Snail induces epithelial cell extrusion through transcriptional control of RhoA contractile signalling and cell matrix adhesion

Abstract

Cell extrusion is a morphogenetic process that is implicated in epithelial homeostasis and highly dependent on the cellular insult and context. Minorities of cells expressing HRasV12 or undergoing apoptosis are typically extruded apically in vertebrate cells. However, basal extrusion (delamination) predominates when mammalian cells express oncogenic KRas and during development in Drosophila. To explore if the morphogenetic transcription factor, Snail, induces extrusion, we inducibly expressed a metabolically stabilized Snail6SA transgene mosaically in confluent MCF-7 monolayers. We found that the morphogenetic impact of Snail6SA was critically influenced by the proportion of cells in which it was expressed. When expressed in small clusters (<3 cells) within confluent monolayers, Snail6SA expression induced apical cell extrusion. In contrast, confluent cultures of Snail6SA expressing cells were retained in the monolayer to eventually undergo basal extrusion (delamination). Transcriptomic profiling revealed that Snail6SA did not substantively alter the balance of epithelial:mesenchymal genes. However, we identified a gene transcriptional network that led to the upregulation of RhoA signalling, actomyosin contractility and reduced basal adhesion in Snail6SA expressing cells. We show that this was necessary to drive both apical extrusion and basal delamination. Thus, contractile upregulation by RhoA along with weakened basal adhesion provides a pathway for Snail to influence epithelial morphogenesis independently of classic Epithelial to Mesenchymal Transition (EMT).