Role of thyroidal lysosomes in the hydrolysis of thyroglobulin and its relation to the development of iodide goiter.

Abstract

The 2-fold objective of this study was: 1) to clarify the site of thyroglobulin hydrolysis in the epithelial cells of the thyroid gland, and 2) to investigate the relation between thyroglobulin hydrolysis and the formation of iodide goiter as observed in mice. The particulate fraction of 20,000 × g was obtained from rat and mouse thyroids. This fraction seems to contain colloid droplet-lysosome fused particles as judged by the following results: 1) Thyroid protein included in the fused particles was thyroglobulin. Its content was increased by TSH and decreased by T4. 2) The presence of active lysosomal enzymes and thyro-globulin hydrolysis were coincidentally observed in the same particles. In addition, both were found in the incubation medium after Triton X-100 treatment. 3) The pattern of radioactivity of labeled thyroglobulin and the pattern of lysosomal enzyme activity coincided with each other when subjected to sucrose density gradient centrifugation. In mouse thyroid, thyroglobulin incorporation into the 20,000 × g particulates was significantly decreased, and lysosomal enzyme activities inhibited by the administration of large amounts of Nal. These results can reasonably explain the development of iodide goiter in mice. (Endocrinology95: 1574, 1974)