MutComFocal: an integrative approach to identifying recurrent and focal genomic alterations in tumor samples

BACKGROUND: Most tumors are the result of accumulated genomic alterations in somatic cells. The emerging spectrum of alterations in tumors is complex and the identification of relevant genes and pathways remains a challenge. Furthermore, key cancer genes are usually found amplified or deleted in chromosomal regions containing many other genes. Point mutations, on the other hand, provide exquisite information about amino acid changes that could be implicated in the oncogenic process. Current large-scale genomic projects provide high throughput genomic data in a large number of well-characterized tumor samples. METHODS: We define a Bayesian approach designed to identify candidate cancer genes by integrating copy number and point mutation information. Our method exploits the concept that small and recurrent alterations in tumors are more informative in the search for cancer genes. Thus, the algorithm (Mutations with Common Focal Alterations, or MutComFocal) seeks focal copy number alterations and recurrent point mutations within high throughput data from large panels of tumor samples. RESULTS: We apply MutComFocal to Diffuse Large B-cell Lymphoma (DLBCL) data from four different high throughput studies, totaling 78 samples assessed for copy number alterations by single nucleotide polymorphism (SNP) array analysis and 65 samples assayed for protein changing point mutations by whole exome/whole transcriptome sequencing. In addition to recapitulating known alterations, MutComFocal identifies ARID1B, ROBO2 and MRS1 as candidate tumor suppressors and KLHL6, IL31 and LRP1 as putative oncogenes in DLBCL. CONCLUSIONS: We present a Bayesian approach for the identification of candidate cancer genes by integrating data collected in large number of cancer patients, across different studies. When trained on a well-studied dataset, MutComFocal is able to identify most of the reported characterized alterations. The application of MutComFocal to large-scale cancer data provides the opportunity to pinpoint the key functional genomic alterations in tumors

SAVI: a statistical algorithm for variant frequency identification

BACKGROUND: Many problems in biomedical research can be posed as a comparison between related samples (healthy vs. disease, subtypes of the same disease, longitudinal data representing the progression of a disease, etc). In the cases in which the distinction has a genetic or epigenetic basis, next-generation sequencing technologies have become a major tool for obtaining the difference between the samples. A commonly occurring application is the identification of somatic mutations occurring in tumor tissue samples driving a single cell to expand clonally. In this case, the progression of the disease can be traced through the trajectory of the frequency of the oncogenic alleles. Thus obtaining precise estimates of the frequency of abnormal alleles at various stages of the disease is paramount to understanding the processes driving it. Although the procedure is conceptually simple, technical difficulties arise due to inhomogeneous samples, existence of competing subclonal populations, and systematic and non-systematic errors introduced by the sequencing technologies. RESULTS: We present a method, Statistical Algorithm for Variant Frequency Identification (SAVI), to estimate the frequency of alleles in a set of samples. The method employs Bayesian analysis and uses an iterative procedure to derive empirical priors. The approach allows for the comparison of allele frequencies across several samples, e.g. normal/tumor pairs and more complex experimental designs comparing multiple samples in tumor progression, as well as analyzing sequencing data from RNA sequencing experiments. CONCLUSIONS: Analyzing sequencing data through estimating allele frequencies using empirical Bayes methods is a powerful complement to the ever-increasing throughput of the sequencing technologies

Deregulated BCL6 expression recapitulates the pathogenesis of human diffuse large B cell lymphomas in mice

Diffuse large B cell lymphomas (DLBCL) derive from germinal center (GC) B cells and display chromosomal alterations deregulating the expression of BCL6, a transcriptional repressor required for GC formation. To investigate the role of BCL6 in DLBCL pathogenesis, we have engineered mice that express BCL6 constitutively in B cells by mimicking a chromosomal translocation found in human DLBCL. These mice display increased GC formation and perturbed post-GC differentiation characterized by a decreased number of post-isotype switch plasma cells. Subsequently, these mice develop a lympho- proliferative syndrome that culminates with the development of lymphomas displaying features typical of human DLBCL. These results define the oncogenic role of BCL6 in the pathogenesis of DLBCL and provide a faithful mouse model of this common disease

BLIMP1 Is a Tumor Suppressor Gene Frequently Disrupted in Activated B Cell-like Diffuse Large B Cell Lymphoma

SummaryDiffuse large B cell lymphoma (DLBCL) is a heterogeneous disease composed of at least two distinct subtypes: germinal center B cell-like (GCB) and activated B cell-like (ABC) DLBCL. These phenotypic subtypes segregate with largely unique genetic lesions, suggesting the involvement of different pathogenetic mechanisms. In this report we show that the BLIMP1/PRDM1 gene is inactivated by multiple mechanisms, including homozygous deletions, truncating or missense mutations, and transcriptional repression by constitutively active BCL6, in ∼53% of ABC-DLBCL. In vivo, conditional deletion of Blimp1 in mouse B cells promotes the development of lymphoproliferative disorders recapitulating critical features of the human ABC-DLBCL. These results demonstrate that BLIMP1 is a bona fide tumor-suppressor gene whose loss contributes to lymphomagenesis by blocking plasma cell differentiation

Combined Genetic Inactivation of b2-Microglobulin and CD58 Reveals Frequent Escape from Immune Recognition in Diffuse Large B Cell Lymphoma

We report that diffuse large B cell lymphoma (DLBCL) commonly fails to express cell-surface molecules necessary for the recognition of tumor cells by immune-effector cells. In 29% of cases, mutations and dele- tions inactivate the b2-Microglobulin gene, thus preventing the cell-surface expression of the HLA class-I (HLA-I) complex that is necessary for recognition by CD8+ cytotoxic T cells. In 21% of cases, analogous lesions involve the CD58 gene, which encodes a molecule involved in T and natural killer cell-mediated responses. In addition to gene inactivation, alternative mechanisms lead to aberrant expression of HLA-I and CD58 in >60% of DLBCL. These two events are significantly associated in this disease, suggesting that they are coselected during lymphomagenesis for their combined role in escape from immune-surveillance

Inactivation of the PRDM1/BLIMP1 gene in diffuse large B cell lymphoma

PR domain containing 1 with zinc finger domain (PRDM1)/B lymphocyte–induced maturation protein 1 (BLIMP1) is a transcriptional repressor expressed in a subset of germinal center (GC) B cells and in all plasma cells, and required for terminal B cell differentiation. The BLIMP1 locus lies on chromosome 6q21-q22.1, a region frequently deleted in B cell lymphomas, suggesting that it may harbor a tumor suppressor gene. We report here that the BLIMP1 gene is inactivated by structural alterations in 24% (8 out of 34) activated B cell–like diffuse large cell lymphoma (ABC-DLBCL), but not in GC B cell–like (n = 0/37) or unclassified (n = 0/21) DLBCL. BLIMP1 alterations included gene truncations, nonsense mutations, frameshift deletions, and splice site mutations that generate aberrant transcripts encoding truncated BLIMP1 proteins. In all cases studied, both BLIMP1 alleles were inactivated by deletions or mutations. Furthermore, most non–GC type DLBCL cases (n = 20/26, 77%) lack BLIMP1 protein expression, despite the presence of BLIMP1 mRNA. These results indicate that a sizable fraction of ABC-DLBCL carry an inactive BLIMP1 gene, and suggest that the same gene is inactivated by epigenetic mechanisms in an additional large number of cases. These findings point to a role for BLIMP1 as a tumor suppressor gene, whose inactivation may contribute to lymphomagenesis by blocking post–GC differentiation of B cells toward plasma cells

Loss of PRDM1/BLIMP-1 function contributes to poor prognosis of activated B-cell-like diffuse large B-cell lymphoma

PRDM1/BLIMP-1, a master regulator of plasma-cell differentiation, is frequently inactivated in activated B-cell-like (ABC) diffuse large B-cell lymphoma (DLBCL) patients. Little is known about its genetic aberrations and relevant clinical implications. A large series of patients with de novo DLBCL was effectively evaluated for PRDM1/BLIMP-1 deletion, mutation, and protein expression. BLIMP-1 expression was frequently associated with the ABC phenotype and plasmablastic morphologic subtype of DLBCL, yet 63% of the ABC-DLBCL patients were negative for BLIMP-1 protein expression. In these patients, loss of BLIMP-1 was associated with Myc overexpression and decreased expression of p53 pathway molecules. In addition, homozygous PRDM1 deletions and PRDM1 mutations within exons 1 and 2, which encode for domains crucial for transcriptional repression, were found to show a poor prognostic impact in patients with ABC-DLBCL but not in those with germinal center B-cell-like DLBCL (GCB-DLBCL). Gene expression profiling revealed that loss of PRDM1/BLIMP-1 expression correlated with a decreased plasma-cell differentiation signature and upregulation of genes involved in B-cell receptor signaling and tumor-cell proliferation. In conclusion, these results provide novel clinical and biological insight into the tumor-suppressive role of PRDM1/BLIMP-1 in ABC-DLBCL patients and suggest that loss of PRDM1/BLIMP-1 function contributes to the overall poor prognosis of ABC-DLBCL patients

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at \sqrt{s}=7\TeV

A measurement of the production cross-section for top quark pairs(\ttbar) in $pp$ collisions at \sqrt{s}=7 \TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-\ttbar Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM \ttbar production. The inclusive top quark pair production cross-section is measured to be \sigmattbar=145 \pm 31 ^{+42}_{-27} pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.Comment: 30 pages plus author list (50 pages total), 9 figures, 11 tables, CERN-PH number and final journal adde

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson