Family-wide Investigation of PDZ Domain-Mediated Protein-Protein Interactions Implicates β-Catenin in Maintaining the Integrity of Tight Junctions

Summary β-catenin is a multifunctional protein that plays a critical role in cell-cell contacts and signal transduction. β-catenin has previously been shown to interact with PDZ-domain-containing proteins through its C terminus. Using protein microarrays comprising 206 mouse PDZ domains, we identified 26 PDZ-domain-mediated interactions with β-catenin and confirmed them biochemically and in cellular lysates. Many of the previously unreported interactions involved proteins with annotated roles in tight junctions. We found that four tight-junction-associated PDZ proteins—Scrib, Magi-1, Pard3, and ZO-3—colocalize with β-catenin at the plasma membrane. Disrupting these interactions by RNA interference, overexpression of PDZ domains, or overexpression of the β-catenin C terminus altered localization of the full-length proteins, weakened tight junctions, and decreased cellular adhesion. These results suggest that β-catenin serves as a scaffold to establish the location and function of tight-junction-associated proteins.