Unjamming overcomes kinetic and proliferation arrest in terminally differentiated cells and promotes collective motility of carcinoma.
During wound repair, branching morphogenesis and carcinoma dissemination, cellular rearrangements are fostered by a solid-to-liquid transition known as unjamming. The biomolecular machinery behind unjamming, its physiological and clinical relevance remain, however, a mystery. Here, we combine biophysical and biochemical analysis to study unjamming in a variety of epithelial 2D and 3D collectives: monolayers, differentiated normal mammary cysts, spheroid models of breast ductal carcinoma in situ (DCIS), and ex vivo slices of orthotopically-implanted DCIS. In all cases, elevation of the small GTPase RAB5A sparks unjamming by promoting non-clathrin-dependent internalization of epidermal growth factor receptor that leads to hyper-activation of endosomally-confined ERK1/2 and phosphorylation of the actin nucleator WAVE2. Physically, activation of this pathway causes highly coordinated flocking of the cells, with striking rotational motion in 3D that eventually leads to matrix remodelling and collective invasiveness of otherwise jammed carcinoma. The identified endo-ERK1/2 pathway provides an effective switch for unjamming through flocking to promote epithelial tissues morphogenesis and carcinoma invasion and dissemination.