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Analysis of Cell Cycle Position in Mammalian Cells
12:19

Analysis of Cell Cycle Position in Mammalian Cells

Published on: January 21, 2012

Breast cancer cell proliferation is inhibited by BAD: regulation of cyclin D1

Romaine Fernando1, James S Foster1, Amber Bible1

  • 1Graduate School of Medicine, University of Tennessee Medical Center, Knoxville, Tennessee 37920.

The Journal of Biological Chemistry
|August 3, 2007
PubMed

Insights

The proapoptotic protein BAD regulates cell cycle progression in breast cancer cells by inhibiting the G1 to S phase transition. This occurs independently of apoptosis, involving direct binding to c-Jun and impacting cyclin D1 expression.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • The proapoptotic protein BAD, a member of the BCL2 family, has functions beyond apoptosis regulation.
  • Emerging evidence suggests roles in other cellular processes.

Purpose of the Study:

  • To investigate the role of BAD in cell cycle regulation, specifically the G1 to S phase transition.
  • To elucidate the molecular mechanisms underlying BAD's effect on cell cycle progression in breast cancer cells.

Main Methods:

  • Overexpression and inhibition of BAD in MCF7 breast cancer cells.
  • Analysis of cell cycle transit, cell growth, and cyclin D1 expression.
  • Chromatin immunoprecipitation assays to determine BAD localization at the cyclin D1 promoter.
  • Investigation of BAD's interaction with c-Jun and AP1 activity.
  • Assessment of BAD's role in estrogen-stimulated proliferation.

Main Results:

  • BAD overexpression inhibited G1 to S phase transition, cell growth, and cyclin D1 expression.
  • BAD directly binds to c-Jun, inhibiting AP1 transcriptional activity at the cyclin D1 promoter.
  • Estrogen stimulation displaced BAD from the promoter, while BAD overexpression blocked estrogen-induced proliferation.
  • Inhibition of endogenous BAD increased proliferation, DNA synthesis, and cyclin D1 levels.
  • BAD's cell cycle function requires specific serine residues (Ser75 and Ser99) and is phosphorylation-dependent.

Conclusions:

  • BAD plays a novel role in regulating the G1 to S phase transition in breast cancer cells, independent of its apoptotic function.
  • BAD's mechanism involves direct interaction with c-Jun, modulating AP1 activity at the cyclin D1 promoter.
  • The phosphorylation state of BAD is critical for its nuclear localization and cell cycle regulatory functions.

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