Bistability in the Rac1, PAK, and RhoA Signaling Network Drives Actin Cytoskeleton Dynamics and Cell Motility Switches

Summary

Dynamic interactions between RhoA and Rac1, members of the Rho small GTPase family, play a vital role in the control of cell migration. Using predictive mathematical modeling, mass spectrometry-based quantitation of network components, and experimental validation in MDA-MB-231 mesenchymal breast cancer cells, we show that a network containing Rac1, RhoA, and PAK family kinases can produce bistable, switch-like responses to a graded PAK inhibition. Using a small chemical inhibitor of PAK, we demonstrate that cellular RhoA and Rac1 activation levels respond in a history-dependent, bistable manner to PAK inhibition. Consequently, we show that downstream signaling, actin dynamics, and cell migration also behave in a bistable fashion, displaying switches and hysteresis in response to PAK inhibition. Our results demonstrate that PAK is a critical component in the Rac1-RhoA inhibitory crosstalk that governs bistable GTPase activity, cell morphology, and cell migration switches.

Graphical Abstract

Highlights

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  RhoA and Rac1 are linked by a double-negative feedback loop

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  A model predicts bistability of the system within a physiological parameter range

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  Rac1 and RhoA activity is bistable in response to PAK inhibition

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  Actin dynamics, cell morphology, and migration show hysteresis upon PAK inhibition

Abstract

A mathematical model and experiments demonstrate that RhoA, Rac1, actin dynamics, cell morphology, and migration respond in a bistable manner to perturbations.