Angiogenesis and lymphangiogenesis in thyroid proliferative lesions: relationship to type and tumour behaviour

The role of angiogenesis and lymphangiogenesis in thyroid cancer pathogenesis has not been elucidated. Patterns for tumour behaviour and metastasic spread vary according to tumour type and whether differences in the angiogenic or lymphangiogenic phenotype influence the route for tumour metastases or determine a more aggressive behaviour has not been fully explored. The angiogenic and lymphangiogenic phenotypes of a large cohort of thyroid proliferative lesions (n=191) were studied. Using immunohistochemistry for CD34, lymphatic vessel endothelial receptor-1 (LYVE-1) (specific markers for vascular and lymphatic endothelium respectively), vascular endothelial growth factor (VEGF-A), VEGF-C and fibroblast growth factor-2 (FGF-2), this study analyses microvascular density (MVD), lymphatic vascular density (LVD), and expression of angiogenic and lymphangiogenic factors in normal thyroid (NT; n=19), multinodular goitre (n=25), toxic multinodular goitre (n=8), Graves' hyperplasia (n=22), follicular adenoma (n=54), papillary carcinoma (PC; n=27), incidental papillary microcarcinoma (PMC; n=8), follicular carcinoma (FC; n=20) and medullary carcinoma (MC; n=8). MVD was decreased in proliferative lesions, benign and malignant, compared with NT (P<0.0001). In contrast, VEGF-A expression was increased in thyroid carcinomas (PC, FC and MC) when compared with PMC, benign lesions and NT (P<0.0001). LVD was higher in PC and PMC (P=0.001), and VEGF-C expression was increased in PC (P<0.0001). Despite higher LVD and increased expression of VEGF-A and VEGF-C in thyroid cancers, these markers were not related to poor prognosis in terms of tumour size, multifocality and/or presence of lymphatic or distant metastases. In conclusion, angiogenesis is reduced in thyroid proliferative lesions compared with NT tissue. However, VEGF-A expression is upregulated in thyroid cancers. Lymphangiogenesis and VEGF-C expression are increased in thyroid tumours prone to lymphatic metastases. This may be an important mechanism underlying the differences in metastatic behaviour between papillary and follicular thyroid cancer.     

Thyroid follicular adenomas may display features of follicular carcinoma and follicular variant of papillary carcinoma

Thyroid follicular adenomas (FA) are encapsulated tumors lacking vascular, capsular or lymphatic invasion and the typical nuclear features of papillary carcinoma (PC). However, some FA demonstrate nuclear atypia reminiscent of either follicular carcinomas (FC) or follicular variant of papillary carcinomas (FVPC), suggesting they may represent precursors of malignant transformation. We hypothesized that an objective evaluation of nuclear chromatin patterns could be used to define atypical follicular tumors (AFT) that are likely to be premalignant. To test this hypothesis, we used a computer-aided image analysis system to define the chromatin pattern of nuclei from thyroid tumors. To validate the system, we analyzed 3000 nuclei from 10 FA, 10 FC, and 10 FVPC samples and accurately distinguished between these classes of tumors. Then, we analyzed nine AFT and, in parallel, we analyzed the tumors for activating mutations of N2-RAS and over-expression of RET. The predominant chromatin pattern of AFT was of FA type in two cases, FC type in two cases, and PC type in three cases. One case contained similar numbers of FC and PC nuclei and one was comprised of a mixture of the three nuclear types. Neither RAS mutation nor RET overexpression were detected in FA. N2-RAS mutations were found in 33% of AFT, 20% of FC and 20% of FVPC without correlation with chromatin pattern. Over-expression of RET was detected in 45% of AFT, 20% of FC and 50% of FVPC and was correlated with PC nuclei. These results show that AFT are a heterogeneous group of tumors, containing genuine benign tumors and tumors that share morphological and molecular features with follicular and papillary carcinomas that might be precursors of both types of thyroid carcinomas.     

CD10 expression is useful in the diagnosis of follicular carcinoma and follicular variant of papillary thyroid carcinoma.

CD10/neutral endopeptidase 24.11(NEP) is a membrane-bound zinc metalloproteinase the expression of which represents a useful tool in the classification and diagnosis of malignant leukemia and lymphoma. Recently, CD10 has been found to be expressed in nonhematopoietic tissues and various types of neoplasms. In this study, we examined CD10 immunostaining in paraffin sections of 70 distinct lesions to investigate whether CD10 is a useful diagnostic marker for thyroid neoplasms. CD10 was not detected in normal thyroid tissue, benign lesions (15 follicular lesions and 15 adenomatous goiters), and pure papillary carcinomas except for follicular variants. In contrast, CD10 was expressed in 8 of 10 (80%) follicular carcinomas and 7 of 9 (77%) follicular variant of papillary thyroid carcinomas. This appears to be the first report on the expression of this member of a newly identified gene family in thyroid tumors. In conclusion, immunohistochemistry of CD10 in paraffin sections is valuable in the classification of thyroid follicular lesions into benign and malignant groups and in the diagnosis of follicular variant of papillary thyroid carcinoma.     

Metastin receptor is overexpressed in papillary thyroid cancer and activates MAP kinase in thyroid cancer cells

The development of distant metastasis is the most important predictor of death from thyroid cancer. KiSS-1 is a recently cloned human metastasis suppressor gene whose product, metastin, was recently identified as the endogenous agonist for a novel Gq/11 coupled receptor (metastin receptor). The expression and functional consequences of metastin and the metastin receptor have not been evaluated in thyroid cancer. We measured metastin and metastin receptor mRNA levels in 10 FCs and 13 papillary carcinomas (PCs), 2 benign non-functioning follicular adenomas (FAs), and 11 normal thyroid samples, and evaluated the signaling pathways activated by metastin in ARO thyroid cancer cells that express the metastin receptor endogenously. Paired normal and tumor samples were available for 4 PC and 3 PFC samples. Metastin mRNA was detected in 6/11 normal samples, and 0/2 FA, 2/10 FC, and 9/13 PC samples (p < 0.05 for PC vs. FC). Metastin receptor was not expressed in any normal thyroid or benign FA samples, and was expressed in only a minority (2/10) of FC samples. However, the receptor was expressed in the majority (10/13) of PCs (p = 0.002 for PC vs. normal tissue). Increased levels of metastin receptor were detected in all four PCs compared to adjacent normal tissue. Incubation levels of metastin receptor were detected in all four PCs compared to adjacent normal tissue. Incubation of metastin receptor expressing ARO thyroid cancer cells with metastin resulted in activation of ERK, but not Akt. Taken together, these data suggest a potential role for metastin and/or metastin receptors in modulating the biological behavior of thyroid cancers.     

Diagnosis of thyroid follicular carcinoma by the vascular pattern and velocimetric parameters using high resolution pulsed and power Doppler ultrasonography

The aim of this study was to define the preoperative diagnosis of thyroid follicular carcinoma by the vascular pattern and velocimetric parameters using high resolution pulsed and power Doppler ultrasonography (US). We compared the vascular pattern and the velocimetric parameters, such as peak systolic velocity (Vmax), end-diastolic velocity (Vmin), pulsatility index (PI), or resistance index (RI) between follicular adenoma (FA, n = 25) and follicular carcinoma (FC, n = 10) and analysed them by means of receiver characteristics curves (ROC). Of 10 patients with FC, 8 (80%) patients presented a moderate increase of intranodular vascularization using power Doppler US. In contrast, the majority (84%, 21 out of 25 cases) of FA cases showed only a peripheral rim of color flow even by power Doppler US. These color flow imagings by power Doppler US were suggested to be a reliable tool for the differential diagnosis of thyroid follicular tumor with a sensitivity of 87.5% and a specificity of 92%. In velocimetric analyses, the Vmax/Vmin ratios, PI, and RI were significantly higher in the patients with FC than those with FA (p<0.001, p<0.005, and p<0.001, respectively). By means of ROC, FC could be diagnosed with a cutoff value of ratio of PI (>1.35), RI (>0.78), and Vmax/Vmin (>3.79). The diagnostic efficiency evaluated by ROC curves were 0.898 for PI, 0.876 for RI, and 0.888 for Vmax/Vmin, respectively. In conclusion, the evaluation of the vascular pattern and the velocimetric parameters using pulsed and power Doppler ultrasound may provide important information that is useful in making correct differential diagnosis of malignant or benign thyroid follicular tumor preoperatively.     

Immunostaining for Met/HGF receptor may be useful to identify malignancies in thyroid lesions classified suspicious at fine-needle aspiration biopsy.

The receptor for hepatocyte growth factor (Met) is not expressed in the normal thyroid but it is overexpressed in most thyroid carcinomas. We evaluated whether Met immunostaining of cytological smears from fine-needle aspiration biopsy (FNAB) may be useful for the preoperative diagnosis of thyroid cancer. Notably, routine cytological examination often fails to distinguish well-differentiated follicular carcinomas and a proportion of papillary carcinomas (low-grade papillary carcinomas and papillary carcinomas follicular variant [FVPTC]) from benign lesions: all these lesions are usually classified as suspicious. We examined 80 thyroid lesions diagnosed as suspicious at cytology that had subsequently undergone surgery. The histologic diagnosis had been: papillary carcinomas (n = 14), FVPTC (n = 11), follicular carcinomas (n = 25), atypical follicular adenomas (n = 5), follicular adenomas (n = 20), and nodular goiters (n = 5). We also studied typical papillary carcinomas (n = 30) and nodular goiters (n = 10), all correctly diagnosed at cytology. In lesions classified suspicious at routine cytology, Met immunostaining was positive in 12 of 14 (85.7%) papillary carcinomas, 8 of 11 (72.7%) FVPTC, 7 of 25 (28%) follicular carcinomas, and 5 of 5 atypical adenomas. In contrast, none of the 25 lesions cytologically suspicious but benign at histology were positive. These data suggest that Met immunostaining of suspicious cytological smears are useful for identifying malignant lesions, especially those with a papillary histotype.     

Molecular profiling distinguishes papillary carcinoma from benign thyroid nodules

Recently we identified a molecular basis for differentiating benign and malignant follicular thyroid tumors. The purpose of these studies was to determine whether molecular analysis can be used to differentiate papillary thyroid carcinomas from benign thyroid nodules. Gene expression patterns of 14 papillary thyroid carcinomas and 21 benign tumors were analyzed by oligonucleotide array analysis. The carcinomas included seven classical papillary thyroid carcinomas (PTC) and seven follicular variant of PTC (FVPTC), and the benign tumors included 14 follicular adenomas and seven hyperplastic nodules. A hierarchical clustering analysis was performed to examine the groups for potential differences. The combined PTC and FVPTC groups had a distinct gene expression profile compared with the benign lesions. The sensitivity for a diagnosis of carcinoma was 93%, with a 100% specificity (one FVPTC clustered with the benign nodules). Cancer gene profiles contained both known (Met and galectin-3) and previously unidentified genes. Gene profiling is a reliable means of distinguishing PTC, FVPTC, and benign tumors of the thyroid. These gene profiles may provide insight into the pathogenesis of papillary thyroid carcinoma and may ultimately enhance the preoperative diagnosis of thyroid nodules on a molecular basis.     

Expression of tpo mRNA in thyroid tumors: quantitative PCR analysis and correlation with alterations of ret, Braf , ras and pax8 genes

Immunocytochemistry (ICC) of thyroid peroxidase (TPO) using the monoclonal antibody MoAb47 has been used as malignancy marker on thyroid fine needle aspiration. However, little is known about the fate of TPO in thyroid carcinoma. We performed a qualitative PCR (Q-PCR) analysis to measure the expression of variants of tpo mRNA in 13 normal tissue samples, 30 benign tumors (BT), 21 follicular carcinomas (FC), 20 classical papillary carcinomas (PCc), 12 follicular variants of papillary carcinomas (PCfv) and nine oncocytic carcinomas (OC). We also studied mutations involving the ras, Braf, ret or pax8 genes. Results of Q-PCR were closely correlated with those of ICC (P < 0.0001; R = 0.59) and showed that overall tpo expression was lower in all carcinomas than in normal and BT (P < 0.05). The ratio tpo2 or tpo3 to tpo1 was inversed in follicular tumors. Genetic mutations were observed in 90% of PCc, 61.9% of FC, 41.7% of PCfv, 0% of OC and 10% in BT. pax8-ppar gamma1 rearrangement was correlated with qualitative changes in tpo mRNA (P < 0.01). These results confirmed the decrease of TPO expression in 97% of thyroid carcinomas regardless of histological type and the overexpression of shorter splice variants in follicular tumors. Both reduction in quantity of TPO and impairment of its maturation process could account for the atypical immunohistochemical reaction of MoAb47 with TPO.     

Telomerase activity in thyroid malignancy.

Telomerase activity seems to play a role in the development and pathogenesis of thyroid carcinoma. Its incidence of expression and its application as a tumor marker remain to be elucidated. Thyroid tissues obtained during thyroidectomy from 1996-1998 were rapidly frozen and stored at -80 degrees C until processed. Telomerase activity was determined using telomeric repeat amplification protocol (TRAP). Histology of the tissue examined (67 benign and 59 malignant) was reviewed. Telomerase activity was detected in 15 of 52 papillary carcinomas (29%); 1 of 1 thyroid lymphoma (100%); 1 of 2 anaplastic carcinomas (50%); and 2 of 16 lymphocytic thyroiditis specimens (13%). Telomerase activity was not detectable in 35 normal thyroid, 9 follicular adenoma, 7 nodular hyperplasia, 2 follicular carcinoma, and 2 medullary carcinoma. Lymphocytic thyroiditis was detected in 8 of 37 (22%) apparently normal thyroid tissues adjacent to papillary thyroid carcinoma and telomerase activity was present in 2 of these 8 specimens (25%). In conclusion, telomerase does not appear to be frequently activated in papillary thyroid carcinoma. The association of lymphocytic thyroiditis with papillary thyroid carcinoma may limit its clinical usefulness as a tumor marker.     

Genetic classification of benign and malignant thyroid follicular neoplasia based on a three-gene combination

Thyroid carcinoma is a common endocrine cancer with a favorable prognosis if subjected to timely treatment. However, the clinical identification of follicular thyroid carcinoma (FTC) among patients with benign thyroid nodules is still a challenge. Preoperative fine needle aspiration-based cytology cannot always differentiate follicular carcinomas from benign follicular neoplasias. Because current methods fail to improve preoperative diagnosis of thyroid nodules, new molecular-based diagnoses should be explored. We conducted a microarray-based study to reveal the genetic profiles unique to FTC and follicular adenomas (FAs), to identify the most parsimonious number of genes that could accurately differentiate between benign and malignant follicular thyroid neoplasia. We confirmed our data by quantitative RT-PCR and immunohistochemistry in two independent validation sets with a total of 114 samples. We were able to identify three genes, cyclin D2 (CCND2), protein convertase 2 (PCSK2), and prostate differentiation factor (PLAB), that allow the accurate molecular classification of FTC and FA. Two independent validation sets revealed that the combination of these three genes could differentiate FTC from FA with a sensitivity of 100%, specificity of 94.7%, and accuracy of 96.7%. In addition, our model allowed the identification of follicular variants of papillary thyroid carcinoma with an accuracy of 85.7%. Three-gene profiling of thyroid nodules can accurately predict the diagnosis of FTC and FA with high sensitivity and specificity, thus identifying promising targets for further investigation to ultimately improve preoperative diagnosis.     

Pathogenesis, diagnosis and management of thyroid nodules in children

According to the literature thyroid nodules are quite rare in the first two decades of life. However, there are some exceptions, relating to areas with an iodine deficiency or affected by radioactive fallout, where the risk of nodules and carcinomas is increased. Therefore, it is a great challenge for the physician to distinguish between benign and malignant lesions preoperatively, and not only in these areas of greater risk. A careful work-up, comprising the patient's history, clinical examination, laboratory tests, thyroid ultrasound, scintigraphy, fine-needle aspiration biopsy (FNAB) and molecular studies, is mandatory to improve the preoperative diagnosis. The differential diagnosis should also include benign thyroid conditions such as: (i) congenital hypothyroidism due to dyshormonogenesis or ectopy, (ii) thyroid hemiagenesis, (iii) thyroglossal duct cyst, (iv) simple goiter, (v) cystic lesion, (vi) nodular hyperplasia, (vii) follicular adenoma, (viii) Graves' disease and (ix) Hashimoto thyroiditis, all of which can predispose to the development of thyroid nodules. The majority of thyroid carcinomas derive from the follicular cell (papillary, follicular, insular and undifferentiated (or anaplastic) thyroid carcinoma), whereas medullary thyroid carcinoma derives from calcitonin-producing cells. Inherited forms of thyroid cancer may occur, especially in relation to medullary thyroid carcinoma. FNAB is a critical factor in establishing the preoperative diagnosis. However, we should keep in mind the fact that a conventional cytological evaluation can miss the neoplastic nature of a lesion and the employment of immunocytochemical and molecular studies of aspirates from FNAB can give us a more precise diagnosis of neoplasia in thyroid nodules once they are detected.     

Negative correlation between thyroperoxidase and dual oxidase H2O2-generating activities in thyroid nodular lesions

Iodine incorporation into thyroglobulin is dependent on the activities of both thyroperoxidase (TPO) and thyroid dual oxidase 2 (DuOx2). Although TPO expression is decreased in some thyroid nodular lesions, DuOx1 and 2 mRNA expressions are maintained, but DuOx H2O2-generating activity has never been evaluated in such tumors. Our goal was to determine DuOx activity in hypofunctioning lesions of the thyroid. We evaluated H2O2 generation by DuOx in 12 paranodular to cold nodule samples, 17 non-toxic multinodular goiters (MNG; 33 samples), 3 papillary carcinomas (PC; 4 samples), 3 follicular carcinomas (FC; 4 samples), and 10 follicular adenomas. DuOx activity was detected in all paranodular tissues (121+/-23 nmol H2O2/h per mg protein), but was undetectable (<1 nmol H2O2 generated) in all PC, two out of four FC samples and seven out of ten adenomas. In 11 MNG at least two different areas of the goiter have been evaluated, and in 5 of these goiters one of the samples had DuOx activity below the limit of detection. The coefficient of variation in MNG samples ranged from 11.3 to 57.2%. Interestingly, in all the adenomas studied, TPO activity (486+/-142 U/g protein, n=8) was well within the range found in paranodular tissues (414+/-116 U/g protein, n=3). We found a significant negative correlation between DuOx and TPO activities, suggesting that these enzymes are regulated in opposite directions, at least in thyroid tumors.     

TFF3-based candidate gene discrimination of benign and malignant thyroid tumors in a region with borderline iodine deficiency

BACKGROUND: With the advent of microarray technology, increasing numbers of marker genes are proposed to distinguish benign and malignant thyroid lesions. However, most markers await confirmation through independent studies. In this paper, we re-evaluate the diagnostic potential of 10 proposed candidate genes in benign and malignant thyroid pathologies in a region with borderline iodine deficiency. METHODS: Quantitative real-time PCR was performed for CCND2, PLAB, PCSK2, HGD1, TFF3, B4GALT, LGALS3, ETS1, ADM3, and TG in 150 thyroid specimens, including 52 benign thyroid nodules (28 follicular adenoma and 24 adenomatous nodules), 52 corresponding normal thyroid tissues, 20 follicular carcinomas, 20 papillary carcinomas, and six undifferentiated carcinomas. RESULTS: On a single-gene basis, significant differences in mRNA expression were found for TFF3, PLAB, and ADM3 in benign thyroid nodules and thyroid malignancy. Using two-marker gene sets, we identified 11 combinations, which allowed both a distinction of benign and malignant thyroid nodules and a discrimination of follicular adenoma and carcinoma. However, for cancer prediction, analysis of a minimum of six genes per sample was necessary and allowed correct prediction of a benign thyroid lesion and thyroid cancer with 94% accuracy in the most discriminative set (TFF3/PLAB/TG/ADM3/HGD1/LGALS3). CONCLUSION: We confirm the applicability of a number of recently proposed marker genes for the distinction of benign and malignant thyroid tumor and suggest that their diagnostic usefulness is independent of the iodide supply. We propose that the most discriminative marker set identified in our validation study together with marker combinations proposed by other investigators should now be evaluated in multicenter trials.     

Infiltration of differentiated thyroid carcinoma by proliferating lymphocytes is associated with improved disease-free survival for children and young adults

An immune response directed against thyroid cancer might be important in preventing metastasis and recurrence. This idea is supported by previous observations showing that adults with autoimmune thyroiditis or lymphocytic infiltration surrounding papillary thyroid carcinoma (PTC) have improved disease-free survival. The long-term outcome for differentiated thyroid cancer is even more favorable for children and young adults. If the immune response is important, we hypothesized that tumor-associated lymphocytes with a high proliferation index would be found in thyroid cancers from children and young adults and would be associated with improved disease-free survival. Using immunohistochemistry, we examined 39 childhood PTC, 9 follicular thyroid carcinomas, 2 medullary thyroid carcinomas, 11 benign thyroid lesions, and 2 normal thyroid glands for the presence of lymphocytes (leukocyte common antigen) and lymphocyte proliferation (proliferating cell nuclear antigen, Ki-67). The majority of PTC (65%) and follicular thyroid carcinomas (75%) from children and young adults contained lymphocytes in the immediate vicinity of thyroid cancers, but only 7 (18%) patients with PTC also had a diagnosis of autoimmune thyroiditis. Disease-free survival did not correlate with the presence or number of lymphocytes per high power field. In contrast, disease-free survival was significantly improved (P = 0.01) for thyroid cancers with the greatest number of Ki-67-positive lymphocytes per high power field. The number of lymphocytes per high powered field was greater for multifocal PTC (P: = 0.023), and the number of proliferating lymphocytes was greatest for PTC with regional lymph node involvement (30.5 +/- 12.3 vs. 6.8 +/- 5.0; P = 0.047). We conclude that proliferation of tumor-associated lymphocytes is associated with improved disease-free survival for children and young adults with thyroid cancer.     

P53 and C-FOS overexpression in patients with thyroid cancer: an immunohistochemical study

A sequence of genetic events characterized by deletion and expression of several oncogenes may lead progressively to tumorgenesis. The expression of certain oncogenes is believed to be related with thyroid carcinogenesis and tumor progression. We investigated immunohistochemically p53 tumor suppressor gene and c-fos oncogene expression in forty patients with thyroid cancer. Thyroid biopsies from twenty patients with benign thyroid diseases were also examined. The forty patients with thyroid cancer varied histologically; 24 with papillary carcinoma (60%), 12 with follicular carcinoma (30%), 3 with anaplastic carcinoma (7.5%) and one with medullary carcinoma (2.5%). The patients with benign thyroid diseases consisted of 10 with adenomatous goiter (50%), 7 with goiter (35%) and three with Hashimoto thyroiditis (15%). Individual p53 and c-fos expression was more prevalent in thyroid carcinomas compared to benign tumors (p=0.001 and p=0.04, respectively). A marked increase of p53 and c-fos coexpression was found (p=0.02) in patients with thyroid cancer and metastasis to the regional lymph nodes. Furthermore c-fos was overexpressed in only female thyroid cancer patients. In conclusion, p53 and c-fos are significantly overexpressed in thyroid cancer patients, indicating their role in the genetic mechanisms leading to thyroid tumorigenesis. This hypothesis is further supported by the observation that p53/c-fos coexpression was related with more advanced disease status.     

Mechanisms of aneuploidy in thyroid cancer cell lines and tissues: evidence for mitotic checkpoint dysfunction without mutations in BUB1 and BUBR1

OBJECTIVE: Thyroid follicular adenomas (FA) and carcinomas (FC) have a high prevalence of aneuploidy. We examined the contribution of mitotic checkpoint dysfunction and mutations of BUB1 or BUBR1, components of the spindle assembly checkpoint pathway, to chromosomal instability in thyroid cancer. DESIGN: The integrity of the mitotic checkpoint was studied in 8 aneuploid thyroid tumour cell lines. All cell lines as well as 9 FA, 9 FC, and 1 aneuploid papillary carcinoma were screened for mutations of BUB1 by SSCP and direct sequencing. Cell lines were also examined for mutations of BUBR1. RESULTS: Neither FRO, NPA nor WRO cells arrested in mitosis after treatment with nocodazole, whereas other aneuploid cell lines paused appropriately following microtubule disruption. One FC had a 2-bp somatic deletion (G2480/A2481) of BUB1 leading to a frameshift, and one FC had a silent polymorphism at nucleotide 1049 (TGT-TGC). There was a silent polymorphism of BUBR1 (G1271A) in one sample. CONCLUSION: Some, but not all thyroid cancer cell lines with aneuploidy have an abnormal mitotic checkpoint, indicating that chromosomal instability may arise through alternative cell cycle defects. Moreover, mutations of BUB1 or BUBR1 are infrequent in follicular neoplasms, and do not account for aneuploidy in thyroid cancer.     

The expression of translocator protein in human thyroid cancer and its role in the response of thyroid cancer cells to oxidative stress

The translocator protein (TSPO), formerly known as a peripheral benzodiazepine receptor, exerts pro-apoptotic function via regulation of mitochondrial membrane potential. We examined TSPO expression in human thyroid tumors (25 follicular adenomas (FA), 15 follicular cancers (FC), and 70 papillary cancers (PC)). The role of TSPO in the regulation of cell growth, migration, and apoptosis was examined in thyroid cancer cell lines after TSPO knockdown with siRNA and after treatment with TSPO antagonist (PK11195). Compared with normal thyroid, the level of TSPO expression was increased in FA, FC, and PC in 24, 26.6, and 55.7% of cases respectively. Thyroid cancer cell lines demonstrated variable levels of TSPO expression, without specific association with thyroid oncogene mutations. Treatment with inhibitors of PI3K/AKT or MEK/ERK signaling was not associated with changes in TSPO expression. Treatment with histone deacetylase inhibitor (valproic acid) increased TSPO expression in TSPO-deficient cell lines (FTC236 cells). TSPO gene silencing or treatment with PK11195 did not affect thyroid cancer cell growth and migration but prevented depolarization of mitochondrial membranes induced by oxidative stress. Induction of TSPO expression by valproic acid was associated with increased sensitivity of FTC236 to oxidative stress-inducible apoptosis. Overall, we showed that TSPO expression is frequently increased in PC. In vitro data suggested the role of epigenetic mechanism(s) in the regulation of TSPO in thyroid cells. Implication of TSPO in the thyroid cancer cell response to oxidative stress suggested its potential role in the regulation of thyroid cancer cell response to treatment with radioiodine and warrants further investigation.