Mucosa-associated Lymphoid Tissue Lymphoma Translocation 1 Research Articles

Discovery of orally bioavailable inhibitors of MALT1 with in vivo activity for psoriasis

We report the design, synthesis, and biological activity of a series of compounds that exhibit potent mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) inhibition. Structural transformation of the substructures of a starting compound gave amidomethyl derivatives and sulfonylguanidine derivatives that exhibited potent inhibition of MALT1. Compound 37 had good oral bioavailability and showed anti-psoriatic activity in an imiquimod-induced psoriasis mouse model after oral administration.

Preclinical Translational Research Suggests a Clinical Trial Strategy for a Novel MALT1 Inhibitor ONO-7018/CTX-177 Against Malignant Lymphomas

Introduction Malignant lymphomas, relapsed or refractory B Cell Non-Hodgkin Lymphoma like B-cell diffuse large B-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL), are still clinically intractable as patients with these lymphomas carry a dismal prognosis. Genome sequence analysis data on these lymphomas suggest that the gene mutations of mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) -upstream molecules, such as CD79A/B and CARD11, eventually promotes the activation of MALT1's protease activity; this protease activity of MALT1 is known as a key growth or survival regulator for intractable lymphomas that carry these mutations. Previously, we reported the generation of a novel small molecule inhibitor, CTX-177 (currently renamed to ONO-7018 by Ono Pharmaceutical Co., Ltd.), which acts on MALT1 with high potency and specificity. In addition, we showed that ONO-7018 demonstrated preclinical efficacy along with target engagement in several lymphoma models (Morishita D et al., Blood (2020) 136 (Supplement 1): 3-4.). Results To identify potential strategies for a clinical trial of ONO-7018, we conducted translational research to elucidate (1) combination strategies with other key medications, (2) patient selection biomarkers to illuminate sensitivity to ONO-7018 and (3) pharmacodynamics (PD) markers to monitor the suppression of MALT1. After searching for combination strategies (1), ONO-7018 exhibited synergistic combination effect with a BTK inhibitor in vitro along with target inhibition. In addition, the MALT1 inhibitor showed an anti-tumor effect against an ABC-DLBCL cell line derived xenograft (CDX) model. Thus, combination treatment with BTK inhibitor is expected to be the treatment strategy of ONO-7018. Next, regarding biomarkers of sensitivity (2), we found that ONO-7018 selectively inhibits the in vitro growth of cell lines expressing cleaved forms of MALT1 substrates. Additionally, in vivo data from CDX and patient derived xenograft model were consistent with in vitro data. Interestingly, CRISPR-Cas9 mediated A20 knockout attenuates the sensitivity of cell line model toward ONO-7018 treatment. Given these findings, these cleaved forms of MALT1 substrates and the loss of function gene mutation on A20 could become biomarkers to illuminate sensitivity to ONO-7018. Finally, to identify pharmacodynamic markers of ONO-7018 (3), panel analysis of cytokine production following CD3/CD28 stimulation was conducted. Before starting this experiment, we confirmed that ONO-7018 could inhibit the cellular activity of the two T-cell receptor signaling stimulated forms of MALT1 splice variants. Consistent with the inhibitory mode of ONO-7018 on these MALT1 splicing forms, some cytokines’ production was clearly abrogated; these cytokines could be potential PD markers in a clinical trial. Conclusion The results from these translational research studies support the preparation of a clinical trial by clearly defining patient stratification biomarkers, combination strategies, and PD monitoring. These data underscore the potential therapeutic impact of ONO-7018 as a single-agent or combination partner with other inhibitors like BTK inhibitor and elucidate the sensitivity and response of ONO-7018 for the treatment of malignant lymphomas.

Preclinical Evaluation of a Novel MALT1 Inhibitor CTX-177 for Relapse/Refractory Lymphomas

Among various subtypes of malignant lymphomas, activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL), mantle cell lymphoma (MCL), and adult T-cell leukemia/lymphoma (ATL) are clinically intractable as patients with these lymphomas carry a dismal prognosis, with long-term survival rates of 10-30%. Therefore, a novel therapeutic strategy is required to better manage patients with these malignancies. Recently, we and other investigators performed comprehensive genetic studies and revealed frequent genetic alterations in B and T cell antigen receptor signaling and NF-κB pathway, such as CD79A/B and CARD11 mutations in ABC-DLBCL and PLCG1, PRKCB, and CARD11 mutations in ATL, suggesting the biological relevance of this pathway. To exploit a new treatment strategy in these malignant lymphomas, we focused on the protease mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) which is a key regulator of the antigen receptor signaling and NF-κB pathway and forms a complex with CARD11 and BCL10, and developed a novel compound CTX-177 to inhibit MALT1 with high potency and specificity. CTX-177 was efficacious against ABC-DLBCL and MCL models in vitro and in vivo. Moreover, CTX-177 exhibited combination synergistic effect with BTK inhibitor. In addition, the MALT1 inhibitor showed an anti-tumor effect against CARD11 mutated ABC-DLBCL model, which is resistant to BTK inhibitor. To further explore efficacy of CTX-177 against malignant lymphomas, we generated animal models such as genetically engineered mice and patient-derived xenograft models recapitulating molecular features of these diseases, and examined the response to the MALT1 inhibitor. In these experiments, target engagement of CTX-177 was confirmed by detecting digested substrates of MALT1, and mode of action was evaluated by downregulation of oncogenic transcriptional factor IRF4 which is critical for lymphoma survival. Importantly, the relationship of susceptibility to MALT1 inhibition and gene mutations was analyzed to identity a patient selection biomarker for CTX-177. In summary, the novel, selective, small-molecule MALT1 inhibitor CTX-177 demonstrated preclinical efficacy along with target engagement in several lymphoma models with activated antigen receptor signaling and NF-κB pathway. Our results underscore the preclinical therapeutic potential of CTX-177 as a single-agent or in combination with other inhibitors like BTK inhibitor for the treatment of malignant lymphomas. Disclosures Morishita: Chordia Therapeutics Inc.: Current Employment, Current equity holder in private company. Mizutani:Chordia Therapeutics Inc.: Current Employment, Current equity holder in private company. Tozaki:Chordia Therapeutics Inc.: Current Employment, Current equity holder in private company. Arikawa:Chordia Therapeutics Inc.: Current Employment, Current equity holder in private company. Kataoka:CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Takeda Pharmaceutical Company: Research Funding; Otsuka Pharmaceutical: Research Funding; Asahi Genomics: Current equity holder in private company. Yoda:Chordia Therapeutics Inc.: Research Funding. Izutsu:Symbio: Research Funding; Solasia: Research Funding; Celgene: Research Funding; Chugai: Research Funding; Novartis: Research Funding; Ono Pharmaceutical: Research Funding; Bayer pharmaceuticals: Research Funding; Daiichi Sankyo: Research Funding; AstraZeneca: Research Funding; Eisai: Research Funding; Incyte: Research Funding; Abbvie pharmaceuticals: Research Funding; HUYA Japan: Research Funding; Sanofi: Research Funding; Janssen: Research Funding; Yakult: Research Funding. Minami:Bristol-Myers Squibb Company: Honoraria; Novartis Pharma KK: Honoraria; Pfizer Japan Inc.: Honoraria; Takeda: Honoraria. Shimoda:Otsuka Pharmaceutical: Research Funding; Pfizer Inc.: Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Merck & Co.: Research Funding; Astellas Pharma: Research Funding; AbbVie Inc.: Research Funding; PharmaEssentia Japan: Research Funding; Perseus Proteomics: Research Funding; Celgene: Honoraria; Shire plc: Honoraria; Bristol-Myers Squibb: Honoraria; Takeda Pharmaceutical Company: Honoraria; Novartis: Honoraria, Research Funding; Asahi Kasei Medical: Research Funding; Japanese Society of Hematology: Research Funding; The Shinnihon Foundation of Advanced Medical Treatment Research: Research Funding. Miyake:Chordia Therapeutics Inc.: Current Employment, Current equity holder in private company. Ogawa:KAN Research Institute, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Chordia Therapeutics, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Asahi Genomics Co., Ltd.: Current equity holder in private company; Otsuka Pharmaceutical Co., Ltd.: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding.

Structure elucidation and absolute configuration of metabolites from the soil-derived fungus Dictyosporium digitatum using spectroscopic and computational methods

Following the discovery of a new class of compounds that inhibit the mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) protease in a prior study, further chemical investigation of the Dictyosporium digitatum fungus resulted in the identification of 16 additional metabolites, including 12 undescribed compounds (1–12). The constitution and relative configuration of these new molecules were established by comprehensive NMR and HRMS analyses. Their absolute configurations were determined by employing Mosher's ester analysis and TDDFT ECD calculations. Two sesquiterpenes, dictyosporins A (1) and B (2), possess an undescribed eudesmen-type of structural scaffold. The ability of the isolated compounds to inhibit MALT1 proteolytic activity was evaluated, but none of them exhibited significant inhibition.

N4BP1 restricts HIV-1 and its inactivation by MALT1 promotes viral reactivation.

RNA-modulating factors not only regulate multiple steps of cellular RNA metabolism, but also emerge as key effectors of the immune response against invading viral pathogens including human immunodeficiency virus type-1 (HIV-1). However, the cellular RNA-binding proteins involved in the establishment and maintenance of latent HIV-1 reservoirs have not been extensively studied. Here, we screened a panel of 62 cellular RNA-binding proteins and identified NEDD4-binding protein 1 (N4BP1) as a potent interferon-inducible inhibitor of HIV-1 in primary T cells and macrophages. N4BP1 harbours a prototypical PilT N terminus-like RNase domain and inhibits HIV-1 replication by interacting with and degrading viral mRNA species. Following activation of CD4+ T cells, however, N4BP1 undergoes rapid cleavage at Arg 509 by the paracaspase named mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1). Mutational analyses and knockout studies revealed that MALT1-mediated inactivation of N4BP1 facilitates the reactivation of latent HIV-1 proviruses. Taken together, our findings demonstrate that the RNase N4BP1 is an efficient restriction factor of HIV-1 and suggest that inactivation of N4BP1 by induction of MALT1 activation might facilitate elimination of latent HIV-1 reservoirs.

Inhibition of MALT1 paracaspase activity improves lesion recovery following spinal cord injury

Spinal cord injury (SCI) is a devastating traumatic injury that causes persistent, severe motor and sensory dysfunction. Immune responses are involved in functional recovery after SCI. Mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) has been shown to regulate the survival and differentiation of immune cells and to play a critical role in many diseases, but its function in lesion recovery after SCI remains unclear. In this paper, we generated KI (knock in) mice with a point mutation (C472G) in the active center of MALT1 and found that the KI mice exhibited improved functional recovery after SCI. Fewer macrophages were recruited to the injury site in KI mice and these macrophages differentiated into anti-inflammatory macrophages. Moreover, macrophages from KI mice exhibited reduced phosphorylation of p65, which in turn resulted in decreased SOCS3 expression and increased pSTAT6 levels. Similar results were obtained upon inhibition of MALT1 paracaspase with the small molecule inhibitor “MI-2” or the more specific inhibitor “MLT-827”. In patients with SCI, peripheral blood mononuclear cells (PBMC) displayed increased MALT1 paracaspase. Human macrophages showed reduced pro-inflammatory and increased anti-inflammatory characteristics following the inhibition of MALT1 paracaspase. These findings suggest that inhibition of MALT1 paracaspase activity in the clinic may improve lesion recovery in subjects with SCI.

Treatment of Dextran Sulfate Sodium-Induced Colitis with Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 Inhibitor MI-2 Is Associated with Restoration of Gut Immune Function and the Microbiota.

Disruption of the healthy intestinal microbiome and homeostasis of the intestinal immune system, which are closely interactive, are two key factors for ulcerative colitis. Here, we show that MI-2, a selective inhibitor of mucosa-associated lymphoid tissue lymphoma translocation-1 (MALT1), alleviated excessive inflammatory responses and was associated with restoration of healthy intestinal microbiome in mice suffering from dextran sulfate sodium (DSS)-induced colitis. We found that the diversity of intestinal microbiome of mice with DSS-induced colitis was significantly lower than that of healthy mice. However, MI-2 treatment in mice with DSS-induced colitis resulted in restored microbially diverse populations. To understand the possibility of the beneficial effect of the restored microbially diverse populations of MI-2-treated mice with DSS-induced colitis, we showed that inserting fecal microbiota from MI-2-treated mice with DSS-induced colitis and healthy control mice into mice with DSS-induced colitis could alleviate symptoms of colitis. The possibility of MI-2 treatment in DSS-induced colitis, associated with restoration of healthy microbially diverse populations in addition to reshaping host immune modulating capacity by reducing inflammatory cytokines (tumor necrosis factor alpha, interleukin-1β [IL-1β], IL-17α, and IL-22), may be considered therapeutic for ulcerative colitis.

Mucosa-associated lymphoid tissue lymphoma translocation 1 as a novel therapeutic target for rheumatoid arthritis

Emerging evidence suggests that mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) is a key regulator of inflammatory diseases; however, the pathological role of MALT1 in rheumatoid arthritis (RA) is not well understood. Consequently, this protein has not been therapeutically targeted for the treatment of RA. MALT1 plays a role in the paracaspase pathway, has proteolytic activity and is involved in the regulation of inflammatory responses. In this study, we found that the MALT1-targeting inhibitory small molecule, MALT1 selective inhibitor 2-chloro-N-[4-[5-(3,4-dichlorophenyl)-3-(2-methoxyethoxy)-1H-1,2,4-triazol-1-yl]phenylacetamide (MI-2) strongly suppresses the differentiation of monocytes into osteoclasts in the absence or presence of the inflammatory cytokine tumour necrosis factor α. Furthermore, MI-2 ameliorates pathologic bone erosion and synovitis in an in vivo mouse model of collagen-induced arthritis. Mechanistically, MI-2 blocked expression of the master osteoclast regulator – nuclear factor of activated T cells 1 (NFATc1) – by inhibiting nuclear factor κB (NF-κB), which is a critical regulator of NFATc1. These findings highlight the important regulatory role of MALT1 in the NF-κB–NFATc1-signalling axis during osteoclastogenesis and suggest that targeting MALT1 is a promising treatment option for rheumatoid arthritis.

Abstract 5108: Potent small molecule compounds that selectively inhibit proliferation of ABC-DLBCL cell lines

Abstract Diffuse large B cell lymphoma (DLBCL), which accounts for 25% of all lymphomas cases, has been classified into molecular subtypes including germinal center B cell like (GCB) DLBCL, activated B cell-like (ABC) DLBCL, and primary mediastinal B cell lymphoma (PMBL). Among these subtypes, patients with ABC-DLBCLs have the worst prognosis because of the high chemo-resistance, and require effective therapies. Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 (MALT1) protease activity is linked to the pathogenesis of ABC-DLBCL. Therefore, a focused library of covalent compounds selected based on molecular docking on the reported crystal structure was screened for selective sensitivity to ABC-DLBCL, but not GCB-DLBCL cell lines. Optimization of initial hits resulted in the identification of lead compounds with an anti-proliferative EC50 of <100 nM selectively in ABC-DLBCL cell lines. Consistent with the previously reported role of MALT1 inhibitors, lead compounds also showed anti-proliferative activity in selected melanoma and NSCLC cell lines. The anti-proliferative activity of the lead compounds correlated well with the inhibition IL-6, a downstream marker of MALT1 signaling, in ABC-DLBCL cell line such as OCI-LY3. The lead compounds exhibited excellent drug-like properties including solubility, metabolic stability, lack of CYP inhibition, permeability and desired dose-dependent oral exposure in pharmacokinetic studies. In a repeated dose MTD study, the lead compounds showed good tolerability with an exposure multiple of >10 over cellular EC50 for up to 8 hours. The lead compounds showed dose-dependent tumor growth inhibition in a xenograft model upon oral dosing. In summary, we have identified novel and potent MALT1 inhibitors capable of selectively inhibiting proliferation of DLBCL cell lines with optimized drug-like properties including oral bioavailability. The data presented here strongly support further development of these compounds for DLBCL and other indications. Citation Format: Leena Khare Satyam, Dinesh Chikkanna, Vinayak Khairnar, Manoj Pothuganti, Sunil Panigrahi, Anirudha Lakshminarasimhan, Narasimha Rao, Wesley Balasubramanian, Sandeep Patil, Sreevalsam Gopinath, Gunta Upendra, Jwala Nagaraj, Kiran Aithal, Vijay Ahuja, Sanjeev Giri, Chetan Pandit, Murali Ramachandra. Potent small molecule compounds that selectively inhibit proliferation of ABC-DLBCL cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5108. doi:10.1158/1538-7445.AM2017-5108

Targeting MALT1 with the Small Molecule Inhibitor MI2 Induces a Caspase-Dependent Apoptosis and Inhibits the NF-κb Pathway in Chronic Lymphocytic Leukemia Primary Cells

Targeting the B-cell receptor (BCR) pathway in chronic lymphocytic leukemia (CLL) with the Bruton Tyrosine Kinase (BTK) inhibitor Ibrutinib has transformed the treatment paradigm of this disease. Ibrutinib is currently indicated for treatment of CLL regardless of the line of therapy. However, ibrutinib is not curative, and relapses secondary to C481S mutation in BTK and gain of function mutations in PLCγ2 (R665W and L845F) are being reported.The protease mucosa-associated lymphoid tissue lymphoma translocation 1 (MALT1) is the active component of the CARD11-BCL10-MALT1 (CBM) signaling complex. CBM mediates NF-κB activation downstream of BTK and PLCγ2 within the BCR pathway, which makes of MALT1 an ideal therapeutic target in ibrutinib-resistant clones. Notably, the chemical compound MI2 (C19H17Cl3N4O3) binds to- and suppresses the protease activity of MALT1, and was found to be active against activated B-cell-like diffuse large B-cell lymphoma. However, the role of MALT1 inhibition in CLL has not been investigated.We studied the efficacy of MI2 against a cohort of CLL samples (N=21), and explored its mechanism of action. PBMCs from patients with CLL were tested against serial dilutions of MI2 (0.125-8μM) for 48 h in 96-well plates, and MTS assay was performed to quantify cell viability. We observed a dose-dependent cytotoxicity in all samples, with an inhibitory concentration at 25% (IC25) < 2μM observed in the majority of the samples. MI2 cytotoxicity was independent of the IGHV mutational status, CD38 expression, cytogenetics, previous therapy status, and MALT1 protein level (immunoblot on purified CLL cells). To study the drug apoptosis and drug selectivity, we examined apoptotic induction in both CLL cells and T-cells of the same patients. PBMCs from five patients with CLL were treated with MI2 for 48 h and compared to untreated control. At the end of the incubation, cells were stained with CD5, CD19, and Annexin-V, then analyzed using flow cytometry. We found that MI2 induced a dose-dependent apoptosis in CLL cells (defined as CD5+/CD19+) in all samples, with only mild toxicity to their corresponding T-cells (T-cells represent a fraction of each patient’s PBMCs defined as CD5+/CD19-). This minimal toxicity to T-cells was not statistically significant when compared to untreated control T-cells, and may reflect a T-cell receptor signaling-independence of circulating T-cells, which are mostly composed of terminally differentiated effectors. To determine whether the induced apoptosis is caspase-dependent, we treated PBMCs of CLL patients (N=5) with MI2 (0.5-4 μM) in the presence or absence of 100μM of the pan-caspase inhibitor z-VAD-fmk for 48 h. We found that z-VAD-fmk completely prevented the induction of apoptosis in CD19+/CD5+ CLL cells as determined by Annexin-V staining (flow cytometry), and decreased MI2-induced PARP cleavage (Immunoblot).To determine the effect of the microenvironment on MI2 toxicity, we cultured primary CLL cells with and without MI2 (0.5-4µM) for 48 h, in the presence or absence of Nurse-Like Cells (NLC) (N=5) or anti-IgM (N=4). NLCs and anti-IgM cross-linking of BCR are in-vitromodels for the protective effect of the microenvironment. Co-culture with NLCs or with anti-IgM improved the viability of the untreated primary CLL samples. Similar to ibrutinib, MI2 continues to be effective against CLL cells in the presence of NLCs or anti-IgM, but higher concentrations are required to achieve the desired cytotoxicity against CLL cells. There was no cytotoxic effect on NLCs.To investigate the effect of MI2 on tumor biology, 1 μg of total RNA from purified CLL cells (treated for 8 h with MI2, N=3; and untreated control, N=3) was subjected to RNA sequencing. Out of 56,650 tested genes, there were 438 genes whose expression changed ≥2-fold at P<0.05 (312 down- and 126 up-regulated), several genes are known NF-κB targets. The observer-independent method, Gene Set Enrichment Analysis (GSEA), clearly identified the canonical NF-κB among of the top affected pathways.Further studies aim to verify the RNA sequencing data at the protein level, to determine MI2 efficacy against ibrutinib-resistant clones in vitro, and against CLL growth in mice in vivo.Supported by Hope Foundation SWOG Early Exploration and Development (SEED) Award. We thank the Louisiana Cancer Research Center (LCRC) biospecimen core and our patients for the donation of samples to make this research possible. DisclosuresNo relevant conflicts of interest to declare.

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.

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.

Looks Like a Protease, Walks Like a Protease…

The protein MALT1 (for mucosa-associated lymphoid tissue lymphoma translocation 1) has sequence similarity to proteases, but its best-characterized signaling role is not derived from protease activity. MALT1 is a component of the signalosome protein complex that transmits signals from the T cell and B cell antigen receptors to the transcriptional regulator NF-κB. In the signalosome, MALT1’s presumed protease activity appears not to be essential to activation of NF-κB, and MALT1 instead contributes to ubiquitination of IκB kinase γ (IKKγ). Two papers now show that the protease catalytic domain is indeed put to good use during T cell activation. Rebeaud et al . show that the adaptor protein Bcl-10 (also part of the signalosome) is a target for MALT1-mediated proteolysis. They went on to develop an inhibitor of MALT1 protease activity and showed that although NF-κB through the T cell receptor did not require MALT1 activity, the protease was necessary for optimal activation of NF-κB. Furthermore, depletion of MALT1 or Bcl-10 with siRNA showed that cleavage of Bcl-10 was required for optimal adhesion of activated T cells to fibronectin. Coornaert et al . discovered another target of MALT1-mediated proteolysis--the A20 protein, an inhibitor of NF-κB signaling pathway that they found was also recruited to the signalosome. A20 has deubiquitinase activity, and one of its targets is IKKγ. The MALT-1-mediated cleavage of A20 may inhibit deubiquitination of IKKγ by lopping off a binding domain of A20 that interacts with IKKγ. Thus, MALT1’s protease activity apparently has at least two effects on immune responses to antigen--inactivation of an inhibitor of the NF-κB signaling pathway and facilitation of integrin-mediated adhesion. McAllister-Lucas and Lucas provide background and commentary. F. Rebeaud, S. Hailfinger, A. Posevitz-Fejfar, M. Tapernoux, R. Moser, D. Rueda, O. Gaide, M. Guzzardi, E. M. Iancu, N. Rufer, N. Fasel, M. Thome, The proteolytic activity of the paracaspase MALT1 is key in T cell activation. Nat. Immunol . 9 , 272-281 (2008). [PubMed] B. Coornaert, M. Baens, K. Heyninck, T. Bekaert, M. Haegman, J. Staal, L. Sun, Z. J. Chen, P. Marynen, R. Beyaert, T cell antigen receptor stimulation induces MALT1 paracaspase-mediated cleavage of the NF-κB inhibitor A20. Nat. Immunol. 9 , 263-271 (2008). [PubMed] L. M. McAllister-Lucas, P. C. Lucas, Finally, MALT1 is a protease! Nat. Immunol. 9 , 231-233 (2008). [PubMed]