Reversible transition towards a fibroblastic phenotype in a rat carcinoma cell line

Two distinct mechanisms by which bladder carcinoma cells of the NBT-II cell line dissociate and migrate away from an in vitro reconstituted epithelial sheet were examined as regards intercellular adhesion and cell locomotion. Scattering of NBT-II bladder carcinoma cell line was promoted by 2 distinct culture protocols: (i) deposition of some components of the extracellular matrix onto the culture substratum (glass or plastic) induced cell dispersion of the epithelial sheet of carcinoma cells, and (ii) addition of Ultroser G, a serum substitute, to the culture medium induced scattering and acquisition of motility of NBT-II cells. Under both culture conditions, NBT-II cells dissociated, lost their epithelial morphology, acquired fibroblastic shape and migrated actively. We show that, among different extracellular matrix proteins, only collagens were able to promote the transition towards fibroblastic phenotype (referred as epithelium-to-mesenchyme transition or EMT). Furthermore, the native 3-dimensional helical structure of collagens was required for their function. During induction of EMT of NBT-II cells with Ultroser G, the junctions between epithelial cells were split, polarized epithelial cell organization was lost, and the resulting individual cells became motile and assumed a spindle-like fibroblastoid appearance. Using immunofluorescence microscopy techniques, we demonstrate that this change is accompanied by redistribution of desmosomal plaque proteins (desmoplakins, desmoglein, plakoglobin) and by reorganization of the cytokeratin and the actin-fodrin filament systems. Intermediate-sized filaments of the vimentin type were formed de novo in the fibroblastoid cell form. The observed transition towards fibroblastic phenotype (epithelium-to-mesenchyme transition or EMT) was fully reversed by removing the inducing factors from the culture medium, as shown by the disappearance of vimentin filaments and the reappearance of desmosomes in the newly formed epithelial cells.