Antitumor Responses Stimulated by Dendritic Cells Are Improved by Triiodothyronine Binding to the Thyroid Hormone Receptor β

Bidirectional cross-talk between the neuroendocrine and immune systems orchestrates immune responses in both physiologic and pathologic settings. In this study, we provide in vivo evidence of a critical role for the thyroid hormone triiodothyronine (T3) in controlling the maturation and antitumor functions of dendritic cells (DC). We used a thyroid hormone receptor (TR) β mutant mouse (TRβPV) to establish the relevance of the T3-TRβ system in vivo. In this model, TRβ signaling endowed DCs with the ability to stimulate antigen-specific cytotoxic T-cell responses during tumor development. T3 binding to TRβ increased DC viability and augmented DC migration to lymph nodes. Moreover, T3 stimulated the ability of DCs to cross-present antigens and to stimulate cytotoxic T-cell responses. In a B16-OVA mouse model of melanoma, vaccination with T3-stimulated DCs inhibited tumor growth and prolonged host survival, in part by promoting the generation of IFNγ-producing CD8(+) T cells. Overall, our results establish an adjuvant effect of T3-TRβ signaling in DCs, suggesting an immediately translatable method to empower DC vaccination approaches for cancer immunotherapy.

17β-Estradiol stimulates the translocation of endogenous estrogen receptor α at the plasma membrane of normal anterior pituitary cells

In the present work we aimed at identifying ERα in the plasma membrane of normal anterior pituitary cells and investigated if 17β-estradiol was able to induce their subcellular redistribution. Our results show that about 8% of anterior pituitary cells expressed ERα in the plasma membrane, with the geometrical mean fluorescence intensity being increased after steroid hormone treatment. 17β-Estradiol and the selective ERα agonist PPT induced an increase of ERα expression in the plasma membrane and activated the PKCα/ERK 1/2 pathway in a time-course not compatible with genomic actions, thus supporting the notion of membrane-initiated effects. These findings suggest that 17β-estradiol stimulates the translocation of endogenous ERα to the plasma membrane, consequently modulating this ER pool and leading to cellular biological effects in normal anterior pituitary gland.

17β-Estradiol modulates the prolactin secretion induced by TRH through membrane estrogen receptors via PI3K/Akt in female rat anterior pituitary cell culture

Considering that estradiol is a major modulator of prolactin (PRL) secretion, the aim of the present study was to analyze the role of membrane estradiol receptor-α (mERα) in the regulatory effect of this hormone on the PRL secretion induced by thyrotropin-releasing hormone (TRH) by focusing on the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway activation. Anterior pituitary cell cultures from female rats were treated with 17β-estradiol (E(2), 10 nM) and its membrane-impermeable conjugated estradiol (E(2)-BSA, 10 nM) alone or coincubated with TRH (10 nM) for 30 min, with PRL levels being determined by RIA. Although E(2), E(2)-BSA, TRH, and E(2)/TRH differentially increased the PRL secretion, the highest levels were achieved with E(2)-BSA/TRH. ICI-182,780 did not modify the TRH-induced PRL release but significantly inhibited the PRL secretion promoted by E(2) or E(2)-BSA alone or in coincubation with TRH. The PI3K inhibitors LY-294002 and wortmannin partially inhibited the PRL release induced by E(2)-BSA, TRH, and E(2)/TRH and totally inhibited the PRL levels stimulated by E(2)-BSA/TRH, suggesting that the mER mediated the cooperative effect of E(2) on TRH-induced PRL release through the PI3K pathway. Also, the involvement of this kinase was supported by the translocation of its regulatory subunit p85α from the cytoplasm to the plasma membrane in the lactotroph cells treated with E(2)-BSA and TRH alone or in coincubation. A significant increase of phosphorylated Akt was induced by E(2)-BSA/TRH. Finally, the changes of ERα expression in the plasmalemma of pituitary cells were examined by confocal microscopy and flow cytometry, which revealed that the mobilization of intracellular ERα to the plasma membrane of lactotroph cells was only induced by E(2). These finding showed that E(2) may act as a modulator of the secretory response of lactotrophs induced by TRH through mER, with the contribution by PI3K/Akt pathway activation providing a new insight into the mechanisms underlying the nongenomic action of E(2) in the pituitary.

Dexamethasone counteracts the immunostimulatory effects of triiodothyronine (T3) on dendritic cells

Glucocorticoids (GCs) are widely used as anti-inflammatory and immunosuppressive agents. Several studies have indicated the important role of dendritic cells (DCs), highly specialized antigen-presenting and immunomodulatory cells, in GC-mediated suppression of adaptive immune responses. Recently, we demonstrated that triiodothyronine (T3) has potent immunostimulatory effects on bone marrow-derived mouse DCs through a mechanism involving T3 binding to cytosolic thyroid hormone receptor (TR) β1, rapid and sustained Akt activation and IL-12 production. Here we explored the impact of GCs on T3-mediated DC maturation and function and the intracellular events underlying these effects. Dexamethasone (Dex), a synthetic GC, potently inhibited T3-induced stimulation of DCs by preventing the augmented expression of maturation markers and the enhanced IL-12 secretion through mechanisms involving the GC receptor. These effects were accompanied by increased IL-10 levels following exposure of T3-conditioned DCs to Dex. Accordingly, Dex inhibited the immunostimulatory capacity of T3-matured DCs on naive T-cell proliferation and IFN-γ production while increased IL-10 synthesis by allogeneic T cell cultures. A mechanistic analysis revealed the ability of Dex to dampen T3 responses through modulation of Akt phosphorylation and cytoplasmic-nuclear shuttling of nuclear factor-κB (NF-κB). In addition, Dex decreased TRβ1 expression in both immature and T3-maturated DCs through mechanisms involving the GC receptor. Thus GCs, which are increased during the resolution of inflammatory responses, counteract the immunostimulatory effects of T3 on DCs and their ability to polarize adaptive immune responses toward a T helper (Th)-1-type through mechanisms involving, at least in part, NF-κB- and TRβ1-dependent pathways. Our data provide an alternative mechanism for the anti-inflammatory effects of GCs with critical implications in immunopathology at the cross-roads of the immune-endocrine circuits.

Expanding the universe of cytokines and pattern recognition receptors: galectins and glycans in innate immunity

Effective immunity relies on the recognition of pathogens and tumors by innate immune cells through diverse pattern recognition receptors (PRRs) that lead to initiation of signaling processes and secretion of pro- and anti-inflammatory cytokines. Galectins, a family of endogenous lectins widely expressed in infected and neoplastic tissues have emerged as part of the portfolio of soluble mediators and pattern recognition receptors responsible for eliciting and controlling innate immunity. These highly conserved glycan-binding proteins can control immune cell processes through binding to specific glycan structures on pathogens and tumors or by acting intracellularly via modulation of selective signaling pathways. Recent findings demonstrate that various galectin family members influence the fate and physiology of different innate immune cells including polymorphonuclear neutrophils, mast cells, macrophages, and dendritic cells. Moreover, several pathogens may actually utilize galectins as a mechanism of host invasion. In this review, we aim to highlight and integrate recent discoveries that have led to our current understanding of the role of galectins in host-pathogen interactions and innate immunity. Challenges for the future will embrace the rational manipulation of galectin-glycan interactions to instruct and shape innate immunity during microbial infections, inflammation, and cancer.

Nuclear factor (NF)-kappaB-dependent thyroid hormone receptor beta1 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) beta(1) signaling in modulating dendritic cell (DC) physiology and the intracellular mechanisms underlying these immunoregulatory effects. Exposure of DCs to triiodothyronine (T(3)) resulted in a rapid and sustained increase in Akt phosphorylation independently of phosphatidylinositol 3-kinase activation, which was essential for supporting T(3)-induced DC maturation and interleukin (IL)-12 production. This effect was dependent on intact TR beta(1) signaling as small interfering RNA-mediated silencing of TR beta(1) expression prevented T(3)-induced DC maturation and IL-12 secretion as well as Akt activation and I kappaB-epsilon degradation. In turn, T(3) up-regulated TR beta(1) expression through mechanisms involving NF-kappaB, suggesting an autocrine regulatory loop to control hormone-dependent TR beta(1) signaling. These findings were confirmed by chromatin immunoprecipitation analysis, which disclosed a new functional NF-kappaB consensus site in the promoter region of the TRB1 gene. Thus, a T(3)-induced NF-kappaB-dependent mechanism controls TR beta(1) 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.

Growth hormone (GH) treatment reduces peripheral thyroid hormone action in girls with Turner syndrome

OBJECTIVE

Turner syndrome (TS) is an indication for GH therapy in spite of the modest growth response. Somatic growth depends not only on GH insulin-like growth factor I (IGF-I) axis but also on thyroid hormone (TH) status. We have previously reported that supraphysiological IGF-I levels diminished TH actions in rat tissues by reducing the nuclear TH receptor (TR). GH treatment to TS patients induces high IGF-I levels and therefore a reduction of TH action in tissues may be expected. We aimed at evaluating the effect of GH therapy in TS girls on peripheral TH action.

DESIGN AND PATIENTS

We set up a reverse transcription-polymerase chain reaction (RT-PCR) for TR mRNA estimation in peripheral blood mononuclear cells (PBMC) and compared TR mRNA levels from 10 normal, 10 TS and 10 TS girls under GH therapy (0.33 mg/kg/week for 0.5-2 years).

MEASUREMENTS

After RNA extraction from PBMC, TR and beta-actin mRNAs were coamplified by RT-PCR. In addition serum biochemical markers of TH action were measured: thyrotropin (TSH), sex hormone binding globulin (SHBG), osteocalcin (OC), beta-crosslaps (beta-CL), iodothyronines by electrochemiluminescency and IGF-I by immunoradiometric assay (IRMA) with extraction.

RESULTS

TR mRNAs from PBMC were reduced in TS patients under GH treatment. In turn, serum TSH, OC, beta-CL and IGF-I were increased while SHBG was reduced by GH treatment in TS patients.

CONCLUSIONS

GH treatment reduced TR expression in PBMC and biochemical serum markers of TH action. These results suggest that GH treatment in TS patients impair peripheral TH action at tissue level and prompt a role in the reduced growth response to the therapy.

Endogenous thyrocyte-produced nitric oxide inhibits iodide uptake and thyroid-specific gene expression in FRTL-5 thyroid cells

Nitric oxide (NO) is a free radical that mediates a wide array of cell functions. It is generated from l-arginine by NO-synthase (NOS). Expression of NOS isoforms has been demonstrated in thyroid cells. Previous reports indicated that NO donors induce dedifferentiation in thyrocytes. However, the functional significance of endogenous thyrocyte-produced NO has not been explored. This work aimed to study the influence of endogenous NO on parameters of thyroid cell function and differentiation in FRTL-5 cells. We observed that treatment with the NOS inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME), increased the TSH-stimulated iodide uptake. The TSH-induced sodium iodide symporter (NIS) and thyroglobulin (TG) mRNA expressions were increased after incubation with L-NAME. In transient transfection assays, TSH-stimulated transcriptional activities of NIS and TG promoters were increased by L-NAME. An increment of the TSH-stimulated cell proliferation was observed after NOS inhibition. Similar results were obtained when the action of another NOS inhibitor, N(g)-monomethyl-L-arginine, was analysed for most of these studies. The production of NO, which was not detectable in basal conditions, was increased by TSH. Our data provide strong evidence that endogenous NO could act as a negative signal for TSH-stimulated iodide uptake and thyroid-specific gene expression as well as proliferation in thyrocytes. These findings reveal a possible new inhibitory pathway in the regulation of thyroid cell function.