Afadin couples RAS GTPases to the polarity rheostat Scribble

Goudreault et al. investigate the role of Afadin downstream of RAS GTPases, substantiating this cell adhesion protein as a true RAS effector that couples its activation to cell polarity through the Scribble protein. 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 complex with AFDN are unknown. We used proximity-based proteomics to generate an interaction map for two 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 AFDN and promotes AFDN-SCRIB complex formation. Knockout of AFDN or SCRIB in epithelial cells disrupts MAPK and PI3K activation kinetics and inhibits 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 implicate AFDN as a genuine RAS effector.

Automated summary

Goudreault et al. investigate the role of Afadin as a genuine effector of RAS GTPases, showing its association with cell polarity through Scribble protein. AFDN is essential for cell-cell contacts and has broad specificity for RAS and RAP GTPases. The study also reveals the interaction between the first PDZ domain of SCRIB and the FHA domain of AFDN, and demonstrates the importance of AFDN and SCRIB in MAPK and PI3K activation kinetics and cell motility.