Expression of Murine Mammary Tumor Virus-Related Antigens in Human Breast Carcinoma (MCF-7) Cells 2

Abstract

Tested by the indirect immunofluorescence technique, a human breast carcinoma cell in continuous in vitro cultivation (MCF-7) was found to express antigens cross-reactlve with the murine mammary tumor virus (MuMTV), but not with murine leukemia virus or Mason-Pfizer monkey virus. Antiserum dilution, antiserum absorption, and antiserum blocking experiments showed the cross-reactivity observed in MCF-7 cells to be MuMTV-specific. In long-term passage, only 4–6% of the total population of MCF-7 cells reacted specifically with anti-MuMTV sera. The number of specifically reactive cells could be increased up to 9–14% by treating MCF-7 cells with 10^-7 or 10^-am progesterone. Neither 5-iododeoxyuridine (IUdR), dexamethasone, nor IUdR plus dexamethasone, potent inducers of MuMTV expression in mouse cells, had any effect on MuMTV cross-reactive antligen expression in MCF-7 cells. Late-passage MCF-7 monolayers were phenotypic mixtures of cells. Small cells (S-cells) comprised 80–90% of the cells, and 10–20% were cells two to three times larger (L-cells). L-cells exclusively reacted with MuMTV antisera and responded to progesterone with augmented antigen levels. L-cells were separated from S-cells by cloning. Again, only L-cells In L-cell clones reacted with MuMTV antisera. The number of L-cell clones could be increased from 15% to about 35% by prolonged treatment of cells in the parent monolayer with IUdR; this resulted in a parallel increase in MuMTV-positive L-cells. However, the segregation of L-cells from S-cells and the increase in the number of L-cells by IUdR treatment did not permanently increase the number of MuMTV-positive cells. MuMTV-positive L-cells converted to MuMTV-negatlve L-cells rapidly during cell division such that the number of MuMTV-positive L-cells per clone was inversely related to clone size (I.e., number of cells per clone). To determine the sequence of events in dimunition of antigen synthesis in MCF-7 cell monolayers, earlier MCF-7 passages were examined. Passages 6–10 of one subllne were 50–60% positive in reactivity with anti-MuMTV sera. Approximately 80% of cells in these passages were L-cells. Within four subsequent passages, the percentage of MuMTV-positive cells diminished from 50–60% to 4–6%. During that time, the cultures remained at least 70% L-cells. Two models of growth dynamics were proposed to account for phenotypic Interconversions of MCF-7 cells during in vitro proliferation.