Scribble regulates an EMT polarity pathway through modulation of MAPK-ERK signaling to mediate junction formation

The crucial role the Crumbs and Par polarity complexes play in tight junction integrity has long been established, however very few studies have investigated the role of the Scribble polarity module. Here, we use MCF10A cells, which fail to form tight junctions and express very little endogenous Crumbs3, to show that inducing expression of the polarity protein Scribble is sufficient to promote tight junction formation. We show this occurs through an epithelial-to-mesenchymal (EMT) pathway that involves Scribble suppressing ERK phosphorylation, leading to downregulation of the EMT inducer ZEB. Inhibition of ZEB relieves the repression on Crumbs3, resulting in increased expression of this crucial tight junction regulator. The combined effect of this Scribble-mediated pathway is the upregulation of a number of junctional proteins and the formation of functional tight junctions. These data suggests a novel role for Scribble in positively regulating tight junction assembly through transcriptional regulation of an EMT signaling program.