Endocrinology, Vol 122, 488-494, Copyright © 1988 by Endocrine Society

ARTICLES

Accelerated exocytosis and H2O2 generation in isolated thyroid follicles enhance protein iodination

U Bjorkman and R Ekholm
Department of Anatomy, University of Goteborg, Sweden.

Open pig thyroid follicles in which the apical surface of the follicle cells is in direct contact with the incubation medium were used to study the effect of stimulated exocytosis and stimulated H2O2 generation on the iodination of protein in the incubation medium. In previous studies on this system of follicles we have shown (1) that the apical surface of the follicle cells is a major site of protein iodination and (2), that H2O2 is produced at the apical cell surface. In the present study we confirmed the previous finding that H2O2 generation is greatly stimulated by the Ca2+ ionophore A23187. We further found that TSH at a high concentration (greater than 10 mU/ml) and in the presence of Ca2+ stimulated H2O2 generation; TSH had no such effect on follicles incubated in Ca2+-free medium after pretreatment with EGTA. Forskolin did not stimulate H2O2 generation. Exocytosis of thyroglobulin was stimulated by TSH at a low concentration (0.1 mU/ml), and this stimulation was not dependent on Ca2+. Exocytosis was also stimulated by forskolin but not by A23187. Iodination of protein, including thyroglobulin, in the incubation medium was stimulated by A23187, TSH and forskolin. These observations suggest that stimulation of iodination in association with the apical surface of the follicle cells can be achieved separately by an increased rate of H2O2 generation and increased rate of exocytosis. Generation of H2O2 is Ca2+- dependent, whereas exocytosis is mediated by the adenylate cyclase-cAMP system; TSH at a high concentration can stimulate both these processes.

This article has been cited by other articles:

				L. Ulianich, M. G. Elia, A. S. Treglia, A. Muscella, B. Di Jeso, C. Storelli, and S. Marsigliante The sarcoplasmic-endoplasmic reticulum Ca2+ ATPase 2b regulates the Ca2+ transients elicited by P2Y2 activation in PC Cl3 thyroid cells. J. Endocrinol., September 1, 2006; 190(3): 641 - 649. [Abstract] [Full Text] [PDF]

				M.-C. Nlend, D. M. Cauvi, N. Venot, and O. Chabaud Role of Sulfated Tyrosines of Thyroglobulin in Thyroid Hormonosynthesis Endocrinology, November 1, 2005; 146(11): 4834 - 4843. [Abstract] [Full Text] [PDF]

				L. E. Ericson and M. Nilsson Deactivation of TSH receptor signaling in filter-cultured pig thyroid epithelial cells Am J Physiol Endocrinol Metab, April 1, 2000; 278(4): E611 - E619. [Abstract] [Full Text] [PDF]

				D Prabakaran, R. Ahima, J. Harney, M. Berry, P. Larsen, and P Arvan Polarized targeting of epithelial cell proteins in thyrocytes and MDCK cells J. Cell Sci., January 4, 1999; 112(8): 1247 - 1256. [Abstract] [PDF]

				R. Kuliawat, M. P. Lisanti, and P. Arvan Polarized Distribution and Delivery of Plasma Membrane Proteins in Thyroid Follicular Epithelial Cells J. Biol. Chem., February 10, 1995; 270(6): 2478 - 2482. [Abstract] [Full Text] [PDF]