Down-regulation of the Filamentous Actin Cross-linking Activity of Cortactin by Src-mediated Tyrosine Phosphorylation*
- From the ‡Department of Experimental Pathology, The Holland Laboratory, American Red Cross, Rockville, Maryland 20855, the §Division of Biology, Glaxo and Welcome Research Institute, Research Triangle Park, North Carolina 27709, and the Departments of ¶Pathology and ‖Anatomy and Cell Biology, The George Washington University, Washington, D. C. 20037
Abstract
Cortactin, a prominent substrate for pp60c-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, pp60c-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, pp60c-src moderately inhibits the F-actin binding activity of cortactin. This study presents the first evidence that pp60c-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.
Footnotes
-
↵* This study was supported by National Institutes of Health Grant R29 HL52753 (to X. Z.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵** To whom correspondence should be addressed: Dept. of Experimental Pathology, The Holland Laboratory, American Red Cross, 15601 Crabbs Branch Way, Rockville, MD 20855. Tel.: 301-738-0568; Fax: 301-738-0879.
-
↵1 The abbreviations used are: F-actin, filamentous actin; SH3, Src homology 3; PAGE, polyacrylamide gel electrophoresis.
-
- Received January 16, 1997.
- Revision received February 28, 1997.
