Defective Thyroglobulin Synthesis in an Experimental Rat Thyroid Tumor: Iodination and Thyroid Hormone Synthesis in Isolated Tumor Thyroglobulin

Purified rat tumor thyroglobulin from the experimental rat thyroid tumor, line 1–1C2, was studied for its thyroid hormone content after in vivo and in vitro iodination and compared with normal and desialylated normal rat thyroglobulin. Tumor thyroglobulin had a very low sialic acid and iodine content; after in vivo iodination it contained only small amounts of triiodothyronine (T3) and no detectable thyroxine (T4). After in vitro iodination with 125I it showed a distribution of T3 and T4 very similar to that of normal and desialylated normal thyroglobulin iodinated in vitro. In vitro iodination dissociated tumor and desialylated normal thyroglobulin to a greater extent than normal thyroglobulin. Tumor tissue, on the other hand, showed considerable iodinating activity in the 105,000 × g pellet when studied with exogenous acceptors. These results are compatible with a role for sialic acid in the maturation and migration of thyroglobulin to the iodination site, provided that the intracellular distribution of...