The RhoGAP protein Deleted in Liver Cancer 3 (DLC3) is essential for adherens junctions integrity

G Holeiter,P Erlmann,B Huck,A C Braun,R Herr,T Brummer,A Bischoff,S Schmid,M A Olayioye

doi:10.1038/oncsis.2012.13

Abstract

Epithelial cell–cell contacts are mediated by E-cadherin interactions, which are regulated by the balanced local activity of Rho GTPases. Despite the known function of Rho at adherens junctions (AJs), little is known about the spatial control of Rho activity at these sites. Here we provide evidence that in breast epithelial cells the Deleted in Liver Cancer 3 (DLC3) protein localizes to AJs and is essential for E-cadherin function. DLC3 is a still poorly characterized RhoA-specific GTPase-activating protein that is frequently downregulated in various types of cancer. We demonstrate that DLC3 depletion leads to mislocalization of E-cadherin and catenins, which was associated with impaired cell aggregation and increased migration. This is explained by aberrant local Rho signaling because ROCK inhibition restored cell–cell contacts in DLC3 knockdown cells. We thus identify DLC3 as a novel negative regulator of junctional Rho and propose that DLC3 loss contributes to carcinogenesis by compromising epithelial integrity.

Highlights

Epithelial tissues are characterized by their polarized morphology, specialized cell–cell contacts and attachment to an underlying basement membrane
Adherens junctions (AJs) are sites of epithelial cell–cell contact that are primarily maintained by E-cadherin, a membrane-spanning protein whose extracellular domains engage in calcium-dependent homotypic interactions between E-cadherin molecules on adjacent cells
The Deleted in Liver Cancer 3 (DLC3) gene located on chromosome Xq13 gives rise to two alternative DLC3 is required for adherens junction stability transcripts, DLC3a and DLC3b, which lacks the aminoterminal We examined the functionality of AJs by performing calcium sterile a motif (SAM).[23]

Summary

Introduction

Epithelial tissues are characterized by their polarized morphology, specialized cell–cell contacts and attachment to an underlying basement membrane. The cytoplasmic parts directly interact with b-catenin and p120-catenin that bridge the complex with the actin cytoskeleton This highly organized molecular network required for an intact epithelial architecture is commonly disrupted during the development of epithelial cancers.[1,2]. Rho GTPases (RhoA, Rac and Cdc42) have been shown to participate in these processes, as they are necessary for the formation and maintenance of cadherin-mediated cell–cell contacts, as well as for cytoskeletal reorganization and apicobasolateral polarization.[3,4] Spatiotemporal analysis with FRET biosensors revealed that RhoA is active during de novo cell adhesion, but activity is restricted to the periphery of contacting cell membranes.[5] At later stages, RhoA is required for the formation of actomyosin filaments, which in turn stabilize cell adhesion and participate in the development of the polarized epithelial phenotype.[3,4] Rho can regulate AJs in two opposing ways through the effectors Rho-associated protein kinase (ROCK) and Dia1.6 ROCK is a serine-threonine kinase that phosphorylates and inactivates myosin light chain (MLC) phosphatase, thereby stabilizing phosphorylated active MLC and generating contractile forces that lead to AJ disruption.

Methods

Results

Conclusion