Cancer cells use different modes of migration, including
integrin-dependent mesenchymal migration of elongated cells along elements of the 3D matrix as opposed to low-adhesion-, contraction-based amoeboid motility of rounded cells. We report that MDA-MB-231 human breast
adenocarcinoma cells invade 3D
Matrigel with a characteristic rounded morphology and with
F-actin and
myosin-IIa accumulating at the cell rear in a uropod-like structure. MDA-MB-231 cells display neither lamellipodia nor
bleb extensions at the leading edge and do not require
Arp2/3 complex activity for 3D invasion in
Matrigel. Accumulation of phospho-MLC and blebbing activity were restricted to the uropod as reporters of
actomyosin contractility, and velocimetric analysis of fluorescent beads embedded within the 3D matrix showed that pulling forces exerted to the matrix are restricted to the side and rear of cells. Inhibition of
actomyosin contractility or β1
integrin function interferes with uropod formation, matrix deformation, and invasion through
Matrigel. These findings support a model whereby
actomyosin-based uropod contractility generates
traction forces on the β1
integrin adhesion system to drive cell propulsion within the 3D matrix, with no contribution of lamellipodia extension or blebbing to movement.