共查询到20条相似文献,搜索用时 31 毫秒
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Pan D Estévez-Salmerón LD Stroschein SL Zhu X He J Zhou S Luo K 《The Journal of biological chemistry》2005,280(16):15992-16001
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Xiao Z Brownawell AM Macara IG Lodish HF 《The Journal of biological chemistry》2003,278(36):34245-34252
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Morén A Imamura T Miyazono K Heldin CH Moustakas A 《The Journal of biological chemistry》2005,280(23):22115-22123
Smad4 mediates signaling by the transforming growth factor-beta (TGF-beta) superfamily of cytokines. Smad signaling is negatively regulated by inhibitory (I) Smads and ubiquitin-mediated processes. Known mechanisms of proteasomal degradation of Smads depend on the direct interaction of specific E3 ligases with Smads. Alternatively, I-Smads elicit degradation of the TGF-beta receptor by recruiting the WW and HECT domain E3 ligases, Smurfs, WWP1, or NEDD4-2. We describe an equivalent mechanism of degradation of Smad4 by the above E3 ligases, via formation of ternary complexes between Smad4 and Smurfs, mediated by R-Smads (Smad2) or I-Smads (Smad6/7), acting as adaptors. Smurfs, which otherwise cannot directly bind to Smad4, mediated poly-ubiquitination of Smad4 in the presence of Smad6 or Smad7. Smad4 co-localized with Smad7 and Smurf1 primarily in the cytoplasm and in peripheral cell protrusions. Smad2 or Smad7 mutants defective in Smad4 interaction failed to induce Smurf1-mediated down-regulation of Smad4. A Smad4 mutant defective in Smad2 or Smad7 interaction could not be effectively down-regulated by Smurf1. We propose that Smad4 is targeted for degradation by multiple ubiquitin ligases that can simultaneously act on R-Smads and signaling receptors. Such mechanisms of down-regulation of TGF-beta signaling may be critical for proper physiological response to this pathway. 相似文献
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Baburajendran N Jauch R Tan CY Narasimhan K Kolatkar PR 《Nucleic acids research》2011,39(18):8213-8222
Smad proteins form multimeric complexes consisting of the 'common partner' Smad4 and receptor regulated R-Smads on clustered DNA binding sites. Deciphering how pathway specific Smad complexes multimerize on DNA to regulate gene expression is critical for a better understanding of the cis-regulatory logic of TGF-β and BMP signaling. To this end, we solved the crystal structure of the dimeric Smad4 MH1 domain bound to a palindromic Smad binding element. Surprisingly, the Smad4 MH1 forms a constitutive dimer on the SBE DNA without exhibiting any direct protein-protein interactions suggesting a DNA mediated indirect readout mechanism. However, the R-Smads Smad1, Smad2 and Smad3 homodimerize with substantially decreased efficiency despite pronounced structural similarities to Smad4. Therefore, intricate variations in the DNA structure induced by different Smads and/or variant energetic profiles likely contribute to their propensity to dimerize on DNA. Indeed, competitive binding assays revealed that the Smad4/R-Smad heterodimers predominate under equilibrium conditions while R-Smad homodimers are least favored. Together, we present the structural basis for DNA recognition by Smad4 and demonstrate that Smad4 constitutively homo- and heterodimerizes on DNA in contrast to its R-Smad partner proteins by a mechanism independent of direct protein contacts. 相似文献
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Differential ubiquitination defines the functional status of the tumor suppressor Smad4 总被引:8,自引:0,他引:8
Morén A Hellman U Inada Y Imamura T Heldin CH Moustakas A 《The Journal of biological chemistry》2003,278(35):33571-33582
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Junjing Yu Lei Pan Xincheng Qin Hua Chen Youli Xu Yeguang Chen Hong Tang 《The Journal of biological chemistry》2010,285(11):8454-8462
Homeostasis of Smad phosphorylation at its C-terminal SXS motif is essential for transforming growth factor β (TGFβ) signaling. Whereas it is known that TGFβ signaling can be terminated by phosphatases, which dephosphorylate R-Smads in the nucleus, it is unclear whether there are any cytoplasmic phosphatase(s) that can attenuate R-Smad phosphorylation and nuclear translocation. Here we demonstrate that myotubularin-related protein 4 (MTMR4), a FYVE domain-containing dual-specificity protein phosphatase (DSP), attenuates TGFβ signaling by reducing the phosphorylation level of R-Smads in early endosomes. Co-immunoprecipitation experiments showed that endogenous MTMR4 interacts with phosphorylated R-Smads, and that this interaction is correlated with dephosphorylation of R-Smads. Further analysis showed that overexpression of MTMR4 resulted in the sequestration of activated Smad3 in the early endosomes, thus reducing its nuclear translocation. However, both point mutations at the conserved catalytic site of the phosphatase (MTMR4-C407S) and small interference RNA of endogenous Mtmr4 expression led to sustained Smad3 activation. This work therefore suggests that MTMR4 plays an important role in preventing the overactivation of TGFβ signaling by dephosphorylating activated R-Smads that have been trafficked to early endosomes. 相似文献
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Roles of bone morphogenetic protein type I receptors and Smad proteins in osteoblast and chondroblast differentiation 总被引:18,自引:0,他引:18 下载免费PDF全文
Fujii M Takeda K Imamura T Aoki H Sampath TK Enomoto S Kawabata M Kato M Ichijo H Miyazono K 《Molecular biology of the cell》1999,10(11):3801-3813
The biological effects of type I serine/threonine kinase receptors and Smad proteins were examined using an adenovirus-based vector system. Constitutively active forms of bone morphogenetic protein (BMP) type I receptors (BMPR-IA and BMPR-IB; BMPR-I group) and those of activin receptor-like kinase (ALK)-1 and ALK-2 (ALK-1 group) induced alkaline phosphatase activity in C2C12 cells. Receptor-regulated Smads (R-Smads) that act in the BMP pathways, such as Smad1 and Smad5, also induced the alkaline phosphatase activity in C2C12 cells. BMP-6 dramatically enhanced alkaline phosphatase activity induced by Smad1 or Smad5, probably because of the nuclear translocation of R-Smads triggered by the ligand. Inhibitory Smads, i.e., Smad6 and Smad7, repressed the alkaline phosphatase activity induced by BMP-6 or the type I receptors. Chondrogenic differentiation of ATDC5 cells was induced by the receptors of the BMPR-I group but not by those of the ALK-1 group. However, kinase-inactive forms of the receptors of the ALK-1 and BMPR-I groups blocked chondrogenic differentiation. Although R-Smads failed to induce cartilage nodule formation, inhibitory Smads blocked it. Osteoblast differentiation induced by BMPs is thus mediated mainly via the Smad-signaling pathway, whereas chondrogenic differentiation may be transmitted by Smad-dependent and independent pathways. 相似文献
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Structural mechanism of Smad4 recognition by the nuclear oncoprotein Ski: insights on Ski-mediated repression of TGF-beta signaling 总被引:8,自引:0,他引:8
The Ski family of nuclear oncoproteins represses TGF-beta signaling through interactions with the Smad proteins. The crystal structure of the Smad4 binding domain of human c-Ski in complex with the MH2 domain of Smad4 reveals specific recognition of the Smad4 L3 loop region by a highly conserved interaction loop (I loop) from Ski. The Ski binding surface on Smad4 significantly overlaps with that required for binding of the R-Smads. Indeed, Ski disrupts the formation of a functional complex between the Co- and R-Smads, explaining how it could lead to repression of TGF-beta, activin, and BMP responses. Intriguingly, the structure of the Ski fragment, stabilized by a bound zinc atom, resembles the SAND domain, in which the corresponding I loop is responsible for DNA binding. 相似文献
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Tasima Haque Manuela Mandu-Hrit Frank Rauch Dominique Lauzier Maryam Tabrizian Reggie C Hamdy 《The journal of histochemistry and cytochemistry》2006,54(4):407-415
In this study we investigated the expression of bone morphogenetic protein (BMP)-signaling Smads in distraction osteogenesis (DO). Osteotomy of the right tibia was performed in 14 skeletally mature white New Zealand male rabbits. Lengthening was started 1 week later at a rate of 0.5 mm/12 hr and was maintained for 3 weeks. Expression of Smad proteins 1, 4, 5, 6, 7, and 8 and Smad ubiquitin regulatory factors (Smurfs) 1 and 2 was evaluated in the distracted zone using immunohistochemistry. Expression of receptor-regulated Smads (R-Smads) 1, 5, and 8 showed a significant increase during the distraction phase, followed by a gradual decrease during the consolidation phase. Smad 4 showed significant expression during both distraction and the beginning of the consolidation phase. Smad 6 and Smad 7 were highly expressed during the consolidation phase. Staining for both Smurfs 1 and 2 was maximal at the end of the distraction period. Staining for all proteins was most intense in chondrocyte and fibroblast-like cells. Expression pattern of R-Smads correlated with our previously reported expression pattern of BMPs 2, 4, and 7 and their receptors. These results therefore suggest a role for the whole BMP signaling pathway including the Smad proteins in DO. 相似文献
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Xiaohua Yan Hongwei Liao Minzhang Cheng Xiaojing Shi Xia Lin Xin-Hua Feng Ye-Guang Chen 《The Journal of biological chemistry》2016,291(1):382-392
TGF-β is a pleiotropic cytokine that regulates a wide range of cellular actions and pathophysiological processes. TGF-β signaling is spatiotemporally fine-tuned. As a key negative regulator of TGF-β signaling, Smad7 exerts its inhibitory effects by blocking receptor activity, inducing receptor degradation or interfering with Smad-DNA binding. However, the functions and the molecular mechanisms underlying the actions of Smad7 in TGF-β signaling are still not fully understood. In this study we report a novel mechanism whereby Smad7 antagonizes TGF-β signaling at the Smad level. Smad7 oligomerized with R-Smad proteins upon TGF-β signaling and directly inhibited R-Smad activity, as assessed by Gal4-luciferase reporter assays. Mechanistically, Smad7 competes with Smad4 to associate with R-Smads and recruits the E3 ubiquitin ligase NEDD4L to activated R-Smads, leading to their polyubiquitination and proteasomal degradation. Similar to the R-Smad-Smad4 oligomerization, the interaction between R-Smads and Smad7 is mediated by their mad homology 2 (MH2) domains. A positive-charged basic region including the L3/β8 loop-strand module and adjacent amino acids in the MH2 domain of Smad7 is essential for the interaction. These results shed new light on the regulation of TGF-β signaling by Smad7. 相似文献