ADF/Cofilin Accelerates Actin Dynamics by Severing Filaments and Promoting Their Depolymerization at Both Ends

• Published in: Current biology 2017-07, Vol.27 (13), p.1956-1967.e7
• Main Authors: Wioland, Hugo, Guichard, Berengere, Senju, Yosuke, Myram, Sarah, Lappalainen, Pekka, Jégou, Antoine, Romet-Lemonne, Guillaume
• Format: Article
• Language: English
• Subjects: Actin Cytoskeleton - metabolism; actin dynamics; actin-depolymerizing factor; Actins - metabolism; Animals; barbed-end depolymerization; capping protein; Cattle; cofilin; Cofilin 1 - genetics; Cofilin 1 - metabolism; Cofilin 2 - genetics; Cofilin 2 - metabolism; Destrin - genetics; Destrin - metabolism; Humans; microfluidics; non-muscle actin; Polymerization; Rabbits; single filaments
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2017.05.048

Actin-depolymerizing factor (ADF)/cofilins contribute to cytoskeletal dynamics by promoting rapid actin filament disassembly. In the classical view, ADF/cofilin sever filaments, and capping proteins block filament barbed ends whereas pointed ends depolymerize, at a rate that is still debated. Here, by monitoring the activity of the three mammalian ADF/cofilin isoforms on individual skeletal muscle and cytoplasmic actin filaments, we directly quantify the reactions underpinning filament severing and depolymerization from both ends. We find that, in the absence of monomeric actin, soluble ADF/cofilin can associate with bare filament barbed ends to accelerate their depolymerization. Compared to bare filaments, ADF/cofilin-saturated filaments depolymerize faster from their pointed ends and slower from their barbed ends, resulting in similar depolymerization rates at both ends. This effect is isoform specific because depolymerization is faster for ADF- than for cofilin-saturated filaments. We also show that, unexpectedly, ADF/cofilin-saturated filaments qualitatively differ from bare filaments: their barbed ends are very difficult to cap or elongate, and consequently undergo depolymerization even in the presence of capping protein and actin monomers. Such depolymerizing ADF/cofilin-decorated barbed ends are produced during 17% of severing events. They are also the dominant fate of filament barbed ends in the presence of capping protein, because capping allows growing ADF/cofilin domains to reach the barbed ends, thereby promoting their uncapping and subsequent depolymerization. Our experiments thus reveal how ADF/cofilin, together with capping protein, control the dynamics of actin filament barbed and pointed ends. Strikingly, our results propose that significant barbed-end depolymerization may take place in cells. [Display omitted] •ADF/cofilin domains grow symmetrically and sever mostly at their pointed-end border•Pointed-end depolymerization is accelerated by ADF/cofilin saturation•ADF/cofilin domains reach capped barbed ends and rapidly uncap them•ADF/cofilin-saturated barbed ends depolymerize and are hard to cap or re-elongate Wioland et al. monitor the action of ADF/cofilin isoforms on individual actin filaments and characterize the reactions leading to filament disassembly. ADF/cofilin-saturated filaments differ greatly from bare filaments, as their barbed ends can hardly stop depolymerizing. This situation can arise from severing or from a synergy with