Emerging biology of malignant salivary gland tumors offers new insights into the classification and treatment of mucoepidermoid cancer

Establishment of Mucoepidermoid Carcinoma Cell Lines from Surgical and Recurrence Biopsy Specimens

Patients with advanced/recurrent mucoepidermoid carcinoma (MEC) have a poor prognosis. This study aimed to establish and characterize human mucoepidermoid carcinoma cell lines from the initial surgical specimen and biopsy specimen upon recurrence from the same patient to provide a resource for MEC research. MEC specimens from the initial surgical procedure and biopsy upon recurrence were used to establish cell lines. The established cell lines were cytogenetically characterized using multi-color fluorescence in situ hybridization and detection, and the sequence of the CRTC1-MAML2 chimeric gene was determined. Furthermore, the susceptibility of head and neck mucoepidermoid carcinoma to standard treatment drugs such as cisplatin, 5-fluorouracil, and cetuximab was investigated. We successfully established unique MEC cell lines, AMU-MEC1, from an initial surgical specimen and AMU-MEC1-R1 and AMU-MEC1-R2 from the recurrent biopsy specimen in the same patient. These cell lines exhibited epithelial morphology and developed in vitro-like cobblestones. They shared eight chromosomal abnormalities, including der(19)ins(19;11)(p13;?), which resulted in a chimeric CRTC1-MAML2 gene, indicating the same origin of the cell lines. The susceptibility of all cell lines to cisplatin and 5-fluorouracil was low. Interestingly, EGFR dependency for cell growth decreased in AMU-MEC-R1 and AMU-MEC-R2 but was retained in AMU-MEC1. These cytogenetic and biochemical findings suggest that the established cell lines can be used to investigate the disease progression mechanisms and develop novel therapeutics for MEC.

Expression of HHLA2, TMIGD2, and GITR in salivary gland adenoid cystic carcinoma and mucoepidermoid carcinoma

BACKGROUND

Mucoepidermoid carcinoma and adenoid cystic carcinoma are the two most common malignancies of salivary gland. Our study aims to explore the role of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced tumor necrosis factor receptor in adenoid cystic carcinoma and mucoepidermoid carcinoma, and the relationship between human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, glucocorticoid-induced TNF receptor, oncogenic signaling molecules, and cluster of differentiation 8.

METHODS

Custom-made human salivary gland tissue microarrays included 81 Adenoid cystic carcinoma, 52 mucoepidermoid carcinoma, 76 normal salivary gland, and 14 pleomorphic adenoma samples. Immunohistochemical analysis of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor, oncogenic phosphorylated Erk_1/2 , the epithelial-mesenchymal transition (EMT) molecule transforming growth factor β1, and cluster of differentiation 8 was performed with salivary gland tissue microarray of human samples.

RESULTS

According to a digital pathological system, we analyzed the correlation of immunostaining. The expression levels of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor were significantly enhanced in the adenoid cystic carcinoma and mucoepidermoid carcinoma, compared with those of pleomorphic adenoma and NSG samples. However, the expression levels of human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor were independent of the pathological grade of malignancy of mucoepidermoid carcinoma and histological pattern of adenoid cystic carcinoma. They were closely related to phosphorylated Erk1/2 and transforming growth factor β1, but negligibly related to cluster of differentiation 8.

CONCLUSIONS

These results described that certain immune checkpoint molecules, namely, human endogenous Retrovirus-H long terminal repeat-associating protein 2, transmembrane and immunoglobulin domain-containing 2, and glucocorticoid-induced TNF receptor were overexpressed in Adenoid cystic carcinoma and mucoepidermoid carcinoma, but were independent of pathological grade, and may relate to transforming growth factor β1, phosphorylated Erk1/2, and cluster of differentiation 8.

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.

A Dynamic Role of Mastermind-Like 1: A Journey Through the Main (Path)ways Between Development and Cancer

Major signaling pathways, such as Notch, Hedgehog (Hh), Wnt/β-catenin and Hippo, are targeted by a plethora of physiological and pathological stimuli, ultimately resulting in the modulation of genes that act coordinately to establish specific biological processes. Many biological programs are strictly controlled by the assembly of multiprotein complexes into the nucleus, where a regulated recruitment of specific transcription factors and coactivators on gene promoter region leads to different transcriptional outcomes. MAML1 results to be a versatile coactivator, able to set up synergistic interlinking with pivotal signaling cascades and able to coordinate the network of cross-talking pathways. Accordingly, despite its original identification as a component of the Notch signaling pathway, several recent reports suggest a more articulated role for MAML1 protein, showing that it is able to sustain/empower Wnt/β-catenin, Hh and Hippo pathways, in a Notch-independent manner. For this reason, MAML1 may be associated to a molecular “switch”, with the function to control the activation of major signaling pathways, triggering in this way critical biological processes during embryonic and post-natal life. In this review, we summarize the current knowledge about the pleiotropic role played by MAML proteins, in particular MAML1, and we recapitulate how it takes part actively in physiological and pathological signaling networks. On this point, we also discuss the contribution of MAML proteins to malignant transformation. Accordingly, genetic alterations or impaired expression of MAML proteins may lead to a deregulated crosstalk among the pathways, culminating in a series of pathological disorders, including cancer development. Given their central role, a better knowledge of the molecular mechanisms that regulate the interplay of MAML proteins with several signaling pathways involved in tumorigenesis may open up novel opportunities for an attractive molecular targeted anticancer therapy.

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.

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.

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.

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.

11q21 rearrangement is a frequent and highly specific genetic alteration in mucoepidermoid carcinoma

Mucoepidermoid carcinoma (MEC) is the most common malignant salivary gland tumor. Translocation t(11;19)(q21;p13) involving the MECT1 and MAML2 genes has been suggested as a diagnostic marker in these tumors. To determine the specificity of 11q21 locus rearrangements for MEC, fluorescence in situ hybridization analysis with specific MEC-I Dual Color Break Apart Probe was performed on a tissue microarray containing samples from almost 1200 salivary gland adenomas and carcinomas. Rearrangements of 11q21 were observed in 40% of 217 MECs. The frequency of rearrangements decreased with tumor grade and was found in 53% of G1, 43% of G2, and 31% of G3 tumors (P=0.015). There were no 11q21 rearrangements found in other salivary gland carcinomas including 142 adenoid cystic carcinomas, 104 acinic cell adenocarcinomas, 76 adenocarcinoma not otherwise specified, 38 epithelial-myoepithelial carcinomas, 15 polymorphous low-grade adenocarcinomas, 18 basal cell adenocarcinomas, 19 myoepithelial carcinomas, 12 papillary cystadenocarcinomas, 6 salivary duct carcinomas, and 10 oncocytic carcinomas. Furthermore, all analyzed salivary gland adenomas, including 39 cases of Warthin tumor and control samples, either from the salivary gland or from other organs were negative for 11q21 rearrangements. It is concluded that MECT1-MAML2 gene fusion is a highly specific genetic alteration in MEC with predominance in low-grade and intermediate-grade tumors.

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.

Hidradenocarcinomas: a brief review and future directions

Hidradenocarcinomas are rare, aggressive skin adnexal tumors of sweat gland origin that demonstrate a high potential for local recurrence, metastasis, and poor outcome. These neoplasms can derive from preexisting clear cell hidradenomas but more commonly appear de novo, with the molecular events responsible for the pathogenesis currently unknown. Historically, diagnosis has been difficult because of the few cases, inconsistent nomenclature, variable morphology of cells that compose the neoplasm, and confusion with other visceral metastatic tumors. Presentation is generally benign with an indolent clinical course that typically includes local and multiple recurrences. Despite wide-excision surgery, disease at regional lymph nodes and metastatic sites is common and linked to decreased survival. Currently, molecular markers of pathogenesis as well as effective forms of adjuvant chemotherapy are lacking. Future studies are required to identify the histopathologic and immunohistochemical features, which may facilitate diagnosis and foster development of molecularly targeted forms of adjuvant therapy.

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.

Immunohistochemical expression of the oncogenic molecules active Stat3 and survivin in benign and malignant salivary gland tumors

OBJECTIVE

Signal transducer and activator of transcription 3 (Stat3) and survivin have been shown to exert oncogenic effects in various human neoplasms. The purpose of this study was to evaluate the expression of tyrosine phosphorylated (active) Stat3 and survivin in various benign and malignant salivary gland tumors (SGTs).

STUDY DESIGN

Eighty-six SGTs (65 malignant and 21 benign tumors of various histopathologic subtypes) were immunohistochemically stained with antisurvivin or anti-phosphorylated tyrosine-705 (p-tyr) Stat3 antibodies. Immunohistochemical reactivity was graded in a semiquantitative manner; a combined score of immunohistochemical positivity (0-6) was calculated for each tumor by adding the individual scores for percentage of tumor cells (0-3) and intensity of staining (0-3).

RESULTS

Survivin was immunohistochemically detected in all studied benign and malignant SGTs; p-tyr Stat3 was also detected in the majority (91%) of SGTs. The average combined scores for survivin and p-tyr Stat3 immunohistochemical expression in the studied malignant SGTs was 4.40 and 3.35, respectively; the corresponding combined scores for survivin and p-tyr Stat3 in the studied benign SGTs were 4.37 and 3.22, respectively. No statistically significant differences (P > .05) in p-tyr Stat3 or survivin expression were detected between the benign and malignant groups, or among the various examined histopathologic subtypes of SGTs. In contrast, normal salivary gland tissues revealed only weak and focal survivin or p-tyr Stat3 immunoreactivity, mainly localized to ductal and mucous cells.

CONCLUSIONS

Our data indicate an almost universal expression of activated Stat3 and survivin in benign and malignant SGTs. Considering the well established proliferative and antiapoptotic properties of these molecules and their functional interrelationship, selective targeting techniques against Stat3 and/or survivin may represent promising therapeutic strategies against neoplasms of salivary gland origin.

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.