Thyroid expression of an A2 adenosine receptor transgene induces thyroid hyperplasia and hyperthyroidism

Mouse Models to Examine Differentiated Thyroid Cancer Pathogenesis: Recent Updates

Although the overall prognosis of differentiated thyroid cancer (DTC), the most common endocrine malignancy, is favorable, a subset of patients exhibits aggressive features. Therefore, preclinical models that can be utilized to investigate DTC pathogenesis and novel treatments are necessary. Various mouse models have been developed based on advances in thyroid cancer genetics. This review focuses on recent progress in mouse models that have been developed to elucidate the molecular pathogenesis of DTC.

Constitutive TSH receptor activation as a hallmark of thyroid autonomy

Since its cloning more than 30 years ago, the thyrotropin receptor (TSHR) has emerged as a pivotal player in thyroid physiology and pathophysiology. In particular, hyperthyroidism due to autoimmune disease or thyroid autonomy is linked with TSHR activation via autoantibodies or mutations respectively. This review summarises clinical aspects of constitutive TSH receptor activation by naturally occurring somatic or germline TSHR mutations resulting in TSH-independent thyroid function and cell proliferation.

Dual Activation of cAMP Production Through Photostimulation or Chemical Stimulation

cAMP is a crucial mediator of multiple cell signaling pathways. This cyclic nucleotide requires strict spatiotemporal control for effective function. Light-activated proteins have become a powerful tool to study signaling kinetics due to having quick on/off rates and minimal off-target effects. The photoactivated adenylyl cyclase from Beggiatoa (bPAC) produces cAMP rapidly upon stimulation with blue light. However, light delivery is not always feasible, especially in vivo. Hence, we created a luminescence-activated cyclase by fusing bPAC with nanoluciferase (nLuc) to allow chemical activation of cAMP activity. This dual-activated adenylyl cyclase can be stimulated using short bursts of light or long-term chemical activation with furimazine and other related luciferins. Together these can be used to mimic transient, chronic, and oscillating patterns of cAMP signaling. Moreover, when coupled to compartment-specific targeting domains, these reagents provide a new powerful tool for cAMP spatiotemporal dynamic studies. Here, we describe detailed methods for working with bPAC-nLuc in mammalian cells, stimulating cAMP production with light and luciferins, and measuring total cAMP accumulation.

Hyperthyroidism and Papillary Thyroid Carcinoma in Thyrotropin Receptor D633H Mutant Mice

BACKGROUND

Constitutively active thyrotropin receptor (TSHR) mutations are the most common etiology of non-autoimmune hyperthyroidism (NAH). Thus far, the functionality of these mutations has been tested in vitro, but the in vivo models are lacking.

METHODS

To understand the pathophysiology of NAH, the patient-derived constitutively active TSHR D633H mutation was introduced into the murine Tshr by homologous recombination.

RESULTS

In this model, both subclinical and overt hyperthyroidism was observed, depending on the age, sex, and genotype. Homozygous mice presented hyperthyroidism at two months of age, while heterozygous animals showed only suppressed thyrotropin. Interestingly, at six months of age, thyroid hormone concentrations in all mutant mice were analogous to wild-type mice, and they showed colloid goiter with flattened thyrocytes. Strikingly, at one year of age, nearly all homozygous mice presented large papillary thyroid carcinomas. Mechanistically, this papillary thyroid carcinoma phenotype was associated with an overactive thyroid and strongly increased stainings of proliferation-, pERK-, and NKX2-1 markers, but no mutations in the "hot-spot" areas of common oncogenes (Braf, Nras, and Kras) were found.

CONCLUSIONS

This is the first study to reveal the dynamic age-, sex-, and genotype-dependent development of NAH. Furthermore, the study shows that a constitutively active TSHR can trigger a malignant transformation of thyrocytes.

Deletion of Rap1b, but not Rap1a or Epac1, Reduces Protein Kinase A-Mediated Thyroid Cancer

BACKGROUND

Thyroid cancer is an emerging health problem in the United States and worldwide. With incidence rates of thyroid cancer rapidly rising, the need to develop new treatment options is becoming a priority, and understanding the molecular mechanisms of this disease is crucial to furthering these efforts. Thyroid growth is driven by the TSH/cAMP/PKA signaling pathway, and it has previously been shown that activation of PKA through genetic ablation of the regulatory subunit Prkar1a (Prkar1a KO) is sufficient to cause follicular thyroid cancer in mouse models. cAMP also activates the Epac proteins and their downstream effectors, Rap1a and Rap1b.

METHODS

Previously, the authors' laboratory generated a mouse model of follicular thyroid cancer by conferring thyroid-specific deletion of Prkar1a (R1a-TpoKO). To probe the roles of other components of the PKA signaling system in the development of thyroid cancer, this study deleted Rap1 and Epac1 in the setting of the Prkar1a knockout.

RESULTS

Deletion of Rap1 significantly decreases thyroid size and cancer incidence in Prkar1a KO thyroids. Further, isoform-specific ablation of Rap1a and Rap1b implicates Rap1b as the downstream effector of PKA during thyroid carcinogenesis. In vivo modeling provides definitive evidence that Epac1 plays little role in thyroid proliferation and is dispensable for thyroid carcinogenesis arising from the deletion of Prkar1a.

CONCLUSIONS

This study demonstrate that PKA signaling to Rap1b is a key signaling node for follicular thyroid carcinogenesis, while Epac1 activity is not required for tumor development. This work sheds new light on the pathways involved in FTC development and identifies a possible target for the development of new therapies in the treatment of FTC.

Genetically modified mouse models to investigate thyroid development, function and growth

The thyroid gland produces thyroid hormones (TH), which are essential regulators for growth, development and metabolism. The thyroid is mainly controlled by the thyroid-stimulating hormone (TSH) that binds to its receptor (TSHR) on thyrocytes and mediates its action via different G protein-mediated signaling pathways. TSH primarily activates the G_s-pathway, and at higher concentrations also the G_q/11-pathway, leading to an increase of intracellular cAMP and Ca²⁺, respectively. To date, the physiological importance of other G protein-mediated signaling pathways in thyrocytes is unclear. Congenital hypothyroidism (CH) is defined as the lack of TH at birth. In familial cases, high-throughput sequencing methods have facilitated the identification of novel mutations. Nevertheless, the precise etiology of CH yet remains unraveled in a proportion of cases. Genetically modified mouse models can reveal new pathophysiological mechanisms of thyroid diseases. Here, we will present an overview of genetic mouse models for thyroid diseases, which have provided crucial insights into thyroid gland development, function, and growth with a special focus on TSHR and microRNA signaling.

Partial thyrocyte-specific Gαs deficiency leads to rapid-onset hypothyroidism, hyperplasia, and papillary thyroid carcinoma-like lesions in mice

Thyroid function is controlled by thyroid-stimulating hormone (TSH), which binds to its G protein-coupled receptor [thyroid-stimulating hormone receptor (TSHR)] on thyrocytes. TSHR can potentially couple to all G protein families, but it mainly activates the Gs- and Gq/11-mediated signaling cascades. To date, there is a knowledge gap concerning the role of the individual G protein cascades in thyroid pathophysiology. Here, we demonstrate that the thyrocyte-specific deletion of Gs-protein α subunit (Gαs) in adult mice [tamoxifen-inducible Gs protein α subunit deficient (iTGαsKO) mice] rapidly impairs thyrocyte function and leads to hypothyroidism. Consequently, iTGαsKO mice show reduced food intake and activity. However, body weight and the amount of white adipose tissue were decreased only in male iTGαsKO mice. Unexpectedly, hyperplastic follicles and papillary thyroid cancer-like tumor lesions with increased proliferation and slightly increased phospho-ERK1/2 staining were found in iTGαsKO mice at an older age. These tumors developed from nonrecombined thyrocytes still expressing Gαs in the presence of highly elevated serum TSH. In summary, we report that partial thyrocyte-specific Gαs deletion leads to hypothyroidism but also to tumor development in thyrocytes with remaining Gαs expression. Thus, these mice are a novel model to elucidate the pathophysiological consequences of hypothyroidism and TSHR/Gs/cAMP-mediated tumorigenesis.-Patyra, K., Jaeschke, H., Löf, C., Jännäri, M., Ruohonen, S. T., Undeutsch, H., Khalil, M., Kero, A., Poutanen, M., Toppari, J., Chen, M., Weinstein, L. S., Paschke, R., Kero, J. Partial thyrocyte-specific Gαs deficiency leads to rapid-onset hypothyroidism, hyperplasia, and papillary thyroid carcinoma-like lesions in mice.

Overexpression of Interleukin-4 in the Thyroid of Transgenic Mice Upregulates the Expression of Duox1 and the Anion Transporter Pendrin

BACKGROUND

The dual oxidases (Duox) are involved in hydrogen peroxide generation, which is essential for thyroid hormone synthesis, and therefore they are markers of thyroid function. During inflammation, cytokines upregulate DUOX gene expression in the airway and the intestine, suggesting a role for these proteins in innate immunity. It was previously demonstrated that interleukin-4 (IL-4) upregulates DUOX gene expression in thyrocytes. Although the role of IL-4 in autoimmune thyroid diseases has been studied extensively, the effects of IL-4 on thyroid physiology remain largely unknown. Therefore, a new animal model was generated to study the impact of IL-4 on thyroid function.

METHODS

Transgenic (Thyr-IL-4) mice with thyroid-targeted expression of murine IL-4 were generated. Transgene expression was verified at the mRNA and protein level in thyroid tissues and primary cultures. The phenotype of the Thyr-IL-4 animals was characterized by measuring serum thyroxine (T4) and thyrotropin levels and performing thyroid morphometric analysis, immunohistochemistry, whole transcriptome sequencing, quantitative reverse transcription polymerase chain reaction, and ex vivo thyroid function assays.

RESULTS

Thyrocytes from two Thyr-IL-4 mouse lines (#30 and #52) expressed IL-4, which was secreted into the extracellular space. Although 10-month-old transgenic animals had T4 and thyrotropin serum levels in the normal range, they had altered thyroid follicular structure with enlarged follicles composed of elongated thyrocytes containing numerous endocytic vesicles. These follicles were positive for T4 staining the colloid, indicating their capacity to produce thyroid hormones. RNA profiling of Thyr-IL-4 thyroid samples revealed modulation of multiple genes involved in inflammation, while no major leukocyte infiltration could be detected. Upregulated expression of Duox1, Duoxa1, and the pendrin anion exchanger gene (Slc26a4) was detected. In contrast, the iodide symporter gene Slc5a5 was markedly downregulated resulting in impaired iodide uptake and reduced thyroid hormone levels in transgenic thyroid tissue. Hydrogen peroxide production was increased in Thyr-IL-4 thyroid tissue compared with wild-type animals, but no significant oxidative stress could be detected.

CONCLUSIONS

This is the first study to show that ectopic expression of IL-4 in thyroid tissue upregulates Duox1/Duoxa1 and Slc26a4 expression in the thyroid. The present data demonstrate that IL-4 could affect thyroid morphology and function, mainly by downregulating Slc5a5 expression, while maintaining a normal euthyroid phenotype.

NADPH oxidases: new actors in thyroid cancer?

Hydrogen peroxide (H2O2) is a crucial substrate for thyroid peroxidase, a key enzyme involved in thyroid hormone synthesis. However, as a potent oxidant, H2O2 might also be responsible for the high level of oxidative DNA damage observed in thyroid tissues, such as DNA base lesions and strand breakages, which promote chromosomal instability and contribute to the development of tumours. Although the role of H2O2 in thyroid hormone synthesis is well established, its precise mechanisms of action in pathological processes are still under investigation. The NADPH oxidase/dual oxidase family are the only oxidoreductases whose primary function is to produce reactive oxygen species. As such, the function and expression of these enzymes are tightly regulated. Thyrocytes express dual oxidase 2, which produces most of the H2O2 for thyroid hormone synthesis. Thyrocytes also express dual oxidase 1 and NADPH oxidase 4, but the roles of these enzymes are still unknown. Here, we review the structure, expression, localization and function of these enzymes. We focus on their potential role in thyroid cancer, which is characterized by increased expression of these enzymes.

Purinergic signaling pathways in endocrine system

Adenosine-5'-triphosphate is released by neuroendocrine, endocrine, and other cell types and acts as an extracellular agonist for ligand-gated P2X cationic channels and G protein-coupled P2Y receptors in numerous organs and tissues, including the endocrine system. The breakdown of ATP by ectonucleotidases not only terminates its extracellular messenger functions, but also provides a pathway for the generation of two additional agonists: adenosine 5'-diphosphate, acting via some P2Y receptors, and adenosine, a native agonist for G protein-coupled adenosine receptors, also expressed in the endocrine system. This article provides a review of purinergic signaling pathways in the hypothalamic magnocellular neurosecretory cells and neurohypophysis, hypothalamic parvocellular neuroendocrine system, adenohypophysis, and effector glands organized in five axes: hypothalamic-pituitary-gonadal, hypothalamic-pituitary-thyroid, hypothalamic-pituitary-adrenal, hypothalamic-pituitary-growth hormone, and hypothalamic-pituitary-prolactin. We attempted to summarize current knowledge of purinergic receptor subtypes expressed in the endocrine system, including their roles in intracellular signaling, hormone secretion, and other cell functions. We also briefly review the release mechanism for adenosine-5'-triphosphate by neuroendocrine, endocrine and surrounding cells, the enzymes involved in adenosine-5'-triphosphate hydrolysis to adenosine-5'-diphosphate and adenosine, and the relevance of this pathway for sequential activation of receptors and termination of signaling.

Protein kinase a-mediated cell proliferation in brown preadipocytes is independent of Erk1/2, PI3K and mTOR

The physiological agonist norepinephrine promotes cell proliferation of brown preadipocytes during the process of tissue recruitment. In a primary culture system, cAMP mediates these adrenergic effects. In the present study, we demonstrated that, in contrast to other systems where the mitogenic effect of cAMP requires the synergistic action of (serum) growth factors, especially insulin/IGF, the cAMP effect in brown preadipocytes was independent of serum and insulin. Protein kinase A, rather than Epac, mediated the cAMP mitogenic effect. The Erk 1/2 family of MAPK, the PI3K system and the mTOR complexes were all activated by cAMP, but these activations were not necessary for cAMP-induced cell proliferation; a protein kinase C isoform may be involved in mediating cAMP-activated cell proliferation. We conclude that the generally acknowledged cellular mediators for induction of cell proliferation are not involved in this process in the brown preadipocyte system; this conclusion may be of relevance both for examination of mechanisms for induction of brown adipose tissue recruitment but also for understanding the mechanism behind e.g. certain endocrine neoplasias.

Purinergic signalling in endocrine organs

There is widespread involvement of purinergic signalling in endocrine biology. Pituitary cells express P1, P2X and P2Y receptor subtypes to mediate hormone release. Adenosine 5'-triphosphate (ATP) regulates insulin release in the pancreas and is involved in the secretion of thyroid hormones. ATP plays a major role in the synthesis, storage and release of catecholamines from the adrenal gland. In the ovary purinoceptors mediate gonadotrophin-induced progesterone secretion, while in the testes, both Sertoli and Leydig cells express purinoceptors that mediate secretion of oestradiol and testosterone, respectively. ATP released as a cotransmitter with noradrenaline is involved in activities of the pineal gland and in the neuroendocrine control of the thymus. In the hypothalamus, ATP and adenosine stimulate or modulate the release of luteinising hormone-releasing hormone, as well as arginine-vasopressin and oxytocin. Functionally active P2X and P2Y receptors have been identified on human placental syncytiotrophoblast cells and on neuroendocrine cells in the lung, skin, prostate and intestine. Adipocytes have been recognised recently to have endocrine function involving purinoceptors.

The presence of adenosine A2a receptor in thyrocytes and its involvement in Graves' IgG-induced VEGF expression

Goitrogenesis in Graves' disease (GD) has been attributed to anti-TSH receptor antibody stimulation. Recently, a role for adenosine A2a receptor (A2aR) in goiter formation was reported in the thyroglobulin-A2aR transgenic mice. However, it is unclear whether A2aR is expressed in the thyroid and whether it is associated with the pathogenesis of goiter in GD. Here, we confirmed the expression of A2aR in FRTL-5 cells, primary normal human thyrocytes (both sexes were used without regard to sex), and thyroid tissue (both sexes were used without regard to sex) by PCR, Western blotting, immunohistochemistry, and immunofluorescence. After treatments with A2aR-specific agonist 2-p-(2-Carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine or GD IgG, the mRNA and protein levels of vascular endothelial growth factor (VEGF), a growth factor related to goitrogenesis, were evaluated along with upstream signaling pathways. A2aR activation and GD IgG promoted the expression of VEGF in thyrocytes, which was accompanied by the activation of cAMP/protein kinase A/phosphorylated-cAMP-response element-binding protein, peroxisome proliferator-activated receptor γ coactivator-1α, and hypoxia-inducible factor-1α. The changes induced by GD IgG were partially abrogated by A2aR small interfering RNA and an A2aR antagonist. These results were supported by data on the goiter samples from the thyrotropin receptor adenovirus-induced GD mouse model (female). These data demonstrate that GD IgG could up-regulate the VEGF expression through A2aR, indicating a potential mechanism for goitrogenesis in GD.

Disruption of the melanin-concentrating hormone receptor 1 (MCH1R) affects thyroid function

Melanin-concentrating hormone (MCH) is a peptide produced in the hypothalamus and the zona incerta that acts on one receptor, MCH receptor 1 (MCH1R), in rodents. The MCH system has been implicated in the regulation of several centrally directed physiological responses, including the hypothalamus-pituitary-thyroid axis. Yet a possible direct effect of the MCH system on thyroid function has not been explored in detail. We now show that MCH1R mRNA is expressed in thyroid follicular cells and that mice lacking MCH1R [MCH1R-knockout (KO)] exhibit reduced circulating iodothyronine (T(4), free T(4), T(3), and rT(3)) levels and high TRH and TSH when compared with wild-type (WT) mice. Because the TSH of MCH1R-KO mice displays a normal bioactivity, we hypothesize that their hypothyroidism may be caused by defective thyroid function. Yet expression levels of the genes important for thyroid hormones synthesis or secretion are not different between the MCH1R-KO and WT mice. However, the average thyroid follicle size of the MCH1R-KO mice is larger than that of WT mice and contained more free and total T(4) and T(3) than the WT glands, suggesting that they are sequestered in the glands. Indeed, when challenged with TSH, the thyroids of MCH1R-KO mice secrete lower amounts of T(4). Similarly, secretion of iodothyronines in the plasma upon (125)I administration is significantly reduced in MCH1R-KO mice. Therefore, the absence of MCH1R affects thyroid function by disrupting thyroid hormone secretion. To our knowledge, this study is the first to link the activity of the MCH system to the thyroid function.

Signal transduction in the human thyrocyte and its perversion in thyroid tumors

The study of normal signal transduction pathways regulating the proliferation and differentiation of a cell type allows to predict and to understand the perversions of these pathways which lead to tumorigenesis. In the case of the human thyroid cell, three cascades are mostly involved in tumorigenesis: The pathways and genetic events affecting them are described. Caveats in the use of models and the interpretation of results are formulated and the still pending questions are outlined.

Thyroid hormone receptors are tumor suppressors in a mouse model of metastatic follicular thyroid carcinoma

Aberrant expression and mutations of thyroid hormone receptor genes (TRs) are closely associated with several types of human cancers. To test the hypothesis that TRs could function as tumor suppressors, we took advantage of mice with deletion of all functional TRs (TRalpha1(-/-)TRbeta(-/-) mice). As these mice aged, they spontaneously developed follicular thyroid carcinoma with pathological progression from hyperplasia to capsular invasion, vascular invasion, anaplasia and metastasis to the lung, similar to human thyroid cancer. Detailed molecular analysis revealed that known tumor promoters such as pituitary tumor-transforming gene were activated and tumor suppressors such as peroxisome proliferator-activated receptor gamma and p53 were suppressed during carcinogenesis. In addition, consistent with the human cancer, AKT-mTOR-p70(S6K) signaling and vascular growth factor and its receptor were activated to facilitate tumor progression. This report presents in vivo evidence that functional loss of both TRalpha1 and TRbeta genes promotes tumor development and metastasis. Thus, TRs could function as tumor suppressors in a mouse model of metastatic follicular thyroid cancer.

Adverse effects associated with persistent stimulation of Leydig cells with hCG in vitro

The detrimental effects of persistent stimulation with hCG were investigated in rat Leydig cells in vitro. Significant rise in lipid peroxidation and reactive oxygen species (ROS) with concomitant attenuation in the activities of antioxidant enzymes: superoxide dismutase, catalase, and glutathione-S-transferase was observed. Transcripts for catalase and superoxide dismutase were also depleted. Subsequent to each hCG challenge, the total antioxidant capacity in the target cells also declined significantly (P < 0.05). There was an increase in cell apoptosis (23%), which was associated with a rise in caspase-3 activity, PARP cleavage, and Fas, FasL, caspase-8 expression. While Bax and Caspase-9 expression remained unchanged, Bcl-2 demonstrated a marked decline. Taken together, the above data indicate that persistent hCG stimulation of Leydig cells induced adverse effects leading to oxidative stress and apoptosis which was channeled primarily through the extrinsic pathway.

Lessons from mouse models of thyroid cancer

BACKGROUND

Thyroid cancer is the most common endocrine tumor and is increasing in incidence. The aim of this study was to review mouse models of differentiated thyroid cancer and how they elucidate human thyroid cancer biology.

SUMMARY

Differentiated thyroid cancer, primarily papillary and follicular, comprises the majority of thyroid cancers. There has been tremendous growth in the cross-talk between basic science and clinical practice for thyroid cancer management. Insight into the framework of genes responsible for differentiated thyroid cancer has been gained through the use of mouse models. Common genetic alterations found in human papillary thyroid cancer such as RET/PTC rearrangements or the BRAF(V600E) mutation have genetically modified mouse counterparts. These and other preclinical mouse models have validated the importance of the cyclic adenosine monophosphate (cAMP)/protein kinase A and mitogen-activated protein kinase (MAPK) signaling pathways in papillary thyroid cancer (PTC). RAS mutations have a role in both papillary and follicular thyroid cancer development. Mice with overactivation of the phosphatidylinol-3-kinase (PI3K)-AKT and/or thyrotropin-regulated signaling pathways have been found to develop follicular thyroid cancer. Additional mouse models of thyroid cancer that utilize inducible expression systems are in development or are being characterized and will better reflect the majority of human thyroid cancers which are non-hereditary. Advances in in vivo imaging of mice allow for earlier detection of metastasis and the ability to follow tumor growth or regression which may be used in evaluation of pharmaceutical agents.

CONCLUSIONS

Mouse models have expanded our understanding of the altered signaling pathways that contribute to thyroid cancer tumorigenesis and provide a powerful tool to develop novel diagnostic approaches and therapies.

[New aspects of genetics and molecular mechanisms on thyroid morphogenesis for the understanding of thyroid dysgenesia]

The elucidation of the molecular mechanisms underlying the very early steps of thyroid organogenesis and the etiology of most cases of thyroid dysgenesis are poorly understood. Many genes have been identified as important contributors to survival, proliferation and migration of thyroid cells precursors, acting as an integrated and complex regulatory network. Moreover, by generation of mouse mutants, the studies have provided better knowledge of the role of these genes in the thyroid morphogenesis. In addition, it is likely that a subset of patients has thyroid dysgenesis as a result of mutations in regulatory genes expressed during embryogenesis. This review summarizes molecular aspects of thyroid development, describes the animal models and phenotypes known to date and provides information about novel insights into the ontogeny and pathogenesis of human thyroid dysgenesis.

Inactivation of the Carney complex gene 1 (protein kinase A regulatory subunit 1A) inhibits SMAD3 expression and TGF beta-stimulated apoptosis in adrenocortical cells

The cyclic AMP signaling pathway can be altered at multiple levels in endocrine tumors. Its central component is the protein kinase A (PKA). Carney complex (CNC) is a hereditary multiple neoplasia syndrome resulting from inactivating mutations of the gene encoding the PKA type I alpha regulatory subunit (PRKAR1A). Primary pigmented nodular adrenocortical disease is the most frequent endocrine tumor of CNC. Transforming growth factor beta (TGFbeta) regulates adrenal cortex physiology and signals through SMAD2/3. We used an interference approach to test the effects of PRKAR1A inactivation on PKA and TGFbeta pathways and on apoptosis in adrenocortical cells. PRKAR1A silencing stimulates PKA activity and increases transcriptional activity of a PKA reporter construct and expression of the endogenous PKA target, NR4A2, under basal conditions or after forskolin stimulation. PRKAR1A inactivation also decreased SMAD3 mRNA and protein levels via PKA, altering the cellular response to TGFbeta. SMAD3 expression was also inhibited by adrenocorticorticotropic hormone in the mouse adrenal gland and by forskolin in H295R cells. TGFbeta stimulates apoptosis in H295R cells, and this effect was counteracted by PRKAR1A inactivation. PRKAR1A silencing decreased the percentage of apoptotic cells and the cleavage of apoptosis mediators [caspase-3, poly(ADP-ribose) polymerase, and lamin A/C]. Inactivating mutations of PRKAR1A observed in adrenocortical tumors alter SMAD3, leading to resistance to TGFbeta-induced apoptosis. This cross-talk between the PKA and the TGFbeta signaling pathways reveals a new mechanism of endocrine tumorigenesis.

The DREAM protein is associated with thyroid enlargement and nodular development

G protein-coupled receptors (GPCRs) are involved in the pathophysiology of a wide range of diseases and constitute an attractive therapeutic target. In the thyroid gland, TSH receptor (TSHR), a member of the GPCR family, is a major regulator of thyroid differentiation and function. Alterations in TSHR activity are often involved in the development of pathologies such as thyroid cancer and thyroid enlargement (goiter). Here we show that DREAM (downstream regulatory element antagonist modulator) modulates TSHR activity through a direct protein-protein interaction that promotes coupling between the receptor and Galphas. In transgenic mice, DREAM overexpression provokes a marked enlargement of the thyroid gland. Increased levels of DREAM protein were observed in human multinodular goiters, suggesting a novel etiopathogenic mechanism in nodular development in humans. Taken together, these findings identify a mechanism for the control of TSHR activity and provide a new approach for the study and treatment of thyroid pathologies associated with impaired TSHR function.

Cyclic AMP inhibits the proliferation of thyroid carcinoma cell lines through regulation of CDK4 phosphorylation

How cyclic AMP (cAMP) could positively or negatively regulate G1 phase progression in different cell types or in cancer cells versus normal differentiated counterparts has remained an intriguing question for decades. At variance with the cAMP-dependent mitogenesis of normal thyroid epithelial cells, we show here that cAMP and cAMP-dependent protein kinase activation inhibit S-phase entry in four thyroid carcinoma cell lines that harbor a permanent activation of the Raf/ERK pathway by different oncogenes. Only in Ret/PTC1-positive TPC-1 cells did cAMP markedly inhibit the Raf/ERK cascade, leading to mTOR pathway inhibition, repression of cyclin D1 and p21 and p27 accumulation. p27 knockdown did not prevent the DNA synthesis inhibition. In the other cells, cAMP little affected these signaling cascades and levels of cyclins D or CDK inhibitors. However, cAMP differentially inhibited the pRb-kinase activity and T172-phosphorylation of CDK4 complexed to cyclin D1 or cyclin D3, whereas CDK-activating kinase activity remained unaffected. At variance with current conceptions, our studies in thyroid carcinoma cell lines and previously in normal thyrocytes identify the activating phosphorylation of CDK4 as a common target of opposite cell cycle regulations by cAMP, irrespective of its impact on classical mitogenic signaling cascades and expression of CDK4 regulatory partners.

Thyrocyte-specific Gq/G11 deficiency impairs thyroid function and prevents goiter development

The function of the adult thyroid is regulated by thyroid-stimulating hormone (TSH), which acts through a G protein-coupled receptor. Overactivation of the TSH receptor results in hyperthyroidism and goiter. The Gs-mediated stimulation of adenylyl cyclase-dependent cAMP formation has been regarded as the principal intracellular signaling mechanism mediating the action of TSH. Here we show that the Gq/G11-mediated signaling pathway plays an unexpected and essential role in the regulation of thyroid function. Mice lacking the alpha subunits of Gq and G11 specifically in thyroid epithelial cells showed severely reduced iodine organification and thyroid hormone secretion in response to TSH, and many developed hypothyroidism within months after birth. In addition, thyrocyte-specific Galphaq/Galpha11-deficient mice lacked the normal proliferative thyroid response to TSH or goitrogenic diet, indicating an essential role of this pathway in the adaptive growth of the thyroid gland. Our data suggest that Gq/G11 and their downstream effectors are promising targets to interfere with increased thyroid function and growth.

Thyroid hormone receptor mutations and disease: insights from knock-in mouse models

Thyroid hormone nuclear receptors (TRs) mediate thyroid hormone's activities in growth, differentiation, and development. Two TR genes (α and β ) encode four thyroid hormone-binding receptors that regulate target gene expression. Mutations of the TRβ gene cause the genetic syndrome of resistance to thyroid hormone. Studies indicate a close association between TRβ mutations and several human cancers, suggesting their oncogenic role. A TRβ gene knock-in mutant mouse (TRβ^PV/PV mouse) that spontaneously develops thyroid cancer allows elucidation of the oncogenic functions in vivo. TRβPV is a potent dominant negative mutant identified in a resistance to thyroid hormone patient. Molecular studies indicate that the PV mutant mediates its oncogenic activities via nucleus-initiated transcription and novel extranuclear actions. Thus, the deleterious effects of the gene mutations go beyond resistance to thyroid hormone and are more severe and extensive than previously envisioned. This newly identified oncogene exerts its tumorigenic effects via multiple signaling mechanisms.

Molecular determination of benign and malignant thyroid tumors

Recent molecular studies have revolutionized our understanding of the pathogenesis of thyroid tumors and particular advances have been made in three areas. First, toxic thyroid nodules, which originate from constitutive activation of thyroid-stimulating hormone receptor/Gs α signaling and represent the dominant cause of thyrotoxicosis in regions with iodine deficiency. Second, papillary thyroid cancer, the most frequent thyroid malignancy, which is characterized by a common fingerprint of constitutive mitogen-activated protein kinase activation. Importantly, this is caused by distinct genetic alterations in radiation-induced (RET/PTC, NTRK and AKAP9/BRAF rearrangements) and sporadic tumors (BRAF and RAS point mutation) and, recently, there exciting in vitro have emerged explaining the structural basis for this. These findings suggest a scenario in which the fate of a thyroid tumor is determined by the specific genetic defect at the beginning. Third, application of microarray analysis in nodular pathologies in which the oncogenic pathway is less clear, notably follicular neoplasia, has led to the identification of a number of promising genetic markers (TFF-3, Gal-3, PLAB, CCND2 and PCKD2) for the diagnostic distinction of follicular adenoma and carcinoma. In addition to the diagnostic perspective, the identification of molecular fingerprints of thyroid tumors opens novel avenues for an improved therapeutic approach; for example, selective antagonism of cell signaling in treatment-refractory thyroid cancer.

Acrylamide, an in vivo thyroid carcinogenic agent, induces DNA damage in rat thyroid cell lines and primary cultures

Chronic treatment of rats with acrylamide induces various tumors among which thyroid tumors are the most frequent. The aim of the present study was to develop an in vitro model of acrylamide action on thyroid cells to allow the investigation of the mechanism of this tumorigenic action. The first part of the study considered as targets, characteristics of thyroid metabolism, which could explain the thyroid specificity of acrylamide action: the cAMP mitogenic effect and the important H2O2 generation by thyroid cells. However, acrylamide did not modulate H2O2 or cAMP generation in the thyroid cell models studied. No effect on thyroid cell proliferation was observed in the rat thyroid cell line FRTL5. On the other hand, as shown by the comet assay, acrylamide induced DNA damage, as the positive control H2O2 in the PC Cl3 and FRTL5 rat thyroid cell lines, as well as in thyroid cell primary cultures. The absence of effect of acrylamide on H2AX histone phosphorylation suggests that this effect does not reflect the induction of DNA double strand breaks. DNA damage leads to the generation of mutations. It is proposed that such mutations could play a role in the carcinogenic effect of acrylamide. The mechanism of this effect can now be studied in this in vitro model.

Thyroid targeting of the N-ras(Gln61Lys) oncogene in transgenic mice results in follicular tumors that progress to poorly differentiated carcinomas

Ras oncogenes are frequently mutated in thyroid carcinomas. To verify the role played by N-ras in thyroid carcinogenesis, we generated transgenic mice in which a human N-ras(Gln61Lys) oncogene (Tg-N-ras) was expressed in the thyroid follicular cells. Tg-N-ras mice developed thyroid follicular neoplasms; 11% developed follicular adenomas and approximately 40% developed invasive follicular carcinomas, in some cases with a mixed papillary/follicular morphology. About 25% of the Tg-N-ras carcinomas displayed large, poorly differentiated areas, featuring vascular invasion and forming lung, bone or liver distant metastases. N-ras(Gln61Lys) expression in cultured PC Cl 3 thyrocytes induced thyroid-stimulating hormone-independent proliferation and genomic instability with micronuclei formation and centrosome amplification. These findings support the notion that mutated ras oncogenes could be able to drive the formation of thyroid tumors that can progress to poorly differentiated, metastatic carcinomas.

PPARgamma insufficiency promotes follicular thyroid carcinogenesis via activation of the nuclear factor-kappaB signaling pathway

The molecular genetic events underlying thyroid carcinogenesis are poorly understood. Mice harboring a knock-in dominantly negative mutant thyroid hormone receptor beta (TRbetaPV/PV mouse) spontaneously develop follicular thyroid carcinoma similar to human thyroid cancer. Using this mutant mouse, we tested the hypothesis that the peroxisome proliferator-activated receptor gamma (PPARgamma) could function as a tumor suppressor in thyroid cancer in vivo. Using the offspring from the cross of TRbetaPV/+ and PPARgamma+/- mice, we found that thyroid carcinogenesis progressed significantly faster in TRbetaPV/PV mice with PPARgamma insufficiency from increased cell proliferation and reduced apoptosis. Reduced PPARgamma protein abundance led to the activation of the nuclear factor-kappaB signaling pathway, resulting in the activation of cyclin D1 and repression of critical genes involved in apoptosis. Treatment of TRbetaPV/PV mice with a PPARgamma agonist, rosiglitazone, delayed the progression of thyroid carcinogenesis by decreasing cell proliferation and activation of apoptosis. These results suggest that PPARgamma is a critical modifier in thyroid carcinogenesis and could be tested as a therapeutic target in thyroid follicular carcinoma.

Gene expression in thyroid autonomous adenomas provides insight into their physiopathology

The purpose of this study was to use the microarray technology to define expression profiles characteristic of thyroid autonomous adenomas and relate these findings to physiological mechanisms. Experiments were performed on a series of separated adenomas and their normal counterparts on Micromax cDNA microarrays covering 2400 genes (analysis I), and on a pool of adenomatous tissues and their corresponding normal counterparts using microarrays of 18,000 spots (analysis II). Results for genes present on the two arrays corroborated and several gene regulations previously determined by Northern blotting or microarrays in similar lesions were confirmed. Five overexpressed and 24 underexpressed genes were also confirmed by real-time RT-PCR in some of the samples used for microarray analysis, and in additional tumor specimens. Our results show: (1) a change in the cell populations of the tumor, with a marked decrease in lymphocytes and blood cells and an increase in endothelial cells. The latter increase would correspond to the establishment of a close relation between thyrocytes and endothelial cells and is related to increased N-cadherin expression. It explains the increased blood flow in the tumor; (2) a homogeneity of tumor samples correlating with their common physiopathological mechanism: the constitutive activation of the thyrotropin (TSH)/cAMP cascade; (3) a low proportion of regulated genes consistent with the concept of a minimal deviation tumor; (4) a higher expression of genes coding for specific functional proteins, consistent with the functional hyperactivity of the tumors; (5) an increase of phosphodiesterase gene expression which explains the relatively low cyclic AMP levels measured in these tumors; (6) an overexpression of antiapoptotic genes and underexpression of proapoptotic genes compatible with their low apoptosis rate; (7) an overexpression of N-cadherin and downregulation of caveolins, which casts doubt about the use of these expressions as markers for malignancy.

Molecular pathogenesis of euthyroid and toxic multinodular goiter

The purpose of this review is to summarize current knowledge of the etiology of euthyroid and toxic multinodular goiter (MNG) with respect to the epidemiology, clinical characteristics, and molecular pathology. In reconstructing the line of events from early thyroid hyperplasia to MNG we will argue the predominant neoplastic character of nodular structures, the nature of known somatic mutations, and the importance of mutagenesis. Furthermore, we outline direct and indirect consequences of these somatic mutations for thyroid pathophysiology and summarize information concerning a possible genetic background of euthyroid goiter. Finally, we discuss uncertainties and open questions in differential diagnosis and therapy of euthyroid and toxic MNG.

Resistance to diet-induced obesity in mice globally overexpressing OGH/GPB5

We identified a glycoprotein hormone beta-subunit (OGH, also called GPB5) that, as a heterodimer with the alpha-subunit GPA2, serves as a second ligand for the thyroid-stimulating hormone receptor. Mice in which the OGH gene is deleted (OGH-/-) are indistinguishable from WT littermates in body weight, response to high-fat diet, metabolic parameters, body composition, and insulin tolerance. Mice engineered to transgenically globally overexpress OGH (OGH-TG) develop approximately 2-fold elevations in their basal thyroid levels and weigh slightly less than WT littermates despite increased food intake because of an increase in their metabolic rates. Moreover, when OGH-TG mice are challenged with a high-fat diet, they gain significantly less weight and body fat than their WT littermates. The OGH-TG mice also have reduced blood glucose, insulin, cholesterol, and triglycerides. In contrast to other approaches in which the thyroid axis is activated, OGH-TG mice exhibit only minor changes in heart rate and blood pressure. Our findings suggest that constitutive low-level activation of the thyroid axis (via OGH or other means) may provide a beneficial therapeutic approach for combating diet-induced obesity.

Specific inhibition of nuclear factor-kappaB-dependent inflammatory responses by cell type-specific mechanisms upon A2A adenosine receptor gene transfer

Adenosine is a potent inhibitor of inflammatory processes, and the A(2A) adenosine receptor (A(2A)AR) plays a key nonredundant role as a suppresser of inflammatory responses in vivo. In this study, we demonstrate that increasing A(2A)AR gene expression suppressed multiple inflammatory responses in both human umbilical vein endothelial cells (HUVECs) and rat C6 glioma cells in vitro. In particular, the induction of the adhesion molecule E-selectin by either tumor necrosis factor alpha (TNFalpha) or Escherichia coli lipopolysaccharide (LPS) was reduced by more than 70% in HUVECs, whereas inducible nitric-oxide synthase (iNOS) induction was abolished in C6 cells after exposure to interferon-gamma in combination with LPS and TNFalpha, suggesting that the receptor inhibited a common step in the induction of each of these pro-inflammatory genes. Consistent with this hypothesis, A(2A)AR expression inhibited the activation of NF-kappaB, a key transcription factor whose proper function was essential for optimal iNOS and E-selectin induction. However, although NF-kappaB binding to target DNA was severely compromised in both cell types, the mechanisms by which this occurred were distinct. In C6 cells, A(2A)AR expression blocked IkappaBalpha degradation by inhibiting stimulus-induced phosphorylation, whereas in HUVECs, A(2A)AR expression inhibited NF-kappaB translocation to the nucleus independently of any effect on IkappaBalpha degradation. Together, these observations suggest that A(2A)AR-mediated inhibition NF-kappaB activation is a critical aspect of its anti-inflammatory signaling properties and that the molecular basis of this inhibition varies in a cell type-specific manner.

A tumor suppressor role for thyroid hormone beta receptor in a mouse model of thyroid carcinogenesis

We have created a knockin mutant mouse by targeting a mutation (PV) into the thyroid hormone receptor beta gene (TRbetaPV mouse). TRbetaPV/PV mice, but not TRbetaPV/+ mice, spontaneously develop follicular thyroid carcinoma. To identify other genetic changes in the TRbeta gene that could also induce thyroid carcinoma, we crossed TRbetaPV mice with TRbeta-/- mice. As TRbetaPV/- mice (mutation of one TRbeta allele in the absence of the other wild-type allele) aged, they also spontaneously developed follicular thyroid carcinoma through the pathological progression of hyperplasia, capsular and vascular invasion, anaplasia, and eventually metastasis to the lung, but not to the lymph nodes. The pathological progression of thyroid carcinoma in TRbetaPV/- mice was indistinguishable from that in TRbetaPV/PV mice. Analyses of the expression patterns of critical genes indicated activation of the signaling pathways mediated by TSH, peptide growth factors (epidermal growth factor and fibroblast growth factor), TGF-beta, TNF-alpha, and nuclear factor-kappaB, and also suggested progressive repression of the pathways mediated by the peroxisome proliferator-activated receptor gamma. The patterns in the alteration of these signaling pathways are similar to those observed in TRbeta(PV/PV) mice during thyroid carcinogenesis. These results indicate that in the absence of a wild-type allele, the mutation of one TRbeta allele is sufficient for the mutant mice to spontaneously develop follicular thyroid carcinoma. These results provide, for the first time, in vivo evidence to suggest that the TRbeta gene could function as a tumor suppressor gene. Importantly, these findings present the possibility that TRbeta could serve as a novel therapeutic target in thyroid cancer.

cAMP-dependent oncogenic action of Rap1b in the thyroid gland

cAMP signaling leads to activation and phosphorylation of Rap1b. Using cellular models where cAMP stimulates cell proliferation, we have demonstrated that cAMP-mediated activation, as well as phosphorylation of Rap1b, is critical for cAMP stimulation of DNA synthesis. To determine whether Rap1b stimulates mitogenesis in vivo, we have constructed a transgenic mouse where a constitutively active G12V-Rap1b, flanked by Cre recombinase LoxP sites, is followed by the dominant negative S17N mutant. Employing this novel mouse model, we have switched, in a tissue-specific (thyroid) and temporally controlled manner, the expression of Rap1b from a stimulatory to an inhibitory form. These experiments provide conclusive evidence that Rap1b is oncogenic in the thyroid in ways linked to transduction of the cAMP mitogenic signal.

TSH-activated signaling pathways in thyroid tumorigenesis

Thyrotropin (TSH) is considered the main regulator of thyrocyte differentiation and proliferation. Thus, the characterization of the different signaling pathways triggered by TSH on these cells is of major interest in order to understand the mechanisms implicated in thyroid pathology. In this review we focus on the different signaling pathways involved in TSH-mediated proliferation and their role in thyroid transformation and tumorigenesis. TSH mitogenic activities are mediated largely by cAMP, which in turn may activate protein kinase (PKA)-dependent and independent processes. We analyze the effects of increased cAMP levels and PKA activity during cell cycle progression and the role of this signaling pathway in thyroid tumor initiation. Alternative pathways to PKA in the cAMP-mediated proliferation appear to involve the small GTPases Rap1 and Ras. We analyze the Ras effectors (PI3K, RalGDS and Raf) that are thought to mediate its oncogenic activity, as well as the ability of Ras to induce apoptosis in thyrocytes. Finally, we discuss the activation of the PLC/PKC cascade by TSH in thyroid cells and the role of this signaling pathway in the TSH-mediated proliferation and tumorigenesis.

Critical role of cyclin D3 in TSH-dependent growth of thyrocytes and in hyperproliferative diseases of the thyroid gland

We report that cyclin D3 is rate limiting for G1 progression in thyroid follicular cells and that its constitutive upregulation by chronic stimulation of the TSH/cAMP pathway plays a role in human and experimental hyperproliferative diseases of the thyroid gland. These conclusions are supported by in vitro and in vivo studies. In rat thyrocytes (PC Cl 3 cells), cyclin D3 expression is enhanced in response to activation of the TSH/cAMP pathway. Interference with the expression of G1 cyclins (in particular cyclin D3) by the antisense methodology strongly reduced TSH-dependent proliferation of PC Cl 3 cells, indicating that proper progression through G1 requires cyclin D3. Accordingly, PC Cl 3 cells engineered to overexpress cyclin D3 (PC-D3 cells) show enhanced growth rate and elude hormone-dependence and contact inhibition. Using an animal experimental model of thyroid stimulation, we demonstrate that cyclin D3 is a key mediator of TSH-dependent proliferation of thyroid follicular cells also in vivo. Cyclin D3 protein levels were higher in the thyrocytes from glands of propylthiouracil-treated rats compared with control animals. The increase in cyclin D3 expression occurred after the propylthiouracil-induced increase in TSH levels and preceded the burst of cell proliferation. Finally, we found that cyclin D3 protein is expressed in a fraction of human goiters but it is strongly overexpressed in most follicular adenomas.

Gene expression profile in thyroid of transgenic mice overexpressing the adenosine receptor 2a

Mutations of the TSH receptor leading to constitutive activation of the cAMP cascade are responsible for the development of hot nodules, if arising in a somatic cell, and nonautoimmune hyperthyroidism, when occurring in a germinal cell. An animal model of constitutive activation of the thyroid cAMP cascade has been obtained by generating transgenic mice expressing the adenosine receptor (Tg-A2aR) under the control of the thyroglobulin promoter. These mice develop huge goiters and die prematurely due to hyperthyroidism induced cardiac failure. To identify new genes involved in the tumorigenic pathway of the thyroid, we designed a protocol using microarray technology to study the differential expression, between normal and transgenic thyroid, of +/-13,000 genes. A total of 360 genes or expressed sequence tags showed a strong modulation with background corrected values of fluorescence superior to 2-fold change. The modulated genes were classified according to their proposed gene ontology functions. Approximately half of them were up-regulated. The function of the majority of these genes in thyroid physiology is still to be determined. Some of them, like IGF-I or IGF binding protein 3 or 5, may play an important role in the development of thyroid nodules through paracrine mechanisms. This study demonstrates the feasibility of sequentially following the cascade of events leading to the formation of benign tumors such as hot thyroid nodule or hyperfunctional goiter.

Role of the thyroid-stimulating hormone receptor signaling in development and differentiation of the thyroid gland

The thyroid-stimulating hormone/thyrotropin (TSH) is the most relevant hormone in the control of thyroid gland physiology in adulthood. TSH effects on the thyroid gland are mediated by the interaction with a specific TSH receptor (TSHR). We studied the role of TSHTSHR signaling on gland morphogenesis and differentiation in the mouse embryo using mouse lines deprived either of TSH (pit(dw)pit(dw)) or of a functional TSHR (tshr(hyt)tshr(hyt) and TSHR-knockout lines). The results reported here show that in the absence of either TSH or a functional TSHR, the thyroid gland develops to a normal size, whereas the expression of thyroperoxidase and the sodium/iodide symporter are reduced greatly. Conversely, no relevant changes are detected in the amounts of thyroglobulin and the thyroid-enriched transcription factors TTF-1, TTF-2, and Pax8. These data suggest that the major role of the TSH/TSHR pathway is in controlling genes involved in iodide metabolism such as sodium/iodide symporter and thyroperoxidase. Furthermore, our data indicate that in embryonic life TSH does not play an equivalent role in controlling gland growth as in the adult thyroid.

Radiation-induced thyroid carcinogenesis as a function of time and dietary iodine supply: an in vivo model of tumorigenesis in the rat

It is believed that a combination of environmental factors with mutagens induces carcinomas derived from thyroid follicular cells. In this study we tried to ascertain whether a single short-term exposure to external radiation is sufficient to induce thyroid carcinomas in rats under long-term high or low dietary iodine intake. Rats were tested over a period of 110 wk under high (approximately 10-fold of normal), normal, and low (approximately 0.1-fold of normal) daily iodine intake. Forty-day-old animals were subjected to single external radiation of 4 Gy or sham radiation. Thyroid function was tested weekly, and thyroid morphology was determined after 15, 35, 55, and 110 wk. Iodine deficiency, but not high iodine intake, led to a decrease in T(3) and T(4) plasma levels, but to an increase in TSH, which became significant after 9 and 11 wk of treatment, respectively. Both high and low iodine treatment significantly increased the proliferation rate and induced thyroid adenomas, but no malignancies after 55 and 110 wk. Radiation with 4 Gy resulted in a significant destruction of the follicular structure. Under high and low iodine intakes (50-80% of animals), but not under normal iodine supply, thyroid carcinomas were observed in irradiated rats. Thus, the increased proliferation rate induced under the experimental conditions described in this study is apparently not sufficient to cause thyroid carcinomas, but the presence of a mutagen-like radiation is required. This model may help to define genetic alterations long before histological changes are detectable.

The role of cyclic AMP and its effect on protein kinase A in the mitogenic action of thyrotropin on the thyroid cell

Cyclic AMP has been shown to inhibit cell proliferation in many cell types and to activate it in some. The latter has been recognized only lately, thanks in large part to studies on the regulation of thyroid cell proliferation in dog thyroid cells. The steps that led to this conclusion are outlined. Thyrotropin activates cyclic accumulation in thyroid cells of all the studied species and also phospholipase C in human cells. It activates directly cell proliferation in rat cell lines, dog, and human thyroid cells but not in bovine or pig cells. The action of cyclic AMP is responsible for the proliferative effect of TSH. It accounts for several human diseases: congenital hyperthyroidism, autonomous adenomas, and Graves' disease; and, by default, for hypothyroidism by TSH receptor defect. Cyclic AMP proliferative action requires the activation of protein kinase A, but this effect is not sufficient to explain it. Cyclic AMP action also requires the permissive effect of IGF-1 or insulin through their receptors, mostly as a consequence of PI3 kinase activation. The mechanism of these effects at the level of cyclin and cyclin-dependent protein kinases involves an induction of cyclin D3 by IGF-1 and the cyclic AMP-elicited generation and activation of the cyclin D3-CDK4 complex.

Minireview: branded from the start-distinct oncogenic initiating events may determine tumor fate in the thyroid

Thyroid follicular neoplasms commonly have aneuploidy, presumably due to chromosomal instability. This property is associated with a greater malignant potential and worse prognosis. Recently, there has been considerable progress in our understanding of mechanisms that may account for chromosomal instability in cancer cells. Many tumors with chromosomal instability have abnormalities in the cell cycle checkpoint that monitors the fidelity of mitosis. Mutations of Bub1 or BubR1, genes coding for kinases involved in mitotic spindle assembly checkpoint signaling, are found in a small subset of aneuploid tumors. Other components of protein complexes responsible for attachment of kinetochores to microtubules, or for cohesion between sister chromatids, may also be subject to alterations during tumor progression. Here, we also discuss the evidence that certain oncogenic events, such as Ras mutations, may predispose cells to chromosomal instability by favoring inappropriate posttranslational changes in mitotic checkpoint components through activation of upstream kinases during tumor initiation or progression.

Adenosine receptors: G protein-mediated signalling and the role of accessory proteins

Ever since the discovery of the effects of adenosine in the circulation, adenosine receptors continue to represent a promising drug target. Firstly, this is due to the fact that the receptors are expressed in a large variety of cells; in particular, the actions of adenosine (or, respectively, of the antagonistic methylxanthines) in the central nervous system, in the circulation, on immune cells and on other tissues can be beneficial in certain disorders. Secondly, there exists a large number of ligands, which have been generated by introducing several modifications in the structure of the lead compounds (adenosine and methylxanthine), some of them highly specific. Four adenosine receptor subtypes have been identified by molecular cloning; they belong to the family of G protein-coupled receptors, which transfer signals by activating heterotrimeric G proteins. It has been appreciated recently that accessory proteins impinge on the receptor/G protein interaction and thus modulate the signalling reaction. These accessory components may be thought as adaptors that redirect the signalling pathway to elicit a cell-specific response. Here, we review the recent literature on adenosine receptors and place a focus on the role of accessory proteins in the organisation of adenosine receptor signalling. These components have been involved in receptor sorting, in the control of signal amplification and in the temporal regulation of receptor activity, while the existence of others is postulated on the basis of atypical cellular reactions elicited by receptor activation.

Feline hyperthyroidism: advances towards novel molecular therapeutics

Feline hyperthyroidism is the most common endocrine disorder of the elderly cat. Traditionally, the disease is treated by surgical thyroidectomy, medical management with antithyroid drugs or radiation therapy using iodine-131. However, none of these treatments is ideal and molecular therapeutics may offer novel methods of treating the disease. This article reviews the background of, and preliminary investigations into, the development of a transcriptionally targeted somatic gene therapy strategy for the treatment of this feline condition.

Low TSH requirement and goiter in transgenic mice overexpressing IGF-I and IGF-Ir receptor in the thyroid gland

Through the cAMP signaling pathway, TSH stimulates thyroid follicular cell proliferation, differentiation, and function. Although the autocrine production of IGF-I in the thyroid gland suggests an important physiological function for this factor in these processes, the exact role of the IGF-I/IGF-I receptor system in vivo remains unclear. Although the mitogenic action of TSH requires the presence of IGF-I or insulin in primary culture of dog and human thyroid cells, IGF-I has an effect equal to and independent of the effect of TSH on cell proliferation in rat thyroid cell lines and may even be the main growth regulator in this case. To investigate the in vivo function of the IGF-I/IGF-I receptor system, transgenic mice overexpressing human IGF-I, IGF-I receptor, or both in the thyroid were generated. Adult transgenic mice did not present external signs of thyroid dysfunction, but mice overexpressing both transgenes had significantly increased gland weight and follicular lumen area. A decreased TSH level together with a slightly increased serum T(4) concentration and increased thyroidal iodine uptake were also observed, suggesting that IGF-I and IGF-I receptor stimulate thyroid function to some extent in vivo.