title: Follicular thyroglobulin enhances gene expression necessary for thyroid hormone secretion.
abstract: We have previously shown that follicular thyroglobulin (Tg) has an unexpected function as an autocrine negative-feedback regulator of thyroid hormone (TH) biosynthesis. Tg significantly suppressed the expression of genes necessary for iodide transport and TH synthesis by counteracting stimulation by TSH. However, whether follicular Tg also regulates intracellular TH transport and its secretion from thyrocytes is not known. In the present study, we examined the potential effect of follicular Tg on TH transport and secretion by quantifying the expression of two TH transporters: monocarboxylate transporter 8 (MCT8) and μ-crystallin (CRYM). Our results showed that follicular Tg at physiologic concentrations enhanced both the mRNA and protein expression levels of MCT8 and CRYM in a time- and dose-dependent manner in rat thyroid FRTL-5 cells. Although both the sodium/iodide symporter (NIS), an essential transporter of iodide from blood into the thyroid, and MCT8, a transporter of synthesized TH from the gland, were co-localized on the basolateral membrane of rat thyrocytes in vivo, Tg decreased NIS expression and increased the expression of MCT8 by counteracting TSH action. Thus, the effect of Tg on TH secretion opposed its previously described negative-feedback suppression of TH synthesis. Our results indicate that Tg mediates a complex intrinsic regulation of gene expression that is necessary to balance two opposing vectorial transport systems: the inflow of newly synthesized TH and the outflow of TH by external secretion.
authors.affiliation: Laboratory of Molecular Diagnostics, Department of Mycobacteriology, Leprosy Research Center, National Institute of Infectious Disease, Tokyo 189-0002, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ishido
authors.forename: Yuqian
authors.initials: Y
authors.lastname: Luo
authors.forename: Aya
authors.initials: A
authors.lastname: Yoshihara
authors.forename: Moyuru
authors.initials: M
authors.lastname: Hayashi
authors.forename: Akio
authors.initials: A
authors.lastname: Yoshida
authors.forename: Ichiro
authors.initials: I
authors.lastname: Hisatome
authors.forename: Koichi
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D002460:Cell Line; D003459:Crystallins / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects; D027501:Monocarboxylic Acid Transporters / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D013954:Thyroglobulin / Q000494:pharmacology*; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D000090803:mu-Crystallins
chemical_list: C000716471:Crym protein, rat; D003459:Crystallins; D027501:Monocarboxylic Acid Transporters; C478998:monocarboxylate transporter 8, rat; D013954:Thyroglobulin; D000090803:mu-Crystallins