The synthesis of a proteinase inhibitor, α‐1‐antichymotrypsin, by human breast epithelial cells

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Abstract
The synthesis and release of glycoproteins were studied in organ cultures of human breast surgical specimens and in established breast epithelial cell lines, MCF‐7 and MDA‐MB‐231. Biosynthesis was monitored by the incorporation of 14C‐glucosamine. Labeled macromolecules in the culture supernatants were analyzed by biochemical and immunological techniques. One to 8% of the labeled glycoproteins from benign breast and infiltrating ductal carcinoma specimens was precipitated by antibodies produced against human serum 7α‐1‐antichymotrypsin. Twelve percent of the total glycoproteins from the culture supernatants of the MCF‐7 cell line was identified as α‐1‐antichymo‐trypsin. Both the normal serum and the human breast epithelia‐derived proteinase inhibitor can be resolved into similar subclasses by two‐dimensional gel electrophoresis. MDA‐MB‐231 and MCF‐7 cells which were extensively washed with EDTA, serum‐free medium, and phosphate‐buffered saline retain this proteinase inhibitor on their cell surfaces. Three to 4% of the total cell‐surface iodinated components was immunoprecipitated by these specific antibodies. Since α‐1‐antichymotrypsin is a potent inhibitor of neutral proteinases such as cathepsin G, the demonstration of its synthesis by benign and malignant breast epithelial cells is of considerable interest. This glycoprotein may represent the epithelia's own protective shield of cell surface components and the cell's attempt to moderate the effects of invading leukocytes. In addition, it may play a regulatory role in the maintenance of three‐dimensional glandular structures.