Force generation by the molecular motor myosin II (MII) at the actin cortex is a universal feature of animal cells. Despite its central role in driving cell shape changes, the mechanisms underlying MII regulation at the actin cortex remain incompletely understood. Here we show that Myosin Light Chain Kinase (MLCK) promotes MII turnover at the mitotic cortex. Inhibition of MLCK resulted in an alteration of the relative levels of phosphorylated Regulatory Light Chain (RLC), with MLCK preferentially creating a short-lived pRLC species and Rho associated kinase (ROCK) preferentially creating a stable ppRLC species during metaphase. Slower turnover of MII and altered RLC homeostasis upon MLCK inhibition correlated with increased cortex tension, driving increased membrane bleb initiation and growth, but reduced bleb retraction during mitosis. Taken together, we show that ROCK and MLCK play distinct roles at the actin cortex during mitosis; ROCK activity is required for recruitment of MII to the cortex, while MLCK activity promotes MII turnover. Our findings support the growing evidence that MII turnover is an essential dynamic process influencing the mechanical output of the actin cortex.

肌动蛋白皮层的分子运动肌球蛋白 II (MII) 产生力是动物细胞的普遍特征。尽管 MII 在驱动细胞形状变化方面发挥着核心作用，但肌动蛋白皮层 MII 调节的机制仍不完全清楚。在这里，我们表明肌球蛋白轻链激酶 (MLCK) 促进有丝分裂皮层的 MII 周转。 MLCK 的抑制导致磷酸化调节轻链 (RLC) 的相对水平发生变化，其中 MLCK 优先产生短寿命的 pRLC 种类，而 Rho 相关激酶 (ROCK) 优先在中期产生稳定的 ppRLC 种类。 MLCK 抑制后 MII 周转速度减慢和 RLC 稳态改变与皮质张力增加相关，从而导致膜泡起始和生长增加，但有丝分裂期间泡回缩减少。综上所述，我们发现 ROCK 和 MLCK 在有丝分裂过程中在肌动蛋白皮层中发挥着不同的作用。 ROCK 活动是 MII 募集至皮质所必需的，而 MLCK 活动则促进 MII 周转。我们的研究结果支持越来越多的证据表明 MII 周转是影响肌动蛋白皮层机械输出的重要动态过程。