Induction of apically mistrafficked epiregulin disrupts epithelial polarity via aberrant EGFR signaling.

In polarized MDCK cells, disruption of the tyrosine-based YXXΦ basolateral trafficking motif (Y156A) in the EGFR ligand, epiregulin (EREG), results in its apical mistrafficking and transformation in vivo. However, mechanism(s) underlying these dramatic effects are unknown. Using a doxycycline-inducible system in 3D Matrigel cultures, we now show induction of Y156A EREG in fully formed MDCK cysts results in direct and complete delivery of mutant EREG to the apical cell surface. Within three days of induction, ectopic lumens were detected in mutant, but not wild-type, EREG-expressing cysts. Of note, these structures resemble histological features found in subcutaneous xenografts of mutant EREG-expressing MDCK cells. These ectopic lumens form de novo rather than budding from the central lumen and depend on metalloprotease cleavage of EREG and subsequent EGFR activity. Moreover, the most frequent EREG mutation in human cancer (R147stop) results in its apical mistrafficking in engineered MDCK cells. Thus, induction of EREG apical mistrafficking is sufficient to disrupt selective aspects of polarity of a preformed polarized epithelium.