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Endocrinology, doi:10.1210/en.2007-1588
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Endocrinology Vol. 149, No. 6 3062-3066
Copyright © 2008 by The Endocrine Society

Thyroid-Stimulating Hormone Induces Interleukin-6 Release from Human Adipocytes through Activation of the Nuclear Factor-{kappa}B Pathway

Tayze T. Antunes, AnneMarie Gagnon, Melanie L. Langille and Alexander Sorisky

Departments of Medicine and Biochemistry, Microbiology, and Immunology, University of Ottawa, Chronic Disease Program, Ottawa Health Research Institute, Ottawa, Canada K1Y 4E9

Address all correspondence and requests for reprints to: Dr. Alexander Sorisky, Ottawa Health Research Institute, 725 Parkdale Avenue, Ottawa Ontario, Canada K1Y 4E9. E-mail: asorisky{at}ohri.ca.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Our objective was to identify the signaling pathway activated by TSH that induces IL-6 secretion from human abdominal sc differentiated adipocytes. Human abdominal sc preadipocytes in culture were differentiated into adipocytes. IL-6 release stimulated by TSH was inhibited by 35% (P < 0.05) with SN50, an inhibitor of nuclear factor-{kappa}B (NF-{kappa}B) nuclear translocation, and 60% (P < 0.01) with sc-514, an inhibitor of inhibitory-{kappa}B (I{kappa}B) kinase (IKK)-β. Phosphorylation of IKKβ increased upon TSH treatment (10.3-fold, P < 0.01), and I{kappa}B{alpha} levels were reduced by 78% (P < 0.01). TSH activated NF-{kappa}B (23-fold, P < 0.001), a process that was inhibited (60%, P < 0.01) by SN50. Inhibition of protein kinase A by H89 did not affect TSH-stimulated IKKβ phosphorylation or I{kappa}B{alpha} degradation. TSH-mediated NF-{kappa}B activation and IL-6 induction also specifically occurred in Chinese hamster ovarian cells expressing the human TSH receptor, resulting in a 5.9-fold (P < 0.001) increase in IKKβ phosphorylation and a 9.5-fold increase in IL-6 mRNA expression. Our data demonstrate that the IKKβ/NF-{kappa}B pathway is a novel TSH target that is required for TSH-induced IL-6 release from human adipocytes.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
IN ADDITION TO energy storage and release, adipose tissue releases a variety of cytokines (adipokines) with wide-ranging physiological effects, including appetite, energy expenditure, insulin sensitivity, and coagulation. Deregulation of adipokine production is associated with a proinflammatory, proatherogenic state. Adipose tissue constitutes a significant source of circulating IL-6 (1). IL-6 has been identified as an independent risk factor for cardiovascular disease. A recent systematic review confirmed that serum IL-6 levels predict the development of cardiovascular disease (CVD) with an adjusted relative risk between 1.1 and 3.1 (2). Studies published subsequently continue to demonstrate IL-6 is a significant prognostic indicator of CVD (3, 4, 5). However, our understanding of hormonal regulators of adipocyte production of IL-6 is incomplete.

In subclinical hypothyroidism, TSH levels rise to compensate for mild thyroid gland failure and thereby maintain thyroid hormone levels in the normal range. However, a higher risk for CVD appears to be independently associated with subclinical hypothyroidism. A recent metaanalysis concluded that subclinical hypothyroidism is associated with an elevated risk of CVD in observational studies (odds ratio 1.65, 95% confidence interval 1.28–2.12), with a similar trend noted in prospective studies (odds ratio 1.42, 95% confidence interval 0.91–2.21) (6). Furthermore, acute administration of TSH to biochemically euthyroid patients (healthy thyroid cancer patients on L-thyroxine treatment after thyroid gland excision and radioablation) caused endothelial dysfunction and increased serum levels of C-reactive protein, TNF{alpha}, several indices of oxidative stress, and notably, IL-6 (7, 8). This extrathyroidal effect of TSH is consistent with our studies demonstrating the ability of TSH to stimulate IL-6 mRNA expression and release of IL-6 protein from 3T3-L1 and human abdominal sc differentiated adipocytes in culture (8, 9).

IL-6 transcription is positively regulated by nuclear factor-{kappa}B (NF-{kappa}B) in a variety of cells, including adipocytes (10). NF-{kappa}B is retained in the cytoplasm in an inactive form bound to inhibitory-{kappa}B (I{kappa}B) protein. Upon appropriate stimulation, I{kappa}B is phosphorylated by I{kappa}B kinase (IKK)-β, resulting in I{kappa}B degradation and release of NF-{kappa}B. Free active NF-{kappa}B translocates to the nucleus, binds to sequence-specific DNA regions, and triggers a variety of transcriptional events and cell responses, including initiation of inflammation (11).

In this report, we investigated the novel possibility that TSH activates the IKKβ/NF-{kappa}B pathway in human abdominal sc differentiated adipocytes and whether this pathway is required for TSH-stimulated IL-6 release.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Isolation, culture, and differentiation of human stromal preadipocytes
Human abdominal sc adipose tissue were obtained from 13 patients (10 females, three males), aged 49 ± 7 yr (mean ± SD), with a body mass index (28 ± 6 kg/m2) (mean ± SD) undergoing elective abdominal surgery. Written consent was obtained for each patient and the study was approved by The Ottawa Hospital Research Ethics Committee (1995023-01H). The stromal preadipocytes were isolated as described (8). Briefly, blood vessels and fibrous tissue were carefully removed, followed by collagenase digestion (CLS type I; 600 U/g of tissue). Stromal preadipocytes were obtained after sequential centrifugation, size filtration, and treatment with erythrocytes lysis buffer. Preadipocytes were grown in DMEM supplemented with 20% fetal bovine serum (FBS) and antibiotics (100 U/ml penicillin, 0.1 mg/ml streptomycin, and 50 U/ml nystatin). Upon reaching 80–90% confluence, cells were either seeded for a maximum of three passages or cryopreserved until needed. Preadipocytes were thawed and grown in DMEM supplemented with 10% FBS in the presence of antibiotics.

Preadipocytes were seeded overnight at a density of 3 x 104 cells/cm2 in DMEM supplemented with 10% FBS and antibiotics and placed in differentiation medium the next day. Differentiation was induced with DMEM supplemented with 10% FBS, 0.85 µmol/liter insulin, 100 µmol/liter indomethacin, 0.5 µmol/liter dexamethasone, 0.25 mmol/liter isobutyl methylxanthine, and antibiotics for 14 d. On d 14, differentiation medium was removed, cells were washed once in DMEM supplemented with 10% FBS and antibiotics, and maintained in this same medium for 2 more days, and cell stimulation studies occurred on d 17. The extent of differentiation averaged 50%.

Chinese hamster ovarian (CHO) cell culture
CHO-JP02 (vector control) and CHO-JP2626 cells overexpressing the human TSH receptor (TSHR) were kindly provided by Dr. J. E. Dumont (Erasme University Hospital, Free University of Brussels, Brussels, Belgium) (12). Cells were plated and grown in Ham’s F12 medium supplemented with 10% FBS, antibiotics, and 400 µg/ml G418. Medium was changed every 2 d until cells were confluent.

Quantification of IL-6 release
Human abdominal sc differentiated adipocytes were placed in DMEM supplemented with 1% calf serum and antibiotics. Cells were treated with 50 mU/ml TSH (Calbiochem, La Jolla, CA) or vehicle (H2O) for 4 h. Where specified, adipocytes were pretreated with either 100 µmol/liter sc-514 (inhibitor of IKKβ) or vehicle (0.1% dimethyl sulfoxide) or 50 µg/ml SN50; (Calbiochem product no. 481480 inhibitor of NF-{kappa}B) or vehicle (H2O) for the times indicated before TSH stimulation. After treatment, medium was collected and centrifuged (500 x g for 5 min at 4 C) to remove cell debris. The supernatants were collected and IL-6 protein was measured by enzyme immunometric assay (Assay Designs, Ann Arbor, MI), following the manufacturer’s instructions.

Cell monolayers were lysed, and protein concentration was measured by the modified Lowry method (Bio-Rad; Mississauga, Ontario, Canada), using BSA as a standard. IL-6 released into the medium was normalized to total cell lysate protein.

Cell stimulation and Western blot analysis
Human abdominal sc differentiated adipocytes or confluent CHO cells were placed in Krebs Ringer HEPES buffer supplemented with 1% calf serum and treated with 50 mU/ml TSH or vehicle for 30 min. Where indicated, cells were treated with 20 µmol/liter H89 or vehicle (0.1% dimethylsulfoxide) for 1 h in DMEM with 1% calf serum and antibiotics before addition of TSH. After treatment, cells were lysed in Laemmli buffer (13) supplemented with 5 mmol/liter EGTA, 5 mmol/liter sodium pyrophosplate, and 50 mmol/liter NaF. Lysate protein concentration was determined as described above. Equal amounts of solubilized protein (10–80 µg, depending on the experiment) were resolved by SDS-PAGE, followed by electrophoretic transfer to a nitrocellulose membrane. Nonspecific binding sites were blocked, and the membrane was probed with either antiphospho-IKK{alpha} ser180/IKKβ ser181 (1:500); anti-I{kappa}B{alpha} (1:500), antiphospho-cAMP response element-binding protein (CREB) Ser 133 (1:1000; all from Cell Signaling Technology, Beverly, MA), or anti-IKKβ (clone 10AG2; 2 µg/ml; Upstate Biotechnology, Lake Placid, NY) followed by the appropriate horseradish peroxidase-conjugated antibody. Immunoreactivity was detected by enhanced chemiluminescence. Relative intensity of the bands was determined with AlphaEaseFC software (Alpha Innotech, San Leandro, CA) and data expressed as integrated OD units.

Preparation of nuclear extracts and measurement of NF-{kappa}B DNA binding
Human abdominal sc differentiated adipocytes were placed in DMEM supplemented with 1% calf serum and antibiotics. Cells were pretreated with 50 µg/ml SN50 or vehicle for 15 min and treated with 50 mU/ml TSH or vehicle for 1 h. Cells were washed twice with ice-cold PBS containing phosphatase inhibitors (125 mmol/liter NaF, 250 mmol/liter β-glycerophosphate, 250 mmol/liter phenylphosphate, and 25 mmol/liter sodium orthovanadate), and nuclear extracts were prepared according to the TransAM NF{kappa}B p65 Activation assay (Active Motif, Carlsbad, CA). Briefly, cells were lysed in 1 ml hypotonic buffer (pH 7.5) [20 mmol/liter HEPES (pH 7.5), 5 mmol/liter NaF, 10 µmol/liter Na2MoO4, and 0.1 mmol/liter EDTA]. Cells were scraped and allowed to swell for 15 min on ice. After the addition of 50 µl of 10% Nonidet P-40, the homogenates were centrifuged at 14,000 x g for 1 min at 4 C. Supernatants were discarded, and nuclear pellets were resuspended in 50 µl of complete lysis buffer and incubated for 30 min at 4 C with continuous mixing. Samples were centrifuged at 14,000 x g for 10 min at 4 C, and the supernatants were collected. NF-{kappa}B DNA binding was determined using the TransAM NF{kappa}B p65 Activation assay (Active Motif) using 1 µg of the nuclear extracts.

Real-time PCR
Confluent CHO cells were placed in Ham’s F12 medium supplemented with 1% calf serum and treated with 50 mU/ml TSH or vehicle for 2 h. After stimulation, RNA was extracted with TRI reagent, and treated with DNase I, according to the manufacturer’s instructions (Ambion, Austin, TX). Total RNA (1 µg) was heat denatured before addition of reverse transcriptase (RT). RT was performed with Retroscript kit (Ambion). Real-time PCR was performed in 25-µl reaction volume consisting of 5 µl RT, 5 µl primers, 900 nmol/liter IL-6 primers, and 10 µl SYBR Green PCR master mix (Applied Biosystems, Hercules, CA). IL-6-specific primer pairs were: forward, 5'-TTGGGAAATTTGCCTACTGAA-3', and reverse, 5'-AGGCATGACTATTTTATCTGGA-3'. 18S was used as an internal control. All samples were run in triplicate and RT– control assays were performed for both IL-6 and 18S. Amplification consisted of one cycle at 50 C for 2 min, one cycle at 95 C for 10 min, and 40 cycles at 95 C for 15 sec (denaturation) followed by 1 min at 60 C (annealing/extension) performed in an 7500 real-time PCR system (Applied Biosystems). mRNA expression data are expressed as relative quantification.

Statistical analysis
Statistical analysis was performed with Student’s t test for paired values or ANOVA with Student-Newman-Keuls post hoc test, as appropriate, for multiple means, using GraphPad Instat version 3.05 (GraphPad Software Inc., San Diego, CA), with P < 0.05 considered significant.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
We have previously shown that human abdominal sc differentiated adipocytes in culture release IL-6 in response to TSH (8). We have now performed dose-response studies to characterize the TSH-dependent effect. Human abdominal sc differentiated adipocytes were exposed to increasing concentrations of TSH (from 0 to 50 mU/ml), and IL-6 release into the medium was quantified. We observed a strong increase in IL-6 secretion (9.4 ± 1.6-fold, n = 2) with 5 mU/ml TSH (Fig. 1Go). The dose response observed here correlates with our previously reported data on 3T3-L1 adipocytes (9), and it also approximates the doses used for thyroid cell studies (14).


Figure 1
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  		FIG. 1. Dose-response of TSH on IL-6 release: Human abdominal sc differentiated adipocytes were stimulated for 4 h with 0 to 50 mU/ml TSH. IL-6 protein in the medium was measured as described. Data are expressed as fold change of control and represent means ± range of two separate patient samples, each performed in duplicate.

 
We investigated whether activation of the IKKβ/NF-{kappa}B pathway was required for TSH-stimulated IL-6 release. Human abdominal sc differentiated adipocytes were pretreated with 100 µmol/liter sc-514, a selective inhibitor of IKKβ, followed by TSH treatment (Fig. 2AGo). Sc-514 resulted in a 60% inhibition of TSH-induced IL-6 release (132.2 ± 9 pg/ml·µg protein vs. 55 ± 14.7 pg/ml·µg protein, P < 0.01; n = 3). To further implicate the NF-{kappa}B pathway in TSH-induced IL-6 release, cells were pretreated with 50 µg/ml SN50, a peptide that blocks NF-{kappa}B nuclear translocation, followed by TSH treatment. SN50 decreased TSH-induced IL-6 release by 35% (222 ± 54 pg/ml·µg protein vs. 144 ± 31 pg/ml·µg protein when SN50 was present, P < 0.05; n = 4) (Fig. 2BGo). Thus, both inhibitor studies indicate that NF-{kappa}B is a signaling target that is necessary for TSH to fully induce IL-6 release.


Figure 2
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  		FIG. 2. Inhibitors of the NF-{kappa}B pathway blunt TSH-induced IL-6 secretion. Cells were pretreated with 100 µmol/liter sc-514 or vehicle for 1 h (A) or with 50 µg/ml SN50 or vehicle for 15 min (B) and then stimulated with 50 mU/ml TSH or vehicle for 4 h. IL-6 protein in the medium was measured as described. Data are expressed as mean ± SE of three (A) or four (B) separate patient samples, each performed in duplicate. a, P < 0.001, compared with control and sc-514 or SN50, P < 0.01, compared with sc-514-TSH, and P < 0.05, compared with SN50-TSH, b, P < 0.05, compared with control and sc-514 (both for A), and P < 0.01, compared with control and to SN50 (both for B).

 
We investigated whether TSH could stimulate the phosphorylation of IKKβ and the reduction of I{kappa}B{alpha} and lead to NF-{kappa}B activation. TSH treatment substantially increased IKKβ phosphorylation (10.3-fold, P < 0.01; n = 4) and reduced the levels of I{kappa}B{alpha} (by 78%; P < 0.01; n = 3) (Fig. 3Go, A and B). We next determined whether NF-{kappa}B translocates to the nucleus and is activated in response to TSH. Human abdominal sc differentiated adipocytes were pretreated with 50 µg/ml SN50 and then stimulated with TSH. Nuclear lysates were evaluated for specific binding of the activated p65 subunit of NF-{kappa}B to DNA. TSH increased NF-{kappa}B (p65 subunit) binding to DNA by 23-fold (P < 0.001; n = 3). SN50 reduced TSH-induced NF-{kappa}B DNA binding by 60% (P < 0.01, n = 3) (Fig. 3CGo). TSH-stimulated IKKβ phosphorylation was not dependent on protein kinase A (PKA). Pretreatment with 20 µmol/liter H89 did inhibit TSH-stimulated phosphorylation of CREB, a known PKA-dependent event, but did not alter the IKKβ response (Fig. 3DGo). Similarly, the TSH-induced I{kappa}B{alpha} degradation was not affected by H89.


Figure 3
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  		FIG. 3. TSH stimulates the IKKβ/NF-{kappa}B pathway, independently of PKA. A, B, and D, Human abdominal sc differentiated adipocytes were stimulated for 30 min with 50 mU/ml TSH or vehicle. Where indicated, cells were pretreated with 20 µmol/liter H89 or vehicle for 1 h before TSH treatment. Equal amounts of solubilized protein were separated by SDS-PAGE and immunoblotted with antibody against phospho-IKK (pIKK), IKKβ, I{kappa}B{alpha}, or phospho-CREB (pCREB). Representative immunoblots from a single experiment are shown. Densitometric data from four (A) or three (B and D) separate patient samples are expressed as means ± SE. *, P < 0.05, compared with TSH alone; **, P < 0.01, compared with control (A and B) or control and H89 (D). IOD, Integrated optical density. C, Cells were pretreated with 50 µg/ml SN50 or vehicle for 15 min and then stimulated with 50 mU/ml TSH or vehicle for 1 h. p65 nuclear translocation was measured as described. Data are expressed as fold change of control and represent means ± SD of three separate patient samples. a, P < 0.001, compared with control and SN50, and P < 0.01, compared with SN50-TSH; b, P < 0.01, compared with SN50 and P < 0.05, compared with control.

 
To further demonstrate our novel observation that TSH activates NF-{kappa}B, we used a well-known cell model for studying TSH actions, the CHO cell line stably transfected with either human TSHR (JP2626) or a control vector (JP02) (12). We assessed whether the NF-{kappa}B pathway is activated by TSH by monitoring IKKβ phosphorylation. JP02 and JP2626 cells were both exposed to TSH. IKKβ phosphorylation increased by 5.9-fold in JP2626 cells specifically (P < 0.001, n = 3), with no effect in JP02 cells (Fig. 4AGo). To determine whether TSH could activate IL-6 expression in this model system, the cells were treated with TSH, and IL-6 induction was measured by real-time PCR. TSH increased IL-6 mRNA expression by 9.5-fold (n = 2) in JP2626 cells, with no response in the control JP02 cells (Fig. 4BGo).


Figure 4
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  		FIG. 4. TSH stimulates IKKβ phosphorylation and increases IL-6 mRNA in TSHR-overexpressing cells. JP02 and JP2626 cells were stimulated with or without 50 mU/ml TSH for 30 min (A) or 2 h (B). A, Equal amounts of solubilized protein were separated by SDS-PAGE and immunoblotted with antibody against phospho-IKK (pIKK). Blots were stripped and reprobed with antibody against IKKβ. Representative immunoblots from a single experiment are shown. Densitometric data analyzing pIKK, derived from three separate experiments, are expressed as means ± SE. *, P < 0.001, compared with other conditions. IOD, Integrated optical density. B, RNA was extracted, and quantified by real-time PCR. Data are expressed relative to 18S rRNA levels (relative quantification) and represent the means ± range of two separated experiments.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
We recently reported that TSH induces IL-6 release from human abdominal sc differentiated adipocytes (8). In the present study, we clarified the signaling mechanism of this TSH action by identifying an important role for NF-{kappa}B in this process. Upon TSH stimulation, IKKβ was phosphorylated, and there was an increase in NF-{kappa}B nuclear activation. Either inhibiting the activity of IKKβ or blocking the translocation of NF-{kappa}B to the nucleus reduced TSH-mediated IL-6 release.

The TSHR is a member of the G protein-coupled receptor (GPCR) family. In thyrocyte-based models, TSHR has been found to stimulate two principal signaling pathways (15). When coupled to Gs, TSHR leads to activation of adenylyl cyclase and elevation of cAMP, and this route of signaling in thyrocytes has been linked to thyroid hormone secretion. TSHR coupling to Gq triggers activation of phospholipase C and the generation of inositol phosphates and diacyglycerol, and these events are required for thyroid hormone synthesis (16).

However, the ability of TSHR to activate NF-{kappa}B has not been reported previously in either adipocytes or thyrocytes. TSH has been shown to enhance the ability of TNF{alpha} to activate NF-{kappa}B and up-regulate IL-6 expression in rat thyroid follicular cells; this effect was proposed to be due to the formation of a complex consisting of the PKA catalytic subunit with I{kappa}B in the presence of TNF{alpha} (17). However, in that experimental system, an independent effect of TSH on NF-{kappa}B on IL-6 expression was not described in the absence of TNF{alpha}. Our data demonstrate that in human differentiated adipocytes, TSH alone is sufficient to activate the NF-{kappa}B pathway and does not depend on PKA, based on the observations that H89 did inhibit CREB phosphorylation but had no effect either on IKKβ phosphorylation or I{kappa}B{alpha} degradation.

The residual release of IL-6 in response to TSH in the presence of SN50 or sc-514 might be because of incomplete pharmacological inhibition of the IKKβ/NF-{kappa}B pathway or might indicate the operation of other TSH signaling routes that regulate this event. Further analysis of candidate TSH-stimulated signaling targets will be helpful to provide a more comprehensive view of TSH action in this regard.

The classical cell surface receptors that activate NF-{kappa}B and induce inflammation are cytokine receptors, such as those for TNF{alpha}. Recently the GPCRs have also been shown to activate the NF-{kappa}B pathway in a variety of cell types (18). However, there is only a single report of NF-{kappa}B activation in adipocytes by a GPCR in the literature, specifically the angiotensin II type 1 receptor. Angiotensin II was shown to act on the AT1 receptor to increase IL-6 and IL-8 release from human adipocytes, and this depended on NF-{kappa}B activation (19). Our data show that NF-{kappa}B signaling may be activated in adipocytes by another GPCR, the TSHR. TSH-induced NF-{kappa}B activation was also confirmed in CHO cells expressing human TSHR, an established cell model to explore TSHR signaling (12, 16). TSH treatment clearly augmented IKKβ phosphorylation and IL-6 mRNA expression in a TSHR-specific fashion.

As with the studies on angiotensin II noted above, we monitored NF-{kappa}B activity in the differentiated adipocytes using an assay that traces p65 subunit nuclear translocation and its activated state through its ability to bind DNA in a sequence-specific manner. Our studies with SN50, which blocks p50 nuclear import, suggest that the p65-p50 dimer is the NF-{kappa}B form regulated by TSH. The p50-p65 form is mainly regulated by IKKβ (20), and this is consistent with our studies using sc-514. It is, of course, possible that other NF-{kappa}B components are operative in human adipocytes (21).

In summary, we show that TSH modulates NF-{kappa}B signaling to induce IL-6 release in human abdominal sc differentiated adipocytes. Low-grade inflammation induced by adipocyte hypertrophy has been proposed to explain how either obesity or lipodystrophy predisposes to metabolic and vascular dysfunction (22). Our results suggest that TSH may also trigger a proinflammatory and proatherogenic adipocyte response. Elevated IL-6 and TNF{alpha} serum levels, as well as impaired endothelial physiology, have been observed in patients exposed to high TSH levels (7, 8). Learning more about the mechanism by which TSH acts on adipocytes may enlarge our understanding of inflammation and cardiovascular disease in subclinical hypothyroidism.


   Acknowledgments
 
We thank the surgeons and patients of The Ottawa Hospital for adipose tissue samples.


   Footnotes
 
This work was supported by a grant-in-aid from the Heart and Stroke Foundation of Ontario (to A.S.). T.T.A. is a recipient of a Heart and Stroke Foundation of Canada Doctoral Research Award. M.L.L. is a recipient of an Ontario Graduate Scholarship in Science and Technology.

Disclosure Statement: All of the authors have nothing to disclose.

First Published Online February 28, 2008

Abbreviations: CHO, Chinese hamster ovarian; CREB, cAMP response element-binding protein; CVD, cardiovascular disease; FBS, fetal bovine serum; GPCR, G protein-coupled receptor; I{kappa}B, inhibitory-{kappa}B; kinase; IKK, inhibitor of I{kappa}B kinase; NF-{kappa}B, nuclear factor-{kappa}B; PKA, protein kinase A; RT, reverse transcriptase; TSHR, TSH receptor.

Received November 19, 2007.

Accepted for publication February 15, 2008.


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 Introduction
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 Discussion
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Endocrinology Endocrine Reviews J. Clin. End. & Metab.
Molecular Endocrinology Recent Prog. Horm. Res. All Endocrine Journals