Daniela Virginia Frau

Aneuploidy in oncocytic lesions of the thyroid gland: Diffuse accumulation of mitochondria within the cell is associated with trisomy 7 and progressive numerical chromosomal alterations

Oncocytic cells are characterized by a greatly increased number of mitochondria that distend the cell cytoplasm and result in a distinctive granular appearance of the cell on conventional histology sections. Oncocytes are frequently found in metabolically active human tissues including the thyroid gland, and, as a general rule, when their proportion in a thyroid tumor is greater than 75% the tumor is referred to as oncocytic (Hürthle cell) adenoma or carcinoma. Such tumors represent a subset of thyroid lesions, and recently, both interphase fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) studies reported that they may show aneuploidy, with widespread numerical chromosomal alterations. In contrast, very few cases have been studied by conventional cytogenetic analysis. Whether the cells with chromosomal changes are the same as those with mitochondrial accumulation or whether lesions only partially composed of oncocytic cells also have cytogenetic alterations is unclear. To investigate the relationship between acquisition of the oncocytic phenotype and numerical chromosomal changes, we analyzed a random selection of thyroid lesions with (18 cases) and without (11 cases) morphological evidence of oncocytic differentiation. Lesions with oncocytes included hyperplastic nodules, adenomas, Hürthle cell tumors, and papillary carcinomas with lymphocytic stroma (Whartin‐like tumors of the thyroid). Karyotypic changes were analyzed by cytogenetic analysis, FISH, or CGH, and the results were compared with in situ analysis of mitochondrial accumulation by immunofluorescence. A striking correlation between the presence of oncocytes and the presence of aneuploid katyotypes was seen in the oncocytic follicular thyroid nodules, but not in the oncocytic papillary tumors. Structural chromosome changes or normal karyotypes were observed in the lesions lacking oncocytic features. Extending the FICTION technique to the evaluation of a cytoplasmic antigen (mitochondrial membrane antigen), we pursued the simultaneous visualization of both mitochondrial increase and numerical chromosomal alterations, and showed that oncocytes of follicular lesions are prone to become aneuploid. Our data support the contention that follicular tumors composed of oncocytes should be regarded as a distinct subset.

Telomere Abnormalities and Chromosome Fragility in Patients Affected by Familial Papillary Thyroid Cancer

INTRODUCTION Genomic instability has been proposed to play a role in cancer development and can occur through different mechanisms including telomere association and telomere loss. Studies carried out in our unit have demonstrated that familial papillary thyroid cancer (fPTC) patients display an imbalance, at the germinal level, in telomere-telomerase complex. AIM We aimed to verify whether familial fPTC patients show an increased spontaneous chromosome fragility. METHODS To this purpose, we compared telomeric fusions and associations as well as other chromosomal fragility features by conventional and molecular cytogenetic analyses, in phytohemagglutinin stimulated T-lymphocytes from fPTC patients, unaffected family members, sporadic papillary thyroid cancer patients, and healthy subjects. RESULTS We demonstrate that fPTC patients have a significant increase in spontaneous telomeric associations and telomeric fusions compared with healthy subjects and sporadic cases in the frame of an otherwise common spontaneous chromosome fragility pattern. A quantitative fluorescence in situ hybridization analysis demonstrates that familial cases display a significant decrease in the telomeric peptide nucleic acid-fluorescence in situ hybridization signal intensity in the metaphase chromosome. Moreover, three copies of the hTERT gene were found only in familial cases, although the result was not statistically significant. CONCLUSIONS These results contribute in defining familial thyroid cancer as a clinical entity characterized by an altered telomere stability, which may be associated with the predisposition to develop the familial form of thyroid cancer.

Assessing RET/PTC in thyroid nodule fine needle aspirates: the FISH point of view

RET/PTC rearrangement and BRAF(V600E) mutation are the two prevalent molecular alterations associated with papillary thyroid carcinoma (PTC), and their identification is increasingly being used as an adjunct to cytology in diagnosing PTC. However, there are caveats associated with the use of the molecular approach in fine-needle aspiration (FNA), particularly for RET/PTC, that should be taken into consideration. It has been claimed that a clonal or sporadic presence of this abnormality in follicular cells can distinguish between malignant and benign nodules. Nevertheless, the most commonly used PCR-based techniques lack the capacity to quantify the number of abnormal cells. Because fluorescence in situ hybridization (FISH) is the most sensitive method for detecting gene rearrangement in a single cell, we compared results from FISH and conventional RT-PCR obtained in FNA of a large cohort of consecutive patients with suspicious nodules and investigated the feasibility of setting a FISH-FNA threshold capable of distinguishing non-clonal from clonal molecular events. For this purpose, a home brew break-apart probe, able to recognize the physical breakage of RET, was designed. While a ≥3% FISH signal for broken RET was sufficient to distinguish nodules with abnormal follicular cells, only samples with a ≥6.8% break-apart FISH signal also exhibited positive RT-PCR results. On histological analysis, all nodules meeting the ≥6.8% threshold proved to be malignant. These data corroborate the power of FISH when compared with RT-PCR in quantifying the presence of RET/PTC in FNA and validate the RT-PCR efficiency in detecting clonal RET/PTC alterations.

Leukocyte telomere length positively correlates with duration of lithium treatment in bipolar disorder patients.

Bipolar disorder (BD) has been suggested to be associated with accelerated aging and premature cell senescence. While findings on shorter telomeres in BD are controversial, a recent study showed that long-term lithium treatment correlates with longer telomeres in BD. In our study, we sought to investigate the correlation between leukocyte telomere length (LTL) and long-term lithium treatment in a sample of 200 BD patients characterized for lithium response. We also compared data from two different methods commonly used to measure telomere length, quantitative PCR (qPCR) and quantitative fluorescence in situ hybridization (Q-FISH). We also measured, for the first time, the effect of lithium in vitro on the expression of the telomerase gene in human-derived neural progenitor cells (NPCs). Our findings showed that LTL correlated negatively with age (p=0.0002) and was independent of sex, diagnosis, age at onset, suicidal behavior, number of mood episodes, response to lithium and use of other psychotropic medications. After correcting for age, LTL was positively correlated with lithium treatment duration in patients treated for more than two years (n=150, R=0.17, p=0.037). There was a significant correlation between data measured with qPCR and Q-FISH (p=0.012, R=0.826). Lithium treatment increased telomerase expression in NPCs, though this effect was not statistically significant. Our data support previous findings showing that long-term lithium treatment associates with longer telomeres in BD, though this effect appeared to be independent from clinical response to the treatment. Moreover, we suggested for the first time that lithium increases the expression of telomerase gene in human neural progenitor cells.

Deep fibrous histiocytoma with a clonal karyotypic alteration: molecular cytogenetic characterization of a t(16;17)(p13.3;q21.3)

Deep fibrous histiocytoma, a rare lesion occuring in deep soft tissues, has recently been formally characterized as a diagnostically distinguishable variant of the benign fibrous histiocytoma spectrum with distinct morphological features. Nevertheless, because of the small number of cases published, information on their clinical behavior, including propensity for local recurrence and metastasis, is quite limited, and no molecular genetic or cytogenetic data are available. We report a 46,XY,t(16;17)(p13.3;q21.3) karyotype in a deep fibrous histiocytoma. Fluorescence in situ hybridization using bacterial artificial chromosome (BAC) clones refined the translocation breakpoints within 119.9 kb at 16p13.3 and 214 kb at 17q21.3. Moreover, to ascertain whether they may be nonrandomly involved in changes in this rare tumor type, we designed two dual-color break-apart probes with BAC clones, mapping proximally and distally to the two breakpoints, to be tested in additional archival cases by interphase fluorescence in situ hybridization. No break-apart signals were observed in the six additional cases studied, indicating either that the translocation is sporadic or that it is rare in deep fibrous histiocytoma. In conclusion, our data show that chromosome aberrations may be found in deep fibrous histiocytoma and that, as with cutaneous lesions, they may have clonal, at present nonrecurrent, chromosome changes.

Simultaneous occurrence of PAX8-PPARg and RET-PTC3 rearrangements in a follicular variant of papillary thyroid carcinoma.

Specific genotype-phenotype correlations have been identified in conventional-type papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC). In contrast, the genetic alterations underlying the pathogenesis of the follicular variant of PTC (FV-PTC), which shares some clinicopathologic and molecular features with both PTC and FTC, remain to be clarified. This entity shows a PAX8-PPARg fusion gene (associated with FTC), more frequently than BRAF or RET-PTC alterations (associated with PTC). Herein, we report, for the first time, an FV-PTC with the simultaneous occurrence of both RET-PTC and PAX8-PPARg alterations. Neoplastic cells were of the wild type for BRAF and H,K,N-RAS, had an apparently normal karyotype by conventional cytogenetics, and had a balanced genome by array comparative genomic hybridization analysis. In fact, submicroscopic chromosome rearrangements producing RET-PTC3 and PAX8-PPARg chimeric genes were found by interphase fluorescence in situ hybridization. We demonstrated that these 2 genetic alterations coexisted in the same tumor and were confined to 2 different clones. Our findings indicate that molecular heterogeneity, although an uncommon phenomenon, may occur in thyroid carcinoma and demonstrate the coexistence in a case of FV-PTC not only of the histologic but also of the molecular features of both PTC (RET-PTC) and FTC (PAX8-PPARg).

Centrosomal and mitotic abnormalities in cell lines derived from papillary thyroid cancer harboring specific gene alterations

BackgroundDifferentiated thyroid carcinoma offers a good model to investigate the possible correlation between specific gene mutations and chromosome instability. Papillary thyroid neoplasms are characterized by different mutually exclusive genetic alterations, some of which are associated with aneuploidy and aggressive phenotype.ResultsWe investigated the centrosome status and mitotic abnormalities in three thyroid carcinoma-derived cell lines, each maintaining the specific, biologically relevant gene alteration harbored by the parental tumors: RET/PTC1 rearrangement in TPC1; heterozygous and homozygous BRAFV600E mutation in K1 and in B-CPAP, respectively. B-CPAP cells showed a statistically significant (P < 0.01) higher frequency of abnormal mitotic figures compared to TPC1 and K1 cells.ConclusionsOur data indicate that RET/PTC1 oncogenic activity is not related to mitotic chromosome impairment and missegregation whereas, based on the consistent difference in types/frequencies of centrosome and spindle abnormalities observed between K1 and B-CPAP cells, the hetero/homozygous allelic status of BRAFV600E mutation seems to be not irrelevant in respect to chromosomal instability development.

Optimizing detection of RET and PPARg rearrangements in thyroid neoplastic cells using a home-brew tetracolor probe

Fluorescence in situ hybridization (FISH) to identify specific DNA target sequences in the nuclei of nondividing cells of numerous solid neoplasms has contributed to the introduction of molecular cytogenetics as a useful adjunct to cytology, leading recently to the “marriage” of the 2 disciplines. Numerous cancer molecular markers can now be investigated using different technical approaches, at both the gene and expression levels, in biopsies of various suspected cancers, including differentiated thyroid carcinoma. The limited amount of bioptic material is often insufficient to carry out multiple tests, and optimizing handling of the biopsy is desirable.

Thyrospheres from B-CPAP cell line with BRAF and TERT promoter mutations have different functional and molecular features than parental cells

Human thyroid cancer derived cell lines are widely used to study the mechanisms involved in thyroid carcinogenesis. However, there is limited availability of non-cross-contaminated cancer cell lines derived from papillary thyroid carcinoma (PTC), and the B-CPAP cell line is one of the few such lines. B-CPAP cells have been genetically and cytogenetically well-characterized, but details of their stemness features remain uncertain. Considering that this cell line is extensively used for in vitro studies on thyroid tumorigenesis, we broaden its functional and molecular profiles as well as the tumorigenic capacity. We used functional assays (sphere-forming capacity and efficiency), assessed self-renewal and propagation efficiency and tested in vivo tumorigenicity in Hsd:Athymic Nude-Foxn1nu mice. Expression of markers of stemness, differentiation, and epithelial-mesenchymal transition were estimated at RNA and protein levels in adherent parental cells and sphere-forming cells. Functional aspects and stemness features were compared with normal thyrocytes. Protein expression of xenograft tumors was evaluated by immunohistochemistry. B-CPAP sphere-forming cells were able to form thyrospheres theoretically indefinitely in an appropriate serum-free medium, reverting to the adherent parental cell phenotype when cultured in differentiation medium. Different expression of ALDH1-A1 and CD44 stemness markers and TTF-1 and CK19 differentiation markers allowed discrimination between isolated sphere-forming cells and adherent parental cells, indicating that sphere-forming cells retained stem-like features. In keeping with these observations, tumorigenicity assays confirmed that, relative to parental adherent cells, thyrospheres had enhanced capacity to initiate xenograft tumors. Thyrospheres from normal cell line retained very low functional capacity, as well as different stemness markers expression compared to tumor thyrospheres. Our findings may constitute a useful background to develop an in vitro model for assessing the origin and progression of papillary thyroid carcinoma bearing BRAFV600E and TERT promoter mutations.

Genetic Heterogeneity of HER2 Amplification and Telomere Shortening in Papillary Thyroid Carcinoma

Extensive research is dedicated to understanding if sporadic and familial papillary thyroid carcinoma are distinct biological entities. We have previously demonstrated that familial papillary thyroid cancer (fPTC) cells exhibit short relative telomere length (RTL) in both blood and tissues and that these features may be associated with chromosome instability. Here, we investigated the frequency of HER2 (Human Epidermal Growth Factor Receptor 2) amplification, and other recently reported genetic alterations in sporadic PTC (sPTC) and fPTC, and assessed correlations with RTL and BRAF mutational status. We analyzed HER2 gene amplification and the integrity of ALK, ETV6, RET, and BRAF genes by fluorescence in situ hybridization in isolated nuclei and paraffin-embedded formalin-fixed sections of 13 fPTC and 18 sPTC patients. We analyzed BRAFV600E mutation and RTL by qRT-PCR. Significant HER2 amplification (p = 0.0076), which was restricted to scattered groups of cells, was found in fPTC samples. HER2 amplification in fPTCs was invariably associated with BRAFV600E mutation. RTL was shorter in fPTCs than sPTCs (p < 0.001). No rearrangements of other tested genes were observed. These findings suggest that the association of HER2 amplification with BRAFV600E mutation and telomere shortening may represent a marker of tumor aggressiveness, and, in refractory thyroid cancer, may warrant exploration as a site for targeted therapy.