Unliganded thyroid hormone receptor beta1 inhibits proliferation of murine fibroblasts by delaying the onset of the G1 cell-cycle signals

Thyroid Hormone Receptor Beta as Tumor Suppressor: Untapped Potential in Treatment and Diagnostics in Solid Tumors

There is compelling evidence that the nuclear receptor TRβ, a member of the thyroid hormone receptor (TR) family, is a tumor suppressor in thyroid, breast, and other solid tumors. Cell-based and animal studies reveal that the liganded TRβ induces apoptosis, reduces an aggressive phenotype, decreases stem cell populations, and slows tumor growth through modulation of a complex interplay of transcriptional networks. TRβ-driven tumor suppressive transcriptomic signatures include repression of known drivers of proliferation such as PI3K/Akt pathway, activation of novel signaling such as JAK1/STAT1, and metabolic reprogramming in both thyroid and breast cancers. The presence of TRβ is also correlated with a positive prognosis and response to therapeutics in BRCA+ and triple-negative breast cancers, respectively. Ligand activation of TRβ enhances sensitivity to chemotherapeutics. TRβ co-regulators and bromodomain-containing chromatin remodeling proteins are emergent therapeutic targets. This review considers TRβ as a potential biomolecular diagnostic and therapeutic target.

MAPK and SHH pathways modulate type 3 deiodinase expression in papillary thyroid carcinoma

Type 3 deiodinase (DIO3, D3) is reactivated in human neoplasias. Increased D3 levels in papillary thyroid carcinoma (PTC) have been associated with tumor size and metastatic disease. The objective of this study is to investigate the signaling pathways involved in DIO3 upregulation in PTC. Experiments were performed in human PTC cell lines (K1 and TPC-1 cells) or tumor samples. DIO3 mRNA and activity were evaluated by real-time PCR and ion-exchange column chromatography respectively. Western blot analysis was used to determine the levels of D3 protein. DIO3 gene silencing was performed via siRNA transfection. DIO3 mRNA levels and activity were readily detected in K1 (BRAF(V6) (0) (0E)) and, at lower levels, in TPC-1 (RET/PTC1) cells (P<0.007 and P=0.02 respectively). Similarly, DIO3 mRNA levels were higher in PTC samples harboring the BRAF(V600E) mutation as compared with those with RET/PTC1 rearrangement or negative for these mutations (P<0.001). Specific inhibition of BRAF oncogene (PLX4032, 3 μM), MEK (U0126, 10-20 μM) or p38 (SB203580, 10-20 μM) signaling was associated with decreases in DIO3 expression in K1 and TPC-1 cells. Additionally, the blockage of the sonic hedgehog (SHH) pathway by cyclopamine (10  μM) resulted in markedly decreases in DIO3 mRNA levels. Interestingly, siRNA-mediated DIO3 silencing induced decreases on cyclin D1 expression and partial G1 phase cell cycle arrest, thereby downregulating cell proliferation. In conclusion, sustained activation of the MAPK and SHH pathways modulate the levels of DIO3 expression in PTC. Importantly, DIO3 silencing was associated with decreases in cell proliferation, thus suggesting a D3 role in tumor growth and aggressiveness.

Implication from thyroid function decreasing during chemotherapy in breast cancer patients: chemosensitization role of triiodothyronine

Background

Thyroid hormones have been shown to regulate breast cancer cells growth, the absence or reduction of thyroid hormones in cells could provoke a proliferation arrest in G0-G1 or weak mitochondrial activity, which makes cells insensitive to therapies for cancers through transforming into low metabolism status. This biological phenomenon may help explain why treatment efficacy and prognosis vary among breast cancer patients having hypothyroid, hyperthyroid and normal function. Nevertheless, the abnormal thyroid function in breast cancer patients has been considered being mainly caused by thyroid diseases, few studied influence of chemotherapy on thyroid function and whether its alteration during chemotherapy can influence the respose to chemotherapy is still unclear. So, we aimed to find the alterations of thyroid function and non-thyroidal illness syndrome (NTIS) prevalence druing chemotherapy in breast cancer patients, and investigate the influence of thyroid hormones on chemotherapeutic efficacy.

Methods

Thyroid hormones and NTIS prevalence at initial diagnosis and during chemotherapy were analyzed in 685 breast diseases patients (369 breast cancer, 316 breast benign lesions). The influence of thyroid hormones on chemotherapeutic efficacy was evaluated by chemosensitization test, to compare chemotherapeutic efficacy between breast cancer cells with chemotherapeutics plus triiodothyronine (T₃) and chemotherapeutics only.

Results

In breast cancer, NTIS prevalence at the initial diagnosis was higher and increased during chemotherapy, but declined before the next chemotherapeutic course. Thyroid hormones decreased signigicantly during chemotherapy. T₃ can enhance the chemosensitivity of MCF-7 to 5-Fu and taxol, with progression from G0-G1 phase to S phase. The similar chemosensitization role of T₃ were found in MDA-MB-231. We compared chemotherapeutic efficacy among groups with different usage modes of T₃, finding pretreatment with lower dose of T₃, using higher dose of T₃ together with 5-Fu or during chemotherapy with 5-Fu were all available to achieve chemosensitization, but pretreatment with lower dose of T₃ until the end of chemotherapy may be a safer and more efficient therapy.

Conclusions

Taken together, thyroid hormones decreasing during chemotherapy was found in lots of breast cancer patients. On the other hand, thyroid hormones can enhance the chemotherapeutic efficacy through gatherring tumor cells in actively proliferating stage, which may provide a new adjuvant therapy for breast cancer in furture, especially for those have hypothyroidism during chemotherapy.

Neo-endocrinochemotherapy: a novel approach for enhancing chemotherapeutic efficacy in clinic?

Chemosensitization means enhancing the sensitivity of tumor cells to chemotherapy with certain methods for better efficacy. Tumor progression depends on stimulation of multiple hormones, decrease in hormones during chemotherapy induces G0/G1 arrest of tumor cells, which may be the main cause for chemoresistance. Some of the choriocarcinoma and testicular tumors are curable with chemotherapy only, underlying mechanism may refer high level of human chorionic gonadotropin, which has thyroid stimulating hormone like effect and even induce hyperthyroidism in these patients. Some of these patients usually have high levels of thyroid hormones or suffer thyroid crisis during chemotherapy. Possibly owning to the proliferative or metabolic promotion effect of thyroid hormones and/or other endocrine hormones, which can promote tumor cells in G0 phase metabolizing actively or stepping into division cycle again, tumors are more sensitive to chemotherapy. Both endocrinotherapy and chemotherapy are major therapies for tumor, traditional endocrinotherapy suppresses tumor progression through decreasing tumor-dependent hormones or competitively combining and blocking hormone receptors. While, chemotherapy mostly killed tumor cells that proliferate actively, because tumor cells retardant in G0 phase by endocrinotherapy are no more sensitive to chemotherapy, endocrinotherapy cannot be concurrently used with chemotherapy. Nevertheless, decrease in hormones during chemotherapy is similar to concurrently using endocrinotherapy and chemotherapy. It has been found in some basic researches that some chemotherapeutics concurrently combined with endocrine hormones can achieve better efficacy compared with chemotherapy only. It is therefore hypothesized in this article that decrease in hormones during chemotherapy causes cell cycle arrest and renders tumor cells insensitive to chemotherapy; addition of endocrine hormones to mimic the hormones and microenvironment changes during chemotherapy for patients with choriocarcinoma or testicular tumor-curable with chemotherapy only, will rescue tumor cells from cell cycle arrest rendering them sensitive to chemotherapy. This new combinative therapy of concurrently using endocrine hormones and chemotherapy is defined as choriocarcinoma-mimic chemotherapy or neo-endocrinochemotherapy to distinguish the routine term of endocrinochemotherapy and is expected to be a novel approach to enhance chemotherapeutic efficacy in clinic.

[Thyroid dysfunction in patients with advanced renal cell carcinoma treated with sunitinib: a multifactorial issue]

OBJECTIVE

Several studies have reported the substantial prevalence of sunitinib-induced thyroid dysfunction. However, the underlying mechanism and the benefit of thyroid hormone replacement therapy remain to be determined. To evaluate the effect of sunitinib on thyroid function, we carried out a descriptive study in patients with advanced renal cell carcinoma.

PATIENTS AND METHODS

A total of 24 patients treated by sunitinib between 2006 and 2008 at Hospital Clínico San Carlos were included. The data were collected retrospectively and analyzed with SPSS 15.0.

RESULTS

Treatment duration was 30 weeks (18-42) [median (IQR)]. Five patients (20.8%) developed subclinical hypothyroidism and three (12.5%) developed overt hypothyroidism. The number of weeks needed to observe an increase in thyroid-stimulating hormone (TSH) values in these patients was 15 (6-20) [median (IQR)]. TSH levels were below the normal range in five patients (20.8%) before or during the treatment period, but the diagnosis of subclinical hyperthyroidism could not be established because of concomitant factors. Fourteen patients (58.3%) showed sunitinib adverse events, but these were not related to the development of hypothyroidism (p=0.388).

CONCLUSIONS

Because of the high prevalence of sunitinib-induced hypothyroidism, thyroid function should be systematically monitored in patients with renal cell carcinoma treated with this drug. However, several pathophysiological and pharmacological factors may interfere with monitoring. Consequently, it might be useful to determine not only TSH and free T4 but also free T3 and, ideally, reverse T3. Evidence-based recommendations to manage hypothyroidism in oncology patients are not available at present.

Implication of type 3 deiodinase induction in zebrafish fin regeneration

Thyroid hormones are critical determinants of cellular differentiation. We used the zebrafish model to evaluate the involvement of thyroid hormones in regeneration processes after caudal fin amputation. We examined early events following fin amputation, i.e., blastema formation and nerve repair by growth cone formation. Here, we show that the abolition of thyroid gland activity by methimazole treatment had no effect on blastema formation, but slowed growth cone formation of the lateral line. Conversely, the addition of exogenous thyroid hormones enhanced growth cone formation without affecting blastema formation. However, amputation triggered a strong induction in the blastema of type 3 deiodinase mRNA and enzymatic activity, which degrades thyroid hormone (TH). We therefore blocked deiodinase activity with iopanoic acid (IOP) and saw a reduction in blastema formation, suggesting that local degradation of TH is permissive for cell proliferation in the blastema. The effect of IOP on the blastema required endogenous or exogenous TH. Our findings support a model in which local degradation of TH by type 3 deiodinase is permissive for epimorphic regeneration.

Cellular and molecular basis of deiodinase-regulated thyroid hormone signaling

The iodothyronine deiodinases initiate or terminate thyroid hormone action and therefore are critical for the biological effects mediated by thyroid hormone. Over the years, research has focused on their role in preserving serum levels of the biologically active molecule T(3) during iodine deficiency. More recently, a fascinating new role of these enzymes has been unveiled. The activating deiodinase (D2) and the inactivating deiodinase (D3) can locally increase or decrease thyroid hormone signaling in a tissue- and temporal-specific fashion, independent of changes in thyroid hormone serum concentrations. This mechanism is particularly relevant because deiodinase expression can be modulated by a wide variety of endogenous signaling molecules such as sonic hedgehog, nuclear factor-kappaB, growth factors, bile acids, hypoxia-inducible factor-1alpha, as well as a growing number of xenobiotic substances. In light of these findings, it seems clear that deiodinases play a much broader role than once thought, with great ramifications for the control of thyroid hormone signaling during vertebrate development and metamorphosis, as well as injury response, tissue repair, hypothalamic function, and energy homeostasis in adults.

Thyroid hormone - triiodothyronine - has contrary effect on proliferation of human proximal tubules cell line (HK2) and renal cancer cell lines (Caki-2, Caki-1) - role of E2F4, E2F5 and p107, p130

Background

Triiodothyronine regulates proliferation acting as stimulator or inhibitor. E2F4 and E2F5 in complexes with pocket proteins p107 or p130 stop cells in G1, repressing transcription of genes important for cell cycle progression. p107 and p130 inhibits activity of cyclin/cdk2 complexes. Expression of all those proteins could be regulated by triiodothyronine. In clear cell renal cell carcinoma many disturbances in T3 signaling pathway was described, in that type of cancer also expression of some key G1 to S phase progression regulators was shown.

Methods

We investigated role of T3 and its receptors in regulation of proliferation of HK2, Caki-2, Caki-1 cell lines (cell counting, cytometric analysis of DNA content) and expression of thyroid hormone receptors, E2F4, E2F5, p107 and p130 (western blot and semi-quantitative real time PCR). Statistical analysis was performed using one-way ANOVA.

Results and Conclusion

We show that T3 inhibits proliferation of HK2, and stimulates it in Caki lines. Those differences are result of disturbed expression of TR causing improper regulation of E2F4, E2F5, p107 and p130 in cancer cells.

A novel role for thyroid hormone receptor beta in cellular radiosensitivity

Thyroid hormone receptors (THRs) widely govern cell growth, differentiation and metabolism acting in a ligand- and cofactor-dependent manner to modulate tissue-specific gene expression. Given a large variety of genes regulated by THRs and multiplicity of cellular processes potentially influenced by THRs, we addressed the role of THRB (thyroid hormone receptor beta) in cellular radiosensitivity. Wild-type and mutant THRB were overexpressed in several cell lines using an adenovirus-mediated gene delivery and their effects were examined after cell exposure to gamma-rays. Wild-type THRB decreased clonogenic survival of the cell lines with low levels of endogenous THRB, retarded their growth and synergized with radiation in decreasing proliferative potential and promoting cellular senescence. These changes were accompanied by the accumulation of p21 (CDKN1A, CIP1, WAF1) and p16 (CDKN2A, INK4a) inhibitors of cyclin-dependent kinases and by the decrease of Rb (retinoblastoma protein) phosphorylation. Mutant THRB produced a radioprotective effect, attenuated radiation-induced growth inhibition and cellular senescence. The results suggest that THRB may modulate cellular radiosensitivity and stress-induced senescence.

Thyroid hormone receptor-beta (TR beta 1) impairs cell proliferation by the transcriptional inhibition of cyclins D1, E and A2

Thyroid hormone receptor-beta1 (TRbeta1) belongs to the ligand-inducible transcription factor superfamily. We have previously described that stable TRbeta1 expression impairs fibroblast proliferation diminishing levels and activity of the main regulators of the G(1)/S transition. To unmask the underlying molecular mechanism of this action, we have investigated the expression of cyclin D1, E and A2 upon serum stimulation in TRbeta1 expressing cells, finding a strong downregulation of their mRNAs, concomitant with low protein levels. The inhibition of the transcriptional activation in response to serum of these cyclins is differently exerted. For cyclin D1, we demonstrate that TRbeta1 represses its promoter as a consequence of the downregulation of c-jun levels, diminished AP-1 activation and loss of c-jun recruitment to its binding sites on cyclin D1 promoter. For cyclin E and A2, it is the impairment of the cyclinD/Rb/E2F pathway by TRbeta1 that prevents the activation of these two E2F target genes. Indeed, recruitment of E2F-1 to cyclin A2 promoter could not be detected. In summary, we propose that apo-TRbeta1 exerts its antiproliferative action through a mechanism that could constitute a model by which other nuclear receptors may control cell division.

Sonic hedgehog-induced type 3 deiodinase blocks thyroid hormone action enhancing proliferation of normal and malignant keratinocytes

The Sonic hedgehog (Shh) pathway plays a critical role in hair follicle physiology and is constitutively active in basal cell carcinomas (BCCs), the most common human malignancy. Type 3 iodothyronine deiodinase (D3), the thyroid hormone-inactivating enzyme, is frequently expressed in proliferating and neoplastic cells, but its role in this context is unknown. Here we show that Shh, through Gli2, directly induces D3 in proliferating keratinocytes and in mouse and human BCCs. We demonstrate that Gli-induced D3 reduces intracellular active thyroid hormone, thus resulting in increased cyclin D1 and keratinocyte proliferation. D3 knockdown caused a 5-fold reduction in the growth of BCC xenografts in nude mice. Shh-induced thyroid hormone degradation via D3 synergizes with the Shh-mediated reduction of the type 2 deiodinase, the thyroxine-activating enzyme, and both effects are reversed by cAMP. This previously unrecognized functional cross-talk between Shh/Gli2 and thyroid hormone in keratinocytes is a pathway by which Shh produces its proliferative effects and offers a potential therapeutic approach to BCC.