Acquisition of tumorigenic potential in the human myoepithelial HBL100 cell line is associated with decreased expression of HLA class I, class II and integrin β3 and increased expression of c-myc

The human breast cell line HBL100 acquires the capacity to invade normal tissues and to replace them by proliferation in vitro only at high passage levels (HPL). These cells therefore are a useful model for studying tumor progression in vitro. We have analyzed the expression of cell-surface markers supposed to be involved in the control of the neoplastic process. Quantitative flow cytometry has revealed that: (1) spontaneous expression of HLA class-I antigens strongly decreases in HPL HBL100 cells vs LPL cells, which parallels amplification and over-expression of c-myc oncogene; (2) HLA DR antigens can be induced by IFN-gamma in LPL but not in HPL HBL100 cells; (3) HBL100 cells secrete a soluble protein factor which specifically inhibits HLA DR induction by IFN-gamma even in heterologous cell systems; (4) 50% of LPL HBL100 cells express integrin β3, whereas HPL HBL100 cells lose this antigen; (5) this cell line is myoepithelial in origin, since 100% of HBL100 cells exhibit the CD10 antigen. Our data stress a role of HLA antigens, of some integrins and of c-myc in the acquisition of malignant potential by myoepithelial mammary cells of the HBL100 line.