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Smad signaling antagonizes STAT5-mediated gene transcription and mammary epithelial cell differentiation

Eftihia Cocolakis1, Meiou Dai1, Loren Drevet1

  • 1Hormones and Cancer Research Unit, Department of Medicine, Royal Victoria Hospital, McGill University, Montreal, Quebec H3A 1A1, Canada.

The Journal of Biological Chemistry
|November 21, 2007
PubMed

Insights

Transforming growth factor-beta (TGFbeta)/Smad signaling antagonizes prolactin/JAK/STAT pathways in mammary glands. Activated Smads block STAT5 co-activator binding, inhibiting mammary gland growth and differentiation.

Area of Science:

  • Cellular signaling pathways
  • Mammary gland biology
  • Molecular mechanisms of gene regulation

Background:

  • The transforming growth factor-beta (TGFbeta)/Smad and prolactin/JAK/STAT pathways are crucial for mammary epithelial tissue development and function.
  • Opposing roles of these pathways in mammary gland development are known, but their interaction remains unclear.

Purpose of the Study:

  • To elucidate the regulatory cross-talk between Smad and STAT signaling pathways in mammary epithelial cells.
  • To investigate how TGFbeta signaling influences prolactin-mediated JAK/STAT signaling.
  • To understand the molecular basis of antagonism between these pathways.

Main Methods:

  • Investigated the effects of TGFbeta and activin on JAK/STAT signaling in mammary epithelial cells.
  • Analyzed the impact of Smad activation on STAT5 transactivation and target gene expression (beta-casein, cyclin D1).
  • Examined the interaction between activated Smads, STAT5, and CREB-binding protein.

Main Results:

  • TGFbeta-induced Smad signaling was found to antagonize prolactin-mediated JAK/STAT signaling.
  • Activin and TGFbeta efficiently blocked STAT5 signaling and beta-casein expression.
  • Activated Smads directly inhibited STAT5 transactivation by blocking its association with CREB-binding protein.
  • This antagonism blocked mammary gland growth, differentiation, and lactation.

Conclusions:

  • A novel cross-talk mechanism exists where Smad signaling inhibits JAK/STAT signaling in mammary epithelial cells.
  • Smad activation blocks STAT5-mediated transcription of key genes like beta-casein and cyclin D1.
  • This pathway interaction is critical for regulating mammary gland development, differentiation, and lactation.

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