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

Local cell contraction dynamics play a crucial role in tissue and cell morphogenesis. Contractions near the cell edge drive highly dynamic cell shape changes during cell migration and contraction pulses in central cell attachment areas are involved in mechanotransduction. Previously, we identified a signal network in adherent mammalian cells, that generates mechanosensitive contraction pulses, in which the cell contraction regulator Rho is controlled by fast positive feedback amplification via GEF-H1, and by a slow negative feedback that depends on actomyosin activity. However, the precise mechanism of this negative feedback in adherent cells, in particular if it is mediated via actin or Myosin-based components, was still unclear. Here, using numerical simulations of this system, we predicted that the cell contraction signal network dynamics are strongly inhibited both by inhibition and by constitutive activation of the actomyosin component Myosin-II. We confirmed these predictions experimentally by direct inhibition of Myosin-II and by activation via constitutively active ROCK1. Furthermore, constitutive activation of Myosin-II leads to an accumulation of Myosin-II next to the nuclei which spatially correlated with a corresponding shift of Rho activity dynamics from the cell center to the cell edge, showing that constant Myosin activation can spatially restrict cell contraction dynamics. Finally, light-induced rapid recruitment of ROCK1 to the plasma membrane strongly activated and recruited Myosin-II, and at the same time depleted Actin and inhibited Rho activity at the plasma membrane. We conclude that negative feedback in the cell contraction signal network of adherent mammalian cells is mediated by Myosin-II, and that actin does not act as the predominant inhibitor in this system.