Non-muscle myosin II induces disassembly of actin stress fibres independently of myosin light chain dephosphorylation

Abstract

Dynamic remodelling of actin stress fibres (SFs) allows non-muscle cells to adapt to applied forces such as uniaxial cell shortening. However, the mechanism underlying rapid and selective disassembly of SFs oriented in the direction of shortening remains to be elucidated. Here, we investigated how myosin crossbridge cycling induced by MgATP is associated with SF disassembly. Moderate concentrations of MgATP, or [MgATP], induced SF contraction. Meanwhile, at [MgATP] slightly higher than the physiological level, periodic actin patterns emerged along the length of SFs and dispersed within seconds. The actin fragments were diverse in length, but comparable to those in characteristic sarcomeric units of SFs. These results suggest that MgATP-bound non-muscle myosin II dissociates from the individual actin filaments that constitute the sarcomeric units, resulting in unbundling-induced disassembly rather than end-to-end actin depolymerization. This rapid SF disassembly occurred independent of dephosphorylation of myosin light chain. In terms of effects on actin-myosin interactions, a rise in [MgATP] is functionally equivalent to a temporal decrease in the total number of actin-myosin crossbridges. Actin-myosin crossbridges are known to be reduced by an assisting load on myosin. Thus, the present study suggests that reducing the number of actin-myosin crossbridges promotes rapid and orientation-dependent disassembly of SFs after cell shortening.

Myosin II Activity Softens Cells in Suspension

“…This finding argues against myosin-induced actin fluidization as the main mechanism for cell stiffening upon myosin inhibition. We therefore propose an alternative mechanism based on myosin-induced actin depolymerization, inspired by recent experiments that demonstrated the role of myosin II in active disassembly of actin filaments (43)(44)(45). In these publications, actin depolymerization was attributed to an increased bending of actin fibers by active myosin motors.…”

The relationship between serum ferritin and metabolic syndrome in healthy Korean men

“…To sense and transmit the constantly varying hemodynamic forces from the EC surface to its cytoplasm and further into the nucleus, a variety of mechano‐sensors and transducers (with size in the range from 10 −9 to 10 −6 m) are required. So far, at least 10 candidates have been identified as mechano‐sensors and transducers, including cell adhesion proteins (e.g., VE‐cadherin, PECAM‐1),8,9 ion channels,10,11 tyrosine kinase receptors (e.g., vascular endothelial growth factor receptor 2),9 G‐protein‐coupled receptors and G‐proteins,6 caveolae,12 primary cilia,13 actin filaments,14 nesprins,15 integrins,16 and endothelial surface glycocalyx (ESG)17 (Figure 2). Because of its proteoglycan and glycosaminoglycan (GAG) composition and structure, the ESG may cover the entire surface of the EC as shown in Figure 2 (the yellow coat), and thus can interact with other EC sensors and transducers to play a role in sensing and transmitting hemodynamic forces.…”

The position and size of individual focal adhesions are determined by intracellular stress‐dependent positive regulation

“…Activated RhoA is responsible for serine/threonine phosphorylations of myosin regulatory light chain (MLC) of NMII through myosin phosphatase inactivation and direct activation by ROCK [Kimura et al, 1996]. The ATPase activity of the myosin head, which is essential for motor activity and resulting development of cellular tension, is enhanced when MLC is phosphorylated [Matsui et al, 2010[Matsui et al, , 2011. In addition, a GTPase activating protein (GAP) for RhoA, which facilitates RhoA inactivation, is activated at FXs [Arthur and Burridge, 2001;Tomar and Schlaepfer, 2009].…”