Afadin couples RAS GTPases to the polarity rheostat Scribble

Abstract

AFDN/Afadin is required for establishment and maintenance of cell-cell contacts and is a unique effector of RAS GTPases. The biological consequences of RAS signalling to AFDN are unknown. Here, we use proximity-based proteomics to generate an interaction map for the long and short isoforms of AFDN, identifying the polarity protein SCRIB/Scribble as the top hit. We reveal that the first PDZ domain of SCRIB and the AFDN FHA domain mediate a direct but non-canonical interaction between these important adhesion and polarity proteins. Further, the dual RA domains of AFDN have broad specificity for RAS and RAP GTPases, and KRAS co-localizes with and promotes AFDN-SCRIB complex formation. Knockout of AFDN or SCRIB in MCF7 epithelial cells disrupts MAPK and PI3K activation and inhibits cell motility in a growth factor-dependent manner. These data have important implications for understanding why cells with activated RAS have reduced cell contacts and polarity defects, and finally begin to characterize AFDN as a RAS effector.