Huang C, Ni Y, Wang T, Gao Y, Haudenschild C C, Zhan X
Department of Experimental Pathology, The Holland Laboratory, American Red Cross, Rockville, Maryland 20855, USA.
J Biol Chem. 1997 May 23;272(21):13911-5. doi: 10.1074/jbc.272.21.13911.
Cortactin, a prominent substrate for pp60(c-src), is a filamentous actin (F-actin) binding protein. We show here that cortactin can promote sedimentation of F-actin at centrifugation forces under which F-actin is otherwise not able to be precipitated. Electron microscopic analysis after negative staining further revealed that actin filaments in the presence of cortactin are cross-linked into bundles of various degrees of thickness. Hence, cortactin is also an F-actin cross-linking protein. We also demonstrate that the optimal F-actin cross-linking activity of cortactin requires a physiological pH in a range of 7.3-7.5. Furthermore, pp60(c-src) phosphorylates cortactin in vitro, resulting in a dramatic reduction of its F-actin cross-linking activity in a manner depending on levels of tyrosine phosphorylation. In addition, pp60(c-src) moderately inhibits the F-actin binding activity of cortactin. This study presents the first evidence that pp60(c-src) can directly regulate the activity of its substrate toward the cytoskeleton and implies a role of cortactin as an F-actin modulator in tyrosine kinase-regulated cytoskeleton reorganization.
皮层肌动蛋白（Cortactin）是pp60（c-src）的主要底物，是一种丝状肌动蛋白（F-肌动蛋白）结合蛋白。我们在此表明，皮层肌动蛋白能在离心力作用下促进F-肌动蛋白沉降，而在这种离心力下F-肌动蛋白原本无法沉淀。负染后的电子显微镜分析进一步显示，在有皮层肌动蛋白存在的情况下，肌动蛋白丝会交联成不同厚度的束状结构。因此，皮层肌动蛋白也是一种F-肌动蛋白交联蛋白。我们还证明，皮层肌动蛋白的最佳F-肌动蛋白交联活性需要7.3 - 7.5范围内的生理pH值。此外，pp60（c-src）在体外使皮层肌动蛋白磷酸化，导致其F-肌动蛋白交联活性显著降低，其降低方式取决于酪氨酸磷酸化水平。另外，pp60（c-src）适度抑制皮层肌动蛋白的F-肌动蛋白结合活性。本研究首次证明pp60（c-src）可直接调节其底物对细胞骨架的活性，并暗示皮层肌动蛋白在酪氨酸激酶调节的细胞骨架重组中作为F-肌动蛋白调节剂的作用。
