The L45 loop in type I receptors for TGF-β family members is a critical determinant in specifying Smad isoform activation (original) (raw)
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Molecular and cellular biology, 2012
In vivo cells receive simultaneous signals from multiple extracellular ligands and must integrate and interpret them to respond appropriately. Here we investigate the interplay between pathways downstream of two transforming growth factor β (TGF-β) superfamily members, bone morphogenetic protein (BMP) and TGF-β. We show that in multiple cell lines, TGF-β potently inhibits BMP-induced transcription at the level of both BMP-responsive reporter genes and endogenous BMP target genes. This inhibitory effect requires the TGF-β type I receptor ALK5 and is independent of new protein synthesis. Strikingly, we show that Smad3 is required for TGF-β's inhibitory effects, whereas Smad2 is not. We go on to demonstrate that TGF-β induces the formation of complexes comprising phosphorylated Smad1/5 and Smad3, which bind to BMP-responsive elements in vitro and in vivo and mediate TGF-β-induced transcriptional repression. Furthermore, loss of Smad3 confers on TGF-β the ability to induce transcrip...
TGF-beta receptor-mediated signalling through Smad2, Smad3 and Smad4
The EMBO Journal, 1997
Dijke et al., 1996). The molecular mechanism for TGF-β Japanese Foundation for Cancer Research, and Research for the Future receptor activation, in which a constitutively active type Program, Japan Society for the Promotion of Science, II receptor phosphorylates and activates a type I receptor,
Journal of Biological Chemistry, 2004
Transforming growth factor  (TGF-) ligands exert their biological effects through type II (TRII) and type I receptors (TRI). Unlike TGF-1 and-3, TGF-2 appears to require the co-receptor betaglycan (type III receptor, TRIII) for high affinity binding and signaling. Recently, the TRIII null mouse was generated and revealed significant non-overlapping phenotypes with the TGF-2 null mouse, implying the existence of TRIII independent mechanisms for TGF-2 signaling. Because a variant of the type II receptor, the type II-B receptor (TRII-B), has been suggested to mediate TGF-2 signaling in the absence of TRIII, we directly tested the ability of TRII-B to bind TGF-2. Here we show that the soluble extracellular domain of the type II-B receptor (sTRII-B.Fc) bound TGF-1 and TGF-3 with high affinity (K d values ؍ 31.7 ؎ 22.8 and 74.6 ؎ 15.8 pM, respectively), but TGF-2 binding was undetectable at corresponding doses. Similar results were obtained for the soluble type II receptor (sTRII.Fc). However, sTRII.Fc or sTRII-B.Fc in combination with soluble type I receptor (sTRI.Fc) formed a high affinity complex that bound TGF-2, and this complex inhibited TGF-2 in a biological inhibition assay. These results show that TGF-2 has the potential to signal in the absence of TRIII when sufficient TGF-2, TRI, and TRII or TRII-B are present. Our data also support a cooperative model for receptor-ligand interactions, as has been suggested by crystallization studies of TGF- receptors and ligands. Our cell-free binding assay system will allow for testing of models of receptor-ligand complexes prior to actual solution of crystal structures.
Journal of Biological Chemistry, 1997
Members of the transforming growth factor-beta (TGF-beta) superfamily signal via different heteromeric complexes of two sequentially acting serine/threonine kinase receptors, i.e. type I and type II receptors. We generated two different chimeric TGF-beta superfamily receptors, i.e. TbetaR-I/BMPR-IB, containing the extracellular domain of TGF-beta type I receptor (TbetaR-I) and the intracellular domain of bone morphogenetic protein type IB receptor (BMPR-IB), and TbetaR-II/ActR-IIB, containing the extracellular domain of TGF-beta type II receptor (TbetaR-II) and the intracellular domain of activin type IIB receptor (ActR-IIB). In the presence of TGF-beta1, TbetaR-I/BMPR-IB and TbetaR-II/ActR-IIB formed heteromeric complexes with wild-type TbetaR-II and TbetaR-I, respectively, upon stable transfection in mink lung epithelial cell lines. We show that TbetaR-II/ActR-IIB restored the responsiveness upon transfection in mutant cell lines lacking functional TbetaR-II with respect to TGF-beta-mediated activation of a transcriptional signal, extracellular matrix formation, growth inhibition, and Smad phosphorylation. Moreover, TbetaR-I/BMPR-IB and TbetaR-II/ActR-IIB formed a functional complex in response to TGF-beta and induced phosphorylation of Smad1. However, complex formation is not enough for signal propagation, which is shown by the inability of TbetaR-I/BMPR-IB to restore responsiveness to TGF-beta in cell lines deficient in functional TbetaR-I. The fact that the TGF-beta1-induced complex between TbetaR-II/ActR-IIB and TbetaR-I stimulated endogenous Smad2 phosphorylation, a TGF-beta-like response, is in agreement with the current model for receptor activation in which the type I receptor determines signal specificity.
Journal of Biological Chemistry, 1998
Members of the transforming growth factor- (TGF-) family transmit signals from membrane to nucleus via intracellular proteins known as Smads. A subclass of Smad proteins has recently been identified that antagonize, rather than transduce, TGF- family signals. Smad7, for example, binds to and inhibits signaling downstream of TGF- receptors. Here we report that the C-terminal MAD homology domain of murine Smad7 (mSmad7) is sufficient for both of these activities. In addition, we show that mSmad7 interacts with activated bone morphogenetic protein (BMP) type I receptors (BMPR-Is), inhibits BMPR-I-mediated Smad phosphorylation, and phenocopies the effect of known BMP antagonists when overexpressed in ventral cells of Xenopus embryos. Xenopus Smad7 (XSmad7, previously termed Smad8) and mSmad7 are nearly identical within their bioactive C-domain, but have quite distinct Ndomains. We found that XSmad7, similar to mSmad7, interacted with BMP and TGF- type I receptors and inhibited receptor-mediated phosphorylation of downstream signal-transducing Smads. However, XSmad7 is a less efficient inhibitor of TR-I-mediated responses in mammalian cells than is mSmad7. Furthermore, overexpression of XSmad7 in Xenopus embryos produces patterning defects that are not observed following overexpression of mSmad7, suggesting that mSmad7 and XSmad7 may preferentially target distinct signaling pathways. Our results are consistent with the possibility that the C-domain of antagonistic Smads is an effector domain whereas the N-domain may confer specificity for distinct signaling pathways.
The Life Story of TGFβs superfamily: from the beginning to the end
International Journal of Aquatic Biology, 2020
TGFβ-superfamily consists a plethora of extracellular growth factors, modulating developmental procedures and homeostasis in vertebrates and invertebrates. TGFβ-superfamily ligands, synthesized as the large inactive precursors, transform into active ligands following by their interaction with extracellular proteolytic enzymes. Principally, TGFβs ligation to their responsive receptors can trigger two distinct transduction cascades, including 1- SMAD dependent or canonical pathway and 2- SMAD independent or non-canonical ones. R-SMADs are substrates for the type I receptors, as their GS domains act as a docking site for R-SMADs. In the canocical pathway, upon phosphorylation of SSXS of MH2, two phosphorylated-SMADs (P-SMADs) in accordance with receptor tetra-dimerization, homo or heterodimerize and then form a trimer complex by SMAD4. The trimers translocate to the nucleus, where in association with other transcription factors (activators and repressors) modulate their target genes ex...