CHARACTERIZATION OF THE PROGRESSIVE SUBLINES DERIVED FROM A WEAKLY MALIGNANT CLONED CELL-LINE, ER-1, CO-INOCULATED SUBCUTANEOUSLY WITH A FOREIGN-BODY

We previously established an experimental model of tumor progression u sing a weakly malignant rat mammary carcinoma cell line, ER-1. Using t his model, we demonstrated that ER-1 cells converted into highly tumor igenic and metastatic cells, ERpP, by s.c. co-inoculation with plastic plates, We here compared in vitro biological properties associated wi th malignancy of ER-1 cells with those of ERpP cells which were highly malignant when inoculated into syngeneic rats. In vitro growth rate o f ERpP cells was higher than that of ER-1 cells under a low nutrient c ondition. Invasion capacity of ERpP cells to rat lung endothelial cell monolayer or reconstituted basement membrane, Matrigel, was higher th an that of ER-1 cells, Migration of ERpP cells toward fibronectin or l aminin was also significantly higher than that of ER-1 cells. There wa s no difference in gelatinolytic or plasminogen activator activity det ected in conditioned media between ER-1 and ERpP cells, Furthermore, w e found that ER-1 cells communicated better among themselves and with normal fibroblasts through gap junctions compared to ERpP cells. These results suggest that growth advantage in a poor nutrient condition, e nhancement of cell motility, and loss or decrease of junctional commun ication may be associated with tumor progression of ER-1 cells. (C) 19 98 Lippincott-Raven Publishers.