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RNA editing modulates pathways critical to B cell lymphomagenesis

ABSTRACT: Diffuse large B cell lymphoma (DLBCL) is one of the most common and aggressive types of B cell lymphoma. Subtype heterogeneity cannot be completely explained by genomic alterations and/or gene expression differences, suggesting that additional mechanisms are involved. Here, we explore the contribution of an epitranscriptomic modification to B cell lymphomagenesis. Our data demonstrate that ADAR1-mediated RNA editing (deamination of adenosine to inosine) targets novel candidate driver genes within well-known disease-associated pathways in DLBCL. Within these pathways, DNA mutations and RNA editing events are often mutually exclusive at the gene level, suggesting that tumours can modulate pathway outcomes by altering sequence at either the genomic or the transcriptomic level. In contrast to what has been found in solid tumours, in DLBCL low ADAR1 expression correlates with low interferon-stimulated gene (ISG) scores and with a microenvironment that is not inflamed. To investigate the molecular mechanism behind the inability of DLBCL to mount an ISG response upon loss of ADAR1, we focused on one candidate MAVS, a central regulator of ISG (as well as NFkB) signaling. MAVS is never mutated but robustly edited by ADAR1 at its 3’UTR, and editing correlates with increased MAVS protein levels and increased downstream activation of the ISG as well as NFkB pathways. Using targeted base editing tools to specifically restore MAVS editing in ADAR1-deficient cells, we demonstrate that MAVS editing is directly causal to an increase in expression of genes downstream this signaling pathway. Our data imply that DLBCL tumours edit MAVS to strengthen NFkB signaling, to which they are dependent on survival; thus, targeted loss of MAVS editing might sensitize tumours to cell death. Overall, ADAR1-mediated RNA editing represents a new tumour evasion mechanism underlying DLBCL lymphomagenesis, with features distinct from those derived from solid tumours to date.

ORGANISM(S): Homo sapiens

PROVIDER: GSE145011 | GEO | 2022/09/01

REPOSITORIES: GEO

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Project description:Diffuse large B-cell lymphoma (DLBCL), the most common form of lymphoma in adulthood, comprises multiple biologically and clinically distinct subtypes including germinal center B cell-like (GCB) and activated B cell like (ABC) DLBCL. Gene expression profile studies have shown that its most aggressive subtype, ABC-DLBCL, is associated with constitutive activation of the NF-kB transcription complex. However, except for a small fraction of cases, it remains unclear whether NF-kB activation in these tumors represents an intrinsic program of the tumor cell of origin or a pathogenetic event. Here we show that >50% of ABC-DLBCL and a smaller fraction of GCB-DLBCL carry somatic mutations at multiple genes, including negative (TNFAIP3/A20) and positive (CARD11, TRAF2, TRAF5, MAP3K7/TAK1 and TNFRSF11A/RANK) regulators of NF-kB. Of these, the A20 gene, which encodes for a ubiquitin-modifying enzyme involved in termination of NF-kB responses, is the most commonly affected one, with ~30% of the patients displaying biallelic inactivation by mutations and/or deletions, suggesting a tumor suppressor role. Less frequently, missense mutations of TRAF2 and CARD11 produce molecules with significantly enhanced ability to activate NF-kB. Thus, our results demonstrate that NF-kB activation in DLBCL is caused by genetic lesions affecting multiple genes, whose loss or activation may promote lymphomagenesis by leading to abnormally prolonged NF-kB responses. We show that most ABC-DLBCL and a smaller fraction of GCB-DLBCL display genetic lesions affecting multiple NFkB pathway genes, with A20 representing the most frequently mutated gene Experiment Overall Design: DLBCL biopsies from 73 patients were collected from the archives of the Departments of Pathology at Columbia University and Weill Cornell Medical College. Total RNA was extracted from frozen tumor biopsies and processed according to Affymetrix standard protocols. Purified tonsillar geminal center cells (centroblasts and centrocytes, 5 samples each from different individuals) were purified by magnetic cell separation as described in Klein et al, PNAS 2003.

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RNA editing modulates pathways critical to B cell lymphomagenesis

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