Structural basis for distinct roles of SMAD2 and SMAD3 in FOXH1 pioneer-directed TGF-β signaling.
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ABSTRACT:
SUBMITTER: Aragon E
PROVIDER: S-EPMC6824466 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Smad2 and Smad3 (Smad2/3) are key intracellular signal transducers for TGF-beta signaling, and their transcriptional activities are controlled through reversible phosphorylation and nucleocytoplasmic shuttling. However, the precise mechanism underlying nuclear export of Smad2/3 remains elusive. Here we report the essential function of RanBP3 in selective nuclear export of Smad2/3 in the TGF-beta pathway. RanBP3 directly recognizes dephosphorylated Smad2/3, which results from the activity of nuclear Smad phosphatases, and mediates nuclear export of Smad2/3 in a Ran-dependent manner. As a result, increased expression of RanBP3 inhibits TGF-beta signaling in mammalian cells and Xenopus embryos. Conversely, depletion of RanBP3 expression or dominant-negative inhibition of RanBP3 enhances TGFbeta-induced antiproliferative and transcriptional responses. In conclusion, our study supports a definitive role for RanBP3 in mediating Smad2/3 nuclear export and terminating TGF-beta signaling.
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Project description:Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine signaling to the nucleus through cell surface transmembrane receptor serine/threonine kinases and cytoplasmic effectors, including Smad proteins. We describe a novel modulator of this pathway, TLP (TRAP-1-like protein), which is 25% identical to the previously described Smad4 chaperone, TRAP-1, and shows identical expression patterns in human tissues. Endogenous TLP associates with both active and kinase-deficient TGF-beta and activin type II receptors, but interacts with the common-mediator Smad4 only in the presence of TGF-beta/activin signaling. Overexpression of TLP represses the ability of TGF-beta to induce transcription from SBE-Luc, a Smad3/4-specific reporter, while it potentiates transcription from ARE-Luc, a Smad2/4-specific reporter. Consistent with this, TLP inhibits the formation of Smad3/4 complexes in the absence of effects on phosphorylation of Smad3, while it affects neither Smad2 phosphorylation nor hetero-oligomerization. We propose that TLP might regulate the balance of Smad2 and Smad3 signaling by localizing Smad4 intracellularly, thus contributing to cellular specificity of TGF-beta transcriptional responses in both normal and pathophysiology.
| S-EPMC202370 | biostudies-literature
Project description:TGF-?s regulate fibroblast responses, by activating Smad2 or Smad3 signaling, or via Smad-independent pathways. We have previously demonstrated that myofibroblast-specific Smad3 is critically implicated in repair of the infarcted heart. However, the role of fibroblast Smad2 in myocardial infarction remains unknown. This study investigates the role of myofibroblast-specific Smad2 signaling in myocardial infarction, and explores the mechanisms responsible for the distinct effects of Smad2 and Smad3. In a mouse model of non-reperfused myocardial infarction, Smad2 activation in infarct myofibroblasts peaked 7?days after coronary occlusion. In vitro, TGF-?1, -?2 and -?3, but not angiotensin 2 and bone morphogenetic proteins-2, -4 and -7, activated fibroblast Smad2. Myofibroblast-specific Smad2 and Smad3 knockout mice (FS2KO, FS3KO) and corresponding control littermates underwent non-reperfused infarction. In contrast to the increase in rupture rates and adverse remodeling in FS3KO mice, FS2KO animals had mortality comparable to Smad2 fl/fl controls, and exhibited a modest but transient improvement in dysfunction after 7?days of coronary occlusion. At the 28?day timepoint, FS2KO and Smad2 fl/fl mice had comparable adverse remodeling. Although both FS3KO and FS2KO animals had increased myofibroblast density in the infarct, only FS3KO mice exhibited impaired scar organization, associated with perturbed alignment of infarct myofibroblasts. In vitro, Smad3 but not Smad2 knockdown downmodulated fibroblast ?2 and ?5 integrin expression. Moreover, Smad3 knockdown reduced expression of the GTPase RhoA, whereas Smad2 knockdown markedly increased fibroblast RhoA levels. Smad3-dependent integrin expression may be important for fibroblast activation, whereas RhoA may transduce planar cell polarity pathway signals, essential for fibroblast alignment. Myofibroblast-specific Smad3, but not Smad2 is required for formation of aligned myofibroblast arrays in the infarct. The distinct in vivo effects of myofibroblast Smad2 and Smad3 may involve Smad3-dependent integrin synthesis, and contrasting effects of Smad2 and Smad3 on RhoA expression.
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Project description:Insulin-like growth factor-I inhibits transforming growth factor-beta (TGF-beta) signaling by blocking activation of Smad3 (S3), via a phosphatidylinositol 3-kinase (PI3K)/Akt-dependent pathway. Here we provide the first report that the kinase activity of Akt is necessary for its ability to suppress many TGF-beta responses, including S3 activation and induction of apoptosis. Wild-type and myristoylated Akts (Akt(WT) and Akt(Myr)) suppress TGF-beta-induced phospho-activation of S3 but not Smad2 (S2), whereas kinase-dead Akt1 (Akt1K179M) or dominant-negative PI3K enhances TGF-beta-induced phospho-activation of both S2 and S3. Using siRNA, rapamycin (Rap), and adenoviral expression for FKBP12-resistant and constitutively active TGF-beta type I receptor (ALK5), we demonstrate that mammalian target of Rap (mTOR) mediates Akt1 suppression of phospho-activation of S3. These and further data on Akt1-S3 binding do not support a recently proposed model that Akt blocks S3 activation through physical interaction and sequestration of S3 from TGF-beta receptors. We propose a novel model whereby Akt suppresses activation of S3 in an Akt kinase-dependent manner through mTOR, a likely route for loss of tumor suppression by TGF-beta in cancers.
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Project description:Transforming growth factor-beta 1 (TGF-beta1) is an important growth inhibitor of epithelial cells and insensitivity to this cytokine results in uncontrolled cell proliferation and can contribute to tumorigenesis. TGF-beta1 signals through the TGF-beta type I and type II receptors, and activates the Smad pathway via phosphorylation of Smad2 and Smad3. Since little is known about the selective activation of Smad2 versus Smad3, we set out to identify novel Smad2 and Smad3 interacting proteins in epithelial cells. A non-transformed human cell line was transduced with Myc-His(6)-Smad2 or Myc-His(6)-Smad3-expressing retrovirus and was treated with TGF-beta1. Myc-His(6)-Smad2 or Myc-His(6)-Smad3 was purified by tandem affinity purification, eluates were subject to SDS-PAGE and Colloidal Blue staining, and select protein bands were digested with trypsin. The resulting tryptic peptides were analyzed by liquid chromatography (LC) and tandem mass spectrometry (MS/MS) and the SEQUEST algorithm was employed to identify proteins in the bands. A number of proteins that are known to interact with Smad2 or Smad3 were detected in the eluates. In addition, a number of putative novel Smad2 and Smad3 associated proteins were identified that have functions in cell proliferation, apoptosis, actin cytoskeleton regulation, cell motility, transcription, and Ras or insulin signaling. Specifically, the interaction between Smad2/3 and the Cdc42 guanine nucleotide exchange factor, Zizimin1, was validated by co-immunoprecipitation. The discovery of these novel Smad2 and/or Smad3 associated proteins may reveal how Smad2 and Smad3 are regulated and/or uncover new functions of Smad2 and Smad3 in TGF-beta1 signaling.
| S-EPMC2700048 | biostudies-literature
Project description:Transforming growth factor β (TGF-β) signaling plays a fundamental role in metazoan development and tissue homeostasis. However, the molecular mechanisms concerning the ubiquitin-related dynamic regulation of TGF-β signaling are not thoroughly understood. Using a combination of proteomics and an siRNA screen, we identify pVHL as an E3 ligase for SMAD3 ubiquitination. We show that pVHL directly interacts with conserved lysine and proline residues in the MH2 domain of SMAD3, triggering degradation. As a result, the level of pVHL expression negatively correlates with the expression and activity of SMAD3 in cells, Drosophila wing, and patient tissues. In Drosophila, loss of pVHL leads to the up-regulation of TGF-β targets visible in a downward wing blade phenotype, which is rescued by inhibition of SMAD activity. Drosophila pVHL expression exhibited ectopic veinlets and reduced wing growth in a similar manner as upon loss of TGF-β/SMAD signaling. Thus, our study demonstrates a conserved role of pVHL in the regulation of TGF-β/SMAD3 signaling in human cells and Drosophila wing development.
| S-EPMC8650352 | biostudies-literature
Project description:The transforming growth factor beta (TGF?) related signaling is one of the most important signaling pathways regulating early developmental events. Smad2 and Smad3 are structurally similar and it is mostly considered that they are equally important in mediating TGF? signals. Here, we show that Smad3 is an insensitive TGF? transducer as compared with Smad2. Smad3 preferentially localizes within the nucleus and is thus sequestered from membrane signaling. The ability of Smad3 in oligomerization with Smad4 upon agonist stimulation is also impaired given its unique linker region. Smad2 mediated TGF? signaling plays a crucial role in epiblast development and patterning of three germ layers. However, signaling unrelated nuclear localized Smad3 is dispensable for TGF? signaling-mediated epiblast specification, but important for early neural development, an event blocked by TGF?/Smad2 signaling. Both Smad2 and Smad3 bind to the conserved Smads binding element (SBE), but they show nonoverlapped target gene binding specificity and differential transcriptional activity. We conclude that Smad2 and Smad3 possess differential sensitivities in relaying TGF? signaling and have distinct roles in regulating early developmental events.
| S-EPMC4764856 | biostudies-literature
Project description:TGFβ is the quintessential cytokine of T cell homeostasis. TGFβ signaling is required for the efficient differentiation and maintenance of CD4(+)FOXP3(+) T cells that inhibit immune responses. Conversely, in conjunction with the inflammatory cytokine IL-6, TGFβ promotes Th17 cell differentiation. The mechanism by which TGFβ signals synergize with IL-6 to generate inflammatory versus immunosuppressive T cell subsets is unclear. TGFβ signaling activates receptor SMADs, SMAD2 and SMAD3, which associate with a variety of nuclear factors to regulate gene transcription. Defining relative contributions of distinct SMAD molecules for CD4 T cell differentiation is critical for mapping the versatile intracellular TGFβ-signaling pathways that tailor TGFβ activities to the state of host interaction with pathogens. We show here that SMAD2 is essential for Th17 cell differentiation and that it acts in part by modulating the expression of IL-6R on T cells. Although mice lacking SMAD2 specifically in T cells do not develop spontaneous lymphoproliferative autoimmunity, Smad2-deficient T cells are impaired in their response to TGFβ in vitro and in vivo, and they are more pathogenic than controls when transferred into lymphopenic mice. These results demonstrate that SMAD2 is uniquely essential for TGFβ signaling in CD4(+) T effector cell differentiation.
| S-EPMC2937934 | biostudies-literature
Project description:Prevailing insulin resistance and the resultant hyperglycemia elicits a compensatory response from pancreatic islet beta cells (β-cells) that involves increases in β-cell function and β-cell mass. However, the sustained metabolic stress eventually leads to β-cell failure characterized by severe β-cell dysfunction and progressive loss of β-cell mass. Whereas, β-cell dysfunction is relatively well understood at the mechanistic level, the avenues leading to loss of β-cell mass are less clear with reduced proliferation, dedifferentiation, and apoptosis all potential mechanisms. Butler and colleagues documented increased β-cell apoptosis in pancreas from lean and obese human Type 2 diabetes (T2D) subjects, with no changes in rates of β-cell replication or neogenesis, strongly suggesting a role for apoptosis in β-cell failure. Here, we describe a permissive role for TGF-β/Smad3 in β-cell apoptosis. Human islets undergoing β-cell apoptosis release increased levels of TGF-β1 ligand and phosphorylation levels of TGF-β's chief transcription factor, Smad3, are increased in human T2D islets suggestive of an autocrine role for TGF-β/Smad3 signaling in β-cell apoptosis. Smad3 phosphorylation is similarly increased in diabetic mouse islets undergoing β-cell apoptosis. In mice, β-cell-specific activation of Smad3 promotes apoptosis and loss of β-cell mass in association with β-cell dysfunction, glucose intolerance, and diabetes. In contrast, inactive Smad3 protects from apoptosis and preserves β-cell mass while improving β-cell function and glucose tolerance. At the molecular level, Smad3 associates with Foxo1 to propagate TGF-β-dependent β-cell apoptosis. Indeed, genetic or pharmacologic inhibition of TGF-β/Smad3 signals or knocking down Foxo1 protects from β-cell apoptosis. These findings reveal the importance of TGF-β/Smad3 in promoting β-cell apoptosis and demonstrate the therapeutic potential of TGF-β/Smad3 antagonism to restore β-cell mass lost in diabetes.
| S-EPMC7070087 | biostudies-literature
Project description:BackgroundProgression of pancreatic ductal adenocarcinoma (PDAC) is largely the result of genetic and/or epigenetic alterations in the transforming growth factor-beta (TGF-?)/Smad signalling pathway, eventually resulting in loss of TGF-?-mediated growth arrest and an increase in cellular migration, invasion, and metastasis. These cellular responses to TGF-? are mediated solely or partially through the canonical Smad signalling pathway which commences with activation of receptor-regulated Smads (R-Smads) Smad2 and Smad3 by the TGF-? type I receptor. However, little is known on the relative contribution of each R-Smad, the possible existence of functional antagonism, or the crosstalk with other signalling pathways in the control of TGF-?1-induced growth inhibition and cell migration. Using genetic and pharmacologic approaches we have inhibited in PDAC cells endogenous Smad2 and Smad3, as well as a potential regulator, the small GTPase Rac1, and have analysed the consequences for TGF-?1-mediated growth inhibition and cell migration (chemokinesis).ResultsSiRNA-mediated silencing of Smad3 in the TGF-? responsive PDAC cell line PANC-1 reduced TGF-?1-induced growth inhibition but increased the migratory response, while silencing of Smad2 enhanced growth inhibition but decreased chemokinesis. Interestingly, siRNA-mediated silencing of the small GTPase Rac1, or ectopic expression of a dominant-negative Rac1 mutant largely mimicked the effect of Smad2 silencing on both TGF-?1-induced growth inhibition, via upregulation of the cdk inhibitor p21WAF1, and cell migration. Inhibition of Rac1 activation reduced both TGF-?1-induction of a Smad2-specific transcriptional reporter and Smad2 C-terminal phosphorylation in PDAC cells while Smad3-specific transcriptional activity and Smad3 C-terminal phosphorylation appeared increased. Disruption of autocrine TGF-? signalling in PANC-1 cells rendered cells less susceptible to the growth-suppressive effect of Rac1 inhibition, suggesting that the decrease in "basal" proliferation upon Rac1 inhibition was caused by potentiation of autocrine TGF-? growth inhibition.ConclusionsIn malignant cells with a functional TGF-? signalling pathway Rac1 antagonizes the TGF-?1 growth inhibitory response and enhances cell migration by antagonistically regulating Smad2 and Smad3 activation. This study reveals that Rac1 is prooncogenic in that it can alter TGF-? signalling at the R-Smad level from a tumour-suppressive towards a tumour-promoting outcome. Hence, Rac1 might represent a viable target for therapeutic intervention to inhibit PDAC progression.
| S-EPMC3112431 | biostudies-literature