An active Src kinase-β-actin association is linked to actin dynamics at the periphery of colon cancer cells

Src controls the dynamic actin cytoskeleton in fibroblasts and in cancer cells, although it is not known how direct its effects are. Using FRET/FLIM imaging, we found that wild type Src associates directly, or indirectly, with peripheral β-actin at integrin adhesions after serum stimulation, and that an active Src kinase domain is essential. β-Actin can be directly tyrosine-phosphorylated by Src in vitro, and in a Src-dependent manner in cells. Moreover, β-actin dynamics are suppressed when Src is rendered kinase-inactive. Surprisingly, debilitating mutations in the Src SH2 or SH3 domains do not suppress association of Src with β-actin. This may therefore be an example of a spatially regulated Src kinase/substrate interaction that is controlling peripheral actin dynamics. Interestingly, there is no FRET between Src and β-actin at cadherin-mediated cell–cell contacts, despite apparent co-localization there, demonstrating precise spatial specificity of Src/β-actin complexes.