ENHANCEMENT OF NATURAL-KILLER-CELL SUSCEPTIBILITY OF HUMAN BREAST-CANCER CELLS BY ESTRADIOL AND V-HA-RAS ONCOGENE

Natural killer (NK) cells are putative components of the cellular immune response to transformed cells. Since both estradiol treatment and ras-oncogene overexpression enhance tumorigenicity of hormone-dependent breast-cancer cells, we studied the effects of estrogen and of the activated v-Ha-ras oncogene on NK susceptibility of MCF-7 human breast-cancer cells. MCF-7 cells were sensitive to cytolysis mediated by resting and IL2-activated peripheral-blood non-adherent lymphocytes. Lysis appeared to be mediated by NK cells, since it was abrogated by treatment of effector cells with alpha-CD16 monoclonal antibody (MAb) plus complement (c'). Estradiol treatment of MCF-7 cells was able to significantly increase their sensitivity to the lysis by IL2-activated and unactivated peripheral-blood lymphocytes, as early as 24 hr throughout 10 days of hormone treatment. Hormone-insensitive, estrogen-receptor-negative breast-cancer cells (BT20) did not change their NK susceptibility after estradiol treatment. Increased NK susceptibility was also observed in v-Ha-ras-transfected and oncogene product overexpressing MCF-7 cells (MCF-7-ras) with respect to cells transfected with the selectable gene marker gpt alone (MCF-7-gpt). Overexpression of v-Ha-ras appeared to be able to bypass the need for estrogen to increase NK susceptibility, since estradiol-treated MCF-7-ras cells were not lysed more than untreated MCF-7-ras cells. The enhancement of NK susceptibility observed after both estradiol treatment and v-Ha-ras overexpression suggests that the hormone-mediated and the ras-oncogene-mediated signalling systems share events involved in the control of tumor-cell/host-effector-cell interactions.