Cell Adhesion-dependent Cofilin Serine 3 Phosphorylation by the Integrin-linked Kinase·c-Src Complex

Next Section Abstract Integrin-linked kinase(ILK) is involved in signal transduction by integrin-mediated cell adhesion that leads to dynamic actin reorganization. Actin (de)polymerization is regulated by cofilin, the Ser3 phosphorylation (pS3cofilin) of which inhibits its actin-severing activity. To determine how ILK regulates pS3cofilin, we examined the effects of ILK on pS3cofilin using normal RIE1 cells. Compared with suspended cells, fibronectin-adherent cells showed enhanced pS3cofilin, depending on ILK expression and c-Src activity. The ILK-mediated pS3cofilin in RIE1 cells did not involve Rho-associated kinase, LIM kinase, or testicular protein kinases, which are known to be upstream of cofilin. The kinase domain of ILK, including proline-rich regions, appeared to interact physically with the Src homology 3 domain of c-Src. In vitro kinase assay revealed that ILK immunoprecipitates phosphorylated the recombinant glutathione S-transferase- cofilin, which was abolished by c-Src inhibition. Interestingly, epidermal growth factor treatment abolished the ILK effects, indicating that the linkage from ILK to cofilinis biologically responsive to extracellular cues. Altogether, this study provides evidence for a new signaling connection from ILK to cofilinfor dynamic actin polymerization during cell adhesion, depending on the activity of ILK-associated c-Src.