Association of decreased intercellular communication with the immortal but not the tumorigenic phenotype in human mammary epithelial cells

Intercellular communication was compared in early passage cultures of human mammary epithelial cells (HMEC) from normal and malignant breast tissues and immortalized nontumorigenic human breast cell lines (184A1 and 184B5). A clonogenic assay for the cell-mediated transfer of toxic metabolites of 6-thioguanine (TG) between cells was used as a measure of intercellular communication. We examined the effects of wild-type TG-sensitive (TGs) HMEC density on the survival of mutant TG-resistant (TGr) immortalized HMEC in TG-containing medium. Survival rates of TGr HMEC cocultured with TGs normal HMEC, malignant HMEC, or immortalized nontumorigenic HMEC were dependent on the density of TGs cells. For example, the percentage of recovery of TGr cells cocultured with 10(5) TGs immortalized, normal, or carcinoma HMEC was 88 +/- 4, 41 +/- 10, or 2.0 +/- 1.7, respectively. Gap junction-mediated intercellular communication between homologous HMEC types was also studied, as quantitated on the basis of Lucifer yellow dye transfer between cells in culture. Results from the dye transfer studies supported those from the metabolic cooperation studies. These results using nonimmortalized tumor cells differ from previous reports in which immortal tumor cells have been found to communicate less than their normal counterparts. Previous reports suggesting that tumor cell lines communicate less than normal cells may have resulted from the confounding influence of the immortal phenotype on the tumor phenotype.