Positive regulation of spondin 2 by thyroid hormone is associated with cell migration and invasion

The thyroid hormone 3,3',5-triiodo-L-thyronine (T(3)) regulates growth, development, and differentiation processes in animals. These activities are mediated by the nuclear thyroid hormone receptors (TRs). Microarray analyses were performed previously to study the mechanism of regulation triggered by T(3) treatment in hepatoma cell lines. The results showed that spondin 2 was regulated positively by T(3). However, the underlying mechanism and the physiological role of T(3) in the regulation of spondin 2 are not clear. To verify the microarray results, spondin 2 was further investigated using semi-quantitative reverse transcription-PCR and western blotting. After 48 h of T(3) treatment in the HepG2-TR alpha 1#1 cell line, spondin 2 mRNA and protein levels increased by 3.9- to 5.7-fold. Similar results were observed in thyroidectomized rats. To localize the regulatory region in spondin 2, we performed serial deletions of the promoter and chromatin immunoprecipitation assays. The T(3) response element on the spondin 2 promoter was localized in the -1104/-1034 or -984/-925 regions. To explore the effect of spondin 2 on cellular function, spondin 2 knockdown cell lines were established from Huh7 cells. Knockdown cells had higher migration ability and invasiveness compared with control cells. Conversely, spondin 2 overexpression in J7 cells led to lower migration ability and invasiveness compared with control cells. Furthermore, this study demonstrated that spondin 2 overexpression in some types of hepatocellular carcinomas is TR dependent. Together, these experimental findings suggest that spondin 2, which is regulated by T(3), has an important role in cell invasion, cell migration, and tumor progression.

Thyroid hormone receptor alpha can control action potential duration in mouse ventricular myocytes through the KCNE1 ion channel subunit

AIMS

The reduced heart rate and prolonged QT(end) duration in mice deficient in thyroid hormone receptor (TR) alpha1 may involve aberrant expression of the K(+) channel alpha-subunit KCNQ1 and its regulatory beta-subunit KCNE1. Here we focus on KCNE1 and study whether increased KCNE1 expression can explain changes in cardiac function observed in TRalpha1-deficient mice.

METHODS

TR-deficient, KCNE1-overexpressing and their respective wildtype (wt) mice were used. mRNA and protein expression were assessed with Northern and Western blot respectively. Telemetry was used to record electrocardiogram and temperature in freely moving mice. Patch-clamp was used to measure action potentials (APs) in isolated cardiomyocytes and ion currents in Chinese hamster ovary (CHO) cells.

RESULTS

KCNE1 was four to 10-fold overexpressed in mice deficient in TRalpha1. Overexpression of KCNE1 with a heart-specific promoter in transgenic mice resulted in a cardiac phenotype similar to that in TRalpha1-deficient mice, including a lower heart rate and prolonged QT(end) time. Cardiomyocytes from KCNE1-overexpressing mice displayed increased AP duration. CHO cells transfected with expression plasmids for KCNQ1 and KCNE1 showed an outward rectifying current that was maximal at equimolar plasmids for KCNQ1-KCNE1 and decreased at higher KCNE1 levels.

CONCLUSION

The bradycardia and prolonged QT(end) time in hypothyroid states can be explained by altered K(+) channel function due to decreased TRalpha1-dependent repression of KCNE1 expression.

Nuclear receptors in head and neck cancer: current knowledge and perspectives

Disease management of head and neck cancer has improved significantly. However, a high rate of early recurrences and metastasis still counteract improvement of long-term survival. Hence, the quest for molecular mechanisms and key regulatory factors exploitable by targeted therapies is still ongoing. Such potential candidates may include also nuclear receptors, belonging to a superfamily of transcription factors implicated in a broad spectrum of physiological and pathophysiological processes. As dysfunction of nuclear receptor signaling contributes to a variety of proliferative diseases, they are major targets for drug discovery and hold promising potential for the development of improved anticancer treatment strategies. Several nuclear receptors have also been associated with head and neck cancer, and strategies targeting these molecules are currently tested in clinical trials. However, reports and molecular knowledge on the pathobiological relevance of nuclear receptors for cancers of the head and neck is currently rather fragmented. Hence, this review provides a general overview of nuclear receptors' molecular functions and summarizes their potential prognostic and therapeutic relevance for this tumor entity.

The effect of hydroxylated polychlorinated biphenyl (OH-PCB) on thyroid hormone receptor (TR)-mediated transcription through native-thyroid hormone response element (TRE)

Polychlorinated biphenyls (PCBs) are known as environmental contaminants that may cause abnormal effect in various organs. We have previously reported that low dose of hydroxylated PCBs (OH-PCBs) including 4'-OH-2',3,3',4',5'-pentachloro biphenyl (4'-OH-PCB 106), suppressed thyroid hormone (TH) receptor (TR)-mediated transcription on several artificial TH-response elements (TREs) due to partial dissociation of TR from TRE. In the present study, we examined the effect of OH-PCB on TR-mediated transcription on native TRE-containing promoter, using malic enzyme (ME)-TRE. Transcriptional activity was measured by transient transfection based reporter gene assay in CV-1, fibroblast-derived clonal cells. TR-mediated transcription was suppressed by 4'-OH-PCB106 significantly and 4'-OH-PCB187 weakly, but not by 4'-OH-PCB165. To examine TR-TRE bindings under exposure of 4'-OH-PCB106, electrophoretic mobility shift assay (EMSA) was performed. In EMSA, TR was dissociated from ME-TRE by 4'-OH-PCB106. These findings suggest that OH-PCB may disrupt TR-mediated transcription on native promoter.

Translational implications of nongenomic actions of thyroid hormone initiated at its integrin receptor

A thyroid hormone receptor on integrin alphavbeta3 that mediates cell surface-initiated nongenomic actions of thyroid hormone on tumor cell proliferation and on angiogenesis has been described. Transduction of the hormone signal into these recently recognized proliferative effects is by extracellular-regulated kinases 1/2 (ERK1/2). Other nongenomic actions of the hormone may be transduced by phosphatidylinositol 3-kinase (PI3K) and are initiated in cytoplasm or at the cell surface. PI3K-mediated effects are important to angiogenesis or other recently appreciated cell functions but apparently not to tumor cell division. For those actions of thyroid hormone [L-thyroxine (T(4)) and 3,3'-5-triiodo-L-thyronine (T(3))] that begin at the integrin receptor, tetraiodothyroacetic acid (tetrac) is an inhibitor of and probe for the participation of the receptor in downstream intracellular events. In addition, tetrac has actions initiated at the integrin receptor that are unrelated to inhibition of the effects of T(4) and T(3) but do involve gene transcription in tumor cells. Discussed here are the implications of translating these nongenomic mechanisms of thyroid hormone analogs into clinical cancer cell biology, tumor-related angiogenesis, and modulation of angiogenesis that is not related to cancer.

Dual functions of thyroid hormone receptors in vertebrate development: the roles of histone-modifying cofactor complexes

Thyroid hormone (TH) receptor (TR) plays critical roles in vertebrate development. Transcription studies have shown that TR activates or represses TH-inducible genes by recruiting coactivators or corepressors in the presence or absence of TH, respectively. However, the developmental roles of these TR cofactors remain largely unexplored. Frog metamorphosis is totally dependent on TH and mimics the postembryonic period in mammalian development during which TH levels are also high. We have previously proposed a dual function model for TR in the development of the anuran Xenopus laevis. That is, unliganded TR recruits corepressors to TH-inducible genes in premetamorphic tadpoles to repress these genes and prevent premature metamorphic changes and subsequently, when TH becomes available, liganded TR recruits coactivators to activate these same genes, leading to metamorphosis. Over the years, we and others have used molecular and genetic approaches to demonstrate the importance of the dual functions of TR in Xenopus laevis. In particular, unliganded TR has been shown to recruit histone deacetylase-containing corepressor complexes in premetamorphic tadpoles to control metamorphic timing. In contrast, metamorphosis requires TH-bound TR to recruit coactivator complexes containing histone acetyltransferases and methyltransferases to activate transcription. Furthermore, the concentrations of coactivators appear to regulate the rate of metamorphic progression. Studies in mammals also suggest that the dual function model for TR is conserved across vertebrates.

Identification of a human helper T cell population that has abundant production of interleukin 22 and is distinct from T(H)-17, T(H)1 and T(H)2 cells

Interleukin 22 (IL-22) is a member of the IL-10 cytokine family that is involved in inflammatory and wound healing processes. Originally considered a T helper type 1 (T(H)1)-associated cytokine, IL-22 has since been shown to be produced mainly by IL-17-producing helper T cells (T(H)-17 cells). Here we describe a previously uncharacterized IL-22-producing human helper T cell population that coexpressed the chemokine receptor CCR6 and the skin-homing receptors CCR4 and CCR10. These cells were distinct from both T(H)-17 cells and T(H)1 cells. Downregulation of either the aryl hydrocarbon receptor (AHR) or the transcription factor RORC by RNA-mediated interference affected IL-22 production, whereas IL-17 production was affected only by downregulation of RORC by RNA-mediated interference. AHR agonists substantially altered the balance of IL-22- versus IL-17-producing cells. This subset of IL-22-producing cells may be important in skin homeostasis and pathology.

Kinetics of Micronucleus Induction by125I-labelled Thyroid Hormone in Hormone-responsive Cells

Two cell lines, CHO and GC, different in their tissue origin, were investigated with the aim of discovering the correlation between the level of 125I-T3 binding and chromosomal damage induced by 125I decay. Incubation of cells with 125I-T3 has been performed in two exposure schedules: continuous incubation for one to six cell cycles and a pulse-chase schedule involving exposure for one cell cycle. The cellular uptake of 125I-T3, its compartmentization and kinetics were different in the two cell lines. GC cells contained about 7 times more 125I-T3 than CHO cells when incubated with the same external 125I activity concentration (74 kBq of 125I-T3 ml-1 medium). Approximately 70% of the cellular 125I-T3 was found in nuclei of GC cells and only 5% in the nuclei of CHO cells. During the long-term incubation of GC cells with 74 kBq of 125I-T3 ml-1 medium, the 125I activity concentration in cells and their nuclei initially decreased by a half, and thereafter reached a plateau after the third doubling time. In CHO cells and nuclei a very slow linear increase of 125I activity was observed. In GC cells, micronucleus frequency was found to be correlated with nuclear 125I activity. One cell cycle pulse labelling with 74 kBq of 125I-T3 ml-1 medium caused a significant enhancement of micronucleus frequency above the control level during six doubling times, with a maximum at the first post-labelling doubling time. In GC cells continuously incubated with 74 kBq of 125I-T3 ml-1 medium, the micronucleus frequency increased with the incubation time. A model of T3 receptor-dependent dose delivery to nuclei of GC cells continuously incubated with 125I-T3 is proposed. The frequency of micronuclei in the CHO cell line continuously incubated with 125I-T3 did not differ significantly from the control, whereas in the pulse-chase schedule the mean frequency of micronucleated binuclear cells was lower during 4 post-labelling doubling times (significantly at the first and second post-labelling doubling time and insignificantly at the later doubling times) than in the control. Incubation of GC cells with various activity concentrations in medium for four cell cycles resulted in a linear increase of 125I activity in cells and nuclei; however, with a saturation in the region of highest 125I-T3 concentrations used. The frequency of binuclear cells bearing micronuclei was linearly dependent on the nuclear 125I-T3 concentration.

Thyroid disorders in mental patients

PURPOSE OF REVIEW

Thyroid hormones play important roles in brain development and function. Recent findings concerning thyroid hormones secretion, transport, and metabolism in the brain have provided a better understanding of the role of thyroid hormones in mental disorders.

RECENT FINDINGS

The intracellular actions of thyroid hormones in brain are determined by a complex of factors, including circulating concentrations of thyroid hormones, availability of free hormone, activity of thyroid hormone transporters and deiodinase enzymes, and activity of thyroid hormone receptors. Individual genetic variations and mutations of thyroid-axis-related proteins influence thyroid hormone activity in the brain and contribute to the presentation of mental disorders, as well as to response to psychiatric treatments.

SUMMARY

Consideration of molecular mechanism related to genetic alterations in thyroid hormone transport into the neuron, intracellular thyroid hormone metabolism in the brain, as well as polymorphism in thyroid hormone receptors, opens new venues for better understanding of thyroid hormone effects in the brain as well as for finding genetic markers and new targets for the treatment of mental disorders.

Nongenomic activation of phosphatidylinositol 3-kinase signaling by thyroid hormone receptors

Thyroid hormone (T3) is critical in growth, development, differentiation, and maintenance of metabolic homeostasis. Recent studies suggest that thyroid hormone receptors (TRs) not only mediate the biological activities of T3 via nucleus-initiated transcription, but also could act via nongenomic pathways. The striking phenotype of thyroid cancer exhibited by a knockin mutant mouse that harbors a dominant negative TRbeta mutant (TRbeta(PV/PV) mouse) allows the elucidation of novel oncogenic activity of a TRbeta mutant (PV) via extra-nuclear actions. PV physically interacts with the regulatory p85alpha subunit of phosphatidylinositol 3-kinase (PI3K) to activate the downstream AKT-mammalian target of rapamycin (mTOR) and p70(S6K) and PI3K-integrin-linked kinase-matrix metalloproteinase-2 signaling pathways. The PV-mediated PI3K activation results in increased cell proliferation, motility, migration, and metastasis. Remarkably, a nuclear receptor corepressor (NCoR) was found to regulate the PV-activated PI3K signaling by competing with PV for binding to the C-terminal SH2 domain of p85alpha. Over-expression of NCoR in thyroid tumor cells of TRbeta(PV/PV) mice reduces AKT-mTOR-p70(S6K) signaling. Conversely, lowering cellular NCoR by siRNA knockdown in tumor cells leads to over-activated PI3K-AKT signaling to increase cell proliferation and motility. Furthermore, NCoR protein levels are significantly lower in thyroid tumor cells than in wild type thyrocytes, allowing more effective binding of PV to p85alpha to activate PI3K signaling, thereby contributing to tumor progression. Thus, PV, an apo-TRbeta, could act via direct protein-protein interaction to mediate critical oncogenic actions. These studies also uncovered a novel extra-nuclear role of NCoR in modulating the nongenomic actions of a mutated TRbeta in controlling thyroid carcinogenesis.

Altering PPARgamma ligand selectivity impairs adipogenesis by thiazolidinediones but not hormonal inducers

Peroxisome proliferator-activated receptor gamma (PPARgamma) acts as a ligand-dependent transcription factor with a key role in mediating adipocyte differentiation and insulin sensitivity. Recently, we and others have shown that PPARgamma recruits the nuclear corepressors NCoR and silencing mediator for retinoid and thyroid hormone receptors (SMRT) to modulate adipogenesis. While the synthetic ligands for PPARgamma, the thiazolidinediones (TZD), are widely used in the treatment of type 2 diabetes mellitus, the biologically relevant endogenous PPARgamma ligand involved in adipogenesis remains unidentified. To further understand the role of ligand binding and corepressor interaction in PPARgamma-mediated adipogenesis, a mutation was introduced in the ligand-binding domain (LBD) of murine PPARgamma. PPARgammamut was created via two amino acid substitutions known to be major determinants of ligand selectivity among PPAR isotypes, H323Y and R288M. These mutations alter PPARgamma to the corresponding residues of the PPARalpha. Characterizing the in vitro functional properties of this mutant, we show that PPARgammamut preferentially responds to the PPARalpha agonist, WY-14643, over the TZD, pioglitazone. When expressed in 3T3-L1 preadipocytes using recombinant adenovirus, wild-type PPARgamma leads to adipocyte formation with both hormonal and TZD treatment. PPARgammamut blocks the upregulation of adipocyte-specific proteins by TZD, but surprisingly, not by standard hormonal inducers. Our data suggest that TZDs and the purported endogenous ligand do not interact in the same way with the PPARgamma LBD. We propose that the endogenous ligand has distinct properties that allow for promiscuity within the hydrophobic PPAR ligand-binding pocket, yet fosters appropriate cofactor recruitment and release to allow adipogenesis to proceed.

[Osteoporosis treatment in patients with hyperthyroidism]

Childhood thyroid hormone (T3) is essential for the normal development of endochondral and intramembranous bone and plays an important role in the linear growth and maintenance of bone mass. In adult, T3 stimulates osteoclastic bone resorption mediated primarily by TR alpha and local conversion by deiodinase D2 may play a role in local activation. TSH seems to be an inhibitor of bone resorption and formation. In thyrotoxicosis patients with Graves' disease, there is increased bone remodelling, characterized by an imbalance between bone resorption and formation, which results in a decrease of bone mineral density (BMD) and an increased risk for osteoporotic fracture. Antithyroid treatment is able to reduce dramatically the bone resorption and to normalize BMD reduction. But previous hyperthyroidism is independently associated with an increased risk for fracture. Although further studies relating to the mechanism for possible impaired bone strength in these patients will be needed, bisphosphonates may be beneficial treatment for prevention of bone fractures in patients with severe risk for fractures, such as post-menopausal women.

Roles of testicular orphan nuclear receptors 2 and 4 in early embryonic development and embryonic stem cells

The testicular orphan nuclear receptors (TRs) 2 and 4 act as either transcriptional activators or regulatory proteins of other nuclear receptor superfamily members. With no identified cognate ligands, their physiological roles remain unclear. Here we showed the phenotypes of TR2(-/-):TR4(-/-) mutant embryos, which reveal that the loss of TR2 and TR4 causes early embryonic lethality and increased cell death. We also found that TR2 and TR4 are expressed in blastocysts and embryonic stem (ES) cells, and can act as transcriptional activators in ES cells. The results on further investigating the roles of TR2 and TR4 in ES cells showed that TR2 and TR4 were differentially expressed when ES cells were induced into different specialized cell types, and their expression is regulated by retinoic acid. Knocking down TR2 and TR4 mRNAs decreased the expression of Oct-3/4 and Nanog genes. Mechanism dissection suggests that TR2 and TR4 may affect the Oct-3/4 gene by binding to a direct repeat-1 element located in its promoter region, which is influenced by retinoic acid. Together, our findings highlight possible roles for TR2 and TR4 in early embryonic development by regulating key genes involved in stem cell self-renewal, commitment, and differentiation.

Minireview: Thyrotropin-releasing hormone and the thyroid hormone feedback mechanism

Thyroid hormone (TH) plays a critical role in development, growth, and cellular metabolism. TH production is controlled by a complex mechanism of positive and negative regulation. Hypothalamic TSH-releasing hormone (TRH) stimulates TSH secretion from the anterior pituitary. TSH then initiates TH synthesis and release from the thyroid gland. The synthesis of TRH and TSH subunit genes is inhibited at the transcriptional level by TH, which also inhibits posttranslational modification and release of TSH. Although opposing TRH and TH inputs regulate the hypothalamic-pituitary-thyroid axis, TH negative feedback at the pituitary was thought to be the primary regulator of serum TSH levels. However, study of transgenic animals showed an unexpected, dominant role for TRH in regulating the hypothalamic-pituitary-thyroid axis and an unanticipated involvement of the thyroid hormone receptor ligand-dependent activation function (AF-2) domain in TH negative regulation. These results are summarized in the review.

Molecular characterization, gene expression and transcriptional regulation of thyroid hormone receptors in Senegalese sole

Thyroid hormones (THs) play a key role in larval development, growth and metamorphosis in flatfish. Their genomic effects are mediated by thyroid hormone receptors (TRs). In this study, cDNAs encoding for TRalphaA, TRalphaB, and TRbeta have been sequenced in Senegalese sole (Soleasenegalensis). Main domains and conserved motifs were identified. Also, a truncated TRalphaB isoform (referred to as TRalphaBtr) and a spliced TRbeta variant (referred to as TRbetav) were detected. A phylogenetic analysis grouped both TRalpha and TRbeta genes into two separate clusters with their fish and mammalian counterparts. Expression profiles during larval development and in juvenile tissues were analyzed using a real-time PCR approach. In juvenile fish, TRalphaA, TRalphaB, TRbetav, and TRbeta showed distinct transcript levels in tissues. During metamorphosis, only TRbetav and TRbeta modified their mRNA levels in a similar way to the T4 contents. To evaluate the possible regulation of TRs by their cognate ligand T4 during sole metamorphosis, larvae were exposed to the goitrogen thiourea (TU). TRbeta transcripts decreased significantly at 11 and 15 days after treatment. Moreover, adding exogenous T4 hormone to TU-treated larvae restored the steady-state levels or even increased TRbeta and TRbetav mRNAs with respect to the untreated control. Overall, these results demonstrate that TRbeta transcription is up-regulated by THs playing a major role during metamorphosis in Senegalese sole.

Influence of the transcription factor RORgammat on the development of NKp46+ cell populations in gut and skin

NKp46+CD3- natural killer lymphocytes isolated from blood, lymphoid organs, lung, liver and uterus can produce granule-dependent cytotoxicity and interferon-gamma. Here we identify in dermis, gut lamina propria and cryptopatches distinct populations of NKp46+CD3- cells with a diminished capacity to degranulate and produce interferon-gamma. In the gut, expression of the transcription factor RORgammat, which is involved in the development of lymphoid tissue-inducer cells, defined a previously unknown subset of NKp46+CD3- lymphocytes. Unlike RORgammat- lamina propria and dermis natural killer cells, gut RORgammat+NKp46+ cells produced interleukin 22. Our data show that lymphoid tissue-inducer cells and natural killer cells shared unanticipated similarities and emphasize the heterogeneity of NKp46+CD3- cells in innate immunity, lymphoid organization and local tissue repair.

RORgamma-expressing Th17 cells induce murine chronic intestinal inflammation via redundant effects of IL-17A and IL-17F

BACKGROUND AND AIMS

IL-17-producing CD4(+) T-helper cells (Th17) contribute to chronic autoimmune inflammation in the brain, and levels of Th17-derived cytokines increase in patients with colitis, suggesting a role in pathogenesis. We analyzed the roles of Th17 cells and the transcription factor retinoic acid receptor-related organ receptor (ROR)gamma, which regulates Th17 differentiation, in chronic intestinal inflammation.

METHODS

Using an adoptive transfer model of colitis, we compared the colitogenic potential of wild-type, interleukin-17A (IL-17A)-, IL-17F-, IL-22-, and RORgamma-deficient CD4(+)CD25(-) T cells in RAG1-null mice.

RESULTS

Adoptive transfer of IL-17A-, IL-17F-, or IL-22-deficient T lymphocytes into RAG1-null mice caused severe colitis that was indistinguishable from that caused by wild-type cells. In contrast, transfer of RORgamma-null T cells failed to increase mucosal IL-17 cytokine levels and did not induce colitis. Treatment with IL-17A was able to restore colitis after transfer of RORgamma-null T cells, indicating a crucial role for Th17 cells in pathogenesis. Treatment of RAG1 mice that received IL-17F-null (but not wild-type) T cells with a neutralizing anti-IL-17A antibody significantly suppressed disease, indicating redundant biological effects of IL-17A and IL-17F.

CONCLUSIONS

We have identified a crucial role of RORgamma-expressing Th17 cells in chronic intestinal inflammation. RORgamma controls IL-17A and IL-17F production, and these cytokines have a redundant but highly pathogenic role in gut inflammation. Reagents that target RORgamma or a combination of anti-IL-17A and anti-IL-17F might be developed as therapeutics for chronic colitis.

Connexin40 messenger ribonucleic acid is positively regulated by thyroid hormone (TH) acting in cardiac atria via the TH receptor

Thyroid hormone (TH) regulates many cardiac genes via nuclear thyroid receptors, and hyperthyroidism is frequently associated with atrial fibrillation. Electrical activity propagation in myocardium depends on the transfer of current at gap junctions, and connexins (Cxs) 40 and 43 are the predominant junction proteins. In mice, Cx40, the main Cx involved in atrial conduction, is restricted to the atria and fibers of the conduction system, which also express Cx43. We studied cardiac expression of Cx40 and Cx43 in conjunction with electrocardiogram studies in mice overexpressing the dominant negative mutant thyroid hormone receptor-beta Delta337T exclusively in cardiomyocytes [myosin heavy chain (MHC-mutant)]. These mice develop the cardiac hypothyroid phenotype in the presence of normal serum TH. Expression was also examined in wild-type mice rendered hypothyroid or hyperthyroid by pharmacological treatment. Atrial Cx40 mRNA and protein levels were decreased (85 and 55%, respectively; P < 0.001) in MHC-mt mice. Atrial and ventricular Cx43 mRNA levels were not significantly changed. Hypothyroid and hyperthyroid animals showed a 25% decrease and 40% increase, respectively, in Cx40 mRNA abundance. However, MHC-mt mice presented very low Cx40 mRNA expression regardless of whether they were made hypothyroid or hyperthyroid. Atrial depolarization velocity, as represented by P wave duration in electrocardiograms of unanesthetized mice, was extremely reduced in MHC-mt mice, and to a lesser extent also in hypothyroid mice (90 and 30% increase in P wave duration). In contrast, this measure was increased in hyperthyroid mice (19% decrease in P wave duration). Therefore, this study reveals for the first time that Cx40 mRNA is up-regulated by TH acting in cardiac atria via the TH receptor and that this may be one of the mechanisms contributing to atrial conduction alterations in thyroid dysfunctions.

Cytoplasm-to-nucleus shuttling of thyroid hormone receptor-beta1 (Trbeta1) is directed from a plasma membrane integrin receptor by thyroid hormone

INTRODUCTION

In CV-1 cells, shuttling from cytoplasm to nucleus of the nuclear thyroid hormone receptor-beta1 (TRbeta1, TR) is shown in this report to be regulated by extracellular thyroid hormone at a hormone receptor on cell surface integrin alphav3.

METHODS

The receptor was introduced into cells as a GFP-TR1 chimera and intracellular movement of the receptor was monitored by confocal microscopy of cells treated with L-thyroxine (T(4)).

RESULTS AND DISCUSSION

TR-GFP translocation in the presence of T(4) requires activation of extracellular-regulated protein kinases 1/2 (ERK1/2). Inhibition of T(4)-binding to alphavbeta3 with anti-alphavbeta3 or Arg-Gly-Asp (RGD) peptide blocks T(4)-stimulated GFP-TR nuclear translocation, as do the hormone-binding inhibitor tetraiodothyroacetic acid (tetrac) and the ERK1/2 inhibitor, PD98059. TR1 is an ERK1/2 substrate.

CONCLUSIONS

Via a nongenomic mechanism initiated at plasma membrane integrin v3, T(4)-activated ERK1/2 and TR1 move transiently in an immunoprecipitable complex to the nuclei of T(4)-treated cells.

RORgammat and commensal microflora are required for the differentiation of mucosal interleukin 22-producing NKp46+ cells

The mucosal immune system of the intestine is separated from a vast array of microbes by a single layer of epithelial cells. Cues from the commensal microflora are needed to maintain epithelial homeostasis, but the molecular and cellular identities of these cues are unclear. Here we provide evidence that signals from the commensal microflora contribute to the differentiation of a lymphocyte population coexpressing stimulatory natural killer cell receptors and the transcription factor RORgammat that produced interleukin 22 (IL-22). The emergence of these IL-22-producing RORgammathiNKp46+NK1.1(int) cells depended on RORgammat expression, which indicated that these cells may have been derived from lymphoid tissue-inducer cells. IL-22 released by these cells promoted the production of antimicrobial molecules important in the maintenance of mucosal homeostasis.

Developmental regulation and function of thyroid hormone receptors and 9-cis retinoic acid receptors during Xenopus tropicalis metamorphosis

Amphibian metamorphosis serves as an excellent model to study T3 function during postembryonic development in vertebrate due to its total dependence on T3. Earlier molecular studies in the model species Xenopus laevis have led to a number of important in vivo findings on the function and mechanisms of T3 receptor (TR) action during vertebrate development. However, the lack of genomic sequence information, its tetraploid genome, and lengthy developmental cycle hinder further analyses on TR functions. In this regard, the highly related species, Xenopus tropicalis, is much more advantageous. Toward developing X. tropicalis for genome-wide and genetic studies of TR function, we analyzed the expression profiles of TRs and their heterodimerization partners, retinoid X receptors (RXRs) or 9-cis retinoic acid receptors. We show that their expression correlates with transformations in different organs and that TR/RXR heterodimers are capable of repressing and activating gene expression in vivo in the absence and presence of T3, respectively. We further demonstrate that TRs are bound to endogenous target genes in X. tropicalis tadpoles. Our results thus support a role of TRs in mediating the metamorphic effects of T3 in X. tropicalis. More importantly, the similarities in the expression and function between X. tropicalis and X. laevis TRs and RXRs as demonstrated by our study also pave the way to take advantages of existing morphological, molecular, and cellular knowledge of X. laevis development and the genetic and sequence superiority of X. tropicalis to dissect the molecular pathways governing tissue/organ-specific transformations during vertebrate postembryonic development.

Xenopus laevis as a model for studying thyroid hormone signalling: from development to metamorphosis

Amphibian metamorphosis is a well-established model for dissecting the mechanisms underlying thyroid hormone (TH) action. How the pro-hormone, T(4), the active form, T(3), the deiodinases and the nuclear receptors (TRs) contribute to metamorphosis in Xenopus has been extensively investigated. Our recent work has concentrated on two key ideas in TH signalling in Xenopus: first, that there could be active roles for both liganded and unliganded receptors, and second, that ligand availability is a determining factor orchestrating these actions and is tightly controlled in target tissues. Recently, we addressed these questions at stages preceding metamorphosis, i.e. during embryogenesis, before differentiation of a functional thyroid gland. We show that repression by unliganded TR is essential to craniofacial and eye development during early development and that at these stages all three deiodinases are active. These results open new perspectives on the potential roles of TH signalling during embryogenesis.

Functional significance of a truncated thyroid receptor subtype lacking a hormone-binding domain in goldfish

Thyroid hormones are important mediators of growth and development in vertebrates and act by binding to a specific family of thyroid receptors (TRs). The TRs belong to the nuclear receptor superfamily, with two conserved regions, a DNA binding domain and a ligand binding domain (LBD). We recently demonstrated the presence of four TR subtypes in goldfish, two with complete DNA binding domains and LBDs (TRalpha-1 and TRbeta) and two novel forms including a transcript resembling TRalpha with variation in the LBD as well as a TRalpha-truncated (TRalpha-t) form lacking a LBD. To study the functional significance of TR subtypes, we first investigated the regulation of hepatic goldfish deiodinase type 3 (D3) by T3 and validated a bioassay in which D3 gene expression is up-regulated significantly in vivo and in vitro. Using short interfering RNA, TRalpha-1, TRbeta, or TRalpha-t was specifically knocked down and thyroid hormone-induced D3 gene expression was measured. Short interfering RNA against TRalpha-1 or TRbeta reduced the T3 induction of deiodinase gene expression to 50% or less than 25% of control (T3 treated) cells, respectively. Knocking down TRalpha-t alone, however, increased D3 expression 500-fold supporting the hypothesis that TRalpha-t plays a modulatory role in thyroid hormone-induced gene expression. Our results provide important insight into thyroid receptor biology in goldfish and a framework for the better understanding of thyroid receptor function in all vertebrates.

Thyroid hormone promotes cell invasion through activation of furin expression in human hepatoma cell lines

The objective of this study was to identify genes regulated by thyroid hormone (T(3)) and associated with tumor invasion. The gene encoding furin, as previously identified by cDNA microarray, is known to be up-regulated by T(3) treatment, and stimulated furin production occurs in thyroidectomized rats after administration of T(3). Presently, by using serial deletion of the promoter and EMSAs, the T(3) response element on the furin promoter was localized to the -6317/-6302 region. T(3)-mediated furin up-regulation was cooperative with TGF-beta because T(3) induction increased after Smad3/4 addition. Furthermore, the invasiveness of HepG2-thyroid hormone receptor (TR) cells was significantly increased by T(3) treatment, perhaps due to furin processing of matrix metalloproteinase-2 and -9. In addition, furin up-regulation either by stable overexpression or T(3) and/or TGF-beta induction was evident in severe-combined immune-deficient mice inoculated with HepG2-TRalpha1 cells. The HepG2-furin mice displayed a higher metastasis index and tumor size than HepG2-neo mice. Notably, the increased liver and lung tumor number or size in the hyperthyroid severe-combined immune-deficient mice as well as TGF-beta mice was attributed specifically to furin overexpression in the HepG2-TRalpha1 cells. Furthermore, this study demonstrated that furin overexpression in some types of hepatocellular carcinomas is TR dependent and might play a crucial role in the development of hepatocellular carcinoma. Thus, T(3) regulates furin gene expression via a novel mechanism or in cooperation with TGF-beta to enhance tumor metastasis in vitro and in vivo.