PROGESTERONE STIMULATES PRODUCTION AND SECRETION OF MUC1 EPITHELIAL MUCIN IN STEROID-RESPONSIVE BREAST-CANCER CELL-LINES

The effects of oestrogen and progesterone on expression of the MUC1 ep ithelial mucin were examined in MCF7 and ZR-75-1 breast cancer cells g rown in steroid-free medium. Oestrogen caused an increase in cell grow th and both cellular and secreted MUC1 in both cell lines. However, af ter correcting for increases in cellular protein, there was no clear c hanges. Progesterone, in combination with oestrogen, caused significan t increases (over 2-fold, P<0.01) in cellular and secreted MUC1 when c ompared with oestrogen alone in both cell lines despite no or small in creases in cellular protein. Growth of ZR-75-1 cells in a competitive inhibitor of O-glycosylation demonstrated that the increased detection by ELISA was not due to altered glycosylation. Progesterone may modul ate expression of MUC1 in steroid-responsive breast cancer cells.