SCAR/WAVE proteins and Arp2/3 complex assemble branched actin networks at the leading edge. Two isoforms of SCAR/WAVE, WAVE1 and WAVE2, reside at the leading edge, yet it has remained unclear whether they perform similar or distinct roles. Further, there have been conflicting reports about the Arp2/3-independent biochemical activities of WAVE1 on actin filament elongation. To investigate this in vivo, we knocked out WAVE1 and WAVE2 genes, individually and together, in B16-F1 melanoma cells. We demonstrate that WAVE1 and WAVE2 are redundant for lamellipodia formation and motility. However, there is a significant decrease in the rate of leading edge actin extension in WAVE2 KO cells, and an increase in WAVE1 KO cells. The faster rates of actin extension in WAVE1 KO cells are offset by faster retrograde flow, and therefore do not translate into faster lamellipodium protrusion. Thus, WAVE1 restricts the rate of actin extension at the leading edge, and appears to couple actin networks to the membrane to drive protrusion. Overall, these results suggest that WAVE1 and WAVE2 have redundant roles in promoting Arp2/3-dependent actin nucleation and lamellipodia formation, but distinct roles in controlling actin network extension and harnessing network growth to cell protrusion.

SCAR/WAVE 蛋白和 Arp2/3 复合物在前沿组装分支肌动蛋白网络。SCAR/WAVE 的两种同工型 WAVE1 和 WAVE2 位于前沿，但尚不清楚它们是否发挥相似或不同的作用。此外，关于 WAVE1 的 Arp2/3 独立生化活性对肌动蛋白丝伸长的报道相互矛盾。为了在体内研究这一点，我们在 B16-F1 黑色素瘤细胞中单独或一起敲除 WAVE1 和 WAVE2 基因。我们证明 WAVE1 和 WAVE2 对于片状伪足的形成和运动是多余的。然而，WAVE2 KO 细胞前缘肌动蛋白延伸率显着降低，WAVE1 KO 细胞增加。WAVE1 KO 细胞中肌动蛋白延伸的更快速度被更快的逆行流动所抵消，因此不会转化为更快的 lamellipodium 突起。因此，WAVE1 限制了前缘肌动蛋白延伸的速率，并且似乎将肌动蛋白网络耦合到膜以驱动突出。总体而言，这些结果表明 WAVE1 和 WAVE2 在促进 Arp2/3 依赖性肌动蛋白成核和片状伪足形成方面具有多余的作用，但在控制肌动蛋白网络扩展和利用网络生长导致细胞突出方面具有不同的作用。