Abstract：
Cytokinesis, the separation of daughter cells at the end of mitosis, relies in animal cells on a contractile actomyosin ring (CAR) composed of actin and class II myosins, whose activity is strongly influenced by regulatory light chain (RLC) phosphorylation. However, in simple eukaryotes such as the fission yeast Schizosaccharomyces pombe, RLC phosphorylation appears dispensable for regulating CAR dynamics. We found that redundant phosphorylation at Ser35 of the S. pombe RLC homolog Rlc1 by the p21-activated kinases Pak1 and Pak2, modulates myosin II Myo2 activity and becomes essential for cytokinesis and cell growth during respiration. Previously, we showed that the stress-activated protein kinase pathway (SAPK) MAPK Sty1 controls fission yeast CAR integrity by downregulating formin For3 levels (Gómez-Gil et al., 2020). Here, we report that the reduced availability of formin For3-nucleated actin filaments for the CAR is the main reason for the required control of myosin II contractile activity by RLC phosphorylation during respiration-induced oxidative stress. Thus, the restoration of For3 levels by antioxidants overrides the control of myosin II function regulated by RLC phosphorylation, allowing cytokinesis and cell proliferation during respiration. Therefore, fine-tuned interplay between myosin II function through Rlc1 phosphorylation and environmentally controlled actin filament availability is critical for a successful cytokinesis in response to a switch to a respiratory carbohydrate metabolism.
摘要：
细胞分裂,在有丝分裂结束时分离子细胞，动物细胞依赖于由肌动蛋白和II类肌球蛋白组成的收缩肌动蛋白环（CAR），其活性受到调节性轻链(RLC)磷酸化的强烈影响。然而,在简单的真核生物中，如裂殖酵母裂殖酵母，RLC磷酸化对于调节CAR动力学似乎是可有可无的。我们发现p21激活的激酶Pak1和Pak2在S.pombeRLC同源物Rlc1的Ser35处的冗余磷酸化调节了肌球蛋白IIMyo2的活性，并成为呼吸过程中胞质分裂和细胞生长所必需的。以前,我们表明，应激激活的蛋白激酶途径（SAPK）MAPKSty1通过下调For3水平来控制裂殖酵母CAR的完整性（Gomez-Gil等人。,2020）。这里,我们报道,在呼吸诱导的氧化应激过程中,需要通过RLC磷酸化来控制肌球蛋白II收缩活性的主要原因是,用于CAR的For3核肌动蛋白丝的可用性降低.因此，抗氧化剂对For3水平的恢复超过了由RLC磷酸化调节的肌球蛋白II功能的控制，在呼吸过程中允许胞质分裂和细胞增殖。因此,通过Rlc1磷酸化的肌球蛋白II功能与环境控制的肌动蛋白丝可用性之间的微调相互作用对于成功的胞质分裂以响应呼吸碳水化合物代谢的转变至关重要。
