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Celano M, Sponziello M, Tallini G, Maggisano V, Bruno R, Dima M, Di Oto E, Redler A, Durante C, Sacco R, Filetti S, Russo D. Increased expression of pro-angiogenic factors and vascularization in thyroid hyperfunctioning adenomas with and without TSH receptor activating mutations. Endocrine 2013; 43:147-53. [PMID: 22815044 DOI: 10.1007/s12020-012-9747-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Accepted: 07/05/2012] [Indexed: 11/29/2022]
Abstract
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.
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MESH Headings
- Angiogenic Proteins/biosynthesis
- Angiogenic Proteins/genetics
- Angiogenic Proteins/metabolism
- Biomarkers/metabolism
- Cell Proliferation
- Goiter, Nodular/immunology
- Goiter, Nodular/metabolism
- Goiter, Nodular/pathology
- Goiter, Nodular/physiopathology
- Humans
- Lymphatic System/immunology
- Lymphatic System/metabolism
- Lymphatic System/pathology
- Microvessels/metabolism
- Microvessels/pathology
- Mutation
- Neoplasm Proteins/biosynthesis
- Neoplasm Proteins/genetics
- Neoplasm Proteins/metabolism
- Neovascularization, Pathologic/metabolism
- Neovascularization, Pathologic/pathology
- Nitric Oxide Synthase Type III/biosynthesis
- Nitric Oxide Synthase Type III/genetics
- Nitric Oxide Synthase Type III/metabolism
- Platelet-Derived Growth Factor/biosynthesis
- Platelet-Derived Growth Factor/genetics
- Platelet-Derived Growth Factor/metabolism
- Protein Isoforms/biosynthesis
- Protein Isoforms/genetics
- Protein Isoforms/metabolism
- RNA, Messenger/metabolism
- Receptors, Platelet-Derived Growth Factor/biosynthesis
- Receptors, Platelet-Derived Growth Factor/genetics
- Receptors, Platelet-Derived Growth Factor/metabolism
- Receptors, Thyrotropin/deficiency
- Receptors, Thyrotropin/genetics
- Receptors, Thyrotropin/immunology
- Receptors, Thyrotropin/metabolism
- Receptors, Vascular Endothelial Growth Factor/biosynthesis
- Receptors, Vascular Endothelial Growth Factor/genetics
- Receptors, Vascular Endothelial Growth Factor/metabolism
- Thyroid Gland/blood supply
- Thyroid Gland/immunology
- Thyroid Gland/metabolism
- Thyroid Gland/pathology
- Thyrotoxicosis/immunology
- Thyrotoxicosis/metabolism
- Thyrotoxicosis/pathology
- Thyrotoxicosis/physiopathology
- Up-Regulation
- Vascular Endothelial Growth Factor A/biosynthesis
- Vascular Endothelial Growth Factor A/genetics
- Vascular Endothelial Growth Factor A/metabolism
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Affiliation(s)
- Marilena Celano
- Department of Health Sciences, University of Catanzaro "Magna Graecia", Viale Europa, Germaneto, 88100, Catanzaro, Italy
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2
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Akama T, Sue M, Kawashima A, Wu H, Tanigawa K, Suzuki S, Hayashi M, Yoshihara A, Ishido Y, Ishii N, Suzuki K. Identification of microRNAs that mediate thyroid cell growth induced by TSH. Mol Endocrinol 2012; 26:493-501. [PMID: 22301781 DOI: 10.1210/me.2011-1004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
TSH is a major regulator of thyroid cell growth and endocrine function. It is known that cAMP and phosphatidylinositol 3-kinase (PI3K) are responsible for mediating the action of TSH. Activation of these signals results in the induction of a series of transcription factors and cell cycle regulating proteins, which induce cell proliferation. In addition to such canonical transcriptional regulation, it was recently shown that microRNA (miRNA or miR) constitutes another key mechanism for the regulation of gene expression. However, whether TSH action is mediated by miRNA in the thyroid is unknown. In this study, we have performed miRNA microarray analysis and demonstrated that TSH significantly decreases expression of 47 miRNA in thyroid cells. Among these, we have shown, using their specific agonists, that overexpression of miR-16 and miR-195 suppressed cell cycle progression and DNA synthesis that was induced by TSH. In silico analysis predicted that Mapk8, Ccne1, and Cdc6, the expression of which was up-regulated by TSH, are potential target genes for these miRNA, and overexpression of miR-16 and miR-195 suppressed expression of these target genes. The decrease of miR-16 and miR-195 expression by TSH was reproduced by forskolin and N(6),2'-O-dibutyryladenosine cAMP and reversed by the protein kinase A inhibitor H89 and the PI3K inhibitor LY294002. These results suggest that TSH activates cAMP/protein kinase A and PI3K cascades to decrease miR-16 and miR-195, which induce Mapk8, Ccne1, and Cdc6 to activate cell proliferation.
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Affiliation(s)
- Takeshi Akama
- Laboratory of Molecular Diagnostics, Department of Mycobacteriology, Leprosy Research Center, National Institute of Infectious Diseases, 4-2-1 Aoba-cho, Higashimurayama-shi, Tokyo, Japan
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Kloth L, Belge G, Burchardt K, Loeschke S, Wosniok W, Fu X, Nimzyk R, Mohamed SA, Drieschner N, Rippe V, Bullerdiek J. Decrease in thyroid adenoma associated (THADA) expression is a marker of dedifferentiation of thyroid tissue. BMC Clin Pathol 2011; 11:13. [PMID: 22050638 PMCID: PMC3229435 DOI: 10.1186/1472-6890-11-13] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Accepted: 11/04/2011] [Indexed: 12/17/2022] Open
Abstract
Background Thyroid adenoma associated (THADA) has been identified as the target gene affected by chromosome 2p21 translocations in thyroid adenomas, but the role of THADA in the thyroid is still elusive. The aim of this study was to quantify THADA gene expression in normal tissues and in thyroid hyper- and neoplasias, using real-time PCR. Methods For the analysis THADA and 18S rRNA gene expression assays were performed on 34 normal tissue samples, including thyroid, salivary gland, heart, endometrium, myometrium, lung, blood, and adipose tissue as well as on 85 thyroid hyper- and neoplasias, including three adenomas with a 2p21 translocation. In addition, NIS (sodium-iodide symporter) gene expression was measured on 34 of the pathological thyroid samples. Results Results illustrated that THADA expression in normal thyroid tissue was significantly higher (p < 0.0001, exact Wilcoxon test) than in the other tissues. Significant differences were also found between non-malignant pathological thyroid samples (goiters and adenomas) and malignant tumors (p < 0.001, Wilcoxon test, t approximation), anaplastic carcinomas (ATCs) and all other samples and also between ATCs and all other malignant tumors (p < 0.05, Wilcoxon test, t approximation). Furthermore, in thyroid tumors THADA mRNA expression was found to be inversely correlated with HMGA2 mRNA. HMGA2 expression was recently identified as a marker revealing malignant transformation of thyroid follicular tumors. A correlation between THADA and NIS has also been found in thyroid normal tissue and malignant tumors. Conclusions The results suggest THADA being a marker of dedifferentiation of thyroid tissue.
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Affiliation(s)
- Lars Kloth
- Center for Human Genetics, University of Bremen, Leobener Str, ZHG, 28359 Bremen, Germany.
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Abstract
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.
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Brewer C, Yeager N, Di Cristofano A. Thyroid-stimulating hormone initiated proliferative signals converge in vivo on the mTOR kinase without activating AKT. Cancer Res 2007; 67:8002-6. [PMID: 17804710 DOI: 10.1158/0008-5472.can-07-2471] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Thyroid-stimulating hormone (TSH) has long been recognized as the major proliferative and functional stimulus for thyroid follicular cells. TSH receptor (TSHR) engagement stimulates the production of cyclic AMP and the subsequent activation of downstream effector molecules, including protein kinase A, S6K1, and Rap1, whereas the role of the RAS and phosphatidylinositol-3-kinase signaling cascades downstream of TSHR is still controversial. Despite the abundance of candidates, it is still unclear which of these pathways represent(s) the key mitogenic output of TSH-initiated signaling. We have used an in vivo model of goitrogenesis to dissect the contribution of these pathways to TSH-induced thyrocyte proliferation and thyroid hyperplasia. We show that the in vivo proliferative response to chronic TSHR stimulation relies heavily on the activation of the mTOR/S6K1 axis, and that mTOR inhibition during goitrogenic stimulation abrogates the hyperplastic but not the hypertrophic thyrocyte responses to TSH, thus functionally uncoupling these two processes. Strikingly, goitrogenesis was not associated with an increase in AKT phosphorylation levels, underlining the existence of an AKT-independent pathway leading to mTOR activation upon TSH stimulation.
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Affiliation(s)
- Charlene Brewer
- Human Genetics Program, Fox Chase Cancer Center, Philadelphia, PA 19111, USA
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Zhang L, Baker G, Janus D, Paddon CA, Fuhrer D, Ludgate M. Biological effects of thyrotropin receptor activation on human orbital preadipocytes. Invest Ophthalmol Vis Sci 2007; 47:5197-203. [PMID: 17122103 PMCID: PMC1892592 DOI: 10.1167/iovs.06-0596] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Thyrotropin receptor (TSHR) expression is upregulated in the orbits of patients with Graves ophthalmopathy (GO), most of whom have TSHR-stimulating antibodies. The authors investigated the biological effects of TSHR activation in vitro in adipose tissue, the site of orbital TSHR expression. METHODS Activating mutant TSHR (TSHR*) or wild-type (WT) was introduced into human orbital preadipocytes using retroviral vectors. Their proliferation (Coulter counting), basal cAMP accumulation (radioimmunoassay), and spontaneous and peroxisome proliferator-activated receptor (PPARgamma)-induced adipogenesis (quantitative oil red O staining) were assessed and compared with those of nonmodified cells. QRT-PCR was used to measure transcripts of CCAT/enhancer binding protein (C/EBP)beta, PPARgamma, and lipoprotein lipase (LPL; early, intermediate, and late markers of adipogenesis) and for uncoupling protein (UCP)-1 (brown adipose tissue [BAT]). RESULTS Expression of TSHR* significantly inhibited the proliferation of preadipocytes and produced an increase in unstimulated cAMP of 200% to 600%. Basal lipid levels were significantly increased in TSHR* (127%-275%) compared with nonmodified (100%) or WT-expressing (104%-187%) cells. This was accompanied by 2- to 10-fold increases in early-intermediate markers and UCP-1 transcripts (2- to 8-fold); LPL was at the limit of detection. In nonmodified cells, adipogenesis produced significant increases in transcripts of all markers, including LPL (approximately 30-fold). This was not the case in TSHR*-expressing cells, which also displayed 67% to 84% reductions in lipid levels. CONCLUSIONS TSHR activation stimulates early differentiation (favoring BAT formation?) but renders preadipocytes refractory to PPARgamma-induced adipogenesis. In neither case did lipid-containing vacuoles accumulate, suggesting that terminal stages of differentiation were inhibited.
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Affiliation(s)
- Lei Zhang
- Centre for Endocrine and Diabetes Sciences, School of Medicine, Cardiff University, United Kingdom
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7
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Fuhrer D, Lewis MD, Alkhafaji F, Starkey K, Paschke R, Wynford-Thomas D, Eggo M, Ludgate M. Biological activity of activating thyroid-stimulating hormone receptor mutants depends on the cellular context. Endocrinology 2003; 144:4018-30. [PMID: 12933676 DOI: 10.1210/en.2003-0438] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Activating TSH receptor (TSHR) mutations are a major cause of toxic thyroid adenoma and familial hyperthyroidism, and more than 37 such mutations have been described. Previously their functional activity had been assessed in terms of cAMP and inositol phosphate production and predominantly in transiently transfected COS-7 (monkey embryonic kidney cells), a model that does not reflect effects on thyrocyte proliferation and function. Here we have performed a systematic comparison of wild-type and seven gain-of-function TSHR mutants, introduced into rat FRTL-5 and human thyrocytes, using retroviral vectors. Our results show that 1) biological potency of TSHR mutants in thyroid cells does not correlate with their cAMP levels in transfected COS cells, highlighting the importance of cellular context and level of expression when assessing biological effects of oncogenic mutations; 2) dissociation between stimulation of function and growth occurs with thyrocyte differentiated functions more readily stimulated than growth; 3) TSHR mutants show a similar order of potency in FRTL-5 cells and human thyrocytes; 4) mutants inducing the highest stimulation of adenylyl cyclase may paradoxically fail to induce proliferation; and 5) biological effects of cAMP activating TSHR mutants are attenuated by complex counterregulatory mechanisms at least at the level of phosphodiesterases and cAMP regulatory element modulator isoforms.
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Affiliation(s)
- D Fuhrer
- Department of Medicine, Endocrinology, Metabolism and Diabetes Section, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XN, United Kingdom
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Chiefari E, Brunetti A, Arturi F, Bidart JM, Russo D, Schlumberger M, Filetti S. Increased expression of AP2 and Sp1 transcription factors in human thyroid tumors: a role in NIS expression regulation? BMC Cancer 2002; 2:35. [PMID: 12475396 PMCID: PMC139985 DOI: 10.1186/1471-2407-2-35] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2002] [Accepted: 12/10/2002] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Sodium/iodide symporter (NIS) is a key protein in iodide transport by thyroid cells and this activity is a prerequisite for effective radioiodide treatment of thyroid cancer. In the majority of thyroid cancers, however, iodide uptake is reduced, probably as a result of decreased NIS protein expression. METHODS To identify the mechanisms that negatively affect NIS expression in thyroid tumors, we performed electrophoresis mobility shift assays and immunoblot analysis of nuclear protein extracts from normal and tumoral thyroid tissues from 14 unrelated patients. RESULTS Two proteins closely related to the transcription factors AP2 and Sp1 were identified in the nuclear extracts. Expression of both AP2 and Sp1 in nuclear extracts from thyroid tumors was significantly higher than that observed in corresponding normal tissues. CONCLUSION These observations raise the possibility that NIS expression, and subsequently iodide transport, are reduced in thyroid tumors at least in part owing to alterations in the binding activity of AP2 and Sp1 transcription factors to NIS promoter.
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MESH Headings
- Adenoma/chemistry
- Adenoma/genetics
- Adenoma/metabolism
- Adult
- Aged
- Carcinoma, Papillary/chemistry
- Carcinoma, Papillary/genetics
- Carcinoma, Papillary/metabolism
- Carcinoma, Papillary, Follicular/chemistry
- Carcinoma, Papillary, Follicular/genetics
- Carcinoma, Papillary, Follicular/metabolism
- Cell Extracts/chemistry
- Cell Nucleus/chemistry
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/immunology
- DNA-Binding Proteins/metabolism
- DNA-Binding Proteins/physiology
- Electrophoretic Mobility Shift Assay
- Female
- Gene Expression Regulation, Neoplastic/genetics
- Gene Expression Regulation, Neoplastic/physiology
- Humans
- Immunoblotting
- Male
- Middle Aged
- Promoter Regions, Genetic/genetics
- Promoter Regions, Genetic/physiology
- Sp1 Transcription Factor/genetics
- Sp1 Transcription Factor/immunology
- Sp1 Transcription Factor/metabolism
- Sp1 Transcription Factor/physiology
- Symporters/biosynthesis
- Symporters/genetics
- Thyroid Neoplasms/chemistry
- Thyroid Neoplasms/genetics
- Thyroid Neoplasms/metabolism
- Transcription Factor AP-2
- Transcription Factors/genetics
- Transcription Factors/immunology
- Transcription Factors/metabolism
- Transcription Factors/physiology
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Affiliation(s)
- Eusebio Chiefari
- Department of Experimental and Clinical Medicine "G. Salvatore", University of Catanzaro, 88100 Catanzaro, Italy
| | - Antonio Brunetti
- Department of Experimental and Clinical Medicine "G. Salvatore", University of Catanzaro, 88100 Catanzaro, Italy
| | - Franco Arturi
- Department of Experimental and Clinical Medicine "G. Salvatore", University of Catanzaro, 88100 Catanzaro, Italy
| | - Jean-Michel Bidart
- Département de Biologie Clinique and Service de Médecine Nucléaire, Institut Gustave Roussy, 94805 Villejuif, France
| | - Diego Russo
- Department of Pharmacobiological Sciences, University of Catanzaro, 88100 Catanzaro, Italy
| | - Martin Schlumberger
- Département de Biologie Clinique and Service de Médecine Nucléaire, Institut Gustave Roussy, 94805 Villejuif, France
| | - Sebastiano Filetti
- Department of Clinical Sciences, University of Roma "La Sapienza", Roma, Italy
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Sandrini F, Matyakhina L, Sarlis NJ, Kirschner LS, Farmakidis C, Gimm O, Stratakis CA. Regulatory subunit type I-alpha of protein kinase A (PRKAR1A): a tumor-suppressor gene for sporadic thyroid cancer. Genes Chromosomes Cancer 2002; 35:182-92. [PMID: 12203783 DOI: 10.1002/gcc.10112] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The tumor-suppressor gene encoding the cyclic AMP-dependent protein kinase A type I-alpha regulatory subunit PRKAR1A has been mapped to chromosome 17 (17q22-24) and is mutated in Carney complex, a familial neoplasia syndrome that is associated with thyroid tumors. Other genes implicated in cyclic nucleotide-dependent signaling have been investigated in thyroid tumorigenesis. We studied protein kinase A (PKA) activity in noninherited follicular thyroid adenomas and follicular, papillary, and undifferentiated (anaplastic) thyroid carcinomas. We then examined these and additional thyroid tumors for losses of the 17q22-24 PRKAR1A region, mutations of the PRKAR1A gene, and expression of its peptide product. Total PKA activity was markedly increased in carcinomas over that in adenomas, whereas the ratio of free vs. total PKA activity was decreased in cancer. Consistent with these findings, the 17q22-24 region was frequently lost in cancer but not in benign adenomas. A novel inactivating mutation of the PRKAR1A gene (leading to premature termination of the predicted protein) was found in an aggressive thyroid cancer. The tumor with PRKAR1A gene mutation, as well as the tumors with 17q allelic losses, showed decreased PRKAR1A expression by immunostaining. We conclude that PRKAR1A, the most abundant regulatory subunit of protein kinase A and a principal cyclic AMP-signaling modulator, acts as a tumor-suppressor gene in sporadic thyroid cancer. Published 2002 Wiley-Liss, Inc.
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Affiliation(s)
- Fabiano Sandrini
- Unit on Genetics and Endocrinology, Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-1862, USA
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Gereben B, Salvatore D, Harney JW, Tu HM, Larsen PR. The human, but not rat, dio2 gene is stimulated by thyroid transcription factor-1 (TTF-1). Mol Endocrinol 2001; 15:112-24. [PMID: 11145743 DOI: 10.1210/mend.15.1.0579] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Types 1 and 2 iodothyronine deiodinases (D1 and D2) catalyze the production of T(3) from T(4). D2 mRNA is abundant in the human thyroid but very low in adult rat thyroid, whereas D1 activity is high in both. To understand the molecular regulation of these genes in thyroid cells, the effect of thyroid transcription factor 1 (TTF-1) and the paired domain-containing protein 8 (Pax-8) on the transcriptional activity of the deiodinase promoters were studied. Both the approximately 6.5-kb hdio2 sequence and its most 3' 633 bp were activated 10-fold by transiently expressed TTF-1 in COS-7 cells, but the hdio1 was unaffected. Surprisingly, the response of the rdio2 gene to TTF-1 was only 3-fold despite the 73% identity with the proximal 633-bp region of hdio2 including complete conservation of a functional cAMP response element at -90. Neither human nor rat dio2 nor human dio1 was induced by Pax-8. The binding affinity of four putative TTF-1 binding sites in hdio2 were compared by a semiquantitative gel retardation assay using in vitro expressed TTF-1 homeodomain protein. Only two sites, D and C1 (both of which are absent in rdio2), had significant affinity. Functional analyses showed that both sites are required for the full response to TTF-1. These results can explain the differential expression of dio2 in thyroid and potentially other tissues in humans and rats.
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Affiliation(s)
- B Gereben
- Thyroid Division, Department of Medicine Brigham and Women's Hospital, Harvard Medical School Boston, Massachusetts 02115, USA
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