The N-acetylglucosamine-specific receptor of the thyroid: purification, further characterization, and expression patterns on normal and pathological glands

Abstract

The N-acetylglucosamine receptor of the thyroid has been putatively described as both a prohormonal receptor that could play a role in the intrafollicular retention of immature thyroglobulin and a vectorial conveyor of these immature molecules to the iodination site. To further characterize this receptor, we have developed a purification procedure yielding nanomolar amounts of N-acetylglucosamine receptor. This thyroid lectin appeared to have an isoelectric point near 5.2 and to be composed of 51-kilodalton monomers with no Asn-linked glycoconjugates. Recognition of the receptor by antipeptide antibodies (Ab/ROV1) raised against a preselected sequence of cation-dependent lectins indicated immunological kinship with the Gal/GalNAc-specific hepatic lectin. Affinity-purified Ab/ROV1 and polyclonal antibodies against the purified receptor (TGRD-Ab) were used to study the location and expression pattern of the receptor on animal and human thyroid tissue. On porcine slices, positive labeling was observed in various intracellular vesicular compartments with both antibodies and was particularly intense in the apical membrane and subapical compartments. The same pattern was observed in normal human thyroid. In contrast, the receptor 1) could not be found on epithelial cells from thyroid papillary carcinoma; 2) was abundant, but concentrated in the subnuclear region of the thyrocytes in adenomatous goiter; and 3) was almost exclusively located at the basolateral membrane in follicular carcinoma as well as in thyrocytes from glands treated with antithyroid drug before surgery. These observations indicate that expression of the N-acetylglucosamine receptor is characteristic of the fully differentiated phenotype, and its potential function as a thyroglobulin conveyor back to the lumen would be either impaired or abolished in some disease processes.