Caspase-8 and c-FLIPL associate in lipid rafts with NF-kappaB adaptors during T cell activation.

Humans and mice lacking functional caspase-8 in T cells manifest a profound immunodeficiency syndrome due to defective T cell antigen receptor (TCR)-induced NF-kappaB signaling and proliferation. It is unknown how caspase-8 is activated following T cell stimulation, and what is the caspase-8 substrate(s) that is necessary to initiate T cell cycling. We observe that following TCR ligation, a small portion of total cellular caspase-8 and c-FLIP(L) rapidly migrate to lipid rafts where they associate in an active caspase complex. Activation of caspase-8 in lipid rafts is followed by rapid cleavage of c-FLIP(L) at a known caspase-8 cleavage site. The active caspase.c-FLIP complex forms in the absence of Fas (CD95/APO1) and associates with the NF-kappaB signaling molecules RIP1, TRAF2, and TRAF6, as well as upstream NF-kappaB regulators PKC theta, CARMA1, Bcl-10, and MALT1, which connect to the TCR. The lack of caspase-8 results in the absence of MALT1 and Bcl-10 in the active caspase complex. Consistent with this observation, inhibition of caspase activity attenuates NF-kappaB activation. The current findings define a link among TCR, caspases, and the NF-kappaB pathway that occurs in a sequestered lipid raft environment in T cells

Selective C-Rel Activation via Malt1 Controls Anti-Fungal TH-17 Immunity by Dectin-1 and Dectin-2

C-type lectins dectin-1 and dectin-2 on dendritic cells elicit protective immunity against fungal infections through induction of TH1 and TH-17 cellular responses. Fungal recognition by dectin-1 on human dendritic cells engages the CARD9-Bcl10-Malt1 module to activate NF-κB. Here we demonstrate that Malt1 recruitment is pivotal to TH-17 immunity by selective activation of NF-κB subunit c-Rel, which induces expression of TH-17-polarizing cytokines IL-1β and IL-23p19. Malt1 inhibition abrogates c-Rel activation and TH-17 immunity to Candida species. We found that Malt1-mediated activation of c-Rel is similarly essential to induction of TH-17-polarizing cytokines by dectin-2. Whereas dectin-1 activates all NF-κB subunits, dectin-2 selectively activates c-Rel, signifying a specialized TH-17-enhancing function for dectin-2 in anti-fungal immunity by human dendritic cells. Thus, dectin-1 and dectin-2 control adaptive TH-17 immunity to fungi via Malt1-dependent activation of c-Rel

Combined Immunodeficiency Due to MALT1 Mutations, Treated by Hematopoietic Cell Transplantation

PURPOSE: A male infant developed generalized rash, intestinal inflammation and severe infections including persistent cytomegalovirus. Family history was negative, T cell receptor excision circles were normal, and engraftment of maternal cells was absent. No defects were found in multiple genes associated with severe combined immunodeficiency. A 9/10 HLA matched unrelated hematopoietic cell transplant (HCT) led to mixed chimerism with clinical resolution. We sought an underlying cause for this patient’s immune deficiency and dysregulation. METHODS: Clinical and laboratory features were reviewed. Whole exome sequencing and analysis of genomic DNA from the patient, parents and 2 unaffected siblings was performed, revealing 2 MALT1 variants. With a host-specific HLA-C antibody, we assessed MALT1 expression and function in the patient’s post-HCT autologous and donor lymphocytes. Wild type MALT1 cDNA was added to transformed autologous patient B cells to assess functional correction. RESULTS: The patient had compound heterozygous DNA variants affecting exon 10 of MALT1 (isoform a, NM_006785.3), a maternally inherited splice acceptor c.1019-2A > G, and a de novo deletion of c.1059C leading to a frameshift and premature termination. Autologous lymphocytes failed to express MALT1 and lacked NF-κB signaling dependent upon the CARMA1, BCL-10 and MALT1 signalosome. Transduction with wild type MALT1 cDNA corrected the observed defects. CONCLUSIONS: Our nonconsanguineous patient with early onset profound combined immunodeficiency and immune dysregulation due to compound heterozygous MALT1 mutations extends the clinical and immunologic phenotype reported in 2 prior families. Clinical cure was achieved with mixed chimerism after nonmyeloablative conditioning and HCT. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10875-014-0125-1) contains supplementary material, which is available to authorized users

Effects of Once-Weekly Exenatide on Cardiovascular Outcomes in Type 2 Diabetes.

Abstract BACKGROUND: The cardiovascular effects of adding once-weekly treatment with exenatide to usual care in patients with type 2 diabetes are unknown. METHODS: We randomly assigned patients with type 2 diabetes, with or without previous cardiovascular disease, to receive subcutaneous injections of extended-release exenatide at a dose of 2 mg or matching placebo once weekly. The primary composite outcome was the first occurrence of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke. The coprimary hypotheses were that exenatide, administered once weekly, would be noninferior to placebo with respect to safety and superior to placebo with respect to efficacy. RESULTS: In all, 14,752 patients (of whom 10,782 [73.1%] had previous cardiovascular disease) were followed for a median of 3.2 years (interquartile range, 2.2 to 4.4). A primary composite outcome event occurred in 839 of 7356 patients (11.4%; 3.7 events per 100 person-years) in the exenatide group and in 905 of 7396 patients (12.2%; 4.0 events per 100 person-years) in the placebo group (hazard ratio, 0.91; 95% confidence interval [CI], 0.83 to 1.00), with the intention-to-treat analysis indicating that exenatide, administered once weekly, was noninferior to placebo with respect to safety (P<0.001 for noninferiority) but was not superior to placebo with respect to efficacy (P=0.06 for superiority). The rates of death from cardiovascular causes, fatal or nonfatal myocardial infarction, fatal or nonfatal stroke, hospitalization for heart failure, and hospitalization for acute coronary syndrome, and the incidence of acute pancreatitis, pancreatic cancer, medullary thyroid carcinoma, and serious adverse events did not differ significantly between the two groups. CONCLUSIONS: Among patients with type 2 diabetes with or without previous cardiovascular disease, the incidence of major adverse cardiovascular events did not differ significantly between patients who received exenatide and those who received placebo. (Funded by Amylin Pharmaceuticals; EXSCEL ClinicalTrials.gov number, NCT01144338 .)

Analysis of B-cell antigen receptor-mediated NF-&kappa;-B activation.

NF-kappaB transcription factors control physiological and pathological immune cell function. The scaffold proteins Bcl10 and Malt1 couple antigen receptor signals to the canonical NF-kappaB pathway. Here, Bcl10 and Malt1 were shown to differentially regulate B cell receptor-induced activation of the NF-kappaB subunits RelA and c-Rel. Bcl10 was essential for the recruitment of IKK into lipid rafts for the activation of RelA and c-Rel, for blocking apoptosis and for inducing division after B cell receptor ligation. In contrast, Malt1 participated in survival signalling but was not involved in IKK recruitment or activation and was dispensable for RelA induction or proliferation. Malt1 selectively activated c-Rel to control a distinct subprogram. These results provide mechanistic insights into B cell receptor-induced survival and proliferation signals and demonstrate the selective control of c-Rel in the canonical NF-kappaB pathway

Malt1 ubiquitination triggers NF-kB signaling upon T-cell activation.

Triggering of antigen receptors on lymphocytes is critical for initiating adaptive immune response against pathogens. T-cell receptor (TCR) engagement induces the formation of the Carma1-Bcl10-Malt1 (CBM) complex that is essential for activation of the IkB kinase (IKK)/NF-kB pathway. However, the molecular mechanisms that link CBM complex formation to IKK activation remain unclear. Here we report that Malt1 is polyubiquitinated upon T-cell activation. Ubiquitin chains on Malt1 provide a docking surface for the recruitment of the IKK regulatory subunit NEMO/IKKgamma. TRAF6 associates with Malt1 in response to T-cell activation and can function as an E3 ligase for Malt1 in vitro and in vivo, mediating lysine 63-linked ubiquitination of Malt1. Multiple lysine residues in the C-terminus of Malt1 serve as acceptor sites for the assembly of polyubiquitin chains. Malt1 mutants that lack C-terminal ubiquitin acceptor lysines are impaired in rescuing NF-kB signaling and IL-2 production in Malt1-/- T cells. Thus, our data demonstrate that induced Malt1 ubiquitination is critical for the engagement of CBM and IKK complexes, thereby directing TCR signals to the canonical NF-kB pathway

Inhibition of MALT1 protease activity is selectively toxic for activated B cell-like diffuse large B cell lymphoma cells.

Diffuse large B cell lymphoma (DLBCL) is the most common type of lymphoma in humans. The aggressive activated B cell-like (ABC) subtype of DLBCL is characterized by constitutive NF-kappa B activity and requires signals from CARD11, BCL10, and the paracaspase MALT1 for survival. CARD11, BCL10, and MALT1 are scaffold proteins that normally associate upon antigen receptor ligation. Signal-induced CARD11-BCL10-MALT1 (CBM) complexes couple upstream events to I kappa B kinase (IKK)/NF-kappa B activation. MALT1 also possesses a recently recognized proteolytic activity that cleaves and inactivates the negative NF-kappa B regulator A20 and BCL10 upon antigen receptor ligation. Yet, the relevance of MALT1 proteolytic activity for malignant cell growth is unknown. Here, we demonstrate preassembled CBM complexes and constitutive proteolysis of the two known MALT1 substrates in ABC-DLBCL, but not in germinal center B cell-like (GCB) DLBCL. ABC-DLBCL cell treatment with a MALT1 protease inhibitor blocks A20 and BCL10 cleavage, reduces NF-kappa B activity, and decreases the expression of NF-kappa B targets genes. Finally, MALT1 paracaspase inhibition results in death and growth retardation selectively in ABC-DLBCL cells. Thus, our results indicate a growth-promoting role for MALT1 paracaspase activity in ABC-DLBCL and suggest that a pharmacological MALT1 protease inhibition could be a promising approach for lymphoma treatment

MALT1 directs B cell receptor&ndash;induced canonical nuclear factor-kappaB signaling selectively to the c-Rel subunit.

NF-kappaB (Rel) transcription factors control physiological and pathological immune cell function. The scaffold proteins Bcl-10 and MALT1 couple antigen-receptor signals to the canonical NF-kappaB pathway and are pivotal in lymphomagenesis. Here we found that Bcl-10 and MALT1 differentially regulated B cell receptor&ndash;induced activation of RelA and c-Rel. Bcl-10 was essential for recruitment of the kinase IKK into lipid rafts for the activation of RelA and c-Rel, for blocking apoptosis and for inducing division after B cell receptor ligation. In contrast, MALT1 participated in survival signaling but was not involved in IKK recruitment or activation and was dispensable for RelA induction and proliferation. MALT1 selectively activated c-Rel to control a distinct subprogram. Our results provide mechanistic insights into B cell receptor&ndash;induced survival and proliferation signals and demonstrate the selective control of c-Rel in the canonical NF-kappaB pathway