Novel oncogenic actions of TRbeta mutants in tumorigenesis

Molecular functions and clinical impact of thyroid hormone-triggered autophagy in liver-related diseases

The liver is controlled by several metabolic hormones, including thyroid hormone, and characteristically displays high lysosomal activity as well as metabolic stress-triggered autophagy, which is stringently regulated by the levels of hormones and metabolites. Hepatic autophagy provides energy through catabolism of glucose, amino acids and free fatty acids for starved cells, facilitating the generation of new macromolecules and maintenance of the quantity and quality of cellular organelles, such as mitochondria. Dysregulation of autophagy and defective mitochondrial homeostasis contribute to hepatocyte injury and liver-related diseases, such as non-alcoholic fatty liver disease (NAFLD) and liver cancer.

Thyroid hormones (TH) mediate several critical physiological processes including organ development, cell differentiation, metabolism and cell growth and maintenance. Accumulating evidence has revealed dysregulation of cellular TH activity as the underlying cause of several liver-related diseases, including alcoholic or non-alcoholic fatty liver disease and liver cancer. Data from epidemiologic, animal and clinical studies collectively support preventive functions of THs in liver-related diseases, highlighting the therapeutic potential of TH analogs. Elucidation of the molecular mechanisms and downstream targets of TH should thus facilitate the development of therapeutic strategies for a number of major public health issues.

Here, we have reviewed recent studies focusing on the involvement of THs in hepatic homeostasis through induction of autophagy and their implications in liver-related diseases. Additionally, the potential underlying molecular pathways and therapeutic applications of THs in NAFLD and HCC are discussed.

Chiral pharmaceuticals: Environment sources, potential human health impacts, remediation technologies and future perspective

Chiral pharmaceuticals (CPs), including non-steroid anti-inflammatory drugs (NSAIDs), β-blockers and some herbicide and pesticides, are widely used in aquaculture, clinical treatment and many other fields. However, people are increasingly concerned about such ubiquitous pollutants, which can frequently be detected in contaminated soil and water. In large part, the significant sources of chiral pharmaceuticals stem from industrial processes, such as the direct discharge of untreated or incompletely treated wastewaters containing chiral pharmaceuticals, incorrect storage and use, animal wastes and biosolids. The main ways for human exposure to chiral pharmaceuticals are the disease treatment process and chiral pharmaceuticals contaminants. According to the results of a series of toxic studies, some diseases, even cancers, may be associated with exposure to certain chiral pharmaceuticals. Therefore, the treatment of chiral pharmaceuticals has become an important issue. The current advanced remediation techniques for chiral pharmaceuticals include the conventional method (sorption and sonolysis), biotransformation (an aerobic granular sludge-sequencing batch reactor and constructed wetland system) and advanced oxidation processes (ozonation and photocatalysis). Herein, in this review, we summarize the current status and sources of chiral pharmaceuticals, potential effects on human health, as well as the superiority, disadvantages and prospects of current advanced remediation technologies. Moreover, we also anticipate the prospect of the future research needed for chiral pharmaceuticals pollutant remediation.

Analysis of Thyroid Tumorigenesis in Xenograft Mouse Model

Analysis of thyroid tumorigenesis in xenograft mouse model is important to study human thyroid cancer. Recent studies have made big strides toward understanding the molecular mechanisms by which thyroid hormone nuclear receptors (TR) act to maintain normal cellular functions in growth, differentiation, and development. Despite growing interest, the role of TR in oncogenesis remains to be fully elucidated. Two TR genes give rise to three major TR isoforms: TRα1, TRβ1, and TRβ2. These TR subtypes express in a tissue- and development-dependent manner. Research has been directed at understanding the mechanisms by which TR could mediate aberrant cellular signaling that contributes to oncogenesis, at dissecting possible distinct roles of TR isoforms in oncogenesis, and at the differential susceptibility of target tissues to the oncogenic actions of TR. This chapter gives a brief overview of the current undersatanding of known molecular oncogenic actions of TR. Here, we describe analysis of thyroid tumorigenesis used in interrogating the in vivo oncogenic actions of TR.

Inhibition of STAT3 signaling blocks obesity-induced mammary hyperplasia in a mouse model

Compelling epidemiologic evidence indicates that obesity is a risk factor for human cancers, including breast. However, molecular mechanisms by which obesity could contribute to the development of breast cancer remain unclear. To understand the impact of obesity on breast cancer development, we used a mutant mouse that expresses a mutated thyroid hormone receptor β (denoted as PV) with haplodeficiency of the Pten gene (Thrb^PV/PVPten^+/- mice). We previously showed that adult nulliparous female Thrb^PV/PVPten^+/- mice developed extensive mammary hyperplasia and breast tumors. In this study, we induced obesity in Thrb^PV/PVPten^+/- mice by feeding them a high fat diet (HFD). We found HFD exacerbated the extent of mammary hyperplasia in Thrb^PV/PVPten^+/- mice. HFD elevated serum leptin levels but had no effect on the levels of serum thyroid stimulating hormone, thyroid hormones, and estrogens. Molecular analysis showed that the obesity-induced hyperplasia was mediated by the leptin/leptin receptor-JAK1-STAT3 pathway to increase key cell cycle regulators to stimulate mammary epithelial cell proliferation. Activated STAT3 signaling led to altered expression in the key regulators of epithelial-mesenchymal-transition (EMT) to augment invasiveness and migration of mammary proliferating epithelial cells. Moreover, treatment of HFD-Thrb^PV/PVPten^+/- mice with a STAT3 inhibitor, S3I-201, markedly reversed the obesity-induced mammary hyperplasia and reduced EMT signals to lessen cell invasiveness and migration. Our studies not only elucidated how obesity could contribute to mammary hyperplasia at the molecular level, but also, importantly, demonstrated that inhibition of the STAT3 activity could be a novel treatment strategy for obesity-induced breast cancer progression.

Loss of tyrosine phosphorylation at Y406 abrogates the tumor suppressor functions of the thyroid hormone receptor β

We have recently identified that phosphorylation at tyrosine (Y)406 is critical for the tumor suppressor functions of the thyroid hormone receptor β1 (TRβ) in a breast cancer line. However, still unclear is whether the critical tumor suppressor role of phosphorylated Y406 of TRβ is limited to only breast cancer cells or could be extended to other cell types. In the present studies, we addressed this question by stably expressing TRβ, a mutated TRβ oncogene (PV), or a TRβ mutated at Y406 (TRβY406F) in rat PCCL3 thyroid follicular cells and evaluated their tumor characteristics in athymic mice with elevated thyroid stimulating hormone. PCCL3 cells stably expressing PV (PCCL3-PV), TRβY406F (PCCL3-TRβY406F), or vector only (PCCL3-Neo) developed tumors with sizes in the rank order of TRβY406F>PV = Neo, whereas PCCL3 cells expressing TRβ (PCCL3-TRβ) barely developed tumors. As evidenced by markedly elevated Ki67, cyclin D1, and p-Rb protein abundance, proliferative activity was high in PV and TRβY406F tumors, but low in TRβ tumors. These results indicate that TRβ acted as a tumor suppressor in PCCL3 cells, whereas TRβY406F and PV had lost tumor suppressor activity. Interestingly, TRβY406F tumors had very low necrotic areas with decreased TNFα-NFκB signaling to lower apoptotic activity. In contrast, PV tumors had prominent large necrotic areas, with no apparent changes in TNFα-NFκB signaling, indicating distinct oncogenic activities of mutant PV and TRβY406F. Thus, the present studies uncovered a novel mechanism by which TRβ could function as a tumor suppressor through modulation of the TNFα-NFκB signaling. © 2016 Wiley Periodicals, Inc.

Oncogenic mutations of thyroid hormone receptor β

The C-terminal frame-shift mutant of the thyroid hormone receptor TRβ1, PV, functions as an oncogene. An important question is whether the oncogenic activity of mutated TRβ1 is uniquely dependent on the PV mutated sequence. Using four C-terminal frame-shift mutants—PV, Mkar, Mdbs, and AM—we examined that region in the oncogenic actions of TRβ1 mutants. Remarkably, these C-terminal mutants induced similar growth of tumors in mouse xenograft models. Molecular analyses showed that they physically interacted with the p85α regulatory subunit of PI3K similarly in cells. In vitro GST-binding assay showed that they bound to the C-terminal Src-homology 2 (CSH2) of p85α with markedly higher avidity. The sustained association of mutants with p85α led to activation of the common PI3K-AKT-ERK/STAT3 signaling to promote cell proliferation and invasion and to inhibit apoptosis. Thus, these results argue against the oncogenic activity of PV being uniquely dependent on the PV mutated sequence. Rather, these four mutants could favor a C-terminal conformation that interacted with the CSH2 domain of p85α to initiate activation of PI3K to relay downstream signaling to promote tumorigenesis. Thus, we propose that the mutated C-terminal region of TRβ1 could function as an “onco-domain” and TRβ1 is a potential therapeutic target.

Repression of microRNA-130b by thyroid hormone enhances cell motility

BACKGROUND & AIMS

Thyroid hormone (T3) and its receptor (TR) are involved in cell growth and cancer progression. Although deregulation of microRNA (miRNA) expression has been detected in many tumor types, the mechanisms underlying functional impairment and specific involvement of miRNAs in tumor metastasis remain unclear. In the current study, we aimed to elucidate the involvement of deregulated miRNA-130b (miR-130b) and its target genes mediated by T3/TR in cancer progression.

METHODS

Quantitative reverse transcription-PCR, luciferase and chromatin immunoprecipitation assays were performed to identify the miR-130b transcript and the mechanisms implicated in its regulation. The effects of miR-130b on hepatocellular carcinoma (HCC) invasion were further examined in vitro and in vivo. Clinical correlations among miR-130b, TRs and interferon regulatory factor 1 (IRF1) were examined in HCC samples using Spearman correlation analysis.

RESULTS

Our experiments disclosed negative regulation of miR-130b expression by T3/TR. Overexpression of miR-130b led to marked inhibition of cell migration and invasion, which was mediated via suppression of IRF1. Cell migration ability was promoted by T3, but partially suppressed upon miR-130b overexpression. Furthermore, miR-130b suppressed expression of epithelial-mesenchymal transition (EMT)-related genes, matrix metalloproteinase-9, phosphorylated mammalian target of rapamycin (mTOR), p-ERK1/2, p-AKT and p-signal transducer and activator of transcription (STAT)-3. Notably, miR-130b was downregulated in hepatoma samples and its expression patterns were inversely correlated with those of TRα1 and IRF1.

CONCLUSIONS

Our data collectively highlight a novel pathway interlinking T3/TR, miR-130b, IRF1, the EMT-related genes, p-mTOR, p-STAT3 and the p-AKT cascade, which regulates the motility and invasion of hepatoma cells.

Thyroid hormone receptors and cancer

BACKGROUND

Thyroid hormone receptors (TRs) are ligand-dependent transcription factors that mediate the actions of the thyroid hormone (T3) in development, growth, and differentiation. The THRA and THRB genes encode several TR isoforms that express in a tissue- and development-dependent manner. In the past decades, a significant advance has been made in the understanding of TR actions in maintaining normal cellular functions. However, the roles of TRs in human cancer are less well understood. The reduced expression of TRs because of hypermethylation, or deletion of TR genes found in human cancers suggests that TRs could function as tumor suppressors. A close association of somatic mutations of TRs with human cancers further supports the notion that the loss of normal functions of TR could lead to uncontrolled growth and loss of cell differentiation.

SCOPE OF REVIEW

In line with the findings from association studies in human cancers, mice deficient in total functional TRs (Thra1(-/-)Thrb(-/-) mice) or with a targeted homozygous mutation of the Thrb gene (denoted PV; Thrb(PV/PV) mice) spontaneously develop metastatic thyroid carcinoma. This review will examine the evidence learned from these genetically engineered mice that provided strong evidence to support the critical role of TRs in human cancer.

MAJOR CONCLUSIONS

Loss of normal functions of TR by deletion or by mutations could contribute to cancer development, progression and metastasis.

GENERAL SIGNIFICANCE

Novel mechanistic insights are revealed in how aberrant TR activities lead to carcinogenesis. Mouse models of thyroid cancer provide opportunities to identify molecular targets as potential treatment modalities. This article is part of a Special Issue entitled Thyroid hormone signalling.

Thyroid hormone receptors promote metastasis of human hepatoma cells via regulation of TRAIL

Although accumulating evidence has confirmed the important roles of thyroid hormone (T(3)) and its receptors (TRs) in tumor progression, the specific functions of TRs in carcinogenesis remain unclear. In the present study, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) was directly upregulated by T(3) in TR-overexpressing hepatoma cell lines. TRAIL is an apoptotic inducer, but it can nonetheless trigger non-apoptotic signals favoring tumorigenesis in apoptosis-resistant cancer cells. We found that TR-overexpressing hepatoma cells treated with T(3) were apoptosis resistant, even when TRAIL was upregulated. This apoptotic resistance may be attributable to simultaneous upregulation of Bcl-xL by T(3), because (1) knockdown of T(3)-induced Bcl-xL expression suppressed T(3)-mediated protection against apoptosis, and (2) overexpression of Bcl-xL further protected hepatoma cells from TRAIL-induced apoptotic death, consequently leading to TRAIL-promoted metastasis of hepatoma cells. Moreover, T(3)-enhanced metastasis in vivo was repressed by the treatment of TRAIL-blocking antibody. Notably, TRAIL was highly expressed in a subset of hepatocellular carcinoma (HCC) patients, and this high-level expression was significantly correlated with that of TRs in these HCC tissues. Together, our findings provide evidence for the existence of a novel mechanistic link between increased TR and TRAIL levels in HCC. Thus, TRs induce TRAIL expression, and TRAIL thus synthesized acts in concert with simultaneously synthesized Bcl-xL to promote metastasis, but not apoptosis.

Resistance to thyroid hormone is modulated in vivo by the nuclear receptor corepressor (NCOR1)

Mutations in the ligand-binding domain of the thyroid hormone receptor β (TRβ) lead to resistance to thyroid hormone (RTH). These TRβ mutants function in a dominant-negative fashion to interfere with the transcription activity of wild-type thyroid hormone receptors (TRs), leading to dysregulation of the pituitary-thyroid axis and resistance in peripheral tissues. The molecular mechanism by which TRβ mutants cause RTH has been postulated to be an inability of the mutants to properly release the nuclear corepressors (NCORs), thereby inhibiting thyroid hormone (TH)-mediated transcription activity. To test this hypothesis in vivo, we crossed Thrb(PV) mice (a model of RTH) expressing a human TRβ mutant (PV) with mice expressing a mutant Ncor1 allele (Ncor1(ΔID) mice) that cannot recruit a TR or a PV mutant. Remarkably, in the presence of NCOR1ΔID, the abnormally elevated thyroid-stimulating hormone and TH levels found in Thrb(PV) mice were modestly but significantly corrected. Furthermore, thyroid hyperplasia, weight loss, and other hallmarks of RTH were also partially reverted in mice expressing NCOR1ΔID. Taken together, these data suggest that the aberrant recruitment of NCOR1 by RTH TRβ mutants leads to clinical RTH in humans. The present study suggests that therapies aimed at the TR-NCOR1 interaction or its downstream actions could be tested as potential targets in treating RTH.

Thyroid hormone receptor mutations in cancer and resistance to thyroid hormone: perspective and prognosis

Thyroid hormone, operating through its receptors, plays crucial roles in the control of normal human physiology and development; deviations from the norm can give rise to disease. Clinical endocrinologists often must confront and correct the consequences of inappropriately high or low thyroid hormone synthesis. Although more rare, disruptions in thyroid hormone endocrinology due to aberrations in the receptor also have severe medical consequences. This review will focus on the afflictions that are caused by, or are closely associated with, mutated thyroid hormone receptors. These include Resistance to Thyroid Hormone Syndrome, erythroleukemia, hepatocellular carcinoma, renal clear cell carcinoma, and thyroid cancer. We will describe current views on the molecular bases of these diseases, and what distinguishes the neoplastic from the non-neoplastic. We will also touch on studies that implicate alterations in receptor expression, and thyroid hormone levels, in certain oncogenic processes.

Inhibition of mTORC1 signaling reduces tumor growth but does not prevent cancer progression in a mouse model of thyroid cancer

Selective drugs targeting dysregulated oncogenic pathways are promising cancer therapies. Because the mammalian target of rapamycin complex 1 (mTORC1) pathway is hyperactivated in human follicular thyroid cancer (FTC), we hypothesized that its inhibition could block cancer development and progression. We, therefore, analyzed the effect of a treatment with a specific mTORC1 inhibitor (RAD001) in a faithful mouse model of FTC with constitutive mTORC1 activation (TRbeta(PV/PV)Pten(+/-) mice). The treatment did not prevent capsular and vascular invasion of the thyroid and the occurrence of lung metastasis. However, it substantially decelerated thyroid tumor growth, thereby prolonging TRbeta(PV/PV)Pten(+/-) mouse life span. RAD001 efficiently inhibited mTORC1 activity, as shown by the reduced phosphorylation of its downstream targets involved in the activity of the translation machinery, such as ribosomal S6 kinase (p70(S6K)), eukaryotic translation initiation factor 4E binding protein (4E-BP1) and the eukaryotic translation initiation factors eIF-4B and eIF-4G. Whereas mTORC1 signaling inhibition did not alter cell apoptosis, it induced a significant decrease in cell proliferation that was associated with the reduced abundance and altered activity of key regulators of cell cycle progression. Altogether, our data indicate that mTORC1 signaling plays a major role in the integration of the mitogenic signal in FTC. Therefore, our preclinical study with a relevant mouse model of FTC demonstrates for the first time that RAD001 efficaciously stabilizes cancer growth although it does not prevent its fatal outcome. In conclusion, our work underscores that in the treatment of FTC patients, RAD001 can only be used in combination with drugs and therapies inducing tumor shrinkage and blocking metastasis.

Retinoblastoma, an inside job

Why are some cell types more prone to transformation than others? In this issue, Xu et al. (2009) show that retinoblastoma cells co-opt several intrinsic features of cone photoreceptors for their survival and growth.