Plasticity of Mammary Cell Boundaries Governed by EGF and Actin Remodeling

Defined signals that dictate the architecture of cellular boundaries in confluent cultures are poorly characterized. Here, we report dramatic remodeling, invoked by long-term epidermal growth factor (EGF) withdrawal from mammary-derived MCF10A cells. Such intervention generates an interdigitated, desmosome-rich monolayer, wherein cells project actin-containing protrusions deep into neighboring cells. These changes protect cellular sheets from mechanical disruption and dramatically restrict the freedom of cells to roam within the monolayer. Ectopic expression of activated Rac counteracts interdigitation and induces membrane ruffling, but cells remain confined by their interdigitated neighbors. Interdigitations are rapidly dissolved by acute EGF application in a process that is sensitive to actin depolymerization and myosin II inhibition. These assays for formation and dissolution of interdigitations provide a platform for the dissection of novel signaling pathways that are highly specific to EGF receptor (EGFR) activation. [Display omitted] •Major reorganization of MCF10A cellular boundaries occurs upon EGFR activation•EGF-responsive interdigitating cell projections restrict cell mobility•Rapid dissolution of interdigitations requires dynamic actin polymerization•Distinct EGF-dependent pathways exist for formation and reversal of interdigitations Tang et al. describe a dramatic reconfiguration of confluent mammary MCF10A cells controlled by EGF signaling. Withdrawal of EGF leads to wide-scale interdigitation of cells and increased desmosome number. Cells thereby become locked into position and unable to migrate within a monolayer. These interdigitations can be rapidly dissolved by reapplication of EGF, through a process that requires actin polymerization and myosin II activity. These convenient phenotypic assays offer a platform for detailed dissection of relevant effector pathways.