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

Oncogenic Role of ADAM32 in Hepatoblastoma: A Potential Molecular Target for Therapy

Outcomes of pediatric hepatoblastoma (HBL) have improved, but refractory cases still occur. More effective and safer drugs are needed that are based on molecular mechanisms. A disintegrin and metalloproteases (ADAMs) are expressed with high frequency in various human carcinomas and play an important role in cancer progression. In this study, we analyzed expression of ADAMs in HBL with a cDNA microarray dataset and found that the expression level of ADAM32 is particularly high. To investigate the role of ADAM32 in cancer, forced expression or knockdown experiments were conducted with HepG2 and HBL primary cells. Colony formation, cell migration and invasion, and cell viability were increased in HepG2 expressing ADAM32, whereas knockdown of ADAM32 induced a decrease in these cellular functions. Quantitative RT-PCR demonstrated an association between ADAM32 expression and the expression of genes related to cancer stem cells and epithelial–mesenchymal transition (EMT), suggesting a role of ADAM32 in cancer stemness and EMT. Furthermore, knockdown of ADAM32 increased cisplatin-induced apoptosis, and this effect was attenuated by a caspase-8 inhibitor, suggesting that ADAM32 plays a role in extrinsic apoptosis signaling. We conclude that ADAM32 plays a crucial role in progression of HBL, so it might be a promising molecular target in anticancer therapy.

Thymic Mucoepidermoid Carcinoma: A Clinicopathologic and Molecular Study

Thymic mucoepidermoid carcinoma (MEC) is a rare tumor, and its characteristics remain to be clarified. Here we investigated 20 cases of thymic MEC to systematically characterize its clinical, histopathologic, and molecular features. The median age of the patients was 56 years (range, 19 to 80 y), there was a slight male predilection (3:2), and 44% of the patients were asymptomatic at diagnosis. The median tumor size was 6.8 cm in diameter, 55% were pT1 tumors, and 50% were TNM stage I tumors. When 4 tumor grading systems for salivary MEC (Armed Forces Institutes of Pathology, Brandwein, modified Healey, and the Memorial Sloan-Kettering) were employed, low-grade, intermediate-grade, and high-grade tumors accounted for 35% to 70%, 5% to 25%, and 25% to 50%, respectively. Many histologic variants were noted, and 70% of the cases were classified as nonclassic variants. MAML2 rearrangement was detected in 56% of cases, and the fusion partner was CRTC1 in all cases. CRTC1-MAML2 fusion was associated with lower pT classification and lower TNM stage. The overall survival rate of all patients was 69% and 43% at 5 and 10 years, respectively. Worse overall survival was associated with higher pT stage, higher TNM stage, residual tumors, greater tumor size, high-grade tumor histology (Armed Forces Institutes of Pathology and Memorial Sloan-Kettering, but not the other 2), and with the absence of CRTC1-MAML2 fusion. Of note, none of the patients with CRTC1-MAML2 fusion-positive tumors died during the follow-up. In conclusion, the clinicopathologic and molecular findings of thymic MEC presented here are expected to contribute to the management of this rare tumor.

Establishment of a patient‑derived mucoepidermoid carcinoma cell line with the CRTC1‑MAML2 fusion gene

Mucoepidermoid carcinoma (MEC) is the most common malignant tumor of the major and minor salivary glands. Surgical resection is the only curative treatment and there is no effective post-operative therapy for MEC. The present study reports an Institutional Review Board-approved case of a 45-year-old Japanese female diagnosed with low-grade MEC in the hard palate. Radical resection, supraomohyoid neck dissection and antero-lateral thigh flap reconstruction was performed. A MEC cell line was then established from the resected tumor tissue. Short tandem repeat profiling confirmed the origin and authenticity of the cell line, that harbors a CRTC1-MAML2 translocation, which is frequently observed in MEC. Amphiregulin (AREG), identified as one of the targets of the CRTC1-MAML2 fusion gene, was expressed in the cell line. The AREG receptor, epidermal growth factor receptor (EGFR) was also highly phosphorylated. The results predicted that AREG-EGFR signaling, which is required for tumor growth and survival, might be activated in the cell line in a cell-autonomous manner. As AREG expression is associated with EGFR-targeted drug resistance, this cell line might assist with the identification of novel strategies for MEC treatment.

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.

Targeting Notch and EGFR signaling in human mucoepidermoid carcinoma

Mucoepidermoid carcinoma (MEC) is the most common type of salivary gland cancers and patients with advanced, metastatic, and recurrent MECs have limited therapeutic options and poor treatment outcomes. MEC is commonly associated with a chromosomal translocation t(11;19) (q14-21;p12-13) that encodes the CRTC1-MAML2 oncogenic fusion. The CRTC1-MAML2 fusion is required for MEC growth in part through inducing autocrine AREG-EGFR signaling. Growing evidence suggests that MEC malignancy is maintained by cancer stem-like cells. In this study, we aimed to determine critical signaling for maintaining MEC stem-like cells and the effect of combined targeting of stem cell signaling and CRTC1-MAML2-induced EGFR signaling on blocking MEC growth. First, we evaluated the significance of Notch signaling in regulating MEC stem-like cells. Aberrantly activated Notch signaling was detected in human fusion-positive MEC cells. The inhibition of Notch signaling with genetic or pharmacological inhibitors reduced oncosphere formation and ALDH-bright population in vitro and blocked the growth of MEC xenografts in vivo. Next, we investigated the effect of co-targeting Notch signaling and EGFR signaling, and observed enhanced inhibition on MEC growth in vivo. Collectively, this study identified a critical role of Notch signaling in maintaining MEC stem-like cells and tumor growth, and revealed a novel approach of co-targeting Notch and EGFR signaling as a potential effective anti-MEC treatment.

Problematic breast tumors reassessed in light of novel molecular data

Breast cancer is a vastly heterogeneous disease encompassing a panoply of special histological subtypes. Although rare breast tumors have largely not been investigated systematically in large scale genomics series, recent studies have shed light on the genetic underpinnings of special histologic subtypes of breast cancer. Genomic analyses of estrogen receptor-positive special histologic types of breast cancer have not resulted in the identification of novel pathognomonic genetic alterations in addition to the confirmation of the presence of CDH1 loss-of-function mutations in invasive lobular carcinomas. By contrast, the analyses of triple-negative breast cancers have demonstrated that low-grade triple-negative breast cancers categorically differ from the common forms of high-grade triple-negative disease biologically and phenotypically and are underpinned by specific fusion genes or hotspot mutations. A subset of low-grade triple-negative disease has been shown to harbor highly recurrent if not pathognomonic genetic alterations, such as ETV6-NTRK3 fusion gene in secretory carcinomas, the MYB-NFIB fusion gene, MYBL1 rearrangements or MYB gene amplification in adenoid cystic carcinomas, and HRAS Q61 hotspot mutations coupled with mutations in PI3K pathway genes in estrogen receptor-negative adenomyoepitheliomas. A subset of these pathognomonic genetic alterations (e.g., NTRK1/2/3 fusion genes) now constitute an FDA approved indication for the use of TRK inhibitors in the advanced/metastatic setting. These studies have also corroborated that salivary gland-like tumors of the breast, other than acinic cell carcinomas, harbor the repertoire of somatic genetic alterations detected in their salivary gland counterparts. Reassuringly, the systematic study of special histologic types of breast cancer utilizing state-of-the-art sequencing approaches, rather than rendering pathology obsolete, has actually strengthened the importance of breast cancer histologic typing and is providing additional ancillary markers for the diagnosis of these rare but fascinating entities.

Prognostic impact of CRTC1/3-MAML2 fusions in salivary gland mucoepidermoid carcinoma: A multiinstitutional retrospective study

Mucoepidermoid carcinoma (MEC) is rare, but the most common primary malignancy of the salivary gland and not infrequent in young individuals. CRTC1/3-MAML2 fusions are frequently detected in MEC and are useful as a diagnostic biomarker. However, there has been debate as to whether the fusions have prognostic significance. In this study, we retrospectively collected 153 salivary gland MEC cases from 11 tertiary hospitals in Japan. As inclusion criteria, the MEC patients in this study had curative surgery as the initial treatment, received no preoperative treatment, and had no distant metastasis at the time of the initial surgery. The MEC diagnosis was validated by a central pathology review by five expert salivary gland pathologists. The CRTC1/3-MAML2 fusions were detected using FISH and RT-PCR. In 153 MEC cases, 90 (58.8%) were positive for CRTC1/3-MAML2 fusions. During the follow-up period, 28 (18.3%) patients showed tumor recurrence and 12 (7.8%) patients died. The presence of the fusions was associated with favorable tumor features. Of note, none of the fusion-positive patients died during the follow-up period. Statistical analysis showed that the presence of the fusions was a prognostic indicator of a better overall survival in the total and advanced-stage MEC cohorts, but not in the early-stage MEC cohort. In conclusion, CRTC1/3-MAML2 fusions are an excellent biomarker for favorable overall survival of patients with salivary gland MEC.

Expression profile and bioinformatics analysis of circular RNA in intestinal mucosal injury and repair after severe burns

Circular RNA (circRNA) is a novel noncoding RNA that is mostly found in humans and animals. Although the flux of circRNA research has increased in recent years, its precise function is still unclear. Some studies demonstrate that circRNAs can function as microRNA (miRNA) sponges involved in the regulation of competitive endogenous RNAs networks and play a crucial role in many biological processes. Other studies show that circRNAs play multiple biological roles in gastrointestinal diseases. However, the expression characteristics and function of circRNA in intestinal mucosal injury and repair after severe burn have not been reported. This study aims to screen differentially expressed circRNAs in intestinal mucosal injury and repair after severe burns and understand their underlying mechanisms. To test our hypothesis that circRNA may play a role in promoting repair in intestinal mucosa injury after severe burns, we collected the intestinal tissues of three severely burned mice and three pseudo-scalded mice and evaluated the expression of circRNAs via microarray analysis. Quantitative real-time polymerase chain reaction was also used to validate the circRNA microarray data by selecting six based on different multiples, original values, and p values. The host genes of all differentially expressed circRNAs and the downstream target genes of six selected DEcircRNAs were identified by Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes pathway analysis. Meanwhile, we also created a circRNA-miRNA-mRNA network to predict the role and function of circRNAs in intestinal mucosal injury and repair after severe burns.

Gefitinib Represses JAK-STAT Signaling Activated by CRTC1-MAML2 Fusion in Mucoepidermoid Carcinoma Cells

BACKGROUND

Gefitinib is well-known as a tyrosine kinase inhibitor targeting non-smalllung- cancer (NSCLC) containing EGFR mutations. However, its effectiveness in treating mucoepidermoid carcinoma (MEC) without such EGFR mutations suggests additional targets.

OBJECTIVE

The CRTC1-MAML2 (C1-M2) fusion typical for MEC has been proposed to be a gefitinib target.

METHODS

To test this hypothesis, we developed a set of siRNAs to down-regulate C1-M2 expression. RNA-seq and Western blot techniques were applied to analyze the effects of gefitinib and siC1-M2 on the transcriptome of and the phosphorylation of tyrosine kinases in a MEC cell line H292.

RESULTS

Deep-sequencing transcriptome analysis revealed that gefitinib extensively inhibited transcription of genes in JAK-STAT and MAPK/ERK pathways. Both siC1-M2 and gefitinib inhibited the phosphorylation of multiple signaling kinases in these signaling pathways, indicating that gefitinib inhibited JAK-STAT and MAPK/ERK pathways activated by C1-M2 fusion. Moreover, gefitinib inhibition of EGFR and MAPK/ERK was more effective than that of AKT, JAK2 and STATs, and their dependence on C1-M2 could be uncoupled. Taken together, our results suggest that gefitinib simultaneously represses phosphorylation of multiple key signaling proteins which are activated in MEC, in part by C1-M2 fusion. Gefitinib-repressed kinase phosphorylation explains the transcriptional repression of genes in JAK-STAT and MAPK/ERK pathways.

CONCLUSION

These findings provide new insights into the efficacy of gefitinib in treating mucoepidermoid carcinoma, and suggest that a combination of gefitinib and other inhibitors specifically against C1-M2 fusion could be more effective.

Pleomorphic adenomas and mucoepidermoid carcinomas of the breast are underpinned by fusion genes

Primary pleomorphic adenomas (PAs) and mucoepidermoid carcinomas (MECs) of the breast are vanishingly rare. Here we sought to determine whether breast PAs and MECs would be underpinned by the fusion genes reported to occur in their salivary gland counterparts. Our study included three breast PAs and one breast MEC, which were subjected to RNA sequencing (PAs, n = 2; MEC, n = 1) or to Archer FusionPlex sequencing (PA, n = 1). Our analyses revealed the presence of the HMGA2-WIF1 fusion gene in breast PA3, the CTNNB1-PLAG1 fusion gene in breast PA2, and the CRTC1-MAML2 fusion gene in the breast MEC analyzed (1/1). No oncogenic fusion genes were detected in breast PA1, and no additional oncogenic fusion genes were detected in the cases studied. The presence of the fusion genes identified was validated by fluorescence in situ hybridization (n = 1), reverse transcription-PCR (n = 1), or by both methods (n = 1). Taken together, our findings indicate that PAs and MECs arising in the breast resemble their salivary gland counterparts not only phenotypically but also at the genetic level. Furthermore, our data suggest that the molecular analysis of breast PAs and MECs might constitute a useful tool to aid in their differential diagnosis.

The significance of mucinous metaplasia in Warthin tumor: a frequent occurrence and potential pitfall

Mucinous metaplasia in Warthin tumor (WT) is a recognized phenomenon. Nevertheless, its presence can create a diagnostic challenge in the distinction from the newly proposed variant of mucoepidermoid carcinoma (MEC), Warthin-like MEC. In this study, we evaluated the significance and diagnostic relevance of mucinous metaplasia in WTs. A total of 30 WTs diagnosed based on resection specimens formed the basis of this retrospective study. Mucicarmine staining was performed to identify mucinous metaplasia, and fluorescence in situ hybridization (FISH) analysis was used to detect MAML2 gene rearrangement. After review, one MAML2 rearranged case was reclassified as Warthin-like MEC as the classic bilayered epithelium in WT was not identified. The diagnosis of WT was confirmed in the remaining 29 cases. Mucinous metaplasia was encountered in 24 WTs (83%), with 14% (4/29) having an abundant amount. We found that mucinous metaplasia correlated with tumor size (p < 0.05). Age and sex distribution were similar in WT cases with or without mucinous metaplasia. In addition, neither the presence of squamous metaplasia nor the time interval between fine-needle aspiration and surgery was related to mucinous metaplasia (p > 0.05). The MAML2 FISH analyses performed in 18 WTs with variable amounts of mucinous metaplasia were negative for rearrangement. In conclusion, mucinous metaplasia is fairly common in WTs and shows a significant correlation with tumor size. Therefore, caution should be taken to avoid overinterpretation of WT with mucinous metaplasia as MEC in cases showing the classic bilayered oncocytic lining epithelium.

Adaptive Transcriptional Responses by CRTC Coactivators in Cancer

Adaptive stress signaling networks directly influence tumor development and progression. These pathways mediate responses that allow cancer cells to cope with both tumor cell-intrinsic and cell-extrinsic insults and develop acquired resistance to therapeutic interventions. This is mediated in part by constant oncogenic rewiring at the transcriptional level by integration of extracellular cues that promote cell survival and malignant transformation. The cAMP-regulated transcriptional coactivators (CRTCs) are a newly discovered family of intracellular signaling integrators that serve as the conduit to the basic transcriptional machinery to regulate a host of adaptive response genes. Thus, somatic alterations that lead to CRTC activation are emerging as key driver events in the development and progression of many tumor subtypes.

Genomics of mucoepidermoid and adenoid cystic carcinomas

Objective

To report on the current state of the literature on the genetics of mucoepidermoid and adenoid cystic carcinomas of the salivary glands with a focus on genomic screens and recently discovered genetic translocations.

Methods

A PubMed based literature review was performed to query for genetics related basic science and preclinical studies about mucoepidermoid and adenoid cystic carcinomas of the salivary glands.

Results and conclusions

Genetic translocations between CRTC1 and MAML2 in mucoepidermoid carcinoma and between MYB and NFIB in adenoid cystic carcinoma have been recently discovered and have therapeutic implications. Key signaling pathways such as the EGFR pathway in mucoepidermoid carcinoma and the Notch pathway, chromatin regulation, and c‐kit mediated epithelial‐mesenchymal transitions in adenoid cystic carcinoma have recently been elucidated, pointing to possible therapeutic targets in both cancers.

CRTC1-MAML2 fusion-induced lncRNA LINC00473 expression maintains the growth and survival of human mucoepidermoid carcinoma cells

Mucoepidermoid carcinoma (MEC) arises in many glandular tissues and contributes to the most common malignant salivary gland cancers. MEC is specifically associated with a unique t(11;19) translocation and the resulting CRTC1-MAML2 fusion is a major oncogenic driver for MEC initiation and maintenance. However, the molecular basis underlying the CRTC1-MAML2 oncogenic functions remain very limited. Through gene expression profiling analysis, we observed that LINC00473, a long noncoding RNA (lncRNA), was the top down-regulated target in CRTC1-MAML2-depleted human MEC cells. LncRNAs belong to a new class of non-coding RNAs with emerging roles in tumorigenesis and progression, but remain poorly characterized. In this study, we investigated the role of LINC00473 in mediating CRTC1-MAML2 oncogenic activity in human MEC. We found that LINC00473 transcription was significantly induced in human CRTC1-MAML2-positive MEC cell lines and primary MEC tumors, and was tightly correlated with the CRTC1-MAML2 RNA level. LINC00473 induction was dependent on the ability of CRTC1-MAML2 to activate CREB-mediated transcription. Depletion of LINC00473 significantly reduced the proliferation and survival of human MEC cells in vitro and blocked the in vivo tumor growth in a human MEC xenograft model. RNA in situ hybridization analysis demonstrated a predominantly nuclear localization pattern for LINC00473 in human MEC cells. Furthermore, gene expression profiling revealed that LINC00473 depletion resulted in differential expression of genes important in cancer cell growth and survival. LINC00473 likely regulates gene expression in part through its ability to bind to a cAMP signaling pathway component NONO, enhancing the ability of CRTC1-MAML2 to activate CREB-mediated transcription. Our overall results demonstrate that LINC00473 is a downstream target and an important mediator of the CRTC1-MAML2 oncoprotein. Therefore, LINC00473 acts as a promising biomarker and therapeutic target for human CRTC1-MAML2-positive MECs.

Drug screening to target nuclear orphan receptor NR4A2 for cancer therapeutics

Background

Our previous study suggested NR4A2, a subfamily member of orphan nuclear receptors, is essential for survival of human cancer cells such as mucoepidermoid carcinoma (MEC).

Methods

We conducted high throughput drug screening for NR4A2 inhibitors as a novel therapeutic modality. Positive screening was performed using a luciferase reporter vector containing NR4A2 binding sequence, and a CRE-reporter control vector was used to eliminate false positives. In vitro assays for positive hits were conducted.

Results

A total of 23 Food and Drug Administration (FDA) and 43 Life Science Library compounds were identified, including several epidermal growth factor inhibitors and Src inhibitors. Subsequent in vitro assays confirmed that identified compounds were preferentially active in NR4A2+ cancer cells. Several candidate compounds appeared to suppress NR4A2 via inhibition of p-ERK, whereas a novel compound KU0171309 may act as a more direct inhibitor.

Conclusions

Further research should focus on homologue selectivity, in vivo activity, and definitively deciphering the mechanism of action of KU0171309.

Microarray analysis of embryo-derived bovine pluripotent cells: The vulnerable state of bovine embryonic stem cells

Although there are many studies about pluripotent stem cells, little is known about pluripotent pathways and the difficulties of maintaining the pluripotency of bovine cells in vitro. Here, we investigated differently expressed genes (DEG) in bovine embryo-derived stem-like cells (eSLCs) from various origins to validate their distinct characteristics of pluripotency and differentiation. We identified core pluripotency markers and additional markers which were not determined as pluripotency markers yet in bovine eSLCs. Using the KEGG database, TGFβ, WNT, and LIF signaling were related to the maintenance of pluripotency. In contrast, some DEGs related to the LIF pathway were down-regulated, suggesting that reactivation of the pathway may be required for the establishment of true bovine embryonic stem cells (ESCs). Interestingly, oncogenes were co-down-regulated, while tumor suppressor genes were co-up-regulated in eSLCs, implying that this pattern may induce abnormal teratomas. These data analyses of signaling pathways provide essential information on authentic ESCs in addition to providing evidence for pluripotency in bovine eSLCs.

Common Variants Confer Susceptibility to Barrett's Esophagus: Insights from the First Genome-Wide Association Studies

Eight loci have been identified by the two genome-wide association studies of Barrett's esophagus that have been conducted to date. Esophageal adenocarcinoma cases were included in the second study following evidence that predisposing genetic variants for this cancer overlap with those for Barrett's esophagus. Genes with roles in embryonic development of the foregut are adjacent to 6 of the loci identified (FOXF1, BARX1, FOXP1, GDF7, TBX5, and ALDH1A2). An additional locus maps to a gene with known oncogenic potential (CREB-regulated transcription coactivator 1), but expression quantitative trait data implicates yet another gene involved in esophageal development (PBX4). These results strongly support a model whereby dysregulation of genes involved in esophageal and thoracic development increases susceptibility to Barrett's esophagus and esophageal adenocarcinoma, probably by reducing anatomical antireflux mechanisms. An additional signal at 6p21 in the major histocompatibility complex also reinforces evidence that immune and inflammatory response to reflux is involved in the development of both diseases. All of the variants identified are intronic or intergenic rather than coding and are presumed to be or to mark regulatory variants. As with genome-wide association studies of other diseases, the functional variants at each locus are yet to be identified and the genes affected need confirming. In this chapter as well as discussing the biology behind each genome-wide association signal, we review the requirements for successfully conducting genome-wide association studies and discuss how progress in understanding the genetic variants that contribute to Barrett's esophagus/esophageal adenocarcinoma susceptibility compares to other cancers.

Whole-Exome Sequencing of Salivary Gland Mucoepidermoid Carcinoma

PURPOSE

Mucoepidermoid carcinoma (MEC) is the most common salivary gland malignancy. To explore the genetic origins of MEC, we performed systematic genomic analyses of these tumors.

EXPERIMENTAL DESIGN

Whole-exome sequencing and gene copy-number analyses were performed for 18 primary cancers with matched normal tissue. FISH was used to determine the presence or absence of the MECT1-MAML2 translocation in 17 tumors.

RESULTS

TP53 was the most commonly mutated gene in MEC (28%), and mutations were found only in intermediate- and high-grade tumors. Tumors with TP53 mutations had more mutations overall than tumors without TP53 mutations (P = 0.006). POU6F2 was the second most frequently mutated gene, found in three low-grade MECs with the same in-frame deletion. Somatic alterations in IRAK1, MAP3K9, ITGAL, ERBB4, OTOGL, KMT2C, and OBSCN were identified in at least two of the 18 tumors sequenced. FISH analysis confirmed the presence of the MECT1-MAML2 translocation in 15 of 17 tumors (88%).

CONCLUSIONS

Through these integrated genomic analyses, MECT1-MAML2 translocation and somatic TP53 and POU6F2 mutations appear to be the main drivers of MEC. Clin Cancer Res; 23(1); 283-8. ©2016 AACR.

Genetic alterations in salivary gland cancers

Salivary gland cancers are an incredibly heterogeneous group of tumors that include 24 histologically distinct tumor types. The use of new genetic methods has paved the way for promising advancements in our understanding of the molecular biology underlying each type of tumor. The objective of this review was to highlight common oncogenes, tumor suppressor genes, and cytogenetic and epigenetic changes associated with the most common tumor types: mucoepidermoid carcinoma, adenoid cystic carcinoma, salivary duct carcinoma, mammary analogue secretory carcinoma, hyalinizing clear cell carcinoma, carcinoma ex pleomorphic adenoma, and acinic cell carcinoma. Recent insights into the pathogenesis of each cancer subtype have helped better define and classify these tumors. Further research in salivary gland cancers should focus on determining the key genes involved in the tumorigenesis of each distinct malignancy and identifying individualized chemotherapies directed at these targets. Cancer 2016;122:1822-31. © 2016 American Cancer Society.

Primary lung mucoepidermoid carcinoma: analysis of prognostic factors using surveillance, epidemiology and end results program

INTRODUCTION

Mucoepidermoid carcinoma (MEC) primarily occurs in salivary glands, but can also arise in other organs; however, the impact of primary location on patient prognosis is largely unknown.

METHODS

Using Surveillance, Epidemiology and End Results Program (SEER) data we investigated whether the clinical and prognostic features of MEC differed among multiple organ sites. The SEER-18 dataset from 18 cancer registries in the US between 1972 and 2012 was chosen. The common organ sites with 100 or more cases were further analyzed. Survival analysis included Log-rank tests of Kaplan-Meier curves and univariate/multivariate proportional hazard analysis.

RESULTS

A total of 7,191 MEC cases with survival data were identified in the SEER data. Major salivary gland (MSG) was the primary site in 52.9% of cases, followed by gum and other mouth (23.6%), lung (5.9%), tongue (3.4%) and others. Compared to MSG-MEC, primary lung MEC had significantly more patients with age <=70, diagnosis in 2002 and earlier, distant stage, undetermined grade and nonsurgical treatment. Primary lung MEC, older age, male gender, early year of diagnosis, distant stage, high histologic grade and radiation alone were significantly associated with poor 5-year disease-specific survival rate. Among patients with primary lung MEC, univariate analysis demonstrated that those with main bronchus or upper lobe primary sites had significantly decreased 5-year disease-specific survival rate.

CONCLUSIONS

This study suggests that there is a major difference in prognosis of MEC among primary sites. Primary lung MEC might have poor prognosis over MSG-MEC.

Gene expression profiling analysis of CRTC1-MAML2 fusion oncogene-induced transcriptional program in human mucoepidermoid carcinoma cells

Background

Mucoepidermoid carcinoma (MEC) arises from multiple organs and accounts for the most common types of salivary gland malignancies. Currently, patients with unresectable and metastatic MEC have poor long-term clinical outcomes and no targeted therapies are available. The majority of MEC tumors contain a t(11;19) chromosomal translocation that fuses two genes, CRTC1 and MAML2, to generate the chimeric protein CRTC1-MAML2. CRTC1-MAML2 displays transforming activity in vitro and is required for human MEC cell growth and survival, partially due to its ability to constitutively activate CREB-mediated transcription. Consequently, CRTC1-MAML2 is implicated as a major etiologic molecular event and a therapeutic target for MEC. However, the molecular mechanisms underlying CRTC1-MAML2 oncogenic action in MEC have not yet been systematically analyzed. Elucidation of the CRTC1-MAML2-regulated transcriptional program and its underlying mechanisms will provide important insights into MEC pathogenesis that are essential for the development of targeted therapeutics.

Methods

Transcriptional profiling was performed on human MEC cells with the depletion of endogenous CRTC1-MAML2 fusion or its interacting partner CREB via shRNA-mediated gene knockdown. A subset of target genes was validated via real-time RT-PCR assays. CRTC1-MAML2-perturbed molecular pathways in MEC were identified through pathway analyses. Finally, comparative analysis of CRTC1-MAML2-regulated and CREB-regulated transcriptional profiles was carried out to assess the contribution of CREB in mediating CRTC1-MAML2-induced transcription.

Results

A total of 808 differentially expressed genes were identified in human MEC cells after CRTC1-MAML2 knockdown and a subset of known and novel fusion target genes was confirmed by real-time RT-PCR. Pathway Analysis revealed that CRTC1-MAML2-regulated genes were associated with network functions that are important for cell growth, proliferation, survival, migration, and metabolism. Comparison of CRTC1-MAML2-regulated and CREB-regulated transcriptional profiles revealed common and distinct genes regulated by CRTC1-MAML2 and CREB, respectively.

Conclusion

This study identified a specific CRTC1-MAML2-induced transcriptional program in human MEC cells and demonstrated that CRTC1-MAML2 regulates gene expression in CREB-dependent and independent manners. Our data provide the molecular basis underlying CRTC1-MAML2 oncogenic functions and lay a foundation for further functional investigation of CRTC1-MAML2-induced signaling in MEC initiation and maintenance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1827-3) contains supplementary material, which is available to authorized users.

Tumors of the lacrimal gland

Tumors of the lacrimal gland comprise a wide spectrum, of which the most common demonstrate epithelial and lymphoid differentiation. The diagnosis of lacrimal gland tumors depends primarily on histological evaluation, as do the choice of treatment and prognosis. For some lacrimal gland neoplasms, such as adenoid cystic carcinoma, the outlook is grave. Optimal treatment for several lacrimal gland tumors is also a matter of controversy. However, recent progress has been made in the molecular and genetic understanding of tumorigenesis for such lesions. This article presents an overview of the histopathology of lacrimal gland tumors, together with their epidemiological features, clinical characteristics, and treatment strategies.

Role of LKB1-CRTC1 on glycosylated COX-2 and response to COX-2 inhibition in lung cancer

BACKGROUND

Cyclooxygenase-2 (COX-2) directs the synthesis of prostaglandins including PGE-2 linking inflammation with mitogenic signaling. COX-2 is also an anticancer target, however, treatment strategies have been limited by unreliable expression assays and by inconsistent tumor responses to COX-2 inhibition.

METHODS

We analyzed the TCGA and Director's Challenge lung cancer datasets (n = 188) and also generated an LKB1-null lung cancer gene signature (n = 53) to search the Broad Institute/Connectivity-MAP (C-MAP) dataset. We performed ChIP analyses, real-time polymerase chain reaction, immunoblotting, and drug testing of tumor cell lines (n = 8) and primary lung adenocarcinoma surgical resections (n = 13).

RESULTS

We show that COX-2 is a target of the cAMP/CREB coactivator CRTC1 signaling pathway. In addition, we detected a correlation between LKB1 status, CRTC1 activation, and presence of glycosylated, but not inactive hypoglycosylated COX-2 in primary lung adenocarcinoma. A search of the C-MAP drug database discovered that all high-ranking drugs positively associated with the LKB1-null signature are known CRTC1 activators, including forskolin and six different PGE-2 analogues. Somatic LKB1 mutations are present in 20.0% of lung adenocarcinomas, and we observed growth inhibition with COX-2 inhibitors in LKB1-null lung cancer cells with activated CRTC1 as compared with LKB1-wildtype cells (NS-398, P = .002 and Niflumic acid, P = .006; two-tailed t test).

CONCLUSION

CRTC1 activation is a key event that drives the LKB1-null mRNA signature in lung cancer. We also identified a positive feedback LKB1/CRTC1 signaling loop for COX-2/PGE2 regulation. These data suggest a role for LKB1 status and glycosylated COX-2 as specific biomarkers that provide a framework for selecting patients for COX-2 inhibition studies.

CRTC1/MAML2 gain-of-function interactions with MYC create a gene signature predictive of cancers with CREB-MYC involvement

Chimeric oncoproteins created by chromosomal translocations are among the most common genetic mutations associated with tumorigenesis. Malignant mucoepidermoid salivary gland tumors, as well as a growing number of solid epithelial-derived tumors, can arise from a recurrent t (11, 19)(q21;p13.1) translocation that generates an unusual chimeric cAMP response element binding protein (CREB)-regulated transcriptional coactivator 1 (CRTC1)/mastermind-like 2 (MAML2) (C1/M2) oncoprotein comprised of two transcriptional coactivators, the CRTC1 and the NOTCH/RBPJ coactivator MAML2. Accordingly, the C1/M2 oncoprotein induces aberrant expression of CREB and NOTCH target genes. Surprisingly, here we report a gain-of-function activity of the C1/M2 oncoprotein that directs its interactions with myelocytomatosis oncogene (MYC) proteins and the activation of MYC transcription targets, including those involved in cell growth and metabolism, survival, and tumorigenesis. These results were validated in human mucoepidermoid tumor cells that harbor the t (11, 19)(q21;p13.1) translocation and express the C1/M2 oncoprotein. Notably, the C1/M2-MYC interaction is necessary for C1/M2-driven cell transformation, and the C1/M2 transcriptional signature predicts other human malignancies having combined involvement of MYC and CREB. These findings suggest that such gain-of-function properties may also be manifest in other oncoprotein fusions found in human cancer and that agents targeting the C1/M2-MYC interface represent an attractive strategy for the development of effective and safe anticancer therapeutics in tumors harboring the t (11, 19) translocation.

Mucoepidermoid carcinoma does not harbor transcriptionally active high risk human papillomavirus even in the absence of the MAML2 translocation

High risk human papillomavirus (HPV) is firmly established as an important cause of oropharyngeal carcinoma. Recent studies have also implicated HPV as a cause of mucoepidermoid carcinoma (MEC)-a tumor of salivary gland origin that frequently harbors MAML2 translocations. The purpose of this study was to determine the prevalence of transcriptionally active HPV in a large group of MECs and to determine whether HPV infection and the MAML2 translocation are mutually exclusive events. Break-apart fluorescence in situ hybridization for MAML2 was performed on a tissue microarray containing 92 MECs. HPV testing was performed using RNA in situ hybridization targeting high risk HPV mRNA E6/E7 transcripts. Of the 71 MECs that could be evaluated by FISH, 57 (80 %) harbored the MAML2 rearrangement. HPV was not detected in any of the 57 MECs that contained a MAML2 rearrangement, in any of the 14 MECs that did not contain the rearrangement, or in any of the 21 MECs where MAML2 status was unknown. High risk HPV does not appear to play any significant role in the development of MEC. It neither complements nor replaces MAML2 translocation in the tumorigenesis of MEC.

Characterization of tumorigenic cell lines from the recurrence and lymph node metastasis of a human salivary mucoepidermoid carcinoma

The long-term outcome of patients with mucoepidermoid carcinoma is poor. Limited availability of cell lines and lack of xenograft models is considered a major barrier to improved mechanistic understanding of this disease and development of effective therapies.

OBJECTIVE

To generate and characterize human mucoepidermoid carcinoma cell lines and xenograft models suitable for mechanistic and translational studies.

METHODS

Five human mucoepidermoid carcinoma specimens were available for generation of cell lines. Cell line tumorigenic potential was assessed by transplantation and serial in vivo passaging in immunodeficient mice, and cell line authenticity verified by short tandem repeat (STR) profiling.

RESULTS

A unique pair of mucoepidermoid carcinoma cell lines was established from a local recurrence (UM-HMC-3A) and from the metastatic lymph node (UM-HMC-3B) of the same patient, 4 years after surgical removal of the primary tumor. These cell lines retained epithelial-like morphology through 100 passages in vitro, contain the Crtc1-Maml2 fusion oncogene (characteristic of mucoepidermoid carcinomas), and express the prototypic target of this fusion (NR4A2). Both cell lines generated xenograft tumors when transplanted into immunodeficient mice. Notably, the xenografts exhibited histological features and Periodic Acid Schiff (PAS) staining patterns that closely resembled those found in human tumors. STR profiling confirmed the origin and authenticity of these cell lines.

CONCLUSION

These data demonstrate the generation and characterization of a pair of tumorigenic salivary mucoepidermoid carcinoma cell lines representative of recurrence and lymph node metastasis. Such models are useful for mechanistic and translational studies that might contribute to the discovery of new therapies for mucoepidermoid carcinoma.

Tumours of the lacrimal gland. Epidemiological, clinical and genetic characteristics

Tumours of the lacrimal gland are rare, but the prognosis may be grave. To date, no population-based incidence and distribution data on lacrimal gland tumours exist. In addition, almost nothing is known about the genetic profile of epithelial tumours of the lacrimal gland. We collected specimens and clinical files on all biopsied lacrimal gland lesions in Denmark over a 34-year period and re-evaluated the diagnosis to provide updated population-based incidence rates and epidemiological characteristics. Clinical data regarding symptoms, clinical examinations, treatment and follow-up were collected for patients with adenoid cystic carcinoma (ACC), pleomorphic adenoma (PA), carcinoma ex pleomorphic adenoma (Ca-ex-PA) and mucoepidermoid carcinoma (MEC). Using RT-PCR, FISH, immunohistochemistry, Q-PCR and high-resolution array-based comparative genomic hybridization (arrayCGH) we explored the genetic characteristics including copy number alterations (CNA) in ACC, PA, Ca-ex-PA and MEC. The incidence of biopsied lacrimal gland lesions was 1.3/1,000,000/year, and ~50% were neoplastic lesions. Of these, 55% were malignant tumours with epithelial tumours as the most frequent. The overall incidence was increasing, and this was caused by an increase in biopsied non-neoplastic lesions. We found that 10/14 ACCs either expressed the MYB-NFIB fusion gene and/or had rearrangements of MYB. All ACCs expressed the MYB protein. ACC was characterized by recurrent copy number losses involving 6q, 12q and 17q and gains involving 19q, 8q and 11q. ArrayCGH revealed an apparently normal genomic profile in 11/19 PAs. The remaining 8 PAs had recurrent copy number losses involving 1p, 6q, 8q and 13q and gain involving 9p. PA expressed PLAG1 in all tumours whereas only 2/29 tumours expressed HMGA2. Ca-ex-PA was characterized by recurrent copy number gain involving 22q. PLAG1 was expressed in 3/5 Ca-ex-PA whereas none of these tumours expressed HMGA2. MEC expressed the CRTC1-MAML2, and this fusion was found to be tumour-specific for lacrimal gland MEC. In conclusion, lacrimal gland lesions that require pathological evaluation are rare in the Danish population, and the incidence rate of biopsied benign lesions is increasing. Epithelial tumours of the lacrimal gland are molecularly very similar to their salivary gland counterparts in the expression of the tumour-specific fusion genes and in their genomic imbalances as demonstrated by arrayCGH. MYB-NFIB is a useful biomarker for ACC and MYB, and its downstream target genes may be potential therapeutic targets for these tumours.

Aberrantly activated AREG-EGFR signaling is required for the growth and survival of CRTC1-MAML2 fusion-positive mucoepidermoid carcinoma cells

Salivary gland tumors (SGT) are a group of highly heterogeneous head and neck malignancies with widely varied clinical outcomes and no standard effective treatments. The CRTC1-MAML2 fusion oncogene, encoded by a recurring chromosomal translocation t(11;19)(q14-21;p12-13), is a frequent genetic alteration found in >50% of mucoepidermoid carcinomas (MEC), the most common malignant SGT. In this study, we aimed to define the role of the CRTC1-MAML2 oncogene in the maintenance of MEC tumor growth and to investigate critical downstream target genes and pathways for therapeutic targeting of MEC. By performing gene expression analyses and functional studies via RNA interference and pharmacological modulation, we determined the importance of the CRTC1-MAML2 fusion gene and its downstream AREG-EGFR signaling in human MEC cancer cell growth and survival in vitro and in vivo using human MEC xenograft models. We found that CRTC1-MAML2 fusion oncogene was required for the growth and survival of fusion-positive human MEC cancer cells in vitro and in vivo. The CRTC1-MAML2 oncoprotein induced the upregulation of the epidermal growth factor receptor (EGFR) ligand Amphiregulin (AREG) by co-activating the transcription factor CREB, and AREG subsequently activated EGFR signaling in an autocrine manner that promoted MEC cell growth and survival. Importantly, CRTC1-MAML2-positive MEC cells were highly sensitive to EGFR signaling inhibition. Therefore, our study revealed that aberrantly activated AREG-EGFR signaling is required for CRTC1-MAML2-positive MEC cell growth and survival, suggesting that EGFR-targeted therapies will benefit patients with advanced, unresectable CRTC1-MAML2-positive MEC.

Molecular heterogeneity in mucoepidermoid carcinoma: conceptual and practical implications

Mucoepidermoid carcinoma (MEC), the most common salivary gland malignancy of the upper aerodigestive tract and tracheobronchial tree, is also known for its considerable cellular heterogeneity including epidermoid, intermediate and mucin producing cells. Despite this structural and cellular heterogeneity, MEC is uniquely characterized by a specific translocation t(11; 19) (q12; p13), resulting in a fusion between the MECT1 and the MAML2 genes. Although the incidence of this fusion in MEC varies, it is generally accepted that more than 50 % of this entity manifest the MECT1-MAML2. Fusion-positive cases showed significantly better survival than fusion-negative cases, suggesting that MECT1-MAML2 represents a specific prognostic molecular marker in MEC. We contend that fusion in MEC represents a distinct mechanism in the development of this entity. In that context, fusion positive MEC, regardless of grade, manifest a more stable genome and better clinical behaviour, while fusion negative MEC represent a distinctly different pathway characterized by marked genomic instability and relatively aggressive tumors.

Rsf-1, a chromatin remodelling protein, interacts with cyclin E1 and promotes tumour development

Chromosome 11q13.5 containing RSF1 (HBXAP), a gene involved in chromatin remodelling, is amplified in several human cancers including ovarian carcinoma. Our previous studies demonstrated requirement of Rsf-1 for cell survival in cancer cells, which contributed to tumour progression; however, its role in tumourigenesis has not yet been elucidated. In this study, we co-immunoprecipitated proteins with Rsf-1 followed by nanoelectrospray mass spectrometry and identified cyclin E1, besides SNF2H, as one of the major Rsf-1 interacting proteins. Like RSF1, CCNE1 is frequently amplified in ovarian cancer, and both Rsf-1 and cyclin E1 were found co-up-regulated in ovarian cancer tissues. Ectopic expression of Rsf-1 and cyclin E1 in non-tumourigenic TP53(mut) RK3E cells led to an increase in cellular proliferation and tumour formation by activating cyclin E1-associated kinase (CDK2). Tumourigenesis was not detected if either cyclin E1 or Rsf-1 was expressed, or they were expressed in a TP53(wt) background. Domain mapping showed that cyclin E1 interacted with the first 441 amino acids of Rsf-1. Ectopic expression of this truncated domain significantly suppressed G1/S-phase transition, cellular proliferation, and tumour formation of RK3E-p53(R175H) /Rsf-1/cyclin E1 cells. The above findings suggest that Rsf-1 interacts and collaborates with cyclin E1 in neoplastic transformation and TP53 mutations are a prerequisite for tumour-promoting functions of the RSF/cyclin E1 complex.

Genomic profiles and CRTC1-MAML2 fusion distinguish different subtypes of mucoepidermoid carcinoma

Mucoepidermoid carcinoma is the most common salivary gland malignancy, and includes a spectrum of lesions ranging from non-aggressive low-grade tumors to aggressive high-grade tumors. To further characterize this heterogeneous group of tumors we have performed a comprehensive analysis of copy number alterations and CRTC1-MAML2 fusion status in a series of 28 mucoepidermoid carcinomas. The CRTC1-MAML2 fusion was detected by RT-PCR or fluorescence in situ hybridization in 18 of 28 mucoepidermoid carcinomas (64%). All 15 low-grade tumors were fusion-positive whereas only 3 of 13 high-grade tumors were fusion-positive. High-resolution array-based comparative genomic hybridization revealed that fusion-positive tumors had significantly fewer copy number alterations/tumor compared with fusion-negative tumors (1.5 vs 9.5; P=0.002). Twelve of 18 fusion-positive tumors had normal genomic profiles whereas only 1 out of 10 fusion-negative tumors lacked copy number alterations. The profiles of fusion-positive and fusion-negative tumors were very similar to those of low- and high-grade tumors. Thus, low-grade mucoepidermoid carcinomas had significantly fewer copy number alterations/tumor compared with high-grade mucoepidermoid carcinomas (0.7 vs 8.6; P<0.0001). The most frequent copy number alterations detected were losses of 18q12.2-qter (including the tumor suppressor genes DCC, SMAD4, and GALR1), 9p21.3 (including the tumor suppressor genes CDKN2A/B), 6q22.1-q23.1, and 8pter-p12.1, and gains of 8q24.3 (including the oncogene MAFA), 11q12.3-q13.2, 3q26.1-q28, 19p13.2-p13.11, and 8q11.1-q12.2 (including the oncogenes LYN, MOS, and PLAG1). On the basis of these results we propose that mucoepidermoid carcinoma may be subdivided in (i) low-grade, fusion-positive mucoepidermoid carcinomas with no or few genomic imbalances and favorable prognosis, (ii) high-grade, fusion-positive mucoepidermoid carcinomas with multiple genomic imbalances and unfavorable prognosis, and (iii) a heterogeneous group of high-grade, fusion-negative adenocarcinomas with multiple genomic imbalances and unfavorable outcome. Taken together, our studies indicate that molecular genetic analysis can be a useful adjunct to histologic scoring of mucoepidermoid carcinoma and may lead to development of new clinical guidelines for management of these patients.

MAML2 rearrangement in Warthin's tumour: a fluorescent in situ hybridisation study of metaplastic variants

BACKGROUND

Warthin's tumour (WT) is a common benign lesion of the major salivary glands. The nature of WT remains controversial, with particular regard to the presence of clonal chromosomal abnormalities, including the t(11;19) translocation involving the CRTC1 and MAML2 genes, that have been identified in both WT and mucoepidermoid carcinoma. In this study, we focused our attention on metaplastic WT variants, and we conducted a fluorescent in situ hybridisation (FISH) analysis for the presence of MAML2 gene rearrangement.

METHODS

Dual-colour FISH analysis was performed on paraffin-embedded sections of eight WTs showing metaplastic changes (five with squamous metaplasia, two with mucinous metaplasia and one with both) using a MAML2 break-apart probe.

RESULTS

Presence of split signals indicative of gene rearrangement was identified in a subset of cells in areas of squamous metaplasia in two samples of WT. No rearrangement was observed in the oncocytic epithelium, in lymphocytes and in areas of mucinous metaplasia.

CONCLUSIONS

The presence of a small subpopulation of cells carrying MAML2 rearrangement in areas of squamous metaplasia within WT could predispose these lesions to malignant transformation in mucoepidermoid carcinoma and could represent a molecular link between the two entities.

Salivary gland cancers: biology and molecular targets for therapy

Salivary gland carcinomas are a heterogeneous group of tumors with different biologic behavior. Given the lack of large randomized studies, there is no standard treatment for advanced and/or metastatic salivary gland tumors, and systemic therapy is empirically based. Tumor-specific recurrent chromosomal translocations and fusion oncogenes in aggressive head and neck malignancies have diagnostic, therapeutic, and prognostic implications. Pathognomonic fusion transcripts have been identified in subsets of mucoepidermoid carcinoma and adenoid cystic carcinoma. These translocations target 1) transcription factors involved in growth factor signaling and cell cycle regulation, 2) transcriptional co-activators, and 3) tyrosine kinase receptors. Prioritizing studies with a translational component to advance the molecular understanding of these cancers and molecular-targeted therapy clinical trials is critical.

Mutant BRAF induces DNA strand breaks, activates DNA damage response pathway, and up-regulates glucose transporter-1 in nontransformed epithelial cells

Although the oncogenic functions of activating BRAF mutations have been clearly demonstrated in human cancer, their roles in nontransformed epithelial cells remain largely unclear. Investigating the cellular response to the expression of mutant BRAF in nontransformed epithelial cells is fundamental to the understanding of the roles of BRAF in cancer pathogenesis. In this study, we used two nontransformed cyst108 and RK3E epithelial cell lines as models in which to compare the phenotypes of cells expressing BRAF(WT) and BRAF(V600E). We found that transfection of the BRAF(V600E), but not the BRAF(WT), expression vector suppressed cellular proliferation and induced apoptosis in both cell types. BRAF(V600E) generated reactive oxygen species, induced DNA double-strand breaks, and caused subsequent DNA damage response as evidenced by an increased number of pCHK2 and γH2AX nuclear foci as well as the up-regulation of pCHK2, p53, and p21. Because BRAF and KRAS (alias Ki-ras) mutations have been correlated with GLUT1 up-regulation, which encodes glucose transporter-1, we demonstrated here that expression of BRAF(V600E), but not BRAF(WT), was sufficient to up-regulate GLUT1. Taken together, our findings provide new insights into mutant BRAF-induced oncogenic stress that is manifested by DNA damage and growth arrest by activating the pCHK2-p53-p21 pathway in nontransformed cells, while it also confers tumor-promoting phenotypes such as the up-regulation of GLUT1 that contributes to enhanced glucose metabolism that characterizes tumor cells.

Altered LKB1/CREB-regulated transcription co-activator (CRTC) signaling axis promotes esophageal cancer cell migration and invasion

LKB1 is a tumor susceptibility gene for the Peutz-Jeghers cancer syndrome and is a target for mutational inactivation in sporadic human malignancies. LKB1 encodes a serine/threonine kinase that has critical roles in cell growth, polarity and metabolism. A novel and important function of LKB1 is its ability to regulate the phosphorylation of CREB-regulated transcription co-activators (CRTCs) whose aberrant activation is linked with oncogenic activities. However, the roles and mechanisms of LKB1 and CRTC in the pathogenesis of esophageal cancer have not been previously investigated. In this study, we observed altered LKB1-CRTC signaling in a subset of human esophageal cancer cell lines and patient samples. LKB1 negatively regulates esophageal cancer cell migration and invasion in vitro. Mechanistically, we determined that CRTC signaling becomes activated because of LKB1 loss, which results in the transcriptional activation of specific downstream targets including LYPD3, a critical mediator for LKB1 loss-of-function. Our data indicate that de-regulated LKB1-CRTC signaling might represent a crucial mechanism for esophageal cancer progression.

RNAi: a potential new class of therapeutic for human genetic disease

Dominant negative genetic disorders, in which a mutant allele of a gene causes disease in the presence of a second, normal copy, have been challenging since there is no cure and treatments are only to alleviate the symptoms. Current therapies involving pharmacological and biological drugs are not suitable to target mutant genes selectively due to structural indifference of the normal variant of their targets from the disease-causing mutant ones. In instances when the target contains single nucleotide polymorphism (SNP), whether it is an enzyme or structural or receptor protein are not ideal for treatment using conventional drugs due to their lack of selectivity. Therefore, there is a need to develop new approaches to accelerate targeting these previously inaccessible targets by classical therapeutics. Although there is a cooling trend by the pharmaceutical industry for the potential of RNA interference (RNAi), RNAi and other RNA targeting drugs (antisense, ribozyme, etc.) still hold their promise as the only drugs that provide an opportunity to target genes with SNP mutations found in dominant negative disorders, genes specific to pathogenic tumor cells, and genes that are critical for mediating the pathology of various other diseases. Because of its exquisite specificity and potency, RNAi has attracted a considerable interest as a new class of therapeutic for genetic diseases including amyotrophic lateral sclerosis, Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), spinocerebellar ataxia, dominant muscular dystrophies, and cancer. In this review, progress and challenges in developing RNAi therapeutics for genetic diseases will be discussed.

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.

Rsf-1, a chromatin remodeling protein, induces DNA damage and promotes genomic instability

Rsf-1 (HBXAP) has been reported as an amplified gene in human cancer, including the highly aggressive ovarian serous carcinoma. Rsf-1 protein interacts with SNF2H to form an ISWI chromatin remodeling complex, RSF. In this study, we investigated the functional role of Rsf-1 by observing phenotypes after expressing it in nontransformed cells. Acute expression of Rsf-1 resulted in DNA damage as evidenced by DNA strand breaks, nuclear γH2AX foci, and activation of the ATM-CHK2-p53-p21 pathway, leading to growth arrest and apoptosis. Deletion mutation and gene knockdown assays revealed that formation of a functional RSF complex with SNF2H was required for Rsf-1 to trigger DNA damage response (DDR). Gene knock-out of TP53 alleles, TP53 mutation, or treatment with an ATM inhibitor abolished up-regulation of p53 and p21 and prevented Rsf-1-induced growth arrest. Chronic induction of Rsf-1 expression resulted in chromosomal aberration and clonal selection for cells with c-myc amplification and CDKN2A/B deletion. Co-culture assays indicated Rsf-1-induced DDR as a selecting barrier that favored outgrowth of cell clones with a TP53 mutation. The above findings suggest that increased Rsf-1 expression and thus excessive RSF activity, which occurs in tumors harboring Rsf-1 amplification, can induce chromosomal instability likely through DDR.

CRTC1 expression during normal and abnormal salivary gland development supports a precursor cell origin for mucoepidermoid cancer

Dysregulation of the transcription factor CRTC1 by a t(11;19) chromosomal rearrangement mediates the formation of mucoepidermoid salivary gland carcinoma (MEC). Although the CRTC1 promoter is consistently active in fusion-positive MEC and low levels of CRTC1 transcripts have been reported in normal adult salivary glands, the distribution of CRTC1 protein in the normal salivary gland is not known. The aim of this study was to determine if CRTC1, like many known oncogenes, is expressed during early submandibular salivary gland (SMG) development and re-expressed in an experimental tumor model. Our results indicate that CRTC1 protein is expressed in SMG epithelia during early stages of morphogenesis, disappears with differentiation, and reappears in initial tumor-like pathology. This stage-dependent expression pattern suggests that CRTC1 may play a role during embryonic SMG branching morphogenesis but not for pro-acinar/acinar differentiation, supporting a precursor cell origin for MEC tumorigenesis. Moreover, the coincident expression of CRTC1 protein and cell proliferation markers in tumor-like histopathology suggests that CRTC1-mediated cell proliferation may contribute, in part, to initial tumor formation.

Central mucoepidermoid carcinoma, a case report with molecular analysis of the TORC1/MAML2 gene fusion

Mucoepidermoid carcinoma is the most common salivary gland malignancy. The majorities of these tumors arise in the parotid and minor salivary glands, but may rarely develop intraosseously. The latter is not uncommonly associated with diagnostic and management difficulties. We report an example of intraosseous mucoepidermoid carcinoma with positive TORC1/MAML2 gene fusion transcript and discuss the clinical implications.

Unfavorable prognosis of CRTC1-MAML2 positive mucoepidermoid tumors with CDKN2A deletions

The CRTC1-MAML2 fusion oncogene underlies the etiology of mucoepidermoid salivary gland carcinoma (MEC) where it confers a favorable survival outcome as compared with fusion-negative MEC. While these analyses suggested that detection of CRTC1-MAML2 serves as a useful prognostic biomarker, we recently identified outlier cases of fusion-positive MEC associated with advanced-staged lethal disease. To identify additional genetic alterations that might cooperate with CRTC1-MAML2 to promote disease progression, we performed a pilot high-resolution oligonucleotide array CGH (aCGH) and PCR-based genotyping study on 23 MEC samples including 14 fusion-positive samples for which we had clinical outcome information. Unbiased aCGH analysis identified inactivating deletions within CDKN2A as a candidate poor prognostic marker which was confirmed by PCR-based analysis (CDKN2A deletions in 5/5 unfavorable fusion-positive cases and 0/9 favorable fusion-positive cases). We did not detect either activating EGFR mutations, nor copy number gains at the EGFR or ERBB2 loci as poor prognostic features for fusion-positive MEC in any of the tumor specimens. Prospective studies with larger case series will be needed to confirm that combined CRTC1-MAML2 and CDKN2A genotyping will optimally stage this disease.

Enhanced activity of the CREB co-activator Crtc1 in LKB1 null lung cancer

Activation of Crtc1 (also known as Mect1/Torc1) by a t(11;19) chromosomal rearrangement underlies the etiology of malignant salivary gland tumors. As LKB1 is a target for mutational inactivation in lung cancer and was recently shown to regulate hepatic Crtc2/CREB transcriptional activity in mice, we now present evidence suggesting disruption of an LKB1/Crtc pathway in cancer. Although Crtc1 is preferentially expressed in adult brain tissues, we observed elevated levels of steady-state Crtc1 in thoracic tumors. In addition, we show that somatic loss of LKB1 is associated with underphosphorylation of endogenous Crtc1, enhanced Crtc1 nuclear localization and enhanced expression of the Crtc prototypic target gene, NR4A2/Nurr1. Inhibition of NR4A2 was associated with growth suppression of LKB1 null tumors, but showed little effect on LKB1-wildtype cells. These data strengthen the role of dysregulated Crtc as a bona fide cancer gene, present a new element to the complex LKB1 tumorigenic axis, and suggest that Crtc genes may be aberrantly activated in a wider range of common adult malignancies.

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.

Mutation-associated fusion cancer genes in solid tumors

Chromosomal translocations and fusion oncogenes serve as the ultimate biomarker for clinicians as they show specificity for distinct histopathologic malignancies while simultaneously encoding an etiologic mutation and a therapeutic target. Previously considered a minor mutational event in epithelial solid tumors, new methodologies that do not rely on the detection of macroscopic cytogenetic alterations, as well as access to large series of annotated clinical material, are expanding the inventory of recurrent fusion oncogenes in both common and rare solid epithelial tumors. Unexpectedly, related assays are also revealing a high number of tandem or chimeric transcripts in normal tissues including, in one provocative case, a template for a known fusion oncogene. These observations may force us to reassess long-held views on the definition of a gene. They also raise the possibility that some rearrangements might represent constitutive forms of a physiological chimeric transcript. Defining the chimeric transcriptome in both health (transcription-induced chimerism and intergenic splicing) and disease (mutation-associated fusion oncogenes) will play an increasingly important role in the diagnosis, prognosis, and therapy of patients with cancer.

Current concepts in research related to oncogenes implicated in salivary gland tumourigenesis: a review of the literature

BACKGROUND

Salivary gland tumours are relatively uncommon and there exists considerable difficulty in decisions regarding prognosis and management, as well as diagnostic uncertainty that has implications for treatment.

METHOD

Literature pertaining to individual oncogenes has been reviewed and commented upon, specifically looking at the role of these as diagnostic and prognostic markers and as potential targets for treatments.

RESULTS

kit, PLAG1, Mect1-Maml2, HMGIC, HER2/neu, ras, c-fos and Sox-4 all have seminal small-scale studies in the literature with potential for further research and eventual clinical applications.

CONCLUSION

A wide variety of oncogenes are implicated in salivary gland tumourigenesis, with evidence being confined to small murine or in vitro studies more often than not. There are possible roles for different oncogenes in therapeutics, prognosis and management of specific salivary gland tumours.

Treatment and survival outcomes based on histologic grading in patients with head and neck mucoepidermoid carcinoma

BACKGROUND

Histopathologic grade of mucoepidermoid carcinoma (MEC) is an established predictor of prognosis and affects treatment protocol. Tumor behavior is more aggressive in high-grade than in low-grade MEC, leading to a more intensive treatment protocol. Outcomes for patients with intermediate-grade MEC are less clear; therefore, the optimal treatment protocol for this group is not well defined. The treatment protocol and survival outcomes of patients treated for MEC of the head and neck was investigated.

METHODS

A retrospective clinical review and prospective review of histopathologic grading were undertaken using the most recently established grading system of 50 patients with MEC of the head and neck from 1983 through 2004.

RESULTS

As histologic grade increased from low to intermediate to high, overall survival (P < .0001) and disease-free survival (P < .001) were significantly decreased. Overall and disease-free survival were significantly better for patients with intermediate-grade MEC than those with high-grade disease. Overall and disease-free survival were similar for patients with low-grade and intermediate-grade MEC. There was a low rate of disease recurrence in patients with intermediate-grade MEC, but this did not lead to death from disease. Although no patients with low-grade or intermediate-grade MEC died of disease, 52% of patients with high-grade MEC died of disease. Multivariate analysis revealed that histologic grade, age, and surgical margin status significantly predicted prognosis.

CONCLUSIONS

These findings suggest that, under the current histopathologic classification system, the behavior of intermediate-grade MEC is comparable to that of low-grade MEC and different from high-grade MEC, allowing for the establishment of an evidence-based treatment protocol.