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FoxO1a can alter cell cycle progression by regulating the nuclear localization of p27kip in granulosa cells

Melissa A Cunningham1, Qin Zhu, James M Hammond

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

Molecular Endocrinology (Baltimore, Md.)
|April 17, 2004
PubMed

Insights

Forkhead box O1a (FoxO1a) regulates granulosa cell proliferation by controlling cell cycle entry. FoxO1a influences p27Kip1 protein localization, impacting cell cycle progression.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Endocrinology

Background:

  • Forkhead transcription factors (FOXO) are key regulators of cell proliferation and survival, downstream of the phosphatidylinositol 3-kinase pathway.
  • FOXO activation typically induces cell cycle arrest, often via the cell-cycle inhibitor p27Kip1.
  • Granulosa cells undergo rapid proliferation during ovarian follicle development, making them a relevant model for studying cell cycle control.

Purpose of the Study:

  • To investigate the role of FoxO1a in regulating the G1/S cell cycle transition in granulosa cells.
  • To determine the mechanism by which FoxO1a influences cell cycle progression in these cells.

Main Methods:

  • Overexpression of a dominant-negative FoxO1a mutant (Foxo1a-Delta256) in granulosa cells.
  • Assessment of S-phase entry using DNA content and bromodeoxyuridine incorporation assays.
  • Analysis of p27Kip1 protein localization within cells.

Main Results:

  • Overexpressing dominant-negative FoxO1a caused a significant increase in S-phase granulosa cells (>8-fold).
  • This effect was not dependent on the transcriptional activation of p27Kip1.
  • Impaired FoxO1a activity led to increased cytosolic localization of p27Kip1, suggesting altered nuclear import.

Conclusions:

  • FoxO1a is a critical regulator of the G1/S transition in granulosa cells.
  • FoxO1a controls cell cycle entry not solely through p27Kip1 transactivation, but by modulating p27Kip1 compartmentalization.
  • This study reveals a novel mechanism where FoxO1a regulates p27Kip1 nuclear localization to control cell proliferation.

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