Targeting the Oncogenic Transcriptional Regulator MYB in Adenoid Cystic Carcinoma by Inhibition of IGF1R/AKT Signaling.

Background: Adenoid cystic carcinoma (ACC) is an aggressive cancer with no curative treatment for patients with recurrent/metastatic disease. The MYB-NFIB gene fusion is the main genomic hallmark and a potential therapeutic target. Methods: Oncogenic signaling pathways were studied in cultured cells and/or tumors from 15 ACC patients. Phospho-receptor tyrosine kinase (RTK) arrays were used to study the activity of RTKs. Effects of RTK inhibition on cell proliferation were analyzed with AlamarBlue, sphere assays, and two ACC xenograft models (n = 4-9 mice per group). The molecular effects of MYB-NFIB knockdown and IGF1R inhibition were studied with quantitative polymerase chain reaction, immunoblot, and gene expression microarrays. All statistical tests were two-sided. Results: The MYB-NFIB fusion drives proliferation of ACC cells and is crucial for spherogenesis. Intriguingly, the fusion is regulated through AKT-dependent signaling induced by IGF1R overexpression and is downregulated upon IGF1R-inhibition (% expression of control ± SD = 27.2 ± 1.3, P < .001). MYB-NFIB regulates genes involved in cell cycle control, DNA replication/repair, and RNA processing. The transcriptional program induced by MYB-NFIB affects critical oncogenic mediators normally controlled by MYC and is reversed by pharmacological inhibition of IGF1R. Co-activation of epidermal growth factor receptor (EGFR) and MET promoted proliferation of ACC cells, and combined targeting of IGFR1/EGFR/MET induced differentiation and synergistically inhibited the growth of patient-derived xenografted ACCs (ACCX5M1, % growth of control ± SD = 34.9 ± 20.3, P = .006; ACCX6, % growth of control ± SD = 24.1 ± 17.5, P = .04). Conclusions: MYB-NFIB is an oncogenic driver and a key therapeutic target in ACC that is regulated by AKT-dependent IGF1R signaling. Our studies uncover a new strategy to target an oncogenic transcriptional master regulator and provide new important insights into the biology and treatment of ACC.

Clinically significant copy number alterations and complex rearrangements of MYB and NFIB in head and neck adenoid cystic carcinoma.

Adenoid cystic carcinoma (ACC) of the head and neck is a malignant tumor with poor long-term prognosis. Besides the recently identified MYB-NFIB fusion oncogene generated by a t(6;9) translocation, little is known about other genetic alterations in ACC. Using high-resolution, array-based comparative genomic hybridization, and massively paired-end sequencing, we explored genomic alterations in 40 frozen ACCs. Eighty-six percent of the tumors expressed MYB-NFIB fusion transcripts and 97% overexpressed MYB mRNA, indicating that MYB activation is a hallmark of ACC. Thirty-five recurrent copy number alterations (CNAs) were detected, including losses involving 12q, 6q, 9p, 11q, 14q, 1p, and 5q and gains involving 1q, 9p, and 22q. Grade III tumors had on average a significantly higher number of CNAs/tumor compared to Grade I and II tumors (P = 0.007). Losses of 1p, 6q, and 15q were associated with high-grade tumors, whereas losses of 14q were exclusively seen in Grade I tumors. The t(6;9) rearrangements were associated with a complex pattern of breakpoints, deletions, insertions, inversions, and for 9p also gains. Analyses of fusion-negative ACCs using high-resolution arrays and massively paired-end sequencing revealed that MYB may also be deregulated by other mechanisms in addition to gene fusion. Our studies also identified several down-regulated candidate tumor suppressor genes (CTNNBIP1, CASP9, PRDM2, and SFN) in 1p36.33-p35.3 that may be of clinical significance in high-grade tumors. Further, studies of these and other potential target genes may lead to the identification of novel driver genes in ACC.

Analysis of MYB expression and MYB-NFIB gene fusions in adenoid cystic carcinoma and other salivary neoplasms.

Recent studies have shown that the recurrent t(6;9)(q22-23;p23-24) translocation in adenoid cystic carcinoma results in a novel fusion of the MYB proto-oncogene with the transcription factor gene NFIB. To determine the frequency of this finding, we used RT-PCR assays of the MYB and MYB-NFIB fusion transcripts, and immunohistochemistry for the MYB protein, to study adenoid cystic carcinomas and other epithelial tumors of the salivary glands, and head and neck region. MYB-NFIB fusion transcript was detected in 25 of 29 (86%) frozen adenoid cystic carcinoma tumor samples, and in 14 of 32 (44%) formalin-fixed paraffin-embedded adenoid cystic carcinoma tumor specimens. In contrast, the MYB-NFIB fusion was not expressed in non-adenoid cystic carcinoma neoplasms of the head and neck, confirming the high specificity of the MYB-NFIB fusion. Adenoid cystic carcinomas from various anatomic sites, including salivary gland, sinonasal cavity, tracheobronchial tree, larynx, breast, and vulva were repeatedly fusion-positive, indicating that adenoid cystic carcinomas located in different anatomic sites not only have important morphologic features in common, but also probably evolve through activation of the same molecular pathways. Studies of the expression of MYB revealed that 89% of the tumors, including both fusion-positive and fusion-negative cases, overexpressed MYB RNA. Similarly, 82% of adenoid cystic carcinomas stained positive for MYB protein, compared with 14% of non-adenoid cystic carcinoma neoplasms, indicating that MYB immunostaining may be useful for the diagnosis of adenoid cystic carcinoma, but that neoplasms sometimes in the differential diagnosis are also labeled. The latter are, however, fusion-negative. In summary, our studies show that MYB activation through gene fusion or other mechanisms is a major oncogenic event in adenoid cystic carcinoma occurring at various anatomic sites. In addition to being a diagnostically useful biomarker for adenoid cystic carcinoma, MYB and its downstream effectors are also novel potential therapeutic targets.

New tricks from an old oncogene: gene fusion and copy number alterations of MYB in human cancer.

MYB is a leucine zipper transcription factor that is essential for hematopoesis and for renewal of colonic crypts. There is also ample evidence showing that MYB is leukemogenic in several animal species. However, it was not until recently that clear evidence was presented showing that MYB actually is an oncogene rearranged in human cancer. In a recent study, a novel mechanism of activation of MYB involving gene fusion was identified in carcinomas of the breast and head and neck. A t(6;9) translocation was shown to generate fusions between MYB and the transcription factor gene NFIB. The fusions consistently result in loss of the 3'-end of MYB, including several highly conserved target sites for microRNAs that negatively regulate MYB expression. Deletion of these target sites may disrupt the repression of MYB, leading to overexpression of MYB-NFIB transcripts and protein and to transcriptional activation of critical MYB target genes associated with apoptosis, cell cycle control, cell growth/angiogenesis and cell adhesion. This study, together with previous and recent data showing rearrangements and copy number alterations of the MYB locus in T-cell leukemia and certain solid tumors, will be the main focus of this review.

Recurrent fusion of MYB and NFIB transcription factor genes in carcinomas of the breast and head and neck.

The transcription factor gene MYB was identified recently as an oncogene that is rearranged/duplicated in some human leukemias. Here we describe a new mechanism of activation of MYB in human cancer involving gene fusion. We show that the t(6;9)(q22-23;p23-24) translocation in adenoid cystic carcinomas (ACC) of the breast and head and neck consistently results in fusions encoding chimeric transcripts predominantly consisting of MYB exon 14 linked to the last coding exon(s) of NFIB. The minimal common part of MYB deleted as the result of fusion was exon 15 including the 3'-UTR, which contains several highly conserved target sites for miR-15a/16 and miR-150 microRNAs. These microRNAs recently were shown to regulate MYB expression negatively. We suggest that deletion of these target sites may disrupt repression of MYB leading to overexpression of MYB-NFIB transcripts and protein and to activation of critical MYB targets, including genes associated with apoptosis, cell cycle control, cell growth/angiogenesis, and cell adhesion. Forced overexpression of miR-15a/16 and miR-150 in primary fusion-positive ACC cells did not significantly alter the expression of MYB as compared with leukemic cells with MYB activation/duplication. Our data indicate that the MYB-NFIB fusion is a hallmark of ACC and that deregulation of the expression of MYB and its target genes is a key oncogenic event in the pathogenesis of ACC. Our findings also suggest that the gain-of-function activity resulting from the MYB-NFIB fusion is a candidate therapeutic target.

High-resolution genomic profiling of adenomas and carcinomas of the salivary glands reveals amplification, rearrangement, and fusion of HMGA2.

Carcinoma ex pleomorphic adenoma (Ca-ex-PA) is an epithelial malignancy developing within a benign salivary gland pleomorphic adenoma (PA). Here we have used genome-wide, high-resolution array-CGH, and fluorescence in situ hybridization to identify genes amplified in double min chromosomes and homogeneously staining regions in PA and Ca-ex-PA and to identify additional genomic imbalances characteristic of these tumor types. Ten of the 16 tumors analyzed showed amplification/gain of a 30-kb minimal common region, consisting of the 5'-part of HMGA2 (encoding the three DNA-binding domains). Coamplification of MDM2 was found in nine tumors. Five tumors had cryptic HMGA2-WIF1 gene fusions with amplification of the fusion oncogene in four tumors. Expression analysis of eight amplified candidate genes in 12q revealed that tumors with amplification/rearrangement of HMGA2 and MDM2 had significantly higher expression levels when compared with tumors without amplification. Analysis of individual HMGA2 exons showed that the expression of exons 3-5 were substantially reduced when compared with exons 1-2 in 9 of 10 tumors with HMGA2 activation, indicating that gene fusions and rearrangements of HMGA2 are common in tumors with amplification. In addition, recurrent amplifications/gains of 1q11-q32.1, 2p16.1-p12, 8q12.1, 8q22-24.1, and 20, and losses of 1p21.3-p21.1, 5q23.2-q31.2, 8p, 10q21.3, and 15q11.2 were identified. Collectively, our results identify HMGA2 and MDM2 as amplification targets in PA and Ca-ex-PA and suggest that amplification of 12q genes (in particular MDM2), deletions of 5q23.2-q31.2, gains of 8q12.1 (PLAG1) and 8q22.1-q24.1 (MYC), and amplification of ERBB2 may be of importance for malignant transformation of benign PA.

Frequent fusion of the CRTC1 and MAML2 genes in clear cell variants of cutaneous hidradenomas.

Fusion of the CREB regulated transcription coactivator CRTC1 (a.k.a. MECT1, TORC1, or WAMTP1) to the Notch coactivator MAML2 is a characteristic feature of low-grade mucoepidermoid carcinomas of salivary and bronchial glands. The CRTC1-MAML2 fusion protein acts by inducing transcription of cAMP/CREB target genes, and this activity is crucial for the transforming properties of the protein. Here we show that the CRTC1-MAML2 gene fusion is also frequent in benign hidradenomas of the skin. FISH and RT-PCR analyses revealed that hidradenomas are genetically heterogeneous, and that 10 of the 20 tumors analyzed (50%) contained the CRTC1-MAML2 gene fusion and expressed the resulting fusion transcript. Immunohistochemical analysis demonstrated expression of the fusion protein in the majority of tumor cells, including clear cells, poroid cells, and cells with epidermoid and ductal differentiation. In addition, we could show that all fusion-positive tumors were morphologically distinguished by the presence of more or less abundant areas of clear cells whereas all fusion-negative tumors lacked clear cells. Our findings thus demonstrate that the CRTC1-MAML2 gene fusion is frequent in hidradenomas and is associated with clear cell variants of this tumor. Taken together, the present and previous observations indicate that the CRTC1-MAML2 fusion is etiologically linked to benign and low-grade malignant tumors originating from diverse exocrine glands rather than being linked to a separate tumor entity.

Molecular classification of mucoepidermoid carcinomas-prognostic significance of the MECT1-MAML2 fusion oncogene.

Mucoepidermoid carcinomas (MECs) of the salivary and bronchial glands are characterized by a recurrent t(11;19)(q21;p13) translocation resulting in a MECT1-MAML2 fusion in which the CREB-binding domain of the CREB coactivator MECT1 (also known as CRTC1, TORC1 or WAMTP1) is fused to the transactivation domain of the Notch coactivator MAML2. To gain further insights into the molecular pathogenesis of MECs, we cytogenetically and molecularly characterized a series of 29 MECs. A t(11;19) and/or an MECT1-MAML2 fusion was detected in more than 55% of the tumors. Several cases with cryptic rearrangements that resulted in gene fusions were detected. In fusion-negative MECs, the most common aberration was a single or multiple trisomies. Western blot and immunohistochemical studies demonstrated that the MECT1-MAML2 fusion protein was expressed in all MEC-specific cell types. In addition, cotransfection experiments showed that the fusion protein colocalized with CREB in homogeneously distributed nuclear granules. Analyses of potential downstream targets of the fusion revealed differential expression of the cAMP/CREB (FLT1 and NR4A2) and Notch (HES1 and HES5) target genes in fusion-positive and fusion-negative MECs. Moreover, clinical follow-up studies revealed that fusion-positive patients had a significantly lower risk of local recurrence, metastases, or tumor-related death compared to fusion-negative patients (P = 0.0012). When considering tumor-related deaths only, the estimated median survival for fusion-positive patients was greater than 10 years compared to 1.6 years for fusion-negative patients. These findings suggest that molecularly classifying MECs on the basis of an MECT1-MAML2 fusion is histopathologically and clinically relevant and that the fusion is a useful marker in predicting the biological behavior of MECs.

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

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