LeClaire Lawrence L, Rana Manish, Baumgartner Martin, Barber Diane L
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143 Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, CA 94143.
J Cell Biol. 2015 Jan 19;208(2):161-70. doi: 10.1083/jcb.201404095.
The nucleating activity of the Arp2/3 complex promotes the assembly of branched actin filaments that drive plasma membrane protrusion in migrating cells. Arp2/3 complex binding to nucleation-promoting factors of the WASP and WAVE families was previously thought to be sufficient to increase nucleating activity. However, phosphorylation of the Arp2 subunit was recently shown to be necessary for Arp2/3 complex activity. We show in mammary carcinoma cells that mutant Arp2 lacking phosphorylation assembled with endogenous subunits and dominantly suppressed actin filament assembly and membrane protrusion. We also report that Nck-interacting kinase (NIK), a MAP4K4, binds and directly phosphorylates the Arp2 subunit, which increases the nucleating activity of the Arp2/3 complex. In cells, NIK kinase activity was necessary for increased Arp2 phosphorylation and plasma membrane protrusion in response to epidermal growth factor. NIK is the first kinase shown to phosphorylate and increase the activity of the Arp2/3 complex, and our findings suggest that it integrates growth factor regulation of actin filament dynamics.
Arp2/3复合物的成核活性促进了分支肌动蛋白丝的组装，这些丝驱动迁移细胞中的质膜突出。Arp2/3复合物与WASP和WAVE家族的成核促进因子的结合以前被认为足以增加成核活性。然而，最近研究表明，Arp2亚基的磷酸化对于Arp2/3复合物的活性是必需的。我们在乳腺癌细胞中发现，缺乏磷酸化的突变型Arp2与内源性亚基组装在一起，并显著抑制肌动蛋白丝的组装和膜突出。我们还报告称，Nck相互作用激酶（NIK），即一种MAP4K4，结合并直接磷酸化Arp2亚基，这增加了Arp2/3复合物的成核活性。在细胞中，NIK激酶活性对于响应表皮生长因子而增加Arp2磷酸化和质膜突出是必需的。NIK是首个被证明可磷酸化并增加Arp2/3复合物活性的激酶，我们的研究结果表明它整合了生长因子对肌动蛋白丝动力学的调节。
