NADPH oxidase DUOX1 promotes long-term persistence of oxidative stress after an exposure to irradiation.

Ionizing radiation (IR) causes not only acute tissue damage, but also late effects in several cell generations after the initial exposure. The thyroid gland is one of the most sensitive organs to the carcinogenic effects of IR, and we have recently highlighted that an oxidative stress is responsible for the chromosomal rearrangements found in radio-induced papillary thyroid carcinoma. Using both a human thyroid cell line and primary thyrocytes, we investigated the mechanism by which IR induces the generation of reactive oxygen species (ROS) several days after irradiation. We focused on NADPH oxidases, which are specialized ROS-generating enzymes known as NOX/DUOX. Our results show that IR induces delayed NADPH oxidase DUOX1-dependent H2O2 production in a dose-dependent manner, which is sustained for several days. We report that p38 MAPK, activated after IR, increased DUOX1 via IL-13 expression, leading to persistent DNA damage and growth arrest. Pretreatment of cells with catalase, a scavenger of H2O2, or DUOX1 down-regulation by siRNA abrogated IR-induced DNA damage. Analysis of human thyroid tissues showed that DUOX1 is elevated not only in human radio-induced thyroid tumors, but also in sporadic thyroid tumors. Taken together, our data reveal a key role of DUOX1-dependent H2O2 production in long-term persistent radio-induced DNA damage. Our data also show that DUOX1-dependent H2O2 production, which induces DNA double-strand breaks, can cause genomic instability and promote the generation of neoplastic cells through its mutagenic effect.

Sodium/iodide symporter (NIS) gene expression is the limiting step for the onset of thyroid function in the human fetus.

CONTEXT: Terminal differentiation of the human thyroid is characterized by the onset of follicle formation and thyroid hormone synthesis at 11 gestational weeks (GW). OBJECTIVE: This study aimed to investigate the ontogeny of thyroglobulin (Tg), thyroid peroxidase (TPO), sodium/iodide symporter (NIS), pendrin (PDS), dual oxidase 2 (DUOX2), thyroid-stimulating hormone receptor (TSHR), and thyroid transcription factor 1 (TITF1), forkhead box E1 (FOXE1), and paired box gene 8 (PAX8) in the developing human thyroid. DESIGN: Thyroid tissues from human embryos and fetuses (7-33 GW; n = 45) were analyzed by quantitative PCR to monitor mRNA expression for each gene and by immunohistochemistry to determine the cellular distribution of TITF1, TSHR, Tg, TPO, NIS, and the onset of T4 production. A broken line regression model was fitted for each gene to compare the loglinear increase in expression before and after the onset of T4 synthesis. RESULTS: TITF1, FOXE1, PAX8, TSHR, and DUOX2 were stably expressed from 7 to 33 GW. Tg, TPO, and PDS expression was detectable as early as 7 GW and was correlated with gestational age (all, P < 0.01), and the slope of the regression line was significantly different before and after the onset of T4 synthesis at 11 GW (all, P < 0.01). NIS expression appeared last and showed the highest fit by the broken line regression model of all genes (correlation age P < 0.0001, broken line regression P < 0.0001). Immunohistochemical studies detected TITF1, TSHR, and Tg in unpolarized thyrocytes before follicle formation. T(4) and NIS labeling were only found in developing follicles from 11 GW on. CONCLUSION: These results imply a key role of NIS for the onset of human thyroid function.

Poorly differentiated follicular thyroid carcinoma: prognostic factors and relevance of histological classification.

OBJECTIVE: Poorly differentiated follicular thyroid carcinoma (PDFC) is a tumor of follicular cell origin with attributes intermediate between well-differentiated carcinomas and anaplastic carcinomas, but neither a clear histological description nor an established definition of prognostic indicators are available. DESIGN: This study correlates the clinical outcome and survival of 40 PDFC patients with histological architecture, cytological characteristics, and expression of various markers of cell proliferation and differentiation (cyclin A, cyclin B1, cyclin D1, cyclin E, Ki67, thyroperoxidase, galectin 3, dual oxidase [Duox], vascular endothelial growth factor, epidermal growth factor receptor, and p53). MAIN OUTCOME: At 5 years, the overall survival rate was 63% and the metastasis-free survival rate was 57%. An older age at the time of diagnosis and a larger tumor size were associated with an increased risk of distant metastases and of cancer-related death. Polymorph architecture was associated with a reduced risk of metastases, whereas a high expression of Duox was associated with a reduced risk of death. In these patients with PDFC, no other histological features or expression of any other marker had a prognostic significance. CONCLUSION: PDFC has a more aggressive behavior than well-differentiated carcinomas; prognosis is related to indicators that are also relevant in patients with well-differentiated carcinomas.

Functional characterization of human thyroid tissue with immunohistochemistry.

Immunohistochemistry provides insights in the expression of functional proteins and of their localization in normal thyroid tissue and in thyroid diseases. In hyperfunctional thyroid tissues, staining for sodium/iodide symporter (NIS), pendrin, thyroid peroxidase (TPO), and thyroglobulin (Tg) is increased. In hypofunctioning thyroid tissues, NIS staining is markedly decreased; in benign hypofunctioning adenomas, the expression of the other functional proteins is unmodified or slightly decreased, whereas their expression is profoundly decreased or absent in differentiated thyroid carcinoma.

Iodotyrosine dehalogenase 1 (DEHAL1) is a transmembrane protein involved in the recycling of iodide close to the thyroglobulin iodination site.

In the thyroid, iodotyrosine dehalogenase acts on the mono and diiodotyrosines released during the hydrolysis of thyroglobulin to liberate iodide, which can then reenter the hormone-producing pathways. It has been reported that the deiodination of iodotyrosines occurs predominantly in the microsomes and is mediated by NADPH. Recently, two cDNAs, 7401- and 7513-base pairs long that encode proteins with a conserved nitroreductase domain were published in GenBank as iodotyrosine dehalogenase 1 (DEHAL1) and iodotyrosine dehalogenase 1B (DEHAL1B), respectively. We report here our investigation of the localization and activity of one of these isoforms, DEHAL1. DEHAL1 mRNA is highly expressed in the thyroid, is up-regulated by cAMP, and encodes a transmembrane protein that efficiently catalyzes the NADPH-dependent deiodination of mono (L-MIT) and diiodotyrosine (L-DIT), with greater activity vs. L-MIT. Iodotyrosine deiodinase was active in HEK293 cells transfected by DEHAL1 cDNA, but not in CHO cells. A fraction of DEHAL1 protein is exposed to the cell surface, as indicated by biotinylation experiments. Immunohistochemistry studies showed that DEHAL1 proteins accumulate at the apical pole of thyrocytes. Taken together, these findings indicate that the deiodination reaction occurs at the apical pole of the thyrocyte and is involved in a rapid iodide recycling process at and/or close to the organification site.

Expression of the apical iodide transporter in human thyroid tissues: a comparison study with other iodide transporters.

Iodide transport by thyrocytes involves two transporters, namely the Na(+)/I (-) symporter located at the basolateral pole and possibly pendrin in the apical membranes of the cell. Recently, we identified a human gene and its protein product, designated hAIT, as a putative new transporter involved in iodide transfer across the apical membrane of thyrocytes. In the present report, we analyzed both hAIT gene and protein expressions in a large series of benign and malignant human thyroid tissues. Using immunohistochemistry, hAIT staining was detected in normal thyroid tissue in about 10% of follicles; in positive follicles, 10-40% of thyrocytes, mostly the tall cells, were stained. In thyroid tissues obtained from patients with Graves' disease and toxic adenomas, hAIT mRNA and protein levels were similar to those found in normal tissue. In hypofunctioning adenomas, hAIT mRNA levels were slightly decreased, and apical iodide transporter (AIT) immunostaining was similar to that observed in normal thyroid tissue. AIT staining was stronger in Hürthle cell adenomas and in microfollicular adenomas. In thyroid carcinomas, the mean and median hAIT mRNA levels were significantly decreased. Expression of AIT protein was undetectable in most papillary carcinomas and was weak but detectable in most follicular carcinomas; it was negative in anaplastic carcinomas.

Age-dependent variation of follicular size and expression of iodine transporters in human thyroid tissue.

UNLABELLED: The high sensitivity of the thyroid gland to the carcinogenic effects of radiation during childhood contrasts with the absence of demonstrable carcinogenic effects of radiation in adults. To better understand these age-related variations, we studied follicular morphometry, functional status, and proliferative activity in 31 thyroid glands removed from relatives of medullary thyroid carcinoma patients, with ages ranging from 3 to 39 y. METHODS: The mean follicular diameter (MFD) was estimated, and immunohistochemistry was performed with antibodies directed to molecules involved in iodide transport (Na(+)/I(-) symporter [NIS], pendrin, and apical iodide transporter), in organification (thyroperoxidase [TPO] and Duox), in cell cycle and growth (Ki-67, cyclin A and D1, and galectin-3), and in angiogenesis (vascular endothelial growth factor and nitric oxide synthase III [NOSIII]). RESULTS: Compared with older patients, patients who were < or =12 y old had a smaller MFD (P < 0.001) and more frequently positive NIS, pendrin, and Duox (P < 0.01). Proliferation rate as indicated by cyclin A expression was also higher in patients < 12 y (P < 0.01) but peaked at the time of puberty. Staining for NIS, pendrin, TPO, Duox, and NOSIII was stronger in thyroid glands with a smaller MFD (P < 0.001). On multiple tests adjusted for age and thyroid mass, TPO, Duox, and NOSIII remained significantly correlated to MFD (P < 0.001), whereas staining for NIS and pendrin did not. This finding suggests that NIS and pendrin expression is related mainly to the age of the patient. CONCLUSION: Smaller follicles with a higher expression of proteins involved in iodide metabolism were found in younger children. In cases of radioiodine contamination in children, the result will be a higher radioactive concentration and, hence, higher radiation doses. This event may induce the development of thyroid cancer under conditions of accelerated proliferation, as evidenced at puberty.

PAX8 and peroxisome proliferator-activated receptor gamma 1 gene expression status in benign and malignant thyroid tissues.

OBJECTIVE: Genetic alterations involving the thyroid transcription factor PAX8 and the peroxisome proliferator-activated receptor gamma 1 (PPARgamma1) genes have been described in thyroid neoplasms. We investigated in a series of thyroid samples, including 14 normal, 13 hyperfunctioning tissues, 26 follicular adenomas, 21 follicular and 41 papillary carcinomas, both the frequency of the PAX8-PPARgamma1 rearrangement and the expression of the PAX8 and PPARgamma transcripts. METHODS: Using RT-PCR followed by sequencing PCR products, PAX8-PPARgamma1 translocation was not detected in benign tissues nor in papillary carcinomas and was detected in 4 (19%) of 21 follicular carcinomas and in one (4%) of 26 follicular adenomas. RESULTS: Specific real-time quantitative RT-PCR (Q RT-PCR) methods detected high levels of PPARgamma transcripts in follicular carcinomas presenting the rearrangement. Interestingly, the level of PPARgamma transcripts was significantly decreased in papillary carcinomas in comparison with those found in benign adenomas and follicular carcinomas. Finally, PAX8 gene expression was decreased in both papillary and follicular thyroid carcinomas, and in these tumors to the same extent in the presence or absence of the rearrangement. These alterations in both PPARgamma and PAX8 gene expression may explain the poorly differentiated histotype of follicular carcinomas harboring the translocation. Immunohistochemistry showed that nuclear PPARgamma staining was weak in normal tissues, adenomas, papillary carcinomas and in some follicular carcinomas, and strong in the follicular carcinomas positive for the PAX8-PPARgamma1 translocation, but also in some follicular tumors in which no translocation could be evidenced. CONCLUSION: These observations confirm that the PAX8-PPARgamma1 translocation characterizes a subset of thyroid follicular carcinomas but is not a specific marker of carcinoma and that its frequency is lower than that initially reported. Finally, immunohistochemistry is not a reliable method for the specific detection of the translocation, that can be specifically evidenced by Q RT-PCR.

Changes in signaling pathways induced by vandetanib in a human medullary thyroid carcinoma model, as analyzed by reverse phase protein array.

BACKGROUND: Medullary thyroid carcinoma (MTC) is a rare tumor that is caused by activating mutations in the proto-oncogene RET. Vandetanib, a tyrosine-kinase inhibitor, has been recently approved to treat adult patients with metastatic MTC. The aim of this study was to investigate changes in signaling pathways induced by vandetanib treatment in preclinical MTC models, using the reverse-phase protein array method (RPPA). METHODS: The human TT cell line was used to assess in vitro and in vivo activity of vandetanib. Protein extracts from TT cells or TT xenografted mice, treated by increasing concentrations of vandetanib for different periods of time, were probed with a set of 12 antibodies representing major signaling pathways, using RPPA. Results were validated using two distinct protein detection methods: Western immunoblotting and immunohistochemistry. RESULTS: Vandetanib displays antiproliferative and antiangiogenic activities and inhibits RET autophosphorylation. The MAPK and AKT pathways were the two major signaling pathways inhibited by vandetanib. Interestingly, phosphorylated levels of NFκB-p65 were significantly increased by vandetanib. Comparable results were obtained in both the in vitro and in vivo approaches, as well as for the protein detection methods. However, some discrepancies were observed between RPPA and Western immunoblotting, possibly due to lack of specificity of the primary antibodies used. CONCLUSIONS: Overall, our results confirmed the interest of RPPA for screening global changes induced in signaling pathways by kinase inhibitors. MAPK and AKT were identified as the main pathways involved in vandetanib response in MTC models. Our results also suggest alternative routes for controlling the disease, and provide a rationale for the development of therapeutic combinations based on the comprehensive identification of molecular events induced by inhibitors.

Changes in signaling pathways induced by vandetanib in a human medullary thyroid carcinoma model, as analyzed by reverse phase protein array.

BACKGROUND: Medullary thyroid carcinoma (MTC) is a rare tumor that is due to activating mutations in the proto-oncogene RET. Vandetanib, a tyrosine-kinase inhibitor, has been recently approved to treat adult patients with metastatic MTC. The aim of this study was to investigate changes in signaling pathways induced by vandetanib treatment in preclinical MTC models, using the reverse-phase protein array method (RPPA). METHODS: The human TT cell line was used to assess in vitro and in vivo activity of vandetanib. Protein extracts from TT cells or TT xenografted mice, treated by increasing concentrations of vandetanib for different periods of time, were probed with a set of 12 antibodies representing major signaling pathways, using RPPA. Results were validated using two distinct protein detection methods, western-immunoblotting and immunohistochemistry. RESULTS: Vandetanib displays antiproliferative and antiangiogenic activities and inhibits RET auto-phosphorylation. MAPK and AKT pathways were the two major signaling pathways inhibited by vandetanib. Interestingly, phosphorylated levels of NFκB-p65 were significantly increased by vandetanib. Comparable results were obtained in both the in vitro and in vivo approaches as well as for the protein detection methods, although some discrepancies were observed between RPPA and western-immunoblotting. CONCLUSIONS: Results confirmed the reliability and the utility of RPPA for screening global changes induced in signaling pathways by kinase inhibitors. MAPK and AKT were identified as the main pathways involved in vandetanib response in MTC models. Our results also suggest alternative routes for controlling the disease and provide a rationale for the development of therapeutic combinations based on the comprehensive identification of molecular events induced by inhibitors.

Cisplatin resistance associated with PARP hyperactivation.

Non-small cell lung carcinoma patients are frequently treated with cisplatin (CDDP), most often yielding temporary clinical responses. Here, we show that PARP1 is highly expressed and constitutively hyperactivated in a majority of human CDDP-resistant cancer cells of distinct histologic origin. Cells manifesting elevated intracellular levels of poly(ADP-ribosyl)ated proteins (PAR(high)) responded to pharmacologic PARP inhibitors as well as to PARP1-targeting siRNAs by initiating a DNA damage response that translated into cell death following the activation of the intrinsic pathway of apoptosis. Moreover, PARP1-overexpressing tumor cells and xenografts displayed elevated levels of PAR, which predicted the response to PARP inhibitors in vitro and in vivo more accurately than PARP1 expression itself. Thus, a majority of CDDP-resistant cancer cells appear to develop a dependency to PARP1, becoming susceptible to PARP inhibitor-induced apoptosis.

An immunosurveillance mechanism controls cancer cell ploidy.

Cancer cells accommodate multiple genetic and epigenetic alterations that initially activate intrinsic (cell-autonomous) and extrinsic (immune-mediated) oncosuppressive mechanisms. Only once these barriers to oncogenesis have been overcome can malignant growth proceed unrestrained. Tetraploidization can contribute to oncogenesis because hyperploid cells are genomically unstable. We report that hyperploid cancer cells become immunogenic because of a constitutive endoplasmic reticulum stress response resulting in the aberrant cell surface exposure of calreticulin. Hyperploid, calreticulin-exposing cancer cells readily proliferated in immunodeficient mice and conserved their increased DNA content. In contrast, hyperploid cells injected into immunocompetent mice generated tumors only after a delay, and such tumors exhibited reduced DNA content, endoplasmic reticulum stress, and calreticulin exposure. Our results unveil an immunosurveillance system that imposes immunoselection against hyperploidy in carcinogen- and oncogene-induced cancers.

Wnt/ß-catenin signaling pathway is a direct enhancer of thyroid transcription factor-1 in human papillary thyroid carcinoma cells.

The Wnt/ß-catenin signaling pathway is involved in the normal development of thyroid gland, but its disregulation provokes the appearance of several types of cancers, including papillary thyroid carcinomas (PTC) which are the most common thyroid tumours. The follow-up of PTC patients is based on the monitoring of serum thyroglobulin levels which is regulated by the thyroid transcription factor 1 (TTF-1): a tissue-specific transcription factor essential for the differentiation of the thyroid. We investigated whether the Wnt/ß-catenin pathway might regulate TTF-1 expression in a human PTC model and examined the molecular mechanisms underlying this regulation. Immunofluorescence analysis, real time RT-PCR and Western blot studies revealed that TTF-1 as well as the major Wnt pathway components are co-expressed in TPC-1 cells and human PTC tumours. Knocking-down the Wnt/ß-catenin components by siRNAs inhibited both TTF-1 transcript and protein expression, while mimicking the activation of Wnt signaling by lithium chloride induced TTF-1 gene and protein expression. Functional promoter studies and ChIP analysis showed that the Wnt/ß-catenin pathway exerts its effect by means of the binding of ß-catenin to TCF/LEF transcription factors on the level of an active TCF/LEF response element at [-798, -792 bp] in TTF-1 promoter. In conclusion, we demonstrated that the Wnt/ß-catenin pathway is a direct and forward driver of the TTF-1 expression. The localization of TCF-4 and TTF-1 in the same area of PTC tissues might be of clinical relevance, and justifies further examination of these factors in the papillary thyroid cancers follow-up.

Tumor-associated macrophages (TAMs) form an interconnected cellular supportive network in anaplastic thyroid carcinoma.

BACKGROUND: A relationship between the increased density of tumor-associated macrophages (TAMs) and decreased survival was recently reported in thyroid cancer patients. Among these tumors, anaplastic thyroid cancer (ATC) is one of the most aggressive solid tumors in humans. TAMs (type M2) have been recognized as promoting tumor growth. The purpose of our study was to analyze with immunohistochemistry the presence of TAMs in a series of 27 ATC. METHODOLOGY/PRINCIPAL FINDINGS: Several macrophages markers such as NADPH oxidase complex NOX2-p22phox, CD163 and CD 68 were used. Immunostainings showed that TAMs represent more than 50% of nucleated cells in all ATCs. Moreover, these markers allowed the identification of elongated thin ramified cytoplasmic extensions, bestowing a "microglia-like" appearance on these cells which we termed "Ramified TAMs" (RTAMs). In contrast, cancer cells were totally negative. Cellular stroma was highly simplified since apart from cancer cells and blood vessels, RTAMs were the only other cellular component. RTAMs were evenly distributed and intermingled with cancer cells, and were in direct contact with other RTAMs via their ramifications. Moreover, RTAMs displayed strong immunostaining for connexin Cx43. Long chains of interconnected RTAMs arose from perivascular clusters and were dispersed within the tumor parenchyma. When expressed, the glucose transporter Glut1 was found in RTAMs and blood vessels, but rarely in cancer cells. CONCLUSION: ATCs display a very dense network of interconnected RTAMs in direct contact with intermingled cancer cells. To our knowledge this is the first time that such a network is described in a malignant tumor. This network was found in all our studied cases and appeared specific to ATC, since it was not found in differentiated thyroid cancers specimens. Taken together, these results suggest that RTAMs network is directly related to the aggressiveness of the disease via metabolic and trophic functions which remain to be determined.

New insight into the Nox4 subcellular localization in HEK293 cells: first monoclonal antibodies against Nox4.

Nox4, a member of Nox family of NADPH oxidase expressed in nonphagocytic cells, is a major source of reactive oxygen species in many cell types. But understanding of the role of Nox4 in the production of ROS and of regulation mechanism of oxidase activity is largely unknown. This study reports for the first time the generation and characterization of 5 mAbs against a recombinant Nox4 protein (AA: 206-578). Among 5 novel mAbs, 3 mAbs (8E9, 5F9, 6B11) specifically recognized Nox4 protein in HEK293 transfected cells or human kidney cortex by western blot analysis; mAb 8E9 reacted with intact tet-induced T-REx™ Nox4 cells in FACS studies. The other 2 mAbs 10B4 and 7C9 were shown to have a very weak reactivity after purification. Immunofluorescence confocal microscopy showed that Nox4 localized not only in the perinuclear and endoplasmic reticulum regions but also at the plasma membrane of the cells which was further confirmed by TIRF-microscopy. Epitope determination showed that mAb 8E9 recognizes a region on the last extracellular loop of Nox4, while mAbs 6B11 and 5F9 are directed to its cytosolic tail. Contrary to mAb 6B11, mAb 5F9 failed to detect Nox4 at the plasma membrane. Cell-free oxidase assays demonstrated a moderate but significant inhibition of constitutive Nox4 activity by mAbs 5F9 and 6B11. In conclusion, 5 mAbs raised against Nox4 were generated for the first time. 3 of them will provide powerful tools for a structure/function relationship of Nox4 and for physiopathological investigations in humans.

Identification of soluble candidate biomarkers of therapeutic response to sunitinib in medullary thyroid carcinoma in preclinical models.

PURPOSE: Medullary thyroid carcinoma (MTC), an aggressive rare tumor due to activating mutations in the proto-oncogene RET, requires new therapeutic strategies. Sunitinib, a potent inhibitor of RET, VEGF receptor (VEGFR)-1, VEGFR-2, VEGFR-3, and platelet-derived growth factor receptor (PDGFR)α/ß, has been reported as clinically effective in some patients with advanced MTC. In this study, we examine molecular mechanisms of action of sunitinib and identify candidate soluble biomarkers of response. EXPERIMENTAL DESIGN: Both in vitro and in vivo assays, using the human TT RET(C634W) MTC cell line, were done to assess the activity of sunitinib. Kinetic microarray studies were used to analyze molecular pathways modified by sunitinib and to identify candidate biomarkers that were subsequently investigated in the serum of patients. RESULTS: Sunitinib displayed antiproliferative and antiangiogenic activities and inhibited RET autophosphorylation and activation of downstream signaling pathways. We showed that sunitinib treatment induced major changes in the expression of genes involved in tissue invasion and metastasis including vimentin (VIM), urokinase plasminogen (PLAU), tenascin-C (TN-C), SPARC, and CD44. Analyzing downregulated genes, we identified those encoding secreted proteins and, among them, interleukin (IL)-8 was found to be modulated in the serum of xenografted mice under sunitinib treatment. Furthermore, we demonstrated that metastatic MTC patients presented increased serum levels of IL-8 and TGF-ß2. CONCLUSIONS: Experimental models confirm the clinical efficacy of sunitinib observed in a few studies. Molecular pathways revealed by genomic signatures underline the impact of sunitinib on tissue invasion. Selected soluble candidate biomarkers could be of value for monitoring sunitinib response in metastatic MTC patients.

Functional consequences of dual oxidase-thyroperoxidase interaction at the plasma membrane.

CONTEXT: Thyroperoxidase (TPO) and dual oxidase (DUOX) are present at the apical membrane of thyrocytes, where TPO catalyzes thyroid hormone biosynthesis in the presence of H2O2 produced by DUOX. Both enzymes are colocalized and associated, but the consequences of this interaction remain obscure. OBJECTIVE: The objective of this study was to evaluate the functional consequences of TPO-DUOX interaction at the plasma membrane. DESIGN: The functional consequences of DUOX-TPO interaction were studied by measuring extracellular H2O2 concentration and TPO activity in a heterologous system. For this purpose, HEK293 cells were transiently transfected with a combination of human TPO with human DUOX1 or DUOX2 in the presence of their respective maturation factors, DUOXA1 or DUOXA2. The effect of human DUOX2 mutants in which cysteine residues in the N-terminal domain were replaced by glycines was also analyzed. RESULTS: We observed that production of H2O2 decreases both TPO and DUOX activities. We show that TPO presents a catalase-like effect that protects DUOX from inhibition by H2O2. This catalase-like effect depends on the association between both enzymes, which probably occurs through the DUOX peroxidase-like domain because this effect was not observed with human DUOX2 mutants. CONCLUSION: The DUOX-TPO association at the plasma membrane is relevant for normal enzyme properties. Normally, TPO consumes H2O2 produced by DUOX, decreasing the availability of this substance at the apical membrane of thyrocytes and, in turn, probably decreasing the oxidative damage of macromolecules.

Role of H2O2 in RET/PTC1 chromosomal rearrangement produced by ionizing radiation in human thyroid cells.

During childhood, the thyroid gland is one of the most sensitive organs to the carcinogenetic effects of ionizing radiation that may lead to papillary thyroid carcinoma (PTC) associated with RET/PTC oncogene rearrangement. Exposure to ionizing radiation induces a transient "oxidative burst" through radiolysis of water, which can cause DNA damage and mediates part of the radiation effects. H(2)O(2) is a potent DNA-damaging agent that induces DNA double-strand breaks, and consequently, chromosomal aberrations. Irradiation by 5 Gy X-ray increased extracellular H(2)O(2). Therefore, we investigated the implication of H(2)O(2) in the generation of RET/PTC1 rearrangement after X-ray exposure. We developed a highly specific and sensitive nested reverse transcription-PCR method. By using the human thyroid cell line HTori-3, previously found to produce RET/PTC1 after gamma-irradiation, we showed that H(2)O(2), generated during a 5 Gy X-ray irradiation, causes DNA double-strand breaks and contributes to RET/PTC1 formation. Pretreatment of cells with catalase, a scavenger of H(2)O(2), significantly decreased RET/PTC1 rearrangement formation. Finally, RET/PTC chromosomal rearrangement was detected in HTori-3.1 cells after exposure of cells to H(2)O(2) (25 micromol/L), at a dose that did not affect the cell viability. This study shows for the first time that H(2)O(2) is able to cause RET/PTC1 rearrangement in thyroid cells and consequently highlights that oxidative stress could be responsible for the occurrence of RET/PTC1 rearrangement found in thyroid lesions even in the absence of radiation exposure.

Intracellular expression of reactive oxygen species-generating NADPH oxidase NOX4 in normal and cancer thyroid tissues.

NADPH oxidase 4 (NOX4) belongs to the NOX family that generates reactive oxygen species (ROS). Function and tissue distribution of NOX4 have not yet been entirely clarified. To date, in the thyroid gland, only DUOX1/2 NOX systems have been described. NOX4 mRNA expression, as shown by real-time PCR, was present in normal thyroid tissue, regulated by TSH and significantly increased in differentiated cancer tissues. TSH increased the protein level of NOX4 in human thyroid primary culture and NOX4-dependent ROS generation. NOX4 immunostaining was detected in normal and pathologic thyroid tissues. In normal thyroid tissue, staining was heterogeneous and mostly found in activated columnar thyrocytes but absent in quiescent flat cells. Papillary and follicular thyroid carcinomas displayed more homogeneous staining. The p22(phox) protein that forms a heterodimeric enzyme complex with NOX4 displayed an identical cellular expression pattern and was also positively regulated by TSH. ROS may have various biological effects, depending on the site of production. Intracellular NOX4-p22(phox) localization suggests a role in cytoplasmic redox signaling, in contrast to the DUOX localization at the apical membrane that corresponds to an extracellular H(2)O(2) production. Increased NOX4-p22(phox) in cancer might be related to a higher proliferation rate and tumor progression but a role in the development of tumors has to be further studied and established in the future.

Expression of cell cycle biomarkers and telomere length in papillary thyroid carcinoma: a comparative study between radiation-associated and spontaneous cancers.

OBJECTIVE: Radiation exposure during childhood is the only well-established risk factor for papillary thyroid carcinoma (PTC). To better define the biologic profile of radiation-induced and sporadic PTC, we compared in these two groups of PTC the expression of cell cycle regulatory proteins and telomere length. METHODS: Cell cycle markers (cyclin A, B1, D1, E, and Ki67) were evaluated on 100 PTC specimens (26 radiation-induced and 74 sporadic PTCs). The expression of cell cycle regulators was studied using immunohistochemistry; telomere length heterogeneity was studied using in situ hybridization in a subset of 16 formalin-fixed samples (8 radiation-induced and 8 sporadic PTCs). RESULTS: At multivariate analysis, only cytoplasmic cyclin E staining was overexpressed in sporadic cases (P = 0.006). The other cell cycle markers and telomere length did not differ significantly between sporadic PTC and radiation-induced PTC. CONCLUSIONS: These markers cannot be used to differentiate radiation-induced from sporadic PTCs.