Basu Dipanwita, Le Jie, Zakharova Taya, Mallery Eileen L, Szymanski Daniel B
Department of Agronomy, Purdue University, Lilly Hall, 915 W. State Street, West Lafayette, IN 47907-2054, USA.
Proc Natl Acad Sci U S A. 2008 Mar 11;105(10):4044-9. doi: 10.1073/pnas.0710294105. Epub 2008 Feb 28.
During morphogenesis, the actin cytoskeleton mediates cell-shape change in response to growth signals. In plants, actin filaments organize the cytoplasm in regions of polarized growth, and the filamentous arrays can be highly dynamic. Small GTPase signaling proteins termed Rho of plants (ROP)/RAC control actin polymerization. ROPs cycle between inactive GDP-bound and active GTP-bound forms, and it is the active form that interacts with effector proteins to mediate cytoskeletal rearrangement and cell-shape change. A class of proteins termed guanine nucleotide exchange factors (GEFs) generate GTP-ROP and positively regulate ROP signaling. However, in almost all experimental systems, it has proven difficult to unravel the complex signaling pathways from GEFs to the proteins that nucleate actin filaments. In this article, we show that the DOCK family protein SPIKE1 (SPK1) is a GEF, and that one function of SPK1 is to control actin polymerization via two heteromeric complexes termed WAVE and actin-related protein (ARP) 2/3. The genetic pathway was constructed by using a combination of highly informative spk1 alleles and detailed analyses of spk1, wave, and arp2/3 single and double mutants. Remarkably, we find that in addition to providing GEF activity, SPK1 associates with WAVE complex proteins and may spatially organize signaling. Our results describe a unique regulatory scheme for ARP2/3 regulation in cells, one that can be tested for widespread use in other multicellular organisms.
在形态发生过程中，肌动蛋白细胞骨架介导细胞形状变化以响应生长信号。在植物中，肌动蛋白丝在极性生长区域组织细胞质，且丝状阵列可能具有高度动态性。一类称为植物Rho（ROP）/RAC的小GTPase信号蛋白控制肌动蛋白聚合。ROP在无活性的GDP结合形式和活性的GTP结合形式之间循环，正是活性形式与效应蛋白相互作用以介导细胞骨架重排和细胞形状变化。一类称为鸟嘌呤核苷酸交换因子（GEF）的蛋白质产生GTP-ROP并正向调节ROP信号传导。然而，在几乎所有实验系统中，已证明难以阐明从GEF到使肌动蛋白丝成核的蛋白质的复杂信号通路。在本文中，我们表明DOCK家族蛋白SPIKE1（SPK1）是一种GEF，且SPK1的一个功能是通过两种异源复合物WAVE和肌动蛋白相关蛋白（ARP）2/3来控制肌动蛋白聚合。通过使用信息丰富的spk1等位基因组合以及对spk1、wave和arp2/3单突变体和双突变体的详细分析构建了遗传途径。值得注意的是，我们发现除了提供GEF活性外，SPK1还与WAVE复合物蛋白结合，并可能在空间上组织信号传导。我们的结果描述了细胞中ARP2/3调节的一种独特调控机制，一种可在其他多细胞生物中广泛测试其用途的机制。
