A novel bidirectional positive-feedback loop between Wnt–b- catenin and EGFR–ERK plays a role in context-specific modulation of epithelial tissue regeneration

By operating as both a subunit of the cadherin complex and a key component of Wnt signalling, b-catenin acts as the lynchpin between cell–cell contact and transcriptional regulation of proliferation, coordinating epithelial tissue homeostasis and regeneration. The integration of multiple growth-regulatory inputs with b-catenin signalling has been observed in cancer-derived cells, yet the existence of pathway crosstalk in normal cells is unknown. Using a highly regenerative normal human epithelial culture system that displays contact inhibition, we demonstrate that the receptor tyrosine kinase (RTK)-driven MAPK and Wnt–b-catenin signalling axes form a bidirectional positive-feedback loop to drive cellular proliferation. We show that b-catenin both drives and is regulated by proliferative signalling cues, and its downregulation coincides with the switch from proliferation to contact-inhibited quiescence. We reveal a novel contextual interrelationship whereby positive and negative feedback between three major signalling pathways – EGFR–ERK, PI3K–AKT and Wnt–b-catenin – enable autocrineregulated tissue homeostasis as an emergent property of physical interactions between cells. Our work has direct implications for normal epithelial tissue homeostasis and provides insight as to how dysregulation of these pathways could drive excessive and sustained cellular growth in disease.