ARHGAP21 protein, a new partner of α-tubulin involved in cell-cell adhesion formation and essential for epithelial-mesenchymal transition.

Cell-cell adhesions and the cytoskeletons play important and coordinated roles in cell biology, including cell differentiation, development, and migration. Adhesion and cytoskeletal dynamics are regulated by Rho-GTPases. ARHGAP21 is a negative regulator of Rho-GTPases, particularly Cdc42. Here we assess the function of ARHGAP21 in cell-cell adhesion, cell migration, and scattering. We find that ARHGAP21 is localized in the nucleus, cytoplasm, or perinuclear region but is transiently redistributed to cell-cell junctions 4 h after initiation of cell-cell adhesion. ARHGAP21 interacts with Cdc42, and decreased Cdc42 activity coincides with the appearance of ARHGAP21 at the cell-cell junctions. Cells lacking ARHGAP21 expression show weaker cell-cell adhesions, increased cell migration, and a diminished ability to undergo hepatocyte growth factor-induced epithelial-mesenchymal transition (EMT). In addition, ARHGAP21 interacts with α-tubulin, and it is essential for α-tubulin acetylation in EMT. Our findings indicate that ARHGAP21 is a Rho-GAP involved in cell-cell junction remodeling and that ARHGAP21 affects migration and EMT through α-tubulin interaction and acetylation.

Competitive enhancement of HGF-induced epithelial scattering by accessory growth factors.

HGF signaling induces epithelial cells to disassemble cadherin-based adhesion and increase cell motility and invasion, a process termed epithelial-mesenchymal transition (EMT). EMT plays a major role in cancer metastasis, allowing individual cells to detach from the primary tumor, invade local tissue, and colonize distant tissues with new tumors. While invasion of vascular and lymphatic networks is the predominant route of metastasis, nerves also can act as networks for dissemination of cancer cell to distant sites in a process termed perineual invasion (PNI). Signaling between nerves and invasive cancer cells remains poorly understood, as does cellular decision making that selects the specific route of invasion. Here we examine how HGF signaling contributes to PNI using reductionist culture model systems. We find that TGFß, produced by PC12 cells, enhances scattering in response to HGF stimulation, increasing both cell-cell junction disassembly and cell migration. Further, gradients of TGFß induce migratory mesenchymal cells to undergo chemotaxis towards the source of TGFß. Interestingly, VEGF suppresses TGFß-induced enhancement of scattering. These results have broad implications for how combinatorial growth factor signaling contributes to cancer metastasis, suggesting that VEGF and TGFß might modulate HGF signaling to influence route selection during cancer progression.

Zyxin controls migration in epithelial-mesenchymal transition by mediating actin-membrane linkages at cell-cell junctions.

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.