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Endocrinology, doi:10.1210/endo-114-2-375
Endocrinology Vol. 114, No. 2 375-382
Copyright © 1984 by the Endocrine Society.
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Stimulation of Thyroidal Thiol Endopeptidases by Thyrotropin*

ANN D. DUNN

Division of Endocrinology, University of Virginia School of Medicine Charlottesville, Virginia 22908

Address requests for reprints to: Dr. Ann D. Dunn, Department of Internal Medicine, Division of Endocrinology, University of Virginia School of Medicine, Box 511, Charlottesville, Virginia 22908.

Abstract

Rabbit thyroids contain cathepsin D (CD) and several thiol endopeptidases including cathepsin B and three newly described enzymes (cathepsins 180K, 110K, and 45K). The present paper assesses the relative physiological importance of these enzymes in thyroglobulin degradation in rabbits. Thyroidal thiol endopeptidase [thiol thyroglobulin hydrolase (thiol TgH)] activity increased in the absence of changes in CD activity in animals treated with 10 U bovine TSH. Peak enzyme activity occurred 24 h after injection of hormone. After 20 U bovine TSH, thiol endopeptidase activity increased by approximately 100%, whereas CD increased by 50%. The increase in thiol enzyme activity was attributed both to cathepsin B and to the other thiol endopeptidases. The lysosomal acid hydrolases acid phosphatase and dipeptidyl peptidase II were unaffected by TSH at either dose level. Thiol TgH activity, but not CD activity, was decreased in thyroids of rabbits treated with T4 [5 µg/(100 g BW·day)] for 1 week. All thyroidal acid hydrolases examined were suppressed in animals receiving T4 for 3 weeks. Thiol TgH activity was localized primarily to a lysosome-enriched fraction of thyroid homogenates.

Our results suggest that the thiol proteases probably are the most important endopeptidases in thyroglobulin hydrolysis in vivo and that their activities are influenced by TSH. (Endocrinology 114: 375, 1984)

Footnotes

* Supported by Grant AM-1043 from the National Institutes of Health. Part of this work was presented at the 64th Annual Meeting of The Endocrine Society, San Francisco, CA, June 1982 (Abstracts).

Received June 24, 1983.




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Copyright © 1984 by The Endocrine Society