Raf-MEK-Erk cascade in anoikis is controlled by Rac1 and Cdc42 via Akt

Signals from the extracellular matrix are essential for the survival of man y cell types. Dominant-negative mutants of two members of Rho family GTPase s, 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 signa l-regulated mitogen-activated protein kinases (Erks). Here we characterize the proapoptotic Erk signal and show that it differs from the classically o bserved survival-promoting one by the intensity of the kinase activation. T he disappearance of the GTP-bound forms of Rac1 and Cdc42 gives rise to pro apoptotic, moderate activation of the Raf-MEK-Erk cascade via a signaling p athway involving the kinases phosphatidlyinositol 3-kinase and Akt. Moreove r, concomitant activation of p53 and inhibition of Akt are both necessary a nd sufficient to signal anoikis in primary fibroblasts. Our data demonstrat e that the GTPases of the Rho family control three major components of cell ular signal transduction, namely, p53, Akt, and Erks, which collaborate in the induction of apoptosis due to the loss of anchorage.