livers, and transplanted S2HeKO hepatocytes repopulated recipient liver at dramatically increased rates compared to Ctrl hepatocytes in vivo. Using primary hepatocytes, we found that TGF-beta-induced G1 arrest, apoptosis, and epithelial-to-mesenchymal transition in Ctrl and S2HeKO but not in S3KO hepatocytes. Interestingly, S2HeKO cells spontaneously acquired mesenchymal features characteristic of epithelial-to-mesenchymal transition (EMT). Collectively, these results demonstrate that Smad2 suppresses hepatocyte growth and dedifferentiation independent of TGF-beta signaling. Smad2 is not required for TGF-beta-stimulated apoptosis, EMT, and growth inhibition in hepatocytes.
Mol Cell Biol 2006 Jan
PMID:Deletion of Smad2 in mouse liver reveals novel functions in hepatocyte growth and differentiation. 1638 55

Endometrial decidualization results from the differentiation of stromal cells in an ovarian steroid-sensitive manner. Human endometrial tissues obtained from fertile women at various stages of the menstrual cycle were subjected to immunohistochemistry to localize the components of the transforming growth factor-beta (TGF-beta) system. TGF-beta receptor-I and -II expression was higher in stromal cells than in epithelial cells during the secretory phase while no such variation was observed during the proliferative phase. The expression of phosphorylated Smad3 (pSmad2/3), an activated form of a component of the TGF-beta signalling pathway, and translocation of pSmad2/3 from the cytoplasm to the nucleus were more pronounced in secretory endometrium. In coculture of human endometrial epithelial with stromal cells, each isolated from the proliferative endometrium, administration of progesterone stimulated decidualization as well as TGF-beta signalling activation in stromal cells. Progesterone also significantly elevated the concentration of TGF-beta1 in the coculture medium. Careful manipulation of the coculture, i.e. selective addition and omission of the cellular components, showed that this progesterone-induced increase in secretion of TGF-beta1 come mainly from epithelial cells. Moreover, administration of TGF-beta1 (10 ng/ml) directly to cultured stromal cells enhanced the expression of prolactin as well as pSamd2/3 even without progesterone. Taken together, our present data support the notion that progesterone induces stromal decidualization indirectly, i.e. by enhancing the expression and secretion of TGF-beta1 from epithelial cells. The secreted, epithelial-derived TGF-beta1 then acts on adjacent stromal cells, at least in part, to turn on Smad signalling that could lead to stromal decidualization.
Mol Hum Reprod 2005 Nov
PMID:Progesterone-dependent release of transforming growth factor-beta1 from epithelial cells enhances the endometrial decidualization by turning on the Smad signalling in stromal cells. 1640 3

TGFbeta is a major regulator of extracellular matrix deposition and a potent inducer of type-1 plasminogen activator inhibitor (PAI-1) gene expression. We have reported that liganded glucocorticoid receptor (GR) represses TGFbeta transactivation of PAI-1 in Hep3B human hepatoma cells and that it interacts functionally and physically with the C-terminal activation domain of Smad3, a mediator of TGFbeta signaling. The ligand binding domain of GR is required for GR-mediated transrepression, but the GR DNA binding domain and activation function 1 domains are not. We report here that overexpression of steroid receptor coactivator-1 (SRC-1) and GR-interacting protein-1 (GRIP-1) enhanced repression by liganded GR, and by a GR mutant defective in repression. Surprisingly, SRC-1 and GRIP-1 also enhanced TGFbeta-induced activation from the TGFbeta-responsive sequence of the PAI-1 gene by a GR-independent mechanism. Coimmunoprecipitation and mammalian one-hybrid experiments demonstrated that SRC-1 and GRIP-1 interact physically with endogenous Smad3 and functionally with the C-terminal domain of Smad3 to directly enhance transcription. Thus, the GR coactivators, SRC-1 and GRIP-1, act as both corepressors of the glucocorticoid repression of PAI-1 gene transcription, and coactivators of TGFbeta-induced activation of the PAI-1 promoter.
Mol Endocrinol 2006 May
PMID:Role of steroid receptor coactivators in glucocorticoid and transforming growth factor beta regulation of plasminogen activator inhibitor gene expression. 1642 81

Transforming growth factor beta (TGF-beta) receptors phosphorylate Smad3 and induce its nuclear import so it can regulate gene transcription. Smad3 can return to the cytoplasm to propagate further cycles of signal transduction or to be degraded. We demonstrate that Smad3 is exported by a constitutive mechanism that is insensitive to leptomycin B. The Mad homology 2 (MH2) domain is responsible for Smad3 export, which requires the GTPase Ran. Inactive, GDP-locked RanT24N or nuclear microinjection of Ran GTPase activating protein 1 blocked Smad3 export. Inactivation of the Ran guanine nucleotide exchange factor RCC1 inhibited Smad3 export and led to nuclear accumulation of phosphorylated Smad3. A screen for importin/exportin family members that associate with Smad3 identified exportin 4, which binds a conserved peptide sequence in the MH2 domain of Smad3 in a Ran-dependent manner. Exportin 4 is sufficient for carrying the in vitro nuclear export of Smad3 in cooperation with Ran. Knockdown of endogenous exportin 4 completely abrogates the export of endogenous Smad3. A short peptide representing the minimal interaction domain in Smad3 effectively competes with Smad3 association to exportin 4 and blocks nuclear export of Smad3 in vivo. We thus delineate a novel nuclear export pathway for Smad3.
Mol Cell Biol 2006 Feb
PMID:The mechanism of nuclear export of Smad3 involves exportin 4 and Ran. 1644 45

Transforming growth factor-beta superfamily has been implicated in tumorigenesis. We have recently shown that Nodal, a member of transforming growth factor-beta superfamily, and its receptor, activin receptor-like kinase 7 (ALK7), inhibit proliferation and induce apoptosis in human epithelial ovarian cancer cell lines. In this study, we further investigated the cellular mechanisms underlying the apoptotic action of ALK7 using an immortalized ovarian surface epithelial cell line, IOSE397, and an epithelial ovarian cancer cell line, OV2008. Infection of these cells with an adenoviral construct carrying constitutively active ALK7 (Ad-ALK7-ca) potently induced cell death; all cells died after 3 and 5 days of Ad-ALK7-ca infection in IOSE397 and OV2008 cells, respectively. ALK7-ca induced the expression of proapoptotic factor Bax but suppressed the expression of antiapoptotic factors Bcl-2, Bcl-XL, and Xiap. Silencing of Bax by small interfering RNA in IOSE397 cells significantly reduced ALK7-ca-induced apoptosis as measured by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay but partially blocked ALK7-ca-induced caspase-3 activation and did not affect the down-regulation of Xiap by ALK7-ca. Dominant-negative Smad2, Smad3, and Smad4 blocked ALK7-ca-regulated Xiap and Bax expression and caspase-3 activation. Thus, ALK7-induced apoptosis is at least in part through two Smad-dependent pathways, Bax/Bcl-2 and Xiap.
Mol Cancer Res 2006 Apr
PMID:Activin receptor-like kinase 7 induces apoptosis through up-regulation of Bax and down-regulation of Xiap in normal and malignant ovarian epithelial cell lines. 1660 37

Surfactant protein A (SP-A) and transforming growth factor-beta1 (TGF-beta1) have been shown to modulate the functions of different immune cells and specifically to inhibit T lymphocyte proliferation. The aim of the present study was to elucidate whether the Smad signaling pathway, which is activated by TGF-beta1, also plays a role in SP-A-mediated inhibition of CD4+ T lymphocyte activation. Recombinant human SP-A1 expressed in Chinese hamster ovary cells [rSP-A1m (mammalian)], but not recombinant Baculovirus-derived rSP-A1hyp (hydroxyproline-deficient), suppressed T lymphocyte proliferation and IL-2 mRNA expression. To test whether SP-A induced Smad signaling, a Smad3/4-specific reporter gene was transfected in primary human CD4+ T lymphocytes. Only rSP-A1m, but not rSP-A1hyp, induced Smad-specific reporter genes, Smad2 phosphorylation, and Smad7 mRNA expression. The effect of rSP-A1m was mediated through the TGF-betaRII and could be antagonized by anti-TGF-beta1 neutralizing antibodies and sTGF-betaRII. Western blot and ELISA analysis revealed that rSP-A1m, but not rSP-A1hyp, contained TGF-beta1. TGF-beta1 was responsible for the differences in inhibition of CD4+ T lymphocyte proliferation and activation of the Smad signaling pathway between rSP-A1m and rSP-A1hyp. After acidification, native SP-A, obtained from patients with alveolar proteinosis, also induced Smad signaling in human CD4+ T lymphocytes leading to an increased inhibition of T lymphocyte proliferation, thus indicating the presence of inactive, latent TGF-beta1 in native SP-A samples. Association between SP-A and latent TGF-beta1 provides a possible novel mechanism to regulate TGF-beta1-mediated inflammation and fibrosis reactions in the lung but also leads to possible misinterpretation of immune-modulator functions of SP-A. Monitoring of SP-A preparations for possible TGF-beta1 is essential.
Am J Physiol Lung Cell Mol Physiol 2006 Oct
PMID:TGF-beta1 in SP-A preparations influence immune suppressive properties of SP-A on human CD4+ T lymphocytes. 1664 38


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