Non-muscle Myosin II acts as a negative feedback mediator to control cell contraction dynamics in adherent cells

Pulsatile cell contraction dynamics play a crucial role in tissue and cell morphogenesis. Previously, we identified a signal network in adherent mammalian cells, that can transduce mechanical signals via cell contraction pulses, which are generated by fast positive feedback amplification of the signal molecule Rho via GEF-H1, and by slow negative feedback that depends on actomyosin. However, the precise mechanism was still unclear, in particular if it is mediated via actin or Myosin-based components. Here, using numerical simulations, we predicted that network dynamics are strongly reduced both by Myosin II inhibition and by constitutive, Rho-activity independent Myosin II activation. We confirmed these predictions experimentally by direct inhibition of Myosin II activity and by constant, non-dynamic activation via constitutively active ROCK1. Furthermore, constitutive activation of Myosin II leads to an accumulation of Myosin II next to the nuclei which locally inhibited Rho activity dynamics. Finally, light-induced recruitment of ROCK1 to the plasma membrane strongly activated Myosin II, and at the same time depleted Actin and inhibited Rho activity. We conclude that negative feedback in the cell contraction signal network of adherent mammalian cells is implemented by Myosin II, and that actin is not the predominant inhibitory factor in this system.