Regulation of dome formation in differentiated epithelial cell cultures

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Abstract
Rat mammary (Rama 25) and dog kidney (MDCK) epithelial cell cultures formed ‘domes’ of cells due to fluid accumulation in focal regions between the culture dish and the cell monolayer. Addition of ouabain caused collapse of domes, suggesting that transport functions were required for maintenance of domes. Dome formation in both epithelial cell lines was stimulated by a broad spectrum of known inducers of erythroid differentiation in Friend erythroleukemia cells. Among these inducers were: (1) polar solvents such as dimethylsulfoxide, dimethylformamide, and hexamethylene bisacetamide; (2) purines such as hypoxanthine, inosine, and adenosine; (3) low-molecular-weight fatty acids such as n-butyrate; and (4) conditions expected to elevate levels of cyclic AMP. In the latter group were activators of adenylate cyclase such as cholera toxin and prostaglandin E1; cyclic AMP phosphodiesterase inhibitors such as theophylline and 1-methyl-3-isobutylxanthine; and analogs of cyclic AMP. Induction of domes occurred 15–30 h after addition of inducer to the culture medium. Induction by chemicals was serum-dependent and required protein synthesis but not DNA synthesis. Induced dome formation was reversible after removal of inducer, requiring the contiuous presence of inducer. Reversal was also observed after either removal of serum or addition of inhibitors of protein synthesis. These results suggest the hypothesis that domes arise in these epithelial cultures by a process that is similar to cell differentiation and is influenced by cyclic AMP.