MALT1-dependent cleavage of CYLD promotes NF-κB signaling and growth of aggressive B-cell receptor-dependent lymphomas

Loss of CYLD promotes splenic marginal zone lymphoma

Splenic marginal zone lymphoma (SMZL) is a distinct clinical and pathological entity among marginal zone lymphomas. Genetic and microenvironmental factors leading to aberrant activation of the NF-κB pathway have been implicated in SMZL pathogenesis. CYLD is a negative regulator of NF-κB and other signaling pathways acting as a deubiquitinase of regulatory molecules and has been reported as a tumor suppressor in different types of cancer, including B-cell malignancies. To assess whether CYLD is implicated in the natural history of SMZL, we profiled primary cells from patients with SMZL and SMZL cell lines for CYLD expression and functionality. We report that CYLD is downregulated in patients with SMZL and that CYLD ablation in vitro leads to NF-κB pathway hyperactivation, promoting the proliferation of SMZL cells. In addition, we found that CYLD deficiency was associated with increased migration of SMZL cells in vitro, through CCR7 receptor signaling, and with increased dissemination in vivo. CYLD loss was sufficient to induce BcR signaling, conferring increased resistance to ibrutinib treatment in vitro. In summary, our work uncovers a novel role of CYLD as a key regulator in SMZL pathogenesis, dissemination, and resistance to targeted agents. On these grounds, CYLD could be proposed as a novel target for patient stratification and personalized interventions.

Deciphering the role of the MALT1-RC3H1 axis in regulating GPX4 protein stability

Ferroptosis, a unique form of iron-dependent cell death triggered by lipid peroxidation accumulation, holds great promise for cancer therapy. Despite the crucial role of GPX4 in regulating ferroptosis, our understanding of GPX4 protein regulation remains limited. Through FACS-based genome-wide CRISPR screening, we identified MALT1 as a regulator of GPX4 protein. Inhibition of MALT1 expression enhances GPX4 ubiquitination-mediated degradation by up-regulating the E3 ubiquitin ligase RC3H1. Using both rescue assays and functional genetic screening, we demonstrate that pharmacologically targeting MALT1 triggers ferroptosis in liver cancer cells. Moreover, we show that targeting MALT1 synergizes with sorafenib or regorafenib to induce ferroptosis across multiple cancer types. These findings elucidate the modulatory effects of the MALT1-RC3H1 axis on GPX4 stability, revealing a molecular mechanism that could be exploited to induce ferroptosis for cancer therapy.

VPO1 Promotes Programmed Necrosis of Cardiomyocytes in Rats with Chronic Heart Failure by Upregulating CYLD

BACKGROUND

Chronic heart failure (CHF) is a serious cardiovascular condition. Vascular peroxidase 1 (VPO1) is associated with various cardiovascular diseases, yet its role in CHF remains unclear. This research aims to explore the involvement of VPO1 in CHF.

METHODS

CHF was induced in rats using adriamycin, and the expression levels of VPO1 and cylindromatosis (CYLD) were assessed. In parallel, the effects of VPO1 on programmed necrosis in H9c2 cells were evaluated through cell viability assays, lactate dehydrogenase (LDH) level measurements, and analysis of receptor-interacting protein kinase 1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein (RIPK1/RIPK3/MLKL) pathway-related proteins. The impact of CYLD on RIPK1 protein stability and ubiquitination was also investigated, along with the interaction between VPO1 and CYLD. Additionally, cardiac structure and function were assessed using echocardiography, Hematoxylin-eosin (HE) staining, Masson staining, and measurements of myocardial injury-related factors, including N-terminal prohormone of brain natriuretic peptide (NT-proBNP), Aspartate aminotransferase (AST), LDH, and creatine kinase-myocardial band (CK-MB).

RESULTS

VPO1 expression was upregulated in CHF rats and in H9c2 cells treated with adriamycin. In cellular experiments, VPO1 knockdown improved cell viability, inhibited necrosis and the expression of proteins associated with the RIPK1/RIPK3/MLKL pathway. Mechanistically, VPO1 promoted cardiomyocyte programmed necrosis by interacting with the deubiquitinating enzyme CYLD, which enhanced RIPK1 ubiquitination and degradation, leading to activation of the RIPK1/RIPK3/MLKL signaling pathway. At animal level, overexpression of CYLD counteracted the cardiac failure, cardiac hypertrophy, myocardial injury, myocardial fibrosis, and tissue necrosis caused by VPO1 knockdown.

CONCLUSIONS

VPO1 exacerbates cardiomyocyte programmed necrosis in CHF rats by upregulating CYLD, which activates the RIPK1/RIPK3/MLKL signaling pathway. Thus, VPO1 may represent a potential therapeutic target for CHF.

miR-21-loaded bone marrow mesenchymal stem cell-derived exosomes inhibit pyroptosis by targeting MALT1 to repair chemotherapy-induced premature ovarian insufficiency

Chemotherapy is essential for treating malignant tumors, but it can cause premature ovarian insufficiency (POI). Recent studies suggest that exosomes enriched with miR-21 (miR-21-Exo) may help mitigate POI, though the underlying mechanisms remain largely unexplored. This research investigates how miR-21-Exo influences chemotherapy-induced POI using an experimental model where KGN cells are exposed to cisplatin. We assessed the impact of miR-21 on cellular activity and generated miR-21 overexpressing bone marrow mesenchymal stem cells (miR-21-BMSC) via lentiviral modification. Isolated miR-21-Exo was analyzed for its effects on cellular function. Bioinformatics identified Mucosa-Associated Lymphoid Tissue Lymphoma Translocation Protein 1 (MALT1) as a target of miR-21. We confirmed that miR-21-Exo regulates MALT1 and the NF-κB signaling pathway to prevent cell pyroptosis. Further studies in a rat model demonstrated the therapeutic potential and safety of miR-21-Exo. Overall, our findings highlight a novel strategy for addressing chemotherapy-induced POI by modulating MALT1 and the NF-κB pathway, offering significant therapeutic implications.

Ubiquitin proteasome system in cardiac fibrosis

BACKGROUND

Cardiac fibrosis, including reactive fibrosis and replacement fibrosis, is a common pathological process in most cardiovascular diseases. The ubiquitin proteasome system (UPS) plays an important role in the development of fibrosis by mediating the degradation and synthesis of proteins involved in transforming growth factor-β (TGF-β)-dependent and TGF-β-independent fibrous pathways.

AIM OF REVIEW

This review aims to provide an overview of ubiquitinated and deubiquitinated molecules that participating in cardiac fibrosis, with the ultimate purpose to identify promising targets for therapeutic strategies.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The UPS primarily impacts cardiac fibrosis through modulation of the TGF-β signaling pathway targeting key molecules involved, including the TGF-β receptors, Smad2/3/4 complexes, and inhibitory Smad7, thereby influencing fibrotic processes. In addition to its effect on TGF-β signaling, UPS also regulates pro-fibrotic pathways independent of TGF-β, including p53, AKT1-p38, and JNK1/2. Understanding these pathways is critical due to their involvement in diverse fibrotic mechanisms. The interplay between ubiquitination and deubiquitination of crucial pathways and molecules is pivotal in cardiac fibrosis and represents a promising area for identifying novel therapeutic targets. Different types of cardiac fibrosis involve distinct fibrotic pathways, leading to differential effects of ubiquitin ligases (E3 ligases) and deubiquitinating enzymes (DUBs) across various cardiac fibrotic diseases. Insights into UPS-mediated regulation of cardiac fibrosis provide potential anti-fibrotic therapeutic strategies, emphasizing the importance of targeting UPS components specific to the heart for effective therapy against cardiac fibrosis.

Halting multiple myeloma with MALT1 inhibition: suppressing BCMA-induced NF-κB and inducing immunogenic cell death

ABSTRACT

Because multiple myeloma (MM) poses a formidable therapeutic challenge despite recent progress, exploring novel targets is crucial. Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) emerges as a promising paracaspase with druggable potential, especially unexplored in MM. Our study provided compelling evidence demonstrating a statistically significant elevation of MALT1 expression in human primary MM cells. Moreover, elevated MALT1 expression was associated with a poorer prognosis in MM. Genetic deletion of MALT1 reduced cell growth, colony formation, and tumor growth in vivo. Pharmacological inhibition with 1 μM of a small-molecular MALT1 inhibitor, Mi-2, effectively inhibited cell growth, inducing mitochondria-dependent apoptotic cell death. Mechanistically, MALT1 inhibition disrupted diverse signal transduction pathways, notably impeding nuclear factor κB (NF-κB). Significantly, the inhibition of MALT1 demonstrated a substantial suppression of NF-κB activation by elevating inhibitor of NF-κB, disrupting the nuclear localization of p65 and c-REL. This effect was observed in both the basal state and when stimulated by B-cell maturation antigen, highlighting the pivotal role of MALT1 inhibition in influencing MM cell survival. It was noteworthy that Mi-2 induces properties associated with immunogenic cell death (ICD), as evidenced by increased calreticulin, adenosine triphosphate release, and high-mobility group protein B1 upregulation, consequently triggering ICD-associated immune activation and enhancing CD8+ T-cell cytotoxicity in vitro. In conclusion, our research highlights MALT1 as a promising druggable target for therapeutic interventions in MM, providing insights into its molecular mechanisms in MM progression.

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.

MALT1 substrate cleavage: what is it good for?

CARD-BCL10-MALT1 (CBM) signalosomes connect distal signaling of innate and adaptive immune receptors to proximal signaling pathways and immune activation. Four CARD scaffold proteins (CARD9, 10, 11, 14) can form seeds that nucleate the assembly of BCL10-MALT1 filaments in a cell- and stimulus-specific manner. MALT1 (also known as PCASP1) serves a dual function within the assembled CBM complexes. By recruiting TRAF6, MALT1 acts as a molecular scaffold that initiates IκB kinase (IKK)/NF-κB and c-Jun N-terminal kinase (JNK)/AP-1 signaling. In parallel, proximity-induced dimerization of the paracaspase domain activates the MALT1 protease which exerts its function by cleaving a set of specific substrates. While complete MALT1 ablation leads to immune deficiency, selective destruction of either scaffolding or protease function provokes autoimmune inflammation. Thus, balanced MALT1-TRAF6 recruitment and MALT1 substrate cleavage are critical to maintain immune homeostasis and to promote optimal immune activation. Further, MALT1 protease activity drives the survival of aggressive lymphomas and other non-hematologic solid cancers. However, little is known about the relevance of the cleavage of individual substrates for the pathophysiological functions of MALT1. Unbiased serendipity, screening and computational predictions have identified and validated ~20 substrates, indicating that MALT1 targets a quite distinct set of proteins. Known substrates are involved in CBM auto-regulation (MALT1, BCL10 and CARD10), regulation of signaling and adhesion (A20, CYLD, HOIL-1 and Tensin-3), or transcription (RelB) and mRNA stability/translation (Regnase-1, Roquin-1/2 and N4BP1), indicating that MALT1 often targets multiple proteins involved in similar cellular processes. Here, we will summarize what is known about the fate and functions of individual MALT1 substrates and how their cleavage contributes to the biological functions of the MALT1 protease. We will outline what is needed to better connect critical pathophysiological roles of the MALT1 protease with the cleavage of distinct substrates.

FPFT-2216, a Novel Anti-lymphoma Compound, Induces Simultaneous Degradation of IKZF1/3 and CK1α to Activate p53 and Inhibit NFκB Signaling

Reducing casein kinase 1α (CK1α) expression inhibits the growth of multiple cancer cell lines, making it a potential therapeutic target for cancer. Herein, we evaluated the antitumor activity of FPFT-2216-a novel low molecular weight compound-in lymphoid tumors and elucidated its molecular mechanism of action. In addition, we determined whether targeting CK1α with FPFT-2216 is useful for treating hematopoietic malignancies. FPFT-2216 strongly degraded CK1α and IKAROS family zinc finger 1/3 (IKZF1/3) via proteasomal degradation. FPFT-2216 exhibited stronger inhibitory effects on human lymphoma cell proliferation than known thalidomide derivatives and induced upregulation of p53 and its transcriptional targets, namely, p21 and MDM2. Combining FPFT-2216 with an MDM2 inhibitor exhibited synergistic antiproliferative activity and induced rapid tumor regression in immunodeficient mice subcutaneously transplanted with a human lymphoma cell line. Nearly all tumors in mice disappeared after 10 days; this was continuously observed in 5 of 7 mice up to 24 days after the final FPFT-2216 administration. FPFT-2216 also enhanced the antitumor activity of rituximab and showed antitumor activity in a patient-derived diffuse large B-cell lymphoma xenograft model. Furthermore, FPFT-2216 decreased the activity of the CARD11/BCL10/MALT1 (CBM) complex and inhibited IκBα and NFκB phosphorylation. These effects were mediated through CK1α degradation and were stronger than those of known IKZF1/3 degraders. In conclusion, FPFT-2216 inhibits tumor growth by activating the p53 signaling pathway and inhibiting the CBM complex/NFκB pathway via CK1α degradation. Therefore, FPFT-2216 may represent an effective therapeutic agent for hematopoietic malignancies, such as lymphoma.

SIGNIFICANCE

We found potential vulnerability to CK1α degradation in certain lymphoma cells refractory to IKZF1/3 degraders. Targeting CK1α with FPFT-2216 could inhibit the growth of these cells by activating p53 signaling. Our study demonstrates the potential therapeutic application of CK1α degraders, such as FPFT-2216, for treating lymphoma.

miR-130b regulates B cell proliferation via CYLD-mediated NF-κB signaling

Previous studies have revealed that B cell activation is regulated by various microRNAs(miRNAs). However, the role of microRNA-130b regulating B cell activation and apoptosis is still unclear. In the present study, we first found that the expression of miR-130b was the lowest in Pro/Pre-B cells and the highest in immature B cells. Besides, the expression of miR-130b decreased after activation in B cells. Through the immuno-phenotypic analysis of miR-130b transgenic and knockout mice, we found that miR-130b mainly promoted the proliferation of B cells and inhibited B cell apoptosis. Furthermore, we identified that Cyld, a tumor suppressor gene was the target gene of miR-130b in B cells. Besides, the Cyld-mediated NF-κB signaling was increased in miR-130b overexpressed B cells, which further explains the enhanced proliferation of B cells. In conclusion, we propose that miR-130b promotes B cell proliferation via Cyld-mediated NF-κB signaling, which provides a new theoretical basis for the molecular regulation of B cell activation.

Oncogene-induced MALT1 protease activity drives posttranscriptional gene expression in malignant lymphomas

Constitutive mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) activity drives survival of malignant lymphomas addicted to chronic B-cell receptor signaling, oncogenic CARD11, or the API2-MALT1 (also BIRC3::MALT1) fusion oncoprotein. Although MALT1 scaffolding induces NF-κB-dependent survival signaling, MALT1 protease function is thought to augment NF-κB activation by cleaving signaling mediators and transcriptional regulators in B-cell lymphomas. However, the pathological role of MALT1 protease function in lymphomagenesis is not well understood. Here, we show that TRAF6 controls MALT1-dependent activation of NF-κB transcriptional responses but is dispensable for MALT1 protease activation driven by oncogenic CARD11. To uncouple enzymatic and nonenzymatic functions of MALT1, we analyzed TRAF6-dependent and -independent as well as MALT1 protease-dependent gene expression profiles downstream of oncogenic CARD11 and API2-MALT1. The data suggest that by cleaving and inactivating the RNA binding proteins Regnase-1 and Roquin-1/2, MALT1 protease induces posttranscriptional upregulation of many genes including NFKBIZ/IκBζ, NFKBID/IκBNS, and ZC3H12A/Regnase-1 in activated B-cell-like diffuse large B-cell lymphoma (ABC DLBCL). We demonstrate that oncogene-driven MALT1 activity in ABC DLBCL cells regulates NFKBIZ and NFKBID induction on an mRNA level via releasing a brake imposed by Regnase-1 and Roquin-1/2. Furthermore, MALT1 protease drives posttranscriptional gene induction in the context of the API2-MALT1 fusion created by the recurrent t(11;18)(q21;q21) translocation in MALT lymphoma. Thus, MALT1 paracaspase acts as a bifurcation point for enhancing transcriptional and posttranscriptional gene expression in malignant lymphomas. Moreover, the identification of MALT1 protease-selective target genes provides specific biomarkers for the clinical evaluation of MALT1 inhibitors.

CARD11 gain of function upregulates BCL2A1 expression and promotes resistance to targeted therapies combination in B-cell lymphoma

A strategy combining targeted therapies is effective in B-cell lymphomas (BCL), such as mantle cell lymphoma (MCL), but acquired resistances remain a recurrent issue. In this study, we performed integrative longitudinal genomic and single-cell RNA-sequencing analyses of patients with MCL who were treated with targeted therapies against CD20, BCL2, and Bruton tyrosine kinase (OAsIs trial). We revealed the emergence of subclones with a selective advantage against OAsIs combination in vivo and showed that resistant cells were characterized by B-cell receptor (BCR)-independent overexpression of NF-κB1 target genes, especially owing to CARD11 mutations. Functional studies demonstrated that CARD11 gain of function not only resulted in BCR independence but also directly increased the transcription of the antiapoptotic BCL2A1, leading to resistance against venetoclax and OAsIs combination. Based on the transcriptional profile of OAsIs-resistant subclones, we designed a 16-gene resistance signature that was also predictive for patients with MCL who were treated with conventional chemotherapy, underlying a common escape mechanism. Among druggable strategies to inhibit CARD11-dependent NF-κB1 transduction, we evaluated the selective inhibition of its essential partner MALT1. We demonstrated that MALT1 protease inhibition led to a reduction in the expression of genes involved in OAsIs resistance, including BCL2A1. Consequently, MALT1 inhibition induced synergistic cell death in combination with BCL2 inhibition, irrespective of CARD11 mutational status, both in vitro and in vivo. Taken together, our study identified mechanisms of resistance to targeted therapies and provided a novel strategy to overcome resistance in aggressive BCL. The OAsIs trial was registered at www.clinicaltrials.gov #NCT02558816.

Inactivation of Tumor Suppressor CYLD Inhibits Fibroblast Reprogramming to Pluripotency

CYLD is a tumor suppressor gene coding for a deubiquitinating enzyme that has a critical regulatory function in a variety of signaling pathways and biological processes involved in cancer development and progression, many of which are also key modulators of somatic cell reprogramming. Nevertheless, the potential role of CYLD in this process has not been studied. With the dual aim of investigating the involvement of CYLD in reprogramming and developing a better understanding of the intricate regulatory system governing this process, we reprogrammed control (CYLDWT/WT) and CYLD DUB-deficient (CYLDΔ9/Δ9) mouse embryonic fibroblasts (MEFs) into induced pluripotent stem cells (iPSCs) through ectopic overexpression of the Yamanaka factors (Oct3/4, Sox2, Klf4, c-myc). CYLD DUB deficiency led to significantly reduced reprogramming efficiency and slower early reprogramming kinetics. The introduction of WT CYLD to CYLDΔ9/Δ9 MEFs rescued the phenotype. Nevertheless, CYLD DUB-deficient cells were capable of establishing induced pluripotent colonies with full spontaneous differentiation potential of the three germ layers. Whole proteome analysis (Data are available via ProteomeXchange with identifier PXD044220) revealed that the mesenchymal-to-epithelial transition (MET) during the early reprogramming stages was disrupted in CYLDΔ9/Δ9 MEFs. Interestingly, differentially enriched pathways revealed that the primary processes affected by CYLD DUB deficiency were associated with the organization of the extracellular matrix and several metabolic pathways. Our findings not only establish for the first time CYLD's significance as a regulatory component of early reprogramming but also highlight its role as an extracellular matrix regulator, which has profound implications in cancer research.

Function and targeting of MALT1 paracaspase in cancer

The paracaspase MALT1 has emerged as a key regulator of immune signaling, which also promotes tumor development by both cancer cell-intrinsic and -extrinsic mechanisms. As an integral subunit of the CARD11-BCL10-MALT1 (CBM) signaling complex, MALT1 has an intriguing dual function in lymphocytes. MALT1 acts as a scaffolding protein to drive activation of NF-κB transcription factors and as a protease to modulate signaling and immune activation by cleavage of distinct substrates. Aberrant MALT1 activity is critical for NF-κB-dependent survival and proliferation of malignant cancer cells, which is fostered by paracaspase-catalyzed inactivation of negative regulators of the canonical NF-κB pathway like A20, CYLD and RelB. Specifically, B cell receptor-addicted lymphomas rely strongly on this cancer cell-intrinsic MALT1 protease function, but also survival, proliferation and metastasis of certain solid cancers is sensitive to MALT1 inhibition. Beyond this, MALT1 protease exercises a cancer cell-extrinsic role by maintaining the immune-suppressive function of regulatory T (Treg) cells in the tumor microenvironment (TME). MALT1 inhibition is able to convert immune-suppressive to pro-inflammatory Treg cells in the TME of solid cancers, thereby eliciting a robust anti-tumor immunity that can augment the effects of checkpoint inhibitors. Therefore, the cancer cell-intrinsic and -extrinsic tumor promoting MALT1 protease functions offer unique therapeutic opportunities, which has motivated the development of potent and selective MALT1 inhibitors currently under pre-clinical and clinical evaluation.