Thyroid Hormone Response Elements Research Articles

Conferring liver selectivity to a thyromimetic using a novel nanoparticle increases therapeutic efficacy in a diet-induced obesity animal model.

Optimization of metabolic regulation is a promising solution for many pathologies, including obesity, dyslipidemia, type 2 diabetes, and inflammatory liver disease. Synthetic thyroid hormone mimics-based regulation of metabolic balance in the liver showed promise but was hampered by the low biocompatibility and harmful effects on the extrahepatic axis. In this work, we show that specifically directing the thyromimetic to the liver utilizing a nanogel-based carrier substantially increased therapeutic efficacy in a diet-induced obesity mouse model, evidenced by the near-complete reversal of body weight gain, liver weight and inflammation, and cholesterol levels with no alteration in the thyroxine (T4) / thyroid stimulating hormone (TSH) axis. Mechanistically, the drug acts by binding to thyroid hormone receptor β (TRβ), a ligand-inducible transcription factor that interacts with thyroid hormone response elements and modulates target gene expression. The reverse cholesterol transport (RCT) pathway is specifically implicated in the observed therapeutic effect. Overall, the study demonstrates a unique approach to restoring metabolic regulation impacting obesity and related metabolic dysfunctions.

Thyroid hormones regulate Zfp423 expression in regionally distinct adipose depots through direct and cell-autonomous action.

The hypothalamic pituitary thyroid axis is a major regulator of many differentiation processes, including adipose tissue. However, it remains unclear whether and how thyroid hormone (TH) signaling contributes to preadipocyte commitment and differentiation into mature adipocytes. Here, we show a cell-autonomous effect of TH on the transcriptional regulation of zinc finger protein 423 (Zfp423), an early adipogenic determination factor, in murine adipose depots. Mechanistically, binding of the unliganded TH receptor to a negative TH responsive element within the Zfp423 promoter activates transcriptional activity that is reversed upon TH binding. Zfp423 upregulation is associated with increased GFP+ preadipocyte recruitment in stromal vascular fraction isolated from white fat of hypothyroid Zfp423GFP reporter mice. RNA sequencing identified Zfp423-driven gene programs that are modulated in response to TH during adipogenic differentiation. Collectively, we identified Zfp423 as a key molecule that integrates TH signaling into the regulation of adipose tissue plasticity.

Functional Definition of Thyroid Hormone Response Elements Based on a Synthetic STARR-seq Screen.

When bound to thyroid hormone, the nuclear receptor TRα1 activates the transcription of a number of genes in many cell types. It mainly acts by binding DNA as a heterodimer with retinoid X receptors at specific response elements related to the DR4 consensus sequence. However, the number of DR4-like elements in the genome exceed by far the number of occupied sites, indicating that minor variations in nucleotides composition deeply influence the DNA-binding capacity and transactivation activity of TRα1. An improved protocol of synthetic self-transcribing active regulatory region sequencing was used to quantitatively assess the transcriptional activity of thousands of synthetic sites in parallel. This functional screen highlights a strong correlation between the affinity of the heterodimers for DNA and their capacity to mediate the thyroid hormone response.

Sperm associated antigen 7 is activated by T3 during Xenopus tropicalis metamorphosis via a thyroid hormone response element within the first intron.

Thyroid hormone (T3) affects many diverse physiological processes such as metabolism, organogenesis, and growth. The two highly related frog species, diploid Xenopus tropicalis and pseudo tetraploid Xenopus laevis, have been used as models for analyzing the effects of T3 during vertebrate development. T3 regulates T3-inducible gene transcription through T3 receptor (TR)-binding to T3-response elements (TREs). We have previously identified sperm associated antigen 7 (spag7) as a candidate T3 target gene that is potentially involved in adult stem cell development and/or proliferation during intestinal metamorphosis. To investigate whether T3 regulates spag7 directly at the transcriptional level via TR, we first conducted qRT-PCR to analyze its expression during natural and T3-induced metamorphosis and found that spag7 was up-regulated during natural metamorphosis in the intestine, tail, brain and hindlimb, peaking at the climax of metamorphosis in all those organs, and upon T3 treatment of premetamorphic tadpoles. Next, we demonstrated that an intronic TRE in spag7, first identified through bioinformatic analysis, could bind to TR in vitro and in vivo during metamorphosis. A dual luciferase assay utilizing a reconstituted frog oocyte transcription system showed that the TRE could mediate promoter activation by liganded TR. These results indicate that spag7 expression is directly regulated by T3 through the TRE in the first intron during metamorphosis, implicating a role for spag7 early during T3-regulated tissue remodeling and resorption.

Identification of a Long Non-Coding RNA Derived From the Antisense Strand of the Thyroid Hormone Receptor Beta Gene

Background: Long non-coding RNAs (lncRNAs) have various functions. Here, we describe a novel lncRNA which is induced from the antisense strand of the thyroid hormone receptor beta (THRB) gene. Methods: We sequenced RNA from leukocytes and identified a novel lncRNA derived from the antisense strand of the THRB gene. The lncRNA was named THRB antisense RNA 2 (THRB-AS2). Transcriptional regulation by THRB-AS2 was assessed by reporter assays. The putative translation initiation codons of THRB-AS2 were mutated to assess potential THRB-AS2 protein function. Results: THRB-AS2 stimulated the activities of multiple promoters irrespective of thyroid hormone response elements. Thyroid hormone treatment did not affect the function of THRB-AS2. These data suggest that THRB-AS2 is a potential general transcriptional activator and has broad specificity on target genes. Mutations in putative translation initiation codons of THRB-AS2 did not affect function, suggesting that THRB-AS2 acts as an RNA molecule. Conclusions: Although a small number of lncRNAs derived from antisense strand of the THRB gene, such as THRB-AS1, has been already reported, their functions remain largely unknown. To our knowledge, this is the first report of the functions of a lncRNA derived from the antisense strand of the THRB gene.

MicroRNAs and thyroid hormone action

MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally repress gene expression by binding generally to the 3′-untranslated regions of their target mRNAs. miRNAs regulate a large fraction of the genome, playing a key role in most physiological and pathological processes. The thyroid hormones (T4 and T3) are major regulators of development, metabolism and cell growth. The thyroid hormones (THs) are synthetized in the thyroid gland and enter the cells through transporter proteins. In the cells, T4 and T3 are metabolized by deiodinase enzymes and bind to nuclear receptors (TRs), which have a higher affinity by T3. TRs act as hormone dependent transcription factors by binding to thyroid hormone response elements (TREs) in the target genes and recruiting transcriptional coregulators. There is increasing evidence that a variety of miRNAs target deiodinases and the receptor, thus regulating TH signaling is different tissues. In turn, the THs have been shown to modulate the expression of specific miRNAs and their mRNA targets in different cell types and organs. In many cases, the existence of TREs in the regulatory regions of these miRNAs has been identified, and the hormone bound receptors transcriptionally regulate expression of these molecules. Changes in the levels of miRNAs have been demonstrated to mediate some of the important actions of the THs in processes such as muscle and heart function, lipid liver metabolism or skin physiology. In addition, miRNA regulation is involved in the effects of TRs on cell proliferation and cancer.

T3 Critically Affects the Mhrt/Brg1 Axis to Regulate the Cardiac MHC Switch: Role of an Epigenetic Cross-Talk.

The LncRNA my-heart (Mhrt) and the chromatin remodeler Brg1 inhibit each other to respectively prevent or favor the maladaptive α-myosin-heavy-chain (Myh6) to β-myosin-heavy-chain (Myh7) switch, so their balance crucially guides the outcome of cardiac remodeling under stress conditions. Even though triiodothyronine (T3) has long been recognized as a critical regulator of the cardiac Myh isoform composition, its role as a modulator of the Mhrt/Brg1 axis is still unexplored. Here the effect of T3 on the Mhrt/Brg1 regulatory circuit has been analyzed in relation with chromatin remodeling and previously identified T3-dependent miRNAs. The expression levels of Mhrt, Brg1 and Myh6/Myh7 have been assessed in rat models of hyperthyroidism or acute myocardial ischemia/reperfusion (IR) treated with T3 replacement therapy. To gain mechanistic insights, in silico analyses and site-directed mutagenesis have been adopted in combination with gene reporter assays and loss or gain of function strategies in cultured cardiomyocytes. Our results indicate a pivotal role of Mhrt over-expression in the T3-dependent regulation of Myh switch. Mechanistically, T3 activates the Mhrt promoter at two putative thyroid hormone responsive elements (TRE) located in a crucial region that is necessary for both Mhrt activation and Brg1-dependent Mhrt repression. This newly identified T3 mode of action requires DNA chromatinization and is critically involved in mitigating the repressive function of the Brg1 protein on Mhrt promoter. In addition, T3 is also able to prevent the Brg1 over-expression observed in the post-IR setting through a pathway that might entail the T3-mediated up-regulation of miR-208a. Taken together, our data evidence a novel T3-responsive network of cross-talking epigenetic factors that dictates the cardiac Myh composition and could be of great translational relevance.

Thyroid hormones suppress FOXM1 expression to reduce liver cancer progression.

Thyroid hormones (TH) are multifunctional mediators that fine‑tune several physiological processes, including metabolic rate, digestive function and tissue development via interactions with type II nuclear thyroid hormone receptors (TR). Upon binding of TH, TRs interact specifically with thyroid hormone response elements of target gene promoter regions to regulate their transcription. Earlier studies suggested a correlation between aberrant TR regulation and hepatocellular carcinoma (HCC). THs are involved in a crosstalk between hepatoma and stromal cells, and disruption of TH signaling is associated with tumorigenesis. Previous cDNA microarray analysis of target gene expression following T3 treatment of wild‑type TR‑expressing hepatoma cells led to the identification of forkhead box M1 (FOXM1) as a factor negatively regulated by T3 and associated with poor prognosis in several cancer types. Increased FOXM1 expression during late stages of HCC was associated with poorer overall and recurrence‑free survival in patients with HCC. However, the specific mechanisms underlying FOXM1 activity in liver cancer progression remain to be elucidated. Experiments from the present study showed that TH/TR signaling suppresses FOXM1 mRNA and protein expression. Depletion of FOXM1 induced inhibition of the cell growth rate and a decline in oncogenic cyclin D1, cyclin E and CDK2 expression. Conversely, overexpression of FOXM1 enhanced cell proliferation and expression of oncogenic factors, which was decreased upon FOXM1 depletion. Re‑expression of FOXM1 partially rescued suppression of cell proliferation induced by T3. Collectively, the present findings suggest that TH/TR participates in HCC progression via modulation of FOXM1 expression.

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.

SAT-441 Transcriptome Analysis Under Differential Thyroid Hormone Treatment During Mouse Cerebellar Development

Background: Thyroid hormone (TH) plays essential roles in the development of the cerebellum by regulating transcription of target genes. TH binds to TH receptor (TR) located in the cell nucleus and stimulates transcription through TH response element (TRE). The expression of many genes is temporary and spatially regulated by TH during cerebellar development. However, the mode of transcription by TR may vary among target genes. In the liver, different duration of TH exposure resulted in distinct gene expression profiles. To examine the mechanisms of transcriptional regulation by TH in cerebellar development, gene expression profile induced by various TH exposure duration was studied. Methods: Anti-thyroid drug propylthiouracil (250 ppm in drinking water) was administered to C57BL/6J mice from the gestational day 14 to postnatal day (P) 7 to generate perinatal hypothyroid mice. To study the effect of continuous TH exposure, TH was subcutaneously administered to hypothyroid pups from P2 to P7 (6 days group). To study the effect of single TH administration, TH was injected on P7 and mice were sacrificed either 6 (6 hours group) or 24 hours (24 hours group) after injection. Cerebellar samples were collected to extract RNA and subject to microarray analysis. Microarray results were confirmed by RT-qPCR. Results: In microarray result, compared with mRNA levels of hypothyroid mice, 6 days group induced upregulation in 1007 genes and downregulation in 1009 genes, 6 hours group induced upregulation in 355 genes and downregulation in 977 genes, and 24 hours group induced upregulation in 365 genes and downregulation in 1121 genes. Only 7.6% of the genes were overlapped in three groups among positively regulated genes. In contrast, 57.2% of the genes were common in the negatively regulated genes. In RT-qPCR result, among genes known to harbor TRE, Hairless, Pcp2, and Nrgn, showed differential upregulation patterns. Hairless was upregulated in all groups, whereas Pcp2 was upregulated only in 5 days group and Nrgn was not upregulated in all groups. These results suggest that different mode of transcriptional regulation occurred in an exposure time-dependent manner of TH. Conclusion: We identified gene groups whose expression were modified by TH during cerebellar development. TH distinctively regulates transcription of target genes depending on the exposure schedule in mouse developing cerebellum.

Noncanonical Action of Thyroid Hormone Receptors α and β.

Thyroid hormone (TH) is essential for the regulation of many physiological processes, especially growth, organ development, energy metabolism and cardiovascular effects. TH acts via the TH receptors (TR) α and β. By binding to thyroid hormone responsive elements (TREs) on the DNA, TRs regulate expression of TH target genes. Thus, TRs are mainly characterized as ligand dependent transcription factors and regulation of gene expression and protein synthesis is considered the canonical mode of TH/TR action. The demonstration that the ligand-bound TRs α and β also mediate activation of the phosphatidylinositol-3-kinase (PI3K) pathway established noncanonical TH/TR action as an additional mode of TH signaling. Recently, TR mutant mouse models allowed to determine the underlying mode of TH/TR action, either canonical or noncanonical TH/TR signaling, for several physiological TH effects in vivo: Regulation of the hypothalamic-pituitary-thyroid axis requires DNA-binding of TRβ, whereas hepatic triglyceride content appears to be regulated by noncanonical TRβ signaling. TRα mediated effects in bone development are dependent on DNA-binding, whereas several cardiovascular TRα effects are rapid and independent from DNA-binding. Therefore, noncanonical TH/TR action contributes to the overall effects of TH in physiology.

TRIIODOTHYRONINE ACTIVATES GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE 3 VIA AGGTCA-LIKE-DIRECT-REPEAT-4 TYPE THYROID HORMONE RESPONSE ELEMENT.

Thyroid hormone participates in lipid metabolism regulation. However, the effects on triacyleride or triacylglycerol metabolism are complex and not fully clarified yet. In this study, we try to identify novel thyroid hormone-targeting lipogenic metabolic genes and analyze their molecular regulative mechanism. Thirty-five promoters of twenty-nine human lipogenic regulative enzyme genes were constructed into pXP1 luciferase reporter plasmid (PFK2/FBP2-luc) and transfected into HeGP2 cells, respectively. Gene expression induced by triiodothyronine (T3) was detected by luciferase assay. The T3-activated gene promoter was then analyzed by sequence analysis, deletion and mutation, and electrophoretic mobility shift assay (EMSA). After 10 nM T3 stimulation for 36 h, phosphogluconate dehydrogenase, malic enzyme, Glycerol-3-phosphate acyltransferase (GPAT) 3, and 1-acylglycerol-3-phosphate O-acyltransferase (AGPAT) 2 were significantly activated, respectively. A AGGTCA-like-direct-repeat-4 consensus thyroid hormone response element (DR4-TRE)-like sequence was found in the GPAT3 promoter, which was then verified to be necessary for T3-induced GPAT3 activation by gene deletion and mutation analysis. EMSA further identified that T3-thyroid receptor (TR) α-retinoid-X receptor (RXR) complex directly bound on the GPAT3 promoter. Triiodothyronine could activate the GPAT3 through DR4-TRE-like sequence binding to participate in lipogenic regulation. AGPAT2 may be another thyroid hormone target enzyme.

The Thyroid Hormone Receptor-RUNX2 Axis: A Novel Tumor Suppressive Pathway in Breast Cancer.

Metastatic breast cancer is refractory to conventional therapies and isan end-stage disease. RUNX2 is a transcription factor that becomes oncogenic when aberrantly expressed in multiple tumor types, including breast cancer, supporting tumor progression and metastases. Our previous work demonstrated that the thyroid hormone receptor beta (TRβ) inhibits RUNX2 expression and tumorigenic characteristics in thyroid cells. As TRβ is a tumor suppressor, we investigated the compelling question whether TRβ also regulates RUNX2 in breast cancer. The Cancer Genome Atlas indicates that TRβ expression is decreased in the most aggressive basal-like subtype of breast cancer. We established that modulated levels of TRβ results in corresponding changes in the high levels of RUNX2 expression in metastatic, basal-like breast cells. The MDA-MB-231 triple-negative breast cancer cell line exhibits low expression of TRβ and high levels of RUNX2. Increased expression of TRβ decreased RUNX2 levels. The thyroid hormone-mediated suppression of RUNX2 is TRβ specific as TRα overexpression failed to alter RUNX2 expression. Consistent with these findings, knockdown of TRβ in non-tumor MCF10A mammary epithelial-like cells results in an increase in RUNX2 and RUNX2 target genes. Mechanistically, TRβ directly interacts with the proximal promoter of RUNX2 through a thyroid hormone response element to reduce promoter activity. The TRβ suppression of the oncogene RUNX2 is a signaling pathway shared by thyroid and breast cancers. Our findings provide a novel mechanism for TRβ-mediated tumor suppression in breast cancers. This pathway may be common to many solid tumors and impact treatment for metastatic cancers.

The In Vitro Functional Impairment of Thyroid Hormone Receptor Alpha 1 Isoform Mutants Is Mainly Dictated by Reduced Ligand Sensitivity.

Background: Thyroid hormone (TH) acts on TH receptors (TRs) and regulates gene transcription by binding of TRs to TH response elements (TREs) in target gene promoters. The transcriptional activity of TRs is modulated by interactions with TR-coregulatory proteins. Mutations in TRα cause resistance to thyroid hormone alpha (RTHα). In this study, we analyzed if, beyond reduced triiodothyronine (T3) affinity, altered interactions with cofactors or different TREs could account for the differential impaired transcriptional activity of different mutants. Methods: We evaluated four mutants derived from patients (D211G, M256T, A263S, and R384H) and three artificial mutants at equivalent positions in patients with RTHβ (T223A, L287V, and P398H). The in vitro transcriptional activity was evaluated on TRE-luciferase reporters (DR4, IR0, and ER6). The affinity for T3 and interaction with coregulatory proteins (nuclear receptor corepressor 1 [NCoR1] and steroid receptor coactivator 1 [SRC1]) were also determined. Results: We found that the affinity for T3 was significantly reduced for all mutants, except for TRα1-T223A. The reduction in the T3 sensitivity of the transcriptional activity on three TREs, the dissociation of the corepressor NCoR1, and the association of the coactivator SRC1 recruitment for each mutant correlated with the reduced affinity for T3. We did not observe mutation-specific alterations in interactions with cofactors or TREs. Conclusions: In summary, the degree of impaired transcriptional activity of mutants is mainly determined by their reduced affinity for T3.

Molecular Functions of Thyroid Hormone Signaling in Regulation of Cancer Progression and Anti-Apoptosis.

Several physiological processes, including cellular growth, embryonic development, differentiation, metabolism and proliferation, are modulated by genomic and nongenomic actions of thyroid hormones (TH). Several intracellular and extracellular candidate proteins are regulated by THs. 3,3,5-Triiodo-L-thyronine (T3) can interact with nuclear thyroid hormone receptors (TR) to modulate transcriptional activities via thyroid hormone response elements (TRE) in the regulatory regions of target genes or bind receptor molecules showing no structural homology to TRs, such as the cell surface receptor site on integrin αvβ3. Additionally, L-thyroxine (T4) binding to integrin αvβ3 is reported to induce gene expression through initiating non-genomic actions, further influencing angiogenesis and cell proliferation. Notably, thyroid hormones not only regulate the physiological processes of normal cells but also stimulate cancer cell proliferation via dysregulation of molecular and signaling pathways. Clinical hypothyroidism is associated with delayed cancer growth. Conversely, hyperthyroidism is correlated with cancer prevalence in various tumor types, including breast, thyroid, lung, brain, liver and colorectal cancer. In specific types of cancer, both nuclear thyroid hormone receptor isoforms and those on the extracellular domain of integrin αvβ3 are high risk factors and considered potential therapeutic targets. In addition, thyroid hormone analogs showing substantial thyromimetic activity, including triiodothyroacetic acid (Triac), an acetic acid metabolite of T3, and tetraiodothyroacetic acid (Tetrac), a derivative of T4, have been shown to reduce risk of cancer progression, enhance therapeutic effects and suppress cancer recurrence. Here, we have reviewed recent studies focusing on the roles of THs and TRs in five cancer types and further discussed the potential therapeutic applications and underlying molecular mechanisms of THs.

OR10-1 Regulation of Glucocorticoid Metabolism: A Novel Function for Thyroid Hormones?

Glucocorticoid hormone metabolism and action are regulated by the 11-beta hydroxysteroid dehydrogenase (11βHSD) isozymes: the 11βHSD2, mostly expressed in the distal nephron, converts cortisol [F] into cortisone [E] in humans or corticosterone [B] into 11-dehydrocorticosterone [A] in rodents (11-dehydro derivatives being inactive compounds), and the 11βHSD1, ubiquitously expressed but abundant in the liver, catalyzes the opposite reaction. Under pathophysiological conditions of severe hypothyroidism, altered glucocorticoid metabolism has been observed, with decreased [F] to [E] conversion1,2. However, direct functional relationship between these two hormonal pathways has never been demonstrated to date. Using bioinformatics analyses, we identified five thyroid hormone response elements in the promoter region of the murine hsd11b2 gene. Therefore, we aimed at investigating whether thyroid hormones (T3) directly regulate expression and/or activity of the 11βHSD2 enzyme. We used three complementary models: human and mouse translational studies and molecular analyses in HEK293T cells and in fully differentiated KC3AC1 cortical collecting duct cells. Children and adults in hypo- or hyperthyroidism status were first compared either to age- and sex-matched euthyroid controls, or to themselves after reaching a euthyroid status. The urinary [E]/[F] ratio measured by LC-MS/MS method, was used as an index of renal 11βHSD2 activity. Interestingly, a 60% decrease in the [E]/[F] ratio was observed in hypothyroid patients, corroborating our hypothesis (p<0.05). Next, a mouse model of hyperthyroidism, generated by administrating T3 in drinking water, led to a significant 10% increase in renal 11βHSD2 mRNA and protein levels compared to wild type mice (n=10, p<0.05). Furthermore, we demonstrated in HEK293T cells that T3 transactivates the mouse hsd11b2 promoter cloned upstream the luciferase reporter gene via the Thyroid Receptor α1(TRα1). Finally, we showed that T3 exposure induces a 50% increase in 11βHSD2 mRNA levels in KC3AC1 cells, in a dose-dependent and time-dependent manner (as early as 6 h) (p<0.01). This induction was abrogated by Actinomycin D or DRB, two inhibitors of transcription, underlining a transcriptional regulatory mechanism. In addition, 11βHSD2 enzymatic activity, quantified by the [F] to [E] conversion ratio measured by LC-MS/MS in cell supernatants, increased significantly by 20% (p<0.05) after 24 h exposure to 100 nM T3. ChIP experiments further demonstrated a T3-dependent specific recruitment of the TRα1 onto the hsd11b2 promoter region. Altogether, our findings constitute the first demonstration that thyroid hormones directly regulate expression and activity of the renal 11βHSD2 enzyme, thereby controlling glucocorticoid metabolism and action.

VITAMIN A, RETINOIC ACID AND TAMIBAROTENE, A FRONT TOWARD ITS ADVANCES: A REVIEW

Vitamin A and its derivative retinoic acid (13-cis RA, 9-cis RA, all-trans RA) and recent tamibarotene have been shown a broad variety of biological actives in human, such as vision, embryonic development, cell growth and cellular differentiation and immune function. These precise functions of RA are mediated by their retinoic acid receptors (RARs). In the past five decades, retinoic acid (RA) proved therapeutic benefits in cancer prevention, in skin diseases and in acute promyelocytic leukemia (APL).The elucidation of the molecular basis of vitamin A acid and its retinoid pharmacology in APL has been illustrated in several publications, the detail molecular model of gene regulation had also been proposed by Zhu in earlier 90s. A molecular model is further revised. As an approach to APL treatment, one possible the action of retinoic acid (RA), A consensus sequence (TCAGGTCA motif ) has been postulated for thyroid hormone (TRE) and retinoic acid responsive element (RARE)-containing in the promoter region of target genes. High dose of RA-RARE-PML/RARa complexes in intracellular localization appears to relieve repressors from DNA-bound receptor, including the dissociation of co-re pressor complexes N-CoR, SMRT and HDACs from PML-RARa or PML-RARa/RXR. Also release PML/RARa -mediated transcription repression. This transcriptional derepression occurs at RARa target gene promoter. Consequentially, PML-RARa chimera converted receptor from a repressor to a RA-dependent activator of transcription. The resulting pml-RARA oncoprotein proteolytic degradation occurs through the autophagy-lysosome pathway and the ubiquitin SUMO-proteasome system(UPS) as well as caspase 3, or lysosomal protease (cathepsin D) enzyme or/and EI-like ubiquitin-activating enzyme(UBEIL) induction. Accordingly the expression level of PML-RARa downregulated. PML protein relocalizes into the wild-type nuclear body (PML-NB) configuration or a truncated PML-RARa fusion fragment detected or/and the wild-type RAR upregulated. An effect is to relieve the blockade of pml/RARa-mediated RA dependent promyelocytic differentiation, and retinoic acid (9-cid RA,ATRA, Am80) in APL therapy. Here, oncogenic pml/RARa as constitutive transcriptional repressor that block myeloid differentiation at promyelocytic phenotype. RA can overcome the transcrptional repressor activity of pml/RARa. The oncogenic pml/RARa uncovers a pathogenic role in leukemogenesis of APL through blocking promyelocytic differentiation. This oncogenic receptor derivative pml/ RARa chimera is locked in their "off" regular mode thereby constitutively repressing transcription of target genes or key enzymes (such as AP-1, PTEN, DAPK2,UP.1, p21WAF/CCKN1A）that are critical for differentiation of hematopoietic cells. This is first described in eukaryotes.

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.

Does thyrotoxic periodic paralysis have a genetic predisposition? A case report.

Thyrotoxic periodic paralysis is a rare complication of hyperthyroidism where increased influx of potassium into skeletal muscle cells leads to profound hypokalaemia and paralysis. Most cases arise sporadically in Asians; however, it is being increasingly reported in Caucasians. It is regarded as a channelopathy where a genetic and/or acquired defect in the sodium-potassium (Na/K-ATPase) pump renders it more sensitive to excess thyroid hormone in susceptible individuals. Because the clinical presentation is similar to familial hypokalaemic periodic paralysis, genes implicated in this autosomal-dominant condition became candidates for thyrotoxic periodic paralysis, particularly if they were known to have thyroid hormone-responsive elements. These include the voltage-gated calcium (CACNA1S) and sodium (SCN4A) channel genes, KCNJ18 which encodes the inwardly rectifying potassium channel Kir2.6, and subunits of the Na/K-ATPase genes. Although no single pathogenetic mutation has been identified in thyrotoxic periodic paralysis, several single-nucleotide polymorphisms in these genes have been associated with it. We describe a 27-year-old Caucasian Irish male who presented with acute onset limb paralysis and severe hypokalaemia. He was diagnosed as having thyrotoxic periodic paralysis secondary to Graves' disease based on clinical presentation, biochemical findings and rapid response to intravenous potassium. Genetic analysis identified heterozygous variants in three candidate genes: KCNJ18 (c.576G>C), SCN4A (c.2341G>A) and CACNA1S (c.1817G>A). Since these variants are not disease causing and occur at high prevalences of 50%, 2-3% and 1%, respectively, in the normal population, they do not explain the clinical phenotype in our patient suggesting that acquired environmental triggers or as-yet unidentified gene mutations remain as leading pathogenetic co-factors in thyrotoxic periodic paralysis.

Abstract 5206: The biological significance of CCL 16 regulated by thyroid hormone in liver cancer cells

Abstract Thyroid hormones(THs) are multi-function mediators that modulate various physiological processes. Thyroid hormone receptors(TRs) are type II nuclear receptors, TRs binds to thyroid hormone response elements (TREs) of target promoter regions modulates target gene expression at the transcriptional level upon THs binding. Previous literatures illustrate an association between aberrant TR regulation and human hepatocellular carcinoma (HCC). We employed cDNA microarrays and SILAC secretome analysis to identify the T3-regulated secreted proteins after T3 treatment in TR-expressing hepatoma cell lines, Chemokine (C-C motif) ligand 16 (CCL16) expression is positively regulated by T3 treatment. The patients with higher expression of CCL16 have poor recurrence survival rate. Ectopic expression of CCL16 in HCC cell lines increased tumor growth rate in vivo but not in vitro. CCL16 induced chemotaxis of monocytes and macrophages via interacting with its receptors CCR1 and CCR5. Expression of proangiogenic genes in macrophages were increased while co-cultured with HCC cell lines. The motility of HUVECs were increased after treated with conditional medium of macrophages co-cultured with HCC cell lines. Our study revealed that CCL16 recruited macrophage and promoted tumor progression. Citation Format: Cheng-Heng Wu, Kwang-Huei Lin. The biological significance of CCL 16 regulated by thyroid hormone in liver cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5206.