The Howard Hughes Medical Institute, Laboratory of Mammalian Cell Biology and Development, Rockefeller University, New York, NY 10065, USA.
Cell. 2011 Feb 4;144(3):341-52. doi: 10.1016/j.cell.2010.12.033.
Homeostasis and wound healing rely on stem cells (SCs) whose activity and directed migration are often governed by Wnt signaling. In dissecting how this pathway integrates with the necessary downstream cytoskeletal dynamics, we discovered that GSK3β, a kinase inhibited by Wnt signaling, directly phosphorylates ACF7, a > 500 kDa microtubule-actin crosslinking protein abundant in hair follicle stem cells (HF-SCs). We map ACF7's GSK3β sites to the microtubule-binding domain and show that phosphorylation uncouples ACF7 from microtubules. Phosphorylation-refractile ACF7 rescues overall microtubule architecture, but phosphorylation-constitutive mutants do not. Neither mutant rescues polarized movement, revealing that phospho-regulation must be dynamic. This circuitry is physiologically relevant and depends upon polarized GSK3β inhibition at the migrating front of SCs/progeny streaming from HFs during wound repair. Moreover, only ACF7 and not GSKβ-refractile-ACF7 restore polarized microtubule-growth and SC-migration to ACF7 null skin. Our findings provide insights into how this conserved spectraplakin integrates signaling, cytoskeletal dynamics, and polarized locomotion of somatic SCs.
内稳态和伤口愈合依赖于干细胞 (SCs)，其活性和定向迁移通常受 Wnt 信号的控制。在剖析这条途径如何与必要的下游细胞骨架动力学整合时，我们发现 GSK3β（一种被 Wnt 信号抑制的激酶）可直接磷酸化 ACF7，这是一种富含毛囊干细胞 (HF-SCs) 的 >500 kDa 微管-肌动蛋白交联蛋白。我们将 ACF7 的 GSK3β 位点映射到微管结合域，并表明磷酸化使 ACF7 与微管解偶联。磷酸化抗性的 ACF7 挽救了整体微管结构，但磷酸化组成型突变体则不能。这两种突变体都不能挽救极化运动，表明磷酸化调节必须是动态的。该电路具有生理相关性，并且取决于在伤口修复过程中，SCs/源自 HF 的后代从迁移前沿极化抑制 GSK3β。此外，只有 ACF7 而不是 GSKβ-磷酸化抗性 ACF7 可以恢复极化微管生长和 ACF7 缺失皮肤中的 SC 迁移。我们的发现为深入了解这种保守的 spectrin 如何整合信号、细胞骨架动力学和体细胞干细胞的极化运动提供了思路。
