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Transforming growth factor beta signaling through Smad1 in human breast cancer cells

X Liu1, J Yue, R S Frey

  • 1Department of Pharmacology, Pennsylvania State University College of Medicine, Hershey 17033, USA.

Cancer Research
|October 27, 1998
PubMed

Insights

Transforming growth factor beta (TGF-beta) and bone morphogenetic proteins (BMPs) can both signal through Smad1. This study shows TGF-beta regulates Smad1 phosphorylation, nuclear translocation, and transcriptional activity in breast cancer cells.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Cancer research

Background:

  • Smad1 is known to mediate bone morphogenetic protein (BMP) signaling.
  • Previous research suggested Smad1 does not respond to transforming growth factor beta (TGF-beta).
  • Hs578T human breast cancer cells are responsive to both TGF-beta and BMPs.

Purpose of the Study:

  • To investigate TGF-beta's regulation of Smad1.
  • To examine Smad1 phosphorylation, Smad1-Smad4 hetero-oligomerization, nuclear translocation, and transcriptional activation.
  • To determine if TGF-beta signals through Smad1 in breast cancer cells.

Main Methods:

  • Utilized epitope-tagged Smad1 and specific antibodies to detect phosphorylation.
  • Assessed Smad1-Smad4 hetero-oligomerization in response to TGF-beta3 and BMP2.
  • Visualized Smad1 nuclear translocation using green fluorescent protein (GFP) tagging in live cells.
  • Measured transcriptional activation using a 3TP-luciferase reporter assay.

Main Results:

  • Smad1 phosphorylation was induced by both TGF-beta3 and BMP2 in Hs578T cells.
  • Both TGF-beta3 and BMP2 enhanced Smad1-Smad4 hetero-oligomerization.
  • TGF-beta and BMP2 stimulation led to significant nuclear accumulation of Smad1.
  • Smad1 expression increased 3TP-luciferase activity, which was further potentiated by TGF-beta treatment.

Conclusions:

  • TGF-beta, similar to BMPs, can signal through Smad1.
  • TGF-beta regulates Smad1 activity, including its phosphorylation, hetero-oligomerization, nuclear translocation, and transcriptional function.
  • These findings reveal a novel signaling mechanism for TGF-beta in breast cancer cells involving Smad1.

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