Opposing Roles of Zyxin/LPP ACTA Repeats and the LIM Domain Region in Cell-Cell Adhesion

Marc D.H Hansen,Mary C Beckerle

doi:10.1074/jbc.m512771200

Abstract

Cadherins mediate cell-cell adhesion by linking cell junctions to actin networks. Although several actin regulatory systems have been implicated in cell-cell adhesion, it remains unclear how such systems drive cadherin-actin network formation and how they are regulated to coincide with initiation of adhesion. Previous work implicated VASP in assembly of cell-cell junctions in keratinocytes and the VASP-binding protein zyxin colocalizes with VASP at cell-cell junctions. Here we examine how domains in zyxin and its relative LPP contribute to cell-cell junction assembly. Using a quantitative assay for cell-cell adhesion, we demonstrate that zyxin and LPP function to increase the rate of early cell-cell junction assembly through the VASP-binding ActA repeat region. We also identify the LIM region of zyxin and LPP to be a regulatory domain that blocks function of these proteins. Deletion of the LIM domains drives adhesion and increases VASP level in detergent insoluble cadherin-actin. Dominant-negative zyxin/LPP mutants reduce the rate of adhesion, lower VASP levels in detergent-insoluble cadherin-actin networks, and allow for the accumulation of capping protein at cell-cell contacts. These data implicate the LIM domains of zyxin and LPP in regulating cell-cell junction assembly through VASP.

Highlights

Understanding actin assembly mechanisms has been greatly improved by studies of the intracellular pathogen, Listeria monocytogenes [15]
Zyxin/LPP LIM Domain Deletion Mutants Alter Balance of VASP and Capping Protein at Cell-Cell Junctions—To determine whether zyxin or LPP alter the incorporation of actin regulatory proteins into the cadherin-actin network at cell-cell junctions, we examined how the balance of VASP and capping protein was affected by alterations in the activity of either zyxin or LPP
Far less is known about how other actin regulatory pathways might contribute to adhesion and how these pathways might be activated by cadherin engagement

Summary

Introduction

Understanding actin assembly mechanisms has been greatly improved by studies of the intracellular pathogen, Listeria monocytogenes [15]. MDCK cells expressing DSred2 fusion protein containing either fulllength zyxin or LPP assemble and strengthen cell-cell junctions at a rate that does not significantly differ from parental MDCK cells (Fig. 3, B and F ).

Results

Conclusion