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Myeloid Innate Signaling Pathway Regulation by MALT1 Paracaspase Activity

Published: January 7th, 2019



1Autoimmunity, Transplantation and Inflammation, Novartis Institutes for BioMedical Research
* These authors contributed equally

MALT1 regulates innate immunity but how this occurs remains ill-defined. We used the selective MALT1 paracaspase inhibitor MLT-827 to unravel the contribution of MALT1 to innate signaling downstream of Toll-like or C-type lectin-like receptors, demonstrating that MALT1 regulates the production of myeloid cytokines, and downstream of C-type lectin-like receptors, selectively.

Besides its function in lymphoid cells, which has been addressed by numerous studies, the paracaspase MALT1 also plays an important role in innate cells downstream of pattern recognition receptors. Best studied are the Dectin-1 and Dectin-2 members of the C-type lectin-like receptor family that induce a SYK- and CARD9-dependent signaling cascade leading to NF-κB activation, in a MALT1-dependent manner. By contrast, Toll-like receptors (TLR), such as TLR-4, propagate NF-κB activation but signal via an MYD88/IRAK-dependent cascade. Nonetheless, whether MALT1 might contribute to TLR-4 signaling has remained unclear. Recent evidence with MLT-827, a potent and selective inhibitor of MALT1 paracaspase activity, indicates that TNF- production downstream of TLR-4 in human myeloid cells is independent of MALT1, as opposed to TNF- production downstream of Dectin-1, which is MALT1 dependent. Here, we addressed the selective involvement of MALT1 in pattern recognition sensing further, using a variety of human and mouse cellular preparations, and stimulation of Dectin-1, MINCLE or TLR-4 pathways. We also provided additional insights by exploring cytokines beyond TNF-, and by comparing MLT-827 to a SYK inhibitor (Cpd11) and to an IKK inhibitor (AFN700). Collectively, the data provided further evidence for the MALT1-dependency of C-type lectin-like receptor —signaling by contrast to TLR-signaling.

The paracaspase activity of MALT1 (Mucosa-associated lymphoid tissue lymphoma translocation protein 1) was revealed in 20081,2. Since then, a number of studies have reported its critical contribution to antigen receptor responses in lymphocytes. Genetic models in the mouse as well as pharmacology data support a key role in T cells, in T-cell dependent autoimmunity and in B-cell lymphoma settings3,4. In lymphocytes, MALT1 paracaspase activation occurs upon assembly of a CARD11-BCL10-MALT1 complex5, which is triggered by antigen-r....

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Experiments were conducted according to the guidelines and standards of the Novartis Human Research Ethics Committee.

1. Preparation of Peripheral Blood Mononuclear Cells (PBMCs) from Human Buffy Coats

NOTE: We received buffy coats from healthy volunteers one day after collection, in 50 mL bags. They were provided under informed consent and collected through the Interregionale Blutspende Schweizeriches Rotes Kreuz. We handled them using the p.......

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In myeloid cells, MALT1 relays activation signals downstream of several C-type lectin-like receptors, such as Dectin-1, Dectin-2 and MINCLE6. These pathways rely on (hem)ITAM motif-containing receptors (e.g., Dectin-1) or ITAM motif-containing co-receptors (e.g., FcRγ, for Dectin-2 and MINCLE) that recruit and activate the SYK kinase (Figure 1). This leads to activation of a protein kinase C isoform, namely PKC&#.......

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In this work, we used simple experimental settings to study signaling pathways in human and mouse innate cells, and interrogate their dependency on MALT1 proteolytic function. Expanding on previous work11, our study showed that MALT1 paracaspase activity controls C-type lectin-like receptor induced cytokine production, including TNF-α. In contrast, TLR-4-induced TNF-α was independent of MALT1 in both species. Collectively, these data corroborated the key and selective contribution of the.......

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We thank Elsevier for their authorization (license number 4334770630127) to reproduce here Figure 2A from Unterreiner et al. (2017).


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Name Company Catalog Number Comments
100 µm nylon cell strainer Sigma CLS431752
14 ml Falcon tube BD Falcon 352057
15 mL Falcon tube Falcon 352090
50 mL Falcon tube Falcon 352070
6 well plates Costar 3516
96 well flat-bottom plate, with low evaporation lid Costar 3595
96 well V-bottom plate Costar 734-1798
Ammonium Chloride - NH4Cl Sigma A9434
Assay diluent RD1-W ELISA R&D 895038 Assay diluent
Cell culture microplate, 384 well, black Greiner 781986
Depleted Zymosan Invivogen tlrl-dzn now: tlrl-zyd
Dimethyl sulfoxide Sigma D2650 DMSO
EDTA-Na2 Sigma E5134 Ethylenediaminetetraacetic acid disodium salt dihydrate
Ficoll-Paque Plus GE Healthcare 17-1440-03
gentleMACS C tubes MACS Miltenyi Biotec 130-096-334
gentleMACS dissociator MACS Miltenyi Biotec 130-093-235
GM-CSF Novartis -
Heat-inactivated Fetal bovine serum Gibco 10082 FBS
HTRF hu IL-23 CisBio 62HIL23PEG
HTRF reconstitution buffer CisBio 62RB3RDE 50mM Phosphate buffer, pH 7.0, 0.8M KF, 0.2% BSA
IFN-γ R&D L4516
IL-4 Novartis -
Isoflurane Abbott Forene
Lipopolysaccharides (LPS) Sigma L4391 LPS used in human samples
Lipopolysaccharides Sigma L4516 LPS used in murine samples
Lysis buffer Self-made - 155 mM NH4Cl, 10 mM KHCO3, 1 mM EDTA, pH 7.4
Magnet Stemcell 18001
Microplate, 384 well white Greiner 784075
Monocytes enrichment kit Stemcell 19059
Nalgene Mr. Frosty Cryo 1 °C Freezing Container Nalgene 5100-0001 cooling device (containing Propanol-2)
PBS 1x pH 7.4 [-] CaCl2 [-] MgCl2 Gibco 10010 Phosphate-buffered saline
Penicillin/Streptomycin Gibco 15140 Pen/Strep
Potassium bicarbonate - KHCO3 Sigma P9144
PrestoBlue Invitrogen A13262 Resazurin solution for viability assessment
Propanol-2 Merck 1.09634
Read buffer MesoScale Discovery R92TC-3 Tris-based buffer containing tripropylamine
Recovery cell culture freezing medium Gibco 12648-010 freezing medium
Roswell Park Memorial Institute Medium (RPMI) with Glutamax Gibco 61870 + 10% FBS for iMoDCs
+ 10% FBS + 1 mM Sodium Pyruvate + 100 U/mL Pen/Strep + 5 µM β-mercaptoethanol for human PBMCs and monocytes
+ 10% FBS + Pen/Strep + 5 µM β-mercaptoethanol for murine splenocytes
Separation buffer Self-made - PBS pH 7.4 + 2% FBS + 1 mM EDTA pH 8.0
Sodium Pyruvate Gibco 11360
Trehalose-6,6-dibehenate Invivogen tlrl-tdb TDB
Tween 20 Sigma P7949 Polysorbate 20
UltraPure 0.5 M EDTA pH 8.0 Invitrogen 15675 Ethylenediaminetetraacetic acid
Viewseal sealer Greiner BioOne 676070
V-PLEX Proinflammatory Panel 1 Human Kit MesoScale Discovery K15049D electrochemiluminescent multiplex assay (IL-1β, TNF-α, IL-6, IL-8)
β-Mercaptoethanol Gibco 31350

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