Regulation of the secretion of proteins synthesized by the human breast cancer cell line, MCF-7

Abstract

In two sublines of the estrogen receptor-positive human breast cancer cell line, MCF-7, propagated with 0.5% fetal calf serum (FCS) (subline 0.5) and without serum (subline 9), respectively, addition of 10% newborn calf serum (NCS) inhibits cell proliferation and stimulates the secretion of a 42 kDa protein. Both with and without NCS, estradiol (E 2) stimulates the secretion of a 61 kDa and a 52 kDa protein in subline 9, and an additional third protein (66 kDa) is stimulated in subline 0.5. E 2 inhibits the synthesis of the 42 kDa protein in both sublines. Different cell proliferation rates of MCF-7 cells can be established in cultures with 10% NCS and varying concentrations of E 2. In such experiments final cell number after 6 days is positively correlated to the relative amount of the 66 kDa, the 61 kDa and the 52 kDa proteins, whereas the relative amount of the 42 kDa protein is negatively correlated to the final cell number. These results indicate that the 52 kDa, the 61 kDa and the 66 kDa proteins may act as positive growth factors, whereas the 42 kDa protein may act as a negative growth factor. The 42 kDa, the 52 kDa and the 61 kDa proteins are apparently glycoproteins, and the 66 kDa protein is not glycosylated. The 61 kDa protein is immunoreactive with antitrypsin antibodies.