Thome Miazza Margot, Associate Professor
Margot Thome studied Biochemistry at the University of Tübingen (Germany) and the University of Arizona (USA), and carried out her PhD work in the laboratory of Oreste Acuto at the Pasteur Institute (Paris, France). As a postdoctoral fellow in the laboratory of Jürg Tschopp at the University of Lausanne (Switzerland), she identified human and viral FLIP proteins as key apoptosis regulators. She was appointed Assistant Professor of the Swiss National Science Foundation at the University of Lausanne in 2004, and became Associate Professor in 2009. Her present work focuses on the study of signaling pathways that control lymphocyte activation and survival and the development of lymphomas.
MOLECULAR MECHANISMS OF LYMPHOCYTE ACTIVATION AND LYMPHOMA DEVELOPMENT
Lymphocytes play a crucial role in the defense against pathogens and tumor cells. One focus of our research is to understand the molecular mechanisms that control the activation of T-lymphocytes, initiated upon triggering of the T-cell antigen receptor by MHC-bound antigen. This leads to the initiation of multiple signaling pathways that regulate changes in cell shape and gene expression that are critical for efficient T-cell activation, proliferation and survival. Another focus of our research is to understand the molecular mechanisms underlying aberrant lymphocyte proliferation and survival that occurs in certain lymphoid tumors (lymphomas).
By uncovering new molecular players and enzymatic activities relevant to these pathways, we aim at identifying possible targets for therapeutic immuno-modulation or treatment of lymphomas.
Signaling pathways relevant for lymphocyte activation and survival
The initiation of the adaptive immune response depends on the recognition of pathogenic substances or tumor-specific molecules (microbial or tumor antigens) by antigen receptors on the lymphocyte cell surface. Antigen recognition leads to formation of a complex of signaling proteins comprising CARMA1, BCL10 and MALT1 (CBM proteins). An important role of CBM proteins is the activation of the transcription factor NF-κB, which controls genes that are essential for lymphocyte proliferation and survival (for recent reviews, see: Thome, 2008; Hailfinger et al., 2009b; Thome et al., 2010). Mutations of the genes encoding CARMA1, BCL10 or MALT1 or their upstream regulators are associated with constitutive CBM-dependent signaling, and the development of human B-cell lymphomas, such as lymphomas of the mucosa-associated lymphoid tissue (MALT lymphomas) and diffuse large B-cell lymphomas (DLBCL).
The main focus of our recent work has been the identification and characterization of a protease activity of MALT1 (Rebeaud et al., 2008), and the demonstration of constitutive MALT1 activity in cells derived from ABC-DLBCL, which critically depend on MALT1 protease activity for growth and survival (Hailfinger et al. 2009). More recently, we have identified RelB as a new substrate for MALT1 (Hailfinger et al., 2011) and identified a new mechanism of MALT1 activation that requires its C-terminal mono-ubiquitination (Pelzer et al., 2013).
MALT1 controls NF-κB activation via its scaffold and protease functions
The transcription factor NF-κB is pivotal to the expression of genes that control lymphocyte activation and the generation of the immune response. In resting lymphocytes, NF-κB family members are present in the cytoplasm in an inactive form, bound to inhibitory κ-B (IκB) proteins. Triggering of the T-cell antigen receptor leads to activation of the IκB kinase (IKK) complex that induces phosphorylation and subsequent degradation of IκB proteins. This allows NF-κB to translocate into the nucleus and to initiate the transcription of genes that control lymphocyte proliferation and survival.
MALT1 contributes to NF-κB activation as a scaffold protein, by binding to the ubiquitin ligase TRAF6, which in turn controls the recruitment and activation of the IKK complex. MALT1 also contributes to NF-κB activation by its protease domain, which has Arg-directed substrate specificity (Rebeaud et al., 2008; Thome et al., 2010). Interestingly, the development of a peptide-based inhibitor of MALT1 has allowed us to show that inhibition of its protease activity impairs NF-κB activation in an IKK-independent manner. Based on these findings, we had predicted the existence of a MALT1 cleavage substrate that affects NF-κB activity independently of the IKK complex.
MALT1-dependent cleavage of RelB controls NF-κB activation in an IKK-independent manner
In a recent study, we have now identified RelB as the MALT1 substrate responsible for the protease-dependent, IKK-independent control of the NF-κB pathway by MALT1 (Hailfinger et al., 2011). We showed that Malt1 cleaves the NF-κB family member RelB after Arg 85, at a conserved LVSR sequence that acts as an optimal MALT1 substrate in vitro. RelB cleavage induced its proteasomal degradation, which promoted DNA binding of RelA- or c-Rel-containing NF-κB complexes. In contrast, overexpression of RelB inhibited expression of canonical NF-κB target genes. Interestingly, RelB was constitutively cleaved in cell lines derived from ABC-DLBCL, and overexpression of RelB led to impaired survival of these diffuse large B-cell lymphoma cell lines, which are characterized by constitutive MALT1 activity. Collectively, these findings support the idea that MALT1 controls NF-κB activation in lymphocytes by both, its scaffold and its protease function (Figure 1). Moreover, our findings provide a rationale for the targeting of MALT1 in immuno-modulation and cancer treatment.
The MALT1 protease activity is controlled by inducible mono-ubiquitination
Our previous work had demonstrated that the protease activity of the paracaspase MALT1 is central to lymphocyte activation and lymphomagenesis, but how the catalytic activity was controlled remained unknown. In a recent study, we have now identified a monoubiquitination of Malt1 on lysine 644 (K644), which activates Malt1 protease function (Pelzer et al., 2013). Monoubiquitinated Malt1 showed increased protease activity, while a ubiquitination-deficient lysine to arginine mutant (K644R) had reduced protease activity correlating with impaired TCR-induced IL-2 induction in activated T cells. Expression of the K644R mutant diminished survival of cells derived from diffuse large B-cell lymphomas of the activated B-cell subtype (ABC DLBCL), which require constitutive Malt1 protease activity for survival. Monoubiquitinated MALT1 preferentially formed dimers in vitro, suggesting that monoubiquitination promotes or stabilizes the formation of catalytically active dimers. Thus, monoubiquitination of Malt1 is essential for its catalytic activation (Figure 2) and the responsible ubiquitin ligase should be an interesting target for immuno-modulation and treatment of ABC DLBCL. Further studies are now targeted at the identification of the enzyme responsible for MALT1 monoubiquitination.
Parts of this work were done in collaboration with the laboratories of Georg Lenz (Charité, Berlin, Germany) and Louis Staudt (National Cancer Institute, Bethesda, MD, USA).
Communique_Eclosion.pdf (12 Kb)
- Cabalzar K, Pelzer C, Wolf A, Lenz G, Iwaszkiewicz J, Zoete V, Hailfinger S, Thome M. Monoubiquitination and Activity of the Paracaspase MALT1 Requires Glutamate 549 in the Dimerization Interface. PLoS One. 2013 Aug 19;8(8):e72051. doi: 10.1371/journal.pone.0072051.
- Nogai H, Wenzel SS, Hailfinger S, Grau M, Kaergel E, Seitz V, Wollert-Wulf B, Pfeifer M, Wolf A, Frick M, Dietze K, Madle H, Tzankov A, Hummel M, Dörken B, Scheidereit C, Janz M, Lenz P,Thome M, Lenz G. IκB-ζ controls the constitutive NF-κB target gene network and survival of ABC DLBCL. Blood. 2013 Jul 18. [Epub ahead of print]. PMID: 23869088.
- Pelzer C, Cabalzar K, Wolf A, Gonzalez M, Lenz G, Thome M. The protease activity of the paracaspase MALT1 is controlled by monoubiquitination. Nat Immunol. 2013 Apr;14(4):337-45. doi: 10.1038/ni.2540. Epub 2013 Feb 17.
- Thuille N, Wachowicz K, Hermann-Kleiter N, Kaminski S, Fresser F, Lutz-Nicoladoni C, Leitges M, Thome M, Massoumi R, Baier G. PKC theta/beta and CYLD are antagonistic partners in the NF-kB and NFAT transactivation pathways in primary mouse CD3+ T lymphocytes. PLoS One. 2013;8(1):e53709. doi: 10.1371/journal.pone.0053709. Epub 2013 Jan 15.
- Wenzel SS, Grau M, Mavis C, Hailfinger S, Wolf A, Madle H, Deeb G, Dörken B, Thome M, Lenz P, Dirnhofer S, Hernandez-Ilizaliturri FJ, Tzankov A and Lenz G. MCL1 is deregulated and mediates therapy resistance in subgroups of diffuse large B-cell lymphoma. Leukemia. 2012 Dec 21. doi: 10.1038/leu.2012.367. [Epub ahead of print]
- Marion S, Mazzolini J, Herit F, Bourdoncle P, Kambou-Pene N, Hailfinger S, Sachse M, Benmerah A, Echard A, Thome M, Niedergang F. The NF-κB signaling protein Bcl10 regulates actin dynamics by controlling the focal delivery of AP1 and OCRL-bearing vesicles. Dev Cell. 2012 Nov 13;23(5):954-67. doi: 10.1016/j.devcel.2012.09.021.
- Mühlethaler-Mottet A, Flahaut M, Bourloud KB, Nardou K, Coulon A, Liberman J, Thome M, Gross N. Individual caspase-10 isoforms play distinct and opposing roles in the initiation of death receptor-mediated tumour cell apoptosis.
Cell Death Dis. 2011 Mar 3;2:e125. doi: 10.1038/cddis.2011.8.
- Hailfinger S, Nogai H, Pelzer C, Jaworski M, Cabalzar K, Charton JE, Guzzardi M, Décaillet C, Grau M, Dörken B, Lenz P, Lenz G, Thome M. Malt1- dependent RelB cleavage promotes canonical NF-κB activation in lymphocytes and lymphoma cell lines. Proc Natl Acad Sci U S A. 2011 Aug 30;108(35):14596-601. doi: 10.1073/pnas.1105020108. Epub 2011 Aug 22.
- Jevnikar Z, Obermajer N, Doljak B, Turk S, Gobec S, Svajger U, Hailfinger S, Thome M, Kos J. Cathepsin X cleavage of the beta2 integrin regulates talin-binding and LFA-1 affinity in T cells. J Leukoc Biol. 2011 Jul;90(1):99-109. doi: 10.1189/jlb.1110622. Epub 2011 Mar 31.
- Schmid DA, Irving MB, Posevitz V, Hebeisen M, Posevitz-Fejfar A, Sarria JC, Gomez-Eerland R, Thome M, Schumacher TN, Romero P, Speiser DE, Zoete V, Michielin O, Rufer N. Evidence for a TCR affinity threshold delimiting maximal CD8 T cell function. J Immunol. 2010 May 1;184(9):4936-46. doi: 10.4049/jimmunol.1000173. Epub 2010 Mar 29.
- Hailfinger S, Lenz G, Ngo V, Posevitz-Fejfar A, Rebeaud F, Guzzardi M, Murga Penas E, Dierlamm J, Chan WC, Staudt LM, Thome M. Essential role of MALT1 protease activity in activated B cell-like diffuse large B-cell lymphoma. Proc Natl Acad Sci U S A. 2009 Nov 24;106(47):19946-51. doi: 10.1073/pnas.0907511106. Epub 2009 Nov 6.
- Thurau M, Marquardt G, Gonin-Laurent N, Weinländer K, Naschberger E, Jochmann R, Alkharsah KR, Schulz TF, Thome M, Neipel F, Stürzl M. Viral inhibitor of apoptosis vFLIP/K13 protects endothelial cells against superoxide-induced cell death. J Virol. 2009 Jan;83(2):598-611. doi: 10.1128/JVI.00629-08. Epub 2008 Nov 5.
- Brenner D, Brechmann M, Rohling S, Tapernoux M, Mock T, Winter D, Lehmann WD, Kiefer F, Thome M, Krammer PH, Arnold R. Phosphorylation of CARMA1 by HPK1 is critical for NF-κB activation in T cells. Proc Natl Acad Sci U S A. 2009 Aug 25;106(34):14508-13. doi: 10.1073/pnas.0900457106. Epub 2009 Aug 11.
- Rebeaud F, Hailfinger S, Posevitz-Fejfar A, Tapernoux M, Moser R, Rueda D, Gaide O, Guzzardi M, Iancu E, Rufer N, Fasel N, Thome M. The proteolytic activity of the paracaspase MALT1 is key in T cell activation. Nat Immunol. 2008 Mar;9(3):272-81. doi: 10.1038/ni1568. Epub 2008 Feb 10.
- Torgler R, Bongfen SE, Romero JC, Tardivel A, Thome M, Corradin G. Sporozoite-Mediated Hepatocyte Wounding Limits Plasmodium Parasite Development via MyD88-Mediated NF-kappaB Activation and Inducible NO Synthase Expression. J Immunol. 2008 Mar 15;180(6):3990-9.
- Pelzer C, Thome M. IKKα takes control of canonical NF-κB activation. Nat Immunol. 2011 Aug 18;12(9):815-6. doi: 10.1038/ni.2082.
- Thome M, Charton J, Pelzer C, Hailfinger S. Antigen receptor signaling to NF-κB via CARMA1, BCL10 and MALT1. Cold Spring Harb Perspect Biol. 2010 Sep;2(9):a003004. doi: 10.1101/cshperspect.a003004. Epub 2010 Aug 4.
- Hailfinger S, Rebeaud F, Thome M. Adapter and enzymatic functions of proteases in T-cell activation. Immunol Rev. 2009 Nov;232(1):334-47. doi: 10.1111/j.1600-065X.2009.00830.x.
- Thome M. Multifunctional roles for MALT1 in T cell activation. Nat Rev Immunol. 2008 Jul;8(7):495-500. doi: 10.1038/nri2338.
|Luca Bonsignore||Ph.D student|
|Katrin Cabalzar||Ph.D student|
|Maike Jaworski||Postdoctoral fellow|
|Zala Jevnikar Rojnik||Postoctoral fellow|
|Mélanie Juilland||Ph.D student|
|Christiane Pelzer||Postdoctoral fellow|
|Virginie Philippe||Postdoctoral fellow|
|Ivana Ubezzi||Ph.D student|