Actin protrusions push on E-cadherin to maintain epithelial cell-cell adhesion

Abstract

9Cadherin mediated cell-cell adhesion is actin dependent, but the precise role of actin in 10 maintaining cell-cell adhesion is not fully understood. Actin polymerization-dependent 11 protrusive activity is required to push distally separated cells close enough together to initiate 12 contact. Whether protrusive activity is required to maintain adhesion in confluent sheets of 13 epithelial cells is not known. By electron microscopy as well as live cell imaging, we have 14 identified a population of protruding actin microspikes that operate continuously near apical 15 junctions of polarized MDCK cells. Live imaging shows that microspikes containing E-cadherin 16 extend into gaps between E-cadherin clusters on neighboring cells while reformation of cadherin 17 clusters across the cell-cell boundary triggers microspike withdrawal. We identify Arp2/3, EVL, 18 and CRMP-1 as three actin assembly factors necessary for microspike formation. Depleting these 19 factors from cells using RNAi results in myosin II-dependent unzipping of cadherin adhesive 20 bonds. Therefore, actin polymerization-dependent protrusive activity operates continuously at 21 cadherin cell-cell junctions to keep them shut and to prevent myosin II-dependent contractility 22 from tearing cadherin adhesive contacts apart. 23 2 1