Mechanism Of Oncogene Activation Research Articles

Focal deletions of a promoter tether activate the IRX3 oncogene in T-cell acute lymphoblastic leukemia

AbstractOncogenes can be activated in cis through multiple mechanisms including enhancer hijacking events and noncoding mutations that create enhancers or promoters de novo. These paradigms have helped parse somatic variation of noncoding cancer genomes, thereby providing a rationale to identify noncanonical mechanisms of gene activation. Here we describe a novel mechanism of oncogene activation whereby focal copy number loss of an intronic element within the FTO gene leads to aberrant expression of IRX3, an oncogene in T-cell acute lymphoblastic leukemia. Loss of this CTCF-bound element downstream to IRX3 (+224 kb) leads to enhancer hijack of an upstream developmentally active super-enhancer of the CRNDE long noncoding RNA (−644 kb). Unexpectedly, the CRNDE super-enhancer interacts with the IRX3 promoter with no transcriptional output until it is untethered from the FTO intronic site. We propose that “promoter tethering” of oncogenes to inert regions of the genome is a previously unappreciated biological mechanism preventing tumorigenesis.

Pseudogene-mediated DNA demethylation leads to oncogene activation.

Pseudogenes, noncoding homologs of protein-coding genes, once considered nonfunctional evolutionary relics, have recently been linked to patient prognoses and cancer subtypes. Despite this potential clinical importance, only a handful of >12,000 pseudogenes in humans have been characterized in cancers to date. Here, we describe a previously unrecognized role for pseudogenes as potent epigenetic regulators that can demethylate and activate oncogenes. We focused on SALL4, a known oncogene in hepatocellular carcinoma (HCC) with eight pseudogenes. Using a locus-specific demethylating technology, we identified the critical CpG region for SALL4 expression. We demonstrated that SALL4 pseudogene 5 hypomethylates this region through interaction with DNMT1, resulting in SALL4 up-regulation. Intriguingly, pseudogene 5 is significantly up-regulated in a hepatitis B virus model before SALL4 induction, and both are increased in patients with HBV-HCC. Our results suggest that pseudogene-mediated demethylation represents a novel mechanism of oncogene activation in cancer.

HNRNPL Circularizes ARHGAP35 to Produce an Oncogenic Protein.

Circular RNAs (circRNAs) are an intriguing class of widely prevalent endogenous RNAs, the vast majority of which have not been characterized functionally. Here, we identified a novel oncogenic circRNA originating from the back‐splicing of Exon2 and Exon3 of a tumor suppressor gene, ARHGAP35 (also known as P190‐A), termed as circARHGAP35. have observe that circARHGAP35 and linear ARHGAP35 have antithetical expression and functions. Interestingly, circARHGAP35 contains a 3867 nt long ORF with an m6A‐modified start codon and encodes a truncated protein comprising four FF domains and lacking the Rho GAP domain. Mechanistically, circARHGAP35 protein promotes cancer cell progression by interacting with TFII‐I protein in the nucleus. The RNA binding protein, HNRNPL, facilitates the formation of circARHGAP35. Clinically, circARHGAP35 is associated with poor survival in cancer patients. Our findings characterize an oncogenic circRNA and demonstrate a novel mechanism of oncogene activation in cancer by circRNA through the production of a truncated protein.

Novel Regulatory Factors and Small-Molecule Inhibitors of FGFR4 in Cancer.

Fibroblast growth factor receptor 4 (FGFR4) is a tyrosine kinase receptor that is a member of the fibroblast growth factor receptor family and is stimulated by highly regulated ligand binding. Excessive expression of the receptor and its ligand, especially FGF19, occurs in many types of cancer. Abnormal FGFR4 production explains these cancer formations, and therefore, this receptor has emerged as a potential target for inhibiting cancer development. This review discusses the diverse mechanisms of oncogenic activation of FGFR4 and highlights some currently available inhibitors targeting FGFR4.

Abstract 4355: Identification and functional characterization of glioma structural variants

Abstract Adult diffuse gliomas are a diverse class of brain tumors that ultimately result in fatal malignant progression. The highly variable disease progression intervals and poor treatment response observed in glioma have been explained, in part, by the extent of heterogeneity within and across gliomas. Somatic structural variants such as deletions, duplications, insertions, inversions, translocations, and extrachromosomal DNA contribute to glioma heterogeneity by generating genomic instability, a hallmark of cancer genomes. While comprehensive approaches such as whole genome sequencing have begun to catalog the glioma structural variant landscape, the molecular mechanisms by which they contribute to tumor progression remains poorly understood. Here, we identified genomic rearrangements in the whole genomes of 147 gliomas and glioma cell lines. Among the whole-genome sequencing samples were 62 glioblastomas (TCGA), 52 low-grade gliomas (TCGA), and our own set of 33 patient-derived glioma sphere-forming cells. On average, glioblastomas demonstrated a greater frequency of high-confidence structural variants (162 per tumor) than low-grade gliomas (130 per tumor, P=0.02) with two glioblastomas displaying evidence of chromothripsis. Across the World Heath Organization's molecular classifications, the IDH-mutant 1p/19q co-deleted tumors demonstrated the lowest structural variant burden when compared with both IDH-wildtype and IDH-mutant non-co-deleted tumors. Structural variant frequencies were found to be similar between patient tumors and an independent set of patient-derived cell lines. Across all samples, a majority of the structural variant breakpoints were found in intronic (42%) and intergenic regions (55%) suggesting that rearrangements predominantly impact distal regulatory regions. To investigate the functional consequences of structural variants in these regions we integrated these samples with available RNA-sequencing and epigenetic data to characterize deregulated transcriptional circuits. Analyses examining the association between genomic rearrangements and chromatin states to determine potential mechanisms of oncogene activation in select tumor and cell line samples are now underway. Together, our study demonstrates the importance of integrating structural variant calls from whole genome sequencing with expression and epigenetic data to define functional genomic rearrangements. Citation Format: Kevin C. Johnson, Floris P. Barthel, Ming Tang, Samirkumar Amin, Qianghu Wang, Erik P. Sulman, Kunal Rai, Roel G.W Verhaak. Identification and functional characterization of glioma structural variants [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4355.

Advances in the Molecular Diagnosis and Therapy of Relapsed/Refractory Diffuse Large B-cell Lymphoma -Review

Diffuse large B-cell lymphoma (DLBCL) is biologically aggressive and most common pathological type of non-Hodgkin's lymphoma (NHL), and about one-third of these patients are refractory or relapsed ultimately. Based on the molecular heterogeneity, DLBCL can be divided into 3 main molecular subtypes: germinal center B-cell like (GCB), activated B-cell like (ABC) and primary mediastinal B-cell lymphoma (PMBL). Arising from B cells at distinct stages of differentiation, these subtypes are also diverse in mechanisms of oncogenic activation. So targeting specific oncogene addictions within the DLBCL subtypes offers a more-precise approach to therapy in comparison with the traditional chemotherapies, undoubtedly bringing a bright hope for the treatment of relapsed/refractory DLBCL. In this article, the advances in diagnosis and therapy of GCB-DLBCL, ABC-DLBCL and PMBL relapsed/refractory diffuse large B-cell lymphoma are summarized.

Abstract 1024: Genome-wide examination of topological variability reveals cell type-specific mechanisms of oncogene activation

Abstract INTRODUCTION: The organization of chromatin within the nucleus into hierarchical three-dimensional (3D) structures plays a key role in the regulation of gene expression. Differences in 3D architecture, such as the presence or absence of “loops” between specific enhancers and their target genes, are a major driver of transcriptional and phenotypic variation. By determining the accessibility of genes to transcriptional machinery and distal regulatory regions, mechanisms mediating oncogene activation can be discerned. Recent studies have implicated pathogenic alterations in genome topology with the activation of proto-oncogenes in a multitude of cancers. METHODS: To characterize the topological changes associated with different cancer states, we developed a computational suite of tools that facilitates the systematic discovery, annotation, and visualization of features in chromatin topology and assigns statistical confidence estimates to regions with variability between cellular phenotypes. Our framework facilitates the integration of heterogeneous genomic data, including gene expression, histone modification, DNA methylation, open chromatin, and genetic variation, to further characterize changes in 3D genome. Ultimately, we propose a joint model that functionalizes the effect of epigenetic modifications on transcription as mediated through hierarchical chromatin structure. RESULTS: We identify regions of topological variation unique to breast cancer, cervical cancer, glioblastomas with and without an IDH1 mutation, melanoma, and leukemia. Patterns of disrupted insulation and subsequent localization of enhancers to proto-oncogenes can be attributed to variation in the epigenome, including variation in DNA methylation and open chromatin, at distal regulatory regions. These 3D alterations provide a mechanism for activation of specific oncogenic pathways, including signaling mediated by p38, PLK3, and BRCA. CONCLUSIONS: Variable patterns of chromatin topology provide a unique signature and mechanism of oncogenes for the cancer phenotypes considered. Additionally, our framework provides a novel means for interpreting epigenetic variability, particularly at distal regulatory regions, and explaining transcriptional variation associated with cancer phenotypes as mediated through structural changes in the DNA. Citation Format: Caleb Lareau, Martin Aryee. Genome-wide examination of topological variability reveals cell type-specific mechanisms of oncogene activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1024. doi:10.1158/1538-7445.AM2017-1024

Abstract 1023: Activation of proto-oncogenes by enhancer-hijacking in high-risk neuroblastoma

Abstract Background: Neuroblastoma (NB), a neural crest-derived tumor of the sympathetic nervous system, is the most common extracranial solid tumor in children. We have previously shown that genomic rearrangements activate proto-oncogenic telomerase by juxtaposing active enhancer elements to the TERT gene in a large fraction of high-risk NBs. In the present study, we applied a global approach integrating whole genome sequencing (WGS), Chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) data of NB cells and tumors to identify further key oncogenes activated by enhancer-hijacking in NB. Methods: WGS was applied to search for structural rearrangements in 120 NB tumors and five NB cell lines. Corresponding RNA-seq data were used to discover mono-allelic and/or outlier expression of candidate genes potentially involved in enhancer hijacking events. ChIP-seq of 34 NB tumors and 17 NB cell lines was applied to identify active enhancer elements in NB. Circular chromatin conformation capture sequencing (4C-seq) was used to confirm physical promoter-enhancer interactions in NB cell lines. Results: WGS analyses revealed that chromosomal rearrangements are common events in NB tumors and cell lines and frequently affect regions harboring proto-oncogenes and lineage specific enhancers. ChIP-seq analyses of the chromatin mark histone 3 lysine 27 acetylation (H3K27ac), surrogate for enhancer activity, confirmed that these rearrangements recurrently juxtapose active enhancer elements to oncogenes including MYCN and MYC in NB. Intriguingly, quantification of H3K27ac ChIP-seq profiles uncovered that the enhancer elements translocated to MYC were among the most active ones within the respective epigenomes. 4C-seq analyses proofed physical interactions between translocated enhancer elements and promoters of the respective oncogenes, which is in line with their elevated expression in rearranged cases. Conclusions: Our study reveals that structural rearrangements in high-risk neuroblastoma frequently juxtapose strong enhancers to key oncogenes, including MYCN and MYC, leading to physical promoter-enhancer interactions which likely drive overexpression of the oncogenes observed in rearranged cases. The common mechanism of oncogene activation by enhancer-hijacking may open a therapeutic window for epigenetic drugs including BET or CDK7 inhibitors in high-risk NBs. Citation Format: Daniel Dreidax, Moritz Gartlgruber, Sebastian Steinhauser, Larisa Savelyeva, Ron Schwessinger, Umut Toprak, Nati Ha, Dilafruz Juraeva, Martin Peifer, Matthias Fischer, Stefan Gröschel, Kai-Oliver Henrich, Young-Gyu Park, Benedikt Brors, Matthias Schlesner, Carl Herrmann, Frank Westermann. Activation of proto-oncogenes by enhancer-hijacking in high-risk neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1023. doi:10.1158/1538-7445.AM2017-1023

Activation of the LMO2 Oncogene in T-ALL through a Somatically Acquired Neomorphic Promoter

LMO2is a crucial regulator of normal hematopoiesis but is progressively silenced from the early T-cell progenitor stage of thymic development. Aberrant LMO2 expression leads to a block in differentiation, increased self-renewal and aggressive T-cell acute lymphoblastic leukemia (T-ALL). Although ≈50% of T-ALL patients overexpress LMO2, this can be attributed to a cytogenetic lesion in only ≈10% of patients, leaving a significant portion mechanistically unaccounted for. We recently discovered somatic mutations that create an oncogenic super-enhancer driving TAL1 expression (Mansour et al., 2014, Science). Therefore, we investigated whether comparable mutations may be causing dysregulated LMO2 expression.Aberrant H3K27ac marks indicative of active chromatin were identified prior to and encompassing the non-coding exon 2 of the LMO2 gene by ChIP-seq in DU.528 and PF-382 T-ALL cell lines, both of which exhibit upregulated LMO2 expression but lack chromosomal lesions at this locus. Sequencing across this peak revealed a heterozygous 20bp duplication in PF-382 cells and a heterozygous 1bp deletion in DU.528 cells, located close to a region recently described as an intermediate promoter. Both indels generated a de novo MYB consensus motif. MYB ChIP-seq showed that ≥96% of reads aligned to the mutant rather than the wild-type allele, suggesting that MYB was preferentially recruited to the mutant allele. Heterozygous mutations were also detected in diagnostic samples from 3% (5/159) of pediatric and 6% (10/164) of adult T-ALL patients. Absence of the mutations in 7 available patient-matched remission samples confirmed that they were somatic. The mutations were densely distributed around highly conserved native ETS1, MYB and GATA motifs; 5 patients had an additional MYB site, 3 both a MYB and an ETS1 site, 1 an ETS1 site alone, and 4 had new RUNX1 binding sites. This suggests that this region may have a regulatory role that is exploited by the mutations to constitutively activate LMO2.All 6 mutant-positive patients with available RNA showed LMO2 overexpression as determined by qRT-PCR, consistent with the hypothesis that these mutations activate gene expression. Furthermore, monoallelic LMO2 expression could be demonstrated in DU.528 cells and 3 of 4 informative T-ALL samples using a heterozygous germline SNP. Expression of the mutations in luciferase reporter assays also indicated that they all markedly activated luciferase activity to between 2x and 57x compared to the wild-type sequence.To assess causality between the mutations and LMO2 dysregulation, we used CRISPR/Cas9 genome-editing with a guide RNA designed to target the mutant MYB site in PF-382 cells. Reduction of LMO2 expression to ≤10% of PF-382 mutant activity was observed in a clone where the mutant allele had been reverted to wild-type and in another clone with a single T>C substitution disrupting the mutant MYB binding site. Interestingly, 2 clones that increased the distance between the native and the mutant MYB sites also resulted in a reduction in LMO2 expression to 19% and 25% of PF-382 activity, suggesting that there are functionally limiting spatial constraints on the mutant MYB site in relation to other neighboring transcription factor binding sites. This was further validated by the lack of reduction in LMO2 expression in a clone where the sequence between the two MYB sites was altered but the spacing distance was unchanged.In conclusion, we have identified and functionally validated a novel recurrent mutation hotspot occurring in a non-coding site whereby introduction of additional binding sites for a number of different transcription factors drives monoallelic LMO2 overexpression from a neomorphic promoter in a substantial proportion of both adult and pediatric T-ALL patients. This mechanism of oncogene activation may be relevant to a wide variety of human cancers. DisclosuresFielding:Baxalta: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees.

Abstract B02: Oncogene MCT-1 deregulates oxidative metabolism and promotes tumor metastasis via YY1 signaling network

Abstract The underlying mechanism of oncogene activation that induces reactive oxygen species (ROS) generation and promotes tumor progression and metastasis is still ambiguous. We now demonstrate that the oncogenic MCT-1 activation protects cells from oxidative damage via increase of YY1 and subsequently enhances EGFR expression and activation. Overexpressing MCT-1 induces cell invasion, intracellular ROS generation and MnSOD expression in mitochondria via YY1 pathway, thus targeting YY1 suppresses cancer cell invasion and blocks EGFR-MnSOD signaling function enhanced by MCT-1. Recapitulating in vitro outcomes, MCT-1 increment promotes tumor angiogenesis, necrosis and metastasis with oxidative metabolism deregulation and malignant microenvironment development in xenograft mice. Clinical data also confirms that MCT-1 enrichment connects to poor survival and prognosis coincident with YY1, EGFR and MnSOD upregulation in patients with lung cancer. Collectively, MCT-1 is a key inducer of YY1-EGFR-MnSOD axis involving the redox mechanism in the process of carcinogenesis. Citation Format: Hong-Yu Tseng, Yen-An Chen, Yi-Rong Chen, Hsin-Ling Hsu. Oncogene MCT-1 deregulates oxidative metabolism and promotes tumor metastasis via YY1 signaling network. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr B02.

Abstract IA26: Oncogenic mechanisms in diffuse intrinsic pontine gliomas

Abstract Diffuse intrinsic pontine glioma (DIPG) is a devastating disease with no effective cures. DIPG arises in the brainstem and is found almost exclusively in children. Mutations in canonical cancer signalling pathways including the RTK/RAS/PI3K pathway, the Tp53 pathway, and the CDK4/6 G1 checkpoint occur in DIPGs, targeting different effectors within these pathways and resulting in significant genetic heterogeneity between tumors. However, genome-wide studies provided abundant evidence that unique selective pressures drive HGG in children compared to adults, identifying novel oncogenic mutations connecting tumorigenesis and chromatin regulation as well as developmental signaling pathways. Recurrent mutations of the BMP receptor ACVR1/ALK2 are found in 25-30% of DIPGs, and are further restricted to the youngest patients, highlighting critical connections between development and gliomagenesis. The molecular hallmark of DIPGs is frequent recurrent somatic mutation in histone H3. Mutually exclusive somatic heterozygous H3F3A or HIST1H3B mutations encoding a K27M variant of histone H3.3 or H3.1, respectively, are found in nearly 80 percent of DIPGs. These recurrent mutations provide clear evidence of an important role for chromatin regulation in DIPG disease pathogenesis, and present a unifying molecular mechanism driving DIPG. We have evaluated the contribution of H3.3 K27M mutation to DIPG tumor growth in vitro to gain insights into molecular mechanisms of oncogenic activity, and to assess the potential of histone H3 mutation as a therapeutic sensitivity in this incurable brain tumor. Citation Format: Andre B. Silveira, Lawryn H. Kasper, Jon D. Larson, Xiaoyan Zhu, Alexander K. Diaz, Suzanne J. Baker. Oncogenic mechanisms in diffuse intrinsic pontine gliomas. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr IA26.

Alternative transcription initiation leads to expression of a novel ALK isoform in cancer

Activation of oncogenes by mechanisms other than genetic aberrations such as mutations, translocations, or amplifications is largely undefined. Here we report a novel isoform of the anaplastic lymphoma kinase (ALK) that is expressed in ∼11% of melanomas and sporadically in other human cancer types, but not in normal tissues. The novel ALK transcript initiates from a de novo alternative transcription initiation (ATI) site in ALK intron 19, and was termed ALK(ATI). In ALK(ATI)-expressing tumours, the ATI site is enriched for H3K4me3 and RNA polymerase II, chromatin marks characteristic of active transcription initiation sites. ALK(ATI) is expressed from both ALK alleles, and no recurrent genetic aberrations are found at the ALK locus, indicating that the transcriptional activation is independent of genetic aberrations at the ALK locus. The ALK(ATI) transcript encodes three proteins with molecular weights of 61.1, 60.8 and 58.7 kilodaltons, consisting primarily of the intracellular tyrosine kinase domain. ALK(ATI) stimulates multiple oncogenic signalling pathways, drives growth-factor-independent cell proliferation in vitro, and promotes tumorigenesis in vivo in mouse models. ALK inhibitors can suppress the kinase activity of ALK(ATI), suggesting that patients with ALK(ATI)-expressing tumours may benefit from ALK inhibitors. Our findings suggest a novel mechanism of oncogene activation in cancer through de novo alternative transcription initiation.

Site- and allele-specific polycomb dysregulation in T-cell leukaemia.

T-cell acute lymphoblastic leukaemias (T-ALL) are aggressive malignant proliferations characterized by high relapse rates and great genetic heterogeneity. TAL1 is amongst the most frequently deregulated oncogenes. Yet, over half of the TAL1+ cases lack TAL1 lesions, suggesting unrecognized (epi)genetic deregulation mechanisms. Here we show that TAL1 is normally silenced in the T-cell lineage, and that the polycomb H3K27me3-repressive mark is focally diminished in TAL1+ T-ALLs. Sequencing reveals that >20% of monoallelic TAL1+ patients without previously known alterations display microinsertions or RAG1/2-mediated episomal reintegration in a single site 5′ to TAL1. Using ‘allelic-ChIP’ and CrispR assays, we demonstrate that such insertions induce a selective switch from H3K27me3 to H3K27ac at the inserted but not the germline allele. We also show that, despite a considerable mechanistic diversity, the mode of oncogenic TAL1 activation, rather than expression levels, impact on clinical outcome. Altogether, these studies establish site-specific epigenetic desilencing as a mechanism of oncogenic activation.

The Ubiquitin-associated (UBA) Domain of SCCRO/DCUN1D1 Protein Serves as a Feedback Regulator of Biochemical and Oncogenic Activity

Amplification of squamous cell carcinoma-related oncogene (SCCRO) activates its function as an oncogene in a wide range of human cancers. The oncogenic activity of SCCRO requires its potentiating neddylation domain, which regulates its E3 activity for neddylation. The contribution of the N-terminal ubiquitin-associated (UBA) domain to SCCRO function remains to be defined. We found that the UBA domain of SCCRO preferentially binds to polyubiquitin chains in a linkage-independent manner. Binding of polyubiquitin chains to the UBA domain inhibits the neddylation activity of SCCRO in vivo by inhibiting SCCRO-promoted nuclear translocation of neddylation components and results in a corresponding decrease in cullin-RING-ligase-promoted ubiquitination. The results of colony formation and xenograft assays showed a mutation in the UBA domain of SCCRO that reduces binding to polyubiquitin chains, significantly enhancing its oncogenic activity. Analysis of 47 lung and head and neck squamous cell carcinomas identified a case with a frameshift mutation in SCCRO that putatively codes for a protein that lacks a UBA domain. Analysis of data from The Cancer Genome Atlas showed that recurrent mutations cluster in the UBA domains of SCCRO, lose the ability to bind to polyubiquitinated proteins, and have increased neddylation and transformation activities. Combined, these data suggest that the UBA domain functions as a negative regulator of SCCRO function. Mutations in the UBA domain lead to loss of inhibitory control, which results in increased biochemical and oncogenic activity. The clustering of mutations in the UBA domain of SCCRO suggests that mutations may be a mechanism of oncogene activation in human cancers.

Integrated Genetic Profiling Of JAK2 Wildtype Chronic-Phase Myeloproliferative Neoplasms

BackgroundThe Myeloproliferative Neoplasms (MPNs), including Polycythemia Vera (PV), Essential Thrombocythemia (ET), and Primary Myelofibrosis (PMF) are clonal hematopoietic disorders. JAK2V617F mutations are observed in approximately 90-95% of PV cases, but only 40-50% of ET and PMF cases. Although JAK2 exon 12 and LNK mutations are observed in the majority of JAK2V617F-negative PV patients, candidate gene and exome sequencing studies to date have not identified activating oncogenes in the majority of JAK2V617F-negative ET/PMF patients. Thus, further genetic investigations are needed to define the mutational architecture of these JAK2 wildtype MPNs in order to gain insight into the biology of these diseases, the clinical implications of genetic events that do occur, and the elucidation of potential therapeutic targets. AimsTo characterize the spectrum of genetic alterations in JAK2 wildtype chronic-phase myeloproliferative neoplasms. MethodsWe identified 32 patients with a confirmed diagnosis of an MPN (per 2008 WHO criteria), including MF, PV and ET, who were negative for JAK2V617F using a CLIA-certified allele specific assay for the JAK2 disease allele. Genomic DNA and total RNA was isolated from formalin fixed paraffin embedded (FFPE) tissue, blood and bone marrow aspirates. Adaptor ligated sequencing libraries were captured by solution hybridization using two custom baitsets targeting 374 cancer-related genes and 24 genes frequently rearranged for DNA-seq, and 258 genes frequently rearranged for RNA-seq. All captured libraries were sequenced to high depth (Illumina HiSeq), averaging >590X for DNA and >20,000,000 total pairs for RNA, to enable the sensitive and specific detection of genomic alterations. ResultsHigh coverage sequencing allowed us to identify JAK2V617F mutations in two patients (allele burden 3-5%) that were below the limit of detection of the CLIA assay. The most common mutations observed in JAK2V617F-negative MPN were in ASXL1 (22% of patients) and in TET2 (9%). Taken together, mutations in known epigenetic modifiers (ASXL1, TET2, DNMT3A, EZH2, MLL) were observed in 43% of samples, including a MLL-PTD mutation in one patient with PMF. We identified mutations in spliceosome components (SRSF2, U2AF1), in a subset of patients, consistent with previous reports, and in each case mutations in spliceosome components were mutually exclusive.We identified mutations in the JAK-STAT pathway (MPL, TYK2) and the RAS pathway components (KRAS, NF1) in 9% of this patient cohort, suggesting that there are alternate disease alleles that activate signaling in JAK2V617F-negative MPN. RNA-sequencing identified a ETV6-ABL1 fusion in one patient, and we identified amplification of PIK3CA in one patient in our cohort; these data suggest fusion genes and amplifications activate signaling in a subset of patients with JAK2V617F-negative MPN. We also identified novel mutations in MPN patients which have not been reported to date, including mutations in DNA repair genes (ATM and BRCA) in 25% of cases and mutations in the Notch signaling pathway (NOTCH1-4) in 31% of cases. The functional implications of these novel mutations remain to be elucidated.In univariate analysis, ASXL1 mutations were found to associate with impaired overall survival (Figure 1, p=0.049). These findings are consistent with data demonstrating an impaired survival in patients with MDS and PMF, and suggest that ASXL1 mutations represent an important biomarker for adverse outcome in JAK2V617F-negative MPN. [Display omitted] ConclusionsThese data demonstrate that the mutational spectra of JAK2V617F-negative MPN includes genes implicated in epigenetic regulation, novel mutations which activate gene signaling, and fusion genes/copy number alterations which provide a novel mechanism of oncogenic activation not previously reported in MPN. ASXL1 mutations occur frequently in JAK2 wildtype Philadelphia-Chromosome negative MPNs, and are associated with impaired overall survival. Collectively, these findings support the importance of ASXL1 mutations in predicting outcome in JAK2V617F-negative MPN, demonstrate that mutations in signaling effectors and in epigenetic regulators are common in MPN, and illustrate the genetic heterogeneity of JAK2V617F-negative MPN. Disclosures:Rampal:Foundation Medicine: Consultancy. Levine:Foundation Medicine, Inc: Consultancy.

USP6-induced neoplasms: the biologic spectrum of aneurysmal bone cyst and nodular fasciitis

USP6 (also known as TRE17) is a ubiquitin-specific protease that was identified as an oncogene in transfection experiments with Ewing sarcoma DNA 2 decades ago. Until recently, little was known about USP6 function and mechanisms of oncogenic activation. The identification of USP6 fusion genes in aneurysmal bone cyst (ABC) and, more recently, in nodular fasciitis led to a better understanding of the pathogenesis of these lesions. Furthermore, the detection of USP6 genomic rearrangements or USP6 fusion genes may be used as a diagnostic tool for these lesions. In this review, we discuss the clinicopathologic features, molecular pathology, and pathogenesis of ABC and nodular fasciitis. We also discuss the possible line of differentiation of ABC and its relationship to nodular fasciitis and other lesions.

Abstract 1139: Complete characterization of prostate cancer genomes by massively parallel sequencing

Abstract Prostate cancer is the most common type of cancer diagnosed among men in the United States, accounting for 200,000 new cases and 27,000 deaths per year. Prior genetic studies have shown that chromosomal rearrangements comprise a major mechanism of oncogene activation in prostate cancer. For example, androgen-regulated gene fusions involving ETS family transcription factors are present in the majority of prostate cancers, yet the full repertoire of genomic alterations driving prostate carcinogenesis and progression remains unknown. Toward this end, recent technological advances have made it possible to characterize the full complement of somatic mutations in a single tumor through whole genome sequencing. We are using massively parallel sequencing technology to characterize the complete genomes of several primary prostate adenocarcinomas at >30x coverage. All samples are high-grade primary tumors (Gleason grade 7 to 9) and include cases with and without known ETS family translocations. For each tumor, we are also obtaining >30x sequence coverage of matched normal DNA from blood of these same patients in order to determine the somatic component of the overall variation we observe. Our results indicate that translocations and other chromosomal rearrangements occur frequently in prostate cancer, at a rate of >100 per genome. Further, we have discovered many nonsynonymous sequence mutations (point mutations and indels) in each tumor, some of which may represent novel candidate drivers of tumor progression. The overall rate of somatic point mutations is approximately 1 per Megabase. Integrated analysis of all genomes reveals both recurrent and private alterations. Together, these results illuminate potential avenues for target discovery and demonstrate the unparalleled value in performing complete genome sequencing in this malignancy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1139.

Physical and functional interaction between polyoma virus middle T antigen and insulin and IGF-I receptors is required for oncogene activation and tumour initiation

Polyoma virus middle T antigen (PyVmT) is a powerful viral oncogene; however, the mechanisms of PyVmT activation are poorly understood. The IGF-I receptor (IGF-IR) and the insulin receptor (IR) are known to be implicated in the development of many cancers. Furthermore, PyVmT-overexpressing mouse mammary carcinoma Met-1 cells are highly responsive to IGF-I and insulin. Herein, we demonstrate that PyVmT physically interacts with IGF-IR and IR in Met-1 cells. Insulin and IGF-I increase association of the IR and IGF-IR with PyVmT, enhance tyrosine phosphorylation of PyVmT and augment the recruitment of Src and PLCγ1 to PyVmT. This is accompanied by robust and sustained phosphorylation of Akt and ERK1/2, which are implicated in both PyVmT and IGF-IR/IR signalling. Both ligands significantly increase proliferation, survival, migration and invasion of Met-1 cells. Furthermore, orthotopic inoculation of Met-1 cells with shRNAmir-mediated knockdown of IR or IGF-IR fails to initiate tumour growth in recipient mice. In conclusion, our data indicate that the physical and functional interaction between PyVmT and cellular receptor tyrosine kinases, including IR and IGF-IR, is critical for PyVmT activation and tumour initiation. These results also provide a novel mechanism for oncogene activation in the host cell.

Hyperactivation of Ha-ras oncogene, but not Ink4a/Arf deficiency, triggers bladder tumorigenesis

Although ras is a potent mitogenic oncogene, its tumorigenicity depends on cellular context and cooperative events. Here we show that low-level expression of a constitutively active Ha-ras in mouse urothelium induces simple urothelial hyperplasia that is resistant to progression to full-fledged bladder tumors even in the absence of Ink4a/Arf. In stark contrast, doubling of the gene dosage of the activated Ha-ras triggered early-onset, rapidly growing, and 100% penetrant tumors throughout the urinary tract. Tumor initiation required superseding a rate-limiting step between simple and nodular hyperplasia, the latter of which is marked by the emergence of mesenchymal components and the coactivation of AKT and STAT pathways as well as PTEN inactivation. These results indicate that overactivation of Ha-ras is both necessary and sufficient to induce bladder tumors along a low-grade, noninvasive papillary pathway, and they shed light on the recent findings that ras activation, via point mutation, overexpression, or intensified signaling from FGF receptor 3, occurs in 70%-90% of these tumors in humans. Our results highlight the critical importance of the dosage/strength of Ha-ras activation in dictating its tumorigenicity--a mechanism of oncogene activation not fully appreciated to date. Finally, our results have clinical implications, as inhibiting ras and/or its downstream effectors, such as AKT and STAT3/5, could provide alternative means to treat low-grade, superficial papillary bladder tumors, the most common tumor in the urinary system.

Analysis of Retroviral Vector Insertion Sites after T-Cell Directed Gene Therapy.

Gene transfer into peripheral blood lymphocytes has several potential applications including the correction of genetic diseases and therapeutic approaches for HIV-1 infection and cancer. Integrating gene transfer system based on murine oncoretroviruses are a convenient tool for such strategies. However, the recent occurrence of uncontrolled clonal T cell expansions in two patients treated with retroviral gene transfer for X-linked severe combined immune deficiency has raised the concern of the risk of insertional oncogenesis associated with the clinical use of integrating viral systems. In vitro studies have indicated that murine viral vectors tend to integrate in the vicinity of transcription start regions of the genome, thus providing a possible mechanism for oncogene activation, however, data from clinical gene transfer trials is lacking.We are following patients affected with adenosine deaminase (ADA) deficiency who have received T-lymphocyte-directed, retroviral-mediated gene transfer starting in 1990. The first treated patient received the last infusion of gene-corrected cells 12 years ago, has never shown any sign of lymphoproliferation and still carries ~20% of gene-corrected peripheral blood lymphocytes. We set out to study the integration sites in the cells of this patient with the aim of mapping the regions involved by retroviral integrations, determining their localization with respect to known genes, and assessing whether a preferred pattern could be defined. Genomic DNA was prepared from stored lymphocyte samples dating 1991, 1992, 1995, 1998, 2000, and 2003. By inverse PCR and ligation-mediated PCR, we have identified ~860 bona fide insertion sites. Search for homology within the human genome using BLAT returned ~330 unique hits that involved a variety of genes, including transcription factors and oncogenes (e.g. RUNX1, STAT5, FYN). To evaluate the distribution pattern of these integration sites, 2000 randomly generated data sets of genomic coordinates were assembled and their distribution relative to annotations of the human genome was analyzed. A preliminary comparison of the random distribution to our experimental samples showed that retroviral integrations in cells obtained from the patient were significantly skewed toward regions within 2 kb of genes (p<0.002) and CpG islands (p<0.001).These results suggest that, similar to what observed in murine fibroblast and human cancer cell lines, transcriptionally active regions of the genome may be preferred targets of retroviral vectors in human primary T lymphocytes. At the same time, our observations show that the resulting integration events are compatible with long-term, event-free in vivo survival of gene-modified cells in clinical settings.