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Biomedical subjects

Yuri E Nikiforov

Publications and source records attributed to Yuri E Nikiforov.

At least 19 recordsLinked to original sources
PubMed2026

Fibrotubular Tumors of the Thyroid: An Emerging Thyroid Neoplasm Characterized by Distinctive Morphology and Recurrent OCLN::PRKCI Gene Fusions Spanning the Adenoma-Carcinoma Spectrum.

The histopathologic and genomic landscape of thyroid tumors is well characterized, although new genetic alterations and tumor types are being described. We present 2 cases of thyroid tumors originating from follicular cells that had highly unusual and distinct morphologic features and carried an OCLN::PRKCI gene fusion. These tumors were well circumscribed, encapsulated, and composed of irregularly shaped tubular and follicular structures surrounded by layers of distinct fibrocollagenous basement membrane material positive for type IV collagen and laminin; they showed no definitive nuclear features of papillary carcinoma. Importantly, whereas one of the tumors had no invasive growth, the other demonstrated tumor capsule invasion, compatible with the adenoma-carcinoma spectrum seen in thyroid follicular and oncocytic tumors. Gene expression profiles of these tumors differed from those of common types of papillary thyroid carcinoma. The unusual and reproducible histopathologic characteristics and unique molecular profiles of these tumors support their designation as a distinct type of thyroid neoplasm that exists in noninvasive and invasive forms and, therefore, can be designated as fibrotubular adenoma and carcinoma. Recognition of this distinct entity is important for improving diagnostic accuracy and avoiding overtreatment of this likely indolent type of thyroid neoplasia.

Humans↗
PubMed2006

RET/PTC rearrangements and BRAF mutations in thyroid tumorigenesis.

Thyroid papillary carcinoma is the most common type of endocrine cancer. It is frequently associated with genetic alterations leading to activation of the MAPK signaling pathway. The two most frequently affected genes, BRAF and RET, are activated by either point mutation or as a result of chromosomal rearrangement. These mutations are tumorigenic in thyroid follicular cells and correlate with specific phonotypical features and biological properties of papillary carcinomas, including tumor aggressiveness and response to radioiodine therapy. Molecular inhibitors that block RET/PTC or BRAF kinase activity have shown substantial therapeutic effects in the experimental systems and are currently being tested in clinical trials.

Animals↗
PubMed2006

Prevalence of RET/PTC rearrangements in thyroid papillary carcinomas: effects of the detection methods and genetic heterogeneity.

CONTEXT: RET/PTC rearrangements have been reported in papillary thyroid carcinomas with variable frequency in studies that used different detection methods. OBJECTIVE: Our objective was to determine the role of different detection methods and tumor genetic heterogeneity on RET/PTC detection. DESIGN: Sixty-five papillary carcinomas were analyzed for RET/PTC1 and RET/PTC3 using five detection methods: standard-sensitivity RT-PCR, high-sensitivity RT-PCR, real-time LightCycler RT-PCR, Southern blot analysis, and fluorescence in situ hybridization. RESULTS: RET/PTC rearrangements were detected by standard-sensitivity RT-PCR in 14 tumors. High-sensitivity RT-PCR detected RET/PTC in all of these and in 12 additional cases, where the levels of expression corresponded to one to five positive cells. Real-time LightCycler RT-PCR detected RET/PTC in 12 and Southern blot analysis in 11 tumors. By fluorescence in situ hybridization, 14 tumors were positive, including nine cases with 50-86% positive cells and five cases with 17-35% positive cells. Overall, nine (14%) tumors harbored clonal rearrangements, which were present in the majority of tumor cells and detected by all five methods. Five (8%) cases had subclonal rearrangements present in a smaller portion of tumor cells and detected by most methods. Twelve (18%) tumors had nonclonal RET/PTC that were detected only by high-sensitivity RT-PCR. No other mutations were found in tumors harboring clonal RET/PTC, whereas 60% of tumors with subclonal and 42% of tumors with nonclonal RET/PTC harbored additional mutations. CONCLUSIONS: Our data suggest that broad variability in the reported prevalence of RET/PTC rearrangement is at least in part a result of the use of different detection methods and tumor genetic heterogeneity.

Blotting, Southern↗
PubMed2006

Proliferative activity of human thyroid cells in various age groups and its correlation with the risk of thyroid cancer after radiation exposure.

CONTEXT: The thyroid gland is vulnerable to the carcinogenic effects of ionizing radiation, and there is a well-documented inverse correlation between thyroid cancer and age at exposure, particularly for ages less than 20 yr. One of the factors responsible for this phenomenon may be more rapid cell proliferation in children. OBJECTIVE: The objective of this study was to determine the proliferative rate of normal human thyroid cells in different age groups. DESIGN: We used immunohistochemical analysis to determine the Ki-67 proliferative index in 117 thyroid glands obtained at autopsy, including 25 fetal thyroids (11-40 wk gestation), 55 childhood thyroids (0-19 yr), and 37 adult thyroids (20-60 yr). RESULTS: The rate of Ki-67 labeling in the three groups was 7.4 +/- 6.10, 0.23 +/- 0.15, and 0.08 +/- 0.04% respectively, demonstrating an overall trend for diminishing proliferative activity of thyroid cells with increasing age. However, a lack of correlation was noted between the slopes of cancer risk calculated from previous studies of irradiated populations and proliferative rate in the pediatric age intervals of 0-4 and 5-9 yr, suggesting that other factors are likely to be responsible for the particularly high sensitivity to radiation-induced thyroid cancer among the youngest children. CONCLUSIONS: Our findings of a general decrease in proliferative activity of thyroid cells with age may explain, at least in part, the higher risks of radiation-related thyroid cancer in children compared with adults. However, the variation in the rate of cell proliferation is unlikely to be responsible entirely for this phenomenon and other factors may also be involved.

Adolescent↗
PubMed2006

Delineation, functional validation, and bioinformatic evaluation of gene expression in thyroid follicular carcinomas with the PAX8-PPARG translocation.

A subset of follicular thyroid carcinomas contains a balanced translocation, t(2;3)(q13;p25), that results in fusion of the paired box gene 8 (PAX8) and peroxisome proliferator-activated receptor gamma (PPARG) genes with concomitant expression of a PAX8-PPARgamma fusion protein, PPFP. PPFP is thought to contribute to neoplasia through a mechanism in which it acts as a dominant-negative inhibitor of wild-type PPARgamma. To better understand this type of follicular carcinoma, we generated global gene expression profiles using DNA microarrays of a cohort of follicular carcinomas along with other common thyroid tumors and used the data to derive a gene expression profile characteristic of PPFP-positive tumors. Transient transfection assays using promoters of four genes whose expression was highly associated with the translocation showed that each can be activated by PPFP. PPFP had unique transcriptional activities when compared with PAX8 or PPARgamma, although it had the potential to function in ways qualitatively similar to PAX8 or PPARgamma depending on the promoter and cellular environment. Bioinformatics analyses revealed that genes with increased expression in PPFP-positive follicular carcinomas include known PPAR target genes; genes involved in fatty acid, amino acid, and carbohydrate metabolism; micro-RNA target genes; and genes on chromosome 3p. These results have implications for the neoplastic mechanism of these follicular carcinomas.

Adenocarcinoma, Follicular↗
PubMed2006

Correlation between genetic alterations and microscopic features, clinical manifestations, and prognostic characteristics of thyroid papillary carcinomas.

Papillary carcinoma is the most common type of thyroid malignancy. It has been recently shown that these tumors commonly have one of three genetic alterations: BRAF point mutations, RET/PTC rearrangements, or RAS point mutations. In this study, we analyze the relationship between these alterations and the microscopic features of papillary carcinomas, their clinical features, and prognostic characteristics. Ninety-seven papillary carcinomas were studied; in all cases, frozen tissue was available for nucleic acid extraction. Of 96 unselected cases, 42% were positive for BRAF, 18% for RET/PTC, and 15% for RAS mutations. Morphologic features were evaluated in detail in 61 cases and 6 characteristic nuclear features and 3 additional microscopic features were assessed quantitatively. At least 4 nuclear features were found in each tumor, with nuclear pseudoinclusions being the least frequent finding in all mutation groups. BRAF mutations were associated with older patient age, typical papillary appearance or the tall cell variant, a higher rate of extrathyroidal extension, and more advanced tumor stage at presentation. RET/PTC rearrangements presented at younger age and had predominantly typical papillary histology, frequent psammoma bodies, and a high rate of lymph node metastases. Tumors with RAS mutations were exclusively the follicular variant of papillary carcinoma and correlated with significantly less prominent nuclear features and low rate of lymph node metastases. These findings demonstrate that BRAF, RET/PTC, and RAS mutations are associated with distinct microscopic, clinical, and biologic features of thyroid papillary carcinomas.

Adult↗
PubMed2005

Molecular classification of papillary thyroid carcinoma: distinct BRAF, RAS, and RET/PTC mutation-specific gene expression profiles discovered by DNA microarray analysis.

Thyroid cancer poses a significant clinical challenge, and our understanding of its pathogenesis is incomplete. To gain insight into the pathogenesis of papillary thyroid carcinoma, transcriptional profiles of four normal thyroids and 51 papillary carcinomas (PCs) were generated using DNA microarrays. The tumors were genotyped for their common activating mutations: BRAF V600E point mutation, RET/PTC1 and 3 rearrangement and point mutations of KRAS, HRAS and NRAS. Principal component analysis based on the entire expression data set separated the PCs into three groups that were found to reflect tumor morphology and mutational status. By combining expression profiles with mutational status, we defined distinct expression profiles for the BRAF, RET/PTC and RAS mutation groups. Using small numbers of genes, a simple classifier was able to classify correctly the mutational status of all 40 tumors with known mutations. One tumor without a detectable mutation was predicted by the classifier to have a RET/PTC rearrangement and was shown to contain one by fluorescence in situ hybridization analysis. Among the mutation-specific expression signatures were genes whose differential expression was a direct consequence of the mutation, as well as genes involved in a variety of biological processes including immune response and signal transduction. Expression of one mutation-specific differentially expressed gene, TPO, was validated at the protein level using immunohistochemistry and tissue arrays containing an independent set of tumors. The results demonstrate that mutational status is the primary determinant of gene expression variation within these tumors, a finding that may have clinical and diagnostic significance and predicts success for therapies designed to prevent the consequences of these mutations.

Base Sequence↗
PubMed2005

Targeted expression of BRAFV600E in thyroid cells of transgenic mice results in papillary thyroid cancers that undergo dedifferentiation.

The BRAFT1799A mutation is the most common genetic alteration in papillary thyroid carcinomas (PTC). It is also found in a subset of papillary microcarcinomas, consistent with a role in tumor initiation. PTCs with BRAFT1799A are often invasive and present at a more advanced stage. BRAFT1799A is found with high prevalence in tall-cell variant PTCs and in poorly differentiated and undifferentiated carcinomas arising from PTCs. To explore the role of BRAFV600E in thyroid cancer pathogenesis, we targeted its expression to thyroid cells of transgenic FVB/N mice with a bovine thyroglobulin promoter. Two Tg-BRAFV600E lines (Tg-BRAF2 and Tg-BRAF3) were propagated for detailed analysis. Tg-BRAF2 and Tg-BRAF3 mice had increased thyroid-stimulating hormone levels (>7- and approximately 2-fold, respectively). This likely resulted from decreased expression of thyroid peroxidase, sodium iodine symporter, and thyroglobulin. All lines seemed to successfully compensate for thyroid dysfunction, as serum thyroxine/triiodothyronine and somatic growth were normal. Thyroid glands of transgenic mice were markedly enlarged by 5 weeks of age. In Tg-BRAF2 mice, PTCs were present at 12 and 22 weeks in 14 of 15 and 13 of 14 animals, respectively, with 83% exhibiting tall-cell features, 83% areas of invasion, and 48% foci of poorly differentiated carcinoma. Tg-BRAF3 mice also developed PTCs, albeit with lower prevalence (3 of 12 and 4 of 9 at 12 and 22 weeks, respectively). Tg-BRAF2 mice had a 30% decrease in survival at 5 months. In summary, thyroid-specific expression of BRAFV600E induces goiter and invasive PTC, which transitions to poorly differentiated carcinomas. This closely recapitulates the phenotype of BRAF-positive PTCs in humans and supports a key role for this oncogene in its pathogenesis.

Animals↗
PubMed2005

BRAF kinase activation via chromosomal rearrangement in radiation-induced and sporadic thyroid cancer.

Activating point mutations of the BRAF gene have been recently described in a variety of human tumors. In a study published in the Journal of Clinical Investigation, we reported a novel mechanism of activation of this gene via paracentric inversion of chromosome 7q. The fusion protein, AKAP9-BRAF, contains the intact kinase domain and lacks the autoinhibitory N-terminal portion of BRAF. It exhibited constitutive activation of BRAF kinase and was transforming for NIH3T3 cells. This finding represents the first demonstration of RAF activation by chromosomal rearrangement in human tumors. AKAP9-BRAF was more common in radiation-induced thyroid tumors, whereas point mutations of BRAF predominated in sporadic tumors of the same type, demonstrating the association between environmental factors and specific mechanisms of BRAF activation.

Animals↗
PubMed2005

Detection of SYT-SSX rearrangements in synovial sarcomas by real-time one-step RT-PCR.

Synovial sarcomas are aggressive tumors of adolescent and young adults that account for up to 10% of soft tissue sarcomas. Cytogenetically, they are characterized by translocation t(X;18), which is found in more than 95% of tumors. In most cases, it results in fusion of the SYT gene with the SSX1 or SSX2 gene, thus creating SYT-SSX1 or SYT-SSX2 rearrangement. The 2 types of gene fusion have been correlated with histologic variants and prognosis of synovial sarcomas. In this study, we developed a simple and rapid method for the simultaneous detection of SYT-SSX1 and SYT-SSX2 rearrangements by using a LightCycler real-time one-step reverse transcriptase polymerase chain reaction (RT-PCR) technology (Roche). Oligonucleotide probes were designed so that the donor probe would span a fusion point and the acceptor probe would be complementary to the SSX1 sequence but have 2 nucleotide mismatches with SSX2 sequence. Such a design allows simultaneous amplification of 2 types of rearrangement in the same reaction but distinguishes them based on differences in melting temperature detected by melting curve analysis after PCR. With this method, 27 tumors (9 synovial sarcomas and 18 nonsynovial sarcomas) were studied and showed SYT-SSX1 rearrangement in 6 cases and SYT-SSX2 in 3 cases. These results had complete correlation with the finding of conventional RT-PCR and direct sequencing. In conclusion, we have developed a fast, accurate, and simple method for the detection of 2 major types of SYT-SSX rearrangement by using LightCycler RT-PCR and melting curve analysis.

Biomarkers, Tumor↗
PubMed2005

Dose-dependent generation of RET/PTC in human thyroid cells after in vitro exposure to gamma-radiation: a model of carcinogenic chromosomal rearrangement induced by ionizing radiation.

Ionizing radiation is a well-known risk factor for thyroid cancer in human populations. Chromosomal rearrangements involving the RET gene, known as RET/PTC, are prevalent in thyroid papillary carcinomas from patients with radiation history. We studied the generation of RET/PTC in HTori-3 immortalized human thyroid cells exposed to a range of doses of gamma-radiation and harvested 2, 5-6, and 9 d later. RET/PTC1 and RET/PTC3 were detected by RT-PCR followed by Southern blotting and hybridization with internal oligonucleotide probes. No RET/PTC was found in cells harvested 2 and 5-6 d after irradiation, whereas 59 RET/PTC events were detected in cells collected 9 d after exposure. The average rate of RET/PTC induction was 0.1 x 10(-6) after exposure to 0.1 Gy, 1.6 x 10(-6) after 1 Gy, 3.0 x 10(-6) after 5 Gy, and 0.9 x 10(-6) after 10 Gy. When adjusted for cell survival, the rate after 10 Gy was comparable with those after 5 Gy. RET/PTC1 was more common than RET/PTC3 after each dose, comprising 80% of all rearrangements. In this study, we demonstrate a dose-dependent induction of RET/PTC rearrangements in human thyroid cells after exposure to 0.1-10 Gy gamma-radiation. This provides additional evidence for a direct link between this genetic event and radiation exposure and offers a powerful experimental system for studying radiation-induced carcinogenesis in the thyroid gland.

Cell Proliferation↗
PubMed2005

Molecular profile of hyalinizing trabecular tumours of the thyroid: high prevalence of RET/PTC rearrangements and absence of B-raf and N-ras point mutations.

Hyalinizing trabecular tumour (HTT) of the thyroid is a neoplasm of follicular derivation that shares several morphological similarities with papillary thyroid carcinoma (PTC). In this study, we investigated the prevalence of B-raf point mutations, RET/PTC rearrangements and N-ras point mutations in a large HTT series (28 samples). Twenty benign thyroid lesions and 10 PTC served as control cases. A high (47%) prevalence of RET/PTC rearrangements was found in HTT. By contrast, neither B-raf nor N-ras mutations were found in HTT. These findings suggest that, although RET/PTC, N-ras, and B-raf proteins may act along the same signalling cascade, the biological and morphological outcome of their oncogenic activation is not completely overlapping. Thus, in clinical practice, the detection of B-raf mutations in a thyroid follicular tumour may prove to be a valuable tool, supplementing histological examination, and allowing a differential diagnosis between PTC and HTT.

Adult↗
PubMed2005

Oncogenic AKAP9-BRAF fusion is a novel mechanism of MAPK pathway activation in thyroid cancer.

Genes crucial for cancer development can be mutated via various mechanisms, which may reflect the nature of the mutagen. In thyroid papillary carcinomas, mutations of genes coding for effectors along the MAPK pathway are central for transformation. BRAF point mutation is most common in sporadic tumors. By contrast, radiation-induced tumors are associated with paracentric inversions activating the receptor tyrosine kinases RET and NTRK1. We report here a rearrangement of BRAF via paracentric inversion of chromosome 7q resulting in an in-frame fusion between exons 1-8 of the AKAP9 gene and exons 9-18 of BRAF. The fusion protein contains the protein kinase domain and lacks the autoinhibitory N-terminal portion of BRAF. It has elevated kinase activity and transforms NIH3T3 cells, which provides evidence, for the first time to our knowledge, of in vivo activation of an intracellular effector along the MAPK pathway by recombination. The AKAP9-BRAF fusion was preferentially found in radiation-induced papillary carcinomas developing after a short latency, whereas BRAF point mutations were absent in this group. These data indicate that in thyroid cancer, radiation activates components of the MAPK pathway primarily through chromosomal paracentric inversions, whereas in sporadic forms of the disease, effectors along the same pathway are activated predominantly by point mutations.

A Kinase Anchor Proteins↗
PubMed2005

BRAF copy number gains in thyroid tumors detected by fluorescence in situ hybridization.

Point mutation of the BRAF gene is a common genetic event in papillary thyroid carcinomas. More recently, it has been found that BRAF can also participate in chromosomal rearrangement. In this study, we explore yet another possible mechanism of BRAF alteration, which involves copy number gain. Using fluorescence in situ hybridization with BRAF specific and chromosome 7 centromeric probes, we studied 62 follicular thyroid tumors and 32 papillary carcinomas. We found that numerical changes in BRAF copy number were rare in papillary thyroid carcinomas, while they occurred in 16-45% of follicular tumors of conventional and oncocytic (Hürthle cell) types. They were due to amplification of the gene or gain of one or more copies of chromosome 7. Tetrasomy for chromosome 7 was overall the most common finding. The changes in BRAF copy number did not overlap with RAS mutations in follicular tumors. In a group of follicular carcinomas, tumors with BRAF copy number gain were significantly more often widely invasive (67%) compared to tumors with no copy number change (18%). By Western blotting, the tumors carrying four copies of the gene revealed higher expression of BRAF protein, suggesting that copy number gain may represent another mechanism of BRAF activation in thyroid tumors.

Adenocarcinoma, Follicular↗
PubMed2005

Alterations of the BRAF gene in thyroid tumors.

BRAF belongs to the RAF family of protein kinases that are important components of the MAPK signaling pathway mediating cell growth, differentiation and survival. Activating point mutation of the BRAF gene resulting in V600E (previously designated as V599E) is a common event in thyroid papillary carcinoma, being found in approx 40% of this tumor. It has strong association with classical papillary carcinoma and tall cell and possibly Warthin-like variants. This mutation also occurs in thyroid poorly differentiated and anaplastic carcinomas, usually those containing areas of papillary carcinoma. Alterations in the BRAF gene do not overlap with RAS mutations and RET/PTC rearrangement, indicating that activation of one of the effectors of the MAPK pathway is sufficient for papillary thyroid carcinogenesis. Recently, another mechanism of BRAF activation has been identified, which involves chromosome 7q inversion that results in the AKAP9-BRAF fusion. It is rare in sporadic papillary carcinomas and is more common in tumors associated with radiation exposure. Yet another mechanism of BRAF activation may involve copy number gain, which is seen in a significant portion of thyroid follicular tumors of both conventional and oncocytic (Hürthle cell) types.

A Kinase Anchor Proteins↗
PubMed2004

Low prevalence of BRAF mutations in radiation-induced thyroid tumors in contrast to sporadic papillary carcinomas.

Point mutations of the BRAF gene have been recently described with high prevalence in papillary thyroid carcinomas. However, this molecular alteration has not been studied in radiation-induced thyroid tumors. We analyzed the prevalence of BRAF point mutations and RET/PTC rearrangements in 55 post-Chernobyl papillary carcinomas, compared with 82 sporadic papillary carcinomas. Radiation-induced tumors demonstrated a low prevalence (4%) of BRAF point mutations and high prevalence (58%) of RET/PTC rearrangements. Sporadic papillary carcinomas revealed a clearly distinct pattern, with 37% of tumors harboring BRAF mutations and 20% RET/PTC rearrangements. These results demonstrate a significant difference in the molecular genetic profile of sporadic and radiation-induced thyroid tumors.

Adolescent↗