Takahashi Katsunori, Kanno Shin-Ichiro, Mizuno Kensaku
Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan.
Division of Dynamic Proteome in Cancer and Aging, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi 980-8575, Japan.
Biochem Biophys Res Commun. 2014 Nov 21;454(3):471-7. doi: 10.1016/j.bbrc.2014.10.108. Epub 2014 Oct 27.
Slingshot-1 (SSH1) is a protein phosphatase that dephosphorylates and activates cofilin, an actin-severing and -disassembling protein. SSH1 is bound to and activated by F-actin, but not G-actin. SSH1 is accumulated in the F-actin-rich lamellipodium but is also diffusely distributed in the cytoplasm. It remains unknown whether SSH1 is activated by soluble (low-level polymerized) actin filaments in the cytoplasm. In this study, we show that SSH1 binds to gelsolin via actin filaments in the cytosolic fraction. Gelsolin promoted solubilization of actin filaments and SSH1 in cell-free assays and in cultured cells. SSH1 was activated by gelsolin-generated soluble actin filaments. Furthermore, gelsolin enhanced cofilin dephosphorylation in neuregulin-stimulated cells. Our results suggest that cytosolic SSH1 forms a complex with gelsolin via soluble actin filaments and is activated by gelsolin-generated soluble actin filaments and that gelsolin promotes stimulus-induced cofilin dephosphorylation through increasing soluble actin filaments, which support SSH1 activation in the cytoplasm.
弹弓蛋白-1（SSH1）是一种蛋白质磷酸酶，可使丝切蛋白去磷酸化并激活该蛋白，丝切蛋白是一种可切断和拆解肌动蛋白的蛋白质。SSH1与丝状肌动蛋白（F-肌动蛋白）结合并被其激活，但不与球状肌动蛋白（G-肌动蛋白）结合。SSH1在富含F-肌动蛋白的片状伪足中积累，但也分散分布于细胞质中。细胞质中可溶性（低水平聚合）的肌动蛋白丝是否能激活SSH1尚不清楚。在本研究中，我们发现SSH1在胞质组分中通过肌动蛋白丝与凝溶胶蛋白结合。在无细胞试验和培养细胞中，凝溶胶蛋白促进了肌动蛋白丝和SSH1的溶解。SSH1被凝溶胶蛋白产生的可溶性肌动蛋白丝激活。此外，凝溶胶蛋白增强了神经调节蛋白刺激的细胞中丝切蛋白的去磷酸化。我们的结果表明，胞质中的SSH1通过可溶性肌动蛋白丝与凝溶胶蛋白形成复合物，并被凝溶胶蛋白产生的可溶性肌动蛋白丝激活，并且凝溶胶蛋白通过增加可溶性肌动蛋白丝促进刺激诱导的丝切蛋白去磷酸化，这支持了细胞质中SSH1的激活。
