Thyroxine promotes association of mitogen-activated protein kinase and nuclear thyroid hormone receptor (TR) and causes serine phosphorylation of TR

Nrf2-Mediated Antioxidant Defense and Thyroid Hormone Signaling: A Focus on Cardioprotective Effects

Thyroid hormones (TH) perform a plethora of actions in numerous tissues and induce an overall increase in metabolism, with an augmentation in energy demand and oxygen expenditure. Oxidants are required for normal thyroid-cell proliferation, as well as for the synthesis of the main hormones secreted by the thyroid gland, triiodothyronine (T3) and thyroxine (T4). However, an uncontrolled excess of oxidants can cause oxidative stress, a major trigger in the pathogenesis of a broad spectrum of diseases, including inflammation and cancer. In particular, oxidative stress is implicated in both hypo- and hyper-thyroid diseases. Furthermore, it is important for the TH system to rely on efficient antioxidant defense, to maintain balance, despite sustained tissue exposure to oxidants. One of the main endogenous antioxidant responses is the pathway centered on the nuclear factor erythroid 2-related factor (Nrf2). The aim of the present review is to explore the multiple links between Nrf2-related pathways and various TH-associated conditions. The main aspect of TH signaling is described and the role of Nrf2 in oxidant-antioxidant homeostasis in the TH system is evaluated. Next, the antioxidant function of Nrf2 associated with oxidative stress induced by TH pathological excess is discussed and, subsequently, particular attention is given to the cardioprotective role of TH, which also acts through the mediation of Nrf2. In conclusion, the interaction between Nrf2 and most common natural antioxidant agents in altered states of TH is briefly evaluated.

Comparison of transcriptome responses of the liver, tail fin, and olfactory epithelium of Rana [Lithobates] catesbeiana tadpoles disrupted by thyroid hormones and estrogen

Thyroid hormones (THs) are important developmental regulators in vertebrates, including during the metamorphosis of a tadpole into a frog. Metamorphosis is a post-embryonic developmental period initiated by TH production in the tadpole thyroid gland. The two main bioactive forms of TH are L-thyroxine (T₄) and 3,5,3'-triiodothyronine (T₃); these hormones have overlapping but distinct mechanisms of action. Premetamorphic tadpoles are highly responsive to TH and can be induced to metamorphose through exogenous TH exposure, making them an important model for both the study of vertebrate TH signaling and endocrine disrupting chemicals (EDCs). It is important to differentiate TH-mediated responses from estrogenic responses in premetamorphic tadpoles when assessing dysregulation by EDCs as crosstalk between the two endocrine systems is well-documented. Herein, we compare the RNA-sequencing-derived transcriptomic profiles of three TH-responsive tissues (liver, olfactory epithelium, and tail fin) in premetamorphic bullfrog (Rana [Lithobates] catesbeiana) tadpoles exposed to T₃, T₄, and estradiol (E₂). These profiles were generated using the latest available genome assembly for the species. The data indicate that there is a clear distinction, and little overlap, between the transcriptomic responses elicited by E₂ and the THs. In contrast, within the THs, the T₃- and T₄-induced transcriptomic profiles generally show considerable overlap; however, the degree of overlap is highly tissue-dependent, illustrating the importance of distinguishing the two THs and the affected signaling pathways within the target tissue type when evaluating hormone active agents. The data herein also show that E₂ and TH treatment can uniquely induce significant changes in expression of their respective "classic" bioindicator transcripts vtg (E₂) and thra, thrb, and thibz (THs). However, care must be taken in the interpretation of increased vep or esr1 transcripts as a change in transcript levels can be induced by THs rather than solely E₂.

Thyroid hormone receptor phosphorylation regulates acute fasting-induced suppression of the hypothalamic-pituitary-thyroid axis

Fasting induces profound changes in the hypothalamic-pituitary-thyroid (HPT) axis. After binding thyroid hormone (TH), the TH receptor beta 2 isoform (THRB2) represses Trh and Tsh subunit genes and is the principle negative regulator of the HPT axis. Using mass spectrometry, we identified a major phosphorylation site in the AF-1 domain of THRB2 (serine 101, S101), which is conserved among many members of the nuclear hormone receptor superfamily. More than 50% of THRB2 is phosphorylated at S101 in cultured thyrotrophs (TαT1.1) and in the mouse pituitary. All other THR isoforms lack this site and exhibit limited overall levels of phosphorylation. To determine the importance of THRB2 S101 phosphorylation, we used the TαT1.1 cell line and S101A mutant knock-in mice (Thrb2 ^S101A ). We found that TH promoted S101 THRB2 phosphorylation and was essential for repression of the axis at physiologic TH concentrations. In mice, THRB2 phosphorylation was also increased by fasting and mimicked Trh and Tshb repression by TH. In vitro studies demonstrated that a master metabolic sensor, AMP-activated kinase (AMPK) induced phosphorylation at the same site and caused Tshb repression independent of TH. Furthermore, we identified cyclin-dependent kinase 2 (CDK2) as a direct kinase phosphorylating THRB2 S101 and propose that AMPK or TH increase S101 phosphorylation through the activity of CDK2. This study provides a physiologically relevant function for THR phosphorylation, which permits nutritional deprivation and TH to use a common mechanism for acute suppression of the HPT axis.

New Aspects of Uptake and Metabolism of Non-organic and Organic Iodine Compounds-The Role of Vanadium and Plant-Derived Thyroid Hormone Analogs in Lettuce

The process of uptake and translocation of non-organic iodine (I) ions, I^- and IO₃ ^-, has been relatively well-described in literature. The situation is different for low-molecular-weight organic aromatic I compounds, as data on their uptake or metabolic pathway is only fragmentary. The aim of this study was to determine the process of uptake, transport, and metabolism of I applied to lettuce plants by fertigation as KIO₃, KIO₃ + salicylic acid (KIO₃+SA), and iodosalicylates, 5-iodosalicylic acid (5-ISA) and 3,5-diiodosalicylic acid (3,5-diISA), depending on whether additional fertilization with vanadium (V) was used. Each I compound was applied at a dose of 10 μM, SA at a dose of 10 μM, and V at a dose of 0.1 μM. Three independent 2-year-long experiments were carried out with lettuce; two with pot systems using a peat substrate and mineral soil and one with hydroponic lettuce. The effectiveness of I uptake and translocation from the roots to leaves was as follows: 5-ISA > 3,5-diISA > KIO₃. Iodosalicylates, 5-ISA and 3,5-diISA, were naturally synthesized in plants, similarly to other organic iodine metabolites, i.e., iodotyrosine, as well as plant-derived thyroid hormone analogs (PDTHA), triiodothyronine (T3) and thyroxine (T4). T3 and T4 were synthesized in roots with the participation of endogenous and exogenous 5-ISA and 3,5-diISA and then transported to leaves. The level of plant enrichment in I was safe for consumers. Several genes were shown to perform physiological functions, i.e., per64-like, samdmt, msams5, and cipk6.

Role of thyroid hormone-integrin αvβ3-signal and therapeutic strategies in colorectal cancers

Thyroid hormone analogues-particularly, L-thyroxine (T₄) has been shown to be relevant to the functions of a variety of cancers. Integrin αvβ3 is a plasma membrane structural protein linked to signal transduction pathways that are critical to cancer cell proliferation and metastasis. Thyroid hormones, T₄ and to a less extend T₃ bind cell surface integrin αvβ3, to stimulate the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway to stimulate cancer cell growth. Thyroid hormone analogues also engage in crosstalk with the epidermal growth factor receptor (EGFR)-Ras pathway. EGFR signal generation and, downstream, transduction of Ras/Raf pathway signals contribute importantly to tumor cell progression. Mutated Ras oncogenes contribute to chemoresistance in colorectal carcinoma (CRC); chemoresistance may depend in part on the activity of ERK1/2 pathway. In this review, we evaluate the contribution of thyroxine interacting with integrin αvβ3 and crosstalking with EGFR/Ras signaling pathway non-genomically in CRC proliferation. Tetraiodothyroacetic acid (tetrac), the deaminated analogue of T₄, and its nano-derivative, NDAT, have anticancer functions, with effectiveness against CRC and other tumors. In Ras-mutant CRC cells, tetrac derivatives may overcome chemoresistance to other drugs via actions initiated at integrin αvβ3 and involving, downstream, the EGFR-Ras signaling pathways.

Effect of L-thyroxine administration on long-term potentiation and accompanying mitogen-activated protein kinases in rats

The present study investigated the differences in the activation of c-Jun NH2-terminal kinases (JNK), p38 mitogen-activated protein kinases (p38^MAPK ), and extracellular signal-regulated kinases 1/2 (Erk1/2) 1 hr after the induction of long-term potentiation (LTP) between rats with hyperthyroidism that was produced at two different stages of development. Hyperthyroidism was produced in rats by daily injections of L-thyroxine (T4, ip., 0.2 mg/kg) to their dams for lactation period or to the rats itself during the young adult period. LTP was induced by application of high-frequency stimulation protocol. Five-min averages of the excitatory postsynaptic potential (EPSP) slopes and population spike (PS) amplitudes at the end of recording were averaged to measure the magnitude of LTP. Total and phosphorylated levels of Erk1/2, JNK, and P38-MAPK were assessed via western blotting in these hippocampi. LTP was found to be impaired in both groups of hyperthyroidisms, but this impairment observed together with increased expression and phosphorylation of ERK1/2, and increased phosphorylation of JNK in rats treated maternally with T4 compared to those treated adultly. These results suggest that excessiveness of thyroid hormone has longstanding effects on hippocampal function and may account for failed LTP in both early and relatively late stage of development depending on various molecular pathways, such as ERK1/2 and JNK.

Actions of L-thyroxine (T4) and Tetraiodothyroacetic Acid (Tetrac) on Gene Expression in Thyroid Cancer Cells

The clinical behavior of thyroid cancers is seen to reflect inherent transcriptional activities of mutated genes and trophic effects on tumors of circulating pituitary thyrotropin (TSH). The thyroid hormone, L-thyroxine (T4), has been shown to stimulate proliferation of a large number of different forms of cancer. This activity of T4 is mediated by a cell surface receptor on the extracellular domain of integrin αvβ3. In this brief review, we describe what is known about T4 as a circulating trophic factor for differentiated (papillary and follicular) thyroid cancers. Given T4′s cancer-stimulating activity in differentiated thyroid cancers, it was not surprising to find that genomic actions of T4 were anti-apoptotic. Transduction of the T4-generated signal at the integrin primarily involved mitogen-activated protein kinase (MAPK). In thyroid C cell-origin medullary carcinoma of the thyroid (MTC), effects of thyroid hormone analogues, such as tetraiodothyroacetic acid (tetrac), include pro-angiogenic and apoptosis-linked genes. Tetrac is an inhibitor of the actions of T4 at αvβ3, and it is assumed, but not yet proved, that the anti-angiogenic and pro-apoptotic actions of tetrac in MTC cells are matched by T4 effects that are pro-angiogenic and anti-apoptotic. We also note that papillary thyroid carcinoma cells may express the leptin receptor, and circulating leptin from adipocytes may stimulate tumor cell proliferation. Transcription was stimulated by leptin in anaplastic, papillary, and follicular carcinomas of genes involved in invasion, such as matrix metalloproteinases (MMPs). In summary, thyroid hormone analogues may act at their receptor on integrin αvβ3 in a variety of types of thyroid cancer to modulate transcription of genes relevant to tumor invasiveness, apoptosis, and angiogenesis. These effects are independent of TSH.

Nongenomic Actions of Thyroid Hormone: The Integrin Component

The extracellular domain of plasma membrane integrin αvβ3 contains a cell surface receptor for thyroid hormone analogues. The receptor is largely expressed and activated in tumor cells and rapidly dividing endothelial cells. The principal ligand for this receptor is l-thyroxine (T₄), usually regarded only as a prohormone for 3,5,3'-triiodo-l-thyronine (T₃), the hormone analogue that expresses thyroid hormone in the cell nucleus via nuclear receptors that are unrelated structurally to integrin αvβ3. At the integrin receptor for thyroid hormone, T₄ regulates cancer and endothelial cell division, tumor cell defense pathways (such as anti-apoptosis), and angiogenesis and supports metastasis, radioresistance, and chemoresistance. The molecular mechanisms involve signal transduction via mitogen-activated protein kinase and phosphatidylinositol 3-kinase, differential expression of multiple genes related to the listed cell processes, and regulation of activities of other cell surface proteins, such as vascular growth factor receptors. Tetraiodothyroacetic acid (tetrac) is derived from T₄ and competes with binding of T₄ to the integrin. In the absence of T₄, tetrac and chemically modified tetrac also have anticancer effects that culminate in altered gene transcription. Tumor xenografts are arrested by unmodified and chemically modified tetrac. The receptor requires further characterization in terms of contributions to nonmalignant cells, such as platelets and phagocytes. The integrin αvβ3 receptor for thyroid hormone offers a large panel of cellular actions that are relevant to cancer biology and that may be regulated by tetrac derivatives.

Thyroid Hormone in Hepatocellular Carcinoma: Cancer Risk, Growth Regulation, and Anticancer Drug Resistance

Thyroid hormone (TH) and its receptor (TR) are involved in differentiation, metabolic process, and growth regulation in hepatocellular carcinoma (HCC). The TH/TR complexes are ligand-dependent transcriptional factors, functioning through binding to thyroid hormone response elements (TREs) upstream of the target genes. To date, deciphering the biological effects of TH in cancer progression remains challenging. Several lines of evidence suggest a growth inhibitory effect of TH in liver cancer. Mutation and aberrant expression of TRs are highly correlated with several types of cancers including HCC. Several reports show that TH inhibits cell growth in liver cancer through regulation of cell-cycle-related genes and non-coding RNAs. A case–control study indicates that hypothyroidism is associated with an increased risk of HCC. Moreover, TH/TR suppresses hepatocarcinogenesis via selective autophagy. Conversely, other groups have indicated that TH promotes cancer cell proliferation. In vitro and in vivo experiments show that TH/TR enhances cancer cell migration and invasion, anticancer drug resistance, angiogenesis, and cancer stem cell self-renewal. Adding to the complexity of this issue, non-genomic effects of TH mediated by integrin receptor on cell surface can also modulate several biological functions. Accumulating evidence indicate that regulations by genomic and non-genomic effects of TH overlap. Taken together, these observations suggest that the functions of TH depend largely on cell context, and TH/TR plays a duel role in cancer progression. Therefore, understanding the maze of biological effects of TH has become a necessity when attempting to develop effective therapeutic and preventive strategies in liver cancer.

Synthesis and characterization of 64Cu- and Cy5.5-labeled tetraiodothyroacetic acid derivatives for tumor angiogenesis imaging

It was previously reported that tetraiodothyroacetic acid (tetrac) inhibits angiogenesis by binding to the cell surface receptor for thyroid hormone on integrin α_Vβ₃. Therefore, we synthesized and evaluated two ⁶⁴Cu-labeled tetrac derivatives and a Cy5.5-labeled tetrac derivative for tumor angiogenesis imaging. Tetrac was structurally modified to conjugate with 1,4,7,10-tetraazacyclododecane-N,N',N″,N″'-tetraacetic acid (DOTA) via its hydroxy or carboxylic acid end, and the resulting DOTA-conjugated tetrac derivatives were then labeled with ⁶⁴Cu. Tetrac was also conjugated with Cy5.5 via its carboxylic acid end. All three tetrac derivatives (1-3) exhibited greater inhibitory activity than tetrac against endothelial cell tube formation. The U87MG cell binding of [⁶⁴Cu]2 showed a time-dependent increase over 24 h and it was inhibited by 38% at 4 h in the presence of tetrac, indicating specificity of [⁶⁴Cu]2 to the thyroid hormone receptor site on integrin α_Vβ₃. Positron emission tomography (PET) images of U87MG tumor-bearing mice injected with [⁶⁴Cu]1 and [⁶⁴Cu]2 revealed that high radioactivity accumulated in the tumors, and that the tumor uptake and tumor-to-nontarget uptake ratio were higher in small tumors than in large tumors. In addition, the Cy5.5-labeled tetrac derivative (3) displayed a strong near-infrared (NIR) signal in the tumors. Taken together, these results suggest that these ligands hold promise as imaging agents for visualization of tumor angiogenesis.

Thyroid Hormones in the Brain and Their Impact in Recovery Mechanisms After Stroke

Thyroid hormones are of fundamental importance for brain development and essential factors to warrant brain functions throughout life. Their actions are mediated by binding to specific intracellular and membranous receptors regulating genomic and non-genomic mechanisms in neurons and populations of glial cells, respectively. Among others, mechanisms include the regulation of neuronal plasticity processes, stimulation of angiogenesis and neurogenesis as well modulating the dynamics of cytoskeletal elements and intracellular transport processes. These mechanisms overlap with those that have been identified to enhance recovery of lost neurological functions during the first weeks and months after ischemic stroke. Stimulation of thyroid hormone signaling in the postischemic brain might be a promising therapeutic strategy to foster endogenous mechanisms of repair. Several studies have pointed to a significant association between thyroid hormones and outcome after stroke. With this review, we will provide an overview on functions of thyroid hormones in the healthy brain and summarize their mechanisms of action in the developing and adult brain. Also, we compile the major thyroid-modulated molecular pathways in the pathophysiology of ischemic stroke that can enhance recovery, highlighting thyroid hormones as a potential target for therapeutic intervention.

Bisphenol A attenuates thyroxine-induced apoptosis in ovarian granulosa cells of pigs

Bisphenol A (BPA) is a chemical of high production volume that is used widely in many industries and is known as a xenooestrogen and anti-thyroid hormone endocrine disrupter. There is little information regarding the effects of BPA in the presence of thyroid hormone on porcine granulosa cell development. Thus, the primary granulosa cells were treated with thyroxine (T4, 10 nM), BPA (10 µM) or T4 plus BPA; we subsequently evaluated the effects of T4 or BPA on 17β-estradiol synthesis, cellular proliferation and apoptosis. Our data showed that BPA significantly increased the accumulation of 17β-estradiol and promoted granulosa cell proliferation, whereas T4 significantly decreased 17β-estradiol and had no effect on cellular proliferation. In addition, it was noteworthy that T4 treatment induced apoptosis in porcine granulosa cells and BPA co-incubation attenuated T4-induced apoptosis as shown from flow cytometric assay analysis. We hypothesized that BPA attenuates T4-induced apoptosis by regulating 17β-estradiol accumulation and oestrogen receptor-mediated signalling pathways. In conclusion, our results demonstrated that T4 affected 17β-estradiol accumulation and induced cellular apoptosis, but did not affect granulosa cell proliferation. Exposure to BPA increased 17β-estradiol accumulation, promoted granulosa cell proliferation and attenuated T4-induced apoptosis in porcine granulosa cells in vitro.

Expression of proteins related to thyroid hormone function in the uterus is down-regulated at the day of implantation in hypothyroid pregnant rats

Hypothyroidism has been linked to infertility, but the mechanisms underlying infertility-related hypothyroidism have yet to be fully elucidated. Therefore, in this study, effects of hypothyroidism on expression of the proteins related to thyroid hormone function in the uterus, which were thought to play a role implantation, including thyroid hormone receptor (TR), thyroid stimulating hormone receptor (TSHR), retinoic acid receptor (RAR) and extracellular kinase (ERK) were identified. Pregnant female rats were rendered hypothyroid by giving methimazole (MMI), orally. Following hypothyroid induction, rats were grouped into control (non-treated) and received subcutaneous thyroxine at 20, 40, and 80 μg/kg/day for five consecutive days. At Day 6, which is the day of implantation (GD 6), rats were sacrificed and the number of embryo implantation site in the uterus was calculated. Then, uterine horns were harvested and expression of the above proteins and their mRNAs were identified by Western blotting and real-time PCR, respectively. In non-treated hypothyroid pregnant rats, the number of embryo implantation sites decreased as compared to euthyroid and hypothyroid rats receiving thyroxine treatment. Similarly, expression of TRα-1, TRβ-1, TSHR, ERK1/2 and RAR proteins and mRNA in the uterus of non-treated hypothyroid rats also decreased (P < 0.05 when compared to euthyroid and thyroxine-treated hypothyroid rats). In conclusion, downregulated expression of the thyroid hormone related proteins in the uterus at the day of implantation might result in infertility as reported in hypothyroid condition.

Novel Transcriptional Mechanisms for Regulating Metabolism by Thyroid Hormone

The thyroid hormone plays a key role in energy and nutrient metabolisms in many tissues and regulates the transcription of key genes in metabolic pathways. It has long been believed that thyroid hormones (THs) exerted their effects primarily by binding to nuclear TH receptors (THRs) that are associated with conserved thyroid hormone response elements (TREs) located on the promoters of target genes. However, recent transcriptome and ChIP-Seq studies have challenged this conventional view as discordance was observed between TH-responsive genes and THR binding to DNA. While THR association with other transcription factors bound to DNA, TH activation of THRs to mediate effects that do not involve DNA-binding, or TH binding to proteins other than THRs have been invoked as potential mechanisms to explain this discrepancy, it appears that additional novel mechanisms may enable TH to regulate the mRNA expression. These include activation of transcription factors by SIRT1 via metabolic actions by TH, the post-translational modification of THR, the THR co-regulation of transcription with other nuclear receptors and transcription factors, and the microRNA (miR) control of RNA transcript expression to encode proteins involved in the cellular metabolism. Together, these novel mechanisms enlarge and diversify the panoply of metabolic genes that can be regulated by TH.

Thyroid hormones and breast cancer association according to menopausal status and body mass index

BACKGROUND

Thyroxine (T4) has been positively associated with tumor cell proliferation, while the effect of triiodothyronine (T3) on cell proliferation has not been well-established because it differs according to the type of cell line used. In Mexico, it has been reported that 14.5% of adult women have some type of thyroid dysfunction and abnormalities in thyroid function tests have been observed in a variety of non-thyroidal illnesses, including breast cancer (BC). These abnormalities might change with body mass index (BMI) because thyroid hormones are involved in the regulation of various metabolic pathways and probably by menopausal status because obesity has been negatively associated with BC in premenopausal women and has been positively associated with BC in postmenopausal women.

METHODS

To assess the association between serum thyroid hormone concentration (T4 and T3) and BC and the influence of obesity as an effect modifier of this relationship in premenopausal and postmenopausal women, we measured serum thyroid hormone and thyroid antibody levels in 682 patients with incident breast cancer (cases) and 731 controls, who participated in a population-based case-control study performed from 2004 to 2007 in three states of Mexico. We tested the association of total T4 (TT4) and total T3 (TT3) stratifying by menopausal status and body mass index (BMI), and adjusted for other health and demographic risk factors using logistic regressions models.

RESULTS

Higher serum total T4 (TT4) concentrations were associated with BC in both premenopausal (odds ratio (OR) per standard deviation = 5.98, 95% CI 3.01-11.90) and postmenopausal women (OR per standard deviation = 2.81, 95% CI 2.17-3.65). In premenopausal women, the effect of TT4 decreased as BMI increased while the opposite was observed in postmenopausal women. The significance of the effect modification was marginal (p = 0.059) in postmenopausal women and was not significant in premenopausal women (p = 0.22). Lower TT3 concentrations were associated with BC in both premenopausal and postmenopausal women and no effect modification was observed.

CONCLUSIONS

There is a strong association between BC and serum concentrations of TT3 and TT4; this needs to be further investigated to understand why it happens and how important it is to consider these alterations in treatment.

Macrophage migration inhibitory factor (MIF) in the development and progression of pulmonary arterial hypertension

Macrophage migration inhibitory factor (MIF) has been described as a pro-inflammatory cytokine and regulator of neuro-endocrine function. It plays an important upstream role in the inflammatory cascade by promoting the release of other inflammatory cytokines such as TNF-alpha and IL-6, ultimately triggering a chronic inflammatory immune response. As lungs can synthesize and release MIF, many studies have investigated the potential role of MIF as a biomarker in assessment of patients with pulmonary arterial hypertension (PAH) and using anti-MIFs as a new therapeutic modality for PAH.

Posttranslational Modification of Thyroid Hormone Nuclear Receptor by Phosphorylation

TR phosphorylation promotes TR binding to DNA and heterodimerization with RXR. TRβ phosphorylation is induced by thyroid hormone on the cell membrane and phosphorylation by extracellular signal-regulated kinases (ERK), presumably at serine 142. TRα1 N-termini harbors two phosphorylation sites at serine 12 and serine 28/29. Serine 12 is phosphorylated by casein 2 and serine 28/29 by protein kinase A. Mutation analysis of TRα2 identified 2 serine sites, S472 and S473, as the substrates for casein kinase II. Phosphorylated TRα2 does not bind to DNA and dephosphorylated TRα binds to DNA and antagonizes TRα1 binding. Phosphorylation of TR is critical for TR function and T3 signaling and approaches to detection and analysis of phosphorylated TR are described.

Thyroid hormones derivatives reduce proliferation and induce cell death and DNA damage in ovarian cancer

Ovarian cancer is a highly aggressive disease and novel treatments are required. Thyroid hormones binding to αvβ3 integrin produced growth-promoting activities in ovarian cancer and we hypothesized that natural thyroid hormone derivatives may antagonize these actions. The effect of three antagonists, tetraiodoacetic acid (tetrac), triiodothyroacetic acid (triac) and 3-iodothyronamine (T1AM), on cell proliferation, cell death and DNA damage was studied in two ovarian cancer cell lines (OVCAR3 and A2780), normal hamster ovary control cells (CHOK1) and αvβ3-deficient or transfected HEK293 cells. A differential inhibition of cell proliferation was observed in ovarian cancer cells compared to CHOK1. In OVCAR3, an induction of cell cycle regulators was further shown. Apoptosis was confirmed (annexin-PI, SubG1/cell-cycle, apoptotic genes, caspase-3 and poly ADP ribose polymerase-1 (PARP-1) cleavage) and was reversed by a pan-caspase inhibitor. Induction in apoptosis inducing factor (AIF) was observed, suggesting a parallel caspase-independent mechanism. Integrin-involvement in triac/T1AM apoptotic action was shown in αvβ3-transfected HEK293 cells. Lastly, in ovarian cancer models, key proteins that coordinate recognition of DNA damage, ataxia-telangiectasia mutated (ATM) and PARP-1, were induced. To conclude, the cytotoxic potential of thyroid hormone derivatives, tetrac, triac and T1AM, in ovarian cancer may provide a much-needed novel therapeutic approach.

Role of thyroid hormones in the neoplastic process: an overview

Thyroid hormones (TH) are critical regulators of several physiological processes, which include development, differentiation and growth in virtually all tissues. In past decades, several studies have shown that changes in TH levels caused by thyroid dysfunction, disruption of deiodinases and/or thyroid hormone receptor (TR) expression in tumor cells, influence cell proliferation, differentiation, survival and invasion in a variety of neoplasms in a cell type-specific manner. The function of THs and TRs in neoplastic cell proliferation involves complex mechanisms that seem to be cell specific, exerting effects via genomic and nongenomic pathways, repressing or stimulating transcription factors, influencing angiogenesis and promoting invasiveness. Taken together, these observations indicate an important role of TH status in the pathogenesis and/or development of human neoplasia. Here, we aim to present an updated and comprehensive picture of the accumulated knowledge and the current understanding of the potential role of TH status on the different hallmarks of the neoplastic process.

Molecular Basis of Nongenomic Actions of Thyroid Hormone

Nongenomic actions of thyroid hormone are initiated by the hormone at receptors in the plasma membrane, in cytoplasm, or in mitochondria and do not require the interaction of nuclear thyroid hormone receptors (TRs) with their primary ligand, 3,5,3'-triiodo-l-thyronine (T₃). Receptors involved in nongenomic actions may or may not have structural homologies with TRs. Certain nongenomic actions that originate at the plasma membrane may modify the state and function of intranuclear TRs. Reviewed here are nongenomic effects of the hormone-T₃ or, in some cases, l-thyroxine (T₄)-that are initiated at (a) truncated TRα isoforms, e.g., p30 TRα1, (b) cytoplasmic proteins, or (c) plasma membrane integrin αvβ3. p30 TRα1 is not transcriptionally competent, binds T₃ at the cell surface, and consequently expresses a number of important functions in bone cells. Nongenomic hormonal control of mitochondrial respiration involves a TRα isoform, and another truncated TRα isoform nongenomically regulates the state of cellular actin. Cytoplasmic hormone-binding proteins involved in nongenomic actions of thyroid hormone include ketimine reductase, pyruvate kinase, and TRβ that shuttle among intracellular compartments. Functions of the receptor for T₄ on integrin αvβ3 include stimulation of proliferation of cancer and endothelial cells (angiogenesis) and regulation of transcription of cancer cell survival pathway genes. T₄ serves as a prohormone for T₃ in genomic actions of thyroid hormone, but T₄ is a hormone at αvβ3 and more important to cancer cell function than is T₃. Thus, characterization of nongenomic actions of the hormone has served to broaden our understanding of the cellular roles of T₃ and T₄.

Thyroxine Increases Collagen Type II Expression and Accumulation in Scaffold-Free Tissue-Engineered Articular Cartilage

Low collagen accumulation in the extracellular matrix is a pressing problem in cartilage tissue engineering, leading to a low collagen-to-glycosaminoglycan (GAG) ratio and poor mechanical properties in neocartilage. Soluble factors have been shown to increase collagen content, but may result in a more pronounced increase in GAG content. Thyroid hormones have been reported to stimulate collagen and GAG production, but reported outcomes, including which specific collagen types are affected, are variable throughout the literature. Here we investigated the ability of thyroxine (T4) to preferentially stimulate collagen production, as compared with GAG, in articular chondrocyte-derived scaffold-free engineered cartilage. Dose response curves for T4 in pellet cultures showed that 25 ng/mL T4 increased the total collagen content without increasing the GAG content, resulting in a statistically significant increase in the collagen-to-GAG ratio, a fold change of 2.3 ± 1.2, p < 0.05. In contrast, another growth factor, TGFβ1, increased the GAG content in excess of threefold more than the increase in collagen. In large scaffold-free neocartilage, T4 also increased the total collagen/DNA at 1 month and at 2 months (fold increases of 2.1 ± 0.8, p < 0.01 and 2.1 ± 0.4, p < 0.001, respectively). Increases in GAG content were not statistically significant. The effect on collagen was largely specific to collagen type II, which showed a 2.8 ± 1.6-fold increase of COL2A1 mRNA expression (p < 0.01). Western blots confirmed a statistically significant increase in type II collagen protein at 1 month (fold increase of 2.2 ± 1.8); at 2 months, the fold increase of 3.7 ± 3.3 approached significance (p = 0.059). Collagen type X protein was less than the 0.1 μg limit of detection. T4 did not affect COL10A1 and COL1A2 gene expression in a statistically significant manner. Biglycan mRNA expression increased 2.6 ± 1.6-fold, p < 0.05. Results of this study show that an optimized dosage of T4 is able to increase collagen type II content, and do so preferential to GAG. Moreover, the upregulation of COL2A1 gene expression and type II collagen protein accumulation, without a concomitant increase in collagens type I or type X, signifies a direct enhancement of chondrogenesis of hyaline articular cartilage without the induction of terminal differentiation.

Action of Thyroid Hormones, T3 and T2, on Hepatic Fatty Acids: Differences in Metabolic Effects and Molecular Mechanisms

The thyroid hormones (THs) 3,3′,5,5′-tetraiodo-l-thyronine (T4) and 3,5,3′-triiodo-l-thyronine (T3) influence many metabolic pathways. The major physiological function of THs is to sustain basal energy expenditure, by acting primarily on carbohydrate and lipid catabolism. Beyond the mobilization and degradation of lipids, at the hepatic level THs stimulate the de novo fatty acid synthesis (de novo lipogenesis, DNL), through both the modulation of gene expression and the rapid activation of cell signalling pathways. 3,5-Diiodo-l-thyronine (T2), previously considered only a T3 catabolite, has been shown to mimic some of T3 effects on lipid catabolism. However, T2 action is more rapid than that of T3, and seems to be independent of protein synthesis. An inhibitory effect on DNL has been documented for T2. Here, we give an overview of the mechanisms of THs action on liver fatty acid metabolism, focusing on the different effects exerted by T2 and T3 on the regulation of the DNL. The inhibitory action on DNL exerted by T2 makes this compound a potential and attractive drug for the treatment of some metabolic diseases and cancer.

Mitochondrial Actions of Thyroid Hormone

The hypermetabolic effects of thyroid hormones (THs), the major endocrine regulators of metabolic rate, are widely recognized. Although, the cellular mechanisms underlying these effects have been extensively investigated, much has yet to be learned about how TH regulates diverse cellular functions. THs have a profound impact on mitochondria, the organelles responsible for the majority of cellular energy production, and several studies have been devoted to understand the respective importance of the nuclear and mitochondrial pathways for organelle activity. During the last decades, several new aspects of both THs (i.e., metabolism, transport, mechanisms of action, and the existence of metabolically active TH derivatives) and mitochondria (i.e., dynamics, respiratory chain organization in supercomplexes, and the discovery of uncoupling proteins other than uncoupling protein 1) have emerged, thus opening new perspectives to the investigation of the complex relationship between thyroid and the mitochondrial compartment. In this review, in the light of an historical background, we attempt to point out the present findings regarding thyroid physiology and the emerging recognition that mitochondrial dynamics as well as the arrangement of the electron transport chain in mitochondrial cristae contribute to the mitochondrial activity. We unravel the genomic and nongenomic mechanisms so far studied as well as the effects of THs on mitochondrial energetics and, principally, uncoupling of oxidative phosphorylation via various mechanisms involving uncoupling proteins. The emergence of new approaches to the question as to what extent and how the action of TH can affect mitochondria is highlighted. © 2016 American Physiological Society. Compr Physiol 6:1591-1607, 2016.

Emerging role of thyroid hormone metabolites

Thyroid hormones (THs) are essential for the regulation of development and metabolism in key organs. THs produce biological effects both by directly affecting gene expression through the interaction with nuclear receptors (genomic effects) and by activating protein kinases and/or ion channels (short-term effects). Such activations can be either direct, in the case of ion channels, or mediated by membrane or cytoplasmic receptors. Short-term-activated signalling pathways often play a role in the regulation of genomic effects. Several TH intermediate metabolites, which were previously considered without biological activity, have now been associated with a broad range of actions, mostly attributable to short-term effects. Here, we give an overview of the physiological roles and mechanisms of action of THs, focusing on the emerging position that TH metabolites are acquiring as important regulators of physiology and metabolism.

The combination of tetraiodothyroacetic acid and cetuximab inhibits cell proliferation in colorectal cancers with different K-ras status

Thyroid hormone induces cancer cell proliferation through its cell surface receptor integrin αvβ3. Acting via integrin αvβ3, the deaminated T4 analog tetraiodothyroacetic acid (tetrac), and its nanoparticle formulation nano-diamino-tetrac (NDAT) could inhibit cell proliferation and xenograft growth. In this study, we investigated the T4 effects on proliferation in colorectal cancer cell lines based on the proliferation marker expressions at both mRNA and protein levels. The effects of tetrac/NDAT, the monoclonal anti-EGFR antibody cetuximab, and their combinations on colorectal cancer cell proliferation were examined according to the relevant gene expression profiles and cell count analysis. The results showed that T4 significantly enhanced PCNA, Cyclin D1 and c-Myc levels in both K-ras wild type HT-29 and mutant HCT 116 cells. In HCT 116 cells, the combination of NDAT and cetuximab significantly suppressed the mRNA expressions of proliferative genes PCNA, Cyclin D1, c-Myc and RRM2 raised by T4 compared to cetuximab alone. In addition, T4-suppressed mRNA expressions of pro-apoptotic genes p53 and RRM2B could be significantly elevated by the combination of NDAT and cetuximab compared to cetuximab alone. In the K-ras mutant HCT 116 cells, but not in the K-ras wild type COLO 205 cells, the combinations of tetrac/NDAT and cetuximab significantly reduced cell proliferation compared to cetuximab alone. In conclusion, T4 promoted colorectal cancer cell proliferation which could be repressed by tetrac and NDAT. The combinations of tetrac/NDAT and cetuximab potentiated cetuximab actions in K-ras mutant colorectal cancer cells.

Arsenic impacted the development, thyroid hormone and gene transcription of thyroid hormone receptors in bighead carp larvae (Hypophthalmichthys nobilis)

Arsenic (As) contamination in aquatic environment adversely impacts aquatic organisms. The present study assessed the toxicity of different As species and concentrations on bighead carp (Hypophthalmichthys nobilis) at early life stage, a major fish in Yangtze River, China. We measured the changes in embryo and larvae survival rate, larvae aberration, concentrations of thyroid hormone thyroxine, and transcription levels of thyroid hormone receptors (TRs) in fish larvae after exposing to arsenite (AsIII) or arsenate (AsV) at 0, 10, 30, 50, 100, or 150 μg L(-1) for 78 h. As concentrations ≤ 150 μg L(-1) had limited effect on embryo survival rate (6-8% inhibition), but larvae survival rate decreased to 53-57% and larvae aberration rate increased to 20-24% after As exposure. Moreover, thyroxine levels elevated by 23% and 50% at 100 μg L(-1) AsIII and 150 μg L(-1) AsV. Besides, AsIII and AsV decreased the transcriptional levels of TRα by 72 and 53%, and TRβ by 91 and 81% at 150 μg L(-1) As. Our data showed that AsIII and AsV had limited effect on carp embryo survival, but they were both toxic to carp larvae, with AsIII showing more effect than AsV. As concentrations <150μg L(-1) adversely influenced the development of bighead carp larvae and disturbed their thyroid hormone homeostasis.

In silico modelling of prostacyclin and other lipid mediators to nuclear receptors reveal novel thyroid hormone receptor antagonist properties

Prostacyclin (PGI2) is a key mediator involved in cardiovascular homeostasis, acting predominantly on two receptor types; cell surface IP receptor and cytosolic peroxisome proliferator activated receptor (PPAR) β/δ. Having a very short half-life, direct methods to determine its long term effects on cells is difficult, and little is known of its interactions with nuclear receptors. Here we used computational chemistry methods to investigate the potential for PGI2, beraprost (IP receptor agonist), and GW0742 (PPARβ/δ agonist), to bind to nuclear receptors, confirmed with pharmacological methods. In silico screening predicted that PGI2, beraprost, and GW0742 have the potential to bind to different nuclear receptors, in particular thyroid hormone β receptor (TRβ) and thyroid hormone α receptor (TRα). Docking analysis predicts a binding profile to residues thought to have allosteric control on the TR ligand binding site. Luciferase reporter assays confirmed that beraprost and GW0742 display TRβ and TRα antagonistic properties; beraprost IC50 6.3 × 10(-5)mol/L and GW0742 IC50 4.9 × 10(-6) mol/L. Changes to triiodothyronine (T3) induced vasodilation of rat mesenteric arteries measured on the wire myograph were measured in the presence of the TR antagonist MLS000389544 (10(-5) mol/L), beraprost (10(-5) mol/L) and GW0742 (10(-5) mol/L); all significantly inhibited T3 induced vasodilation compared to controls. We have shown that both beraprost and GW0742 exhibit TRβ and TRα antagonist behaviour, and suggests that PGI2 has the ability to affect the long term function of cells through binding to and inactivating thyroid hormone receptors.

Hypothyroxinemia induced by maternal mild iodine deficiency impairs hippocampal myelinated growth in lactational rats

Hypothyroxinemia induced by maternal mild iodine deficiency causes neurological deficits and impairments of brain function in offspring. Hypothyroxinemia is prevalent in developing and developed countries alike. However, the mechanism underlying these deficits remains less well known. Given that the myelin plays an important role in learning and memory function, we hypothesize that hippocampal myelinated growth may be impaired in rat offspring exposed to hypothyroxinemia induced by maternal mild iodine deficiency. To test this hypothesis, the female Wistar rats were used and four experimental groups were prepared: (1) control; (2) maternal mild iodine deficiency diet inducing hypothyroxinemia; (3) hypothyroidism induced by maternal severe iodine deficiency diet; (4) hypothyroidism induced by maternal methimazole water. The rats were fed the diet from 3 months before pregnancy to the end of lactation. Our results showed that the physiological changes occuring in the hippocampal myelin were altered in the mild iodine deficiency group as indicated by the results of immunofluorescence of myelin basic proteins on postnatal day 14 and postnatal day 21. Moreover, hypothyroxinemia reduced the expressions of oligodendrocyte lineage transcription factor 2 and myelin-related proteins in the treatments on postnatal day 14 and postnatal day 21. Our data suggested that hypothyroxinemia induced by maternal mild iodine deficiency may impair myelinated growth of the offspring.

Overlapping nongenomic and genomic actions of thyroid hormone and steroids

The genomic actions of thyroid hormone and steroids depend upon primary interactions of the hormones with their specific nuclear receptor proteins. Formation of nuclear co-activator or co-repressor complexes involving the liganded receptors subsequently result in transcriptional events-either activation or suppression-at genes that are specific targets of thyroid hormone or steroids. Nongenomic actions of thyroid hormone and steroids are in contrast initiated at binding sites on the plasma membrane or in cytoplasm or organelles and do not primarily require formation of intranuclear receptor protein-hormone complexes. Importantly, hormonal actions that begin nongenomically outside the nucleus often culminate in changes in nuclear transcriptional events that are regulated by both traditional intranuclear receptors as well as other nuclear transcription factors. In the case of thyroid hormone, the extranuclear receptor can be the classical "nuclear" thyroid receptor (TR), a TR isoform, or integrin αvβ3. In the case of steroid hormones, the membrane receptor is usually, but not always, the classical "nuclear" steroid receptor. This concept defines the paradigm of overlapping nongenomic and genomic hormone mechanisms of action. Here we review some examples of how extranuclear signaling by thyroid hormone and by estrogens and androgens modulates intranuclear hormone signaling to regulate a number of vital biological processes both in normal physiology and in cancer progression. We also point out that nongenomic actions of thyroid hormone may mimic effects of estrogen in certain tumors.

The thyroid hormone-αvβ3 integrin axis in ovarian cancer: regulation of gene transcription and MAPK-dependent proliferation

Ovarian carcinoma is the fifth common cause of cancer death in women, despite advanced therapeutic approaches. αvβ3 integrin, a plasma membrane receptor, binds thyroid hormones (L-thyroxine, T4; 3,5,3'-triiodo-L-thyronine, T3) and is overexpressed in ovarian cancer. We have demonstrated selective binding of fluorescently labeled hormones to αvβ3-positive ovarian cancer cells but not to integrin-negative cells. Physiologically relevant T3 (1 nM) and T4 (100 nM) concentrations in OVCAR-3 (high αvβ3) and A2780 (low αvβ3) cells promoted αv and β3 transcription in association with basal integrin levels. This transcription was effectively blocked by RGD (Arg-Gly-Asp) peptide and neutralizing αvβ3 antibodies, excluding T3-induced β3 messenger RNA, suggesting subspecialization of T3 and T4 binding to the integrin receptor pocket. We have provided support for extracellular regulated kinase (ERK)-mediated transcriptional regulation of the αv monomer by T3 and of β3 monomer by both hormones and documented a rapid (30-120 min) and dose-dependent (0.1-1000 nM) ERK activation. OVCAR-3 cells and αvβ3-deficient HEK293 cells treated with αvβ3 blockers confirmed the requirement for an intact thyroid hormone-integrin interaction in ERK activation. In addition, novel data indicated that T4, but not T3, controls integrin's outside-in signaling by phosphorylating tyrosine 759 in the β3 subunit. Both hormones induced cell proliferation (cell counts), survival (Annexin-PI), viability (WST-1) and significantly reduced the expression of genes that inhibit cell cycle (p21, p16), promote mitochondrial apoptosis (Nix, PUMA) and tumor suppression (GDF-15, IGFBP-6), particularly in cells with high integrin expression. At last, we have confirmed that hypothyroid environment attenuated ovarian cancer growth using a novel experimental platform that exploited paired euthyroid and severe hypothyroid serum samples from human subjects. To conclude, our data define a critical role for thyroid hormones as potent αvβ3-ligands, driving ovarian cancer cell proliferation and suggest that disruption of this axis may present a novel treatment strategy in this aggressive disease.

Maternal Hypothyroxinemia-Induced Neurodevelopmental Impairments in the Progeny

Maternal hypothyroxinemia can induce neurodevelopmental impairments in the developing fetus. We here review recent studies on the epidemiology and molecular mechanisms associated with this important public health issue. In 2011, the American Thyroid Association defined maternal hypothyroxinemia as low serum free thyroxine (FT4) levels (<5th or <10th percentile) existing in conjunction with normal serum free triiodothyronine (FT3) or thyroid stimulating hormone (TSH) levels during pregnancy. Compared to clinical or subclinical hypothyroidism, hypothyroxinemia is more commonly found in pregnant women. Hypothyroxinemia usually ensues in response to several factors, such as mild iodine deficiency, environmental endocrine disrupters, or certain thyroid diseases. Unequivocal evidence demonstrates that maternal hypothyroxinemia leads to negative effects on fetal brain development, increasing the risks for cognitive deficits and poor psychomotor development in resulting progeny. In support of this, rodent models provide direct evidence of neurodevelopmental damage induced by maternal hypothyroxinemia, including dendritic and axonal growth limitation, neural abnormal location, and synaptic function alteration. The neurodevelopmental impairments induced by hypothyroxinemia suggest an independent role of T4. Increasing evidence indicates that adequate thyroxine is required for the mothers in order to protect against the abnormal brain development in their progeny.

New avenues for regulation of lipid metabolism by thyroid hormones and analogs

Weight loss due to negative energy balance is a goal in counteracting obesity and type 2 diabetes mellitus. The thyroid is known to be an important regulator of energy metabolism through the action of thyroid hormones (THs). The classic, active TH, 3,5,3'-triiodo-L-thyronine (T3) acts predominantly by binding to nuclear receptors termed TH receptors (TRs), that recognize TH response elements (TREs) on the DNA, and so regulate transcription. T3 also acts through "non-genomic" pathways that do not necessarily involve TRs. Lipid-lowering therapies have been suggested to have potential benefits, however, the establishment of comprehensive therapeutic strategies is still awaited. One drawback of using T3 in counteracting obesity has been the occurrence of heart rhythm disturbances. These are mediated through one TR, termed TRα. The end of the previous century saw the exploration of TH mimetics that specifically bind to TR beta in order to prevent cardiac disturbances, and TH derivatives such as 3,5-diiodo-L-thyronine (T2), that possess interesting biological activities. Several TH derivatives and functional analogs have low affinity for the TRs, and are suggested to act predominantly through non-genomic pathways. All this has opened new perspectives in thyroid physiology and TH derivative usage as anti-obesity therapies. This review addresses the pros and cons of these compounds, in light of their effects on energy balance regulation and on lipid/cholesterol metabolism.

Recurrence of differentiated thyroid carcinoma during full TSH suppression: is the tumor now thyroid hormone dependent?

Well-standardized primary treatment and long-term management of differentiated thyroid carcinoma (DTC) include lowering or suppression of host thyrotropin (TSH) with exogenous L-thyroxine (T₄). This treatment recognizes the trophic action of TSH on DTC cells. Suppression of endogenous TSH with T₄ is continued in recurrent disease. However, T₄ can induce proliferation of follicular and papillary thyroid carcinoma cell lines and of other human carcinoma cells. The proliferative mechanism is initiated at a cell surface receptor for T₄ on integrin αvβ3, a receptor by which the hormone also inhibits p53-dependent apoptosis in tumor cells. In recurrent DTC with satisfactory suppression of endogenous TSH, we discuss here the possibility that the tumor is no longer TSH dependent and that T₄ has become a critical growth factor for the cancer.

Clinical significance of integrin β6 as a tumor recurrence factor in follicular thyroid carcinoma

BACKGROUND

Overexpression of integrin β6 plays an important role in a variety of malignant tumor invasion and metastasis.

METHODS

The expression levels of integrin β6, matrix metalloproteinase (MMP)-2 and MMP-9 were analyzed by immunohistochemistry with human follicular thyroid carcinomas. Then we investigated their correlation with clinical outcomes parameters, relationship, and the survival time.

RESULTS

The integrin β6 staining was expressed in cellular membrane and cytoplasm of follicular thyroid carcinoma cells. The MMP-2 and MMP-9 expressions were mainly found in cellular cytoplasm. In correlation with the clinical outcome parameters of 60 patients, there were significant statistical differences of integrin β6, MMP-2, and MMP-9 expression levels in different size of tumor. Integrin β6 and MMP-9 expressions have significant statistical differences in T classifications. MMP-2 and MMP-9 expressions have significant statistical differences in different M classification. Other clinical outcome parameters had no significant statistical differences.

CONCLUSION

Integrin β6 expression correlated significantly with MMP-9 expression, and may be a valuable recurrence indicator for follicular thyroid carcinomas.

Molecular basis of thyrotropin and thyroid hormone action during implantation and early development

BACKGROUND

Implantation and early embryo development are finely regulated processes in which several molecules are involved. Evidence that thyroid hormones (TH: T4 and T3) might be part of this machinery is emerging. An increased demand for TH occurs during gestation, and any alteration in maternal thyroid physiology has significant implications for both maternal and fetal health. Not only overt but also subclinical hypothyroidism is associated with infertility as well as with obstetric complications, including disruptions and disorders of pregnancy, labor, delivery, and troubles in early neonatal life.

METHODS

We searched the PubMed and Google Scholar databases for articles related to TH action on ovary, endometrium, trophoblast maturation and embryo implantation. In addition, articles on the regulation of TH activity at cellular level have been reviewed. The findings are hereby summarized and critically discussed.

RESULTS

TH have been shown to influence endometrial, ovarian and placental physiology. TH receptors (TR) and thyrotropin (thyroid-stimulating hormone: TSH) receptors (TSHR) are widely expressed in the feto-maternal unit during implantation, and both the endometrium and the trophoblast might be influenced by TH either directly or through TH effects on the synthesis and activity of implantation-mediating molecules. Interestingly, due to the multiplicity of mechanisms involved in TH action (e.g. differential expression of TR isoforms, heterodimeric receptor partners, interacting cellular proteins, and regulating enzymes), the TH concentration in blood is not always predictive of their cellular availability and activity at both genomic and nongenomic level.

CONCLUSIONS

In addition to the known role of TH on the hormonal milieu of the ovarian follicle cycle, which is essential for a woman's fertility, evidence is emerging on the importance of TH signaling during implantation and early pregnancy. Based on recent observations, a local action of TH on female reproductive organs and the embryo during implantation appears to be crucial for a successful pregnancy. Furthermore, an imbalance in the spatio-temporal expression of factors involved in TH activity might induce early arrest of pregnancy in women considered as euthyroid, based on their hormonal blood concentration. In conclusion, alterations of the highly regulated local activity of TH may play a crucial, previously underestimated, role in early pregnancy and pregnancy loss. Further studies elucidating this topic should be encouraged.

Thyroid hormone inhibition in L6 myoblasts of IGF-I-mediated glucose uptake and proliferation: new roles for integrin αvβ3

Thyroid hormones L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3) have been shown to initiate short- and long-term effects via a plasma membrane receptor site located on integrin αvβ3. Also insulin-like growth factor type I (IGF-I) activity is known to be subject to regulation by this integrin. To investigate the possible cross-talk between T4 and IGF-I in rat L6 myoblasts, we have examined integrin αvβ3-mediated modulatory actions of T4 on glucose uptake, measured through carrier-mediated 2-deoxy-[3H]-D-glucose uptake, and on cell proliferation stimulated by IGF-I, assessed by cell counting, [3H]-thymidine incorporation, and fluorescence-activated cell sorting analysis. IGF-I stimulated glucose transport and cell proliferation via the cell surface IGF-I receptor (IGFIR) and, downstream of the receptor, by the phosphatidylinositol 3-kinase signal transduction pathway. Addition of 0.1 nM free T4 caused little or no cell proliferation but prevented both glucose uptake and proliferative actions of IGF-I. These actions of T4 were mediated by an Arg-Gly-Asp (RGD)-sensitive pathway, suggesting the existence of crosstalk between IGFIR and the T4 receptor located near the RGD recognition site on the integrin. An RGD-sequence-containing integrin inhibitor, a monoclonal antibody to αvβ3, and the T4 metabolite tetraiodothyroacetic acid all blocked the inhibition by T4 of IGF-I-stimulated glucose uptake and cell proliferation. Western blotting confirmed roles for activated phosphatidylinositol 3-kinase and extracellular regulated kinase 1/2 (ERK1/2) in the effects of IGF-I and also showed a role for ERK1/2 in the actions of T4 that modified the effects of IGF-I. We conclude that thyroid hormone inhibits IGF-I-stimulated glucose uptake and cell proliferation in L6 myoblasts.

Suppression of pancreatic cancer by sulfated non-anticoagulant low molecular weight heparin

Sulfated non-anticoagulant heparins (S-NACHs) might be preferred for potential clinical use in cancer patients without affecting hemostasis as compared to low molecular weight heparins (LMWHs). We investigated anti-tumor effects, anti-angiogenesis effects, and mechanisms of S-NACH in a mouse model of pancreatic cancer as compared to the LMWH tinzaparin. S-NACH or tinzaparin with or without gemcitabine were administered, and tumor luminescent signal intensity, tumor weight, and histopathology were assessed at the termination of the study. S-NACH and LMWH efficiently inhibited tumor growth and metastasis, without any observed bleeding events with S-NACH as compared to tinzaparin. S-NACH distinctly increased tumor necrosis and enhanced gemcitabine response in the mouse pancreatic cancer models. These data suggest the potential implication of S-NACH as a neoadjuvant in pancreatic cancer.

Cancer Cell Gene Expression Modulated from Plasma Membrane Integrin αvβ3 by Thyroid Hormone and Nanoparticulate Tetrac

Integrin αvβ3 is generously expressed by cancer cells and rapidly dividing endothelial cells. The principal ligands of the integrin are extracellular matrix proteins, but we have described a cell surface small molecule receptor on αvβ3 that specifically binds thyroid hormone and thyroid hormone analogs. From this receptor, thyroid hormone (l-thyroxine, T4; 3,5,3'-triiodo-l-thyronine, T3) and tetraiodothyroacetic acid (tetrac) regulate expression of specific genes by a mechanism that is initiated non-genomically. At the integrin, T4 and T3 at physiological concentrations are pro-angiogenic by multiple mechanisms that include gene expression, and T4 supports tumor cell proliferation. Tetrac blocks the transcriptional activities directed by T4 and T3 at αvβ3, but, independently of T4 and T3, tetrac modulates transcription of cancer cell genes that are important to cell survival pathways, control of the cell cycle, angiogenesis, apoptosis, cell export of chemotherapeutic agents, and repair of double-strand DNA breaks. We have covalently bound tetrac to a 200 nm biodegradable nanoparticle that prohibits cell entry of tetrac and limits its action to the hormone receptor on the extracellular domain of plasma membrane αvβ3. This reformulation has greater potency than unmodified tetrac at the integrin and affects a broader range of cancer-relevant genes. In addition to these actions on intra-cellular kinase-mediated regulation of gene expression, hormone analogs at αvβ3 have additional effects on intra-cellular protein-trafficking (cytosol compartment to nucleus), nucleoprotein phosphorylation, and generation of nuclear coactivator complexes that are relevant to traditional genomic actions of T3. Thus, previously unrecognized cell surface-initiated actions of thyroid hormone and tetrac formulations at αvβ3 offer opportunities to regulate angiogenesis and multiple aspects of cancer cell behavior.

Adjunctive input to the nuclear thyroid hormone receptor from the cell surface receptor for the hormone

At thyroid hormone response elements on specific genes, complexes of nuclear thyroid hormone receptors (TRs) and 3,5,3'-triiodo-L-thyronine (T(3)), coactivator or corepressor nucleoproteins, and histone acetylases or deacetylases mediate genomic effects of the hormone. Nongenomic effects of the hormone are those whose initiation does not primarily depend upon formation of the TR-T(3) complex. Among the nongenomic effects of thyroid hormone are a set of actions initiated at a cell surface receptor on integrin αvβ3 that are relevant to a) intracellular trafficking of proteins, including TRβ1, b) serine phosphorylation and acetylation of this nuclear receptor, c) assembly within the nucleus of complexes of coactivators and corepressor, and d) transcription of specific genes, including that for TRβ1. These actions initiated at αvβ3 are reviewed here and appear to be adjunctive to the genomic actions of the TR-T(3) complex.

Mechanisms of ceramide-induced COX-2-dependent apoptosis in human ovarian cancer OVCAR-3 cells partially overlapped with resveratrol

Ceramide is a member of the sphingolipid family of bioactive molecules demonstrated to have profound, diverse biological activities. Ceramide is a potential chemotherapeutic agent via the induction of apoptosis. Exposure to ceramide activates extracellular-signal-regulated kinases (ERK)1/2- and p38 kinase-dependent apoptosis in human ovarian cancer OVCAR-3 cells, concomitant with an increase in the expression of COX-2 and p53 phosphorylation. Blockade of cyclooxygenase-2 (COX-2) activity by siRNA or NS398 correspondingly inhibited ceramide-induced p53 Ser-15 phosphorylation and apoptosis; thus COX-2 appears at the apex of the p38 kinase-mediated signaling cascade induced by ceramide. Induction of apoptosis by ceramide or resveratrol was inhibited by the endocytosis inhibitor, cytochalasin D (CytD); however, cells exposed to resveratrol showed greater sensitivity than ceramide-treated cells. Ceramide-treated cells underwent a dose-dependent reduction in trans-membrane potential. Although both ceramide and resveratrol induced the expressions of caspase-3 and -7, the effect of inducible COX-2 was different in caspase-7 expression induced by ceramide compared to resveratrol. In summary, resveratrol and ceramide converge on an endocytosis-requiring, ERK1/2-dependent signal transduction pathway and induction of COX-expression as an essential molecular antecedent for subsequent p53-dependent apoptosis. In addition, expressions of caspase-3 and -7 are observed. However, a p38 kinase-dependent signal transduction pathway and change in mitochondrial potential are also involved in ceramide-induced apoptosis.

Identification of thyroid receptor ant/agonists in water sources using mass balance analysis and monte carlo simulation

Some synthetic chemicals, which have been shown to disrupt thyroid hormone (TH) function, have been detected in surface waters and people have the potential to be exposed through water-drinking. Here, the presence of thyroid-active chemicals and their toxic potential in drinking water sources in Yangtze River Delta were investigated by use of instrumental analysis combined with cell-based reporter gene assay. A novel approach was developed to use Monte Carlo simulation, for evaluation of the potential risks of measured concentrations of TH agonists and antagonists and to determine the major contributors to observed thyroid receptor (TR) antagonist potency. None of the extracts exhibited TR agonist potency, while 12 of 14 water samples exhibited TR antagonistic potency. The most probable observed antagonist equivalents ranged from 1.4 to 5.6 µg di-n-butyl phthalate (DNBP)/L, which posed potential risk in water sources. Based on Monte Carlo simulation related mass balance analysis, DNBP accounted for 64.4% for the entire observed antagonist toxic unit in water sources, while diisobutyl phthalate (DIBP), di-n-octyl phthalate (DNOP) and di-2-ethylhexyl phthalate (DEHP) also contributed. The most probable observed equivalent and most probable relative potency (REP) derived from Monte Carlo simulation is useful for potency comparison and responsible chemicals screening.