Le Jie, Mallery Eileen L, Zhang Chunhua, Brankle Steven, Szymanski Daniel B
Department of Agronomy, Purdue University, Lilly Hall, 915 W. State Street, West Lafayette, Indiana 47907, USA.
Curr Biol. 2006 May 9;16(9):895-901. doi: 10.1016/j.cub.2006.03.061. Epub 2006 Apr 6.
The actin cytoskeleton dynamically reorganizes the cytoplasm during cell morphogenesis. The actin-related protein (Arp)2/3 complex is a potent nucleator of actin filaments that controls a variety of endomembrane functions including the endocytic internalization of plasma membrane , vacuole biogenesis , plasma-membrane protrusion in crawling cells , and membrane trafficking from the Golgi . Therefore, Arp2/3 is an important signaling target during morphogenesis. The evolutionarily conserved Rac-WAVE-Arp2/3 pathway links actin filament nucleation to cell morphogenesis . WAVE translates Rac-GTP signals into Arp2/3 activation by regulating the stability and/or localization of the activator subunit Scar/WAVE . The WAVE complex includes Sra1/PIR121/CYFIP1, Nap1/NAP125, Abi-1/Abi-2, Brick1(Brk1)/HSPC300, and Scar/WAVE : Defining the in vivo function of each subunit is an important step toward understanding this complicated signaling pathway. Brk1/HSPC300 has been the most recalcitrant WAVE-complex protein and has no known function. In this paper, we report that Arabidopsis brick1 (brk1) is a member of the "distorted group" of trichome morphology mutants, a group that defines a WAVE-ARP2/3 morphogenesis pathway . In this paper we provide the first strong genetic and biochemical evidence that BRK1 is a critical WAVE-complex subunit that selectively stabilizes the Arp2/3 activator SCAR2.
肌动蛋白细胞骨架在细胞形态发生过程中动态重组细胞质。肌动蛋白相关蛋白（Arp）2/3复合物是肌动蛋白丝的有效成核剂，可控制多种内膜功能，包括质膜的内吞内化、液泡生物发生、爬行细胞中的质膜突出以及从高尔基体的膜运输。因此，Arp2/3是形态发生过程中的一个重要信号靶点。进化上保守的Rac-WAVE-Arp2/3途径将肌动蛋白丝成核与细胞形态发生联系起来。WAVE通过调节激活剂亚基Scar/WAVE的稳定性和/或定位，将Rac-GTP信号转化为Arp2/3激活。WAVE复合物包括Sra1/PIR121/CYFIP1、Nap1/NAP125、Abi-1/Abi-2、Brick1（Brk1）/HSPC300和Scar/WAVE：确定每个亚基的体内功能是理解这一复杂信号通路的重要一步。Brk1/HSPC300一直是最难研究的WAVE复合物蛋白，其功能未知。在本文中，我们报道拟南芥brick1（brk1）是毛状体形态突变体“扭曲组”的成员，该组定义了一个WAVE-ARP2/3形态发生途径。在本文中，我们提供了首个强有力的遗传和生化证据，证明BRK1是一个关键的WAVE复合物亚基，可以选择性地稳定Arp2/3激活剂SCAR2。
