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A component of the ARC/Mediator complex required for TGF beta/Nodal signalling

Yoichi Kato1, Raymond Habas, Yu Katsuyama

  • 1Division of Neuroscience, Children's Hospital, Department of Neurology, Harvard Medical School, Boston, Massachusetts 02115, USA.

Nature
|August 9, 2002
PubMed

Insights

ARC105 is crucial for TGF beta/Activin/Nodal/Smad2/3 signaling pathways, linking them to gene transcription. This activator-recruited cofactor (ARC) complex component regulates development and tumorigenesis by mediating Smad-dependent gene expression.

Area of Science:

  • Molecular Biology
  • Developmental Biology
  • Cell Signaling

Background:

  • Transforming growth factor beta (TGF beta) cytokines like Nodal, Activin, and bone morphogenetic protein (BMP) are vital in development and cancer.
  • TGF beta pathways utilize Smad proteins to regulate gene expression, with distinct Smad complexes mediating different signaling routes.
  • The precise mechanisms by which Smad complexes control specific gene expression remain incompletely understood.

Purpose of the Study:

  • To investigate the role of ARC105, a component of the activator-recruited cofactor (ARC) or Mediator complex, in TGF beta superfamily signaling.
  • To determine if ARC105 specifically mediates TGF beta/Activin/Nodal/Smad2/3 signaling distinct from BMP/Smad1 signaling.
  • To elucidate the mechanism by which ARC105 links Smad signaling to transcriptional activation.

Main Methods:

  • Studied the effect of ARC105 expression and depletion on TGF beta/Activin/Nodal/Smad2/3 and BMP/Smad1 signaling in Xenopus laevis embryos and human cells.
  • Assessed ARC105's interaction with Smad2/3-Smad4 complexes.
  • Examined ARC105 recruitment to gene promoters in response to TGF beta signaling.

Main Results:

  • ARC105 expression enhanced Activin/Nodal/Smad2 signaling in Xenopus embryos, promoting axis duplication and mesendoderm differentiation, and boosted TGF beta response in human cells.
  • Depletion of ARC105 inhibited TGF beta/Activin/Nodal/Smad2/3 signaling and Xenopus axis formation but did not affect BMP/Smad1 signaling.
  • ARC105 protein was found to bind Smad2/3-Smad4 complexes upon TGF beta stimulation and was recruited to relevant gene promoters in a Smad2-dependent manner.

Conclusions:

  • ARC105 is an essential component of the ARC/Mediator complex that specifically links TGF beta/Activin/Nodal/Smad2/3 signaling pathways to transcriptional activation.
  • ARC105 plays a critical role in regulating developmental processes and potentially tumorigenesis through its function in Smad-dependent gene regulation.
  • This study identifies a key molecular link between Smad signaling complexes and the transcriptional machinery, clarifying pathway specificity.

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