Production of Acid and Neutral Cysteine-proteinase Inhibitors by a Cultured Human Skin Epithelium Cell Line

Human skin epithelial-like cells (NCTC-strain 2544) were grown in RPMI-1640 medium supplemented with foetal calf serum for up to 2 weeks. The culture medium and extracts made from the cells were subjected to gel-filtration chromatography in a Sephacryl S-200 column for fractionation of the proteins. The fractions were assayed for acid and neutral cysteine-proteinase inhibitor (ACPI, NCPI) using time-resolved fluoroimmunoassay and radioimmunoassay, and the cysteine-proteinase-inhibiting activities were assayed using papain. Free NCPI, i.e. a molecule with isoelectric variants at pHs 6.0 and 6.5, which has an Mr of around 12,000 and is capable of inhibiting papain, was detected both in the culture medium and in the cells. Immunodiffusion studies revealed its immunological identity with human spleen-derived NCPI. The amount of NCPI increased during the incubation period. ACPI--characterized as a molecule having an isoelectric point of 4.9, an Mr of about 12,000, papain-inhibiting capacity and antigenic reactivity with spleen-derived ACPI--was not detected in the culture medium. It was, however, detected in the cells after 2 weeks in culture. These data prove that ACPI and NCPI are synthesized by the NCTC-2544 cells under the present culture conditions.