Multiple forms of human tumor calcitonin demonstrated by denaturing polyacrylamide gel electrophoresis and lectin affinity chromatography

The molecular weight forms of immunoreactive calcitonin in human tumors have been studied using two sodium dodecyl sulfate polyacrylamide gel electrophoretic systems. Under denaturing conditions, which produce monomer peptides, it has been possible to document further the size heterogeneity of this immunoreactivity. Small molecular weight forms (native size human calcitonin of 3, 600 daltons and immunoreactive peptides of 4, 000-6, 000 daltons) predominated in extracts of four medullary thyroid carcinomas. Smaller amounts of larger molecular weight forms (8, 000-22, 000 daltons) were detected. In one medullary thyroid carcinoma and in an extract of small (oat) cell lung carcinoma, the higher molecular weight forms predominated, with the greatest amount of immunoreactivity found in 12, 000-and 10, 000-dalton peptides. Evidence has been obtained that all of the tumors studied contain a component of immunoreactive calcitonin that binds to lectins immobilized on agarose. Five to 20% of the total immunoreactive material from the medullary thyroid carcinomas and from human small (oat) cell lung carcinoma bound to columns of agarose-bound Concanavalin A and/or wheat germ agglutinin. The conditions of binding and elution with specific sugars strongly suggest that this lectinbound immunoreactive calcitonin may contain mannose and Nacetylglucosamine residues. Gel electrophoresis of the carbohydrate-eluted material showed that the lectin-bound forms comprise a portion of each of the several molecular weight classes of immunoreactive calcitonin moieties identified. These studies indicate further that human tumors contain different sizes of calcitonin immunoreactivity and that the ratios among these forms may vary among different neoplasms. The fact that some calcitonin forms may contain carbohydrate moieties is another potential determinant for the heterogeneity of the circulating immunoreactive calcitonin in patients with medullary thyroid carcinoma or small (oat) cell lung cancer.