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Rac-GAP-dependent inhibition of breast cancer cell proliferation by {beta}2-chimerin

Chengfeng Yang1, Ying Liu, Federico Coluccio Leskow

  • 1Department of Pharmacology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6160, USA.

The Journal of Biological Chemistry
|May 3, 2005
PubMed

Insights

Beta2-chimerin, a diacylglycerol-regulated protein, inhibits breast cancer cell proliferation by inactivating Rac GTPase. Its reduced levels in tumors suggest a tumor-suppressive role.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Oncology

Background:

  • Beta2-chimerin is a poorly characterized diacylglycerol-regulated protein.
  • It contains a Rac-GTPase-activating protein (GAP) domain crucial for Rac GTPase inactivation.
  • Its role in cancer progression and proliferation signaling is largely unknown.

Purpose of the Study:

  • To investigate the function of beta2-chimerin in breast cancer proliferation.
  • To elucidate the molecular mechanisms underlying beta2-chimerin's effects on cell cycle progression.
  • To determine the role of its Rac-GAP activity in these processes.

Main Methods:

  • Analysis of beta2-chimerin expression in breast cancer cell lines and tumors.
  • Adenoviral delivery of beta2-chimerin into MCF-7 breast cancer cells.
  • Assessment of cell proliferation, cell cycle arrest, Rac-GTP levels, cyclin D1 expression, and retinoblastoma dephosphorylation.
  • Studies using mutated beta2-chimerin and cells expressing constitutively active Rac or RhoA.

Main Results:

  • Beta2-chimerin messenger levels are significantly down-regulated in human breast cancer.
  • Adenoviral delivery of beta2-chimerin inhibited MCF-7 cell proliferation and induced G(1) cell cycle arrest.
  • These effects were mediated by reduced Rac-GTP levels, decreased cyclin D1 expression, and retinoblastoma dephosphorylation, dependent on Rac-GAP activity.
  • Cells expressing active Rac were insensitive to beta2-chimerin's inhibitory effects.

Conclusions:

  • Beta2-chimerin acts as a tumor suppressor in breast cancer by inhibiting proliferation.
  • Rac GTPase plays a critical role in breast cancer cell proliferation.
  • Diacylglycerol-regulated non-protein kinase C pathways may negatively regulate proliferation via Rho GTPases.

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