Molecular insights into TSH receptor abnormality and thyroid disease

Gene expression profile in functioning and non-functioning nodules of autonomous multinodular goiter from an area of iodine deficiency: unexpected common characteristics between the two entities

PURPOSE

Toxic multinodular goiter is a heterogeneous disease associated with hyperthyroidism frequently detected in areas with deficient iodine intake, and functioning and non-functioning nodules, characterized by increased proliferation but opposite functional activity, may coexist in the same gland. To understand the distinct molecular pathology of each entity present in the same gland, the gene expression profile was evaluated by using the Affymetrix technology.

METHODS

Total RNA was extracted from nodular and healthy tissues of two patients and double-strand cDNA was synthesized. Biotinylated cRNA was obtained and, after chemical fragmentation, was hybridized on U133A and B arrays. Each array was stained and the acquired images were analyzed to obtain the expression levels of the transcripts. Both functioning and non-functioning nodules were compared versus healthy tissue of the corresponding patient.

RESULTS

About 16% of genes were modulated in functioning nodules, while in non-functioning nodules only 9% of genes were modulated with respect to the healthy tissue. In functioning nodules of both patients and up-regulation of cyclin D1 and cyclin-dependent kinase inhibitor 1 was observed, suggesting the presence of a possible feedback control of proliferation. Complement components C1s, C7 and C3 were down-regulated in both types of nodules, suggesting a silencing of the innate immune response. Cellular fibronectin precursor was up-regulated in both functioning nodules suggesting a possible increase of endothelial cells. Finally, Frizzled-1 was down-regulated only in functioning nodules, suggesting a role of Wnt signaling pathway in the proliferation and differentiation of these tumors. None of the thyroid-specific gene was deregulated in microarray analysis.

CONCLUSION

In conclusion, the main finding from our data is a similar modulation for both kinds of nodules in genes possibly implicated in thyroid growth.

Temporal Changes in Thyroid Nodule Volume: Lack of Effect on Paranodular Thyroid Tissue Volume

BACKGROUND

The term "nodular goiter" has long been used to refer to a nodular thyroid gland, based on the assumption that nodule growth may be associated with hyperplasia of the surrounding non-nodular tissue. The aim of this prospective, multicenter, observational study was to determine whether nodule growth is accompanied by growth in the non-nodular tissue.

METHODS

Eight Italian thyroid-disease referral centers enrolled 992 consecutive patients with one to four benign nodules. Nodular and non-nodular thyroid tissue volumes were assessed for five years with annual ultrasound examinations.

RESULTS

In participants whose nodules remained stable (n = 839), thyroid volumes did not change (baseline 15.0 mL [confidence interval (CI) 14.5-15.6]; five-year evaluation 15.1 mL [CI 14.5-15.7]). In participants with significant growth of one or more nodule (n = 153), thyroid volumes increased and by year 5 were significantly greater than those of the former group (17.4 mL [CI 16-18.7]). In 76 individuals with unilateral nodules that grew, the mean nodular lobe volume significantly exceeded that of the contralateral lobe (8.6 mL [CI 7.4-9.8] vs. 6.7 mL [CI 6-7.4]). The unaffected lobe volumes remained stable over time, while nodular lobes grew steadily and were significantly greater at the end of follow-up (10.1 mL [CI 8.9-11.3]). Excluding the volume of the largest growing nodule in these cases, the remaining volume of the affected lobe remained virtually unchanged with respect to its baseline value. Furthermore, there was no significant difference in the non-nodular tissue volume between the unaffected lobe and the affected lobe (with the largest growing nodule volume subtracted), both at baseline and at the end of follow-up.

CONCLUSIONS

The growth of thyroid nodules is a local process, not associated with growth of the surrounding non-nodular tissue. Therefore, a normal-sized thyroid containing nodules should be referred to as a "uni- or multinodular thyroid gland" and considered a distinct entity from "uni- or multinodular goiter."

PDE5 Overexpression in Well-Differentiated Thyroid Carcinomas Is Associated with Lymph Node Metastasis

Overexpression of PDE5 is observed in certain human cancers, but PDE5 expression in well-differentiated thyroid carcinoma (WDTC) is unknown. We therefore examined PDE5 expression and its relationship with the clinicopathological features of WDTC. Real-time qPCR and Western blotting were performed to analyze the expression of PDE5 mRNA and protein in paired WDTC tumor and adjacent nontumor tissues. Immunohistochemistry was used to analyze the expression of PDE5 in paraffin-embedded tissues obtained from 103 cases of WDTC. Statistical analyses were performed to examine the correlation between PDE5 expression and clinicopathological features. The expression of PDE5 mRNA and protein was upregulated in WDTC lesions compared to their paired noncancerous tissues. The expression of PDE5 was significantly correlated with age (P = 0.032), regional lymph node status (P = 0.004), and the presence of distant metastasis (P = 0.020). High PDE5 expression was more closely associated with lymph node involvement in patients over 45 years (OR = 15.60, P ≤ 0.05). Thus, PDE5 may be a potential biomarker in WDTC, particularly in patients with regional lymph node metastasis, which is associated with disease recurrence, treatment failure, and morbidity. PDE5 expression may also help predict the prognosis and recurrence of WDTC after surgery.

PDE5 expression in human thyroid tumors and effects of PDE5 inhibitors on growth and migration of cancer cells

Recent studies have revealed in normal thyroid tissue the presence of the transcript of several phosphodiesterases (PDEs), enzymes responsible for the hydrolysis of cyclic nucleotides. In this work, we analyzed the expression of PDE5 in a series of human papillary thyroid carcinomas (PTCs) presenting or not BRAF V600E mutation and classified according to ATA risk criteria. Furthermore, we tested the effects of two PDE5 inhibitors (sildenafil, tadalafil) against human thyroid cancer cells. PDE5 gene and protein expression were analyzed in two different cohorts of PTCs by real-time PCR using a TaqMan micro-fluid card system and Western blot. MTT and migration assay were used to evaluate the effects of PDE5 inhibitors on proliferation and migration of TPC-1, BCPAP, and 8505C cells. In a first series of 36 PTCs, we found higher expression levels of PDE5A in tumors versus non-tumor (normal) tissues. PTCs with BRAF mutation showed higher levels of mRNA compared with those without mutation. No significant differences were detected between subgroups with low and intermediate ATA risk. Upregulation of PDE5 was also detected in tumor tissue proteins. Similar results were obtained analyzing the second cohort of 50 PTCs. Moreover, all tumor tissues with high PDE5 levels showed reduction of Thyroglobulin, TSH receptor, Thyroperoxidase, and NIS transcripts. In thyroid cancer cells in vitro, sildenafil and tadalafil determined a reduction of proliferation and cellular migration. Our findings demonstrate for the first time an overexpression of PDE5 in PTCs, and the ability of PDE5 inhibitors to block the proliferation of thyroid cancer cells in culture, therefore, suggesting that specific inhibition of PDE5 may be proposed for the treatment of these tumors.

Increased expression of pro-angiogenic factors and vascularization in thyroid hyperfunctioning adenomas with and without TSH receptor activating mutations

Autonomously functioning thyroid nodules (AFTN) are known to receive an increased blood influx necessary to sustain their high rate of growth and hormone production. Here, we investigated the expression of hematic and lymphatic vases in a series of 20 AFTN compared with the contralateral non-tumor tissues of the same patients, and the transcript levels of proteins involved in the control of vascular proliferation, including the vascular endothelial growth factor (VEGF) and platelet-derived growth factors (PDGF) and their receptors and the endothelial nitric oxide synthase (eNOS). In parallel, the expression of the differentiation markers sodium/iodide symporter (NIS), thyroperoxidase (TPO), thyroglobulin (Tg), and TSH receptor (TSHR) was also investigated. The data were further analyzed comparing subgroups of tumors with or without mutations in the TSHR gene. Analysis by means of CD31 and D2-40 immunostaining showed in AFTN an increased number of hematic, but not lymphatic, vessels in parallel with an enhanced proliferation rate shown by increased Ki67 staining. Quantitative RT-PCR analysis revealed an increase of VEGF, VEGFR1 and 2, PDGF-A, PDGF-B, and eNOS expression in tumor versus normal tissues. Also, higher transcript levels of NIS, TPO, and Tg were detected. Comparison of the two subgroups of samples revealed only few differences in the expression of the genes examined. In conclusion, these data demonstrate an increased expression of angiogenesis-related factors associated with an enhanced proliferation of hematic, but not lymphatic, vessels in AFTNs. In this context, the presence of TSHR mutations may only slightly influence the expression of pro-angiogenic growth factors.

Deletion of thyrotropin receptor residue Asp403 in a hyperfunctioning thyroid nodule provides insight into the role of the ectodomain in ligand-induced receptor activation

Somatic mutations of the TSH receptor (TSHR) gene are the main cause of autonomously functioning thyroid nodules. Except for mutations in ectodomain residue S281, all of the numerous reported activating mutations are in the TSHR membrane-spanning region. Here, we describe a patient with a toxic adenoma with a novel heterozygous somatic mutation caused by deletion of ectodomain residue Asp403 (Del-D403). Subsequent in vitro functional studies of the Del-D403 TSHR mutation demonstrated greatly increased ligand-independent constitutive activity, 8-fold above that of the wild-type TSHR. TSH stimulation had little further effect, indicating that the mutation produced near maximal activation of the receptor. In summary, we report only the second TSHR ectodomain activating mutation (and the first ectodomain deletion mutation) responsible for development of a thyroid toxic adenoma. Because Del-D403 causes near maximal activation, our finding provides novel insight into TSHR structure and function; residue D403 is more likely to be involved in the ligand-mediated activating pathway than in the ectodomain inverse agonist property.

The role of the calcium-sensing receptor in the development and progression of cancer

The calcium-sensing receptor (CaR) is responsive to changes in the extracellular Ca(2+) (Ca(2+)(o)) concentration. It is a member of the largest family of cell surface receptors, the G protein-coupled receptors, and it has been shown to be involved in Ca(2+)(o) homeostasis. Apart from its primary role in Ca(2+)(o) homeostasis, the CaR may be involved in phenomena that allow for the development of many types of benign or malignant tumors, from parathyroid adenomas to breast, prostate, and colon cancers. For example, whereas the CaR is expressed in both normal and malignant breast tissue, increased CaR levels have been reported in highly metastatic primary breast cancer cells and breast cancer cell lines, possibly contributing to their malignancy and associated alterations in their biological properties. In these settings the CaR exhibits oncogenic properties. Enhanced CaR expression and altered proliferation of prostate cancer cells in response to increased Ca(2+)(o) have also been described. In contrast, colon and parathyroid cancers often present with reduced or absent CaR expression, and activation of this receptor decreases cell proliferation, suggesting a role for the CaR as a tumor suppressor gene. Thus, the CaR may play an important role in the development of many types of neoplasia. Herein, we review the role of the CaR in various benign and malignant tumors in further detail, describing its contribution to parathyroid tumors, breast, prostate, and colon cancers, and we evaluate how pharmacological manipulations of this receptor may be of interest for the treatment of certain cancers in the future.

TSH signalling and cancer

Thyroid cancers are the most frequent endocrine neoplasms and mutations in the thyrotropin receptor (TSHR) are unusually frequent. Here we present the state-of-the-art concerning the role of TSHR in thyroid cancer and discuss it in light of the cancer stem cell theory or the classical view. We briefly review the gene and protein structure updating the cancer related TSHR mutations database. Intriguingly, hyperfunctioning TSHR mutants characterise differentiated cancers in contrast to undifferentiated thyroid cancers which very often bear silenced TSHR. It remains unclear whether TSHR alterations in thyroid cancers play a role in the onset or they appear as a consequence of genetic instability during evolution, but the presence of functional TSHR is exploited in therapy. We outline the signalling network build up in the thyrocyte between TSHR/PKA and other proliferative pathways such as Wnt, PI3K and MAPK. This networks integrity surely plays a role in the onset/evolution of thyroid cancer and needs further research. Lastly, future investigation of epigenetic events occurring at the TSHR and other loci may give better clues for molecular based therapy of undifferentiated thyroid carcinomas. Targeted demethylating agents, histone deacetylase inhibitors combined with retinoids and specific RNAis may help treatment in the future.

Mutations in the thyrotropin receptor signal transduction pathway in the hyperfunctioning thyroid nodules from multinodular goiters: a study in the Turkish population

Many studies have been carried out to determine G(s) alpha and TSHR mutations in autonomously functioning thyroid nodules. Variable prevalences for somatic constitutively activating TSHR mutations in hot nodules have been reported. Moreover, the increased prevalence of toxic multinodular goiters in iodine-deficient regions is well known. In Turkey, a country with high incidence rates of goiter due to iodine deficiency, the frequency of mutations in the thyrotropin receptor signal transduction pathway has not been evaluated up to now. In the present study, a part of the genes of the TSHR, G(s)alpha and the catalytic subunit of the PKA were checked for activating mutations. Thirty-five patients who underwent thyroidectomy for multinodular goiters were examined. Genomic DNAs were extracted from 58 hyperactive nodular specimens and surrounding normal thyroid tissues. Mutation screening was done by single-strand conformational polymorphism (SSCP) analysis. In those cases where a mutation was detected, the localization of the mutation was determined by automatic DNA sequencing. No G(s)alpha or PKA mutations were detected, whereas ten mutations (17%) were identified in the TSHR gene. All mutations were somatic and heterozygotic. In conclusion, the frequency of mutations in the cAMP signal transduction pathway was found to be lower than expected in the Turkish population most likely because of the use of SSCP as a screening method and sequencing only a part of TSHR exon 10.

Two novel mutations in the sixth transmembrane segment of the thyrotropin receptor gene causing hyperfunctioning thyroid nodules

Autonomously functioning thyroid nodules (AFTNs) can present as hyperfunctioning adenomas or toxic multinodular goiters. In the last decade, a large number of activating mutations have been identified in the thyrotropin receptor (TSHR) gene in autonomously functioning thyroid nodules. Most have been situated close to, or within the sixth transmembrane segment and third intracellular loop of the TSHR where the receptor interacts with the Gs protein. In this study we describe two novel mutations in the sixth transmembrane segment of the TSHR causing hyperfunctioning thyroid nodules. Genomic DNAs were isolated from four hyperfunctioning thyroid nodules, normal tissues and peripheral leukocytes of two patients with toxic multinodular goiter. After amplifying the related regions, TSHR and G(s)alpha genes were analyzed by single-strand conformation polymorphism (SSCP) analysis. The precise localization of the mutations was identified by automatic DNA sequence analysis. Functional studies were done by site-directed mutagenesis and transfection of a mutant construct into COS-7 cells. We identified two novel TSHR mutations in two hyperfunctioning thyroid nodules: Phe631Val in the first patient and Iso630Met in the second patient. Both mutant receptors display an increase in constitutive stimulation of basal cyclic adenosine monophosphate (cAMP) levels compared to the wild-type receptor. This confirms that these mutant receptors cause hyperfunctioning thyroid nodules.

Does a Leu 512 Arg thyrotropin receptor mutation cause an autonomously functioning papillary carcinoma?

In the last decade, studies were first done to determine the frequency of Gsalpha and later thyrotropin receptor (TSHR) mutations in benign autonomously functioning thyroid nodules (AFTN). Different frequencies ranging from 0% to 38% for GSp mutations and from 20% to 86% for TSHR mutations were found. There were only some limited case reports related to TSHR genetic alterations in malignant AFTN. Their role in autonomously functioning thyroid carcinomas is not well established. We present a patient who had thyroidectomy for toxic multinodular goiter and a papillary carcinoma was demonstrated histopathologically. Genomic DNA was isolated from two solid areas in the hot nodule and peripheral leukocytes of the patient. After amplifying the related regions, TSHR and GSalpha genes were analyzed by single-strand conformation polymorphism (SSCP) analysis. The precise localization of the mutations was identified by automatic DNA sequence analysis. An activating mutation of the TSHR gene (Leu 512 Arg) was found in the autonomously functioning papillary carcinoma. It is believed that this mutation causes constitutive activation of the cyclic adenosine monophosphate (cAMP) signal transduction pathway and thereby causes thyrotoxicosis and a hot thyroid nodule in an autonomously functioning papillary carcinoma.

The sodium-iodide symporter protein is always present at a low expression and confined to the cell membrane in nonfunctioning nonadenomatous nodules of toxic nodular goitre

OBJECTIVE

The sodium-iodide (Na(+)/I(-)) symporter (NIS) is known to be overexpressed in toxic adenomas and in about half of benign solitary nonfunctioning adenomas of the thyroid. In nonfunctioning adenomas, however, the protein is localized mainly in the cytoplasm and fails to reach the basolateral membrane of the follicular cell where it is found in normal thyroid tissue and in hyperfunctioning adenomas. Our aim was to study both the level of expression and the cell localization of NIS in nonfunctioning nonadenomatous nodules of toxic nodular goitre.

DESIGN AND PATIENTS

Tissue specimens from nine patients who were submitted to surgery for toxic or functionally autonomous goitre were studied. Tissues from 12 patients who underwent lobectomy for a toxic thyroid adenoma were used as controls.

MEASUREMENTS

Tissue sections embedded in paraffin were stained with haematoxylin-eosin for histological evaluation and for immunohistochemistry using a monoclonal antibody that recognized human (h) NIS.

RESULTS

Functioning and nonfunctioning nodules scattered in multinodular goitres consisted of unencapsulated micro/macrofollicular aggregates. All toxic adenomas were characterized by a micro/macrofollicular pattern of growth and histological examination showed that they were surrounded by a capsule. Like the 12 toxic adenomas, all the 14 functioning hyperplastic nodules and two adenomas of toxic multinodular goitre showed a high level of hNIS protein expression with respect to the normal collateral parenchyma and, in all cases, the protein was confined to the cell membrane.

CONCLUSIONS

Contrary to what was observed for solitary nonfunctioning thyroid adenomas, all the 19 nonfunctioning hyperplastic nodules showed a very low hNIS and this was always confined to the cell membrane. These data suggest that the mechanisms leading to loss of iodide uptake in nonfunctioning hyperplastic nodules of toxic multinodular goitre are different from those that act on solitary nonfunctioning follicular adenomas.

TSH receptor and Gs(alpha) genetic analysis in children with Down's syndrome and subclinical hypothyroidism

The prevalence of thyroid diseases in children with Down's syndrome (DS) is about 3%. The most frequently observed condition is autoimmune subclinical hypothyroidism (SH). Autoimmune SH must be distinguished from defects in the biological activity of the TSH molecule or from the rare inherited condition of thyroid resistance to TSH. To investigate this last aspect we studied 12 patients with DS that had moderately elevated TSH with normal free thyroid hormones without signs of autoimmunity. For the genetic analysis the genomic DNA was extracted from peripheral lymphocytes. All the exons of the TSH receptor (TSHr) and Gs(alpha) genes were sequenced. The genetic analysis of the TSHr gene revealed the presence of four polymorphic variants. In two patients there was an allelic variant in the exon 1 (Pro52Thr--in one patient in the heterozygous state and in the other as a homozygous substitution). In one patient there was an allelic variant in the exon 1 (Asp36His) in the heterozygous state. In 11 patients there was a silent polymorphism in the exon 7 at nucleotide 561. All patients were homozygous for a silent polymorphism in the exon 9 at nucleotide 855. No inactivating mutations of TSHr or Gs(alpha) genes were identified in the 12 patients. In conclusion, our results seem to exclude the role of TSHr or Gs(alpha) gene mutations in the pathogenesis of the non-autoimmune SH observed in some children with DS.

Expression of adenylyl cyclase types III and VI in human hyperfunctioning thyroid nodules

Hyperfunctioning thyroid nodules are characterized by the presence of spontaneous somatic mutations responsible for constitutive activation of the cAMP pathway. However, alterations affecting other elements of the cAMP signaling system may counteract the effects of the mutations. In this study, the expression of the adenylyl cyclase (AC) types III and VI was investigated by Western blot in 18 hyperfunctioning thyroid nodules; in 12 samples, we also assessed the presence of TSH receptor (TSHR) or gsp mutations and levels of AC VI and III mRNA. We found that the expression of nodular AC VI (but not AC III) was significantly lower (85.1% of normal, P=0.014) than the expression of both adenylyl cycles types of perinodular tissue from the same patients. Slightly, but not significant differences were detected in nodules with or without mutations and AC protein levels generally showed correlation with the levels of the transcripts detected by RT-PCR. In addition, AC III and AC VI expression levels within a given nodule were characterized by a significant positive correlation. These findings indicate that a diminished expression of AC type VI may be part of the mechanisms occurring in the hyperfunctioning nodules, independently of the presence of TSHR or gsp mutations, which influence the resulting phenotype.

Thyrotropin receptor mutations and thyroid hyperfunctioning adenomas ten years after their first discovery: unresolved questions

Ten years after the first description of activating mutations in the thyroid stimulating hormone receptor (TSHR) gene in sporadic autonomous hyperfunctioning thyroid adenomas, there is general agreement in assigning a major pathogenic role of this genetic abnormality, acting via the constitutive activation of the cAMP pathway, in both the growth and functional characteristic of these tumours. From the beginning, however, the pathophysiological and clinical relevance of somatic TSHR mutations has been debated and some arguments still exist against a fully causative role of these mutations and the practical value of detecting these mutations for the diagnosis, treatment and prognosis of thyroid hot nodules. Some major issues will be examined herein, including (a) the frequency of TSHR alterations in various reports showing that the genetic abnormality underlying the pathogenesis of a substantial subset of thyroid tumours has yet to be identified; (b) the limitations of the present experimental models, which suggest greater caution in the interpretation of in vitro results; (c) the still unresolved question of absence of genotype-phenotype correlation. Clarification of these issues may hopefully provide new and useful tools for improving the clinical management of this disease.

Similarities and differences in the phenotype of members of an Italian family with hereditary non-autoimmune hyperthyroidism associated with an activating TSH receptor germline mutation

Constitutively activating germline mutations of the TSH receptor (TSH-R) are considered the cause of hereditary non-autoimmune hyperthyroidism. In this study, 10 members (8 affected and 2 unaffected) of an Italian family with hereditary non-autoimmune hyperthyroidism were investigated for the presence of mutations in the TSH-R gene. The clinical features of the disease were also analyzed. PCR-amplified fragments of the TSH-R gene were obtained from genomic DNA extracted from peripheral blood leukocytes of each family member and analyzed by direct nucleotide sequencing and restriction analysis. An identical germline TSH-R mutation was detected in all the patients with hyperthyroidism but in none of the unaffected family members. The mutation was heterozygotic and determined the substitution of valine for methionine (codon 463; ATG-->GTG) in the second transmembrane domain of the TSH-R. When expressed in chinese hamster ovary (CHO) cells, the Val463 mutant TSH-R induced constitutive activation of the TSH receptor. Analysis of the clinical features of our family and those of other families with hereditary non-autoimmune hyperthyroidism, including one with the same Val463 mutation, revealed wide variability in the phenotypical expression of the disease. Our findings indicate that an activating germline mutation in the TSH-R gene plays a key role in hereditary non-autoimmune hyperthyroidism although the onset of clinical manifestations and the evolution of the disease seem to depend heavily on other factors, thus far unidentified. The absence of a clear correlation between mutant genotypes and phenotypic expression of the disease currently limits the prognostic value of genetic testing in families with hereditary non-autoimmune hyperthyroidism.

Evidence for a simplified view of autoantibody interactions with the thyrotropin receptor

Recently, many exceptions have been reported that undermine the concept that the epitopes for thyroid-stimulating autoantibodies (TSAb) and thyrotropin-blocking autoantibodies (TBAb) lie within the N-terminal and C-terminal portions of the thyrotropin receptor (TSHR) ectodomain, respectively. Here we have used a new approach to examine the issue by attempting to neutralize autoantibodies with the purified, N-terminal 289 amino acids of the TSHR ectodomain (TSHR-289), essentially the A subunit. Immunoglobulin G (IgG) with TSAb activity from 10 patients with Graves' disease was preincubated with or without purified active or inactive TSHR-289. Active, but not inactive, TSHR-289 completely neutralized TSAb activity in all sera. We then tested the ability of active TSHR-289 to neutralize TBAb activity in two rare hypothyroid patients with pure TBAb activity lacking agonist activity. IgG from both patients was extremely potent in the TBAb assay. Unlike with TSAb, preincubation of the IgG with a large excess of active TSHR-289 (20 microg/mL) revealed a remarkable divergence. TBAb activity from one patient was totally neutralized whereas in the other patient TBAb activity was totally unaffected. In conclusion, using a new approach, we confirm that the major portion of the TSAb epitope in the 418 amino acid ectodomain lies upstream of residue 289 (within the A subunit). In contrast, TBAb that cause hyperthyroidism can be more heterogeneous, with epitopes that lie largely upstream (A subunit) or downstream (B subunit) of residue 289.

A Phe 486 thyrotropin receptor mutation in an autonomously functioning follicular carcinoma that was causing hyperthyroidism

Hot nodules are rarely found to be carcinomas. We report a case of a nonmetastatic follicular carcinoma that presented as a hot nodule that was causing hyperthyroidism. A base substitution (ATC for TTC) was found in codon 486 of the TSH receptor gene and this resulted in the substitution of an isoleucine for a phenylalanine in the first extracellular loop of the receptor. This was absent in the deoxyribonucleic acid from the surrounding normal thyroid tissue indicating its somatic origin. This mutation, which was previously reported to activate both cyclic adenosine monophosphate and the inositol phosphate-diacylglycerol cascades, may have been responsible for the constitutive activation of the thyrotropin receptor and resulting hyperfunction of this follicular carcinoma.

The 3',5'-cyclic adenosine monophosphate response element binding protein (CREB) is functionally reduced in human toxic thyroid adenomas

In human normal thyrocytes, the cAMP-responsive signaling pathway plays a central role in gene regulation, cell proliferation, and differentiation. Constitutive activation of the cAMP signal transduction system has been documented in thyroid autonomously hyperfunctioning adenomas in which activating mutations in either the TSH receptor gene or the Gsalpha protein gene (gsp oncogene) have been described. The molecular mechanism whereby cAMP induces thyrocyte proliferation is unknown, but recent evidence suggests that the transcription factor cAMP response element binding protein (CREB) may serve as an important biochemical intermediate in this proliferative response. Herein we have investigated the expression of CREB in normal and tumoral thyroid tissues from a series of ten unrelated patients with autonomously hyperfunctioning adenomas, previously screened for mutations in the TSH receptor and Gsalpha genes. In all tumors examined, the expression of the activated, phosphorylated form of CREB was markedly reduced compared with that of the corresponding paired normal thyroid tissue, and this reduction was independent of the presence of mutations in the TSH receptor gene and Gsalpha gene. Moreover, no correlation was observed in these tissues between CREB phosphorylation and either protein kinase A activity or protein phosphatase expression. Thus, these data suggest that in human hyperfunctioning thyroid adenomas, the PKA/CREB system does not play a role in cell proliferation.

Genetic Analysis in Fine-needle Aspiration of the Thyroid: A New Tool for the Clinic

This review will examine the application of genetic analysis to cytological specimens obtained by fine-needle aspiration biopsy in the management of thyroid tumours. In particular, it will consider the use of polymerase chain reaction-based techniques in the diagnosis of the micrometastasis of differentiated thyroid carcinoma to cervical lymph nodes, as well as in the detection of oncogenic alterations in solid thyroid nodules.

Genetic analysis of the TSH receptor gene in differentiated human thyroid carcinomas

Somatic mutations of the TSH receptor (TSHR) gene have been identified as the major cause of toxic thyroid adenoma. Recently, point mutations of the same gene have also been described in some differentiated thyroid carcinomas. The aim of the present study was to investigate the presence TSHR gene mutations in a series of thyroid specimens obtained from 22 consecutive patients with differentiated thyroid carcinomas (8 follicular and 14 papillary). Genomic DNA was extracted from fresh-frozen or paraffin-embedded tumor and normal surrounding parenchyma. Two fragments corresponding to the entire exon 10 and one fragment corresponding to exon 9 were amplified by PCR using biotinylated primers. PCR products were purified on streptavidin-coated magnetic beads and subjected to direct sequencing with Sequenase and 35(3)-labeled d-ATP-alphaS. Adenyl-cyclase activity in membrane preparations of 10 papillary carcinomas was also determined. No TSHR mutations were detected in these tumors. A polymorphism that encoded a single amino acid change Asp727Glu was identified in two follicular thyroid carcinomas. Adenyl-cyclase activity was normal in the ten papillary thyroid carcinomas we analyzed. In conclusion, our results suggest that clonal somatic mutations of the TSHR gene do not play a role in the pathogenesis of differentiated thyroid carcinoma.

A Val 677 activating mutation of the thyrotropin receptor in a Hürthle cell thyroid carcinoma associated with thyrotoxicosis

Thyroid nodules presenting as hot at 131I-scintigraphy are usually benign follicular adenomas. We report a 42-year-old female patient with an autonomously functioning Hürthle cell thyroid carcinoma causing thyrotoxicosis. Genetic analysis of her thyroid tumoral DNA revealed a heterozygotic activating mutation of the thyrotropin receptor (TSHR) gene that was located downstream to all of the other genetic alterations currently identified, and is due to a base substitution at codon 677 (normal cytosine replaced by guanine, CTG for GTG causing leucine substitution by valine in the seventh transmembrane domain of the receptor). This mutation was detected in the tumor, but not in the leucocytes from the same patient. The Val 677-TSHR mutant showed constitutive activity, in terms of cyclic adenosine monophosphate (cAMP) production, when permanently transfected in Chinese hamster ovary (CHO) cells. Gsp and ras oncogenes and the p53 tumor suppressor gene were not present in the Hürthle cell cancer. The TSHR mutation in this Hürthle cell carcinoma may be responsible for maintaining differentiated thyroid function and hyperthyroidism.

Thyroid disease mediated by molecular defects in cell surface and nuclear receptors

The proposed mechanisms of RTH are not mutually exclusive. In fact, there is considerable experimental evidence that many if not all of these complex receptor interactions with elements of the transcriptional unit are involved in RTH. Several aspects of RTH remain unclear, in particular on a clinical level. We still do not completely understand the seeming paradox of a tight distribution of receptor mutations and wide variability in phenotypic presentation. The discovery that many of the RTH receptors have defects in corepressor interaction makes it tempting to speculate that the variability in RTH phenotype within kindreds is secondary to differences in corepressor expression. These issues may be better understood as research further proceeds into cofactors and their control of transcription. We also need better tools to determine thyroid status at a peripheral level. Basal metabolic rate, serum measurement of thyroid-responsive gene products, echocardiographic techniques, and other clinical measures have for the most part been unhelpful in determining thyroid status of specific organ systems. Consequently, therapeutic interventions for RTH are directed toward normalizing biochemical indices of thyroid homeostasis, without really knowing whether these efforts correct imbalances within crucial tissues. These studies, and the more widespread investigation of hormone receptor action in general, are moving at a breathtaking pace, and there is a keen interest in applying these principals to understanding the pathophysiologic mechanism of a variety of diseases.

TSH Receptor Mutations and Thyroid Disease

Mutations of the thyrotropin receptor (TSHr) can be loss of function or gain of function. Loss-of-function mutations can affect a variety of loci in the TSHr gene. Their most common manifestation is resistance to TSH; they may also be the cause of a subset of cases of congenital hypothyroidism. Gain-of-function mutations are of greater theoretical interest. Somatic mutations constitutively activating the TSHr are the major cause of benign toxic thyroid adenomas, and of some cases of multinodular goiters. They underlie hereditary toxic thyroid hyperplasia, and have been found in cases of sporadic congenital non-autoimmune hyperthyroidism. A role for TSHr polymorphisms in Graves' disease has not been documented.

Understanding the thyrotropin receptor function-structure relationship

The thyrotropin (TSH) receptor (TSHR) is a key protein in the control of thyroid function and a major thyroid autoantigen. Recently, molecular cloning of the receptor has been carried out and we now review the impact of this work on our understanding of the physiology and pathophysiology of the TSHR. Analysis of recombinant TSHR proteins expressed in prokaryotic and eukaryotic systems has indicated that post-translational processing is important for the formation of active receptors. Studies of TSHR glycosylation have shown that a 'mature' form of the receptor containing mainly complex-type sugar residues is principally involved in TSH and TSHR autoantibody (TRAb) binding. In addition, the processing of the TSHR peptide chain into two subunits observed with native TSHR has been confirmed using recombinant TSHR. However, despite considerable efforts in many laboratories, the binding site(s) for TSH and TRAb on the TSHR have not been well characterized as yet and lessons learned from the discovery of naturally occurring amino acid mutations of the TSHR confirm the complexity of the hormone and autoantibody binding sites. Future progress in producing large amounts of pure TSHR as well as monoclonal TRAbs, followed by crystallographic analysis of TSHR-TSH complexes and TSHR-TRAb complexes, should be helpful in providing a better insight into the relationship between TSHR structure and function.