Knockout of all ErbB-family genes delineates their roles in proliferation, survival, and migration.

The ErbB-family receptors play pivotal roles in the proliferation, migration, and survival of epithelial cells. Because our knowledge on the ErbB-family receptors was obtained largely by the exogenous application of their ligands, it remains unknown to which extent each of the ErbB contributes to these outputs. We here knocked out each ErbB gene, various combinations of ErbB genes, or all in Madin-Darby canine kidney cells to delineate the contribution of each gene. ERK activation waves during collective cell migration were mediated primarily by ErbB1 and secondarily by the ErbB2/ErbB3 heterodimer. Either ErbB1 or the ErbB2/ErbB3 complex was sufficient for the G1/S progression. The saturation cell density was markedly reduced in cells deficient in all ErbB-proteins, but not cells retaining only ErbB2, which cannot bind to ligands. Thus, the ligand-independent ErbB2 activity is sufficient for preventing apoptosis at high cell density. In short, systematic knockout of ErbB-family genes delineated the roles of each ErbB receptor.