The work continues to emphasize iodide transport in thyroid and the relationship of thyroglobulin sialylation and iodination necessary for normal thyroid hormone formation. The project has developed further in the cloning of iodide transport formation. The project has developed further in the cloning of iodide transport proteins from thyroid. For the project, a CDNA expression library, prepared from cultured rat thyroid cells superinduced to actively transport iodide, is being used. The screening assay uses a replica plate assay to detect iodide transport in a mutant line of rat thyroid cells that responds to thyrotropin demonstrated by elevations in cyclic AMP levels, but does not transport iodide. The particular methods for cloning were selected because of the lack of success using more traditional methods for cloning. Previous selection of iodide transport clones in this laboratory were based on the property of stilbene binding, a property associated with iodide loss from the thyroid into the follicular lumen. These clones are related to non-erythroid band 3 proteins. If the reconstitution of both types of iodide carriers (a sodium/iodide symporter and an iodide efflux channel) is successful, studies of the properties of iodide transport in thyroid will be more productive. Collaborative studies demonstrated the role of thyrotropin in sialylation of thyroglobulin in cultured rat thyroid cells. These studies are now extended to address the glycosylation of thyroglobulin prepared from thyroid tissue from patients with two different thyroid diseases. In Graves' disease where there is elevated thyroid hormone levels, thyroglobulin is found to be both hyper and abnormally sialylated. This contrasts with thyroglobulin isolated from endemic goiter which is both hypo-iodinated and hypo-glycosylated. The findings continue to support a significant role for sialylation in thyroglobulin secretion and iodination leading to normal thyroid hormone formation.
