Zyxin controls migration in epithelial–mesenchymal transition by mediating actin‐membrane linkages at cell–cell junctions

Abstract

Development is punctuated by morphogenetic rearrangements of epithelial tissues, including detachment of motile cells during epithelial-mesenchymal transition (EMT). Dramatic actin rearrangements occur as cell-cell junctions are dismantled and cells become independently motile during EMT. Characterizing dynamic actin rearrangements and identifying actin machinery driving these rearrangements is essential for understanding basic mechanisms of cell-cell junction remodeling. Using immunofluorescence and live cell imaging of scattering MDCK cells we examine dynamic actin rearrangement events during EMT and demonstrate that zyxin-VASP complexes mediate linkage of dynamic medial actin networks to adherens junction (AJ) membranes. A functional analysis of zyxin in EMT reveals its role in regulating disruption of actin membrane linkages at cell-cell junctions, altering cells' ability to fully detach and migrate independently during EMT. Expression of a constitutively active zyxin mutant results in persistent actin-membrane linkages and cell migration without loss of cell-cell adhesion. We propose zyxin functions in morphogenetic rearrangements, maintaining collective migration by transducing individual cells' movements through AJs, thus preventing the dissociation of individual migratory cells.

Control of cell mechanics by RhoA and calcium fluxes during epithelial scattering

“…Actin becomes highly decorated with non-muscle myosin II during the reorganization of actin into transcellular networks and obvious deformations are visible at points where these cables abut cell-cell junctions. 9 It is also at this point where cell spreading reverses and cells revert to having a smaller 'footprint' on the culture surface. Consistent with a role for myosin contractility in this process, changes in myosin phosphorylation are observed during epithelial scattering of MDCK cells; phosphorylation is reduced in early scattering, when spreading is observed, and increases in late scattering, when cell compaction, migration, and detachment occur.…”

“…[4][5][6][7] HGF stimulation of MDCK cells results in a dramatic change in cell morphology and cell behavior that ultimately results in cells wrenching apart their cell-cell adhesions in dramatic fashion and 'scattering' about the culture surface. 3,8,9 Cellular imaging, summarized in Figure 1, has shown that scattering is accompanied by a transient cell spreading phase, with cells increasing spreading on the culture surface by roughly double. The spreading phase is immediately followed by compaction of cells as spreading is reduced, an increase in cell migration, and disruption of cell-cell adhesions.…”

“…The spreading phase is immediately followed by compaction of cells as spreading is reduced, an increase in cell migration, and disruption of cell-cell adhesions. 8,9 The underlying actin dynamics during epithelial scattering are equally striking. Cortical actin bundles that run parallel and immediately adjacent to cell-cell junctions resolve into smaller cables whose ends remain affixed to points of cell-cell adhesion and which now radiate across the cell.…”

“…Cortical actin bundles that run parallel and immediately adjacent to cell-cell junctions resolve into smaller cables whose ends remain affixed to points of cell-cell adhesion and which now radiate across the cell. 9 The reorganization of actin at cadherin-mediated junctions is preceded by redistribution of the actin bundling protein a-actinin from cell-cell junctions, perhaps suggesting that actin bundling proteins maintain a tight association of actin with cell-cell junctions and that this activity must be released to initiate cell scattering. 9 The resulting 'transcellular networks' are reminiscent of structures seen during epithelial morphogenesis in developmental systems.…”

“…9 The reorganization of actin at cadherin-mediated junctions is preceded by redistribution of the actin bundling protein a-actinin from cell-cell junctions, perhaps suggesting that actin bundling proteins maintain a tight association of actin with cell-cell junctions and that this activity must be released to initiate cell scattering. 9 The resulting 'transcellular networks' are reminiscent of structures seen during epithelial morphogenesis in developmental systems. 10 Also similar is evidence of cellular contractility in transcellular networks.…”