Constitutive NF-kappaB activation by the t(11;18)(q21;q21) product in MALT lymphoma is linked to deregulated ubiquitin ligase activity

A Novel Age-Based Nomogram as the Best Predictor for Long-Term Overall Survival in Head and Neck Mucosa-Associated Lymphoid Tissue Lymphoma

OBJECTIVES

Head and neck mucosa-associated lymphoid tissue (MALT) lymphoma, a rare subtype of non-Hodgkin lymphoma, has received limited attention regarding its prognosis. This study aimed to illuminate the clinical characteristics and identify prognostic factors for head and neck MALT lymphoma, intending to develop an accessible tool for clinicians to predict long-term survival probabilities and inform therapeutic strategies.

METHODS

This multicentre retrospective study enrolled 424 head and neck MALT lymphoma patients from the Surveillance, Epidemiology, and End Results Program (SEER) database. Least absolute shrinkage and selection operator (LASSO)-Cox regression analysis identified independent prognostic factors for overall survival (OS), leading to the development of an age-based nomogram predicting OS probabilities at 5, 10, and 15 years. Evaluation included time-dependent receiver operating curve (ROC), calibration curves, and decision curve analysis.

RESULTS

Multivariate Cox analysis highlighted age exceeding 65 years [hazards ratio (HR): 2.97, 95% confidence interval (CI): 1.94-4.57; P < 0.001] and unmarried status (HR: 1.58, 95% CI: 1.07-2.33, P = 0.023) as significantly associated with shorter OS, while black race correlated with longer OS (HR: 0.25, 95% CI: 0.09-0.69, P = 0.007). The age-based nomogram, integrating these factors, demonstrated efficacy in predicting 5-year [area under the curve (AUC): 0.640] and 10-year OS (AUC: 0.705), with an impressive AUC of 0.842 for the 15-year OS probability in the training cohort. Decision curve analysis affirmed the nomogram's clinical utility, surpassing individual factors. Consistent results were observed in validation cohorts.

CONCLUSION

Our study provides crucial insights into head and neck MALT lymphoma, filling gaps in understanding its clinical landscape. The validated age-based nomogram serves as a practical tool for clinicians, offering enhanced prognostic precision and guiding personalized treatment strategies in this understudied lymphoma subtype.

RNA-Seq Profiling in Chicken Spleen and Thymus Infected with Newcastle Disease Virus of Varying Virulence

Newcastle disease virus (NDV), known as avian paramyxovirus-1, poses a significant threat to poultry production worldwide. Vaccination currently stands as the most effective strategy for Newcastle disease control. However, the mesogenic vaccine strain Mukteswar has been observed to evolve into a velogenic variant JS/7/05/Ch during poultry immunization. Here, we aimed to explore the mechanisms underlying virulence enhancement of the two viruses. Pathogenically, JS/7/05/Ch mediated stronger virulence and pathogenicity in vivo compared to Mukteswar. Comparative transcriptome analysis revealed 834 differentially expressed genes (DEGs), comprising 339 up-regulated and 495 down-regulated genes, in the spleen, and 716 DEGs, with 313 up-regulated and 403 down-regulated genes, in the thymus. Gene Ontology (GO) analysis indicated that these candidate targets primarily participated in cell and biological development, extracellular part and membrane composition, as well as receptor and binding activity. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis unveiled a substantial portion of candidate genes predominantly involved in cellular processes, environmental information processing, metabolism, and organismal systems. Additionally, five DEGs (TRAT1, JUP, LPAR4, CYB561A3, and CXCR5) were randomly identified through RNA-seq analysis and subsequently confirmed via quantitative real-time polymerase chain reaction (qRT-PCR). The findings revealed a marked up-regulation in the expression levels of these DEGs induced by JS/7/05/Ch compared to Mukteswar, with CYB561A3 and CXCR5 exhibiting significant increases. The findings corroborated the sequencing accuracy, offering promising research directions. Taken together, we comprehensively evaluated transcriptomic alterations in chicken immune organs infected by NDV strains of diverse virulence. This study establishes a basis and direction for NDV virulence research.

Study of individual domains contributing to MALT1 dimerization in BCL10-independent and dependent assembly

The CARMA-BCL10-MALT1 (CBM) signalosome functions as a pivotal supramolecular module, integrating diverse receptor-induced signaling pathways to regulate BCL10-dependent NF-kB activation in innate and adaptive immunity. Conversely, the API2-MALT1 fusion protein in t(11; 18)(q21; q21) MALT lymphoma constitutively induces BCL10-independent NF-kB activation. MALT1 dimer formation is indispensable for the requisite proteolytic activity and is critical for NF-kB activation regulation in both scenarios. However, the molecular assembly of MALT1 individual domains in CBM activation remains elusive. Here we report the crystal structure of the MALT1 death domain (DD) at a resolution of 2.1 Å, incorporating reconstructed residues in previously disordered loops 1 and 2. Additionally, we observe a conformational regulation element (CRE) regulating stem-helix formation in NLRPs pyrin (PYD) within the MALT1 DD structure. The structure reveals a stem-helix-mediated dimer further corroborated in solution. To elucidate how the BCL10 filament facilitates MALT1 dimerization, we reconstitute a BCL10-CARD-MALT1-DD-IG1-IG2 complex model. We propose a N+7 rule for BCL10-dependent MALT1 dimerization via the IG1-IG2 domain and for MALT1-dependent cleavage in trans. Biochemical data further indicates concentration-dependent dimerization of the MALT1 IG1-IG2 domain, facilitating MALT1 dimerization in BCL10-independent manner. Our findings provide a structural and biochemical foundation for understanding MALT1 dimeric mechanisms, shedding light on potential BCL10-independent MALT1 dimer formation and high-order BCL10-MALT1 assembly.

Post-translational modification of MALT1 and its role in B cell- and T cell-related diseases

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a multifunctional protein. MALT1 functions as an adaptor protein to assemble and recruit proteins such as B-cell lymphoma 10 (BCL10) and caspase-recruitment domain (CARD)-containing coiled-coil protein 11 (CARD11). Conversely it also acts as a paracaspase to cleave specified substrates. Because of its involvement in immunity, inflammation and cancer through its dual functions of scaffolding and catalytic activity, MALT1 is becoming a promising therapeutic target in B cell- and T cell-related diseases. There is growing evidence that the function of MALT1 is subtly modulated via post-translational modifications. This review summarized recent progress in relevant studies regarding the physiological and pathophysiological functions of MALT1, post-translational modifications of MALT1 and its role in B cell- and T cell- related diseases. In addition, the current available MALT1 inhibitors were also discussed.

K63 ubiquitination in immune signaling

Ubc13-catalyzed K63 ubiquitination is a major control point for immune signaling. Recent evidence has shown that the control of multiple immune functions, including chronic inflammation, pathogen responses, lymphocyte activation, and regulatory signaling, is altered by K63 ubiquitination. In this review, we detail the novel cellular sensors that are dependent on K63 ubiquitination for their function in the immune signaling network. Many pathogens, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can target K63 ubiquitination to inhibit pathogen immune responses; we describe novel details of the pathways involved and summarize recent clinically relevant SARS-CoV-2-specific responses. We also discuss recent evidence that regulatory T cell (Treg) versus T helper (T_H) 1 and T_H17 cell subset regulation might involve K63 ubiquitination. Knowledge gaps that merit future investigation and clinically relevant pathways are also addressed.

Recent Advances in the Genetic of MALT Lymphomas

Simple Summary

Mucosa-associated lymphoid tissue (MALT) lymphoma is the most common subtype of marginal zone lymphomas. These B-cell neoplasms may arise from many organs and usually have an indolent behavior. Recurrent chromosomal translocations and cytogenetic alterations are well characterized, some of them being associated to specific sites. Through next-generation sequencing technologies, the mutational landscape of MALT lymphomas has been explored and available data to date show that there are considerable variations in the incidence and spectrum of mutations among MALT lymphoma of different sites. Interestingly, most of these mutations affect several common pathways and some of them are potentially targetable. Gene expression profile and epigenetic studies have also added new information, potentially useful for diagnosis and treatment. This article provides a comprehensive review of the genetic landscape in MALT lymphomas.

Abstract

Mucosa-associated lymphoid tissue (MALT) lymphomas are a diverse group of lymphoid neoplasms with B-cell origin, occurring in adult patients and usually having an indolent clinical behavior. These lymphomas may arise in different anatomic locations, sharing many clinicopathological characteristics, but also having substantial variances in the aetiology and genetic alterations. Chromosomal translocations are recurrent in MALT lymphomas with different prevalence among different sites, being the 4 most common: t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), and t(3;14)(p14.1;q32). Several chromosomal numerical abnormalities have also been described, but probably represent secondary genetic events. The mutational landscape of MALT lymphomas is wide, and the most frequent mutations are: TNFAIP3, CREBBP, KMT2C, TET2, SPEN, KMT2D, LRP1B, PRDM1, EP300, TNFRSF14, NOTCH1/NOTCH2, and B2M, but many other genes may be involved. Similar to chromosomal translocations, certain mutations are enriched in specific lymphoma types. In the same line, variation in immunoglobulin gene usage is recognized among MALT lymphoma of different anatomic locations. In the last decade, several studies have analyzed the role of microRNA, transcriptomics and epigenetic alterations, further improving our knowledge about the pathogenic mechanisms in MALT lymphoma development. All these advances open the possibility of targeted directed treatment and push forward the concept of precision medicine in MALT lymphomas.

MALT1 as a promising target to treat lymphoma and other diseases related to MALT1 anomalies

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a key adaptor protein that regulates the NF-κB pathway, in which MALT1 functions as a scaffold protein and protease to trigger downstream signals. The abnormal expression of MALT1 is closely associated with lymphomagenesis and other diseases, including solid tumors and autoimmune diseases. MALT1 is the only protease in the underlying pathogenesis of these diseases, and its proteolytic activity can be pharmacologically regulated. Therefore, MALT1 is a potential and promising target for anti-lymphoma and other MALT1-related disease treatments. Currently, the development of MALT1 inhibitors is still in its early stages. This review presents an overview of MALT1, particularly its X-ray structures and biological functions, and elaborates on the pathogenesis of diseases associated with its dysregulation. We then summarize previously reported MALT1 inhibitors, focusing on their molecular structure, biological activity, structure-activity relationship, and limitations. Finally, we propose future research directions to accelerate the discovery of novel MALT1 inhibitors with clinical applications. Overall, this review provides a comprehensive and systematic overview of MALT1-related research advances and serves as a theoretical basis for drug discovery and research.

Allosteric activation of MALT1 by its ubiquitin-binding Ig3 domain

The catalytic activity of the protease MALT1 is required for adaptive immune responses and regulatory T (Treg)-cell development, while dysregulated MALT1 activity can lead to lymphoma. MALT1 activation requires its monoubiquitination on lysine 644 (K644) within the Ig3 domain, localized adjacent to the protease domain. The molecular requirements for MALT1 monoubiquitination and the mechanism by which monoubiquitination activates MALT1 had remained elusive. Here, we show that the Ig3 domain interacts directly with ubiquitin and that an intact Ig3-ubiquitin interaction surface is required for the conjugation of ubiquitin to K644. Moreover, by generating constitutively active MALT1 mutants that overcome the need for monoubiquitination, we reveal an allosteric communication between the ubiquitination site K644, the Ig3-protease interaction surface, and the active site of the protease domain. Finally, we show that MALT1 mutants that alter the Ig3-ubiquitin interface impact the biological response of T cells. Thus, ubiquitin binding by the Ig3 domain promotes MALT1 activation by an allosteric mechanism that is essential for its biological function.

MALT Lymphoma as a Model of Chronic Inflammation-Induced Gastric Tumor Development

Mucosa-associated lymphoid tissue (MALT) lymphoma, or extranodal marginal zone lymphoma of MALT, is an indolent B-cell non-Hodgkin lymphoma linked with preexisting chronic inflammation. The stomach is the most commonly affected organ and the MALT lymphoma pathogenesis is clearly associated with Helicobacter pylori gastroduodenitis. Inflammation induces the lymphoid infiltrates in extranodal sites, where the lymphoma then subsequently develops. Genetic aberrations arise through the release of reactive oxygen species (ROS), H. pylori-induced endonucleases, and other effects. The involvement of nuclear factor kappa B (NF-κB) pathway activation, a critical regulator of pro-inflammatory responses, further highlights the role of inflammation in gastric MALT lymphoma. The NF-κB pathway regulates key elements of normal lymphocyte function, including the transcription of proliferation-promoting and anti-apoptotic genes. Aberrant constitutive activation of NF-κB signaling can lead to autoimmunity and malignancy. NF-κB pathway activation can happen through both the canonical and non-canonical pathways and can be caused by multiple genetic aberrations such as t(11;18)(q12;q21), t(1;14)(p22;q32), and t(14;18)(q32;q21) translocations, chronic inflammation and even directly by H. pylori-associated mechanisms. Gastric MALT lymphoma is considered one of the best models of how inflammation initiates genetic events that lead to oncogenesis, determines tumor biology, dictates clinical behavior and leads to viable therapeutic targets. The purpose of this review is to present gastric MALT lymphoma as an outstanding example of the close pathogenetic link between chronic inflammation and tumor development and to describe how this information can be integrated into daily clinical practice.

Holding All the CARDs: How MALT1 Controls CARMA/CARD-Dependent Signaling

The scaffold proteins CARMA1-3 (encoded by the genes CARD11, -14 and -10) and CARD9 play major roles in signaling downstream of receptors with immunoreceptor tyrosine activation motifs (ITAMs), G-protein coupled receptors (GPCR) and receptor tyrosine kinases (RTK). These receptors trigger the formation of oligomeric CARMA/CARD-BCL10-MALT1 (CBM) complexes via kinases of the PKC family. The CBM in turn regulates gene expression by the activation of NF-κB and AP-1 transcription factors and controls transcript stability. The paracaspase MALT1 is the only CBM component having an enzymatic (proteolytic) activity and has therefore recently gained attention as a potential drug target. Here we review recent advances in the understanding of the molecular function of the protease MALT1 and summarize how MALT1 scaffold and protease function contribute to the transmission of CBM signals. Finally, we will highlight how dysregulation of MALT1 function can cause pathologies such as immunodeficiency, autoimmunity, psoriasis, and cancer.

Regulation of innate and adaptive antitumor immunity by IAP antagonists

Inhibition of the T-cell co-inhibitory checkpoint receptors or their ligands CTLA-4, PD-1 and PD-L1 using monoclonal antibodies has proven to be highly effective against many cancers. Yet many cancers remain resistant to checkpoint blockade, and durable remissions occur in only a minority of patients. Novel approaches to enhancing antitumor responses are thus necessary in order to expand the reach of these treatments. The inhibitor of apoptosis (IAP) protein family comprises a diverse group of proteins, many of which have immunoregulatory roles. Small molecule IAP antagonists have been developed and are undergoing early phase clinical testing. These drugs were initially developed to promote tumor cell apoptosis; however, a considerable body of work now indicates that IAP antagonists induce antitumor activity through modulation of innate and adaptive immunity. Primarily through inhibition of cellular (c)-IAP1 and c-IAP2, IAP antagonists can activate alternative NF-κB signaling, promoting B-cell survival, activation of dendritic cells and delivering a broad co-stimulatory signal to T cells. At the same time, IAP antagonists can promote tumor cell intrinsic sensitization to innate immune signals, and enhance tumor cell killing by inflammatory cytokines and phagocytic macrophages. These drugs thus represent an attractive investigational approach to immunotherapy, providing a positive signaling counterpart to the relief of signal inhibition conferred by checkpoint blockade.

MALT1 promotes melanoma progression through JNK/c-Jun signaling

Mucosa-associated lymphoma antigen 1 (MALT1) is a lymphoma oncogene that regulates signal transduction as a paracaspase and an adaptor protein. Yet, the role of MALT1 in other solid cancers such as melanoma is not well-understood. Here, we demonstrate that MALT1 is overexpressed in malignant melanoma cells, and predicts a poor disease-free survival. MALT1 inhibition via shRNA-mediated gene silencing or pharmacologically with MI-2 compound markedly reduced cell growth and migration of A2058 and A375 melanoma cell lines in vitro. Subcutaneous tumor growth analysis revealed that MALT1 gene silencing significantly reduced tumor growth and metastasis to the lung. Consistently, the subcutaneous tumors with MALT1 loss had increased cell apoptosis and decreased proliferation. In addition, these tumors showed signs of mesenchymal–epithelial transition as indicated by the upregulation of E-cadherin and downregulation of N-cadherin and β1-intergrin. Further molecular analysis revealed that MALT1 is required for c-Jun and nuclear factor-κB (NF-κB) activation by tumor necrosis factor-α. Forced expression of the c-Jun upstream activator MKK7 reversed the cell growth and migration defects caused by MALT1 loss. In contrast, NF-κB activation via expression of p65ER, a fusion protein containing NF-κB p65 and the tamoxifen-responsive mutant estrogen receptor, induced minimal effects on cell proliferation, but diminished cell death induced by MALT1 loss and TRAIL treatment. Together, these findings demonstrate that MALT1 promotes melanoma cell proliferation and motility through JNK/c-Jun, and enhances melanoma cell survival through NF-κB, underscoring MALT1 as a potential therapeutic target and biomarker for malignant melanoma.

The B-cell-activating factor signalling pathway is associated with Helicobacter pylori independence in gastric mucosa-associated lymphoid tissue lymphoma without t(11;18)(q21;q21)

We previously reported that activation of the B-cell-activating factor (BAFF) pathway upregulates nuclear factor-κB (NF-κB) and induces BCL3 and BCL10 nuclear translocation in Helicobacter pylori (HP)-independent gastric diffuse large B-cell lymphoma (DLBCL) tumours with evidence of mucosa-associated lymphoid tissue (MALT). However, the significance of BAFF expression in HP independence of gastric low-grade MALT lymphomas without t(11;18)(q21;q21) remains unexplored. Sixty-four patients who underwent successful HP eradication for localized HP-positive gastric MALT lymphomas without t(11;18)(q21;q21) were studied. BAFF expression was significantly higher in the HP-independent group than in the HP-dependent group [22/26 (84.6%) versus 8/38 (21.1%); p < 0.001]. Similarly, BAFF receptor (BAFF-R) expression (p = 0.004) and nuclear BCL3 (p = 0.004), BCL10 (p < 0.001), NF-κB (p65) (p = 0.001) and NF-κB (p52) (p = 0.005) expression were closely correlated with the HP independence of these tumours. Moreover, BAFF overexpression was significantly associated with BAFF-R expression and nuclear BCL3, BCL10, NF-κB (p65) and NF-κB (p52) expression. These findings were further validated in an independent cohort, including 40 HP-dependent cases and 18 HP-independent cases of gastric MALT lymphoma without t(11;18)(q21;q21). The biological significance of BAFF signalling in t(11;18)(q21;q21)-negative lymphoma cells was further studied in two types of lymphoma B cell: OCI-Ly3 [non-germinal centre B-cell origin DLBCL without t(11;18)(q21;q21) cell line] and MA-1 [t(14;18)(q32;q21)/IGH-MALT1-positive DLBCL cell line]. In both cell lines, we found that BAFF activated the canonical NF-κB and AKT pathways, and induced the formation of BCL10-BCL3 complexes, which translocated to the nucleus. BCL10 and BCL3 nuclear translocation and NF-κB (p65) transactivation were inhibited by either LY294002 or by silencing BCL3 or BCL10 with small interfering RNA. BAFF also activated non-canonical NF-κB pathways (p52) through tumour necrosis factor receptor-associated factor 3 degradation, NF-κB-inducing kinase accumulation, inhibitor of κB kinase (IKK) α/β phosphorylation and NF-κB p100 processing in both cell lines. Our data indicate that the autocrine BAFF signal transduction pathway contributes to HP independence in gastric MALT lymphomas without the t(11;18)(q21;q21) translocation. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

MALT lymphoma: A paradigm of NF-κB dysregulation

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) invariably arises from a background of chronic microbial infection and/or autoimmune disorder at diverse mucosal sites. The prolonged chronic infection and/or autoimmunity generate active immune and inflammatory responses that provide a setting for evolution and development of autoreactive B-cells, their expansion and eventual malignant transformation following acquisition of genetic changes. The immune responses also play a critical role in sustaining the growth and survival of the transformed cells as shown by complete regression of a high proportion of MALT lymphoma of the stomach, ocular adnexa and skin following anti-microbial treatment. B-cell receptor engagement by auto-antigen as well as T-cell help including both cognate interaction and bystander help via soluble ligands such as CD40L and BAFF are thought to underpin the immunological drive in the lymphoma development through activation of the canonical and non-canonical NF-κB pathway respectively. Similarly, the three MALT lymphoma associated chromosome translocations, namely t(1;14)(p22;q32)/BCL10-IGH, t(14;18)(q32;q21)/IGH-MALT1,and t(11;18)(q21;q21)/BIRC3 (API2)-MALT1, are also capable of activating both canonical and non-canonical NF-κB pathways. Furthermore, TNFAIP3 (A20) inactivation by deletion and/or mutation abolishes the auto-negative feedback to several signalling including BCR and TLR, which connect to the canonical NF-κB activation pathway. Thus, there is a considerable overlap in the molecular pathways dysregulated by immunological drive and somatic genetic changes, strongly arguing for their oncogenic cooperation in the development of MALT lymphoma.

API2-MALT1 oncoprotein promotes lymphomagenesis via unique program of substrate ubiquitination and proteolysis

Lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) is the most common extranodal B cell tumor and accounts for 8% of non-Hodgkin’s lymphomas. Gastric MALT lymphoma is the best-studied example and is a prototypical neoplasm that occurs in the setting of chronic inflammation brought on by persistent infection or autoimmune disease. Cytogenetic abnormalities are commonly acquired during the course of disease and the most common is chromosomal translocation t(11;18)(q21;q21), which creates the API2-MALT1 fusion oncoprotein. t(11;18)-positive lymphomas can be clinically aggressive and have a higher rate of dissemination than t(11;18)-negative tumors. Many cancers, including MALT lymphomas, characteristically exhibit deregulated over-activation of cellular survival pathways, such as the nuclear factor-κB (NF-κB) pathway. Molecular characterization of API2-MALT1 has revealed it to be a potent activator of NF-κB, which is required for API2-MALT1-induced cellular transformation, however the mechanisms by which API2-MALT1 exerts these effects are only recently becoming apparent. The API2 moiety of the fusion binds tumor necrosis factor (TNF) receptor associated factor (TRAF) 2 and receptor interacting protein 1 (RIP1), two proteins essential for TNF receptor-induced NF-κB activation. By effectively mimicking ligand-bound TNF receptor, API2-MALT1 promotes TRAF2-dependent ubiquitination of RIP1, which then acts as a scaffold for nucleating and activating the canonical NF-κB machinery. Activation occurs, in part, through MALT1 moiety-dependent recruitment of TRAF6, which can directly modify NF-κB essential modulator, the principal downstream regulator of NF-κB. While the intrinsic MALT1 protease catalytic activity is dispensable for this canonical NF-κB signaling, it is critical for non-canonical NF-κB activation. In this regard, API2-MALT1 recognizes NF-κB inducing kinase (NIK), the essential upstream regulator of non-canonical NF-κB, and cleaves it to generate a stable, constitutively active fragment. Thus, API2-MALT1 harnesses multiple unique pathways to achieve deregulated NF-κB activation. Emerging data from our group and others have also detailed additional gain-of-function activities of API2-MALT1 that extend beyond NF-κB activation. Specifically, API2-MALT1 recruits and subverts multiple other signaling factors, including LIM domain and actin-binding protein 1 (LIMA1) and Smac/DIABLO. Like NIK, LIMA1 represents a unique substrate for API2-MALT1 protease activity, but unlike NIK, its cleavage sets in motion a major NF-κB-independent pathway for promoting oncogenesis. In this review, we highlight the most recent results characterizing these unique and diverse gain-of-function activities of API2-MALT1 and how they contribute to lymphomagenesis.

The paracaspase MALT1: biological function and potential for therapeutic inhibition

The paracaspase MALT1 has a central role in the activation of lymphocytes and other immune cells including myeloid cells, mast cells and NK cells. MALT1 activity is required not only for the immune response, but also for the development of natural Treg cells that keep the immune response in check. Exaggerated MALT1 activity has been associated with the development of lymphoid malignancies, and recently developed MALT1 inhibitors show promising anti-tumor effects in xenograft models of diffuse large B cell lymphoma. In this review, we provide an overview of the present understanding of MALT1's function, and discuss possibilities for its therapeutic targeting based on recently developed inhibitors and animal models.

Molecular pathogenesis of lymphomas of mucosa-associated lymphoid tissue--from (auto)antigen driven selection to the activation of NF-κB signaling

Lymphomas of mucosa-associated lymphoid tissue (MALT) are typically present at sites such as the stomach, lung or urinary tract, where lymphoid tissues scatter in mucosa lamina propria, intra- or sub-epithelial cells. The infection of certain pathogens, such as Helicobacter pylori, Chlamydophila psittaci, Borrelia burgdorferi, hepatitis C virus, or certain autoantigens cause these sites to generate a germinal center called the "acquired lymphoid tissue". The molecular pathogenesis of MALT lymphoma is a multi-step process. Receptor signaling, such as the contact stimulation of B cell receptors and CD4 positive T cells mediated by CD40/CD40-ligand and T helper cell type 2 cytokines like interleukin-4, contributes to tumor cell proliferation. A number of genetic alterations have been identified in MALT lymphoma, and among them are important translocations, such as t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21) and t(3;14)(p13;q32). Fusion proteins generated by these translocations share the same NF-κB signaling pathway, which is activated by the caspase activation and recruitment domain containing molecules of the membrane associated guanylate kinase family, B cell lymphoma-10 and MALT1 (CBM) protein complex. They act downstream of cell surface receptors, such as B cell receptors, T cell receptors, B cell activating factors and Toll-like receptors, and participate in the biological process of MALT lymphoma. The discovery of therapeutic drugs that exclusively inhibit the antigen receptor signaling pathway will be beneficial for the treatment of B cell lymphomas in the future.

The origin and targeting of mucosa-associated lymphoid tissue lymphomas

PURPOSE OF REVIEW

Extranodal mucosa-associated lymphoid tissue (MALT lymphoma) is a distinct clinical-pathological entity that can be distinguished from other lymphomas by a number of unique features, including their location in various extranodal sites, being preceded by chronic inflammatory or infection processes; a characteristic histopathological picture; and the presence of exclusive chromosomal translocations which increase MALT1 proteolytic activity to promote constitutive NF-κB signaling and eventually drive lymphomagenesis.

RECENT FINDINGS

This review explores the major molecular and cellular events that participate in MALT lymphoma pathogenesis, focusing on gastric MALT lymphoma as a model of chronic inflammation-induced tumor development. In addition, the pivotal roles of activated MALT1 protease, its substrate TNFAIP3/A20, and the MyD88 adaptor protein in abnormally triggering downstream NF-κB pathway are overviewed. These new insights provide a mechanistic basis for using novel therapies targeting MALT1 protease or IRAK4 kinase activities. Finally, the putative cellular origin of MALT lymphomas is also discussed.

SUMMARY

Over the last decade, unraveling the biological complexity of MALT lymphomas has shed light on the fundamental cellular and molecular aspects of the disease that are to be translated into clinical diagnostics and therapy.

Helicobacter pylori-negative gastric mucosa-associated lymphoid tissue lymphomas: A review

Since Isaacson and Wright first reported on the extra-nodal marginal zone B-cell lymphoma of the stomach in 1983, following studies have clarified many aspects of this disease. We now know that the stomach is the most affected organ by this disease, and approximately 90% of gastric mucosa-associated lymphoid tissue (MALT) lymphomas are related to Helicobacter pylori (H. pylori) infection. This implies that approximately 10% of gastric MALT lymphomas occur independent of H. pylori infection. The pathogenesis of these H. pylori-negative gastric MALT lymphomas remains unclear. To date, there have been several speculations. One possibility is that genetic alterations result in nuclear factor-kappa B (NF-κB) activation. Among these alterations, t(11;18)(q21;q21) is more frequently observed in H. pylori-negative gastric MALT lymphomas, and such translocation results in the synthesis of fusion protein API2-MALT1, which causes canonical and noncanonical NF-κB activation. Another possibility is infection with bacteria other than H. pylori. This could explain why H. pylori eradication therapy can cure some proportions of H. pylori-negative gastric MALT lymphoma patients, although the bacteria responsible for MALT lymphomagenesis are yet to be defined. Recent advances in endoscopy suggest magnifying endoscopy with narrow band imaging as a useful tool for both detecting gastric MALT lymphoma lesions and judging the response to treatment. A certain proportion of H. pylori-negative gastric MALT lymphoma patients respond to eradication therapy; hence, H. pylori eradication therapy could be considered as a first-line treatment for gastric MALT lymphomas regardless of their H. pylori infection status.

MALT1--a universal soldier: multiple strategies to ensure NF-κB activation and target gene expression

The paracaspase MALT1 (mucosa associated lymphoid tissue lymphoma translocation gene 1) is an intracellular signaling protein that plays a key role in innate and adaptive immunity. It is essential for nuclear factor κB (NF-κB) activation and proinflammatory gene expression downstream of several cell surface receptors. MALT1 has been most studied in the context of T-cell receptor-induced NF-κB signaling, supporting T-cell activation and proliferation. In addition, MALT1 hyperactivation is associated with specific subtypes of B-cell lymphoma, where it controls tumor cell proliferation and survival. For a long time, MALT1 was believed to function solely as a scaffold protein, providing a platform for the assembly of other NF-κB signaling proteins. However, this view changed dramatically when MALT1 was found to have proteolytic activity that further fine-tunes signaling. MALT1 proteolytic activity is essential for T-cell activation and lymphomagenesis, suggesting that MALT1 is a promising therapeutic target for the treatment of autoimmune diseases and distinct lymphoma entities. However, interference with MALT1 activity may pose a dangerous threat to the normal functioning of the immune system and should be evaluated with great care. Here we discuss the current knowledge on the scaffold and protease functions of MALT1, including an overview of its substrates and the functional implications of their cleavage.

Conversion of the LIMA1 tumour suppressor into an oncogenic LMO-like protein by API2-MALT1 in MALT lymphoma

MALT1 is the only known paracaspase and is a critical mediator of B- and T-cell receptor signalling. The function of the MALT1 gene is subverted by oncogenic chimeric fusions arising from the recurrent t(11;18)(q21;q21) aberration, which is the most frequent translocation in mucosa-associated lymphoid tissue (MALT) lymphoma. API2-MALT1-positive MALT lymphomas manifest antibiotic resistance and aggressive clinical behaviour with poor clinical outcome. However, the mechanisms underlying API2-MALT1-induced MALT lymphomagenesis are not fully understood. Here we show that API2-MALT1 induces paracaspase-mediated cleavage of the tumour suppressor protein LIMA1. LIMA1 binding by API2-MALT1 is API2 dependent and proteolytic cleavage is dependent on MALT1 paracaspase activity. Intriguingly, API2-MALT1-mediated proteolysis generates a LIM domain-only (LMO)-containing fragment with oncogenic properties in vitro and in vivo. Importantly, primary MALT lymphomas harbouring the API2-MALT1 fusion uniquely demonstrate LIMA1 cleavage fragments. Our studies reveal a novel paracaspase-mediated oncogenic gain-of-function mechanism in the pathogenesis of MALT lymphoma.

Targeting B-cell lymphomas with inhibitors of the MALT1 paracaspase

The paracaspase MALT1 is an Arg-specific protease that cleaves multiple substrates to promote lymphocyte proliferation and survival. The catalytic activity of MALT1 is normally tightly regulated by antigen receptor triggering, which promotes MALT1 activation by its inducible monoubiquitination-dependent dimerization. Constitutive MALT1 activity is a hallmark of specific subsets of B-cell lymphomas, which are characterized by chromosomal translocations or point mutations that activate MALT1 or its upstream regulators. Recent findings suggest that such lymphomas may be sensitive to treatment with MALT1 inhibitors. Here we review recent progress in the understanding of MALT1 function and regulation, and the development of small molecule MALT1 inhibitors for therapeutic applications.

Piperlongumine inhibits the proliferation and survival of B-cell acute lymphoblastic leukemia cell lines irrespective of glucocorticoid resistance

Piperlongumine (PL), a pepper plant alkaloid from Piper longum, has anti-inflammatory and anti-cancer properties. PL selectively kills both solid and hematologic cancer cells, but not normal counterparts. Here we evaluated the effect of PL on the proliferation and survival of B-cell acute lymphoblastic leukemia (B-ALL), including glucocorticoid (GC)-resistant B-ALL. Regardless of GC-resistance, PL inhibited the proliferation of all B-ALL cell lines, but not normal B cells, in a dose- and time-dependent manner and induced apoptosis via elevation of ROS. Interestingly, PL did not sensitize most of B-ALL cell lines to dexamethasone (DEX). Only UoC-B1 exhibited a weak synergistic effect between PL and DEX. All B-ALL cell lines tested exhibited constitutive activation of multiple transcription factors (TFs), including AP-1, MYC, NF-κB, SP1, STAT1, STAT3, STAT6 and YY1. Treatment of the B-ALL cells with PL significantly downregulated these TFs and modulated their target genes. While activation of AURKB, BIRC5, E2F1, and MYB mRNA levels were significantly downregulated by PL, but SOX4 and XBP levels were increased by PL. Intriguingly, PL also increased the expression of p21 in B-ALL cells through a p53-independent mechanism. Given that these TFs and their target genes play critical roles in a variety of hematological malignancies, our findings provide a strong preclinical rationale for considering PL as a new therapeutic agent for the treatment of B-cell malignancies, including B-ALL and GC-resistant B-ALL.

MALT1 auto-proteolysis is essential for NF-κB-dependent gene transcription in activated lymphocytes

Mucosa-associated lymphoid tissue 1 (MALT1) controls antigen receptor–mediated signalling to nuclear factor κB (NF-κB) through both its adaptor and protease function. Upon antigen stimulation, MALT1 forms a complex with BCL10 and CARMA1, which is essential for initial IκBα phosphorylation and NF-κB nuclear translocation. Parallel induction of MALT1 protease activity serves to inactivate negative regulators of NF-κB signalling, such as A20 and RELB. Here we demonstrate a key role for auto-proteolytic MALT1 cleavage in B- and T-cell receptor signalling. MALT1 cleavage occurred after Arginine 149, between the N-terminal death domain and the first immunoglobulin-like region, and did not affect its proteolytic activity. Jurkat T cells expressing an un-cleavable MALT1-R149A mutant showed unaltered initial IκBα phosphorylation and normal nuclear accumulation of NF-κB subunits. Nevertheless, MALT1 cleavage was required for optimal activation of NF-κB reporter genes and expression of the NF-κB targets IL-2 and CSF2. Transcriptome analysis confirmed that MALT1 cleavage after R149 was required to induce NF-κB transcriptional activity in Jurkat T cells. Collectively, these data demonstrate that auto-proteolytic MALT1 cleavage controls antigen receptor-induced expression of NF-κB target genes downstream of nuclear NF-κB accumulation.

The API2-MALT1 fusion exploits TNFR pathway-associated RIP1 ubiquitination to promote oncogenic NF-κB signaling

The API2-MALT1 fusion oncoprotein is created by the recurrent t(11;18)(q21;q21) chromosomal translocation in mucosa-associated lymphoid tissue (MALT) lymphoma. We identified receptor interacting protein-1 (RIP1) as a novel API2-MALT1-associated protein, and demonstrate that RIP1 is required for API2-MALT1 to stimulate canonical nuclear factor kappa B (NF-κB). API2-MALT1 promotes ubiquitination of RIP1 at lysine (K) 377, which is necessary for full NF-κB activation. Furthermore, we found that TNF receptor-associated factor 2 (TRAF2) recruitment is required for API2-MALT1 to induce RIP1 ubiquitination, NF-κB activation and cellular transformation. Although both TRAF2 and RIP1 interact with the API2 moiety of API2-MALT1, this moiety alone is insufficient to induce RIP1 ubiquitination or activate NF-κB, indicating that API2-MALT1-dependent RIP1 ubiquitination represents a gain of function requiring the concerted actions of both the API2 and MALT1 moieties of the fusion. Intriguingly, constitutive RIP1 ubiquitination was recently demonstrated in several solid tumors, and now our study implicates RIP1 ubiquitination as a critical component of API2-MALT1-dependent lymphomagenesis.

Targeting the apoptosis pathway in hematologic malignancies

Apoptosis is a cell death program that is well-orchestrated for normal tissue homeostasis and for removal of damaged, old or infected cells. It is regulated by intrinsic and extrinsic pathways. The intrinsic pathway responds to signals such as ultraviolet radiation or DNA damage and activates "executioner" caspases through a mitochondria-dependent pathway. The extrinsic pathway is activated by death signals induced, for example, by an infection that activates the immune system or receptor-mediated pathways. The extrinsic pathway signals also cascade down to executioner caspases that cleave target proteins and lead to cell death. Strict control of cellular apoptosis is important for the hematopoietic system as it has a high turnover rate. However, the apoptosis program is often deregulated in hematologic malignancies leading to the accumulation of malignant cells. Therefore, apoptosis pathways have been identified for the development of anticancer therapeutics. We review here the proteins that have been targeted for anticancer drug development in hematologic malignancies. These include BCL-2 family proteins, death ligands and receptors, inhibitor of apoptosis family proteins and caspases. Except for caspase activators, drugs that target each of these classes of proteins have advanced into clinical trials.

The CBM signalosome: potential therapeutic target for aggressive lymphoma?

The CBM signalosome plays a pivotal role in mediating antigen-receptor induced NF-κB signaling to regulate lymphocyte functions. The CBM complex forms filamentous structure and recruits downstream signaling components to activate NF-κB. MALT1, the protease component in the CBM complex, cleaves key proteins in the feedback loop of the NF-κB signaling pathway and enhances NF-κB activation. The aberrant activity of the CBM complex has been linked to aggressive lymphoma. Recent years have witnessed dramatic progresses in understanding the assembly mechanism of the CBM complex, and advances in the development of targeted therapy for aggressive lymphoma. Here, we will highlight these progresses and give an outlook on the potential translation of this knowledge from bench to bedside for aggressive lymphoma patients.

Marginal zone lymphomas and infectious agents

A link with infectious agents, bacteria and viruses in particular, has been reported for many lymphoma entities. Marginal zone lymphomas (extranodal, nodal and splenic forms) are frequently associated with chronic infections, with important clinical, molecular, biological, and therapeutic implications. The well-known correlation between Helicobacter pylori and gastric MALT-lymphoma, the recently reported links between Chlamydophila psittaci and ocular adnexal MALT-lymphoma and Borrelia burgdorferi and cutaneous MALT lymphoma constitute the best studied examples of lymphomagenic activity of bacteria, while the hepatitis C virus represents the most extensively investigated virus associated with marginal zone lymphomas. Biological and clinical features, therapeutic implications and future perspectives of these lymphoma-microbial associations are discussed in this review.

Molecular and genomic aberrations in Chlamydophila psittaci negative ocular adnexal marginal zone lymphomas

The etiology and pathogenesis of ocular adnexal extranodal marginal zone lymphoma (OAEMZL) are still unknown and the association with Chlamydophila psittaci (C. psittaci) has been shown in only some geographic regions. Herein, we comprehensively examined the frequency of chromosomal translocations as well as CARD11, MYD88 (L265P), and A20 mutations/deletions in 45 C. psittaci negative OAEMZLs. t(14;18)(q32;q21) IGH-MALT1 and t(11;18)(q21;q21) API2-MALT1 were not detected in any of the analyzed tumors while three tumors harbored IGH translocations to an unidentified partner. CARD11 mutations were not found in all analyzed tumors, while the MYD88 L265P mutation was detected in three (6.7%) tumors. A20 mutations and deletions were each detected in seven (15.6%) and six (13.3%) tumors, respectively. Therefore, the observed genetic aberrations could account for the activation of the nuclear factor (NF)-kB signaling pathway in only a minority of the cases. Further studies are needed to identify the molecular mechanisms underlying the pathogenesis of OAEMZL.

c-IAP1 and c-IAP2 redundancy differs between T and B cells

Cellular Inhibitors of Apoptosis 1 and 2 (c-IAP1 and c-IAP2) are ubiquitin protein ligases (E3s) that constitutively ubiquitinate and induce proteasomal-mediated degradation of NF-κB Inducing Kinase (NIK) and repress non-canonical NF-κB activation. Mice expressing an E3-inactive c-IAP2 mutant (c-IAP2(H570A)) have constitutive activation of non-canonical NF-κB, resulting in B cell hyperplasia and T cell costimulation-independence. If, and if so to what extent, c-IAP1 and c-IAP2 are redundant in NF-κB regulation in these mice is not known. Here we have generated mice expressing a mutant c-IAP1 that lacks E3 activity (c-IAP1(H582A)). These mice were phenotypically normal and did not have constitutive NF-κB activation in B cells or MEFs. siRNA-mediated knockdown of c-IAP2 showed that accumulated c-IAP2, resulting from lack of c-IAP1-dependent degradation, compensated for absent c-IAP1 E3 activity. Surprisingly, c-IAP1(H582A) T cells had a lower p100/p52 ratio than wild type T cells, and in the absence of costimulation proliferated to a degree intermediate between wild type and c-IAP2(H570A) T cells. Therefore, although c-IAP1 and c-IAP2 both can repress constitutive NF-κB activation, the relative importance of each varies according to cell type.

Piperlongumine inhibits proliferation and survival of Burkitt lymphoma in vitro

Piperlongumine (PL), a pepper plant alkaloid from Piper longum, kills solid tumor cells in a highly selective, potent fashion. To evaluate whether PL may have similar effects on malignant blood cells, we determined the efficacy with which PL inhibits the B-lymphocyte derived neoplasm, Burkitt lymphoma (BL). Low micromolar concentrations of PL (IC(50) = 2.8 μM × 8.5 μM) curbed growth and survival of two EBV(+) BL cell lines (Daudi, Raji) and two EBV BL cell lines (Ramos, DG-75), but left normal peripheral blood B-lymphocytes unharmed. PL-dependent cytotoxicity was effected in part by reduced NF-κB and MYC activity, with the former being caused by inhibition of IκBα degradation, nuclear translocation of p65, and binding of NF-κB dimers to cognate DNA sequences in gene promoters. In 4 of 4 BL cell lines, the NF-κB/MYC-regulated cellular target genes, E2F1 and MYB, were down regulated, while the stress sensor gene, GADD45B, was up regulated. The EBV-encoded oncogene, LMP-1, was suppressed in Daudi and Raji cells. Considering that NF-κB, MYC and LMP-1 play a crucial role in the biology of many blood cancers including BL, our results provide a strong preclinical rationale for considering PL in new intervention approaches for patients with hematologic malignancies.

Protease activity of MALT1: a mystery unravelled

Constitutive NF-κB (nuclear factor κB) activation in B-cell lymphomas relies greatly on the CARMA1 [CARD (caspase recruitment domain)-containing MAGUK (membrane-associated guanylate kinase) 1]-Bcl10-MALT1 (mucosa-associated lymphoid tissue translocation gene 1) signalling complex. Within this protein complex, MALT1 possesses a rather unique enzymatic activity, which allows it to cleave Bcl10, RelB and CYLD, among other substrates. The catalytic activity of MALT1 promotes activation of canonical and non-canonical NF-κB as well as other signalling pathways. However, even after a decade of intense research on MALT1, many mechanistic aspects of its enzymatic activity remain elusive. A recent article by Hachmann, Snipas, van Raam, Cancino, Houlihan, Poreba, Kasperkiewicz, Drag and Salvesen [(2012) Biochem. J. 443, 287-295] provides novel insight into the activation mechanism and the substrate specificity of MALT1. These intriguing findings convincingly demonstrate the importance of MALT1 dimerization for its catalytic activity and pave the way for novel therapeutic approaches that target this crucial regulator of lymphoma survival and proliferation.

Mechanism and specificity of the human paracaspase MALT1

The paracaspase domain of MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a component of a gene translocation fused to the N-terminal domains of the cellular inhibitor of apoptosis protein 2. The paracaspase itself, commonly known as MALT1, participates in the NF-κB (nuclear factor κB) pathway, probably by driving survival signals downstream of the B-cell antigen receptor through MALT1 proteolytic activity. We have developed methods for the expression and purification of recombinant full-length MALT1 and its constituent catalytic domain alone. Both are activated by dimerization without cleavage, with a similar dimerization barrier to the distantly related cousins, the apical caspases. By using positional-scanning peptidyl substrate libraries we demonstrate that the activity and specificity of full-length MALT1 is recapitulated by the catalytic domain alone, showing a stringent requirement for cleaving after arginine, and with striking peptide length constraints for efficient hydrolysis. Rates of cleavage (kcat/Km values) of optimal peptidyl substrates are in the same order (10(3)-10(4) M(-1)·s(-1)) as for a putative target protein CYLD. Thus MALT1 has many similarities to caspase 8, even cleaving the putative target protein CYLD with comparable efficiencies, but with diametrically opposite primary substrate specificity.

Targeting IAP proteins for therapeutic intervention in cancer

Evasion of apoptosis is one of the crucial acquired capabilities used by cancer cells to fend off anticancer therapies. Inhibitor of apoptosis (IAP) proteins exert a range of biological activities that promote cancer cell survival and proliferation. X chromosome-linked IAP is a direct inhibitor of caspases - pro-apoptotic executioner proteases - whereas cellular IAP proteins block the assembly of pro-apoptotic protein signalling complexes and mediate the expression of anti-apoptotic molecules. Furthermore, mutations, amplifications and chromosomal translocations of IAP genes are associated with various malignancies. Among the therapeutic strategies that have been designed to target IAP proteins, the most widely used approach is based on mimicking the IAP-binding motif of second mitochondria-derived activator of caspase (SMAC), which functions as an endogenous IAP antagonist. Alternative strategies include transcriptional repression and the use of antisense oligonucleotides. This Review provides an update on IAP protein biology as well as current and future perspectives on targeting IAP proteins for therapeutic intervention in human malignancies.

A possible role of cIAP2 in Helicobacter pylori-associated gastric cancer

Cellular inhibitor of apoptosis protein 2 (cIAP2) is a member of the IAP family and is over-expressed in most cancer tissues. In this study, we investigated the role cIAP2 in Helicobacter pylori (HP) related gastric carcinogenesis. We measured the expression of cIAP2 at mRNA and protein levels in a panel of gastric cancer cell lines and human gastric cancer tissues by semi-quantitative reverse transcriptase PCR (RT-PCR), quantitative real time PCR (qPCR), immunoblotting, and immunohistochemistry. The effects of cIAP2 down-regulation on gastric cell proliferation and apoptosis were detected by standard WST-1 assay and flow cytometry, respectively. Infection of gastric mucosa by HP enhances the expression of cIAP2 in mouse gastric tissues. Over 70% of human gastric cancer tissues express higher amount of cIAP2. Well-differentiated gastric cancer cells express more cIAP2 than moderately- and poorly-differentiated gastric cancer cells. Knocking down of cIAP2 in SGC-7901 cells results in a 30% decrease in cell proliferation, a 20% increase in apoptosis and delayed migration. Thus, cIAP2 may play an important role in HP-induced gastric carcinogenesis, and it may serve as a potential target for gastric cancer therapy.

Crystal structure of the mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) paracaspase region

The mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) paracaspase, a key component of the Carma1/Bcl10/MALT1 signalosome, is critical for NF-κB signaling in multiple contexts. MALT1 is thought to function as a scaffold and protease to promote signaling; however, the biochemical and structural basis of paracaspase action remains largely unknown. Here we report the 1.75-Å resolution crystal structure of the MALT1 paracaspase region, which contains the paracaspase domain and an ensuing Ig-like domain. The paracaspase and the Ig domains appear as a single folding unit and interact with each other through extensive van der Waals contacts and hydrogen bonds. The paracaspase domain adopts a fold that is nearly identical to that of classic caspases and homodimerizes similarly to form an active protease. Unlike caspases, the active and mature form of the paracaspase domain remains a single uncleaved polypeptide and specifically recognizes the bound peptide inhibitor Val-Arg-Pro-Arg. In particular, the carboxyl-terminal amino acid Arg of the inhibitor is coordinated by three highly conserved acidic residues. This structure serves as an important framework for deciphering the function and mechanism of paracaspases exemplified by MALT1.

t(11;18)(q21;q21) translocation as predictive marker for non-responsiveness to salvage thalidomide therapy in patients with marginal zone B-cell lymphoma with gastric involvement

PURPOSE

Activation of TNF-α/NF-κB-related signaling pathway is crucial in sustain the growth of Helicobacter pylori-independent gastric mucosa-associated lymphoid tissue type (MALT) lymphoma. Thalidomide is an anti-angiogenic agent with anti-TNF-α and anti-NF-κB activity. This retrospective study evaluated the efficacy of thalidomide in standard therapy-failure gastric MALT lymphoma.

METHODS

Between October 2003 and September 2007, 10 patients with antibiotics-resistant, chemotherapy-refractory gastric MALT lymphoma who received salvage thalidomide therapy at daily doses of 100-200 mg were identified from medical records and included. Status of t(11;18)(q21;q21) was determined by reverse transcriptase polymerase chain reaction for API2-MALT1 transcript, while expression of NF-κB was detected by immunohistochemistry. Tumor response was evaluated by RECIST criteria.

RESULTS

Tumors were of stage IV in seven and IE/IIE-1 in three. The best tumor response after thalidomide was complete response in two and partial in three, with an overall response rate of 50% (95% confidence interval, 12.3-87.7%). At median follow-up of 39.3 months, the 3-year event-free and overall survival rates were 36.0% and 85.7%, respectively. API2-MALT1 transcript was detected in four (40%) tumors. Objective response rates of tumors with and without t(11;18)(q21;q21) were 0% (0/4) and 83% (5/6), respectively, P = 0.048 (Fisher's exact test). Thalidomide treatment was associated with significant down-regulation of nuclear NF-κB expression levels in residual neoplastic cells and microenvironments of responsive tumors, but not in t(11;18)(q21;q21)-positive, thalidomide-refractory tumors.

CONCLUSIONS

Thalidomide is an effective salvage treatment for standard therapy-failure, t(11;18)(q21;q21) translocation-negative gastric MALT lymphoma and deserves further exploration.

Inhibitor of apoptosis proteins: fascinating biology leads to attractive tumor therapeutic targets

Cell death inhibition is a very successful strategy that cancer cells employ to combat the immune system and various anticancer therapies. Inhibitor of apoptosis (IAP) proteins possess a wide range of biological activities that promote cancer survival and proliferation. One of them, X-chromosome-linked IAP is a direct inhibitor of proapoptotic executioners, caspases. Cellular IAP proteins regulate expression of antiapoptotic molecules and prevent assembly of proapoptotic protein signaling complexes, while survivin regulates cell division. In addition, amplifications, mutations and chromosomal translocations of IAP genes are associated with various malignancies. Several therapeutic strategies have been designed to target IAP proteins, including a small-molecule approach that is based on mimicking the IAP-binding motif of an endogenous IAP antagonist - the second mitochondrial activator of caspases. Other strategies involve antisense nucleotides and transcriptional repression. The main focus of this article is to provide an update on IAP protein biology and perspectives on the development of IAP-targeting therapeutics.

Malignant pirates of the immune system

At great human cost, cancer is the largest genetic experiment ever conducted. This review highlights how lymphoid malignancies have genetically perverted normal immune signaling and regulatory mechanisms for their selfish oncogenic goals of unlimited proliferation, perpetual survival and evasion of the immune response.

MALT1 protease: a new therapeutic target in B lymphoma and beyond?

The identification of mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) as a gene that is perturbed in the B-cell neoplasm MALT lymphoma, already more than a decade ago, was the starting point for an intense area of research. The fascination with MALT1 was fueled further by the observation that it contains a domain homologous to the catalytic domain of caspases and thus, potentially, could function as a protease. Discoveries since then initially revealed that MALT1 is a key adaptor molecule in antigen receptor signaling to the transcription factor NF-κB, which is crucial for lymphocyte function. However, recent discoveries show that this function of MALT1 is not restricted to lymphocytes, witnessed by the ever-increasing list of receptors from cells within and outside of the immune system that require MALT1 for NF-κB activation. Yet, a role for MALT1 protease activity was shown only recently in immune signaling, and its importance was then further strengthened by the dependency of NF-κB-addicted B-cell lymphomas on this proteolytic activity. Therapeutic targeting of MALT1 protease activity might, therefore, become a useful approach for the treatment of these lymphomas and, additionally, an effective strategy for treating other neoplastic and inflammatory disorders associated with deregulated NF-κB signaling.

MALT lymphoma: many roads lead to nuclear factor-κb activation

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT) lymphoma is characterized genetically by several recurrent, but mutually exclusive, chromosome translocations. To date, it has been shown that at least the oncogenic products of t(1;14)(p22;q32)/BCL10-IGH, t(14;18)(q32;21)/IGH-MALT1 and t(11;18)(q21;q21)/API2-MALT1 activate the nuclear factor (NF)-κB activation pathway. Recently, A20, an essential global NF-κB inhibitor, was found to be inactivated by somatic deletion and/or mutation in translocation-negative MALT lymphomas. However, these genetic abnormalities alone are not sufficient for malignant transformation and thus need to cooperate with other factors in MALT lymphomagenesis. Recent studies have shown steady, exciting progresses in our understanding of the biological functions of BCL10, MALT1 and A20 in the regulation of the NF-κB activation pathways and the biology of lymphocytes. This review discusses the implication of these recent advances in the molecular pathogenesis of MALT lymphoma, and explores how the above genetic abnormalities cooperate with immunological stimulation in the development of lymphoma.