Direct interaction of two polarity complexes implicated in epithelial tight junction assembly

Area of Science:

• Cell Biology
• Epithelial Biology
• Molecular Cell Biology

Background:

• Tight junctions establish epithelial cell polarity by separating membrane domains.
• Two key complexes, Crumbs (Crb)-PALS1-PATJ and Cdc42-Par6-Par3-aPKC, are vital for epithelial polarization and tight junction assembly.
• These complexes are evolutionarily conserved in organisms like Drosophila melanogaster.

Purpose of the Study:

• To identify and characterize the biochemical and functional link between the Crb-PALS1-PATJ and Cdc42-Par6-Par3-aPKC complexes.
• To elucidate the role of Par6 and PALS1 in mediating this interaction.
• To understand how this link contributes to epithelial polarity and tight junction formation.

Main Methods:

• Investigated direct interaction between Par6 and PALS1 using biochemical assays.
• Utilized dominant-negative PATJ expression and Par6 overexpression in MDCK cells.
• Assessed localization of key proteins including PALS1, Par3-Par6-aPKC complex members, and ZO-1.

Main Results:

• Identified a direct interaction between Par6 and PALS1, dependent on the N-terminus of PALS1 and the PDZ domain of Par6, regulated by Cdc42-GTP.
• Demonstrated that the transmembrane protein Crb recruits wild-type Par6 to the cell surface.
• Showed that dominant-negative PATJ or overexpressed Par6 disrupts the localization of PALS1 and other complex members, including the tight junction marker ZO-1.

Conclusions:

• Established a novel biochemical and functional link between the Crb-PALS1-PATJ and Cdc42-Par6-Par3-aPKC complexes.
• Highlighted the critical role of the Par6-PALS1 interaction in epithelial polarity and tight junction assembly.
• Provided new insights into the molecular mechanisms governing epithelial cell organization.