Non-canonical EGFR signaling promotes MAPK-dependent extrusion of epithelial cells

Individual epithelial cells that express oncogenes are often extruded from monolayers of wild-type cells, but the extrusion mechanism is not fully understood. We examined extrusion of mammary epithelial cells caused by induction of oncogenic Ras(Q61L). Ras-dependent extrusion requires phosphorylation of ERK (herein referring to ERK1 and ERK2, also known as MAPK3 and MAPK1, respectively) but not activation of AKT kinases. Unexpectedly, however, extrusion was suppressed by erlotinib, an inhibitor of epidermal growth factor receptor (EGFR), and by deletion of EGFR. In pancreatic and lung cancers, EGFR is required for full activation of Ras. However, EGFR inhibition or deletion had no impact on Ras(Q61L)-GTP levels or ERK phosphorylation. EGFR expression was not required in surrounding wild-type cells but was needed by the Ras(Q61L) cells for extrusion, yet deletion of the Ras guanine-nucleotide-exchange factors SOS1 and SOS2 (SOS1/2) did not block extrusion. Moreover, expression of a constitutively active MEK instead of Ras was sufficient to drive extrusion, and EGFR inhibition in these cells reduced extrusion. Notably, expression of Ras triggered internalization of E-cadherin (CDH1), which was partially blocked by EGFR inhibition. Together, these data demonstrate an unanticipated requirement for non-canonical EGFR signaling in cancer cell extrusion, which might act in part by promoting E-cadherin endocytosis.