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Receptor-associated Mad homologues synergize as effectors of the TGF-beta response

Y Zhang1, X Feng, R We

  • 1Department of Growth and Development, University of California at San Francisco, 94143-0640, USA.

Nature
|September 12, 1996
PubMed

Insights

Human Mad homologues (hMAD-3 and hMAD-4) are key effectors in transforming growth factor-beta (TGF-beta) signaling pathways. These proteins regulate cell proliferation and tissue differentiation, with hMAD-4 also functioning as a tumor suppressor.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Genetics

Background:

  • Transforming growth factor-beta (TGF-beta) is a crucial protein family regulating cell proliferation and differentiation.
  • TGF-beta and related factors signal through serine/threonine kinase receptors, but signal transduction mechanisms remain unclear.
  • Mad proteins are essential for Dpp signaling in Drosophila.

Purpose of the Study:

  • To identify and characterize human homologues of Mad proteins involved in TGF-beta signaling.
  • To investigate the function of these human Mad homologues (hMADs) in TGF-beta-like responses.
  • To determine the role of hMAD-4/DPC-4 as a potential tumor suppressor.

Main Methods:

  • Isolation of complementary DNAs (cDNAs) for four human Mad homologues.
  • Co-expression of hMAD-3 and hMAD-4 to assess TGF-beta-like responses.
  • Generation of truncated hMAD-3 and hMAD-4 mutants to study dominant-negative inhibition.
  • Analysis of hMAD activity regulation by TGF-beta receptors and ligand-bound receptor complex association.

Main Results:

  • Four human Mad homologues were identified, including hMAD-4, which is identical to the candidate tumor suppressor DPC-4.
  • hMAD-3 and hMAD-4 synergistically induced ligand-independent TGF-beta-like responses.
  • Truncated hMAD-3 and hMAD-4 acted as dominant-negative inhibitors of TGF-beta signaling.
  • hMAD-3, but not hMAD-4, was phosphorylated and associated with the ligand-bound TGF-beta receptor complex, indicating differential regulation.

Conclusions:

  • hMAD-3 and hMAD-4 are identified as critical effectors in the transforming growth factor-beta signaling pathway.
  • The study demonstrates a functional role for DPC-4/hMAD-4 as a tumor suppressor.
  • These findings elucidate key components and mechanisms in TGF-beta signal transduction.

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