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Differential effect of Rac and Cdc42 on p38 kinase activity and cell cycle progression of nonadherent primary mouse
1Institut de Génétique Moléculaire, CNRS, UMR 5535, IFR 24, 1919 route de Mende, 34293 Montpellier cedex 5, France. philips@igm.cnrs-mop.fr
Abstract:
The Rho GTPases play an important role in transducing signals linking plasma membrane receptors to the organization of the cytoskeleton and also regulate gene transcription. Here, we show that expression of constitutively active Ras or Cdc42, but not RhoA, RhoG, and Rac1, is sufficient to cause anchorage-independent cell cycle progression of mouse embryonic fibroblasts. However, in anchorage free conditions, whereas activation of either Cdc42 or Ras results in cyclin A transcription and cell cycle progression, Cdc42 is not required for Ras-mediated cyclin A induction, and the two proteins act in a synergistic manner in this process. Surprisingly, the ability of Cdc42 to induce p38 MAPK activity in suspended mouse embryonic fibroblast was impaired. Moreover, inhibition of p38 activity allowed Rac1 to induce anchorage-independent cyclin A transcription, indicating that p38 MAPK has an inhibitory function on cell cycle progression of primary fibroblasts. Finally, a Rac mutant, which is unable to induce lamellipodia and focal complex formation, promoted cyclin A transcription in the presence of SB203580, suggesting that the organization of the cytoskeleton is not required for anchorage-independent proliferation. This demonstrates a novel function for Cdc42, distinct from that of Rac1, in the control of cell proliferation.
Insights
Ras and Cdc42 GTPases promote cell cycle progression independent of cell adhesion. Cdc42 has a novel role distinct from Rac1 in controlling proliferation, with p38 MAPK inhibiting this process.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Rho GTPases are key regulators of cytoskeleton organization and gene transcription.
- Their role in anchorage-independent cell proliferation is not fully understood.
Purpose of the Study:
- To investigate the specific roles of Rho GTPases, including Ras, Cdc42, RhoA, RhoG, and Rac1, in promoting anchorage-independent cell cycle progression.
- To elucidate the signaling pathways involved in Ras- and Cdc42-mediated cell proliferation.
Main Methods:
- Expression of constitutively active Rho GTPases in mouse embryonic fibroblasts.
- Analysis of cyclin A transcription and cell cycle progression under anchorage-free conditions.
- Investigation of p38 MAPK activity and its role using inhibitors like SB203580.
- Utilizing Rac mutants to assess the role of cytoskeleton organization.
Main Results:
- Constitutively active Ras or Cdc42, but not RhoA, RhoG, or Rac1, induced anchorage-independent cell cycle progression.
- Both Ras and Cdc42 activated cyclin A transcription synergistically, with Cdc42 not being essential for Ras-mediated induction.
- Cdc42's ability to induce p38 MAPK activity was impaired in suspended cells.
- Inhibition of p38 MAPK enabled Rac1 to induce anchorage-independent cyclin A transcription.
- A Rac mutant defective in lamellipodia formation still promoted cyclin A transcription when p38 was inhibited, suggesting cytoskeleton organization is not required.
Conclusions:
- Ras and Cdc42 play distinct roles in promoting anchorage-independent cell proliferation.
- p38 MAPK acts as an inhibitor of cell cycle progression in primary fibroblasts.
- Cytoskeleton organization is not essential for anchorage-independent proliferation mediated by these GTPases.