Key signaling pathways in thyroid cancer Zaballos, Miguel A; Santisteban, Pilar
Journal of Endocrinology/Journal of endocrinology
235, Številka:
2
Journal Article
Recenzirano
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Whole genome sequencing approaches have provided unprecedented insights into the genetic lesions responsible for the onset, progression and dedifferentiation of various types of thyroid carcinomas. ...Through these efforts, the MAPK and PI3K signaling cascades have emerged as the main activation pathways implicated in thyroid tumorigenesis. The nature of these essential pathways is highly complex, with hundreds of components, multiple points of crosstalk, different subcellular localizations and with the ability to potentially regulate many cellular processes. Small-molecule inhibitors targeting key kinases of these pathways hold great promise as novel therapeutics and several have reached clinical trials. However, while some remarkable responses have been reported, the development of resistance remains a matter of concern and limits the benefit for patients. In this review, we discuss the latest findings on the major components of the MAPK and PI3K pathways, including their mechanisms of activation in physiological and pathological contexts, their genetic alterations with respect to the different types of thyroid carcinomas and the more relevant drugs designed to block their activity.
Adenosine deaminases acting on RNA (ADARs) convert adenosine to inosine in double-stranded RNA. A-to-I editing of RNA is a widespread posttranscriptional process that has recently emerged as an ...important mechanism in cancer biology. A-to-I editing levels are high in several human cancers, including thyroid cancer, but ADAR1 editase-dependent mechanisms governing thyroid cancer progression are unexplored. To address the importance of RNA A-to-I editing in thyroid cancer, we examined the role of ADAR1. Loss-of-function analysis showed that ADAR1 suppression profoundly repressed proliferation, invasion, and migration in thyroid tumor cell models. These observations were validated in an in vivo xenograft model, which showed that ADAR1-silenced cells had a diminished ability to form tumors. RNA editing of miRNAs has the potential to markedly alter target recognition. According to TCGA data, the tumor suppressor miR-200b is overedited in thyroid tumors, and its levels of editing correlate with a worse progression-free survival and disease stage. We confirmed miR-200b overediting in thyroid tumors and we showed that edited miR-200b has weakened activity against its target gene ZEB1 in thyroid cancer cells, likely explaining the reduced aggressiveness of ADAR1-silenced cells. We also found that RAS, but not BRAF, modulates ADAR1 levels, an effect mediated predominantly by PI3K and in part by MAPK. Lastly, pharmacological inhibition of ADAR1 activity with the editing inhibitor 8-azaadenosine reduced cancer cell aggressiveness. Overall, our data implicate ADAR1-mediated A-to-I editing as an important pathway in thyroid cancer progression, and highlight RNA editing as a potential therapeutic target in thyroid cancer.
Recent studies have shown that miR-146b is the most upregulated microRNA in thyroid cancer and has a central role in cancer progression through mechanisms that remain largely unidentified. As ...phosphoinositide 3-kinase/protein kinase-B (PI3K/AKT) signaling is a fundamental oncogenic driver in many thyroid cancers, we explored a potential role for miR-146b and its target genes in PI3K/AKT activation. Among the predicted target genes of miR-146b, we found the tumor-suppressor phosphatase and tensin homolog (PTEN). Constitutive overexpression of miR-146b in thyroid epithelial cell lines significantly decreased PTEN mRNA and protein levels by direct binding to its 3'-UTR. This was accompanied by PI3K/AKT hyperactivation, leading to the exclusion of FOXO1 and p27 from the nucleus and a corresponding increase in cellular proliferation. Moreover, miR-146b overexpression led to protection from apoptosis and an increased migration and invasion potential, regulating genes involved in epithelial-mesenchymal transition. Notably, with the single exception of E-cadherin expression, all of these outcomes could be reversed by PTEN coexpression. Further analysis showed that miR-146b directly inhibits E-cadherin expression through binding to its 3'-UTR. Interestingly, miR-146b inhibition in human thyroid tumor xenografts, using a synthetic and clinically amenable molecule, blocked tumor growth when delivered intratumorally. Importantly, this inhibition increased PTEN protein levels. In conclusion, our data define a novel mechanism of PI3K/AKT hyperactivation and outline a regulatory role for miR-146b in suppressing PTEN expression, a frequent observation in thyroid cancer. Both events are related to a more aggressive tumoral phenotype. Targeting miR-146b therefore represents a promising therapeutic strategy for the treatment of this disease.
Identification of the thyroid transcription factors (TTFs), NKX2-1, FOXE1, PAX8 and HHEX, has considerably advanced our understanding of thyroid development, congenital thyroid disorders and thyroid ...cancer. The TTFs are fundamental to proper formation of the thyroid gland and for maintaining the functional differentiated state of the adult thyroid; however, they are not individually required for precursor cell commitment to a thyroid fate. Although knowledge of the mechanisms involved in thyroid development has increased, the full complement of genes involved in thyroid gland specification and the signals that trigger expression of the genes that encode the TTFs remain unknown. The mechanisms involved in thyroid organogenesis and differentiation have provided clues to identifying the genes that are involved in human congenital thyroid disorders and thyroid cancer. Mutations in the genes that encode the TTFs, as well as polymorphisms and epigenetic modifications, have been associated with thyroid pathologies. Here, we summarize the roles of the TTFs in thyroid development and the mechanisms by which they regulate expression of the genes involved in thyroid differentiation. We also address the implications of mutations in TTFs in thyroid diseases and in diseases not related to the thyroid gland.
The global downregulation of microRNAs (miRNAs) is emerging as a common hallmark of cancer. However, the mechanisms underlying this phenomenon are not well known. We identified that the oncogenic ...miR-146b-5p attenuates miRNA biosynthesis by targeting DICER1 and reducing its expression. DICER1 overexpression inhibited all the miR-146b-induced aggressive phenotypes in thyroid cells. Systemic injection of an anti-miR-146b in mice with orthotopic thyroid tumors suppressed tumor growth and recovered DICER1 levels. Notably, DICER1 downregulation promoted proliferation, migration, invasion, and epithelial-mesenchymal transition through miRNA downregulation. Our analysis of The Cancer Genome Atlas revealed a general decrease in DICER1 expression in thyroid cancer that was associated with a worse clinical outcome. Administration of the small-molecule enoxacin to promote DICER1 complex activity reduced tumor aggressiveness both in vitro and in vivo. Overall, our data confirm DICER1 as a tumor suppressor and show that oncogenic miR-146b contributes to its downregulation. Moreover, our results highlight a potential therapeutic application of RNA-based therapies including miRNA inhibitors and restoration of the biogenesis machinery, which may provide treatments for thyroid and other cancers.
Organization of epithelial cells during follicular lumen formation is crucial for thyroid morphogenesis and function of the thyroid gland; however, the molecular mechanisms underlying this are poorly ...understood. To investigate this process, we established three-dimensional (3D) epithelial culture model systems using Fischer rat thyroid (FRT) cells or murine primary thyrocytes that developed polarized spherical structures with a central lumen, mimicking thyroid follicles. Using microarray-based differential expression analysis of FRT cells grown under 2D or 3D conditions, followed by RNA-mediated interference (RNAi) and morphogenetic analysis, we identified a key role for the thyroid transcription factor Pax8 and its target cadherin-16 (Cdh16) in the generation of polarized follicle-like structures. Silencing Pax8 expression inhibited the acquisition of apical-basal membrane polarity and impaired lumen formation. Both laminin and β1-integrin (Itgb1) expression was reduced, and cell cytoskeleton polarized distribution was altered. Silencing Cdh16 expression also led to the formation of defective structures characterized by very low laminin expression at the follicle-matrix interface, downregulation of Itgb1, and unpolarized distribution of cell cytoskeleton. Our results demonstrate that Pax8 controls apical-basal follicular polarization and follicle formation through Cdh16.
To investigate the prognostic value of BRAF V600E mutation for the recurrence of papillary thyroid cancer (PTC).
This was a retrospective multicenter study of the relationship between BRAF V600E ...mutation and recurrence of PTC in 2,099 patients (1,615 women and 484 men), with a median age of 45 years (interquartile range IQR, 34 to 58 years) and a median follow-up time of 36 months (IQR, 14 to 75 months).
The overall BRAF V600E mutation prevalence was 48.5% (1,017 of 2,099). PTC recurrence occurred in 20.9% (213 of 1,017) of BRAF V600E mutation-positive and 11.6% (125 of 1,082) of BRAF V600E mutation-negative patients. Recurrence rates were 47.71 (95% CI, 41.72 to 54.57) versus 26.03 (95% CI, 21.85 to 31.02) per 1,000 person-years in BRAF mutation-positive versus -negative patients (P < .001), with a hazard ratio (HR) of 1.82 (95% CI, 1.46 to 2.28), which remained significant in a multivariable model adjusting for patient sex and age at diagnosis, medical center, and various conventional pathologic factors. Significant association between BRAF mutation and PTC recurrence was also found in patients with conventionally low-risk disease stage I or II and micro-PTC and within various subtypes of PTC. For example, in BRAF mutation-positive versus -negative follicular-variant PTC, recurrence occurred in 21.3% (19 of 89) and 7.0% (24 of 342) of patients, respectively, with recurrence rates of 53.84 (95% CI, 34.34 to 84.40) versus 19.47 (95% CI, 13.05 to 29.04) per 1,000 person-years (P < .001) and an HR of 3.20 (95% CI, 1.46 to 7.02) after adjustment for clinicopathologic factors. BRAF mutation was associated with poorer recurrence-free probability in Kaplan-Meier survival analyses in various clinicopathologic categories.
This large multicenter study demonstrates an independent prognostic value of BRAF V600E mutation for PTC recurrence in various clinicopathologic categories.
Diabetes alters microvascular function in the vascular beds of organs, including the lungs. Cardiovascular complications of pulmonary vascular affectation may be a consequence of the overactivation ...of the vasoconstrictive and proliferative components of the renin-angiotensin system. We previously reported that pulmonary physiology and surfactant production is improved by the glucagon-like peptide 1 receptor (GLP-1R) agonist liraglutide (LIR) in a rat model of lung hypoplasia. Because we hypothesized that streptozotocin-induced diabetes rats would show deficiencies in lung function, including surfactant proteins, and develop an imbalance of the renin-angiotensin system in the lungs. This effect would in turn be prevented by long-acting agonists of the GLP-1R, such as LIR. The induction of diabetes reduced the surfactant protein A and B in the lungs and caused the vasoconstrictor component of the renin-angiotensin system to predominate, which in turn increased angiotensin II levels, and ultimately being associated with right ventricle hypertrophy. LIR restored surfactant protein levels and reversed the imbalance in the renin-angiotensin system in this type 1 diabetes mellitus rat model. Moreover, LIR provoked a strong increase in angiotensin-converting enzyme 2 expression in the lungs of both diabetic and control rats, and in the circulating angiotensin(1–7) in diabetic animals. These effects prompted complete reversion of right ventricle hypertrophy. The consequences of LIR administration were independent of glycemic control and of glucocorticoids, and they involved NK2 homeobox 1 signaling. This study demonstrates by first time that GLP-1R agonists, such as LIR, might improve the cardiopulmonary complications associated with diabetes.
Thyroid cancer is the most common primary endocrine malignancy in adults and its incidence is rapidly increasing. Long non-coding RNAs (lncRNAs), generally defined as RNA molecules longer than 200 ...nucleotides with no protein-encoding capacity, are highly tissue-specific molecules that serve important roles in gene regulation through a variety of different mechanisms, including acting as competing endogenous RNAs (ceRNAs) that 'sponge' microRNAs (miRNAs). In the present study, using an integrated approach through RNA-sequencing of paired thyroid tumor and non-tumor samples, we have identified an interactome network between lncRNAs and miRNAs and examined the functional consequences in vitro and in vivo of one of such interactions. We have identified a likely operative post-transcriptional regulatory network in which the downregulated lncRNA, SPTY2D1-AS1, is predicted to target the most abundant and upregulated miRNAs in thyroid cancer, particularly miR-221, a well-known oncomiRNA in cancer. Indeed, SPTY2D1-AS1 functions as a potent tumor suppressor in vitro and in vivo, it is downregulated in the most advanced stages of human thyroid cancer, and it seems to block the processing of the primary form of miR-221. Overall, our results link SPTY2D1-AS1 to thyroid cancer progression and highlight the potential use of this lncRNA as a therapeutic target of thyroid cancer.
While the signaling pathways and transcription factors involved in the differentiation of thyroid follicular cells, both in embryonic and adult life, are increasingly well understood, the underlying ...mechanisms and potential crosstalk between the thyroid transcription factors Nkx2.1, Foxe1 and Pax8 and inductive signals remain unclear. Here, we focused on the transcription factor Sox9, which is expressed in Nkx2.1-positive embryonic thyroid precursor cells and is maintained from embryonic development to adulthood, but its function and control are unknown. We show that two of the main signals regulating thyroid differentiation, TSH and TGFβ, modulate Sox9 expression. Specifically, TSH stimulates the cAMP/PKA pathway to transcriptionally upregulate Sox9 mRNA and protein expression, a mechanism that is mediated by the binding of CREB to a CRE site within the Sox9 promoter. Contrastingly, TGFβ signals through Smad proteins to inhibit TSH-induced Sox9 transcription. Our data also reveal that Sox9 transcription is regulated by the thyroid transcription factors, particularly Pax8. Interestingly, Sox9 significantly increased the transcriptional activation of Pax8 and Foxe1 promoters and, consequently, their expression, but had no effect on Nkx2.1. Our study establishes the involvement of Sox9 in thyroid follicular cell differentiation and broadens our understanding of transcription factor regulation of thyroid function.
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