Release of estrogen-induced glycoprotein with a molecular weight of 52,000 by breast cancer cells in primary culture.

In an attempt to find estrogen-specific responses in breast cancer, we have established primary cell culture from metastatic pleural effusions of breast cancer and have analyzed the proteins labeled by [35S]methionine and released into the culture medium using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We show that the synthesis of a Mr 52,000 glycoprotein which is released by metastatic breast cancer cells in primary cultures is stimulated by estradiol in four of six patients. This protein is similar to the Mr 52,000 protein of MCF7 cells on the basis of its mobility in one- and two-dimensional gel electrophoresis [the molecular weight of this protein was originally found to be 46,000; it is closer to 52,000 using labeled proteins from New England Nuclear as molecular weight markers], its immunoprecipitation by antisera raised against the Mr 52,000 protein, and its binding to concanavalin A. We conclude that, similar to some breast cancer cell lines, some metastatic breast cancers synthesize a Mr 52,000 glycoprotein which is regulated by estrogens and exported from the cells into the medium. This study also shows that some primary cultures established from metastatic breast cancer remain responsive to estradiol in vitro for the synthesis of specific proteins. More clinical studies are needed to prove the interest of the Mr 52,000 secreted protein as an additional marker of the hormone responsiveness of breast cancer.