The correlation of sodium iodide symporter and BRAFV600E mutation in classical variant papillary thyroid carcinoma

MAPK Inhibition Requires Active RAC1 Signaling to Effectively Improve Iodide Uptake by Thyroid Follicular Cells

Simple Summary

The Sodium/Iodide Simulator (NIS) is responsible for the uptake of iodide in the thyroid follicular cells. NIS is present in most differentiated thyroid carcinomas (DTC), allowing radioactive iodine (RAI) to be used to destroy malignant cells. However, a significant proportion of DTCs stop picking up iodide and become resistant to RAI therapy. This is mainly due to the symporter no longer being produced or not being placed correctly at the cell’s membrane. This has been associated with mechanisms linked to malignant transformation, namely the overactivation of the so-called MAPK pathway. Thus, several drugs have been developed to inhibit this pathway, attempting to increase NIS levels and iodide uptake. However, MAPK inhibitors have had only partial success in restoring NIS expression. We found that the activity of another protein, the small GTPase RAC1, has an important role in this process, determining the outcome of MAPK inhibitors. Thus, our findings open new opportunities to find effective therapeutic alternatives for DTC resistant to RAI.

Abstract

The Sodium/Iodide Symporter (NIS) is responsible for the active transport of iodide into thyroid follicular cells. Differentiated thyroid carcinomas (DTCs) usually preserve the functional expression of NIS, allowing the use of radioactive iodine (RAI) as the treatment of choice for metastatic disease. However, a significant proportion of patients with advanced forms of TC become refractory to RAI therapy and no effective therapeutic alternatives are available. Impaired iodide uptake is mainly caused by the defective functional expression of NIS, and this has been associated with several pathways linked to malignant transformation. MAPK signaling has emerged as one of the main pathways implicated in thyroid tumorigenesis, and its overactivation has been associated with the downregulation of NIS expression. Thus, several strategies have been developed to target the MAPK pathway attempting to increase iodide uptake in refractory DTC. However, MAPK inhibitors have had only partial success in restoring NIS expression and, in most cases, it remained insufficient to allow effective treatment with RAI. In a previous work, we have shown that the activity of the small GTPase RAC1 has a positive impact on TSH-induced NIS expression and iodide uptake in thyroid cells. RAC1 is a downstream effector of NRAS, but not of BRAF. Therefore, we hypothesized that the positive regulation induced by RAC1 on NIS could be a relevant signaling cue in the mechanism underlying the differential response to MEK inhibitors, observed between NRAS- and BRAF-mutant tumors. In the present study, we found that the recovery of NIS expression induced through MAPK pathway inhibition can be enhanced by potentiating RAC1 activity in thyroid cell systems. The negative impact on NIS expression induced by the MAPK-activating alterations, NRAS Q61R and BRAF V600E, was partially reversed by the presence of the MEK 1/2 inhibitors AZD6244 and CH5126766. Notably, the inhibition of RAC1 signaling partially blocked the positive impact of MEK inhibition on NIS expression in NRAS Q61R cells. Conversely, the presence of active RAC1 considerably improved the rescue of NIS expression in BRAF V600E thyroid cells treated with MEK inhibitors. Overall, our data support an important role for RAC1 signaling in enhancing MAPK inhibition in the context of RAI therapy in DTC, opening new opportunities for therapeutic intervention.

Do BRAFV600E mutation and sodium-iodide symporter expression affect the response to radioactive iodine therapy in patients with papillary thyroid carcinoma?

OBJECTIVE

To report on the associations between BRAF and sodium iodide symporter expressions and treatment outcomes in patients with papillary thyroid carcinoma.

METHODS

Inclusion criteria included a pathologic diagnosis of papillary thyroid carcinoma of any stage, thyroidectomy followed by radioactive iodine therapy, and follow-up for at least 12 months after initial therapy. Events were classified as persistent or recurrent disease based on a clinical or investigational evidence of disease within or after, respectively, 1 year from initial therapy. Disease-free survival was calculated between the dates of surgery and confirmed event. Patients with no evidence of disease were censored at their last follow-up (censored group). BRAF mutation and sodium-iodide symporter expressions were evaluated using immunohistochemistry.

RESULTS

The study included 78 patients (60 females, 18 males) with median age 36 years (range: 20-70 years). BRAF was positive in 78%, equivocal in 13%, and negative in 9%. Sodium-iodide symporter was positive in 88%. BRAF mutation was significantly associated with increasing tumor size, presence of lymphovascular invasion, classic subtype of papillary thyroid carcinoma, thyroid capsular infiltration, and lymph node metastasis. Sodium-iodide symporter expression was not associated with any clinical or pathologic characteristics. Patients with negative or equivocal BRAF had significantly better disease-free survival (82%, 3 events) compared to the positive group (41%, 33 events; P=0.02).

CONCLUSION

In patients with papillary thyroid carcinoma, BRAF mutation is associated with high-risk pathological characteristics and worsened disease-free survival.

A meta-analysis evaluating the relationship between B-type Raf kinase mutation and cervical lymphatic metastasis in papillary thyroid cancer

BACKGROUND

B-type Raf kinase (BRAF) mutation is proved to be a critical predictive factor in papillary thyroid cancer (PTC) with aggressive characteristics. However, the association between BRAF mutation and cervical lymphatic metastasis in PTC is controversial.

METHODS

We searched papers on the study of BRAF mutation and cervical lymphatic metastasis in PTC patients through PubMed, Web of Science, Embase, and Cochranelibrary. The BRAF (+) cases, BRAF (-) cases, and cervical lymphphatic metastatic cases in both BRAF (+) and BRAF (-) groups were collected. After Quality assessment, statistical Analysis (funnel plot and Harbord evaluation, Random-effect model, heterogeneity, subgroup analysis, sensitivity analysis, and metacum analysis) were done by the Review Manager (RevMan) 5.3 and stata14 statistical software.

RESULTS

There were 78 cross-section studies which met our inclusion criteria. And all of them had no selection bias, publication bias, or any other bias. A significant association existed between BRAF mutation and cervical lymph node metastasis (LNM) (odds ratio [OR] = 1.63; 95% confidence interval [CI]: 1.44-1.84; P < .05). Overall, 46 studies were conducted among East Asians. Twenty four articles had provided the data of central lymph node metastasis (CLNM), 11 articles with the data of lateral lymph node metastasis (LLNM), and classic/conventional PTC (CPTC) was analyzed in 10 studies. Subgroup analyses were performed based on ethnicity, metastatic site, and subtype of PTC. Significant association between BRAF (+) mutation and cervical LNM were indicated in East Asians (OR = 1.73; 95% CI: 1.49-2.02; P < .05), in non-East Asians (OR = 1.57; 95% CI: 1.26-1.96; P < .05), and in CLNM (OR = 1.80; 95% CI: 1.56-2.07; P < .05). While no significant association was found in LLNM (OR = 1.37; 95% CI: 0.76-2.48; P = .29 > .05) and in CPTC (OR = 1.32; 95% CI: 0.97-1.80; P = .08 > .05). We did not find any other major changes when sensitivity analysis was performed. The metacum analysis showed no significant association existed before 2012. While a significant association began to exist between BRAF mutation and LNM from 2012, and this association became stable from 2017.

CONCLUSIONS

We consider that a significant association exists between BRAF mutation and cervical LNM. Further meta-analysis on subgroup may reveal some valuable factors between BRAF gene mutation and LNM. And we do not recommend that BRAF (+) as the biomarker for LNM in PTC.

Targeting the BRAF Signaling Pathway in CD133pos Cancer Stem Cells of Anaplastic Thyroid Carcinoma

Background:

Cancer stem cells (CSCs) with a self-renewal ability in tumor cells population, execute a pivotal function in tumorigenesis, retrogression, and metastasis of malignant cancers such as anaplastic thyroid carcinoma (ATC).

Materials and Methods:

In this study, we isolated CSCs subpopulation with CD133 surface marker from three ATC cell lines by magnetic cell sorting assay. After confirming the segregation by the flow cytometry method, BRAF and sodium-iodide symporter (NIS) genes were investigated in them before and after incubation with BRAF inhibitor. Also, we evaluated the NIS protein expression and localization.

Results:

Established upon q-RT PCR data, when compared to human normal thyrocytes, the BRAF^V600E gene was over-expressed in CD133^pos cells (>1705.99 ± 55.55 fold, Mean ± SEM, n=3, P- value<0.05), whilst the expression of NIS gene was very restricted (< 0.0008 ± 5.43 fold, Mean ± SEM, n=3, P- value<0.05) in them. Also, our results showed that BRAF inhibition affected NIS protein expression and localization.

Conclusions:

Current study showed that the differentiate genes/proteins expression can be induced in the CSCs via focus on signal transduction pathways and targeting their molecules, that are involved in expression of these genes/proteins. Therefore, attention to targeting CSCs along with routine thyroid cancer therapy, can help to ATC treatment.

A review on the mechanism of iodide metabolic dysfunction in differentiated thyroid cancer

The incidence of differentiated thyroid cancer (DTC) has been increasing rapidly worldwide, and the risk factors remain unclear. With the growing number of patients with DTC, the related issues have been gradually highlighted. ¹³¹Iodide (¹³¹I) is an important treatment for DTC and has the potential to reduce the risk of recurrence. ¹³¹I is also an effective treatment for distant metastases of thyroid carcinoma. However, iodide metabolism dysfunction in metastatic foci causes patients to lose the opportunity of ¹³¹I treatment. This article reviews the related mechanisms of iodide metabolism dysfunction in DTC cells and summarizes the clinical transformation progression.

The Role of the NIS (SLC5A5) Gene in Papillary Thyroid Cancer: A Systematic Review

Papillary thyroid cancer (PTC) is the most common thyroid malignancy. Genetic and epigenetic alterations play a decisive role in the onset of several human neoplasms. Mutations and polymorphisms are two frequent genetic alterations. Located on chromosome 19 (19p13.11), the NIS SLC5A5 (solute carrier family 5 member 5) gene encodes a highly specialized and efficient 80-90 kDa transmembrane glycoprotein that mediates active transport of iodide from the bloodstream into the follicular cells. Given the highly significant role of NIS in the physiology and the cancer pathogenesis process, this paper's objective is to provide a comprehensive assessment of the associations between NIS gene and protein with papillary thyroid cancer.

NIS expression in thyroid tumors, relation with prognosis clinicopathological and molecular features

Thyroid cancer therapy is based on surgery followed by radioiodine treatment. The incorporation of radioiodine by cancer cells is mediated by sodium iodide symporter (NIS) (codified by the SLC5A5 gene), that is functional only when targeted to the cell membrane. We aimed to evaluate if NIS expression in thyroid primary tumors would be helpful in predicting tumor behavior, response to therapy and prognosis. NIS expression was addressed by qPCR and immunohistochemistry. In order to validate our data, we also studied SLC5A5 expression on 378 primary papillary thyroid carcinomas from The Cancer Genome Atlas (TCGA) database. In our series, SLC5A5 expression was lower in carcinomas with vascular invasion and with extrathyroidal extension and in those harboring BRAFV600E mutation. Analysis of SLC5A5 expression from TCGA database confirmed our results. Furthermore, it showed that larger tumors, with locoregional recurrences and/or distant metastases or harboring RAS, BRAF and/or TERT promoter (TERTp) mutations presented significantly less SLC5A5 expression. Regarding immunohistochemistry, 12/211 of the cases demonstrated NIS in the membrane of tumor cells, those cases showed variable outcomes concerning therapy success, prognosis and all but one were wild type for BRAF, NRAS and TERTp mutations. SLC5A5 mRNA lower expression is associated with features of aggressiveness and with key genetic alterations involving BRAF, RAS and TERTp. Mutations in these genes seem to decrease protein expression and its targeting to the cell membrane. SLC5A5 mRNA expression is more informative than NIS immunohistochemical expression regarding tumor aggressiveness and prognostic features.