Fig. 6.

Model of breast cancer round cell invasion and migration in 3D Matrigel. (A) MDA-MB-231 cells invade through Matrigel maintaining a spheroid shape. Actomyosin contractility is restricted to the cell rear (ellipsoid spring), generating tractional forces that are transmitted to the matrix through radial F-actin bundles (arrows) and β1 integrins bound to their matrix ligands (cross at the extremity of integrins). Gray and dotted areas represent regions of matrix compression and remodeling induced by cell movement, respectively. (B) Vertical invasion of cells atop a thick layer of Matrigel. (C) Inhibition of actomyosin contractility leads to cells spreading on the surface of Matrigel. (D) Inhibition of β1 integrin binding to its ligand(s) in the matrix (closed circle at the extremity of integrins) results in spheroid cells having minimal contact with the matrix and unable to invade. See text for details.