 Focal adhesions are macromolecular structures that function in the transmission of mechanical force and regulatory signals.Among the scientific community, pp125 is also referred to as FAK (focal adhesion kinase), due to its aforementioned presence in cellular focal adhesions.The protein tyrosine kinase pp125 is one of the major phosphotyrosine–containing proteins in unaffected (untransformed) avian and rodent fibroblast cells (fibroblast cells are explained above in some detail).