Graziano Brian R, Yu Hoi-Ying E, Alioto Salvatore L, Eskin Julian A, Ydenberg Casey A, Waterman David P, Garabedian Mikael, Goode Bruce L
Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454.
Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454
Mol Biol Cell. 2014 Jun;25(11):1730-43. doi: 10.1091/mbc.E14-03-0850. Epub 2014 Apr 9.
Asymmetric cell growth and division rely on polarized actin cytoskeleton remodeling events, the regulation of which is poorly understood. In budding yeast, formins stimulate the assembly of an organized network of actin cables that direct polarized secretion. Here we show that the Fer/Cip4 homology-Bin amphiphysin Rvs protein Hof1, which has known roles in cytokinesis, also functions during polarized growth by directly controlling the activities of the formin Bnr1. A mutant lacking the C-terminal half of Hof1 displays misoriented and architecturally altered cables, along with impaired secretory vesicle traffic. In vitro, Hof1 inhibits the actin nucleation and elongation activities of Bnr1 without displacing the formin from filament ends. These effects depend on the Src homology 3 domain of Hof1, the formin homology 1 (FH1) domain of Bnr1, and Hof1 dimerization, suggesting a mechanism by which Hof1 "restrains" the otherwise flexible FH1-FH2 apparatus. In vivo, loss of inhibition does not alter actin levels in cables but, instead, cable shape and functionality. Thus Hof1 tunes formins to sculpt the actin cable network.
不对称细胞生长和分裂依赖于极化肌动蛋白细胞骨架重塑事件，而对其调控的了解却很少。在芽殖酵母中，formin蛋白刺激形成有组织的肌动蛋白电缆网络，该网络指导极化分泌。在这里，我们表明，已知在胞质分裂中起作用的Fer/Cip4同源性-Bin amphiphysin Rvs蛋白Hof1，在极化生长过程中也通过直接控制formin蛋白Bnr1的活性发挥作用。缺乏Hof1 C端一半的突变体表现出取向错误和结构改变的电缆，以及分泌囊泡运输受损。在体外，Hof1抑制Bnr1的肌动蛋白成核和延伸活性，而不会将formin蛋白从丝端置换。这些效应取决于Hof1的Src同源3结构域、Bnr1的formin同源1（FH1）结构域和Hof1二聚化，提示了一种Hof1“抑制”原本灵活的FH1-FH2装置的机制。在体内，抑制作用的丧失不会改变电缆中肌动蛋白的水平，而是改变电缆的形状和功能。因此，Hof1调节formin蛋白以塑造肌动蛋白电缆网络。
