Control of epitheliomesenchymal transformation. II. Cross-modulation of cell adhesion and cytoskeletal systems in embryonic neural cells.

Protein kinase (PK) inhibitors like staurosporine induce precocious epitheliomesenchymal transformation (EMT) of quail embryo neural anlagen cultured on the extracellular matrix (ECM) molecule fibronectin (Newgreen and Minichiello, Dev. Biol. 170, 91-101; 1995). We show here that this also occurs on laminin, vitronectin, and collagen type I and type IV, but not on polylysine or BSA. In the absence of cell-ECM adhesion, staurosporine produced a rapid increase in, rather than a loss of, cohesion in isolated neural anlagen and increased the rate of reaggregation of dissociated neural cells. In the absence of cell-cell adhesions (i.e., with dissociated cells), almost all neural cells rapidly adhered to fibronectin in vitro and staurosporine made only a marginal difference to this. Almost no neural cells spread on fibronectin in control conditions but staurosporine stimulated spreading by almost all cells. When cell-cell adhesions were present, neural anlage explants were more difficult to dislodge by controlled shear from fibronectin substrates in the presence of staurosporine than under control conditions, but in both experiments and controls dislodgment was due to the cell bodies breaking proximal to the cell-fibronectin adhesion sites. EMT in neural cells in culture, both spontaneous and induced by staurosporine, involved rapid reduction in circumferential F-actin fibers and an increase in pancytoplasmic G-actin, as shown by fluorescent phalloidin and DNase I labeling. Loss of immunoreactivity for N-cadherin at cell-cell junctions also occurred in both spontaneous and induced EMT. However, in spontaneous EMT the cadherin changes preceded the actin changes, whereas in induced EMT, the reverse occurred. The results suggest that the molecules involved in EMT which are affected by PK inhibitors are cytoskeletal and link elements. These results also suggest that balanced cross-modulation among cell-cell adhesion molecules, cell-ECM adhesion molecules, and cytoskeletal molecules can trigger and orchestrate EMT, without direct genetic supervision.