Active nuclear import and cytoplasmic retention of activation-induced deaminase

The enzyme activation-induced deaminase (AID) triggers antibody diversification in B cells by catalyzing deamination and consequently mutation of immunoglobulin genes. To minimize off-target deamination, AID is restrained by several regulatory mechanisms including nuclear exclusion, thought to be mediated exclusively by active nuclear export. Here we identify two other mechanisms involved in controlling AID subcellular localization. AID is unable to passively diffuse into the nucleus, despite its small size, and its nuclear entry requires active import mediated by a conformational nuclear localization signal. We also identify in its C terminus a determinant for AID cytoplasmic retention, which hampers diffusion to the nucleus, competes with nuclear import and is crucial for maintaining the predominantly cytoplasmic localization of AID in steady-state conditions. Blocking nuclear import alters the balance between these processes in favor of cytoplasmic retention, resulting in reduced isotype class switching.This work was supported by the Canadian Institutes of Health Research (MOP 84543) and a Canada Research Chair (to J.M.D.). A.O. was supported by a fellowship from the Canadian Institutes of Health Research Cancer Training Program at the IRCM. V.A.C. was supported in part by a Michel Saucier fellowship from the Louis-Pasteur Canadian Fund through the University of Montreal

NGS-Based High-Throughput Screen to Identify MicroRNAs Regulating Growth of B-Cell Lymphoma

MicroRNAs (miRNAs) play important roles in development, differentiation, and homeostasis by regulating protein translation. In B-cell lymphoma, many miRNAs have altered expression levels, and for a limited subset of them, experimental data supports their functional relevance in lymphoma pathogenesis. This chapter describes an unbiased next-generation sequencing (NGS)-based high-throughput screening approach to identify miRNAs that are involved in the control of cell growth. First, we provide a protocol for performing high-throughput screening for miRNA inhibition and overexpression. Second, we describe the procedure for next-generation sequencing library preparation. Third, we provide a workflow for data analysis

The RNA-binding protein HuR is essential for the B cell antibody response.

Post-transcriptional regulation of mRNA by the RNA-binding protein HuR (encoded by Elavl1) is required in B cells for the germinal center reaction and for the production of class-switched antibodies in response to thymus-independent antigens. Transcriptome-wide examination of RNA isoforms and their abundance and translation in HuR-deficient B cells, together with direct measurements of HuR-RNA interactions, revealed that HuR-dependent splicing of mRNA affected hundreds of transcripts, including that encoding dihydrolipoamide S-succinyltransferase (Dlst), a subunit of the 2-oxoglutarate dehydrogenase (α-KGDH) complex. In the absence of HuR, defective mitochondrial metabolism resulted in large amounts of reactive oxygen species and B cell death. Our study shows how post-transcriptional processes control the balance of energy metabolism required for the proliferation and differentiation of B cells

Dynamics of genome architecture and chromatin function during human B cell differentiation and neoplastic transformation

To investigate the three-dimensional (3D) genome architecture across normal B cell differentiation and in neoplastic cells from different subtypes of chronic lymphocytic leukemia and mantle cell lymphoma patients, here we integrate in situ Hi-C and nine additional omics layers. Beyond conventional active (A) and inactive (B) compartments, we uncover a highly-dynamic intermediate compartment enriched in poised and polycomb-repressed chromatin. During B cell development, 28% of the compartments change, mostly involving a widespread chromatin activation from naive to germinal center B cells and a reversal to the naive state upon further maturation into memory B cells. B cell neoplasms are characterized by both entity and subtype-specific alterations in 3D genome organization, including large chromatin blocks spanning key disease-specific genes. This study indicates that 3D genome interactions are extensively modulated during normal B cell differentiation and that the genome of B cell neoplasias acquires a tumor-specific 3D genome architecture.This research was funded by the European Union’s Seventh Framework Programme through the Blueprint Consortium (grant agreement 282510), the World Wide Cancer Research Foundation Grant No. 16-1285 (to J.I.M.-S.), the ERC (grant agreement 609989 to M.A.M.-R.), European Union’s Horizon 2020 research and innovation programme (grant agreement 676556 to M.A.M.-R.). We also knowledge the support of Spanish Ministerio de Ciencia, Innovación y Universidades through SAF2012-31138 and SAF2017-86126-R to J.I.M.-S., SAF2015-64885-R to E.C., BFU2017-85926-P to M.A.M.-R. and PMP15/00007 to E.C. which is part of Plan Nacional de I + D + I and co-financed by the ISCIII-Sub-Directorate General for Evaluation and the European Regional Development Fund (FEDER-“Una manera de Hacer Europa”) (to E.C.), the International Cancer Genome Consortium (Chronic Lymphocytic Leukemia Genome consortium to E.C.), La Caixa Foundation (CLLEvolution-HE17-00221, to E.C.). Furthermore, the authors would like to thank the support of the Generalitat de Catalunya Suport Grups de Recerca AGAUR 2017-SGR-736 (to J.I.M.-S.), 2017-SGR-1142 (to E.C.) and 2017-SGR-468 (to E.C.), the Accelerator award CRUK/AIRC/AECC joint funder-partnership, the CERCA Programme/Generalitat de Catalunya and CIBERONC (CB16/12/00225, CB16/12/00334, and CB16/12/00489). R.V.-B. (BES-2013-064328) and P.S.-V. (BES-2014-070327) were supported by a predoctoral FPI Fellowship from the Spanish Government. CRG acknowledges support from ‘Centro de Excelencia Severo Ochoa 2013-2017’, SEV-2012-0208 and the CERCA Programme/Generalitat de Catalunya as well as support of the Spanish Ministry of Science and Innovation through the Instituto de Salud Carlos III and the EMBL partnership, the Generalitat de Catalunya through Departament de Salut and Departament d’Empresa i Coneixement, and the Cofinancing with funds from the European Regional Development Fund (ERDF) by the Spanish Ministry of Science and Innovation coresponding to the Programa Opertaivo FEDER Plurirregional de España (POPE) 2014-2020 and by the Secretaria d’Universitats i Recerca, Departament d’Empresa i Coneixement of the Generalitat de Catalunya corresponding to the programa Operatiu FEDER Catalunya 2014-202