Roles of Rab Family Small G Proteins in Formation of the Apical Junctional Complex in Epithelial Cells

Abstract

Epithelial tissue formation and function require organization of monolayer sheets, which is mediated through the apical junctional complex (AJC). The AJC comprises a diverse set of key factors: adhesion molecules including E-cadherin, claudins, and occludin; polarity proteins that support organization and function of apical and basolateral membranes; and proteins that support adhesion, vesicle transport, actin cytoskeletal rearrangement, and membrane scaffolds. These proteins form a dynamic cooperative network that is engaged in the highly elaborate regulation of AJC. Several lines of evidence indicate that Rab family small G proteins play important roles in the regulation of epithelial apical junctions and that the assembly and disassembly of these junctions can be driven by Rab proteins localized at either endosomes or apical junctions. In this review, we provide an overview of the influence of Rab proteins on AJC functions, focusing especially on the role of the complex containing Rab13 and JRAB/MICAL-L2 (junctional Rab13-binding protein/molecule interacting with CasL-like 2) in the regulation of epithelial apical junctions.