A child with a t(11;19)(q14-21;p12) in a pulmonary mucoepidermoid carcinoma

The CRTC1-MAML2 fusion is the major oncogenic driver in mucoepidermoid carcinoma

No effective systemic treatment is available for patients with unresectable, recurrent, or metastatic mucoepidermoid carcinoma (MEC), the most common salivary gland malignancy. MEC is frequently associated with a t(11;19)(q14-21;p12-13) translocation that creates a CRTC1-MAML2 fusion gene. The CRTC1-MAML2 fusion exhibited transforming activity in vitro; however, whether it serves as an oncogenic driver for MEC establishment and maintenance in vivo remains unknown. Here, we show that doxycycline-induced CRTC1-MAML2 knockdown blocked the growth of established MEC xenografts, validating CRTC1-MAML2 as a therapeutic target. We further generated a conditional transgenic mouse model and observed that Cre-induced CRTC1-MAML2 expression caused 100% penetrant formation of salivary gland tumors resembling histological and molecular characteristics of human MEC. Molecular analysis of MEC tumors revealed altered p16-CDK4/6-RB pathway activity as a potential cooperating event in promoting CRTC1-MAML2–induced tumorigenesis. Cotargeting of aberrant p16-CDK4/6-RB signaling and CRTC1-MAML2 fusion–activated AREG/EGFR signaling with the respective CDK4/6 inhibitor Palbociclib and EGFR inhibitor Erlotinib produced enhanced antitumor responses in vitro and in vivo. Collectively, this study provides direct evidence for CRTC1-MAML2 as a key driver for MEC development and maintenance and identifies a potentially novel combination therapy with FDA-approved EGFR and CDK4/6 inhibitors as a potential viable strategy for patients with MEC.

Childhood and adolescent tracheobronchial mucoepidermoid carcinoma (MEC): a case-series and review of the literature

Tracheobronchial mucoepidermoid carcinomas (MEC) are rare in the pediatric population with literature limited primarily to case reports. Here we present our institutional experience treating MEC in three patients and review the literature of 142 pediatric cases previously published from 1968 to 2013. Although rare, tracheobronchial MEC should be included in the differential diagnosis in a child with recurrent respiratory symptoms. Conservative surgical management is often sufficient to achieve complete resection and good outcomes.

Mucoepidermoid carcinoma of the lung: a case report and literature review

Introduction. Mucoepidermoid carcinoma (MEC) of the lung is a rare form of lung cancer that is classified into low grade and high grade based on histological features. Surgical resection is the primary treatment for low-grade MEC with excellent outcomes, while high-grade MEC is a more aggressive form of malignancy. Clinical Case. We report a case of a 46-year-old woman who presented with dyspnea on exertion. Imaging studies revealed a mass involving the right upper lobe bronchus. Bronchoscopy, surgical resection, and pathological examination revealed a low-grade MEC with tumor-free margins. No adjuvant treatment was given. Discussion. Primary pulmonary MEC is a rare type of lung cancer with only few reported cases. This patient illustrates a typical presentation for low-grade MEC wherein surgical resection is considered curative. In contrast, high-grade MEC is a more aggressive malignancy with a poorer outcome. The role of targeted therapy directed against EGFR or a novel CRTC1-MAML2 fusion protein expressed in some high-grade tumors is yet to be determined.

Mucoepidermoid carcinoma of the lung arising at the primary site of a bronchogenic cyst: clinical, cytogenetic, and molecular findings

Primary lung tumors are rare in children, and mucoepidermoid carcinoma (MEC) represents less than 10% of them. Additionally, MEC arising from bronchogenic cysts (BC) is particularly unusual. We describe the clinical and genetic findings on a MEC occurring within a previous location of a BC in an adolescent. This particular association has not been previously reported. The lesion revealed normal karyotype without the typical t(11;19)(q21;p13) translocation. Cyclin D1 overexpression (165-fold increase) was demonstrated by real-time PCR although FISH assessment showed normal hybridization at 11q13. Information on these unusual clinical presentations may present relevant insight on tumorigenesis of infrequent pediatric pulmonary tumors.

A link between the expression of the stem cell marker HMGA2, grading, and the fusion CRTC1-MAML2 in mucoepidermoid carcinoma

Recently, the concept of cancer stem cells and their expression of embryonic stem cell markers has gained considerable experimental support. In this study, we examined the expression of one such marker, the high-mobility group AT-hook 2 gene (HMGA2) mRNA, in 53 formalin-fixed, paraffin-embedded mucoepidermoid carcinomas (MEC) and four normal parotid tissues using quantitative real-time RT-PCR (qPCR). MECs are often characterized by the fusion gene CRTC1-MAML2, the detection of which is an important tool for the diagnosis and prognosis of MEC. For detection of the CRTC1-MAML2 fusion transcript, we performed RT-PCR. The mean expression level of HMGA2 was higher in fusion negative (302.8 +/- 124.4; n = 14) than in positive tumors (67.3 +/- 13.1; n = 39). Furthermore, the fusion-negative tumors were often high-grade tumors and the HMGA2 expression level rose with the tumor grade (low: 43.7 +/- 11.0, intermediate: 126.2 +/- 28.3, and high: 271.2 +/- 126.5). A significant difference was found in the HMGA2 expression levels between the different grading groups (one-way ANOVA, P = 0.04) and among the fusion-negative and -positive tumors (t-test, P = 0.05), indicating that the expression level of HMGA2 was closely linked to grading, the presence/absence of the CRTC1-MAML2 fusion, and the tumor behavior of MECs. These findings offer further evidence for the theory that the MEC group comprises two subgroups: one group with the CRTC1-MAML2 fusion, which is a group with a moderate aggressiveness and prognosis, and the other group lacking that fusion corresponding to an increased stemness, and thus, higher aggressiveness and worse prognosis.

Mucoepidermoid carcinoma of the cervix: another tumor with the t(11;19)-associated CRTC1-MAML2 gene fusion

Mucoepidermoid carcinoma (MEC) of the uterine cervix is a controversial entity. By strict morphologic criteria, the tumor has features identical to those of salivary gland MEC and is characterized by nests composed of 3 cell types (epidermoid, intermediate, and mucin producing) in the absence of overt glandular differentiation. Nonetheless, the entity is not recognized in the current World Health Organization classification of cervical tumors. Given the morphologic similarity between MEC of the cervix and MEC of the salivary glands, we sought to determine if MEC of the cervix harbors the t(11;19)(q21;p13) characteristic of MEC of the major and minor salivary glands, a rearrangement that results in fusion of the cyclic adenosine 3',5' monophosphate coactivator CRTC1 to the Notch coactivator MAML2. We identified 7 cervical tumors from our departmental files and performed reverse transcription-polymerase chain reaction and fluorescence in situ hybridization-based molecular analysis for rearrangements of CRTC1 and MAML2; 14 conventional cervical adenosquamous carcinomas were used as controls. Analysis of the cervical MECs demonstrated a CRTC1-MAML2 fusion in 1 case, rearrangements of CRTC1 in 4 cases, and aberrations of MAML2 in 5 cases (rearrangements in 2 cases, amplification in 3 cases). All MEC showed aberrations of at least 1 of the loci, whereas none of the cervical adenosquamous carcinomas harbored rearrangements or amplification of either locus. Our results demonstrate that cervical tumors defined as MEC by strict morphologic criteria harbor genetic aberrations involving the genes characteristically rearranged in MEC of the salivary glands, and suggest that cervical MEC is an entity distinct from conventional cervical adenosquamous carcinoma. The development of drug therapy targeted to the genes rearranged in MEC underscores the importance of correct classification of cervical MEC because the diagnosis may hold therapeutic implications different from other cervical malignancies.

The EML4-ALK fusion gene is involved in various histologic types of lung cancers from nonsmokers with wild-type EGFR and KRAS

BACKGROUND

The echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) fusion gene resulting from the chromosome inversion inv(2)(p21;p23) recently was identified in nonsmall cell lung cancer (NSCLC). The authors of this study investigated the frequency, genetic and clinicopathologic profiles of EML4-ALK in Chinese patients with NSCLC.

METHODS

EML4-ALK was investigated in 266 resected primary NSCLC, including adenocarcinomas (AD), lymphoepithelioma-like carcinomas, squamous cell carcinomas, mucoepidermoid carcinomas, and adenosquamous carcinomas, by reverse transcriptase-polymerase chain reaction and was verified by sequencing. EML4-ALK protein expression was studied by immunohistochemistry.

RESULTS

Thirteen tumors (4.9%) had EML4-ALK comprising 4 fusion transcript variants with fusion of the variable segments from 5' EML4 to 3' ALK and with preservation of the ALK kinase domain. The most common variant consisted of 8 tumors with variant 3 that involved EML4 exon 6. The others included 2 tumors with variant 1 (exon 13), 2 tumors with variant 2 (exon 20), and 1 tumor with the novel variant 5 (exon 18). There were 11 ADs and 2 unusual carcinomas with mixed squamous and glandular components. Immunohistochemistry demonstrated diffuse ALK fusion proteins in the tumor cell cytoplasm. EML4-ALK was associated with nonsmokers (P = .009). Tumors with the fusion gene had the wild-type epidermal growth factor receptor (EGFR) (P = .001) and v-Ki-ras2/Kirsten rat sarcoma viral oncogene homolog (KRAS) genes. Patients who had EML4-ALK-positive AD had a younger median age (P = .018) compared with patients who did not have the fusion gene.

CONCLUSIONS

The EML4-ALK fusion gene was present in various histologic types of NSCLC. It occurred in mutual exclusion to EGFR and KRAS mutations and was associated with nonsmokers. The authors concluded that EML4-ALK may be useful for predicting the potential response to ALK inhibitors as a therapeutic option for patients with lung cancer.

CRTC1/MAML2 fusion transcript in Warthin's tumor and mucoepidermoid carcinoma: evidence for a common genetic association

Translocations and gene fusions have an important early role in tumorigenesis. The t(11;19) translocation and its CRTC1/MAML2 fusion transcript have been identified in several examples of both Warthin's tumor and mucoepidermoid carcinoma and are believed to be associated with the development of a subset of these tumors. To determine whether Warthin's tumor and mucoepidermoid carcinoma are genetically related, we used reverse transcriptase-polymerase chain reaction and DNA sequencing to analyze microdissected components of three tumors consisting of Warthin's tumor and mucoepidermoid carcinoma. We also investigated a metastatic melanoma to Warthin's tumor and a Warthin's carcinoma of the parotid gland for comparison. The fusion transcript was identified in both Warthin's tumor and matching mucoepidermoid carcinoma components of all three tumors, in the Warthin's carcinoma, and in the Warthin's tumor component but not in the metastatic melanoma. The results provide evidence for a link between the t(11;19) fusion gene and the development of a subset of Warthin's tumors with concurrent mucoepidermoid carcinoma and possible malignant transformation to Warthin's carcinoma. This article contains Supplementary Material available at http://www.interscience.wiley.com/jpages/1045-2257/suppmat.

A closer look at Warthin tumors and the t(11;19)

The translocation t(11;19)(q21;p13) has been described in mucoepidermoid carcinoma (MEC) and rarely in Warthin tumors (WT), both tumors of the salivary gland. The translocation creates a fusion gene in which exon 1 of CRTC1 is linked to exons 2-5 of MAML2. To verify the translocation in WT, we performed nested reverse transcriptase-polymerase chain reaction using RNA from 48 WTs. This revealed the t(11;19)(q21;p13) translocation and expression of the chimeric gene in two metaplastic WT samples, but in none of the remaining ordinary 46 WTs. On review, the two positive cases were classified as tumors highly suspect for MEC. Indeed, our experience and published observations of the t(11;19)(q21;p13) translocation in WT reveal that only a small subset of WTs are positive, and that these tumors are often classified as infarcted or metaplastic WT, known to overlap considerably with MEC on purely morphological grounds. We therefore conclude that the presence of the t(11;19)(q21;p13) rearrangement favors a diagnosis of MEC.

Mucoepidermoid Carcinoma of the Bronchus: A Review

Although mucoepidermoid carcinoma of the salivary gland is relatively common, mucoepidermoid carcinoma arising from the mucous glands of the bronchus is rare. Bronchial mucoepidermoid carcinoma usually presents as an intraluminal mass producing luminal occlusion. Symptoms are airway obstruction and recurrent pneumonia. Macroscopically, mucoepidermoid carcinoma appears as an exophytic intrabronchial mass with intact or ulcerated bronchial mucosa. Microscopically, the tumors are located in the submucosa of the large bronchi. The tumors are usually well differentiated and contain a combination of mucus-secreting, squamous, and intermediate cells. The increased frequency of this tumor in the pediatric population suggests a genetic abnormality. Recent genetic studies have demonstrated reciprocal chromosomal translocations including t(1;11)(p22;q13), t(11;19)(q14-21;p12), and t(11; 19)(q21;p13). Chromosome 11 in the first translocation appears to have been altered resulting in up-regulation of the cyclin D1 gene and overexpression of cyclin D1. The t(11;19)(q21;p13) encodes a novel fusion product capable of disrupting the Notch signaling pathway.

CRTC1/MAML2 fusion transcript in high grade mucoepidermoid carcinomas of salivary and thyroid glands and Warthin's tumors: implications for histogenesis and biologic behavior

We analyzed 55 primary salivary gland tumors including 22 mucoepidermoid carcinomas (MECs) to determine the association of MECT1/TORC1/CRTC1-MAML2 fusion transcript to tumor types, level of MEC differentiation and clinicopathologic parameters. Our primary salivary gland tumors were composed of 22 MECs, 11 Warthin's tumors, 10 adenoid cystic carcinomas, two basaloid carcinomas, five salivary duct carcinomas, and five adenocarcinomas, not otherwise specified. We also included, for the first time, three primary MECs of the thyroid gland. We used nested RT-PCR and subsequent sequencing techniques for detection and verification of the fusion transcript in fresh and archival specimens. Eighteen (81%) of the 22 primary salivary and one of the three thyroid glands with MEC were positive for the fusion transcript. The transcript was detected equally in low, intermediate and high grade as well as low and high stage MECs. Significant correlation between fusion negative tumors and distant metastasis was noted (P = 0.005). Four (36%) of the 11 Warthin's tumors were also positive for the transcript. None of the 22 primary non-MEC gland salivary carcinomas were positive for the transcript. We conclude that the CRTC1/MAML2 transcript may be detected in both low and high grade MEC, that fusion negative tumors may define a subset of biologically aggressive MEC's tumors, that the fusion is present in primary MECs of the thyroid gland and is also detectable in Warthin's tumor, and that a subset of MECs can be targeted for therapeutic intervention.

t(11;19)(q21;p12~p13.11) and MECT1-MAML2 fusion transcript expression as a prognostic marker in infantile lung mucoepidermoid carcinoma

BACKGROUND

Primary pulmonary mucoepidermoid carcinomas (MECs) are the third most frequent pulmonary malignant neoplasm in children, and new molecular diagnostics may prove useful in determining the biologic course of such tumors.

METHODS

We analyzed the presence of a balanced t(11;19)(q21; p12~p13.11) and the MECT1-MAML2 fusion transcript in a 9-year-old girl with mucoepidermoid lung carcinoma using conventional cytogenetics, fluorescence in-situ hybridization, spectral karyotyping, high-resolution multicolor banding, and reverse transcriptase-polymerase chain reaction.

RESULTS

We confirmed the t(11;19)(q21; p12~p13.11) in the tumor. Molecular analysis of the translocation breakpoint confirmed the presence of the MECT1-MAML2 fusion transcript postulated to lead to an altered cyclic adenosine monophosphate signaling in MEC.

CONCLUSIONS

Our data concur with previously reported cases, in which t(11;19) appears to be the primary chromosomal aberration for pulmonary MEC in children, and that the MECT1-MAML2 fusion transcript is associated with a better prognosis in MEC tumors.

Fusion oncogenes and tumor type specificity--insights from salivary gland tumors

Salivary gland tumors are frequently characterized by recurrent chromosome translocations, which have recently been shown to result in pathogenetically relevant fusion oncogenes. These genes encode novel fusion proteins as well as ectopically expressed normal or truncated proteins, and are found in both benign and malignant salivary gland tumors. The major targets of the translocations are DNA-binding transcription factors (PLAG1 and HMGA2) involved in growth factor signaling and cell cycle regulation, and coactivators of the Notch (MAML2) and cAMP (TORC1) signaling pathways. Identification of these fusion oncogenes has contributed to our knowledge of molecular pathways leading to epithelial tumors in general, and to salivary gland tumors in particular. Interestingly, the fusions in salivary gland tumors do not seem to be as tumor type specific as those in leukemias and sarcomas. Instead, they may function by activating basic transformation pathways that can function in multiple cell types. The downstream gene products of these fusions will be important targets for development of new intracellular therapeutic strategies.

Sustained expression of Mect1-Maml2 is essential for tumor cell growth in salivary gland cancers carrying the t(11;19) translocation

Mucoepidermoid (MEC) salivary gland tumors arise from a t(11;19) rearrangement which generates a fusion oncogene, Mect1-Maml2, that functions to activate CREB-responsive target genes. To determine if sustained expression of Mect1-Maml2 is required for tumor cell growth, we first showed that ectopic expression of Mect1-Maml2 in rat epithelial RK3E cells is tumorigenic in vivo in nude mice and that excised xenografts continue to express the fusion oncogene. We then generated a hairpin RNAi vector that selectively suppressed the fusion peptide and showed that ectopic expression in either parotid or pulmonary MEC tumor cell lines containing the t(11;19) rearrangement resulted in at least 90% colony growth inhibition. In contrast, single nucleotide changes within this RNAi sequence abolished the ability to suppress Mect1-Maml2 protein and abolished all growth inhibition of these MEC tumor lines. In addition, the RNAi-specific vector had no effect on colony growth of non-MEC tumors including a lung tumor or two other salivary gland cell lines that do not express Mect1-Maml2. We also generated a mutant Mect1-Maml2 expression plasmid that carried silent nucleotide changes within the RNAi target sequence and observed that co-transfection of this mutant, but not wild-type Mect1-Maml2, could partially rescue RNAi growth inhibition in the MEC tumor line. The recent detection of acquired fusion oncogenes in epithelial solid tumors has suggested new possibilities for the diagnosis and therapy of these cancers. Our data show that the 'gain-of-function' activity from aberrant Mect1-Maml2 expression is a candidate therapeutic target for this group of malignant salivary gland tumors.

[Significance of molecular-cytogenetic findings in mucoepidermoid carcinoma as an example of salivary gland tumors]

Chromosome translocations in tumors frequently give rise to fusion genes encoding proteins with oncogenic activities. Mucoepidermoid carcinomas (MEC) are characterized by a t(11;19)(q21-22;p13) translocation found in approximately 60% of the tumors. This t(11;19) translocation results in a fusion gene consisting of exon 1 of the MECT 1 gene and exons 2-5 of the MAML 2 gene. As a result of the t(11;19) a fusion protein is generated which, independent of NOTCH-ligands, activates the transcription of the NOTCH target gene HES 1. The altered function of MAML 2 causes a disruption of NOTCH signalling which suggests a novel mechanism of tumorigenesis. Pending the elucidation of the t(11;19) at the molecular level of an apparently identical chromosomal translocation in Warthin's tumor, the identification of the translocation in MEC by FISH- and/or RT-PCR-analyses may become important in diagnosis and might have prognostic relevance. Warthin's tumors are benign salivary gland neoplasms with a distinctive histomorphology and histogenesis completely different from MEC.

Mect1-Maml2 fusion oncogene linked to the aberrant activation of cyclic AMP/CREB regulated genes

Malignant salivary gland tumors can arise from a t(11;19) translocation that fuses 42 residues from Mect1/Torc1, a cyclic AMP (cAMP)/cAMP-responsive element binding protein (CREB)-dependent transcriptional coactivator, with 982 residues from Maml2, a NOTCH receptor coactivator. To determine if the Mect1-Maml2 fusion oncogene mediates tumorigenicity by disrupting cAMP/CREB signaling, we have generated in-frame deletions within the CREB-binding domain of Mect1/Torc1 for testing transformation activity and have also developed a doxycycline-regulated Mect1-Maml2 mammalian expression vector for global gene expression profiling. We observed that small deletions within the CREB-binding domain completely abolished transforming activity in RK3E epithelial cells. Further, we have shown that the ectopic induction of Mect1-Maml2 in HeLa cells strongly activated the expression of a group of known cAMP/CREB-regulated genes. In addition, we detected candidate cAMP-responsive element sites within 100 nucleotides of the transcriptional start sites of other genes activated by Mect1-Maml2 expression. In contrast, we did not observe alterations of known Notch-regulated target genes in these expression array profile experiments. We validated the results by reverse transcription-PCR in transfected HeLa, RK3E, and H2009 lung tumor cells and in mucoepidermoid cancer cells that endogenously express the fusion oncopeptide. Whereas overexpression of components of the cAMP pathway has been associated with a subset of human carcinomas, these data provide a direct genetic link between deregulation of cAMP/CREB pathways and epithelial tumorigenesis and suggest future therapeutic strategies for this group of salivary gland tumors.

Clear cell hidradenoma of the skin-a third tumor type with a t(11;19)--associated TORC1-MAML2 gene fusion

Recent studies have shown that the t(11;19)(q21;p13) translocation in mucoepidermoid carcinomas and benign Warthin's tumors results in a fusion of the N-terminal CREB-binding domain of the cAMP coactivator TORC1 (a.k.a. MECT1 and WAMTP1) to the Notch coactivator MAML2. Here we show that a third tumor type, clear cell hidradenoma of the skin, also expresses this gene fusion. RT-PCR analysis of a clear cell hidradenoma with a t(11;19)(q21;p13) translocation revealed expression of a TORC1-MAML2 fusion transcript consisting of exon 1 of TORC1 fused to exons 2-5 of MAML2. Because the fusion was only detected in a single case, the frequency of this aberration in clear cell hidradenomas remains unknown. These results demonstrate that the t(11;19) in mucoepidermoid carcinoma, Warthin's tumor, and clear cell hidradenoma targets the same genes and results in identical gene fusions, indicating that at least subgroups of these glandular tumors evolve through activation of the same molecular pathways.

Mucoepidermoid carcinoma as an unusual cause for recurrent respiratory infections in a child

Recurrent respiratory infections in a 9-year-old girl prompted a chest radiograph and a CT scan, which showed a right middle lobe consolidation. Bronchoscopy revealed a tumor that totally obstructed the middle lobe. Open lung biopsy revealed a low-grade mucoepidermoid carcinoma. Middle and lower right lung lobectomy was performed, followed by an uneventful recovery. Cytogenetic investigation of tumor cells exhibited the translocation t(11;19). This case shows that further diagnostic modalities such as CT scanning should be performed early in children with recurrent lower respiratory tract infections who have suspicious radiographic findings such as persistent atelectasis or recurrent unifocal infiltration. Bronchial mucoepidermoid carcinoma is infrequent, and molecular investigations might shed additional light on the prognosis.

Modulation of Notch signaling by mastermind-like (MAML) transcriptional co-activators and their involvement in tumorigenesis

Notch signaling is mediated by cell-cell interactions and is critical for cell fate determination in many species. Recently, a family of mastermind-like (MAML) transcriptional co-activator genes was identified that encode proteins that cooperate with Notch and CSL to activate transcription. Here, we review our current understanding of the roles of the MAML proteins in Notch signaling, and their involvement in certain human cancers. The mounting biochemical and functional evidence indicate that the MAML genes are critical components of the Notch signaling pathway, likely regulating cellular events involved in both normal development and oncogenesis.

A study of MECT1-MAML2 in mucoepidermoid carcinoma and Warthin's tumor of salivary glands

The t(11;19)(q21;p13) chromosomal translocation has been described in two distinct types of salivary gland neoplasms: mucoepidermoid carcinoma (MEC) and Warthin's tumor (WT). Since this translocation has been recently shown to generate a MECT1-MAML2 fusion gene, we evaluated 10 primary MEC and seven primary WT to further define the molecular association of these two entities using cytogenetic, as well as in situ hybridization (ISH) and reverse transcriptase-polymerase chain reaction (RT-PCR) analyses directed against the fusion gene. A karyotype was established in all neoplasms except for two MEC cases. Of the eight karyotyped MECs, five showed the t(11;19)(q21;p13), two had a normal karyotype, and one case presented a -Y and +X. Three of the WT revealed a normal karyotype and four had several abnormalities which did not involve chromosomes 11 and 19. ISH analysis performed in cytogenetic suspension and/or in tumor paraffin sections demonstrated MAML2 rearrangement in 7 of 10 cases of MEC: all five cases with t(11;19), one case with normal karyotype, and one unkaryotyped case. RT-PCR analysis confirmed the expression of the MECT1-MAML2 gene in all MEC cases that were positive by ISH analysis. Neither the t(11;19) nor MECT1-MAML2 was detected in any case of WT, nor in control samples from polymorphous low-grade adenocarcinoma, acinic cell carcinoma, or normal parotid gland tissue. We have demonstrated that ISH and RT-PCR are sensitive methods for detecting MECT1-MAML2 in MEC. In contrast, we did not detect the t(11;19) nor MECT1-MAML2 expression in seven cases of WT.

Altered Notch signaling resulting from expression of a WAMTP1-MAML2 gene fusion in mucoepidermoid carcinomas and benign Warthin's tumors

Chromosome translocations in neoplasia commonly result in fusion genes that may encode either novel fusion proteins or normal, but ectopically expressed proteins. Here we report the cloning of a novel fusion gene in a common type of salivary and bronchial gland tumor, mucoepidermoid carcinomas (MEC), as well as in benign Warthin's tumors (WATs). The fusion, which results from a t(11;19)(q21-22;p13) translocation, creates a chimeric gene in which exon 1 of a novel gene of unknown function, designated WAMTP1, is linked to exons 2-5 of the recently identified Mastermind-like Notch coactivator MAML2. In the fusion protein, the N-terminal basic domain of MAML2, which is required for binding to intracellular Notch (Notch ICD), is replaced by an unrelated N-terminal sequence from WAMTP1. Mutation analysis of the N-terminus of WAMTP1-MAML2 identified two regions of importance for nuclear localization (amino acids 11-20) and for colocalization with MAML2 and Notch1 ICD in nuclear granules (amino acids 21-42). Analyses of the Notch target genes HES5 and MASH1 in MEC tumors with and without the WAMTP1-MAML2 fusion revealed upregulation of HES5 and downregulation of MASH1 in fusion positive MECs compared to normal salivary gland tissue and MECs lacking the fusion. These findings suggest that altered Notch signaling plays an important role in the genesis of benign and malignant neoplasms of salivary and bronchial gland origin.