Neuregulin-1/glial growth factor stimulates Schwann cell migration by inducing α5 β1 integrin-ErbB2-focal adhesion kinase complex formation

After peripheral nerve injury, Schwann cells gain a migratory phenotype and remodel their extracellular matrix to provide a supportive environment for axonal regeneration. The soluble neuregulin-1 isoform, that is, glial growth factor (GGF), is expressed in regenerating axons of injured peripheral nerves and regulates Schwann cell motility by activating the ErbB family of tyrosine kinase receptors, but how GGF/ErbB signaling contributes to Schwann cell motility remains unclear. Here, we show that GGF stimulates Schwann cell migration by inducing the formation of a protein complex containing the fibronectin receptor alpha 5 beta 1 integrin, ErbB2, and focal adhesion kinase (FAK). ErbB2 co-localizes and co-immunoprecipitates with the focal complex members including alpha 5 beta 1 integrin and FAK after GGF treatment. These effects of GGF appear to involve FAK activation, which occurs downstream of ErbB2 stimulation. RNAi-mediated down-regulation of alpha 5 integrin expression in primary cultured Schwann cells resulted in significantly decreased interaction between FAK and ErbB2, as well as decreased GGF-induced migration. An increase in the alpha 5 beta 1 integrin-ErbB2-FAK complex formation was observed in injured nerve Schwann cells, but not uninjured control. Taken together, these data suggest that GGF plays an important modulatory role in Schwann cell migration after nerve crush by inducing alpha 5 beta 1 integrin-ErbB2-FAK complex formation.