Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, Spielmannstrasse 7, 38106 Braunschweig, Germany.
Molecular Cell Biology Group, Helmholtz Centre for Infection Research, Inhoffenstrasse 7, 38124 Braunschweig, Germany.
Nat Commun. 2017 Mar 22;8:14832. doi: 10.1038/ncomms14832.
Migration frequently involves Rac-mediated protrusion of lamellipodia, formed by Arp2/3 complex-dependent branching thought to be crucial for force generation and stability of these networks. The formins FMNL2 and FMNL3 are Cdc42 effectors targeting to the lamellipodium tip and shown here to nucleate and elongate actin filaments with complementary activities in vitro. In migrating B16-F1 melanoma cells, both formins contribute to the velocity of lamellipodium protrusion. Loss of FMNL2/3 function in melanoma cells and fibroblasts reduces lamellipodial width, actin filament density and -bundling, without changing patterns of Arp2/3 complex incorporation. Strikingly, in melanoma cells, FMNL2/3 gene inactivation almost completely abolishes protrusion forces exerted by lamellipodia and modifies their ultrastructural organization. Consistently, CRISPR/Cas-mediated depletion of FMNL2/3 in fibroblasts reduces both migration and capability of cells to move against viscous media. Together, we conclude that force generation in lamellipodia strongly depends on FMNL formin activity, operating in addition to Arp2/3 complex-dependent filament branching.
迁移通常涉及 Rac 介导的片状伪足的伸出，片状伪足由 Arp2/3 复合物依赖性分支形成，被认为对力的产生和这些网络的稳定性至关重要。formin 家族成员 FMNL2 和 FMNL3 是 Cdc42 的效应物，靶向片状伪足的尖端，并在此处显示体外具有成核和延伸肌动蛋白丝的互补活性。在迁移的 B16-F1 黑色素瘤细胞中，两种形成素都有助于片状伪足的伸出速度。黑色素瘤细胞和成纤维细胞中 FMNL2/3 功能的丧失会降低片状伪足的宽度、肌动蛋白丝的密度和 -束，而不会改变 Arp2/3 复合物的掺入模式。引人注目的是，在黑色素瘤细胞中，FMNL2/3 基因失活几乎完全消除了由片状伪足施加的伸出力，并改变了它们的超微结构组织。一致地，CRISPR/Cas 介导的成纤维细胞中 FMNL2/3 的耗竭减少了迁移和细胞抵抗粘性介质移动的能力。总之，我们得出结论，片状伪足中的力产生强烈依赖于 FMNL 形成素的活性，除了 Arp2/3 复合物依赖性丝分支之外还起作用。
