Li Guoqing, Huang Shan, Yang Sen, Wang Jiabin, Cao Jingli, Czajkowsky Daniel M, Shao Zhifeng, Zhu Xueliang
1State Key Laboratory of Cell Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai, 200031 China.
2Shanghai Center for Systems Biomedicine, Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240 China.
Cell Discov. 2018 Jul 24;4:42. doi: 10.1038/s41421-018-0040-3. eCollection 2018.
The cell cortex is a layer of cytoskeletal networks underneath the plasma membrane, formed by filamentous actin (F-actin) and cortex proteins including spectrin, adducin, and myosin. It provides cells with proper stiffness, elasticity, and surface tension to allow morphogenesis, division, and migration. Although its architecture and formation have been widely studied in red blood cells, they are poorly understood in non-erythrocytes due to structural complexity and versatile functions. In this study, we identify the actin-binding protein abLIM1 as a novel non-erythroid cell-specific cortex organizer. Endogenous abLIM1 colocalized with cortical βII spectrin but upon overexpression redistributed to thick cortical actin bundles. abLIM1 associated with major cortex proteins such as spectrins and adducin in vivo. Depletion of abLIM1 by RNAi induced prominent blebbing during membrane protrusions of spreading or migrating RPE1 cells and impaired migration efficiency. Reducing cortical tensions by culturing the cells to confluency or inhibiting myosin activity repressed the blebbing phenotype. abLIM1-depleted RPE1 or U2OS cells lacked the dense interwoven cortical actin meshwork observed in control cells but were abundant in long cortical actin bundles along the long axis of the cells. In-vitro assays indicated that abLIM1 was able to crosslink and bundle F-actin to induce dense F-actin network formation. Therefore, abLIM1 governs the formation of dense interconnected cortical actin meshwork in non-erythroid cells to prevent mechanical tension-induced blebbing during cellular activities such as spreading and migration.
细胞皮层是质膜下方的一层细胞骨架网络，由丝状肌动蛋白（F-肌动蛋白）和包括血影蛋白、内收蛋白和肌球蛋白在内的皮层蛋白形成。它为细胞提供适当的硬度、弹性和表面张力，以实现形态发生、分裂和迁移。尽管其结构和形成在红细胞中已得到广泛研究，但由于结构复杂性和功能多样性，在非红细胞中却知之甚少。在本研究中，我们鉴定出肌动蛋白结合蛋白abLIM1是一种新型的非红细胞特异性皮层组织者。内源性abLIM1与皮层βII血影蛋白共定位，但过表达后会重新分布到粗大的皮层肌动蛋白束中。abLIM1在体内与主要的皮层蛋白如血影蛋白和内收蛋白相关联。通过RNAi敲低abLIM1会在RPE1细胞铺展或迁移的膜突起过程中诱导明显的气泡形成，并损害迁移效率。通过将细胞培养至汇合状态或抑制肌球蛋白活性来降低皮层张力可抑制气泡形成表型。abLIM1敲低的RPE1或U2OS细胞缺乏对照细胞中观察到的致密交织的皮层肌动蛋白网络，但沿细胞长轴有丰富的长皮层肌动蛋白束。体外实验表明，abLIM1能够交联并束集F-肌动蛋白以诱导致密F-肌动蛋白网络形成。因此，abLIM1在非红细胞中控制致密互连的皮层肌动蛋白网络的形成，以防止在细胞活动如铺展和迁移过程中机械张力诱导的气泡形成。
