The MAD-Related Protein Smad7 Associates with the TGFβ Receptor and Functions as an Antagonist of TGFβ Signaling

Abstract TGFβ 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 TGFβ signaling. Smad7 prevents TGFβ-dependent formation of Smad2/Smad4 complexes and inhibits the nuclear accumulation of Smad2. Smad7 interacts stably with the activated TGFβ 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 TGFβ family receptors.

[1]  J. Massagué.  TGFβ Signaling: Receptors, Transducers, and Mad Proteins , 1996, Cell.

[2]  Xin Chen,et al.  A transcriptional partner for MAD proteins in TGF-β signalling , 1996, Nature.

[3]  J. Massagué,et al.  Activation of signalling by the activin receptor complex , 1996, Molecular and cellular biology.

[4]  R. W. Padgett,et al.  Caenorhabditis elegans genes sma-2, sma-3, and sma-4 define a conserved family of transforming growth factor beta pathway components. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[5]  A. Dehejia,et al.  Serine Phosphorylation, Chromosomal Localization, and Transforming Growth Factor-β Signal Transduction by Human bsp-1* , 1996, The Journal of Biological Chemistry.

[6]  P. Hoodless,et al.  MADR1, a MAD-Related Protein That Functions in BMP2 Signaling Pathways , 1996, Cell.

[7]  G. Thomsen.  Xenopus mothers against decapentaplegic is an embryonic ventralizing agent that acts downstream of the BMP-2/4 receptor. , 1996, Development.

[8]  C. J. Gimeno,et al.  Vascular MADs: two novel MAD-related genes selectively inducible by flow in human vascular endothelium. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[9]  J. Graff,et al.  Xenopus Mad Proteins Transduce Distinct Subsets of Signals for the TGFβ Superfamily , 1996, Cell.

[10]  J. Massagué,et al.  Complementation between kinase‐defective and activation‐defective TGF‐beta receptors reveals a novel form of receptor cooperativity essential for signaling. , 1996, The EMBO journal.

[11]  Anita B. Roberts,et al.  Tumor suppressor activity of the TGF-β pathway in human cancers , 1996 .

[12]  Scott E. Kern,et al.  DPC4, A Candidate Tumor Suppressor Gene at Human Chromosome 18q21.1 , 1996, Science.

[13]  J. Sekelsky,et al.  Genetic characterization and cloning of mothers against dpp, a gene required for decapentaplegic function in Drosophila melanogaster. , 1995, Genetics.

[14]  Irene L Andrulis,et al.  MADR2 Maps to 18q21 and Encodes a TGFβ–Regulated MAD–Related Protein That Is Functionally Mutated in Colorectal Carcinoma , 1996, Cell.

[15]  P. Hoodless,et al.  MADR2 Is a Substrate of the TGFβ Receptor and Its Phosphorylation Is Required for Nuclear Accumulation and Signaling , 1996, Cell.

[16]  J. Wrana,et al.  Signal transduction by members of the transforming growth factor-β superfamily , 1996 .

[17]  J. Massagué,et al.  GS domain mutations that constitutively activate T beta R‐I, the downstream signaling component in the TGF‐beta receptor complex. , 1995, The EMBO journal.

[18]  T. Musci,et al.  The tumor suppressor Smad4/DPC 4 as a central mediator of Smad function , 1997, Current Biology.

[19]  J. Massagué,et al.  A human Mad protein acting as a BMP-regulated transcriptional activator , 1996, Nature.

[20]  Jeffrey L. Wrana,et al.  Mechanism of activation of the TGF-β receptor , 1994, Nature.

[21]  Jeffrey L. Wrana,et al.  TGFβ signals through a heteromeric protein kinase receptor complex , 1992, Cell.

[22]  J. Massagué,et al.  Partnership between DPC4 and SMAD proteins in TGF-β signalling pathways , 1996, Nature.

[23]  J. Massagué,et al.  The TGF-beta family mediator Smad1 is phosphorylated directly and activated functionally by the BMP receptor kinase. , 1997, Genes & development.

[24]  R. Derynck,et al.  Intracellular signalling: The Mad way to do it , 1996, Current Biology.

[25]  R. Derynck,et al.  Receptor-associated Mad homologues synergize as effectors of the TGF-β response , 1996, Nature.

[26]  J. Wrana,et al.  MAD-related proteins in TGF-β signalling , 1996 .

[27]  Xiao-Fan Wang,et al.  Mammalian dwarfins are phosphorylated in response to transforming growth factor beta and are implicated in control of cell growth. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[28]  J. Sambrook,et al.  Molecular Cloning: A Laboratory Manual , 2001 .

[29]  M. Gimbrone,et al.  Identification of vascular endothelial genes differentially responsive to fluid mechanical stimuli: cyclooxygenase-2, manganese superoxide dismutase, and endothelial cell nitric oxide synthase are selectively up-regulated by steady laminar shear stress. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[30]  J. Baker,et al.  A novel mesoderm inducer, Madr2, functions in the activin signal transduction pathway. , 1996, Genes & development.