Endocrine Abstracts

Recent data have shown that, in parallel to its transcriptional action down-regulating TSH synthesis, triiodothyronine (T₃) also acts on posttranscriptional steps of beta TSH synthesis, reducing the polyadenylation and translational rate of the beta TSH mRNA, when acutely administered to thyroidectomized rats. This study aimed to investigate whether these effects also occur in TalphaT1 cells, and if they are dependent on gene transcription, which would characterize novel actions of T₃ on its own regulatory axis. Cells were seeded on matrigel-coated plates, plated in DMEM high glucose and firstly divided in two groups: control (C) containing 10% FBS and hypothyroid (H) – cells plated with 10% FBS depleted of TH by treatment with AG1X-8 resin for 48 h. After this, 5,6-dichloro-1-β-D-ribobenzimidazole (DRB-50 mM) was administered to inhibit the gene transcription for 2 h, followed by the T₃-treatment in the doses of 10⁻⁸M or 10⁻¹⁰M for 30 min or 10⁻⁷M for 4 h. The total RNA and the fraction correspondent to the polisomes were extracted for investigation of mRNA content by RT/qPCR and polyadenylation degree by RACE-PAT assay. The results obtained showed that the T₃ rapidly reduces the total content of both subunits of TSH mRNA, and that this reduction is lost by DRB treatment only for alpha TSH mRNA subunit. Moreover it was shown that the T₃ (10⁻¹⁰M) specifically decreased the poly(A) tail length of beta TSH mRNA, and diminished the content of mRNA of both subunits associated with ribosome, which indicates that the translational rate of TSH synthesis was reduced. These data led us to conclude that the T₃ down-regulates TSH synthesis in TalphaT1 cells acting in several posttranscriptional steps of gene expression.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.