Inhibition of negative feedback for persistent epithelial cell–cell junction contraction by p21-activated kinase 3

Abstract

Actin-mediated mechanical forces are central drivers of cellular dynamics. They generate protrusive and contractile dynamics, the latter of which are induced in concert with myosin II bundled at the site of contraction. These dynamics emerge concomitantly in tissues and even each cell; thus, the tight regulation of such bidirectional forces is important for proper cellular deformation. Here, we show that contractile dynamics can eventually disturb cell–cell junction contraction in the absence of p21-activated kinase 3 (Pak3). Upon Pak3 depletion, contractility induces the formation of abnormal actin protrusions at the shortening junctions, which causes decrease in E-cadherin levels at the adherens junctions and mislocalization of myosin II at the junctions before they enough shorten, compromising completion of junction shortening. Overexpressing E-cadherin restores myosin II distribution closely placed at the junctions and junction contraction. Our results suggest that contractility both induces and perturbs junction contraction and that the attenuation of such perturbations by Pak3 facilitates persistent junction shortening.

Underlying mechanisms that ensure actomyosin‐mediated directional remodeling of cell–cell contacts for multicellular movement

“…Schematic illustration, adapted from refs. [28, 39] (D) Time‐lapse images of remodeling cell–cell junctions labeled with myosin II (GFP‐tagged myosin II regulatory light chain) in the A8a epithelia. Orange and green arrows, shortening and extending junctions, respectively.…”

“…[ 34,36–38 ] Live‐imaging of the Pak3 mutants at a cellular resolution and semi‐quantification revealed that cell rearrangement was perturbed during the A8a movement, specifically at the step of cell–cell junction shortening; although junctions initiated shortening, they failed to complete it and instead re‐extended, resulting in repetition of shortening and extension of the same cell–cell contacts. [ 28 ]…”

“…[ 28 ] After the emergence of the abnormal protrusions, the junctions failed to complete shortening and instead re‐extended, giving rise to the observed fluctuation in cell–cell junction length. [ 28 ]…”

“…Images, adapted from ref. [28] (B) Simplified schematic illustration of negative feedback underlying actomyosin‐mediated contractility.…”

“…Further genetic analyses, including live‐imaging of myosin II and E‐Cadherin during the A8a movement, revealed a pathway that could explain how formation of the aberrant large protrusions eventually perturbs cell–cell junction shortening. [ 28 ] In the absence of Pak3, abnormal actin protrusions were associated with a decrease in E‐Cadherin levels at the cell–cell junctions. This is probably due to local unfolding of the plasma membrane caused by the aberrant protrusive actin dynamics.…”