Thyroid hormone-mediated activation of the ERK/dual specificity phosphatase 1 pathway augments the apoptosis of GH4C1 cells by down-regulating nuclear factor-kappaB activity

Lack of canonical thyroid hormone receptor α signaling changes regulatory T cell phenotype in female mice

The immune system has emerged as an important target of thyroid hormones (THs); however, the role of TH in T cells has so far remained elusive. In this study, we assessed the effect of TH receptor α (TRα) signaling on activation and function of T cells. Our findings show that lack of canonical TRα action not only increased the frequency of regulatory T cells (Treg) but propelled an activated and migratory Treg phenotype and nuclear factor κB (NF-κB) activation in Treg. Conversely, canonical TRα action reduced activation of the NF-κB pathway previously shown to play a pivotal role in Treg differentiation and function. Taken together, our findings demonstrate that TRα impacts T cell differentiation and phenotype. Given the well-known interaction of inflammation, immune responses, and TH axis in e.g., severe illness, altered TH-TRα signaling may have an important role in regulating T cell responses during disease.

Transcriptomic Analysis Reveals That Excessive Thyroid Hormone Signaling Impairs Phototransduction and Mitochondrial Bioenergetics and Induces Cellular Stress in Mouse Cone Photoreceptors

Thyroid hormone (TH) plays an essential role in cell proliferation, differentiation, and metabolism. Experimental and clinical studies have shown a potential association between TH signaling and retinal degeneration. The suppression of TH signaling protects cone photoreceptors in mouse models of retinal degeneration, whereas excessive TH signaling induces cone degeneration, manifested as reduced light response and a loss of cones. This work investigates the genes/transcriptomic alterations that might be involved in TH-induced cone degeneration in mice using single-cell RNA sequencing (scRNAseq) analysis. One-month-old C57BL/6 mice received triiodothyronine (T3, 20 µg/mL in drinking water) for 4 weeks as a model of hyperthyroidism/excessive TH signaling. At the end of the experiments, retinal cells were dissociated, and cell viability was analyzed before being subjected to scRNAseq. The resulting data were analyzed using the Seurat package and visualized using the Loupe browser. Among 155,866 single cells, we identified 14 cell clusters, representing various retinal cell types, with rod and cone clusters comprising 76% and 4.1% of the total cell population, respectively. Cone cluster transcriptomes demonstrated the most alterations after the T3 treatment, with 450 differentially expressed genes (DEGs), accounting for 38.5% of the total DEGs. Statistically significant changes in the expression of genes in the cone cluster revealed that phototransduction and oxidative phosphorylation were impaired after the T3 treatment, along with mitochondrial dysfunction. A pathway analysis also showed the activation of the sensory neuronal/photoreceptor stress pathways after the T3 treatment. Specifically, the eukaryotic initiation factor-2 signaling pathway and the cAMP response element-binding protein signaling pathway were upregulated. Thus, excessive TH signaling substantially affects cones at the transcriptomic level. The findings from this work provide an insight into how excessive TH signaling induces cone degeneration.

Protein kinase D activity is a risk biomarker in prostate cancer that drives cell invasion by a Snail/ERK dependent mechanism

Protein kinase D (PKD) family members play controversial roles in prostate cancer (PC). Thus, PKD1 is nearly absent in advanced tumours, where PKD2 and PKD3 are upregulated. Additionally, consequences of activation of these kinases on PC progression remain largely unclear. Here, we first investigated PKD function on PC cell motility, analysing the underlying molecular mechanisms. We find a striking decrease of Snail levels after PKD inhibition followed by cell migration and invasion impairment, demonstrating an unprecedented role of PKD activity on the regulation of this key transcription factor in PC progression. Specifically, we show that PKD2 activity mediates the effects of MEK/ERK pathway on Snail expression, establishing a joint function of ERK/PKD2/Snail cascade in PC cell invasion regulation. These results led us to address the clinical relevance of the correlation between PKD2 and ERK activities with Snail abundance in samples from PC patients at different stages, analysing its impact on tumour prognosis and patients´ survival. Importantly, this is the first study defining a direct correlation between active PKD2 and Snail levels, further linked to ERK activity. We also evidence that PKD2 activity is associated with important poor prognostic factors. Thus, PC patients with the expression pattern: active PKD2high/active ERKhigh/Snailhigh exhibit increased invasiveness and metastasis, and decreased survival. Our findings provide new insights for understanding the molecular mechanisms involved in PC progression, pinpointing the combination of active PKD2 and Snail levels, with the additional measurement of active ERK, as a confident biomarker to predict clinical outcome of patients with advanced PC.

Excessive Thyroid Hormone Signaling Induces Photoreceptor Degeneration in Mice

Rod and cone photoreceptors degenerate in inherited and age-related retinal degenerative diseases, ultimately leading to loss of vision. Thyroid hormone (TH) signaling regulates cell proliferation, differentiation, and metabolism. Recent studies have shown a link between TH signaling and retinal degeneration. This work investigates the effects of excessive TH signaling on photoreceptor function and survival in mice. C57BL/6, Thra1 -/-, Thrb2 -/-, Thrb -/-, and the cone dominant Nrl -/- mice received triiodothyronine (T3) treatment (5-20 μg/ml in drinking water) for 30 d, followed by evaluations of retinal function, photoreceptor survival/death, and retinal stress/damage. Treatment with T3 reduced light responses of rods and cones by 50-60%, compared with untreated controls. Outer nuclear layer thickness and cone density were reduced by ∼18% and 75%, respectively, after T3 treatment. Retinal sections prepared from T3-treated mice showed significantly increased numbers of TUNEL-positive, p-γH2AX-positive, and 8-OHdG-positive cells, and activation of Müller glial cells. Gene expression analysis revealed upregulation of the genes involved in oxidative stress, necroptosis, and inflammation after T3 treatment. Deletion of Thra1 prevented T3-induced degeneration of rods but not cones, whereas deletion of Thrb2 preserved both rods and cones. Treatment with an antioxidant partially preserved photoreceptors and reduced retinal stress responses. This study demonstrates that excessive TH signaling induces oxidative stress/damage and necroptosis, induces photoreceptor degeneration, and impairs retinal function. The findings provide insights into the role of TH signaling in retinal degeneration and support the view of targeting TH signaling for photoreceptor protection.

Metformin alleviates the dysregulated testicular steroidogenesis and spermatogenesis induced by carbimazole in levothyroxine-primed rats

Most of the published experiments about carbimazole (CMZ)-induced testicular injury are constructed in normal healthy animals, which lakes the translational identification. Despite metformin (MET) having advantageous effects on injured testicles, its impact on thyroid function is arguable. In the current levothyroxine (LT4)/CMZ model, Wistar rats were primed by LT4 for sixty days. CMZ was then given individually or simultaneously with different doses of MET, 100, 200, and 400 mg, daily for thirty days. Serum was assessed for thyroid profile panel, sex hormones, and gonadotropin levels. Testicular tissues were examined for steroidogenesis, spermatogenesis, inflammation, and apoptosis. Histopathology of thyroid and testes were examined, besides thyroidal nuclear factor (NF)-kB expression. MET in a dose-response manner improved the LT4/CMZ-induced testicular toxicity by increasing the steroidogenic acute regulatory protein (StAR), and 17-β-hydroxysteroid dehydrogenase (17βHSD) activities, the proliferating cell nuclear antigen (PCNA), sperm count and motility, sex hormones, and gonadotropin levels. MET-400 mg markedly decreased the elevated NF-kB expressions, tumour necrosis factor (TNF)-α, caspase-3, and BAX, and increased BCL-2. LT4/CMZ could be used as translational animal modelling. MET displayed a dose-dependent ameliorative effect on the LT4/CMZ model without significant harmful effects on thyroid functions. MET-testicular protective roles in diabetics with thyroidal diseases should be explored.

Thyroid hormones act as modulators of inflammation through their nuclear receptors

Reciprocal crosstalk between endocrine and immune systems has been well-documented both in physiological and pathological conditions, although the connection between the immune system and thyroid hormones (THs) remains largely unclear. Inflammation and infection are two important processes modulated by the immune system, which have profound effects on both central and peripheral THs metabolism. Conversely, optimal levels of THs are necessary for the maintenance of immune function and response. Although some effects of THs are mediated by their binding to cell membrane integrin receptors, triggering a non-genomic response, most of the actions of these hormones involve their binding to specific nuclear thyroid receptors (TRs), which generate a genomic response by modulating the activity of a great variety of transcription factors. In this special review on THs role in health and disease, we highlight the relevance of these hormones in the molecular mechanisms linked to inflammation upon their binding to specific nuclear receptors. In particular, we focus on THs effects on different signaling pathways involved in the inflammation associated with various infectious and/or pathological processes, emphasizing those mediated by NF-kB, p38MAPK and JAK/STAT. The findings showed in this review suggest new opportunities to improve current therapeutic strategies for the treatment of inflammation associated with several infections and/or diseases, such as cancer, sepsis or Covid-19 infection.

Downregulation of Snail by DUSP1 Impairs Cell Migration and Invasion through the Inactivation of JNK and ERK and Is Useful as a Predictive Factor in the Prognosis of Prostate Cancer

Dual specificity phosphatase 1 (DUSP1) is crucial in prostate cancer (PC), since its expression is downregulated in advanced carcinomas. Here, we investigated DUSP1 effects on the expression of mesenchymal marker Snail, cell migration and invasion, analyzing the underlying mechanisms mediated by mitogen-activated protein kinases (MAPKs) inhibition. To this purpose, we used different PC cells overexpressing or lacking DUSP1 or incubated with MAPKs inhibitors. Moreover, we addressed the correlation of DUSP1 expression with Snail and activated MAPKs levels in samples from patients diagnosed with benign hyperplasia or prostate carcinoma, studying its implication in tumor prognosis and survival. We found that DUSP1 downregulates Snail expression and impairs migration and invasion in PC cells. Similar results were obtained following the inhibition of c-Jun N-terminal kinase (JNK) and extracellular-signal-regulated kinase (ERK). In clinical samples, we evidenced an inverse correlation between DUSP1 expression and Snail levels, which are further associated with JNK and ERK activation. Consequently, the pattern DUSP1_high/activated JNK_low/activated ERK_low/Snail_low is associated with an overall extended survival of PC patients. In summary, the ratio between DUSP1 and Snail expression, with additional JNK and ERK activity measurement, may serve as a potential biomarker to predict the clinical outcome of PC patients. Furthermore, DUSP1 induction or inhibition of JNK and ERK pathways could be useful to treat PC.

Resveratrol promotes apoptosis through the induction of dual specificity phosphatase 1 and sensitizes prostate cancer cells to cisplatin

Resveratrol is a polyphenol with chemopreventive properties against prostate cancer; however, the mechanisms underlying its actions are not completely understood. Previously, we demonstrated that DUSP1 induces apoptosis in prostate cancer cells; therefore in the present study we investigated the role of this phosphatase on resveratrol effects. Moreover, we analysed the efficiency of combined treatment of resveratrol and the chemotherapeutic drug cisplatin on cellular viability and apoptosis and its relation with DUSP1 in prostate cancer cells. We found that resveratrol up-regulates DUSP1 expression in androgen-independent prostate cancer cells, which in turn, is involved in the inhibition of the NF-κB pathway and Cox-2 expression. This phosphatase is required for the induction of apoptosis achieved by resveratrol, but does not regulate the effects of this compound on cell cycle. Furthermore, we show that resveratrol cooperates with cisplatin both in the up-regulation of DUSP1 levels and in the promotion of apoptosis, suggesting that DUSP1 is a major determinant of cisplatin sensitivity to apoptosis. These results reveal a novel molecular mechanism by which resveratrol induces apoptosis in prostate cancer cells, and highlight the importance of DUSP1 in future therapeutic approaches based in the use of this polyphenol and cisplatin.

Inhibition of thyroid hormone receptor locally in the retina is a therapeutic strategy for retinal degeneration

Thyroid hormone (TH) signaling regulates cell proliferation, differentiation, and metabolism. Recent studies have implicated TH signaling in cone photoreceptor viability. Using mouse models of retinal degeneration, we demonstrated that antithyroid drug treatment and targeting iodothyronine deiodinases (DIOs) to suppress cellular tri-iodothyronine (T3) production or increase T3 degradation preserves cones. In this work, we investigated the effectiveness of inhibition of the TH receptor (TR). Two genes, THRA and THRB, encode TRs; THRB2 has been associated with cone viability. Using TR antagonists and Thrb2 deletion, we examined the effects of TR inhibition. Systemic and ocular treatment with the TR antagonists NH-3 and 1-850 increased cone density by 30-40% in the Rpe65-/- mouse model of Leber congenital amaurosis and reduced the number of TUNEL+ cells. Cone survival was significantly improved in Rpe65-/- and Cpfl1 (a model of achromatopsia with Pde6c defect) mice with Thrb2 deletion. Ventral cone density in Cpfl1/Thrb2-/- and Rpe65-/- /Thrb2-/- mice was increased by 1- to 4-fold, compared with age-matched controls. Moreover, the expression levels of TR were significantly higher in the cone-degeneration retinas, suggesting locally elevated TR signaling. This work shows that the effects of antithyroid treatment or targeting DIOs were likely mediated by TRs and that suppressing TR protects cones. Our findings support the view that inhibition of TR locally in the retina is a therapeutic strategy for retinal degeneration management.-Ma, H., Yang, F., Butler, M. R., Belcher, J., Redmond, T. M., Placzek, A. T., Scanlan, T. S., Ding, X.-Q. Inhibition of thyroid hormone receptor locally in the retina is a therapeutic strategy for retinal degeneration.

Thyroid states regulate subcellular glucose phosphorylation activity in male mice

The thyroid hormones (THs), triiodothyronine (T₃) and thyroxine (T₄), are very important in organism metabolism and regulate glucose utilization. Hexokinase (HK) is responsible for the first step of glycolysis, catalyzing the conversion of glucose to glucose 6-phosphate. HK has been found in different cellular compartments, and new functions have been attributed to this enzyme. The effects of hyperthyroidism on subcellular glucose phosphorylation in mouse tissues were examined. Tissues were removed, subcellular fractions were isolated from eu- and hyperthyroid (T₃, 0.25 µg/g, i.p. during 21 days) mice and HK activity was assayed. Glucose phosphorylation was increased in the particulate fraction in soleus (312.4% ± 67.1, n = 10), gastrocnemius (369.2% ± 112.4, n = 10) and heart (142.2% ± 13.6, n = 10) muscle in the hyperthyroid group compared to the control group. Hexokinase activity was not affected in brain or liver. No relevant changes were observed in HK activity in the soluble fraction for all tissues investigated. Acute T₃ administration (single dose of T₃, 1.25 µg/g, i.p.) did not modulate HK activity. Interestingly, HK mRNA levels remained unchanged and HK bound to mitochondria was increased by T₃ treatment, suggesting a posttranscriptional mechanism. Analysis of the AKT pathway showed a 2.5-fold increase in AKT and GSK3B phosphorylation in the gastrocnemius muscle in the hyperthyroid group compared to the euthyroid group. Taken together, we show for the first time that THs modulate HK activity specifically in particulate fractions and that this action seems to be under the control of the AKT and GSK3B pathways.

The ligand-bound thyroid hormone receptor in macrophages ameliorates kidney injury via inhibition of nuclear factor-κB activities

In chronic kidney disease (CKD) patients, inflammation plays a pivotal role in the progression of renal fibrosis. Hypothyroidism is associated with an increased occurrence of atherosclerosis and inflammation, suggesting protective roles of thyroid hormones and their receptors against inflammatory processes. The contribution of thyroid hormone receptors to macrophage differentiation has not been well documented. Here, we focused on the endogenous thyroid hormone receptor α (TRα) in macrophages and examined the role of ligand-bound TRα in macrophage polarization-mediated anti-inflammatory effects. TRα-deficient irradiated chimeric mice showed exacerbated tubulointerstitial injury in a unilateral ureteral obstruction model. Compared with wild-type macrophages, macrophages isolated from the obstructed kidneys of mice lacking TRα displayed increased expression of proinflammatory cytokines that was accompanied by enhanced nuclear translocation of p65. Comparison of TRα-deficient bone marrow-derived macrophages with wild-type macrophages confirmed the propensity of the former cells to produce excessive IL-1β levels. Co-culture of these macrophages with renal epithelial cells induced more severe damage to the epithelial cells via the IL-1 receptor. Our findings indicate that ligand-bound TRα on macrophages plays a protective role in kidney inflammation through the inhibition of NF-κB pathways, possibly by affecting the pro- and anti-inflammatory balance that controls the development of CKD.

The Thyroid Hormone Receptors Inhibit Hepatic Interleukin-6 Signaling During Endotoxemia

Decreased thyroidal hormone production is found during lipopolysaccharide (LPS)-induced endotoxic shock in animals as well as in critically ill patients. Here we studied the role of the thyroid hormone receptors (TRs) in activation of STAT3, NF-κB and ERK, which play a key role in the response to inflammatory cytokines during sepsis. TR knockout mice showed down-regulation of hepatic inflammatory mediators, including interleukin 6 (IL-6) in response to LPS. Paradoxically, STAT3 and ERK activity were higher, suggesting that TRs could act as endogenous repressors of these pathways. Furthermore, hyperthyroidism increased cytokine production and mortality in response to LPS, despite decreasing hepatic STAT3 and ERK activity. This suggested that TRs could directly repress the response of the cells to inflammatory mediators. Indeed, we found that the thyroid hormone T3 suppresses IL-6 signalling in macrophages and hepatocarcinoma cells, inhibiting STAT3 activation. Consequently, the hormone strongly antagonizes IL-6-stimulated gene transcription, reducing STAT3 recruitment and histone acetylation at IL-6 target promoters. In conclusion, TRs are potent regulators of inflammatory responses and immune homeostasis during sepsis. Reduced responses to IL-6 should serve as a negative feedback mechanism for preventing deleterious effects of excessive hormone signaling during infections.

Thyroid Hormone Signaling and Cone Photoreceptor Viability

Thyroid hormone (TH) signaling regulates cell proliferation, differentiation, and apoptosis. In the retina, TH signaling plays a central role in cone opsin expression. TH signaling inhibits S opsin expression, stimulates M opsin expression, and promotes dorsal-ventral opsin patterning. TH signaling has also been associated with cone photoreceptor viability. Treatment with thyroid hormone triiodothyronine (T3) or induction of high T3 by deleting the hormone-inactivating enzyme type 3 iodothyronine deiodinase (DIO3) causes cone death in mice. This effect is reversed by deletion of the TH receptor (TR) gene. Consistent with the T3 treatment effect, suppressing TH signaling preserves cones in mouse models of retinal degeneration. The regulation of cone survival by TH signaling appears to be independent of its regulatory role in cone opsin expression. The mechanism by which TH signaling regulates cone viability remains to be identified. The current understanding of TH signaling regulation in photoreceptor viability suggests that suppressing TH signaling locally in the retina may represent a novel strategy for retinal degeneration management.

Essential Role of GATA2 in the Negative Regulation of Type 2 Deiodinase Gene by Liganded Thyroid Hormone Receptor β2 in Thyrotroph

The inhibition of thyrotropin (thyroid stimulating hormone; TSH) by thyroid hormone (T3) and its receptor (TR) is the central mechanism of the hypothalamus-pituitary-thyroid axis. Two transcription factors, GATA2 and Pit-1, determine thyrotroph differentiation and maintain the expression of the β subunit of TSH (TSHβ). We previously reported that T3-dependent repression of the TSHβ gene is mediated by GATA2 but not by the reported negative T3-responsive element (nTRE). In thyrotrophs, T3 also represses mRNA of the type-2 deiodinase (D2) gene, where no nTRE has been identified. Here, the human D2 promoter fused to the CAT or modified Renilla luciferase gene was co-transfected with Pit-1 and/or GATA2 expression plasmids into cell lines including CV1 and thyrotroph-derived TαT1. GATA2 but not Pit-1 activated the D2 promoter. Two GATA responsive elements (GATA-REs) were identified close to cAMP responsive element. The protein kinase A activator, forskolin, synergistically enhanced GATA2-dependent activity. Gel-shift and chromatin immunoprecipitation assays with TαT1 cells indicated that GATA2 binds to these GATA-REs. T3 repressed the GATA2-induced activity of the D2 promoter in the presence of the pituitary-specific TR, TRβ2. The inhibition by T3-bound TRβ2 was dominant over the synergism between GATA2 and forskolin. The D2 promoter is also stimulated by GATA4, the major GATA in cardiomyocytes, and this activity was repressed by T3 in the presence of TRα1. These data indicate that the GATA-induced activity of the D2 promoter is suppressed by T3-bound TRs via a tethering mechanism, as in the case of the TSHβ gene.

The thyroid hormone receptors as tumor suppressors

In addition to the well-known role of the thyroid hormone receptors (TRs) in growth, development and metabolism, there is increasing evidence that they have profound effects on cell proliferation and malignant transformation. TRs repress transcriptional induction of cyclin D1 by the ras oncogene and block transformation and tumor formation by Ras-transformed fibroblasts in nude mice. Mutant receptors that do not bind coactivators are able to display these actions, whereas receptors defective in corepressors binding are unable to antagonize the responses to the ras oncogene. Furthermore, expression of TRβ1 in hepatocarcinoma and breast cancer cells abolishes anchorage-independent growth and migration, blocks responses to growth factors and represses expression of prometastatic genes, reducing tumor growth and strongly inhibiting invasiveness, extravasation and metastasis formation in euthyroid mice. By contrast, when cells are inoculated into hypothyroid host, tumor growth is retarded, but tumors are more invasive and metastatic growth is enhanced. Increased aggressiveness and tumor growth retardation was also observed with parental cells that do not express TRs, showing that changes secondary to hypothyroidism can modulate tumor progression and metastatic growth independently of the presence of TRs on the tumor cells. Finally, increased malignancy of skin tumors is found in mice lacking TRs, further demonstrating the role of these receptors as inhibitors of tumor progression and suggesting that they represent a potential therapeutic target in cancer.

Induction of apoptosis in T lymphoma cells by long-term treatment with thyroxine involves PKCζ nitration by nitric oxide synthase

Thyroid hormones are important regulators of cell physiology, inducing cell proliferation, differentiation or apoptosis, depending on the cell type. Thyroid hormones induce proliferation in short-term T lymphocyte cultures. In this study, we assessed the effect of long-term thyroxine (T4) treatment on the balance of proliferation and apoptosis and the intermediate participants in T lymphoma cells. Treatment with T4 affected this balance from the fifth day of culture, inhibiting proliferation in a time-dependent manner. This effect was associated with apoptosis induction, as characterized through nuclear morphological changes, DNA fragmentation, and Annexin V-FITC/Propidium Iodide co-staining. In addition, increased iNOS gene and protein levels, and enzyme activity were observed. The generation of reactive oxygen species, depolarization of the mitochondrial membrane, and a reduction in glutathione levels were also observed. The imbalance between oxidants and antioxidants species is typically associated with the nitration of proteins, including PKCζ, an isoenzyme essential for lymphoma cell division and survival. Consistently, evidence of PKCζ nitration via proteasome degradation was also observed in this study. Taken together, these results suggest that the long-term culture of T lymphoma cells with T4 induces apoptosis through the increased production of oxidative species resulting from both augmented iNOS activity and the loss of mitochondrial function. These species induce the nitration of proteins involved in cell viability, promoting proteasome degradation. Furthermore, we discuss the impact of these results on the modulation of T lymphoma growth and the thyroid status in vivo.

Suppressing thyroid hormone signaling preserves cone photoreceptors in mouse models of retinal degeneration

Cone phototransduction and survival of cones in the human macula is essential for color vision and for visual acuity. Progressive cone degeneration in age-related macular degeneration, Stargardt disease, and recessive cone dystrophies is a major cause of blindness. Thyroid hormone (TH) signaling, which regulates cell proliferation, differentiation, and apoptosis, plays a central role in cone opsin expression and patterning in the retina. Here, we investigated whether TH signaling affects cone viability in inherited retinal degeneration mouse models. Retinol isomerase RPE65-deficient mice [a model of Leber congenital amaurosis (LCA) with rapid cone loss] and cone photoreceptor function loss type 1 mice (severe recessive achromatopsia) were used to determine whether suppressing TH signaling with antithyroid treatment reduces cone death. Further, cone cyclic nucleotide-gated channel B subunit-deficient mice (moderate achromatopsia) and guanylate cyclase 2e-deficient mice (LCA with slower cone loss) were used to determine whether triiodothyronine (T3) treatment (stimulating TH signaling) causes deterioration of cones. We found that cone density in retinol isomerase RPE65-deficient and cone photoreceptor function loss type 1 mice increased about sixfold following antithyroid treatment. Cone density in cone cyclic nucleotide-gated channel B subunit-deficient and guanylate cyclase 2e-deficient mice decreased about 40% following T3 treatment. The effect of TH signaling on cone viability appears to be independent of its regulation on cone opsin expression. This work demonstrates that suppressing TH signaling in retina dystrophy mouse models is protective of cones, providing insights into cone preservation and therapeutic interventions.

Dual specificity phosphatase 1 expression inversely correlates with NF-κB activity and expression in prostate cancer and promotes apoptosis through a p38 MAPK dependent mechanism

Dual specificity phosphatase 1 (DUSP1) and the transcription factor NF-κB are implicated in prostate cancer since their expression levels are altered along this disease, although there are no evidences up to date demonstrating a crosstalk between them. In this report, we show for the first time that DUSP1 over-expression in DU145 cells promotes apoptosis and decreases NF-κB activity by blocking p65/NF-κB nuclear translocation. Moreover, although DUSP1 impairs TNF-α-induced p38 MAPK and JNK activation, only the specific inhibition of p38 MAPK exerts the same effects than DUSP1 over-expression on both apoptosis and NF-κB activity. Consistently, DUSP1 promotes apoptosis and decreases NF-κB activity in cells in which p38 MAPK is induced by TNF-α treatment. These results demonstrate that p38 MAPK is specifically involved in DUSP1-mediated effects on both apoptosis and NF-κB activity. Interestingly, we show an inverse correlation between DUSP1 expression and activation of both p65/NF-κB and p38 MAPK in human prostate tissue specimens. Thus, most of apparently normal glands, benign prostatic hyperplasia and low-grade prostatic intraepithelial neoplasia samples show high DUSP1 expression and low levels of both nuclear p65/NF-κB and activated p38 MAPK. By contrast, DUSP1 expression levels are low or even absent in high-grade prostatic intraepithelial neoplasia and prostatic adenocarcinoma samples, whereas nuclear p65/NF-κB and activated p38 MAPK are highly expressed in the same samples. Overall, our results provide evidence for a role of DUSP1 in the apoptosis of prostate cancer cells, through a mechanism involving the inhibition of p38 MAPK and NF-κB. Furthermore, our findings suggest that the ratio between DUSP1 and p65/NF-κB expression levels, rather than the individual expression of both molecules, is a better marker for diagnostic purposes in prostate cancer.

Alternative splicing of iodothyronine deiodinases in pituitary adenomas. Regulation by oncoprotein SF2/ASF

Pituitary tumors belong to the group of most common neoplasms of the sellar region. Iodothyronine deiodinase types 1 (DIO1) and 2 (DIO2) are enzymes contributing to the levels of locally synthesized T3, a hormone regulating key physiological processes in the pituitary, including its development, cellular proliferation, and hormone secretion. Previous studies revealed that the expression of deiodinases in pituitary tumors is variable and, moreover, there is no correlation between mRNA and protein products of the particular gene, suggesting the potential role of posttranscriptional regulatory mechanisms. In this work we hypothesized that one of such mechanisms could be the alternative splicing. Therefore, we analyzed expression and sequences of DIO1 and DIO2 splicing variants in 30 pituitary adenomas and 9 non-tumorous pituitary samples. DIO2 mRNA was expressed as only two mRNA isoforms. In contrast, nine splice variants of DIO1 were identified. Among them, five were devoid of exon 3. In silico sequence analysis of DIO1 revealed multiple putative binding sites for splicing factor SF2/ASF, of which the top-ranked sites were located in exon 3. Silencing of SF2/ASF in pituitary tumor GH3 cells resulted in change of ratio between DIO1 isoforms with or without exon 3, favoring the expression of variants without exon 3. The expression of SF2/ASF mRNA in pituitary tumors was increased when compared with non-neoplastic control samples. In conclusion, we provide a new mechanism of posttranscriptional regulation of DIO1 and show deregulation of DIO1 expression in pituitary adenoma, possibly resulting from disturbed expression of SF2/ASF.

Biological significance of a thyroid hormone-regulated secretome

The thyroid hormone, 3,3,5-triiodo-L-thyronine (T3), modulates several physiological processes, including cellular growth, differentiation, metabolism and proliferation, via interactions with thyroid hormone response elements (TREs) in the regulatory regions of target genes. Several intracellular and extracellular protein candidates are regulated by T3. Moreover, T3-regulated secreted proteins participate in physiological processes or cellular transformation. T3 has been employed as a marker in several disorders, such as cardiovascular disorder in chronic kidney disease, as well as diseases of the liver, immune system, endocrine hormone metabolism and coronary artery. Our group subsequently showed that T3 regulates several tumor-related secretory proteins, leading to cancer progression via alterations in extracellular matrix proteases and tumor-associated signaling pathways in hepatocellular carcinomas. Therefore, elucidation of T3/thyroid hormone receptor-regulated secretory proteins and their underlying mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a detailed summary on the known secretory proteins regulated by T3 and their physiological significance. This article is part of a Special Issue entitled: An Updated Secretome.

Thyroid hormone receptors, cell growth and differentiation

BACKGROUND

Tissue homeostasis depends on the balance between cell proliferation and differentiation. Thyroid hormones (THs), through binding to their nuclear receptors, can regulate the expression of many genes involved in cell cycle control and cellular differentiation. This can occur by direct transcriptional regulation or by modulation of the activity of different signaling pathways.

SCOPE OF REVIEW

In this review we will summarize the role of the different receptor isoforms in growth and maturation of selected tissues and organs. We will focus on mammalian tissues, and therefore we will not address the fundamental role of the THs during amphibian metamorphosis.

MAJOR CONCLUSIONS

The actions of THs are highly pleiotropic, affecting many tissues at different developmental stages. As a consequence, their effects on proliferation and differentiation are highly heterogeneous depending on the cell type, the cellular context, and the developmental or transformation status. Both during development and in the adult, stem cells are essential for proper organ formation, maintenance and regeneration. Recent evidence suggests that some of the actions of the thyroid hormone receptors could be secondary to regulation of stem/progenitor cell function. Here we will also include the latest knowledge on the role of these receptors in proliferation and differentiation of embryonic and adult stem cells.

GENERAL SIGNIFICANCE

The thyroid hormone receptors are potent regulators of proliferation and differentiation of many cell types. This can explain the important role of the thyroid hormones and their receptors in key processes such as growth, development, tissue homeostasis or cancer. This article is part of a Special Issue entitled Thyroid hormone signalling.

Src kinase integrates PI3K/Akt and MAPK/ERK1/2 pathways in T3-induced Na-K-ATPase activity in adult rat alveolar cells

We previously reported that the 3,5,3'-triiodo-L-thyronine (T3)-induced increase of Na-K-ATPase activity in rat alveolar epithelial cells (AECs) required activation of Src kinase, PI3K, and MAPK/ERK1/2. In the present study, we assessed the role of Akt in Na-K-ATPase activity and the interaction between the PI3K and MAPK in response to T3 by using MP48 cells, inhibitors, and constitutively active mutants in the MP48 (alveolar type II-like) cell line. The Akt inhibitor VIII blocked T3-induced increases in Na-K-ATPase activity and amount of plasma membrane Na-K-ATPase protein. The Akt inhibitor VIII also abolished the increase in Na-K-ATPase activity induced by constitutively active mutants of either Src kinase or PI3K. Moreover, constitutively active mutants of Akt increased Na-K-ATPase activity in the absence of T3. Thus activation of Akt was required for T3-induced Na-K-ATPase activity in AECs and is sufficient in the absence of T3. Inhibitors of Src kinase (PP1), PI3K (wortmannin), and ERK1/2 (U0126) all blocked the T3-induced Na-K-ATPase activity. PP1 blocked the activation of PI3K and also ERK1/2 by T3, whereas U0126 did not prevent T3 activation of Src kinase or PI3K activity. Wortmannin did not significantly alter T3-increased MAPK/ERK1/2 activity, suggesting that T3-activated PI3K/Akt and MAPK/ERK1/2 pathways acted downstream of the Src kinase. Furthermore, in the absence of T3, a constitutively active mutant of Src kinase increased activities of Na-K-ATPase, PI3K, and MAPK/ERK1/2. A constitutively active mutant of PI3K enhanced Na-K-ATPase activity but did not alter the MAPK/ERK1/2 activity significantly. In summary, in adult rat AECs T3-stimulated Src kinase activity can activate both PI3K/Akt and MAPK/ERK1/2, and activation of Akt is necessary for T3-induced Na-K-ATPase activity.

The thyroid hormone receptors as modulators of skin proliferation and inflammation

We have analyzed the role of the thyroid hormone receptors (TRs) in epidermal homeostasis. Reduced keratinocyte proliferation is found in interfollicular epidermis of mice lacking the thyroid hormone binding isoforms TRα1 and TRβ (KO mice). Similar results were obtained in hypothyroid animals, showing the important role of the liganded TRs in epidermal proliferation. In addition, KO and hypothyroid animals display decreased hyperplasia in response to 12-O-tetradecanolyphorbol-13-acetate. Both receptor isoforms play overlapping functional roles in the skin because mice lacking individually TRα1 or TRβ also present a proliferative defect but not as marked as that found in double KO mice. Defective proliferation in KO mice is associated with reduction of cyclin D1 expression and up-regulation of the cyclin-dependent kinase inhibitors p19 and p27. Paradoxically, ERK and AKT activity and expression of downstream targets, such as AP-1 components, are increased in KO mice. Increased p65/NF-κB and STAT3 phosphorylation and, as a consequence, augmented expression of chemokines and proinflammatory cytokines is also found in these animals. These results show that thyroid hormones and their receptors are important mediators of skin proliferation and demonstrate that TRs act as endogenous inhibitors of skin inflammation, most likely due to interference with AP-1, NF-κB, and STAT3 activation.

Anandamide enhances IL-10 production in activated microglia by targeting CB(2) receptors: roles of ERK1/2, JNK, and NF-kappaB

The endocannabinoid system exhibits anti-inflammatory properties by regulating cytokine production. Anandamide (AEA) down-regulates proinflammatory cytokines in a viral model of multiple sclerosis (MS). However, little is known about the mechanisms by which AEA exerts these effects. Microglial cells are the main source of cytokines within the brain and the first barrier of defense against pathogens by acting as antigen presenting cells. IL-10 is a key physiological negative regulator of microglial activation. In this study we show that AEA enhances LPS/IFNgamma-induced IL-10 production in microglia by targeting CB(2) receptors through the activation of ERK1/2 and JNK MAPKs. AEA also inhibits NF-kappaB activation by interfering with the phosphorylation of IkappaBalpha, which may result in an increase of IL-10 production. Moreover, endogenously produced IL-10 negatively regulates IL-12 and IL-23 cytokines, which in its turn modify the pattern of expression of transcription factors involved in Th commitment of splenocytes. This suggests that by altering the cytokine network, AEA could indirectly modify the type of immune responses within the central nervous system (CNS). Accordingly, pharmacological modulation of AEA uptake and degradation might be a useful tool for treating neuroinflammatory diseases.

Thyroid hormone antagonizes tumor necrosis factor-alpha signaling in pituitary cells through the induction of dual specificity phosphatase 1

Pituitary function has been shown to be regulated by an increasing number of factors, including cytokines and hormones, such as TNFalpha and T(3). Both the proinflammatory cytokine TNFalpha and T(3) have been suggested to be involved in the maintenance of tissue homeostasis in the anterior pituitary gland. In this report we show that T(3) negatively interferes with MAPK p38 and nuclear factor-kappaB (NF-kappaB) activation by TNFalpha in GH4C1 cells. Our data demonstrate that MAPK p38 is specifically activated upon exposure to TNFalpha and that T(3) abolishes this activation in a time-dependent manner by a mechanism that involves the induction of the MAPK phosphatase, DUSP1. Our data show that the pool of up-regulated DUSP1 by T(3) is mainly localized to the cytosol, and that TNFalpha does not affect this localization. On the other hand, we show that T(3) impairs the activation of the NF-kappaB pathway induced by TNFalpha, producing a significant decrease in NF-kappaB-dependent transcription, phosphorylation of IkappaBalpha, translocation of p65/NF-kappaB to the nucleus, and p65/NF-kappaB transactivation potential. Interestingly, the overexpression of DUSP1 inhibits the NF-kappaB activation achieved by either TNFalpha or ectopic expression of the upstream inducer of MAPK p38. Conversely, DUSP1 depletion abrogates the inhibitory effect of T(3) on the induction of NF-kappaB-dependent transcription by TNFalpha. Overall, our results indicate that T(3) antagonizes TNFalpha signaling in rat pituitary tumor cells through the induction of DUSP1.

Genomic analysis of the function of the transcription factor gata3 during development of the mammalian inner ear

We have studied the function of the zinc finger transcription factor gata3 in auditory system development by analysing temporal profiles of gene expression during differentiation of conditionally immortal cell lines derived to model specific auditory cell types and developmental stages. We tested and applied a novel probabilistic method called the gamma Model for Oligonucleotide Signals to analyse hybridization signals from Affymetrix oligonucleotide arrays. Expression levels estimated by this method correlated closely (p<0.0001) across a 10-fold range with those measured by quantitative RT-PCR for a sample of 61 different genes. In an unbiased list of 26 genes whose temporal profiles clustered most closely with that of gata3 in all cell lines, 10 were linked to Insulin-like Growth Factor signalling, including the serine/threonine kinase Akt/PKB. Knock-down of gata3 in vitro was associated with a decrease in expression of genes linked to IGF-signalling, including IGF1, IGF2 and several IGF-binding proteins. It also led to a small decrease in protein levels of the serine-threonine kinase Akt2/PKBbeta, a dramatic increase in Akt1/PKBalpha protein and relocation of Akt1/PKBalpha from the nucleus to the cytoplasm. The cyclin-dependent kinase inhibitor p27(kip1), a known target of PKB/Akt, simultaneously decreased. In heterozygous gata3 null mice the expression of gata3 correlated with high levels of activated Akt/PKB. This functional relationship could explain the diverse function of gata3 during development, the hearing loss associated with gata3 heterozygous null mice and the broader symptoms of human patients with Hearing-Deafness-Renal anomaly syndrome.

Deprival of testicular innervation induces apoptosis of Leydig cells via caspase-8-dependent signaling: a novel survival pathway revealed

Leydig cells are the primary source of testosterone in adult males. Recently, a growing body of evidence has shown that testicular innervation functions as a major regulator in Leydig cell steroidogenesis. The question then arises whether this novel regulatory pathway also plays an important role in other biological behaviors of this cell type. In the present study, we selectively resected the superior spermatic nerves (SSNs) or the inferior spermatic nerves (ISNs) to investigate the effects of testicular denervation on survival of Leydig cells. After testicular denervation, Leydig cells displayed morphological characteristics of apoptosis, such as chromatin condensation, cell shrinkage and apoptotic body formation. Flow cytometry combined with TUNEL labeling demonstrated dramatic and persistent apoptosis of Leydig cells in the denervated testes 14 and 21 days after operation. Meanwhile, serum T concentrations in the SSN- or ISN-denervated rats dramatically decreased on day 14 and declined further on day 21. Plasma LH levels underwent a remarkable rise, while serum FSH levels remained unchanged. Immunofluorescent staining and flow cytometry further demonstrated that testicular denervation activated caspase-3 and caspase-8, but not caspase-9 in Leydig cells. Our data indicate that testicular innervation functions as an important survival factor for Leydig cells in vivo.