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Presence of Proteolytically Processed Keratins in the Culture Medium of MCF-7 Cells¹

Department of Medical Pathology, School of Medicine, University of California, Davis, California 95616

MCF-7 human mammary epithelial cells are known to express three distinct cytoskeletal intermediate filament proteins designated numbers 8 (M_r 52,000), 18 (M_r 45,000), and 19 (M_r 40,000) keratin. Using a panel of monoclonal antibodies and peptide mapping, we have determined that MCF-7 cells release proteolytic derivatives of keratins 18 and 19 into the culture medium. These extracellular keratins consist of multiple isoforms (M_r 38,000–45,000, isoelectric point 5.0–5.2) on two-dimensional gels, many of which are smaller and more acidic than the predominant intracellular forms and appear to be associated together as a soluble, large molecular weight complex. These results may potentially be correlated with observations of keratin-like antigens in body fluids of cancer patients and the presence of antikeratin antibodies in individuals with certain autoimmune diseases and acute viral infections.

¹ This work is supported by a grant from Triton Biosciences, Inc.

² To whom requests for reprints should be addressed.

Received 4/ 7/86. Revised 7/14/86. Accepted 8/20/86.

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