Disruption of Ca2+-dependent cell-matrix adhesion enhances c-Src kinase activity, but causes dissociation of the c-Src/FAK complex and dephosphorylation of tyrosine-577 of FAK in carcinoma cells

Exp Cell Res. 2004 Feb 1;293(1):1-13. doi: 10.1016/j.yexcr.2003.09.008.


The nonreceptor tyrosine kinase c-Src is activated in most invasive cancers. Activated c-Src binds to FAK in the focal adhesion complex, resulting in the activation of the c-Src/FAK signaling cascade, which regulates cytoskeletal functions. However, the mechanisms by which c-Src/FAK signaling is regulated during conditions of anchorage-independent growth, a hallmark of tumor progression, are not clearly known. Here, an in vivo approach to measure c-Src activity was studied using phospho-specific antibodies against phosphorylated Y418 of c-Src (Src[pY418]), an autophosphorylation site of c-Src, and phosphorylated Y577 of FAK (FAK[pY577]), a known substrate of c-Src. Using genetic and pharmacological approaches to modulate c-Src activity, we showed that the levels of Src[pY418] and FAK[pY577], and the formation of a c-Src/FAK[pY577] complex correlated with the activation state of c-Src in adherent cells. Interestingly, both the in vivo level of Src[pY418] and in vitro c-Src kinase activity were increased in carcinoma cells following disruption of Ca(2+)-dependent cell-matrix adhesion. In contrast, the level of FAK[pY577] and its association with c-Src were reduced in suspended cells. The amount of FAK[pY577] in suspended cells was recovered following attachment of rounded cells to fibronectin-coated polystyrene beads, indicating that cell spreading was not required for phosphorylation of FAK. Moreover, cells expressing activated c-Src showed sustained Src[Y418] phosphorylation, but required Ca(2+)-dependent cell adhesion for phosphorylation of FAK[Y577] and association of c-Src with FAK[pY577]. These findings indicate an important role of integrin-based cell-matrix adhesion in regulating c-Src/FAK signaling under decreased anchorage conditions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Substitution
  • Animals
  • CSK Tyrosine-Protein Kinase
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism*
  • Carcinoma / genetics
  • Cell Line, Tumor
  • Cell-Matrix Junctions / metabolism*
  • Enzyme Activation
  • Fibronectins / metabolism
  • Focal Adhesion Kinase 1
  • Focal Adhesion Protein-Tyrosine Kinases
  • Mammary Neoplasms, Animal / genetics
  • Mammary Neoplasms, Animal / metabolism
  • Mice
  • Phenylalanine / metabolism
  • Phosphorylation
  • Protein-Tyrosine Kinases / chemistry
  • Protein-Tyrosine Kinases / genetics
  • Protein-Tyrosine Kinases / metabolism*
  • Signal Transduction
  • Tyrosine / metabolism*
  • src Homology Domains
  • src-Family Kinases


  • Fibronectins
  • Tyrosine
  • Phenylalanine
  • Protein-Tyrosine Kinases
  • CSK Tyrosine-Protein Kinase
  • Focal Adhesion Kinase 1
  • Focal Adhesion Protein-Tyrosine Kinases
  • Ptk2 protein, mouse
  • src-Family Kinases
  • Calcium-Calmodulin-Dependent Protein Kinases