The anchoring protein RACK1 links protein kinase Cepsilon to integrin beta chains. Requirements for adhesion and motility

Integrin affinity is modulated by intracellular signaling cascades, in a process known as "inside-out" signaling, leading to changes in cell adhesion and motility. Protein kinase C (PKC) plays a critical role in integrin-mediated events; however, the mechanism that links PKC to integrins remains unclear. Here, we report that PKCepsilon positively regulates integrin-dependent adhesion, spreading, and motility of human glioma cells. PKCepsilon activation was associated with increased focal adhesion and lamellipodia formation as well as clustering of select integrins, and it is required for phorbol 12-myristate 13-acetate-induced adhesion and motility. We provide novel evidence that the scaffolding protein RACK1 mediates the interaction between integrin beta chain and activated PKCepsilon. Both depletion of RACK1 by antisense strategy and overexpression of a truncated form of RACK1 which lacks the integrin binding region resulted in decreased PKCepsilon-induced adhesion and migration, suggesting that RACK1 links PKCepsilon to integrin beta chains. Altogether, these results provide a novel mechanistic link between PKC activation and integrin-mediated adhesion and motility.