Association of duoxes with thyroid peroxidase and its regulation in thyrocytes

Abstract

Context: Thyroid hormone synthesis requires H2O2 produced by dual oxidases (Duoxes) and thyroperoxidase (TPO). Defects in this system lead to congenital hypothyroidism. H2O2 damage to the thyrocytes may be a cause of cancer. Objective: The objective of the study was to investigate whether Duox and TPO, the H2O2 producer and consumer, might constitute a complex in the plasma membrane of human thyroid cells, thus maximizing efficiency and minimizing leakage and damage. Design: The interaction between Duox and TPO was studied by coimmunoprecipitation and Western blotting of plasma membranes from incubated follicles prepared from freshly resected human thyroid tissue from patients undergoing thyroidectomy, and COS-7 cells transiently transfected with the entire Duoxes or truncated [amino (NH2) or carboxyl (COOH) terminal]. Results: The following results were reached: 1) Duox and TPO from membranes are coprecipitated, 2) this association is up-regulated through the Gq-phospholipase C-Ca2+-protein kinase C pathway and down-regulated through the Gs-cAMP-protein kinase A pathway, 3) H2O2 increases the association of Duox1 and Duox2 to TPO in cells and in membranes, and 4) truncated NH2- or COOH-terminal Duox1 and Duox2 proteins show different binding abilities with TPO. Conclusion: Coimmunoprecipitations show that Duox and TPO locate closely in the plasma membranes of human thyrocytes, and this association can be modulated by H2O2, optimizing working efficiency and minimizing H2O2 spillage. This association could represent one part of a postulated pluriprotein complex involved in iodination. This suggests that defects in this association could impair thyroid hormone synthesis and lead to thyroid insufficiency and cell damage.