Active proteinase inhibitors associated with human breast epithelial cells

The major glycoproteins synthesized by human breast epithelial cells have been characterized [6,8]. The most consistently observed and prominent component in supernatants of organ cultures of breast surgical specimens and of MCF‐7 cells was gp 68 which has been immunologically identified as α‐1‐antichymotrypsin (Achy). In the present study we demonstrate that this glycoprotein can form an irreversible complex with chymotrypsin, which indicates that it is a functional inhibitor. The ¹⁴C‐glucosamine‐labeled gp 68 forms a stable, 88,000‐dalton. enzyme‐inhibitor complex with chymotrypsin. The molecule is secreted continuously for 9 days into a chemically defined, serum‐free medium. In addition to the de novo synthesized inhibitor, another component is adsorbed from fetal bovine scrum and subsequently released into serum‐free medium. This component also forms an irreversible, 88,000‐dalton complex with enzyme. The observations establish that two types of inhibitors are associated with human breast epithelial cells, one actively synthesized and the other derived from serum. Both of these molecules may have significant roles in stabilizing cell surface components and in protecting extracellular matrices from untimely degradation.