Down-regulation of the filamentous actin cross-linking activity of cortactin by Src-mediated tyrosine phosphorylation.
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.
Huang
C
C
Department of Experimental Pathology, The Holland Laboratory, American Red Cross, Rockville, Maryland 20855, USA.
Ni
Y
Y
Wang
T
T
Gao
Y
Y
Haudenschild
C C
CC
Zhan
X
X
D000199:Actins / Q000378:metabolism*; D000818:Animals; D051356:Cortactin; D003599:Cytoskeleton / Q000378:metabolism; D015536:Down-Regulation; D004926:Escherichia coli; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins / Q000378:metabolism*; D010766:Phosphorylation; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
D000199:Actins; D051356:Cortactin; C495869:Cttn protein, mouse; D008840:Microfilament Proteins; D014443:Tyrosine; D016392:Proto-Oncogene Proteins pp60(c-src); D008274:Magnesium