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Prediction and Validation of Gene Regulatory Elements Activated During Retinoic Acid Induced Embryonic Stem Cell Differentiation
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Elevated retinoic acid receptor beta(4) protein in human breast tumor cells with nuclear and cytoplasmic localization

K M Sommer1, L I Chen, P M Treuting

  • 1Department of Pathology, University of Washington, Seattle, WA 98195, USA.

Proceedings of the National Academy of Sciences of the United States of America
|July 21, 1999
PubMed

Insights

Retinoic acid receptor beta(4) (RARbeta(4)) protein, not the expected RARbeta(2), is elevated in breast tumor cells. This RARbeta(4) protein may act as a dominant-negative repressor, inhibiting normal RAR functions and promoting breast cancer growth.

Area of Science:

  • Molecular Biology
  • Cancer Research
  • Cell Biology

Background:

  • Retinoic acid receptor beta(2) (RARbeta(2)) is known to inhibit breast cancer cells.
  • RARbeta(2) expression is often lost in primary breast cancer.
  • RARbeta(2) mRNA is down-regulated in breast tumor cells.

Purpose of the Study:

  • To investigate the discrepancy between RARbeta(2) mRNA down-regulation and protein expression in breast cancer.
  • To identify the specific RARbeta protein isoform expressed in breast tumor cells.
  • To characterize the function of the identified RARbeta isoform in breast cancer.

Main Methods:

  • Western blot analysis to detect RARbeta protein expression in breast tumor cell lines and normal mammary epithelial cells.
  • RNA sequencing and protein analysis to identify the specific RARbeta transcript and its translation product.
  • Immunofluorescence microscopy to determine the subcellular localization of the RARbeta protein.
  • Structural analysis of the identified RARbeta protein.

Main Results:

  • Expression of an RARbeta protein, identified as the human RARbeta(4) transcript's translation product, was elevated in five out of five breast tumor cell lines compared to normal cells.
  • Human RARbeta(4) protein lacks a complete DNA-binding domain and a ligand-independent transactivation domain.
  • RARbeta(4) protein was found in the cytoplasm and subnuclear compartments.
  • Expression of RARbeta(4) is significantly elevated in breast tumor cell lines.

Conclusions:

  • The elevated expression of human RARbeta(4) in breast tumor cells suggests a role in breast cancer development.
  • RARbeta(4) protein's structural characteristics and localization support its function as a dominant-negative repressor.
  • RARbeta(4) may interfere with RAR-mediated growth suppression pathways, contributing to uncontrolled cell proliferation in breast cancer.

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