Purification and partial characterization of high-molecular-weight forms of ectopic calcitonin from a human bronchial carcinoma cell line

Abstract

Studies on the high-MW immunoreactive calcitonin produced ectopically in culture by an epidermoid bronchial carcinoma cell line are reported. In cell-exposed medium, the principal component has a MW of 40,000 and molecules of MW 13,000 and 10,000 also occur. Only a trace amount of material co-eluting with 3500 MW human calcitonin is detectable. No calcitonin shows cross-reactivity with anti-ACTH serum. The 40,000 MW immunoreactive calcitonin is readily proteolyzed to the 13,000 and 10,000 MW components, but the 10,000 MW component behaves as a comparatively stable core molecule. By using immunoprecipitation and high-pressure liquid chromatography (h.p.l.c.), it is possible to prepare radiochemically homogeneous 10,000 MW immunoreactive calcitonin from cells grown in the presence of individual 35S- or 3H-labeled amino acids. Peptide mapping of enzymic digests of this material by h.p.l.c. shows that it contains peptides in common with synthetic human calcitonin.