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Brca1 inactivation induces p27(Kip1)-dependent cell cycle arrest and delayed development in the mouse mammary gland

Andrew J Deans1, Kaylene J Simpson, Melanie K Trivett

  • 1Molecular Oncology Laboratory, Trescowthick Research Laboratories, Peter MacCallum Cancer Centre, St Andrew's Place, East Melbourne 3002, Australia.

Oncogene
|June 23, 2004
PubMed

Insights

Loss of BRCA1 function in breast cancer may increase p27 protein levels, inhibiting cell proliferation. Reducing p27 enhances proliferation in BRCA1-deficient cells, revealing a key cell cycle regulation mechanism.

Area of Science:

  • Oncology
  • Cell Biology
  • Genetics

Background:

  • BRCA1 gene mutations are linked to hereditary breast cancer.
  • Loss of p27(Kip1) (p27) expression is common in BRCA1-related breast cancers.
  • This suggests a potential functional link between BRCA1 and p27.

Purpose of the Study:

  • To investigate the epistatic interaction between BRCA1 and p27.
  • To determine if BRCA1 loss-of-function affects p27 expression and cell cycle control.
  • To explore the role of p27 as a mediator of cell cycle arrest in BRCA1-deficient cells.

Main Methods:

  • Examined p27 expression in mice with a dominant-negative Brca1 allele (MMTV-trBr).
  • Assessed p27 heterozygote effects on MMTV-trBrca1 mice mammary development and cell proliferation.
  • Analyzed p27 mRNA and protein levels in human breast cancer cells (MCF7, HCC1937) with altered BRCA1 status (RNAi, deficiency).

Main Results:

  • MMTV-trBr mice showed increased p27 protein, delayed mammary development, and reduced proliferation.
  • In p27 heterozygote MMTV-trBrca1 mice, increased S phase cells and normal mammary development were observed.
  • p27 was the sole altered protein in the cyclin-cyclin-dependent kinase network.
  • Human cells with BRCA1 disruption (RNAi or deficiency) exhibited elevated p27 mRNA levels.

Conclusions:

  • Disruption of BRCA1 function induces an increase in p27, which acts to inhibit cellular proliferation.
  • p27 appears to be a central mediator of cell cycle arrest in response to BRCA1 loss.
  • Reducing p27 levels enhances proliferation in the absence of functional BRCA1, highlighting its critical role in cell cycle regulation.

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