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

Hyperfunctioning thyroid carcinoma: A systematic review

Hyperthyroidism may be caused by the development of primary or metastatic thyroid carcinoma. The aim of the present study was to collect recently reported cases of hyperfunctioning thyroid carcinoma in order to analyze its pathological characteristics, diagnostic procedures and treatment strategies. A PubMed (https://www.ncbi.nlm.nih.gov/pubmed/) search was performed for studies published between January 1990 and July 2017. Full-text articles were identified using the terms, ‘hyperfunctioning thyroid carcinoma/cancer’, ‘malignant hot/toxic thyroid nodule’, or ‘hyperfunctioning papillary/follicular/Hürthle thyroid carcinoma’. Original research papers, case reports and review articles were included. Among all thyroid carcinoma cases included in the present study, the prevalence of follicular thyroid carcinoma (FTC) was ~10%; however, the prevalence of FTC among hyperfunctioning thyroid carcinomas was markedly higher (46.5% in primary and 71.4% in metastatic disease). The size of hyperfunctioning thyroid tumors was considerably larger compared with that of non-hyperfunctioning thyroid tumors, with a mean size of 4.25±2.12 cm in primary hyperfunctioning thyroid carcinomas. In addition, in cases of metastatic hyperfunctioning thyroid carcinoma, tumor metastases were widespread or large in size. The diagnosis of primary hyperfunctioning thyroid carcinoma is based on the following criteria: i) No improvement in thyrotoxicosis following radioactive iodine (RAI) treatment; ii) development of hypoechoic solid nodules with microcalcifications on ultrasound examination; iii) increase in tumor size over a short time period; iv) fixation of the tumor to adjacent structures; and v) signs/symptoms of tumor invasion. The diagnosis of metastatic hyperfunctioning thyroid carcinoma should be considered in patients suffering from thyrotoxicosis who present with a high number of metastatic lesions (as determined by whole-body scanning), or a history of total thyroidectomy. Surgery is the first-line treatment option for patients with primary hyperfunctioning thyroid carcinoma, as it does not only confirm the diagnosis following pathological examination, but also resolves thyrotoxicosis and is a curative cancer treatment. RAI is a suitable treatment option for patients with hyperfunctioning thyroid carcinoma who present with metastatic lesions.

How genetic errors in GPCRs affect their function: Possible therapeutic strategies

Activating and inactivating mutations in numerous human G protein-coupled receptors (GPCRs) are associated with a wide range of disease phenotypes. Here we use several class A GPCRs with a particularly large set of identified disease-associated mutations, many of which were biochemically characterized, along with known GPCR structures and current models of GPCR activation, to understand the molecular mechanisms yielding pathological phenotypes. Based on this mechanistic understanding we also propose different therapeutic approaches, both conventional, using small molecule ligands, and novel, involving gene therapy.

The Impact of the D727E Polymorphism has no Significant Role in Multi Nodular Goiter

Interactions between individual genetic and environmental factors determine the onset of the multi nodular goiter (MNG). The thyroid-stimulating hormone receptor (TSHR) gene is a convincing candidate gene in the pathogenesis of certain thyroid diseases including MNG. We investigated the codon 727 polymorphism (p.Asp727Glu, p.D727E) of the human TSHR gene using the polymerase chain reaction-restriction fragment length polymorphim (PCR-RFLP) methods in 31 Turkish patients with MNG and in 30 control subjects, aiming to evaluate the relationship between this polymorphism and MNG. After genomic DNA isolation, PCR amplification was performed using a pair of primers in exon 10 of the TSHR gene that contains the p.D727E polymorphism and digested by theNlaIII (Hin1II) restriction enzyme. We found the CC and CG genotype incidence for the patient group to be 0.71 and 0.29, respectively, and for the control group to be 0.8 and 0.2, respectively. No statistically significant difference was found between the genotype and allele distribution of both groups (p = 0.417 and p = 0.449, respectively). However, the polymorphism is significantly correlated with the low serum level of the TSH (p = 0.047). These results suggest that the p.D727E polymorphism of the TSHR gene may not contribute to the pathogenesis of nontoxic MNG diseases.

From molecular details of the interplay between transmembrane helices of the thyrotropin receptor to general aspects of signal transduction in family a G-protein-coupled receptors (GPCRs)

Transmembrane helices (TMHs) 5 and 6 are known to be important for signal transduction by G-protein-coupled receptors (GPCRs). Our aim was to characterize the interface between TMH5 and TMH6 of the thyrotropin receptor (TSHR) to gain molecular insights into aspects of signal transduction and regulation. A proline at TMH5 position 5.50 is highly conserved in family A GPCRs and causes a twist in the helix structure. Mutation of the TSHR-specific alanine (Ala-593⁵·⁵⁰) at this position to proline resulted in a 20-fold reduction of cell surface expression. This indicates that TMH5 in the TSHR might have a conformation different from most other family A GPCRs by forming a regular α-helix. Furthermore, linking our own and previous data from directed mutagenesis with structural information led to suggestions of distinct pairs of interacting residues between TMH5 and TMH6 that are responsible for stabilizing either the basal or the active state. Our insights suggest that the inactive state conformation is constrained by a core set of polar interactions among TMHs 2, 3, 6, and 7 and in contrast that the active state conformation is stabilized mainly by non-polar interactions between TMHs 5 and 6. Our findings might be relevant for all family A GPCRs as supported by a statistical analysis of residue properties between the TMHs of a vast number of GPCR sequences.

Hyperthyroidism caused by a germline activating mutation of the thyrotropin receptor gene: difficulties in diagnosis and therapy

BACKGROUND

Germline activating mutations of the thyrotropin receptor (TSHR) gene have been considered as the only known cause of sporadic nonautoimmune hyperthyroidism in the pediatric population. Here we describe the long-term follow-up and evaluation of a patient with sporadic nonautoimmune primary hyperthyroidism who was found to have a de novo germline activating mutation of the TSHR gene.

SUMMARY

The patient was an infant who presented at the age of 10 months in an unconscious state with exsiccation, wet skin, fever, and tachycardia. Nonautoimmune primary hyperthyroidism was diagnosed, and brain magnetic resonance imaging and computed tomography showed also Arnold-Chiari malformation type I. Continuous propylthiouracil treatment resulted in a prolonged clinical cure lasting for 10 years. At the age of 11 years and 5 months the patient underwent subtotal thyroidectomy because of symptoms of trachea compression caused by a progressive multinodular goiter. However, 2 months after surgery, hormonal evaluation indicated recurrent hyperthyroidism and the patient was treated with propylthiouracil during the next 4 years. At the age of 15 years the patient again developed symptoms of trachea compression. Radioiodine treatment resulted in a regression of the recurrent goiter and a permanent cure of hyperthyroidism without relapse during the last 3 years of his follow-up. Sequencing of exon 10 of the TSHR gene showed a de novo heterozygous germline I630L mutation, which has been previously described as activating mutation at somatic level in toxic thyroid nodules.

CONCLUSIONS

The I630L mutation of the TSHR gene occurs not only at somatic level in toxic thyroid nodules, but also its presence in germline is associated with nonautoimmune primary hyperthyroidism. Our case report demonstrates that in this disorder a continuous growth of the thyroid occurs without any evidence of elevated TSH due to antithyroid drug overdosing. This may justify previous recommendations for early treatment of affected patients with removal of as much thyroid tissue as possible.

Current standards, variations, and pitfalls for the determination of constitutive TSHR activity in vitro

Constitutively activating mutations of the TSHR are the major cause for nonautoimmune hyperthyroidism, which is based on ligand independent, permanent receptor activation. Several reports have highlighted the difficulties to determine whether a TSHR mutation is constitutively active or not especially for borderline cases with only a slight increase of the basal cAMP activity. Current methods to precisely classify such mutants as constitutively active or not, are limited. In some cases, in vitro characterization of TSHR mutants has led to false positive conclusions regarding constitutive TSHR activity and subsequently the molecular origin of hyperthyroidism. For characterization of constitutive TSHR activity, a particular point to consider is that basal receptor activity tightly correlates with the receptor number expressed on the cell surface. Therefore, a comparison of the receptors basal activity in relation to the wild type is only possible with determination of the receptor cell surface expression. Thus, the experimental approaches to determine constitutive TSHR activity should consider the receptor's cell surface expression. We here provide a description of three methods for the determination of constitutive TSHR activity: (A) the evaluation of constitutive TSHR activity under conditions of equal receptor expression; (B) computation of the specific constitutive activity; and (C) the linear regression analysis (LRA). To date, LRA is the best experimental approach to characterize the mutant's basal activity as a function of TSHR cell surface expression. This approach utilizes a parallel measurement of basal cAMP values and receptor cell surface expression and therefore provides a more reliable decision with respect to the presence or absence of constitutive activity.

A somatic gain-of-function mutation in the thyrotropin receptor gene producing a toxic adenoma in an infant

BACKGROUND

Activating mutations of the thyroid stimulating hormone receptor gene (TSHR) are rare in the neonate and in the pediatric population. They are usually present in the germline, and are either inherited or occur de novo. Somatic mutations in TSHR are unusual in the pediatric population.

METHODS

We describe a nine-month-old infant with thyrotoxicosis who harbored an activating somatic mutation in TSHR that was not present in the germline.

RESULTS

As genomic DNA analysis failed to show a TSHR gene mutation, a radioiodide scan was performed to reveal a unilateral localization of uptake suppressing the remaining thyroid tissue. Genomic and complementary DNA analyses of the active thyroid tissue, removed surgically, identified a missense mutation (D633Y) located in the sixth transmembrane domain of the TSHR. The absence of this TSHR mutation in circulating mononuclear cells and in unaffected thyroid tissue confirmed the somatic nature of this genetic alteration.

CONCLUSIONS

To the authors' knowledge, this is the youngest patient to receive definitive treatment for hyperthyroidism due to an activating mutation of TSHR.

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.

Markers of cell proliferation, apoptosis, and angiogenesis in thyroid adenomas: a comparative immunohistochemical and genetic investigation of functioning and nonfunctioning nodules

OBJECTIVE

To perform (i) an immunohistochemical investigation of cell proliferation, apoptosis, angiogenesis, and malignancy markers in 15 functioning and 15 nonfunctioning thyroid adenomas, and in normal adjacent tissue, and (ii) a genetic analysis of thyroid-stimulating hormone receptor (TSH-r), Gsalpha, and RAS mutations in the same group of adenomas, in order to describe their expression within tissues and to correlate them with the hormonal functioning.

DESIGN

Thirty patients who underwent surgery for a solitary thyroid nodule were included in the study. Adenomas and normal adjacent tissues were evaluated by immunohistochemistry using the following antibodies: MIB-1 for proliferative activity, bcl-2 and mutant p53 for apoptosis control, vascular endothelial growth factor-A (VEGF-A) for angiogenic activity, and galectin-3 as a marker for malignancy. To calculate microvascular density, "hot spots" were selected and defined by cells positive for CD34 staining. Genetic analysis for TSH-r, Gsalpha, and H-, K-, and N-RAS mutations was performed on adenoma specimens.

MAIN OUTCOMES

Our results evidenced that a proportion of both functioning and nonfunctioning adenomas showed immunohistochemical phenotypes similar to normal adjacent tissue. No differences were found between functioning and nonfunctioning thyroid adenomas with regard to the expression of markers associated to angiogenesis (VEGF-A, microvascular density) and apoptosis control (mutant p53, bcl-2). All adenomas resulted negative for galectin-3 immunostaining. MIB-1 was the only marker showing a substantial difference of expression between the two groups of adenomas. TSH-r mutations were found in 12 out of 15 functioning adenomas, whereas the absence of Gsalpha and H-, K-, and N-RAS mutations was demonstrated in all adenomas.

CONCLUSIONS

Our data suggest that the differences between functioning and nonfunctioning thyroid adenomas are restricted to the genetic mutations of the TSH-r, to the hormonal status of tumors, and to the proliferative activity, not involving markers of apoptosis control and angiogenesis.

A novel activating mutation in transmembrane helix 6 of the thyrotropin receptor as cause of hereditary nonautoimmune hyperthyroidism

Constitutively-activating germline mutations of the thyrotropin receptor (TSHR) gene are very rare and are considered the cause of hereditary nonautoimmune hyperthyroidism. We describe four affected individuals from a Caucasian family: a mother and her three children, and an unaffected father. The mother and her first two children presented in a similar manner: lifelong histories of heat intolerance, hyperactivity, fast heart rate, reduced energy, increased appetite, and scrawny build. They all developed goiter in childhood and showed a suppressed TSH and elevated thyroxine (T(4)). The last child, a 12-year-old female, presented with no clinical symptoms or palpable neck mass, but with a suppressed TSH, elevated T(4) and thyromegaly detected by ultrasound. Mutation analysis of the TSHR gene in all family members revealed a novel heterozygous germline mutation resulting in the substitution of phenylalanine (TTC) by serine (TCC) at codon 631 in transmembrane helix 6 in the mother and all three children. Functional characterization of this germline mutation showed constitutive activation of the G(s)-mediated cyclic adenosine monophosphate (cAMP) pathway, which controls thyroid hormone production and thyroid growth. Molecular characterization of F631S demonstrates that this activating mutation plays a key role in the development of hereditary hyperthyroidism in this family although the timing of onset of clinical manifestations in the subjects may depend on other, as yet unidentified, factors.

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.