Ohta Yasutaka, Hartwig John H, Stossel Thomas P
Hematology Division, Brigham and Women's Hospital, Department of Medicine, Harvard Medical School, Boston, MA 02115, USA.
Nat Cell Biol. 2006 Aug;8(8):803-14. doi: 10.1038/ncb1437. Epub 2006 Jul 23.
FilGAP is a newly recognized filamin A (FLNa)-binding RhoGTPase-activating protein. The GTPase-activating protein (GAP) activity of FilGAP is specific for Rac and FLNa binding targets FilGAP to sites of membrane protrusion, where it antagonizes Rac in vivo. Dominant-negative FilGAP constructs lacking GAP activity or knockdown of endogenous FilGAP by small interference RNA (siRNA) induce spontaneous lamellae formation and stimulate cell spreading on fibronectin. Knockdown of endogenous FilGAP abrogates ROCK-dependent suppression of lamellae. Conversely, forced expression of FilGAP induces numerous blebs around the cell periphery and a ROCK-specific inhibitor suppresses bleb formation. ROCK phosphorylates FilGAP, and this phosphorylation stimulates its RacGAP activity and is a requirement for FilGAP-mediated bleb formation. FilGAP is, therefore, a mediator of the well-established antagonism of Rac by RhoA that suppresses leading edge protrusion and promotes cell retraction to achieve cellular polarity.
FilGAP是一种新发现的与细丝蛋白A（FLNa）结合的RhoGTP酶激活蛋白。FilGAP的GTP酶激活蛋白（GAP）活性对Rac具有特异性，且FLNa将FilGAP靶向至膜突出部位，在体内它可拮抗Rac。缺乏GAP活性的显性负性FilGAP构建体或通过小干扰RNA（siRNA）敲低内源性FilGAP会诱导自发片状伪足形成，并刺激细胞在纤连蛋白上扩散。敲低内源性FilGAP可消除Rho相关卷曲螺旋蛋白激酶（ROCK）依赖性的片状伪足抑制作用。相反，强制表达FilGAP会在细胞周边诱导大量气泡形成，而ROCK特异性抑制剂可抑制气泡形成。ROCK使FilGAP磷酸化，这种磷酸化会刺激其RacGAP活性，并且是FilGAP介导的气泡形成所必需的。因此，FilGAP是RhoA对Rac的既定拮抗作用的介质，该拮抗作用可抑制前缘突出并促进细胞回缩以实现细胞极性。
