For a cell to move, it must adhere to a substrate and exert traction. Adhesion occurs at specific foci at which the actin cytoskeleton on the inside of the cell is linked via transmembrane receptors (integrins) to the extracellular matrix on the outside. These adhesion sites are composed of complexes of more than 50 different proteins, including structural, signaling and adaptor molecules
Integrin based adhesions sites link to the actin cytoskeleton.
The organization of the actin cytoskeleton is controlled by members of the Rho family of small GTPases.
Adhesion formation and maintenance depends on forces generated by the actin cytoskeleton.
Actin filaments in lamellipodia and filopodia contribute to the construction of contractile arrays for retraction of the cell body.