Mutations of multiple genes cause deregulation of NF-kappa B in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL), the most common form of lymphoma in adulthood, comprises multiple biologically and clinically distinct subtypes including germinal centre B-cell-like (GCB) and activated B-cell-like (ABC) DLBCL(1). Gene expression profile studies have shown that its most aggressive subtype, ABC-DLBCL, is associated with constitutive activation of the NF-kappa B transcription complex(2). However, except for a small fraction of cases(3), it remains unclear whether NF-kappa B activation in these tumours represents an intrinsic program of the tumour 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 in multiple genes, including negative (TNFAIP3, also called A20) and positive (CARD11, TRAF2, TRAF5, MAP3K7 (TAK1) and TNFRSF11A ( RANK)) regulators of NF-kappa B. Of these, the A20 gene, which encodes a ubiquitin-modifying enzyme involved in termination of NF-kappa B responses, is most commonly affected, with similar to 30% of patients displaying biallelic inactivation by mutations and/or deletions. When reintroduced in cell lines carrying biallelic inactivation of the gene, A20 induced apoptosis and cell growth arrest, indicating a tumour suppressor role. Less frequently, missense mutations of TRAF2 and CARD11 produce molecules with significantly enhanced ability to activate NF-kappa B. Thus, our results demonstrate that NF-kappa B activation in DLBCL is caused by genetic lesions affecting multiple genes, the loss or activation of which may promote lymphomagenesis by leading to abnormally prolonged NF-kappa B responses.