TNFAIP3 (A20) is a tumor suppressor gene in Hodgkin lymphoma and primary mediastinal B cell lymphoma

Breaking the chains: structure and function of the deubiquitinases

Ubiquitylation is a reversible protein modification that is implicated in many cellular functions. Recently, much progress has been made in the characterization of a superfamily of isopeptidases that remove ubiquitin: the deubiquitinases (DUBs; also known as deubiquitylating or deubiquitinating enzymes). Far from being uniform in structure and function, these enzymes display a myriad of distinct mechanistic features. The small number (<100) of DUBs might at first suggest a low degree of selectivity; however, DUBs are subject to multiple layers of regulation that modulate both their activity and their specificity. Due to their wide-ranging involvement in key regulatory processes, these enzymes might provide new therapeutic targets.

Mutations in the genes coding for the NF-κB regulating factors IκBα and A20 are uncommon in nodular lymphocyte-predominant Hodgkin's lymphoma

Nodular lymphocyte-predominant Hodgkin's lymphoma (NLPHL) shows constitutive NF-kappaB activity in the malignant lymphocyte-predominant (LP) cells. Constitutive NF-kappaB activity also plays a central pathogenetic role in classical Hodgkin's lymphoma (cHL), where inactivating mutations in the NFKBIA and TNFAIP3 genes, coding for the negative NF-kappaB regulators IkappaBalpha and A20, respectively, contribute to NF-kappaB activation. To determine whether mutations in NFKBIA and TNFAIP3 are also involved in the pathogenesis of NLPHL these genes were sequenced from microdissected LP cells of 10 primary NLPHL. We also studied DEV, the only cell line proposedly derived from LP cells, after we had confirmed its derivation from NLPHL by gene expression analysis. A heterozygous somatic missense mutation in the NFKBIA gene was found in one NLPHL, and a heterozygous, possibly subclonal, two base pair insertion in TNFAIP3 in another case. The low mutation frequency and the absence of biallelic destructive mutations propose a minor contribution of NFKBIA and TNFAIP3 mutations to the NF-kappaB activity of NLPHL, suggesting different mechanisms of NF-kappaB activation in NLPHL and cHL.

The ubiquitin-editing enzyme A20 (TNFAIP3) is a central regulator of immunopathology

Nuclear factor (NF)-kappaB has an important role in immunity and inappropriate NF-kappaB activity has been linked with many autoimmune and inflammatory diseases. Multiple mechanisms normally ensure the proper termination of NF-kappaB activation. In this context, the intracellular ubiquitin-editing protein A20 (also known as Tumor Necrosis Factor Alpha-Induced Protein 3 or TNFAIP3) is a key player in the negative feedback regulation of NF-kappaB signaling in response to multiple stimuli. Moreover, A20 also regulates tumor necrosis factor (TNF)-induced apoptosis. Recent genetic studies demonstrate a clear association between several mutations in the human A20 locus and immunopathologies such as Crohn's disease, rheumatoid arthritis, systemic lupus erythematosus, psoriasis and type 1 diabetes. These findings further illustrate the importance of A20 in the resolution of inflammation and the prevention of human disease.

A20 takes on tumors: tumor suppression by an ubiquitin-editing enzyme

Many B cell cancers are characterized in part by the dysregulation of the NF-kappaB signaling pathway. A new study identifies somatic mutations in TNFAIP3, the gene encoding the NF-kappaB inhibitor A20, in Hodgkin lymphomas and primary mediastinal lymphomas. These data reveal the role of A20 as a tumor suppressor protein.

Molecular biology of Hodgkin lymphoma

Hodgkin lymphoma (HL) is derived from mature B cells and subdivided into classical HL and nodular lymphocyte predominant HL (NLPHL). HL is unique among human B cell lymphomas because of the rarity of the lymphoma cells, the Hodgkin and Reed-Sternberg (HRS) cells in classical HL and the lymphocyte-predominant (LP) cells in NLPHL, which usually account for 0.1% to 10% of the cells in the affected tissues. Moreover, HRS cells are unique in the extent to which they have lost their B cell-typical gene expression pattern. Deregulation of transcription factor networks plays a key role in this reprogramming process. HRS cells show strong constitutive activity of the transcription factor NF-kappaB. Multiple mechanisms likely contribute to this deregulated activation, including signaling through particular receptors and genetic lesions. Inactivating mutations in the TNFAIP3 tumor suppressor gene, encoding a negative regulator of NF-kappaB activity, were recently identified in about 40% of patients with classical HL. HRS cells are latently infected by Epstein-Barr virus in about 40% of patients, and an important role of this virus in HL pathogenesis-in particular for cases in which HRS cells had lost the capacity to express a B-cell receptor due to destructive somatic mutation-was recently substantiated.

Novel treatment strategies for patients with relapsed classical Hodgkin lymphoma

Although classical Hodgkin lymphoma (HL) is considered one of the most curable human cancers, the treatment of patients with relapsed and refractory disease, especially those who relapse after autologous stem cell transplantation, remains challenging. Furthermore, because the median age of the patients is in the mid-30s, the impact of early mortality on the number of years lost from productive life is remarkable. Patients with HL whose disease relapses after stem cell transplantation are rarely cured with current treatment modalities. New drugs and novel treatment strategies that are based on our understanding of the disease biology and signaling pathways are needed to improve treatment outcome for these patients. This review will focus on emerging new treatment modalities that are currently under investigation for patients with relapsed classical HL.