Raf-MEK-Erk cascade in anoikis is controlled by Rac1 and Cdc42 via Akt
1Institut de Génétique Moléculaire, CNRS UMR5535, F-34293 Montpellier Cedex 5, France.
Abstract:
Signals from the extracellular matrix are essential for the survival of many cell types. Dominant-negative mutants of two members of Rho family GTPases, Rac1 and Cdc42, mimic the loss of anchorage in primary mouse fibroblasts and are potent inducers of apoptosis. This pathway of cell death requires the activation of both the p53 tumor suppressor and the extracellular signal-regulated mitogen-activated protein kinases (Erks). Here we characterize the proapoptotic Erk signal and show that it differs from the classically observed survival-promoting one by the intensity of the kinase activation. The disappearance of the GTP-bound forms of Rac1 and Cdc42 gives rise to proapoptotic, moderate activation of the Raf-MEK-Erk cascade via a signaling pathway involving the kinases phosphatidlyinositol 3-kinase and Akt. Moreover, concomitant activation of p53 and inhibition of Akt are both necessary and sufficient to signal anoikis in primary fibroblasts. Our data demonstrate that the GTPases of the Rho family control three major components of cellular signal transduction, namely, p53, Akt, and Erks, which collaborate in the induction of apoptosis due to the loss of anchorage.
Insights
Loss of cell anchorage triggers apoptosis by activating p53 and moderate Erk signaling, involving phosphatidlyinositol 3-kinase and Akt. Rho GTPases control these pathways, crucial for cell death.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Extracellular matrix signals are vital for cell survival.
- Loss of anchorage can induce apoptosis (anoikis).
- Rho family GTPases (Rac1, Cdc42) regulate cell survival and death pathways.
Purpose of the Study:
- To characterize the proapoptotic extracellular signal-regulated kinase (Erk) signal.
- To elucidate the signaling pathway linking Rho GTPases to anoikis.
- To identify key molecular components involved in anchorage-loss-induced apoptosis.
Main Methods:
- Utilized dominant-negative mutants of Rac1 and Cdc42 in primary mouse fibroblasts.
- Investigated the activation of p53, phosphatidlyinositol 3-kinase (PI3K), Akt, and the Raf-MEK-Erk cascade.
- Analyzed the intensity of kinase activation to differentiate survival and death signals.
Main Results:
- Loss of Rac1 and Cdc42 GTP-bound forms induced apoptosis.
- A proapoptotic, moderate activation of the Raf-MEK-Erk cascade was observed.
- This Erk activation involved PI3K and Akt signaling.
- Concomitant activation of p53 and inhibition of Akt were necessary and sufficient for anoikis.
Conclusions:
- Rho family GTPases (Rac1, Cdc42) regulate p53, Akt, and Erk signaling pathways.
- These pathways collaborate to induce apoptosis upon loss of anchorage.
- The intensity of Erk activation distinguishes survival from apoptotic signaling.
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