Bacterial lipopolysaccharide stimulates the thyrotropin-dependent thyroglobulin gene expression at the transcriptional level by involving the transcription factors thyroid transcription factor-1 and paired box domain transcription factor 8

16 pages, 11 figures.The bacterial lipopolysaccharide (LPS) is a biological activator that induces expression of multiple genes in several cell types. LPS has been proposed as an etiopathogenic agent in autoimmune diseases. However, whether LPS affects the expression of autoantigens has not been explored. Thyroglobulin (TG) is a key protein in thyroid hormonogenesis and one of the major thyroid autoantigens. This study aimed to analyze the action of LPS on TG gene expression in Fisher rat thyroid cell line FRTL-5 thyroid cells. We demonstrate that LPS increases the TSH-induced TG protein and mRNA level. Evidence that the effect of LPS is exerted at the transcriptional level was obtained by transfecting the minimal TG promoter. The C element of the TG promoter, which contains sequences for paired box domain transcription factor 8 (Pax8) and thyroid transcription factor (TTF)-1 binding, is essential for full TG promoter expression under TSH stimulation. The transcriptional activity of a construct containing five tandem repeats of the C site is increased by LPS, indicating a possible involvement of the C site in the LPS-induced TG gene transcription. We demonstrate that the TG promoter mutated at the Pax8 or TTF-1 binding element in the C site does not respond to LPS. In band shift assays, binding of Pax8 and TTF-1 to the C site is increased by LPS. The Pax8 and TTF-1 mRNA and protein levels are augmented by LPS. The half-lives of TG, Pax8, and TTF-1 are increased in endotoxin-treated cells. Our results reveal the ability of LPS to stimulate the expression of TG, a finding of potential pathophysiological implication.This work was supported by the Consejo Nacional de Investigaciones Científicas y Técnicas, by the Secretaría de Ciencia y Tecnología de la Universidad Nacional de Córdoba, by the Agencia Córdoba Ciencia, by the Agencia Nacional de Promoción Científica y Tecnológica (Argentina), by Ministerio de Educación y Ciencia, Grant Biología Fundamental 2004-03169, and by Fondo de Investigaciones Sanitarias of the Instituto de Salud Carlos III, Grant RCMN-C03/08 (Spain).Peer reviewe

Nuclear Factor (NF)-κB-dependent Thyroid Hormone Receptor β1 Expression Controls Dendritic Cell Function via Akt Signaling*

Despite considerable progress in our understanding of the interplay between immune and endocrine systems, the role of thyroid hormones and their receptors in the control of adaptive immunity is still uncertain. Here, we investigated the role of thyroid hormone receptor (TR) β1 signaling in modulating dendritic cell (DC) physiology and the intracellular mechanisms underlying these immunoregulatory effects. Exposure of DCs to triiodothyronine (T3) resulted in a rapid and sustained increase in Akt phosphorylation independently of phosphatidylinositol 3-kinase activation, which was essential for supporting T3-induced DC maturation and interleukin (IL)-12 production. This effect was dependent on intact TRβ1 signaling as small interfering RNA-mediated silencing of TRβ1 expression prevented T3-induced DC maturation and IL-12 secretion as well as Akt activation and IκB-ϵ degradation. In turn, T3 up-regulated TRβ1 expression through mechanisms involving NF-κB, suggesting an autocrine regulatory loop to control hormone-dependent TRβ1 signaling. These findings were confirmed by chromatin immunoprecipitation analysis, which disclosed a new functional NF-κB consensus site in the promoter region of the TRB1 gene. Thus, a T3-induced NF-κB-dependent mechanism controls TRβ1 expression, which in turn signals DCs to promote maturation and function via an Akt-dependent but PI3K-independent pathway. These results underscore a novel unrecognized target that regulates DC maturation and function with critical implications in immunopathology at the cross-roads of the immune-endocrine circuits