Human undifferentiated thyroid carcinoma synthesizes and secretes 19S thyroglobulin

Thyroglobulin (Tg) biosynthesis and secretion have been studied in one case of undifferentiated small spindle cell human thyroid carcinoma. From tumor tissue were extracted 32 mg of soluble proteins per gram of wet tissue, compared with 54 mg from control gland; after ammonium sulfate fractionation, density gradient centrifugation, and immunoprecipitation, 1.3 mg of Tg per gram of wet tissue, compared with 31.2 mg from control, were purified. By incubating in vitro up to 3 hours tumor slices with tritiated leucine, galactose, and 125I, the rate of incorporation of leucine and galactose increased with time in tumor tissue. However 125I incorporation into soluble proteins from tumor, at 3 hours of incubation, was only 1.7% of control value. By density gradient centrifugation of labeled soluble proteins a well-separated component sedimenting in the 19S peak was identified. No radioiodine was detected in the 19S fraction which showed the immunoreactive properties of 19S and was poor in 127I and sialic acid. In the incubation medium of tumor were secreted 0.4 mg of 19S Tg per gram of wet tissue compared with 48 mg of tissue in the control gland. Thus the undifferentiated thyroid carcinoma synthesizes a protein with the physiochemical and immunologic properties of 19S Tg. The undifferentiation of thyroid cells does not affect the biochemical steps involved in the synthesis of Tg.