Fusion Oncogenes Are the Main Genetic Events Found in Sporadic Papillary Thyroid Carcinomas from Children

BACKGROUND

Previous studies reported significant differences in the clinical presentation and outcomes of papillary thyroid carcinoma (PTC) in pediatric patients compared with adults. Previous studies have suggested that the clinicopathological differences observed between pediatric and adult PTCs may be due the existence of distinct genetic alterations. However, the knowledge of genetic events in pediatric PTCs is based primarily on studies in radiation-exposed PTCs or in the few studies that enrolled predominantly adolescent patients. The aim of this study was to characterize the known oncogenic alterations of the MAPK pathway found in adult and radiation-exposed PTCs in a cohort of predominantly sporadic pediatric PTC patients.

METHODS

Thirty-five pediatric PTCs were screened for the most prevalent fusions (RET/PTC1, RET/PTC2, RET/PTC3, ETV6-NTRK3, and AGK-BRAF) and point mutations (BRAFV600E and NRASQ61) described in sporadic pediatric PTCs. The mutational status was correlated with clinicopathological data.

RESULTS

Mutations were found in 20 out of 35 (57%) PTC cases. Fusion oncogenes were the main genetic alterations found. RET/PTC1-3 rearrangements were found in 13 (37%), ETV6-NTRK3 in 3 (9%), AGK-BRAF in 4 (11%), and BRAFV600E in 3 (9%). No mutation was found in NRASQ61. BRAFV600E was associated with older age and larger tumor size (p < 0.05), and RET/PTC3 was associated with a larger tumor size and multifocality (p < 0.05).

CONCLUSIONS

The genetic signature in this cohort was remarkably different than that observed in adults. Although observed at a lower prevalence, the spectrum of mutations was quite similar to that described in radiation-exposed pediatric PTCs. As mutations were unidentifiable in over 40% of the PTC cases, more comprehensive studies conducted in these patients will help to decipher the genetic landscape of sporadic pediatric PTCs.

[Clinicopathologic features of mammary analogue secretory carcinoma of salivary glands]

Objective: To investigate the clinicopathological features of mammary analogue secretory carcinoma (MASC) of salivary glands, and its diagnosis, differential diagnosis, immunohistochemistry and molecular pathology. Methods: Seventeen cases of MASC were enrolled, with 9 cases of salivary acinar cell carcinoma and 18 cases of adenoid cystic carcinoma as control groups from Nanjing General Hospital from 1997 to 2014 were included in this retrospective study, combined with immunohistochemistry and molecular detection of ETV6-NTRK3 gene fusion. All cases were histologically reviewed with immunohistochemical staining (EnVision) for S-100 protein, SOX10, GATA3, CD117 expression in each group. Fluorescence in situ hybridization (FISH) was used to detect the ETV6-NTRK3 gene fusion. Results: The age of MASC patients ranged from 27 to 74 years with mean age of 47 and ratio of male and female was 4∶3. All cases showed infiltrative growth and diverse cytology and histology, including lobular (8 cases), cystic papillary (3 cases), cribriform mixed with papillary and glandular structures (6 cases) at various proportions. Some tumors of MASC also exhibited solid growth areas with occasional microcystic honeycombed pattern composed of small cysts merged into larger cysts resembling thyroid follicles. S-100 protein and SOX10 were strongly positive in all MASC cases (17/17). In addition, there was insignificant positivity for GATA3 (3/17) and CD117 (4/17). ETV6 gene fusion detection was informative in 12 MASC cases by FISH with 10 positive cases and 2 negative cases. Conclusions: Combined immunohistochemical positivity of S-100 protein, CD117 and SOX10 are useful in the diagnosis and differential diagnosis of MASC. FISH detection of ETV6-NTRK3 fusion offers an additional molecular diagnostic marker for the diagnosis.

A New Hitherto Unreported Histopathologic Manifestation of Mammary Analogue Secretory Carcinoma: "Masked MASC" Associated With Low-grade Mucinous Adenocarcinoma and Low-grade In Situ Carcinoma Components

We present a salivary gland tumor of the parotid gland in a 54-year-old woman, which contained a minor mammary analogue secretory carcinoma (MASC) component (20%) intermixed with a morphologically entirely different mucinous adenocarcinomatous component that comprised 80% of the tumor mass and a morphologically nondescript low-grade intraductal carcinoma (in situ) component. On fluorescence in situ hybridization, a break in the ETV6 gene was documented in the mucinous adenocarcinomatous, the conventional MASC, and the intraductal (in situ) components. RT-PCR failed to reveal an ETV6-NTRK3 fusion. The entire conventional MASC and only rare mucinous adenocarcinoma tumor cells were mammaglobin positive, whereas the low-grade intraductal carcinoma (in-situ) component was negative. S-100 protein stained only the MASC component.

Infantile Fibrosarcoma With NTRK3-ETV6 Fusion Successfully Treated With the Tropomyosin-Related Kinase Inhibitor LOXO-101

Infantile fibrosarcoma (IFS) is a rare pediatric cancer typically presenting in the first 2 years of life. Surgical resection is usually curative and chemotherapy is active against gross residual disease. However, when recurrences occur, therapeutic options are limited. We report a case of refractory IFS with constitutive activation of the tropomyosin-related kinase (TRK) signaling pathway from an ETS variant gene 6-neurotrophin 3 receptor gene (ETV6-NTRK3) gene fusion. The patient enrolled in a pediatric Phase 1 trial of LOXO-101, an experimental, highly selective inhibitor of TRK. The patient experienced a rapid, radiographic response, demonstrating the potential for LOXO-101 to provide benefit for IFS harboring NTRK gene fusions.

ALK, ROS1 and NTRK3 gene rearrangements in inflammatory myofibroblastic tumours

AIMS

The aim of this study was to elucidate the pathological features of inflammatory myofibroblastic tumour (IMT) with gene rearrangement other than ALK.

METHODS AND RESULTS

We investigated anaplastic lymphoma kinase (ALK), ROS1, ETV6, NTRK3 and RET in 36 cases of IMT by using immunohistochemical (IHC) staining, fluorescence in-situ hybridization, and reverse transcription polymerase chain reaction (RT-PCR). IHC staining showed ALK and ROS1 to be positive in 22 of 36 (61.1%) and two of 36 (5.6%) cases, respectively. In one case with ROS1 positivity, IHC staining showed cytoplasmic and dot-like ROS1 expression, and RT-PCR showed the presence of the TFG-ROS1 fusion transcript. Two cases of pulmonary IMT, in a 7-year-old patient and a 23-year-old patient, had ETV6 rearrangement, and the presence of the ETV6-NTRK3 fusion transcript was confirmed in one case. These tumours were composed of hypocellular myxoid areas and highly cellular areas with rich plasmacytic infiltration; the histological features were different from those of infantile fibrosarcoma. RET rearrangement was not detected.

CONCLUSIONS

These results suggest that a subset of ALK-negative IMTs have rearrangement of ROS1, ETV6 or NTRK3 as a possible oncogenic mechanism, and that the detection of these alterations may be of diagnostic value and helpful for determining promising therapeutic strategies.

NTRK fusion oncogenes in pediatric papillary thyroid carcinoma in northeast United States

BACKGROUND

An increase in thyroid cancers, predominantly papillary thyroid carcinoma (PTC), has been recently reported in children.

METHODS

The histopathology of 28 consecutive PTCs from the northeast United States was reviewed. None of the patients (ages 6-18 years; 20 females, 8 males) had significant exposure to radiation. Nucleic acid from tumors was tested for genetic abnormalities (n = 27). Negative results were reevaluated by targeted next-generation sequencing.

RESULTS

Seven of 27 PTCs (26%) had neurotrophic tyrosine kinase receptor (NTRK) fusion oncogenes (NTRK type 3/ets variant 6 [NTRK3/ETV6], n =5; NTRK3/unknown, n = 1; and NTRK type 1/translocated promoter region, nuclear basket protein [NTRK1/TPR], n = 1), including 5 tumors that measured >2 cm and 3 that diffusely involved the entire thyroid or lobe. All 7 tumors had lymphatic invasion, and 5 had vascular invasion. Six of 27 PTCs (22%) had ret proto-oncogene (RET) fusions (RET/PTC1, n = 5; RET/PTC3, n = 1); 2 tumors measured >2 cm and diffusely involved the thyroid, and 5 had lymphatic invasion, with vascular invasion in 2. Thirteen PTCs had the B-Raf proto-oncogene, serine/threonine kinase (BRAF) valine-to-glutamic acid mutation at position 600 (BRAF(V) (600E)) (13 of 27 tumors; 48%), 11 measured <2 cm, and 6 had lymphatic invasion (46%), with vascular invasion in 3. Fusion oncogene tumors, compared with BRAF(V) (600E) PTCs, were associated with large size (mean, 2.2 cm vs 1.5 cm, respectively; P = .05), solid and diffuse variants (11 of 13 vs 0 of 13 tumors, respectively; P < .001), and lymphovascular invasion (12 of 13 vs 6 of 13 tumors, respectively; P = .02); BRAF(V) (600E) PTCs were predominantly the classic variant (12 of 13 vs 1 of 13 tumors). Two tumors metastasized to the lung, and both had fusion oncogenes (NTRK1/TPR, n = 1; RET/PTC1, n = 1).

CONCLUSIONS

Fusion oncogene PTC presents with more extensive disease and aggressive pathology than BRAF(V) (600E) PTC in the pediatric population. The high prevalence of the NTRK1/NTRK3 fusion oncogene PTCs in the United States is unusual and needs further investigation.

Transcriptome sequencing identifies ETV6-NTRK3 as a gene fusion involved in GIST

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. The vast majority of GISTs are driven by oncogenic activation of KIT, PDGFRA or, less commonly, BRAF. Loss of succinate dehydrogenase complex activity has been identified in subsets of KIT/PDGFRA/BRAF-mutation negative tumours, yet a significant fraction of GISTs are devoid of any of such alterations. To address the pathobiology of these 'quadruple-negative' GISTs, we sought to explore the possible involvement of fusion genes. To this end we performed transcriptome sequencing on five KIT/PDGFRA/BRAF-mutation negative, SDH-proficient tumours. Intriguingly, the analysis unveiled the presence of an ETV6-NTRK3 gene fusion. The screening by FISH of 26 additional cases, including KIT/PDGFRA-mutated GISTs, failed to detect other ETV6 rearrangements beside the index case. This was a 'quadruple-negative' GIST located in the rectum, an uncommon primary site for GIST development (∼4% of all GISTs). The fusion transcript identified encompasses exon 4 of ETV6 and exon 14 of NTRK3 and therefore differs from the canonical ETV6-NTRK3 chimera of infantile fibrosarcomas. However, it retains the ability to induce IRS1 phosphorylation, activate the IGF1R downstream signalling pathway and to be targeted by IGF1R and ALK inhibitors. Thus, the ETV6-NTRK3 fusion might identify a subset of GISTs with peculiar clinicopathological characteristics which could be eligible for such therapies. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Histopathological features of papillary thyroid carcinomas detected during four screening examinations of a Ukrainian-American cohort

BACKGROUND

There are limited data on the histopathology of papillary thyroid carcinomas (PTCs) diagnosed in irradiated populations. We evaluated the associations between iodine-131 dose and the histopathological characteristics of post-Chernobyl PTCs, the changes in these characteristics over time, and their associations with selected somatic mutations.

METHODS

This study included 115 PTCs diagnosed in a Ukrainian-American cohort (n=13,243) during prescreening and four successive thyroid screenings. Of these PTCs, 65 were subjected to somatic mutation profiling. All individuals were <18 years at the time of the Chernobyl accident and had direct thyroid radioactivity measurements. Statistical analyses included multivariate linear and logistic regression.

RESULTS

We identified a borderline significant linear-quadratic association (P=0.063) between iodine-131 dose and overall tumour invasiveness (presence of extrathyroidal extension, lymphatic/vascular invasion, and regional or distant metastases). Irrespective of dose, tumours with chromosomal rearrangements were more likely to have lymphatic/vascular invasion than tumours without chromosomal rearrangements (P=0.020) or tumours with BRAF or RAS point mutations (P=0.008). Controlling for age, there were significant time trends in decreasing tumour size (P<0.001), the extent of lymphatic/vascular invasion (P=0.005), and overall invasiveness (P=0.026).

CONCLUSIONS

We determined that the invasive properties of PTCs that develop in iodine-131-exposed children may be associated with radiation dose. In addition, based on a subset of cases, tumours with chromosomal rearrangements appear to have a more invasive phenotype. The increase in small, less invasive PTCs over time is a consequence of repeated screening examinations.

[The Role of Neurotrophins and Neurexins Genes in the Risk of Paranoid Schizophrenia in Russians and Tatars]

Schizophrenia affects about 1% of the population. Its etiology is not fully understood. Environmental conditions certainly contribute to the development of schizophrenia, but the determining factor is genetic predisposition: the coefficient of heritability of schizophrenia is about 80%, which is typical for the most highly heritable multifactorial diseases. Polymorphic loci of genes of enzymes and receptors involved in the processes of neuroprotection and neurotrophia play significant role in the development of this disease. In this paper we investigated 48 polymorphic variants of genes of the neurotrophins and neurexins family (BDNF, NTRK2, NTRK3, NGF, NXPH1, and NRXN1) in Russian and Tatar cases and in a control group living in the Republic of Bashkortostan. The results of this study confirm the important role of neurotrophin and neurexin genes in paranoid schizophrenia development.

Experimental verification of a conserved intronic microRNA located in the human TrkC gene with a cell type-dependent apoptotic function

Tropomyosin receptor kinase C (TrkC) is involved in cell survival, apoptosis induction and tumorigenesis. We hypothesized that, similar to p75(NTR) receptor, some of the diverse functions of TrkC could be mediated by a microRNA (miRNA) embedded within the gene. Here, we experimentally verified the expression and processing of two bioinformatically predicted miRNAs named TrkC-miR1-5p and TrkC-miR1-3p. Transfecting a DNA fragment corresponding to the TrkC-premir1 sequence in HEK293t cells caused ~300-fold elevation in the level of mature TrkC-miR1 and also a significant downregulation of its predicted target genes. Furthermore, endogenous TrkC-miR1 was detected in several cell lines and brain tumors confirming its endogenous generation. Furthermore, its orthologous miRNA was detected in developing rat brain. Accordingly, TrkC-miR1 expression was increased during the course of neural differentiation of NT2 cell, whereas its suppression attenuated NT2 differentiation. Consistent with opposite functions of TrkC, TrkC-miR1 overexpression promoted survival and apoptosis in U87 and HEK293t cell lines, respectively. In conclusion, our data report the discovery of a new miRNA with overlapping function to TrkC.

Mammary analogue secretory carcinoma of salivary glands: a new entity associated with ETV6 gene rearrangement

Mammary analogue secretory carcinoma (MASC) is a recently described salivary gland tumour that harbours the recurrent ETV6-NTRK3 translocation. This is the first series of MASC cases identified in the historic cohort of carcinomas of salivary glands with clinical/pathological correlation and follow-up data. We reviewed 183 primary carcinomas of major and minor salivary glands resected at the Medical University of Gdańsk, Poland, between 1992 and 2012. Based on morphology and immunohistochemistry, cases suspicious for MASC were selected, and the diagnosis was confirmed by fluorescence in situ hybridization (FISH) for ETV6 rearrangement and by RT-PCR for the ETV6-NTRK3 fusion transcript. Seven carcinomas met the criteria of MASC, as they exhibited a typical appearance with solid/microcystic and papillary architecture and intraluminal secretions, and cells completely devoid of basophilic cytoplasmic zymogen granules indicative of true acinar differentiation. The only paediatric case was an unencapsulated tumour composed of macrocystic structures covered by a mostly single but, focally, double layer of cells with apocrine morphology. In all cases, the neoplastic cells revealed immunoreactivity for S100, mammaglobin, cytokeratin CK7, CK8, STAT5a and vimentin. FISH for ETV6 gene rearrangement was positive in six out of seven cases, and RT-PCR was positive in three cases. MASC is a new entity of malignant epithelial salivary gland tumours not included in the 2005 WHO Classification of Head and Neck Tumours. There is a growing body of evidence that it is not as rare as was assumed, as is also indicated by our series (3.8 %). In most cases, MASC shares some microscopic features with AciCC, adenocarcinoma/cystadenocarcinoma NOS and low-grade MEC. In rare cases, MASC with high-grade transformation may mimic the morphological appearances of high-grade salivary gland malignancies, such as salivary duct carcinoma.

Selective conversion of fibroblasts into peripheral sensory neurons

Humans and mice detect pain, itch, temperature, pressure, stretch and limb position via signaling from peripheral sensory neurons. These neurons are divided into three functional classes (nociceptors/pruritoceptors, mechanoreceptors and proprioceptors) that are distinguished by their selective expression of TrkA, TrkB or TrkC receptors, respectively. We found that transiently coexpressing Brn3a with either Ngn1 or Ngn2 selectively reprogrammed human and mouse fibroblasts to acquire key properties of these three classes of sensory neurons. These induced sensory neurons (iSNs) were electrically active, exhibited distinct sensory neuron morphologies and matched the characteristic gene expression patterns of endogenous sensory neurons, including selective expression of Trk receptors. In addition, we found that calcium-imaging assays could identify subsets of iSNs that selectively responded to diverse ligands known to activate itch- and pain-sensing neurons. These results offer a simple and rapid means for producing genetically diverse human sensory neurons suitable for drug screening and mechanistic studies.

Dual innervation of neonatal Merkel cells in mouse touch domes

Merkel cell-neurite complexes are specialized mechanosensory end organs that mediate discriminative touch sensation. It is well established that type I slowly adapting (SAI) mechanoreceptors, which express neural filament heavy chain (NFH), innervate Merkel cells. It was previously shown that neurotrophic factor NT3 and its receptor TrkC play crucial roles in controlling touch dome Merkel cell innervation of NFH⁺ fibers. In addition, nerve fibers expressing another neurotrophic tyrosine receptor kinase (NTRK), Ret, innervate touch dome Merkel cells as well. However, the relationship between afferents responsive to NT3/TrkC signaling and those expressing Ret is unclear. It is also controversial if these Ret⁺ fibers belong to the early or late Ret⁺ DRG neurons, which are defined based on the co-expression and developmental dependence of TrkA. To address these questions, we genetically traced Ret⁺ and TrkC⁺ fibers and analyzed their developmental dependence on TrkA. We found that Merkel cells in neonatal mouse touch domes receive innervation of two types of fibers: one group is Ret⁺, while the other subset expresses TrkC and NFH. In addition, Ret⁺ fibers depend on TrkA for their survival and normal innervation whereas NFH⁺ Merkel cell innervating fibers are almost unaltered in TrkA mutant mice, supporting that Ret⁺ and NFH⁺/TrkC⁺ afferents are two distinct groups. Ret signaling, on the other hand, plays a minor role for the innervation of neonatal touch domes. In contrast, Merkel cells in the glabrous skin are mainly contacted by NFH⁺/TrkC⁺ afferents. Taken together, our results suggest that neonatal Merkel cells around hair follicles receive dual innervation while Merkel cells in the glabrous skin are mainly innervated by only SAI mechanoreceptors. In addition, our results suggest that neonatal Ret⁺ Merkel cell innervating fibers most likely belong to the late but not early Ret⁺ DRG neurons.

ETV6-NTRK3 is a common chromosomal rearrangement in radiation-associated thyroid cancer

BACKGROUND

In their previous analysis of papillary thyroid carcinomas (PTCs) from an Ukrainian-American cohort that was exposed to iodine-131 ((131) I) from the Chernobyl accident, the authors identified RET/PTC rearrangements and other driver mutations in 60% of tumors.

METHODS

In this study, the remaining mutation-negative tumors from that cohort were analyzed using RNA sequencing (RNA-Seq) and reverse transcriptase-polymerase chain reaction to identify novel chromosomal rearrangements and to characterize their relation with radiation dose.

RESULTS

The ETS variant gene 6 (ETV6)-neurotrophin receptor 3 (NTRK3) rearrangement (ETV6-NTRK3) was identified by RNA-Seq in a tumor from a patient who received a high (131) I dose. Overall, the rearrangement was detected in 9 of 62 (14.5%) post-Chernobyl PTCs and in 3 of 151 (2%) sporadic PTCs (P = .019). The most common fusion type was between exon 4 of ETV6 and exon 14 of NTRK3. The prevalence of ETV6-NTRK3 rearrangement in post-Chernobyl PTCs was associated with increasing (131) I dose, albeit at borderline significance (P = .126). The group of rearrangement-positive PTCs (ETV6-NTRK3, RET/PTC, PAX8-PPARγ) was associated with significantly higher dose response compared with the group of PTCs with point mutations (BRAF, RAS; P < .001). In vitro exposure of human thyroid cells to 1 gray of (131) I and γ-radiation resulted in the formation of ETV6-NTRK3 rearrangement at a rate of 7.9 × 10(-6) cells and 3.0 × 10(-6) cells, respectively.

CONCLUSIONS

The authors report the occurrence of ETV6-NTRK3 rearrangements in thyroid cancer and demonstrate that this rearrangement is significantly more common in tumors associated with exposure to (131) I and has a borderline significant dose response. Moreover, ETV6-NTRK3 rearrangement can be directly induced in thyroid cells by ionizing radiation in vitro and, thus, may represent a novel mechanism of radiation-induced carcinogenesis.

Combinatorial assembly of small molecules into bivalent antagonists of TrkC or TrkA receptors

A library of peptidomimetics was assembled combinatorially into dimers on a triazine-based core. The pharmacophore corresponds to β-turns of the neurotrophin polypeptides neurotrophin-3 (NT-3), nerve growth factor (NGF), or brain-derived neurotrophic factor (BDNF). These are the natural ligands for TrkC, TrkA, and TrkB receptors, respectively. The linker length and the side-chain orientation of each monomer within the bivalent mimics were systematically altered, and the impact of these changes on the function of each ligand was evaluated. While the monovalent peptidomimetics had no detectable binding or bioactivity, four bivalent peptidomimetics (2c, 2d, 2e, 3f) are selective TrkC ligands with antagonistic activity, and two bivalent peptidomimetics (1a, 1b) are TrkC and TrkA ligands with antagonistic activity. All these bivalent compounds block ligand-dependent receptor activation and cell survival, without affecting neuritogenic differentiation. This work adds to our understanding of how the neurotrophins function through Trk receptors, and demonstrates that peptidomimetics can be designed to selectively disturb specific biological signals, and may be used as pharmacological probes or as therapeutic leads. The concept of altering side-chain, linker length, and sequence orientation of a subunit within a pharmacophore provides an easy modular approach to generate larger libraries with diversified bioactivity.

Uncoupling of molecular maturation from peripheral target innervation in nociceptors expressing a chimeric TrkA/TrkC receptor

Neurotrophins and their receptors control a number of cellular processes, such as survival, gene expression and axonal growth, by activating multiple signalling pathways in peripheral neurons. Whether each of these pathways controls a distinct developmental process remains unknown. Here we describe a novel knock-in mouse model expressing a chimeric TrkA/TrkC (TrkAC) receptor from TrkA locus. In these mice, prospective nociceptors survived, segregated into appropriate peptidergic and nonpeptidergic subsets, projected normally to distinct laminae of the dorsal spinal cord, but displayed aberrant peripheral target innervation. This study provides the first in vivo evidence that intracellular parts of different Trk receptors are interchangeable to promote survival and maturation of nociceptors and shows that these developmental processes can be uncoupled from peripheral target innervation. Moreover, adult homozygous TrkAC knock-in mice displayed severe deficits in acute and tissue injury-induced pain, representing the first viable adult Trk mouse mutant with a pain phenotype.

Sensory neurons located in dorsal root ganglia are critical for perception of various stimuli by transmitting information from their peripheral targets to the spinal cord. During embryonic development, distinct populations of sensory neurons are defined based on expression of neurotrophin receptors Trks. Pain and temperature sensing neurons, or nociceptors, express NGF receptor TrkA, which control a number of diverse developmental processes, such as survival, gene expression and skin innervation. How these distinct processes are regulated by activation of same Trk receptor is currently unknown. Using a knock in approach, we generated a mouse with nociceptive neurons expressing a modified TrkA/TrkC receptor, which responds to NGF but signals through the intracellular part of another neurotrophin receptor, TrkC. Contrary to all previously reported NGF and TrkA mutants, these mice were viable and exhibited no obvious defects. Surprisingly, nociceptive neurons from these mice survived and matured normally, but failed to correctly innervate their peripheral target, skin. Thus, the intracellular parts of highly related receptors TrkA and TrkC are interchangeable for support of certain developmental processes but not others. Moreover, adult TrkA/TrkC mice exhibited drastic defects in pain sensation, making it an excellent model to study the role of NGF in nociception.

Identification of kinase fusion oncogenes in post-Chernobyl radiation-induced thyroid cancers

Exposure to ionizing radiation during childhood markedly increases the risk of developing papillary thyroid cancer. We examined tissues from 26 Ukrainian patients with thyroid cancer who were younger than 10 years of age and living in contaminated areas during the time of the Chernobyl nuclear reactor accident. We identified nonoverlapping somatic driver mutations in all 26 cases through candidate gene assays and next-generation RNA sequencing. We found that 22 tumors harbored fusion oncogenes that arose primarily through intrachromosomal rearrangements. Altogether, 23 of the oncogenic drivers identified in this cohort aberrantly activate MAPK signaling, including the 2 somatic rearrangements resulting in fusion of transcription factor ETS variant 6 (ETV6) with neurotrophic tyrosine kinase receptor, type 3 (NTRK3) and fusion of acylglycerol kinase (AGK) with BRAF. Two other tumors harbored distinct fusions leading to overexpression of the nuclear receptor PPARγ. Fusion oncogenes were less prevalent in tumors from a cohort of children with pediatric thyroid cancers that had not been exposed to radiation but were from the same geographical regions. Radiation-induced thyroid cancers provide a paradigm of tumorigenesis driven by fusion oncogenes that activate MAPK signaling or, less frequently, a PPARγ-driven transcriptional program.

Translocation-associated salivary gland tumors: a review and update

In recent years the discovery of translocations and the fusion oncogenes that they result in has changed the way diagnoses are made in the salivary gland. These genetic aberrations are recurrent and reproducible and at the very least serve as powerful diagnostic tools in salivary gland diagnosis and salivary gland classification. They also show promise as prognostic markers and hopefully as targets of therapy. Many of these fusions have been found in other tumor types that show little to no overlap with their salivary gland counterparts, but effectively they are specific within the salivary gland. In this review the 5 tumors currently known to harbor translocations will be discussed, namely pleomorphic adenoma, mucoepidermoid carcinoma, adenoid cystic carcinoma, mammary analog secretory carcinoma, and hyalinizing clear cell carcinoma. The discovery and implications of each fusion will be highlighted and how they have helped reshape the current classification of salivary gland tumors.

Mutation of the salt bridge-forming residues in the ETV6-SAM domain interface blocks ETV6-NTRK3-induced cellular transformation

The ETV6-NTRK3 (EN) chimeric oncogene is expressed in diverse tumor types. EN is generated by a t(12;15) translocation, which fuses the N-terminal SAM (sterile α-motif) domain of the ETV6 (or TEL) transcription factor to the C-terminal PTK (protein-tyrosine kinase) domain of the neurotrophin-3 receptor NTRK3. SAM domain-mediated polymerization of EN leads to constitutive activation of the PTK domain and constitutive signaling of the Ras-MAPK and PI3K-Akt pathways, which are essential for EN oncogenesis. Here we show through complementary biophysical and cellular biological techniques that mutation of Lys-99, which participates in a salt bridge at the SAM polymer interface, reduces self-association of the isolated SAM domain as well as high molecular mass complex formation of EN and abrogates the transformation activity of EN. We also show that mutation of Asp-101, the intermolecular salt bridge partner of Lys-99, similarly blocks transformation of NIH3T3 cells by EN, reduces EN tyrosine phosphorylation, inhibits Akt and Mek1/2 signaling downstream of EN, and abolishes tumor formation in nude mice. In contrast, mutations of Glu-100 and Arg-103, residues in the vicinity of the interdomain Lys-99-Asp-101 salt bridge, have little or no effect on these oncogenic characteristics of EN. Our results underscore the importance of specific electrostatic interactions for SAM polymerization and EN transformation.

TrkC promotes survival and growth of leukemia cells through Akt-mTOR-dependent up-regulation of PLK-1 and Twist-1

It has been suggested that activation of receptor PTKs is important for leukemogenesis and leukemia cell response to targeted therapy in hematological malignancies including leukemia. PTKs induce activation of the PI3K/Akt/mTOR pathway, which can result in prevention of apoptosis. Here, we describe an important role of the TrkC-associated molecular network in the process of leukemogenesis. TrkC was found to be frequently overexpressed in human leukemia cells and leukemia subtypes. In U937 human leukemia cells, blockade of TrkC using small hairpin RNA (shRNA) specific to TrkC or K562a, a specific inhibitor of TrkC, resulted in a significant decrease in growth and survival of the cells, which was closely associated with reduced mTOR level and Akt activity. In addition, TrkC enhances the survival and proliferation of leukemia, which is correlated with activation of the PI3K/Akt pathway. Moreover, TrkC significantly inhibits apoptosis via induction of the expression of PLK-1 and Twist-1 through activation of AKT/mTor pathway; therefore, it plays a key role in leukemogenesis. These findings reveal an unexpected physiological role for TrkC in the pathogenesis of leukemia and have important implications for understanding various hematological malignancies.

NTRK3 is a potential tumor suppressor gene commonly inactivated by epigenetic mechanisms in colorectal cancer

NTRK3 is a member of the neurotrophin receptor family and regulates cell survival. It appears to be a dependence receptor, and thus has the potential to act as an oncogene or as a tumor suppressor gene. NTRK3 is a receptor for NT-3 and when bound to NT-3 it induces cell survival, but when NT-3 free, it induces apoptosis. We identified aberrantly methylated NTRK3 in colorectal cancers through a genome-wide screen for hypermethylated genes. This discovery led us to assess whether NTRK3 could be a tumor suppressor gene in the colon. NTRK3 is methylated in 60% of colon adenomas and 67% of colon adenocarcinomas. NTRK3 methylation suppresses NTRK3 expression. Reconstitution of NTRK3 induces apoptosis in colorectal cancers, if NT-3 is absent. Furthermore, the loss of NTRK3 expression associates with neoplastic transformation in vitro and in vivo. We also found that a naturally occurring mutant NTRK3 found in human colorectal cancer inhibits the tumor suppressor activity of NTRK3. In summary, our findings suggest NTRK3 is a conditional tumor suppressor gene that is commonly inactivated in colorectal cancer by both epigenetic and genetic mechanisms whose function in the pathogenesis of colorectal cancer depends on the expression status of its ligand, NT-3.

NTRK3 is a neurotrophin receptor and appears to be a dependence receptor in certain tissues. NTRK3 has been previously shown to be an oncogene in breast cancer and possibly hepatocellular carcinoma. Through a genome-wide methylation screen, we unexpectedly found that NTRK3 is commonly methylated in colorectal cancers but not in normal colon samples, which led us to assess whether NTRK3 could be a tumor suppressor gene in the colon. We now demonstrate that NTRK3 is frequently methylated in colorectal adenomas and cancers. Induced NTRK3 expression in the absence of its ligand, NT-3, causes apoptosis and suppresses in vitro anchorage-independent colony formation and in vivo tumor growth. Reintroduction of NT-3 releases colon cancer cells from NTRK3-mediated apoptosis, which is consistent with NTRK3 being a dependence receptor in the colon. Finally, somatic mutations of NTRK3 have been observed in primary human colorectal cancer. We provide evidence that a subset of these mutations inactivate tumor suppressor activities of NTRK3. These findings suggest that NTRK3 is a conditional tumor suppressor gene in the colon that is inactivated by both genetic and epigenetic mechanisms and whose function in the pathogenesis of colorectal cancer depends on the expression status of its ligand, NT-3.

Cytogenetic and single nucleotide polymorphism array findings in soft tissue tumors in infants

Soft tissue tumors in children under one year of age (infants) are rare. The etiology is usually unknown, with external factors or congenital birth defects and hereditary syndromes being recognized in only a small proportion of the cases. We ascertained the cytogenetic findings in 16 infants from whom tumor tissue had been obtained during a 25-year period. In eight of them, single nucleotide polymorphism (SNP) array analyses could also be performed. No constitutional chromosome aberrations were detected, and assessment of clinical files did not reveal any congenital or later anatomical defects. Three tumors--one infantile fibrosarcoma, one embryonal rhabdomyosarcoma, and one angiomatoid fibrous histiocytoma (AFH)--had abnormal karyotypes. As the AFH had an exchange between chromosome arms 12p and 15q, additional fluorescence in situ hybridization and reverse transcription-polymerase chain reaction analyses were performed, unexpectedly revealing an ETV6/NTRK3 fusion. Three of the eight tumors, including the AFH with an abnormal karyotype, analyzed by SNP array showed aberrations (loss of heterozygosity or imbalances). The present series suggests that the addition of array-based technologies is valuable for detecting underlying pathogenetic mechanisms.

Enhancing proprioceptive input to motoneurons differentially affects expression of neurotrophin 3 and brain-derived neurotrophic factor in rat hoffmann-reflex circuitry

The importance of neurotrophin 3 (NT-3) for motor control prompted us to ask the question whether direct electrical stimulation of low-threshold muscle afferents, strengthening the proprioceptive signaling, could effectively increase the endogenous pool of this neurotrophin and its receptor TrkC in the Hoffmann-reflex (H-reflex) circuitry. The effects were compared with those of brain-derived neurotrophic factor (BDNF) and its TrkB receptor. Continuous bursts of stimuli were delivered unilaterally for seven days, 80 min daily, by means of a cuff-electrode implanted over the tibial nerve in awake rats. The H-reflex was recorded in the soleus muscle to control the strength of stimulation. Stimulation aimed at activation of Ia fibers produced a strong increase of NT-3 protein, measured with ELISA, in the lumbar L3-6 segments of the spinal cord and in the soleus muscle. This stimulation exerted much weaker effect on BDNF protein level which slightly increased only in L3-6 segments of the spinal cord. Increased protein level of NT-3 and BDNF corresponded to the changes of NT-3 mRNA and BDNF mRNA expression in L3-6 segments but not in the soleus muscle. We disclosed tissue-specificity of TrkC mRNA and TrkB mRNA responses. In the spinal cord TrkC and TrkB transcripts tended to decrease, whereas in the soleus muscle TrkB mRNA decreased and TrkC mRNA expression strongly increased, suggesting that stimulation of Ia fibers leads to sensitization of the soleus muscle to NT-3 signaling. The possibility of increasing NT-3/TrkC signaling in the neuromuscular system, with minor effects on BDNF/TrkB signaling, by means of low-threshold electrical stimulation of peripheral nerves, which in humans might be applied in non-invasive way, offers an attractive therapeutic tool.

NeuroD regulates neuronal migration

NeuroD is required for the survival of many subtypes of developing neurons in the vertebrate central nervous system. Because NeuroD-deficient neurons in the hippocampus, cerebellum, and inner ear die prematurely in the early stage of neurogenesis, the role of NeuroD during the later stages of neurogenesis of these cell subtypes is not well understood. In addition, the mechanism of NeuroDdeficient neuronal death has not been investigated. It was hypothesized that NeuroD-dependent neuronal death occurs through a Bax-dependent apoptotic pathway. Based on this hypothesis, this study attempted to rescue neuronal cell death by deleting the Bax gene in NeuroD null mice to investigate the role of NeuroD in surviving neurons. The NeuroD and Bax double null mice displayed a decrease in the number of apoptotic cells in the hippocampus and the cerebellum and the rescue of vestibulocochlear ganglion (VCG) neurons that failed to migrate and innervate. In addition, at E13.5, the NeuroD(-/-)Bax(-/-) VCG neurons failed to express TrkB and TrkC, which are known to be essential for the survival of those neurons. These data suggest that neuronal death in NeuroD null mice is mediated by Bax-dependent apoptosis and that NeuroD is required for the migration of VCG neurons. Finally, these data show that TrkB and TrkC expression in E13.5 VCG neurons requires NeuroD and that TrkB and TrkC expression may be necessary for the normal migration and innervations of those neurons.

Trypanosoma cruzi coaxes cardiac fibroblasts into preventing cardiomyocyte death by activating nerve growth factor receptor TrkA

Rationale

Cardiomyocytes express neurotrophin receptor TrkA that promotes survival following nerve growth factor (NGF) ligation. Whether TrkA also resides in cardiac fibroblasts (CFs) and underlies cardioprotection is unknown.

Objective

To test whether CFs express TrkA that conveys paracrine signals to neighbor cardiomyocytes using, as probe, the Chagas disease parasite Trypanosoma cruzi, which expresses a TrkA-binding neurotrophin mimetic, named PDNF. T cruzi targets the heart, causing chronic debilitating cardiomyopathy in ∼30% patients.

Methods and Results

Basal levels of TrkA and TrkC in primary CFs are comparable to those in cardiomyocytes. However, in the myocardium, TrkA expression is significantly lower in fibroblasts than myocytes, and vice versa for TrkC. Yet T cruzi recognition of TrkA on fibroblasts, preferentially over cardiomyocytes, triggers a sharp and sustained increase in NGF, including in the heart of infected mice or of mice administered PDNF intravenously, as early as 3-h post-administration. Further, NGF-containing T cruzi- or PDNF-induced fibroblast-conditioned medium averts cardiomyocyte damage by H₂O₂, in agreement with the previously recognized cardioprotective role of NGF.

Conclusions

TrkA residing in CFs induces an exuberant NGF production in response to T cruzi infection, enabling, in a paracrine fashion, myocytes to resist oxidative stress, a leading Chagas cardiomyopathy trigger. Thus, PDNF-TrkA interaction on CFs may be a mechanism orchestrated by T cruzi to protect its heart habitat, in concert with the long-term (decades) asymptomatic heart parasitism that characterizes Chagas disease. Moreover, as a potent booster of cardioprotective NGF in vivo, PDNF may offer a novel therapeutic opportunity against cardiomyopathies.