Thyrotropin induces SOCS-1 (suppressor of cytokine signaling-1) and SOCS-3 in FRTL-5 thyroid cells

Role of SOCS and VHL Proteins in Neuronal Differentiation and Development

The basic helix-loop-helix factors play a central role in neuronal differentiation and nervous system development, which involve the Notch and signal transducer and activator of transcription (STAT)/small mother against decapentaplegic signaling pathways. Neural stem cells differentiate into three nervous system lineages, and the suppressor of cytokine signaling (SOCS) and von Hippel-Lindau (VHL) proteins are involved in this neuronal differentiation. The SOCS and VHL proteins both contain homologous structures comprising the BC-box motif. SOCSs recruit Elongin C, Elongin B, Cullin5(Cul5), and Rbx2, whereas VHL recruits Elongin C, Elongin B, Cul2, and Rbx1. SOCSs form SBC-Cul5/E3 complexes, and VHL forms a VBC-Cul2/E3 complex. These complexes degrade the target protein and suppress its downstream transduction pathway by acting as E3 ligases via the ubiquitin-proteasome system. The Janus kinase (JAK) is the main target protein of the E3 ligase SBC-Cul5, whereas hypoxia-inducible factor is the primary target protein of the E3 ligase VBC-Cul2; nonetheless, VBC-Cul2 also targets the JAK. SOCSs not only act on the ubiquitin-proteasome system but also act directly on JAKs to suppress the Janus kinase-signal transduction and activator of transcription (JAK-STAT) pathway. Both SOCS and VHL are expressed in the nervous system, predominantly in brain neurons in the embryonic stage. Both SOCS and VHL induce neuronal differentiation. SOCS is involved in differentiation into neurons, whereas VHL is involved in differentiation into neurons and oligodendrocytes; both proteins promote neurite outgrowth. It has also been suggested that the inactivation of these proteins may lead to the development of nervous system malignancies and that these proteins may function as tumor suppressors. The mechanism of action of SOCS and VHL involved in neuronal differentiation and nervous system development is thought to be mediated through the inhibition of downstream signaling pathways, JAK-STAT, and hypoxia-inducible factor-vascular endothelial growth factor pathways. In addition, because SOCS and VHL promote nerve regeneration, they are expected to be applied in neuronal regenerative medicine for traumatic brain injury and stroke.

Thyrotropin, Hyperthyroidism, and Bone Mass

Thyrotropin (TSH), traditionally seen as a pituitary hormone that regulates thyroid glands, has additional roles in physiology including skeletal remodeling. Population-based observations in people with euthyroidism or subclinical hyperthyroidism indicated a negative association between bone mass and low-normal TSH. The findings of correlative studies were supported by small intervention trials using recombinant human TSH (rhTSH) injection, and genetic and case-based evidence. Genetically modified mouse models, which disrupt the reciprocal relationship between TSH and thyroid hormone, have allowed us to examine an independent role of TSH. Since the first description of osteoporotic phenotype in haploinsufficient Tshr +/- mice with normal thyroid hormone levels, the antiosteoclastic effect of TSH has been documented in both in vitro and in vivo studies. Further studies showed that increased osteoclastogenesis in Tshr-deficient mice was mediated by tumor necrosis factor α. Low TSH not only increased osteoclastogenesis, but also decreased osteoblastogenesis in bone marrow-derived primary osteoblast cultures. However, later in vivo studies using small and intermittent doses of rhTSH showed a proanabolic effect, which suggests that its action might be dose and frequency dependent. TSHR was shown to interact with insulin-like growth factor 1 receptor, and vascular endothelial growth factor and Wnt pathway might play a role in TSH's effect on osteoblasts. The expression and direct skeletal effect of a biologically active splice variant of the TSHβ subunit (TSHβv) in bone marrow-derived macrophage and other immune cells suggest a local skeletal effect of TSHR. Further studies of how locally secreted TSHβv and systemic TSHβ interact in skeletal remodeling through the endocrine, immune, and skeletal systems will help us better understand the hyperthyroidism-induced bone disease.

Functional analysis of two STAT1 gain-of-function mutations in two Iranian families with autosomal dominant chronic mucocutaneous candidiasis

Candidiasis is characterized by susceptibility to recurrent or persistent infections caused by Candida spp., typically Candida albicans, of cutaneous and mucosal surfaces. In this report, function and frequency of Th17 cells as well as genetics of patients susceptible to mucocutaneous candidiasis were studied. For patients, T-cell proliferation tests in response to Candida antigen, Th17 cell proportions, and STAT1 phosphorylation were evaluated through flow cytometry. Expression of IL17A, IL17F and IL22 genes were measured by real-time quantitative PCR. At the same time, whole exome sequencing was performed for all patients. We identified two heterozygous substitutions, one: c.821G > A (p. R274Q) was found in a multiplex family with three individuals affected, the second one: c.812A > C (p. Q271P) was found in a sporadic case. Both mutations are located in the coiled-coil domain (CCD) of STAT1. The frequency of Th17 cells, IL17A, IL17F, and IL22 gene expression in patients' peripheral blood mononuclear cells (PBMCs), and T-cell proliferation to Candida antigens were significantly reduced in the patients as compared to healthy controls. An increased STAT1 phosphorylation was observed in patients' PBMCs upon interferon (IFN)-γ stimulation as compared to healthy controls. We report two different but neighboring heterozygous mutations, located in exon 10 of the STAT1 gene, in four Iranian patients with CMC, one of whom also had hypothyroidism. These mutations were associated with impaired T cell proliferation to Candida antigen, low Th17 cell proportions, and increased STAT1 phosphorylation upon IFN-γ. We suggest that interfering with STAT1 phosphorylation might be a promising way for potential therapeutic measurements for such patients.

Luciferase Reporter Mice for In Vivo Monitoring and Ex Vivo Assessment of Hypothalamic Signaling of Socs3 Expression

Suppressor of cytokine signaling-3 (SOCS3) is a negative regulator of actions of cytokines and the metabolic hormone leptin. In the hypothalamus, SOCS3 is induced in response to several conditions such as inflammation and high-fat diet feeding, modulates cellular signaling of cytokines and leptin, and mediates the effects of these biological conditions. However, signaling mechanisms controlling hypothalamic Socs3 expression remains to be fully established. To facilitate the identification of molecular pathways of Socs3 induction, we generated a real-time gene expression reporter mouse of Socs3 (Socs3-Luc mice). We successfully detected a remarkable increase in luciferase activity in various tissues of Socs3-Luc mice in response to a peripheral injection of lipopolysaccharide, a potent inducer of inflammation, reflecting expression levels of endogenous Socs3 mRNA. Using ex vivo hypothalamic explants of Socs3-Luc mice, we demonstrate that hypothalamic luciferase activity was significantly elevated in slices stimulated with known inducers of Socs3 such as proinflammatory cytokines IL-6, IL-1β, and TNF-α, lipopolysaccharide, and cAMP-inducing agent forskolin. Using the ex vivo model, we found glycogen synthase kinase-3 (GSK3)β-specific inhibitors to be potent inducers of Socs3. Furthermore, pharmacological inhibitors of β-catenin, a downstream mediator of GSK3β signaling, reduced Socs3 luciferase activity ex vivo. Finally, hypothalamic inhibition of GSK3β hindered leptin-induced phosphorylation of signal transducers and activators of transcription 3 in hypothalamic explants. These results suggest that the Socs3-luciferase mouse is useful for in vivo monitoring of Socs3 gene expression and for ex vivo slice-based screening to identify signaling pathways that control Socs3 in the hypothalamus.

Effects of thyroid-stimulating hormone on adhesion molecules and pro-inflammatory cytokines secretion in human umbilical vein endothelial cells

Atherosclerosis is a multifactorial disorder, which affects the arterial wall. It has been reported that, hypothyroidism and thyroid hormone deficiency are related to cardiovascular disorders. Also, endothelial dysfunction plays an essential role in the development of atherosclerosis. We aimed to evaluate the effects of thyroid-stimulating hormone (TSH) on pro-inflammatory tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), angiogenic vascular endothelial growth factor (VEGF) and leukocyte adhesion, intercellular adhesion molecule 1 (ICAM-1) and E-selectin in human umbilical vein endothelial cells (HUVECs). In this study, HUVEC cells were treated with 1 and 2 μM of TSH in different treatment times. The gene and protein expression of ICAM-1, VEGF, and E-selectin were performed by real-time polymerase chain reaction and western blotting, respectively. Likewise, TNF-α and IL-6 protein levels were determined by the ELISA method. VEGF, ICAM-1, and E-selectin as endothelial dysfunction markers and also, TNF-α and IL-6 as pro-inflammatory cytokines were detectable in HUVEC. Besides, the results of this study revealed that TSH treatment down-regulates TNF-α and IL-6. Evaluating the gene and protein expression data revealed the upregulation of ICAM-1, E-selectin, and VEGF in TSH treated cases in different periods of exposure. Considering the multiple actions of TSH, it could be concluded that TSH plays a controversial role in atherogenesis by anti-inflammatory effects and on the other side, angiogenesis and leukocyte adhesion induction which is related to vascular cell proliferation.

Nuclear Localization of Suppressor of Cytokine Signaling-1 Regulates Local Immunity in the Lung

Suppressor of cytokine signaling 1 (SOCS1) is a negative feedback inhibitor of cytoplasmic Janus kinase and signal transducer and activator of transcription (STAT) signaling. SOCS1 also contains a nuclear localization sequence (NLS), yet, the in vivo importance of nuclear translocation is unknown. We generated transgenic mice containing mutated Socs1ΔNLS that fails to translocate in the cell nucleus (MGL^tg mice). Whereas mice fully deficient for SOCS1 die within the first 3 weeks due to excessive interferon signaling and multiorgan inflammation, mice expressing only non-nuclear Socs1ΔNLS (Socs1^-/-MGL^tg mice) were rescued from early lethality. Canonical interferon gamma signaling was still functional in Socs1^-/-MGL^tg mice as shown by unaltered tyrosine phosphorylation of STAT1 and whole genome expression analysis. However, a subset of NFκB inducible genes was dysregulated. Socs1^-/-MGL^tg mice spontaneously developed low-grade inflammation in the lung and had elevated Th2-type cytokines. Upon ovalbumin sensitization and challenge, airway eosinophilia was increased in Socs1^-/-MGL^tg mice. Decreased transepithelial electrical resistance in trachea epithelial cells from Socs1^-/-MGL^tg mice suggests disrupted epithelial cell barrier. The results indicate that nuclear SOCS1 is a regulator of local immunity in the lung and unravel a so far unrecognized function for SOCS1 in the cell nucleus.

The Extended Clinical Phenotype of 26 Patients with Chronic Mucocutaneous Candidiasis due to Gain-of-Function Mutations in STAT1

Purpose

Gain-of-function (GOF) mutations in the signal transducer and activator of transcription 1 (STAT1) result in unbalanced STAT signaling and cause immune dysregulation and immunodeficiency. The latter is often characterized by the susceptibility to recurrent Candida infections, resulting in the clinical picture of chronic mucocutaneous candidiasis (CMC). This study aims to assess the frequency of GOF STAT1 mutations in a large international cohort of CMC patients.

Methods

STAT1 was sequenced in genomic DNA from 57 CMC patients and 35 healthy family members. The functional relevance of nine different STAT1 variants was shown by flow cytometric analysis of STAT1 phosphorylation in patients’ peripheral blood cells (PBMC) after stimulation with interferon (IFN)-α, IFN-γ or interleukin-27 respectively. Extended clinical data sets were collected and summarized for 26 patients.

Results

Heterozygous mutations within STAT1 were identified in 35 of 57 CMC patients (61 %). Out of 39 familial cases from 11 families, 26 patients (67 %) from 9 families and out of 18 sporadic cases, 9 patients (50 %) were shown to have heterozygous mutations within STAT1. Thirteen distinct STAT1 mutations are reported in this paper. Eight of these mutations are known to cause CMC (p.M202V, p.A267V, p.R274W, p.R274Q, p.T385M, p.K388E, p.N397D, and p.F404Y). However, five STAT1 variants (p.F172L, p.Y287D, p.P293S, p.T385K and p.S466R) have not been reported before in CMC patients.

Conclusion

STAT1 mutations are frequently observed in patients suffering from CMC. Thus, sequence analysis of STAT1 in CMC patients is advised. Measurement of IFN- or IL-induced STAT1 phosphorylation in PBMC provides a fast and reliable diagnostic tool and should be carried out in addition to genetic testing.

Clinical manifestations associated with novel mutations in the coiled-coil domain of STAT1

Monoallelic mutations in STAT1 are associated with a variety of clinical patterns. We studied patients with novel mutations in the coiled-coil domain of STAT1. We found that clinical manifestations can vary from mild Candida infections limited to the oropharyx to serious serial strokes and skin cancer. Autoimmune manifestations were found to be rare and limited to hypothyroidism. Immune evaluations were normal or near normal in all patients with the exception of anergy to Candida. Mutation in the coiled-coil domain results in susceptibility to mucus membrane candidiasis as well as brain vascular anomalies.

Statement of novelty: We describe novel mutations in the coiled-coil domain of STAT1.

A crowd-sourcing approach for the construction of species-specific cell signaling networks

Motivation: Animal models are important tools in drug discovery and for understanding human biology in general. However, many drugs that initially show promising results in rodents fail in later stages of clinical trials. Understanding the commonalities and differences between human and rat cell signaling networks can lead to better experimental designs, improved allocation of resources and ultimately better drugs.

Results: The sbv IMPROVER Species-Specific Network Inference challenge was designed to use the power of the crowds to build two species-specific cell signaling networks given phosphoproteomics, transcriptomics and cytokine data generated from NHBE and NRBE cells exposed to various stimuli. A common literature-inspired reference network with 220 nodes and 501 edges was also provided as prior knowledge from which challenge participants could add or remove edges but not nodes. Such a large network inference challenge not based on synthetic simulations but on real data presented unique difficulties in scoring and interpreting the results. Because any prior knowledge about the networks was already provided to the participants for reference, novel ways for scoring and aggregating the results were developed. Two human and rat consensus networks were obtained by combining all the inferred networks. Further analysis showed that major signaling pathways were conserved between the two species with only isolated components diverging, as in the case of ribosomal S6 kinase RPS6KA1. Overall, the consensus between inferred edges was relatively high with the exception of the downstream targets of transcription factors, which seemed more difficult to predict.

Contact:ebilal@us.ibm.com or gustavo@us.ibm.com.

Supplementary information:Supplementary data are available at Bioinformatics online.

The role of suppressors of cytokine signalling in human neoplasms

Suppressors of cytokine signalling 1-7 (SOCS1-7) and cytokine-inducible SH2-containing protein (CIS) are a group of intracellular proteins that are well known as JAK-STAT and several other signalling pathways negative feedback regulators. More recently several members have been identified as tumour suppressors and dysregulation of their biological roles in controlling cytokine and growth factor signalling may contribute to the development of many solid organ and haematological malignancies. This review explores their biological functions and their possible tumour suppressing role in human neoplasms.

The Role of STAT3 in Thyroid Cancer

Thyroid cancer is the most common endocrine malignancy and its global incidence rates are rapidly increasing. Although the mortality of thyroid cancer is relatively low, its rate of recurrence or persistence is relatively high, contributing to incurability and morbidity of the disease. Thyroid cancer is mainly treated by surgery and radioiodine remnant ablation, which is effective only for non-metastasized primary tumors. Therefore, better understanding of the molecular targets available in this tumor is necessary. Similarly to many other tumor types, oncogenic molecular alterations in thyroid epithelium include aberrant signal transduction of the mitogen-activated protein kinase, phosphatidylinositol 3-kinase/AKT (also known as protein kinase B), NF-кB, and WNT/β-catenin pathways. However, the role of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT3) pathway, a well-known mediator of tumorigenesis in different tumor types, is relatively less understood in thyroid cancer. Intriguingly, recent studies have demonstrated that, in thyroid cancer, the JAK/STAT3 pathway may function in the context of tumor suppression rather than promoting tumorigenesis. In this review, we provide an update of STAT3 function in thyroid cancer and discuss some of the evidences that support this hypothesis.

Thyroid peroxidase autoantibodies are associated with a lesser likelihood of late reversion to hyperthyroidism after successful non-ablative treatment of Graves' disease in Croatian patients

BACKGROUND

Thyroid peroxidase autoantibodies (TPOAbs) are frequently observed in Graves' disease (GD) and tend to persist in patients even after successful treatment with antithyroid drugs. However, there is a lack of consistent data regarding the prognostic significance of TPOAbs during and after non-ablative treatment for Graves' hyperthyroidism.

AIM

To assess the prognostic value of TPOAbs on the long-term outcome of GD patients, who were in remission after the use of antithyroid drugs (block-and-replace regimen).

SUBJECTS

100 remitters were retrospectively investigated for factors associated with the 5-year course of disease recurrence and compared to 60 age/sex-matched patients with intractable GD.

RESULTS

Mild hyperthyroidism, low baseline thyroid-stimulating antibodies levels, and small goiters were predictive of remission. Once attained, the remission was shorter in younger patients, patients with declining post-treatment TSH values, and negative baseline TPOAb levels. The 5-year cumulative incidence of relapse incrementally increased from 24 to 44 to 70 % across decreasing TPOAb tertiles (log-rank, p = 0.00056; the lower tertile representing TPOAb-negative cases). The age-of-onset (p = 0.034), and the baseline TPOAb value [upper tertile, hazard ratio (HR) 0.25; 95 % confidence interval, 0.11-0.59; p = 0.0014; middle tertile, HR 0.47 (0.24-0.9); p = 0.024; Cox regression] were inversely associated with late (>12 months) relapse rates in a level-dependent manner. In contrast, serum logTSH measured 6 months after drug discontinuation was inversely associated with hazard rates at all time points (p = 0.0005).

CONCLUSION

Baseline TPOAb positivity is an independent indicator of long-term remission in GD patients who have been successfully treated, but the mechanism of action and causal relations remain unknown.

Cell-type-specific expression of STAT transcription factors in tissue samples from patients with lymphocytic thyroiditis

Expression of cytokine-regulated signal transducer and activator of transcription (STAT) proteins was histochemically assessed in patients diagnosed as having Hashimoto's disease or focal lymphocytic thyroiditis (n = 10). All surgical specimens showed histological features of lymphocytic thyroiditis, including a diffuse infiltration with mononuclear cells and an incomplete loss of thyroid follicles, resulting in the destruction of glandular tissue architecture. Immunohistochemical analysis demonstrated differential expression patterns of the various members of the STAT transcription factors examined, indicating that each member of this conserved protein family has its distinct functions in the development of the disease. Using an antibody that specifically recognized the phosphorylated tyrosine residue in position 701, we detected activated STAT1 dimers in numerous germinal macrophages and infiltrating lymphocytes as well as in oncocytes. In contrast, STAT3 expression was restricted to epithelial cells and showed a clear colocalization with the antiapoptotic protein Bcl-2. Moreover, expression of phospho-STAT3 was associated with low levels of stromal fibrosis, suggesting that STAT3 serves as a protective factor in the remodeling of the inflamed thyroid gland. Phospho-STAT5 immunoreactivity was detected in numerous infiltrating cells of hematopoietic origin and, additionally, in hyperplastic follicular epithelia. This tissue distribution demonstrated that activated STAT5 molecules participate in both lymphocytopoiesis and possibly also in the buildup of regenerating thyroid follicles. Taken together, the cell-type-specific expression patterns of STAT proteins in human lymphocytic thyroiditis reflect their distinct and partially antagonistic roles in orchestrating the balance between degenerating and regenerating processes within a changing cytokine environment.

Autosomal-dominant chronic mucocutaneous candidiasis with STAT1-mutation can be complicated with chronic active hepatitis and hypothyroidism

PURPOSE

To describe a case of autosomal-dominant (AD)-chronic mucocutaneous candidiasis (CMC) with a signal transducer and activator of transcription (STAT) 1 gene mutation, and some of the important complications of this disease such as chronic hepatitis.

METHODS

We present a 23-year-old woman with CMC, chronic active hepatitis, and hypothyroidism. Her father also had CMC. We performed several immunological analyses of blood and liver samples, and searched for gene mutations for CMC in the patient and her father.

RESULTS

We identified the heterozygous substitution c.821 G > A (p.Arg274Gln) in the STAT1 gene of both the patient and her father. The level of β-glucan induced interferon (IFN)-γ in her blood cells was significantly low. Immunoblot analysis detected serum anti-interleukin (IL)-17 F autoantibody. She was found to have increased (low-titer) antibodies related to her hypothyroidism and hepatitis. Her serum IL-18 levels fluctuated with her AST and ALT levels. Liver biopsy revealed CD68-positive cell infiltration and IL-18 expression in the sinusoidal regions. These results suggest that the chronic active hepatitis in this patient may be exacerbated by the excessive IL-18 accumulation caused by recurrent mucocutaneous fungal infection, and decreased IFN-γ production.

CONCLUSIONS

AD-CMC is known to be caused by a gain-of-function mutation of the STAT1 gene. Chronic active hepatitis is a rare complication of AD-CMC, with currently unknown pathogenesis. It seems that the clinical phenotype in this patient is modified by autoimmune mechanisms and cytokine dysregulation. AD-CMC can be complicated by various immune disorders including autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy.

Insulin-like growth factor-I regulation of immune function: a potential therapeutic target in autoimmune diseases?

This topically limited review explores the relationship between the immune system and insulin-like growth factors (IGF-I and IGF-II) and the proteins through which they act, including IGF-I receptor (IGF-IR) and the IGF-I binding proteins. The IGF/IGF-IR pathway plays important and diverse roles in tissue development and function. It regulates cell cycle progression, apoptosis, and the translation of proteins. Many of the consequences ascribed to IGF-IR activation result from its association with several accessory proteins that are either identical or closely related to those involved in insulin receptor signaling. Relatively recent awareness that IGF-I and IGF-IR regulate immune function has cast this pathway in an unexpected light; it may represent an important switch governing the quality and amplitude of immune responses. IGF-I/IGF-IR signaling may also participate in the pathogenesis of autoimmune diseases, although its relationship with these processes seems complex and relatively unexplored. On the one hand, IGF-I seems to protect experimental animals from developing insulin-deficient diabetes mellitus. In contrast, activating antibodies directed at IGF-IR have been detected in patients with Graves' disease, where the receptor is overexpressed by multiple cell types. The frequency of IGF-IR+ B and T cells is substantially increased in patients with that disease. Potential involvement of IGF-I and IGF-IR in the pathogenesis of autoimmune diseases suggests that this pathway might constitute an attractive therapeutic target. IGF-IR has been targeted in efforts directed toward drug development for cancer, employing both small-molecule and monoclonal antibody approaches. These have been generally well-tolerated. Recognizing the broader role of IGF-IR in regulating both normal and pathological immune responses may offer important opportunities for therapeutic intervention in several allied diseases that have proven particularly difficult to treat.

Evidence for an association between thyroid-stimulating hormone and insulin-like growth factor 1 receptors: a tale of two antigens implicated in Graves' disease

Thyroid-stimulating hormone receptor (TSHR) plays a central role in regulating thyroid function and is targeted by IgGs in Graves' disease (GD-IgG). Whether TSHR is involved in the pathogenesis of thyroid-associated ophthalmopathy (TAO), the orbital manifestation of GD, remains uncertain. TSHR signaling overlaps with that of insulin-like grow factor 1 receptor (IGF-1R). GD-IgG can activate fibroblasts derived from donors with GD to synthesize T cell chemoattractants and hyaluronan, actions mediated through IGF-1R. In this study, we compare levels of IGF-1R and TSHR on the surfaces of TAO and control orbital fibroblasts and thyrocytes and explore the physical and functional relationship between the two receptors. TSHR levels are 11-fold higher on thyrocytes than on TAO or control fibroblasts. In contrast, IGF-1R levels are 3-fold higher on TAO vs control fibroblasts. In pull-down studies using fibroblasts, thyrocytes, and thyroid tissue, Abs directed specifically against either IGF-1Rbeta or TSHR bring both proteins out of solution. Moreover, IGF-1Rbeta and TSHR colocalize to the perinuclear and cytoplasmic compartments in fibroblasts and thyrocytes by confocal microscopy. Examination of orbital tissue from patients with TAO reveals similar colocalization to cell membranes. Treatment of primary thyrocytes with recombinant human TSH results in rapid ERK phosphorylation which can be blocked by an IGF-1R-blocking mAb. Our findings suggest that IGF-1R might mediate some TSH-provoked signaling. Furthermore, they indicate that TSHR levels on orbital fibroblasts are considerably lower than those on thyrocytes and that this receptor associates with IGF-1R in situ and together may comprise a functional complex in thyroid and orbital tissue.

Regulation of inhibitors of differentiation family proteins by thyroid-stimulating hormone in FRTL-5 thyroid cells

Members of the inhibitors of differentiation (Id) family of helix-loop-helix (HLH) proteins are known to play important roles in the proliferation and differentiation of many cell types. Thyroid-stimulating hormone (TSH) regulates proliferation and differentiation by activating TSH receptor (TSHR) in thyrocytes. In this study, we found that Id2, one of the Id family proteins, is a major target for regulation by TSH in FRTL-5 thyroid cells. TSH rapidly increases the Id2 mRNA level in FRTL-5 thyroid cells but the Id2 protein showed biphasic regulatory patterns, being transiently reduced and subsequently induced by TSH treatment. Transient reduction of Id2 protein was noted within 2 hr of TSH treatment and was mediated by proteasomal degradation. Moreover, reduced Id2 expression correlated with the activity of the phosphatidylinositol 3 kinase pathway, which is activated by TSH. Although TSH increases the activity of the Id2 promoter, TSH-induced activation of this promoter was independent of c-Myc. Id2 did not alter TTF-1- and Pax-8-mediated effects on the regulation of the Tg promoter. Thus, in summary, we found that TSH regulates Id2 expression, but that Id2 does not alter the expression of thyroid-specific genes, such as Tg, in FRTL-5 thyroid cells.

Exchange protein activated by cyclic AMP (Epac)-mediated induction of suppressor of cytokine signaling 3 (SOCS-3) in vascular endothelial cells

Here, we demonstrate that elevation of intracellular cyclic AMP (cAMP) in vascular endothelial cells (ECs) by either a direct activator of adenylyl cyclase or endogenous cAMP-mobilizing G protein-coupled receptors inhibited the tyrosine phosphorylation of STAT proteins by an interleukin 6 (IL-6) receptor trans-signaling complex (soluble IL-6Ralpha/IL-6). This was associated with the induction of suppressor of cytokine signaling 3 (SOCS-3), a bona fide inhibitor in vivo of gp130, the signal-transducing component of the IL-6 receptor complex. Attenuation of SOCS-3 induction in either ECs or SOCS-3-null murine embryonic fibroblasts abolished the inhibitory effect of cAMP, whereas inhibition of SHP-2, another negative regulator of gp130, was without effect. Interestingly, the inhibition of STAT phosphorylation and SOCS-3 induction did not require cAMP-dependent protein kinase activity but could be recapitulated upon selective activation of the alternative cAMP sensor Epac, a guanine nucleotide exchange factor for Rap1. Consistent with this hypothesis, small interfering RNA-mediated knockdown of Epac1 was sufficient to attenuate both cAMP-mediated SOCS-3 induction and inhibition of STAT phosphorylation, suggesting that Epac activation is both necessary and sufficient to observe these effects. Together, these data argue for the existence of a novel cAMP/Epac/Rap1/SOCS-3 pathway for limiting IL-6 receptor signaling in ECs and illuminate a new mechanism by which cAMP may mediate its potent anti-inflammatory effects.

Mechanisms underlying the diminished sensitivity to prolactin negative feedback during lactation: reduced STAT5 signaling and up-regulation of cytokine-inducible SH2 domain-containing protein (CIS) expression in tuberoinfundibular dopaminergic neurons

Hyperprolactinaemia during lactation is a consequence of the sucking stimulus and in part due to reduced prolactin (PRL) negative feedback. To date, the mechanisms involved in this diminished sensitivity to PRL feedback are unknown but may involve changes in PRL signal transduction within tuberoinfundibular dopaminergic (TIDA) neurons. Therefore, we investigated signal transducers and activators of transcription (STAT) 5 signaling in the TIDA neurons of lactating rats. Dual-label confocal immunofluorescence studies were used to determine the intracellular distribution of STAT5 within TIDA neurons in the dorsomedial arcuate nucleus. In lactating rats with pups removed for 16 h, injection of ovine PRL significantly (P < 0.05) increased the STAT5 nuclear/cytoplasmic ratio compared with vehicle-treated mothers. In contrast, ovine PRL injection did not increase the STAT5 nuclear/cytoplasmic ratio in lactating mothers with pups, demonstrating that PRL signal transduction through STAT5 is reduced in TIDA neurons in the presence of pups. To investigate possible mechanisms involved in reduced PRL signaling, we examined the expression of suppressors of cytokine signaling (SOCS) proteins. Northern analysis on whole hypothalamus showed that CIS (cytokine-inducible SH2 domain-containing protein), but not SOCS1 or SOCS3, mRNA expression was significantly (P < 0.01) up-regulated in suckled lactating rats. Semiquantitative RT-PCR on arcuate nucleus micropunches also showed up-regulation of CIS transcripts. Immunofluorescence studies demonstrated that CIS is expressed in all TIDA neurons in the dorsomedial arcuate nucleus, and the intensity of CIS staining in these neurons is significantly (P < 0.05) increased in lactating rats with sucking pups. Together, these results support the hypothesis that loss of sensitivity to PRL-negative feedback during lactation is a result of increased CIS expression in TIDA neurons.

Inhibition of pro-inflammatory cytokine receptor signalling by cAMP in vascular endothelial cells

The anti-inflammatory effects of the prototypical second messenger cAMP have been extensively documented in multiple cell types. However, in many instances, the molecular mechanisms by which cAMP elevation disrupts specific pro-inflammatory signalling cascades are unknown. In this review, we will describe the importance of the JAK–STAT (where JAK stands for Janus kinase and STAT for signal transducer and activator of transcription) signalling pathway in vascular endothelial cell function, outline key inhibitory processes that serve to reduce cytokine-stimulated tyrosine phosphorylation and activation of STAT proteins, and discuss possible mechanisms by which intracellular cAMP sensors could interact with these inhibitory processes to diminish cytokine receptor-mediated pro-inflammatory signalling.

Activation of signal transducer and activator of transcription 3 by oncogenic RET/PTC (rearranged in transformation/papillary thyroid carcinoma) tyrosine kinase: roles in specific gene regulation and cellular transformation

Thyroid papillary carcinomas are characterized by RET/PTC (rearranged in transformation/papillary thyroid carcinoma) rearrangements that result in fusion of the tyrosine kinase domain of the RET receptor to the N-terminal sequences encoded by heterologous genes. This thyroid-specific rearrangement causes aberrant expression of RET/PTC and results in constitutive ligand-independent activation of RET kinase. However, it is unclear how RET/PTC activates the specific signaling pathways for cellular transformation. In this study, we show that RET/PTC associates with signal transducer and activator of transcription 3 (STAT3) and activates it by the specific phosphorylation of the tyrosine 705 residue. Activation of STAT3 requires the intrinsic kinase activity of RET/PTC; Janus tyrosine kinase and c-Src kinase are not involved in the RET/PTC-mediated activation of STAT3. RET/PTC-induced activation of STAT3 induces the STAT3-responsive genes, vascular endothelial growth factor, cyclin D1, and intercellular adhesion molecule 1. In addition, RET/PTC-mediated cellular transformation and proliferation of transformed cells require tyrosine 705 phosphorylation of STAT3 in NIH3T3 cells. We conclude that STAT3 activation by the RET/PTC tyrosine kinase is one of the critical signaling pathways for the regulation of specific genes, such as cyclin D1, vascular endothelial growth factor, and intercellular adhesion molecule 1, and for cellular transformation.

Suppressors of cytokine signalling (SOCS) in the immune system

The suppressors of cytokine signalling (SOCS) are a family of intracellular proteins, several of which have emerged as key physiological regulators of cytokine responses, including those that regulate the immune system. The SOCS proteins seem to regulate signal transduction by combining direct inhibitory interactions with cytokine receptors and signalling proteins with a generic mechanism of targeting associated proteins for degradation. Evidence is emerging for the involvement of SOCS proteins in diseases of the human immune system, which raises the possibility that therapeutic strategies that are based on the manipulation of SOCS activity might be of clinical benefit.

Thyrotropin modulates interferon-gamma-mediated intercellular adhesion molecule-1 gene expression by inhibiting Janus kinase-1 and signal transducer and activator of transcription-1 activation in thyroid cells

TSH is known as an important hormone that plays the major role not only in the maintenance of normal physiology but also in the regulation of immunomodulatory gene expression in thyrocytes. The adhesion molecule intercellular adhesion molecule-1 (ICAM-1) was identified as one of the proteins that are abnormally expressed in the thyroid gland during autoimmune thyroid diseases. In this study we found that TSH inhibits interferon-gamma (IFNgamma)-mediated expression of the ICAM-1 gene, and we investigated the involved mechanisms in rat FRTL-5 thyroid cells. After exposure to IFNgamma, ICAM-1 expression is positively regulated at the level of transcription. This effect occurs via the IFNgamma-activated site (GAS) element in the ICAM-1 promoter as a consequence of the activation of STAT1 (signal transducer and activator of transcription-1), but not of STAT3. On the other hand, after exposure to TSH plus IFNgamma, ICAM-1 transcription is negatively modulated. We found that this inhibitory effect of TSH also occurs via the GAS element. Electrophoretic mobility shift assays confirmed that the IFNgamma-induced DNA-binding activities of STAT1 were reduced by TSH. Furthermore, our results showed that the inhibitory effect of TSH on IFNgamma signaling is caused by inhibition of tyrosine phosphorylation on STAT1, Janus kinase-1 (Jak1), and IFNgamma receptor a, but not Jak2. In conclusion, we have identified a novel mechanism in which TSH modulates the IFNgamma-mediated Jak/STAT signaling pathway through the inhibition of Jak1 and STAT1.

Involvement of JAK/STAT (Janus kinase/signal transducer and activator of transcription) in the thyrotropin signaling pathway

TSH is an important physiological regulator of growth and function in thyroid gland. The mechanism of action of TSH depends on interaction with its receptor coupled to heterotrimeric G proteins. We show here that TSH induces the phosphorylation of tyrosine in the intracellular kinases Janus kinase 1 (JAK1) and -2 (JAK2) in rat thyroid cells and in Chinese hamster ovary (CHO) cells transfected with human TSH receptor (TSHR). The JAK family substrates STAT3 (signal transducers and activators of transcription) are rapidly tyrosine phosphorylated in response to TSH. We also find that JAK1, JAK2, and STAT3 coprecipitate with the TSHR, indicating that the TSHR may be able to signal through the intracellular phosphorylation pathway used by the JAK-STAT cascade. TSH increases STAT3-mediated promoter activity and also induces endogenous SOCS-1 (suppressor of cytokine signaling-1) gene expression, a known target gene of STAT3. The expression of a dominant negative form of STAT3 completely inhibited TSH-mediated SOCS-1 expression. These findings suggest that the TSHR is able to signal through JAK/STAT3 pathways.