Tight junction formation by a claudin mutant lacking the COOH‐terminal PDZ domain‐binding motif

Claudin‐based tight junctions (TJs) are formed at the most apical part of cell–cell contacts in epithelial cells. Previous studies suggest that scaffolding proteins ZO‐1 and ZO‐2 (ZO proteins) determine the location of TJs by interacting with claudins, but this idea is not conclusive. To address the role of the ZO proteins binding to claudins at TJs, a COOH‐terminal PDZ domain binding motif‐deleted claudin‐3 mutant, which lacks the ZO protein binding, was stably expressed in claudin‐deficient MDCK cells. The COOH‐terminus‐deleted claudin‐3 was localized at the apicolateral region similar to full‐length claudin‐3. Consistently, freeze‐fracture electron microscopy revealed that the COOH‐terminus‐deleted claudin‐3‐expressing cells reconstituted belts of TJs at the most apical region of the lateral membrane and restored functional epithelial barriers. These results suggest that the interaction of claudins with ZO proteins is not a prerequisite for TJ formation at the most apical part of cell–cell contacts.