Yang Changsong, Pring Martin, Wear Martin A, Huang Minzhou, Cooper John A, Svitkina Tatyana M, Zigmond Sally H
Biology Department, University of Pennsylvania, Philadelphia, PA 19104, USA.
Dev Cell. 2005 Aug;9(2):209-21. doi: 10.1016/j.devcel.2005.06.008.
Actin polymerization in cells occurs via filament elongation at the barbed end. Proteins that cap the barbed end terminate this elongation. Heterodimeric capping protein (CP) is an abundant and ubiquitous protein that caps the barbed end. We find that the mouse homolog of the adaptor protein CARMIL (mCARMIL) binds CP with high affinity and decreases its affinity for the barbed end. Addition of mCARMIL to cell extracts increases the rate and extent of Arp2/3 or spectrin-actin seed-induced polymerization. In cells, GFP-mCARMIL concentrates in lamellipodia and increases the fraction of cells with large lamellipodia. Decreasing mCARMIL levels by siRNA transfection lowers the F-actin level and slows cell migration through a mechanism that includes decreased lamellipodia protrusion. This phenotype is reversed by full-length mCARMIL but not mCARMIL lacking the domain that binds CP. Thus, mCARMIL is a key regulator of CP and has profound effects on cell behavior.
细胞中的肌动蛋白聚合通过在肌动蛋白丝的尖端进行丝延长而发生。封闭尖端的蛋白质会终止这种延长。异二聚体封端蛋白（CP）是一种丰富且普遍存在的蛋白质，它能封闭肌动蛋白丝的尖端。我们发现衔接蛋白CARMIL的小鼠同源物（mCARMIL）与CP具有高亲和力结合，并降低其对肌动蛋白丝尖端的亲和力。将mCARMIL添加到细胞提取物中会增加Arp2/3或血影蛋白 - 肌动蛋白种子诱导的聚合反应的速率和程度。在细胞中，绿色荧光蛋白标记的mCARMIL（GFP - mCARMIL）集中在片状伪足中，并增加具有大的片状伪足的细胞比例。通过小干扰RNA（siRNA）转染降低mCARMIL水平会降低F - 肌动蛋白水平，并通过包括减少片状伪足突出的机制减缓细胞迁移。这种表型可被全长mCARMIL逆转，但不能被缺乏与CP结合结构域的mCARMIL逆转。因此，mCARMIL是CP的关键调节因子，对细胞行为有深远影响。
