?2-syntrophin and Par-3 promote an apicobasal Rac activity gradient at cell-cell junctions by differentially regulating Tiam1 activity.

ABSTRACT: Although Rac and its activator Tiam1 are known to stimulate cell-cell adhesion, the mechanisms regulating their activity in cell-cell junction formation are poorly understood. Here, we identify ?2-syntrophin as a Tiam1 interactor required for optimal cell-cell adhesion. We show that during tight-junction (TJ) assembly ?2-syntrophin promotes Tiam1-Rac activity, in contrast to the function of the apical determinant Par-3 whose inhibition of Tiam1-Rac activity is necessary for TJ assembly. We further demonstrate that ?2-syntrophin localizes more basally than Par-3 at cell-cell junctions, thus generating an apicobasal Rac activity gradient at developing cell-cell junctions. Targeting active Rac to TJs shows that this gradient is required for optimal TJ assembly and apical lumen formation. Consistently, ?2-syntrophin depletion perturbs Tiam1 and Rac localization at cell-cell junctions and causes defects in apical lumen formation. We conclude that ?2-syntrophin and Par-3 fine-tune Rac activity along cell-cell junctions controlling TJ assembly and the establishment of apicobasal polarity.

SUBMITTER: Mack NA 

PROVIDER: S-EPMC3498067 | biostudies-other | 2012 Nov

REPOSITORIES: biostudies-other