Hayes Matthew J, Shao Dongmin, Bailly Maryse, Moss Stephen E
Division of Cell Biology, Institute of Ophthalmology, University College London, UK.
EMBO J. 2006 May 3;25(9):1816-26. doi: 10.1038/sj.emboj.7601078. Epub 2006 Apr 6.
Annexin 2 is a ubiquitous Ca(2+)-binding protein that is essential for actin-dependent vesicle transport. Here, we show that in spontaneously motile cells annexin 2 is concentrated in dynamic actin-rich protrusions, and that depletion of annexin 2 using siRNA leads to the accumulation of stress fibres and loss of protrusive and retractile activity. Cells co-expressing annexin 2-CFP and actin-YFP exhibit Ca(2+)-dependent fluorescense resonance energy transfer throughout the cytoplasm and in membrane ruffles and protrusions, suggesting that annexin 2 may directly interact with actin. This notion was supported by biochemical studies, in which we show that annexin 2 reduces the polymerisation rate of actin monomers in a dose-dependent manner. By measuring actin polymerisation rates in the presence of barbed-end and pointed-end cappers, we further demonstrate that annexin 2 specifically inhibits filament elongation at the barbed ends. These results show that annexin 2 has an essential role in maintaining the plasticity of the dynamic membrane-associated actin cytoskeleton, and that its activity in this context may be at least partly explained through direct interactions with polymerised and monomeric actin.
膜联蛋白2是一种普遍存在的钙离子结合蛋白，对肌动蛋白依赖性囊泡运输至关重要。在此，我们发现，在自发运动的细胞中，膜联蛋白2集中在富含肌动蛋白的动态突起中，并且使用小干扰RNA耗尽膜联蛋白2会导致应力纤维的积累以及突起和收缩活性的丧失。共表达膜联蛋白2-青色荧光蛋白和肌动蛋白-黄色荧光蛋白的细胞在整个细胞质以及膜皱褶和突起中表现出钙离子依赖性荧光共振能量转移，这表明膜联蛋白2可能直接与肌动蛋白相互作用。生化研究支持了这一观点，我们在研究中表明，膜联蛋白2以剂量依赖性方式降低肌动蛋白单体的聚合速率。通过在存在带刺末端和钝端封端剂的情况下测量肌动蛋白聚合速率，我们进一步证明膜联蛋白2特异性抑制带刺末端的丝状体伸长。这些结果表明，膜联蛋白2在维持动态膜相关肌动蛋白细胞骨架的可塑性方面具有重要作用，并且其在这种情况下的活性至少部分可以通过与聚合和单体肌动蛋白的直接相互作用来解释。
