The extracellular domain suppresses constitutive activity of the transmembrane domain of the human TSH receptor: implications for hormone-receptor interaction and antagonist design.

Among glycoprotein hormone receptors the TSH receptor (TSHR) is the most susceptible to constitutive activation by mutations in various regions of the molecule, including mutations in the extracellular domain (ECD) and extracellular loops of the transmembrane domain (TMD). To understand the role of the ECD in TSHR activation we have tested several TSHR constructs with major deletions of the ECD. Previous studies reported very low expression of such truncated glycoprotein hormone receptors, which prevented reliable assessment of their ligand-binding and basal constitutive activities. We have eliminated this problem using TSHR tagged at its N-terminus with a hemagglutinin tag (HA) recognized by the HA-specific monoclonal antibody. Based on such quantitation the TSHR deletion mutant missing 386 N-terminal amino acid residues, constituting 98% of the entire ECD, showed 4-7 fold higher normalized basal activity compared to activity of the corresponding wild-type (WT) TSHR construct. This increase in basal activity was significantly inhibited by linking the common alpha-subunit of glycoprotein hormones at the N-terminus of the truncated TSH receptor. The role of a hypothetical activating fragment (409-418) in TSHR activation was further studied using peptides and mutagenesis of charged residues. This study provides important evidence supporting the "two-state" model of TSHR activation and the potential role of proteolytic cleavage for receptor activation. Accordingly, the mechanism of hormone-induced receptor activation is dependent, at least in part, on the elimination of inhibitory interactions within the receptor. Such intra-molecular inhibition of TSHR may include electrostatic interactions between the ECD and extracellular loops of TMD. Moreover, the truncated, constitutively active receptors described herein provide new insights valuable in the design of TSHR antagonists.

Bioengineering of human thyrotropin superactive analogs by site-directed "lysine-scanning" mutagenesis. Cooperative effects between peripheral loops.

We have previously engineered the first superactive analogs of human thyrotropin (hTSH) by using a novel design strategy. In this study, we have applied homology comparisons focusing on the alphaL3 loop of the common alpha-subunit of human glycoprotein hormones. Seven highly variable amino acid residues were identified, and charge-scanning mutagenesis revealed three previously unrecognized modification permissive domains and four gain-of-function lysine substitutions. Such gain-of-function mutations were hormone- and receptor-specific and dependent on location and basic charge. Cooperativity of individual substitutions was established in double and triple lysine mutants. In combinations of the most potent alphaL3 loop analog with two previously characterized loop analogs, a higher degree of cooperativity for the alphaL3 loop analog compared with both the alphaL1 loop analog and the hTSH-betaL3 loop analog was observed. We demonstrated that spatially distinct regions of the common alpha-subunit contribute differentially to the interaction of hTSH with its receptor and that combinations of two modified loops on the same and on opposite sides of the hTSH molecule display similar increases in in vitro biopotency. In addition, combination of all three superactive loops showed cooperativity in receptor binding and activation resulting in the most potent hTSH superactive analog described to date.

Human thyroid-stimulating hormone: structure-function analysis.

This article provides the reader with an overview of methodological strategies to investigate structure-function relationships of human thyroid-stimulating hormone (hTSH). Various aspects of hTSH production, purification, and characterization described here in more detail are not only relevant to studies on other members of the glycoprotein hormone family, but also applicable to studies of other glycosylated proteins. Knowledge of structure-function relationships of specific hTSH domains is important for a better understanding of the molecular mechanisms of its action. New insights from such studies permit the design of glycoprotein hormone analogs with specific pharmacological properties and potential clinical applications.

A comparison of recombinant human thyrotropin and thyroid hormone withdrawal for the detection of thyroid remnant or cancer.

Recombinant human TSH has been developed to facilitate monitoring for thyroid carcinoma recurrence or persistence without the attendant morbidity of hypothyroidism seen after thyroid hormone withdrawal. The objectives of this study were to compare the effect of administered recombinant human TSH with thyroid hormone withdrawal on the results of radioiodine whole body scanning (WBS) and serum thyroglobulin (Tg) levels. Two hundred and twenty-nine adult patients with differentiated thyroid cancer requiring radioiodine WBS were studied. Radioiodine WBS and serum Tg measurements were performed after administration of recombinant human TSH and again after thyroid hormone withdrawal in each patient. Radioiodine whole body scans were concordant between the recombinant TSH-stimulated and thyroid hormone withdrawal phases in 195 of 220 (89%) patients. Of the discordant scans, 8 (4%) had superior scans after recombinant human TSH administration, and 17 (8%) had superior scans after thyroid hormone withdrawal (P = 0.108). Based on a serum Tg level of 2 ng/mL or more, thyroid tissue or cancer was detected during thyroid hormone therapy in 22%, after recombinant human TSH stimulation in 52%, and after thyroid hormone withdrawal in 56% of patients with disease or tissue limited to the thyroid bed and in 80%, 100%, and 100% of patients, respectively, with metastatic disease. A combination of radioiodine WBS and serum Tg after recombinant human TSH stimulation detected thyroid tissue or cancer in 93% of patients with disease or tissue limited to the thyroid bed and 100% of patients with metastatic disease. In conclusion, recombinant human TSH administration is a safe and effective means of stimulating radioiodine uptake and serum Tg levels in patients undergoing evaluation for thyroid cancer persistence and recurrence.

Ligand-induced recruitment of a histone deacetylase in the negative-feedback regulation of the thyrotropin beta gene.

We have investigated ligand-dependent negative regulation of the thyroid-stimulating hormone beta (TSHbeta) gene. Thyroid hormone (T3) markedly repressed activity of the TSHbeta promoter that had been stably integrated into GH(3 )pituitary cells, through the conserved negative regulatory element (NRE) in the promoter. By DNA affinity binding assay, we show that the NRE constitutively binds to the histone deacetylase 1 (HDAC1) present in GH(3 )cells. Significantly, upon addition of T3, the NRE further recruited the thyroid hormone receptor (TRbeta) and another deacetylase, HDAC2. This recruitment coincided with an alteration of in vivo chromatin structure, as revealed by changes in restriction site accessibility. Supporting the direct interaction between TR and HDAC, in vitro assays showed that TR, through its DNA binding domain, strongly bound to HDAC2. Consistent with the role for HDACs in negative regulation, an inhibitor of the enzymes, trichostatin A, attenuated T3-dependent promoter repression. We suggest that ligand-dependent histone deacetylase recruitment is a mechanism of the negative-feedback regulation, a critical function of the pituitary-thyroid axis.

Development and in vitro characterization of human recombinant thyrotropin.

We have gained insight into the molecular mechanism of human thyrotropin (hTSH) action through cloning of the human TSHbeta subunit gene, development of recombinant TSH and novel analogues and chimeras produced by site-directed as well as cassette mutagenesis. A variety of loss of function mutations have shown several key domains in both the alpha- and beta-subunits that are important for high-affinity ligand interaction with the receptor. In contrast the specificity of receptor interaction was shown to be determined primarily by areas within the hTSH-beta "seat-belt" region. We have also designed various gain of function mutants (superagonists) using evolutionary considerations, homology modeling, and sequence comparisons within the cystine knot growth factor superfamily. Such superagonists resulted from increasing the positive charge by introduction of lysine or arginine residues or neutralization of negatively charged residues of the peripheral hairpin loops of each subunit in various combinations. Certain superagonists increased receptor binding, in vitro and in vivo bioactivity 100- to 1000-fold, more than that achieved previously for any other known protein ligand. In vivo metabolic clearance and biologic activity could be separately modulated by alteration of TSH carbohydrate structure including production of chimeras that added sites of O-glycosylation and/or covalently linked the alpha- and beta-subunits. These data suggest that electrostatic interactions resulting from net positive charge in TSH and net negative charge in its receptor play an important role in high-affinity TSH receptor binding and signal transduction. Insights gained from the design of such novel recombinant TSH analogues and chimeras should have many diagnostic and therapeutic applications. These include the design of improved in vitro assays for thyrotropic factors as well as the design of second generation recombinant TSH analogues for the detection and treatment of thyroid cancer.

Thyrotropin-secreting pituitary tumors: diagnostic criteria, thyroid hormone sensitivity, and treatment outcome in 25 patients followed at the National Institutes of Health.

We report a large series of 25 patients with TSH-secreting tumors (23 macroadenomas) followed at the NIH. Hyperthyroid symptoms were severe in 14 patients, mild in 8, and absent in 3. Patients were divided into 2 groups according to whether their thyroid had been treated (n = 11) or not (n = 14). In untreated patients, the classical diagnostic criteria (unresponsive TRH test, high alpha-subunit, and high alpha-subunit/TSH ratio) were present, respectively, in 10, 8, and 12 cases (sensitivity, 71%, 75%, and 83%; specificity, 96%, 90%, and 65%). In treated patients, the respective sensitivities of the TRH test, alpha-subunit, and alpha-subunit/TSH ratio were 64%, 90%, and 90%, and their specificities were 100%, 82%, and 73%. Studies of thyroid hormone action revealed no evidence of acquired resistance to thyroid hormone in TSH-secreting tumors. Apparent cure was achieved in 35% of cases by surgery alone and in 22% more by combined therapies. Three deaths occurred, including 1 from metastatic thyrotroph carcinoma. Six patients had residual tumor, with symptoms of hyperthyroidism controlled with octreotide in 5. The size and invasiveness of the tumor, duration of symptoms, and intensity of hyperthyroidism were the main prognostic factors. Thus, early diagnosis and treatment are the keys to a good outcome.

A rational design strategy for protein hormone superagonists.

By combining evolutionary considerations, sequence comparisons and homology modeling we have designed recombinant human thyroid-stimulating hormone (hTSH) analogs with increased receptor binding and activity. The introduction of seven basic residues into the peripheral loops of hTSH resulted in up to a 50,000-fold increase in receptor binding affinity and 1300-fold increase in intrinsic activity. Such analogs are not only of potential clinical interest but can be tools to explore molecular aspects of conventional as well as nonclassical actions of glycoprotein hormones. These design strategies should be applicable to the development of novel analogs of other related hormones and growth factors with a variety of therapeutic and basic science applications, particularly for proteins that have undergone evolutionary decrease in bioactivity.

Rat mitochondrial glycerol-3-phosphate dehydrogenase gene: multiple promoters, high levels in brown adipose tissue, and tissue-specific regulation by thyroid hormone.

Mitochondrial FAD-linked glycerol-3-phosphate dehydrogenase (mtGPDH) is one of the two enzymes of the glycerol phosphate shuttle. This shuttle transfers reducing equivalents from the cytoplasm to the mitochondria in a unidirectional, exothermic manner. Here, the isolation and characterization of the rat nuclear gene (Gpd2) encoding mtGPDH is reported. The mtGPDH gene spans 100 kb and consists of 17 exons. The use of alternate promoters was suggested by the presence of three different first exons and confirmed by transient expression for two of them. The first exons are expressed in a tissue-restricted manner. Exon 1a was found primarily in brain, exon 1b was used in all tissues examined, and exon 1c was detected predominantly in testis. Depending on the tissue, different transcript lengths were also observed: 5.9 kb (all tissues), 3.6 kb (skeletal muscle), and 2.5 kb (testis). The length isoforms are attributable to alternate splicing and polyadenylation site use. Very high mtGPDH mRNA levels were found in brown adipose tissue, 75 fold greater than in white adipose tissue. Thyroid hormone increased mtGPDH mRNA levels in liver and heart but not in brown adipose tissue, brain, or testis. This pattern corresponds to that of thyroid hormone-induced oxygen consumption and is consistent with a role for mtGPDH in thyroid hormone-induced thermogenesis. Both thyroid-responsive and nonresponsive tissues used promoter 1b, suggesting that tissue-specific factor(s) contribute to the tissue-restricted responsiveness to thyroid hormone.

Comparison of administration of recombinant human thyrotropin with withdrawal of thyroid hormone for radioactive iodine scanning in patients with thyroid carcinoma.

BACKGROUND: To detect recurrent disease in patients who have had differentiated thyroid cancer, periodic withdrawal of thyroid hormone therapy may be required to raise serum thyrotropin concentrations to stimulate thyroid tissue so that radioiodine (iodine-131) scanning can be performed. However, withdrawal of thyroid hormone therapy causes hypothyroidism. Administration of recombinant human thyrotropin stimulates thyroid tissue without requiring the discontinuation of thyroid hormone therapy. METHODS: One hundred twenty-seven patients with thyroid cancer underwent whole-body radioiodine scanning by two techniques: first after receiving two doses of thyrotropin while thyroid hormone therapy was continued, and second after the withdrawal of thyroid hormone therapy. The scans were evaluated by reviewers unaware of the conditions of scanning. The serum thyroglobulin concentrations and the prevalence of symptoms of hypothyroidism and mood disorders were also determined. RESULTS: Sixty-two of the 127 patients had positive whole-body radioiodine scans by one or both techniques. The scans obtained after stimulation with thyrotropin were equivalent to the scans obtained after withdrawal of thyroid hormone in 41 of these patients (66 percent), superior in 3 (5 percent), and inferior in 18 (29 percent). When the 65 patients with concordant negative scans were included, the two scans were equivalent in 106 patients (83 percent). Eight patients (13 percent of those with at least one positive scan) were treated with radioiodine on the basis of superior scans done after withdrawal of thyroid hormone. Serum thyroglobulin concentrations increased in 15 of 35 tested patients: 14 after withdrawal of thyroid hormone and 13 after administration of thyrotropin. Patients had more symptoms of hypothyroidism (P<0.001) and dysphoric mood states (P<0.001) after withdrawal of thyroid hormone than after administration of thyrotropin. CONCLUSIONS: Thyrotropin stimulates radioiodine uptake for scanning in patients with thyroid cancer, but the sensitivity of scanning after the administration of thyrotropin is less than that after the withdrawal of thyroid hormone. Thyrotropin scanning is associated with fewer symptoms and dysphoric mood states.

Human thyroid-stimulating hormone (hTSH) subunit gene fusion produces hTSH with increased stability and serum half-life and compensates for mutagenesis-induced defects in subunit association.

The human thyroid-stimulating hormone (hTSH) subunits alpha and beta are transcribed from different genes and associate noncovalently to form the bioactive hTSH heterodimer. Dimerization is rate-limiting for hTSH secretion, and dissociation leads to hormone inactivation. Previous studies on human chorionic gonadotropin (hCG) and human follicle-stimulating hormone had shown that it was possible by subunit gene fusion to produce a bioactive, single chain hormone. However, neither the stability nor the clearance from the circulation of such fused glycoprotein hormones has been studied. We show here that genetic fusion of the hTSH alpha- and beta-subunits using the carboxyl-terminal peptide of the hCG beta-subunit as a linker created unimolecular hTSH whose receptor binding and bioactivity were comparable to native hTSH. Interestingly, the fused hTSH had higher thermostability and a longer plasma half-life than either native or dimeric hTSH containing the hCG beta-subunit-carboxyl-terminal peptide, suggesting that dimer dissociation may contribute to glycoprotein hormone inactivation in vivo. In addition, we show for the first time that synthesis of hTSH as a single polypeptide chain could overcome certain mutagenesis-induced defects in hTSH secretion, therefore enabling functional studies of such mutants. Thus, in addition to prolongation of plasma half-life, genetic fusion of hTSH subunits should be particularly relevant for the engineering of novel analogs where desirable features are offset by decreased dimer formation or stability. Such methods provide a general approach to expand the spectrum of novel recombinant glycoprotein hormones available for in vitro and in vivo study.

Substitution of the seat-belt region of the thyroid-stimulating hormone (TSH) beta-subunit with the corresponding regions of choriogonadotropin or follitropin confers luteotropic but not follitropic activity to chimeric TSH.

The region between the 10th and 12th cysteine (Cys88-Cys105 in human thyroid-stimulating hormone beta-subunit (hTSHbeta)) of the glycoprotein hormone beta-subunits corresponds to the disulfide-linked seat-belt region. It wraps around the common alpha-subunit and has been implicated in regulating specificity between human choriogonadotropin (hCG) and human follicle-stimulating hormone (hFSH), but determinants of hTSH specificity are unknown. To characterize the role of this region for hTSH, we constructed hTSH chimeras in which the entire seat-belt region Cys88-Cys105 or individual intercysteine segments Cys88-Cys95 and Cys95-Cys105 were replaced with the corresponding sequences of hCG and hFSH or alanine cassettes. Alanine cassette mutagenesis of hTSH showed that the Cys95-Cys105 segment of the seat-belt was more important for TSH receptor binding and signal transduction than the Cys88-Cys95 determinant loop region. Replacing the entire seat-belt of hTSHbeta with the hCG sequence conferred full hCG receptor binding and activation to the hTSH chimera, whereas TSH receptor binding and activation were abolished. Conversely, introduction of the hTSHbeta seat-belt sequence into hCGbeta generated an hCG chimera that bound to and activated the TSH receptor but not the CG/lutropin (LH) receptor. In contrast, an hTSH chimera bearing hFSH seat-belt residues did not possess any follitropic activity, and its thyrotropic activity was only slightly reduced. This may in part be due to the fact that the net charge of the seat-belt is similar in hTSH and hFSH but different from hCG. However, exchanging other regions of charge heterogeneity between hTSHbeta and hFSHbeta did not confer follitropic activity to hTSH. Thus, exchanging the seat-belt region between hTSH and hCG switches hormonal specificity in a mutually exclusive fashion. In contrast, the seat-belt appears not to discriminate between the TSH and the FSH receptors, indicating for the first time that domains outside the seat-belt region contribute to glycoprotein hormone specificity.

Transgenic mice bearing a human mutant thyroid hormone beta 1 receptor manifest thyroid function anomalies, weight reduction, and hyperactivity.

BACKGROUND: Resistance to thyroid hormone (RTH) is a syndrome characterized by refractoriness of the pituitary and/or peripheral tissues to the action of thyroid hormone. Mutations in the thyroid hormone receptor beta (TR beta) gene result in TR beta 1 mutants that mediate the clinical phenotype by interfering with transcription of thyroid hormone-regulated genes via a dominant negative effect. In this study, we developed transgenic mice harboring PV, a potent dominant negative human mutant TR beta 1 devoid of thyroid hormone binding and transcriptional activation, as an animal model to understand the molecular basis of this human disease. MATERIALS AND METHODS: Standard molecular biology approaches were used to obtain a cDNA fragment containing mutant PV which was injected into the pronucleus of fertilized egg. Founders were identified by Southern analysis and the expression of PV in tissues was determined by RNA and immunohistochemistry. Thyroid function was determined by radioimmunoassays of the hormones and the behavior of mice was observed using standard methods. RESULTS: The expression of mutant PV was directed by the beta-actin promoter. Mutant PV mRNA was detected in all tissues of transgenic mice, but the levels varied with tissues and with different lines of founders. Thyroid function tests in transgenic mice with high expression of mutant PV showed a significantly (approximately 1.5-fold) higher mean serum total of L-thyroxine levels (p < 0.01) than those of nontransgenic mice. Moreover, thyroid-stimulating hormone levels were not significantly different from those of nontransgenic mice. In addition, these mice displayed decreased weights and a behavioral phenotype characterized by hyperactivity. CONCLUSIONS: These mice have phenotypic features consistent with the commonly observed clinical features of RTH and could be used as a model system to better understand the action of mutant TR beta 1 in a physiological context, which could lead to better treatment for this disease.

Thyroid hormones correlate with symptoms of hyperactivity but not inattention in attention deficit hyperactivity disorder.

The diagnostic validity of dividing attention deficit hyperactivity disorder (ADHD) into two distinct subgroups, one with and one without hyperactivity, is controversial since there have been no physiological differences demonstrated between these two subgroups. In this study, the relationship between thyroid hormones and symptoms of hyperactivity was examined in subjects with resistance to thyroid hormone (RTH) and their unaffected family members. Clinical data were collected on 152 subjects; 75 subjects with RTH and 77 family members without RTH. Each subject was assessed using DSM-III-R criterion based, structured psychiatric interviews, and Total T3 (TT3), Total T4 (TT4) and TSH concentrations were measured. The total number of ADHD symptoms were assigned to either inattention or hyperactivity subgroups using DSM-III-R criteria. The total number of ADHD symptoms were then reassigned to inattention or hyperactivity/impulsivity subgroups using DSM-IV criteria. Pearson R correlation coefficients were calculated separately for the RTH and unaffected family members groups in order to determine the relationships between TSH, TT3 and TT4 concentrations, and the DSM-III-R and DSM-IV symptom categories of ADHD in both groups. TSH concentrations were not significantly correlated with any of the symptom categories in either group. However, in the RTH group, both TT3 and TT4 concentrations were significantly and positively correlated with total symptoms of ADHD (DSM-III-R) as well as symptoms of inattention (DSM-III-R) and symptoms of hyperactivity (DSM-III-R). When DSM-IV criteria were used, which reassigns symptoms of impulsivity from the inattention to the hyperactivity category, only the positive correlation between TT3 and TT4 concentrations and symptoms of hyperactivity/impulsivity (DSM-IV) remained significant. In the group of unaffected family members, the relationship between TT3 concentrations and symptoms of hyperactivity/impulsivity (DSM-IV) was the only significant correlation. The data support the hypothesis that thyroid hormones may provide a physiological basis for the dichotomy between symptoms of inattention and symptoms of hyperactivity, particularly when DSM-IV criteria are applied.

Expression of biologically active human thyrotropin (hTSH) in a baculovirus system: effect of insect cell glycosylation on hTSH activity in vitro and in vivo.

To obtain large amounts of hTSH and to study the role of the N-linked oligosaccharides for its biological activity, hTSH was produced using recombinant baculovirus containing the human alpha-subunit and a hTSH beta-minigene, respectively, both under the control of the polyhedrin promoter. Expression in insect cells was 800-1000 ng/ml, 30-fold higher than in our optimized mammalian transient transfection system using Chinese hamster ovary (CHO) cells (20-50 ng/ml). The in vitro activity of insect-cell expressed hTSH (IC-hTSH) was increased 5-fold compared with CHO-hTSH, judged by the ability to induce cAMP production in CHO cells stably transfected with the hTSH receptor (JP09) and the rat thyroid cell line FRTL-5, as well as growth promotion in FRTL-5 cells. Lectin binding and enzymatic desialylation studies suggested that in contrast to CHO-hTSH, IC-hTSH lacked complex-type oligosaccharides terminating with sialic acid but contained predominantly high mannose-type oligosaccharides. The in vitro activity of CHO-hTSH also increased 5- to 6-fold upon treatment of the hTSH-producing cells with the oligosaccharide processing inhibitors swainsonine and castanospermine, which inhibit formation of complex, terminally sialylated oligosaccharides, and upon enzymatic desialylation. In contrast, insect cell-expression or treatment with processing inhibitors did not affect TSH receptor binding. Despite the higher in vitro activity, IC-hTSH had a much lower in vivo activity than CHO-hTSH, due to rapid clearance from the circulation. In summary, this study shows for the first time that relatively high levels of recombinant hTSH with high in vitro bioactivity can be produced in a baculovirus system. Cell-dependent glycosylation is a major factor that determines the final in vivo biopotency of recombinant glycoproteins, a finding that should be of general relevance for all insect cell-produced glycosylated proteins. Although not suitable for clinical use, highly bioactive recombinant hTSH derived from high expression in insect cells should be useful in defining structure-function relations of hormone analogs.

Regulation of the human TRH (hTRH) gene by human thyroid hormone receptor beta 1 (hTR beta 1) mutants.

TRH is negatively regulated by T3 both in the hypothalamic paraventricular nucleus and transient transfection models. Mutations in hTR beta 1 genes are associated with the syndrome of generalized resistance to thyroid hormone. To investigate potential effects of mutant TRs on T3 regulation of the hTRH gene, transient gene expression assays were performed in human neuroblastoma (HTB-11) cells with an hTRH promoter-luciferase construct, wild type (WT) hTR beta 1, and three qualitatively distinct hTR beta 1 mutant forms (ED, OK and PV). In the presence of T3 (10(-9) M), liganded WT-hTR beta 1 inhibited hTRH promoter activity significantly (40%). Cotransfection of each of the two mutants (ED and OK) achieved similar levels of inhibition only at 10 to 100 fold increased T3 concentrations. Of interest, a 10x excess of mutant ED or OK could also exert dominant negative effects upon WT hTR beta 1-T3 mediated inhibitory actions on the hTRH promoter. In contrast, mutant TR-PV exerted neither inhibitory nor dominant negative effects at even higher concentrations of T3. Moreover, all three unliganded mutant forms stimulated TRH promoter activity significantly in the absence of T3, despite their different mutations in the ligand-binding domain (LBD). These data demonstrate that thyroid hormone resistance at the level of TRH gene regulation, due to reduced inhibitory actions of mutant TR-T3 complexes, as well as dominant negative effects upon WT hTR beta 1 mediated inhibition, likely contribute to elevated TSH values observed in the syndrome of thyroid hormone resistance.

False-positive iodine-131 whole-body scans due to cholecystitis and sebaceous cyst.

False-positive whole-body 131I scans are not frequent but have serious consequences in the management of patients with thyroid cancer. They can be classified in four main groups: elimination of iodine in body fluids, infection or inflammation, cysts or transudates and nonthyroid tumors. We report on two patients with false-positive post-therapy 131I scans. The first patient had uptake projected in the right pelvic area which was later proven to be a large gluteal sebaceous cyst. The second patient had uptake in the gallbladder area that did not disappear after 131I treatment; she underwent exploratory laparotomy which revealed extensive chronic cholecystitis. These cases illustrate two new causes of false-positive 131I whole-body scans (sebaceous cyst and cholecystitis), which highlights two mechanisms (elimination in body fluid and inflammation).

Structure-function studies of human TSH: new advances in design of glycoprotein hormone analogs.

Recent progress in structure-function studies of glycoprotein hormones has provided new insights into the molecular mechanisms of action of these hormones and has further supported the concept that physiological modulation of assembly, bioactivity, and clearance of these hormones is dependent on specific structural components. This review emphasizes current advances in the structure-function relationships of human TSH, which have contributed to further elucidation of common and hormone specific features within the glycoprotein hormones family. Novel strategies are now being applied to investigate the role of individual structural elements. The principks discovered in such studies are essential to understand the physiological regulation of hormone bioactivity and allow for the rational design of novel analogs with potential therapeutic applications.