CONTROL OF EPITHELIOMESENCHYMAL TRANSFORMATION .2. CROSS-MODULATION OF CELL-ADHESION AND CYTOSKELETAL SYSTEMS IN EMBRYONIC NEURAL CELLS

Protein kinase (PK) inhibitors Like staurosporine induce precocious ep itheliomesenchymal transformation (EMT) of quail embryo neural anlagen cultured on the extracellular matrix (ECM) molecule fibronectin (Newg reen and Minichiello, Dev. Biol. 170, 91-101; 1995). We show here that this also occurs on laminin, vitronectin, and collagen type I and typ e IV, but not on polylysine or BSA. In the absence of cell-ECM adhesio n, staurosporine produced a rapid increase in, rather than a loss of, cohesion in isolated neural anlagen and increased the rate of reaggreg ation of dissociated neural cells. In the absence of cell-cell adhesio ns (i.e., with dissociated cells), almost all neural cells rapidly adh ered to fibronectin in vitro and staurosporine made only a marginal di fference to this. Almost no neural cells spread on fibronectin in cont rol conditions but staurosporine stimulated spreading by almost all ce lls. When cell-cell adhesions were present, neural anlage explants wer e more difficult to dislodge by controlled shear from fibronectin subs trates 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 i n neural cells in culture, both spontaneous and induced by staurospori ne, 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. How ever, in spontaneous EMT the cadherin changes preceded the actin chang es, 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 b alanced cross-modulation among eel-cell adhesion molecules, cell-ECM a dhesion molecules, and cytoskeletal molecules can trigger and orchestr ate EMT, without direct genetic supervision. (C) 1996 Academic Press, Inc.