title: A Novel TRAF6 binding site in MALT1 defines distinct mechanisms of NF-kappaB activation by API2middle dotMALT1 fusions.
abstract: The recurrent translocation t(11;18)(q21;q21) associated with mucosa-associated lymphoid tissue (MALT) lymphoma results in the expression of an API2.MALT1 fusion protein that constitutively activates NF-kappaB. The first baculovirus IAP repeat (BIR) domain of API2 and the C terminus of MALT1, which contains its caspase-like domain, are present in all reported fusion variants and interact with TRAF2 and TRAF6, respectively, suggesting their contribution to NF-kappaB signaling by API2.MALT1. Also, the involvement of BCL10 has been suggested via binding to BIR1 of API2 and via its interaction with the immunoglobulin domains of MALT1, present in half of the fusion variants. However, conflicting reports exist concerning their roles in API2.MALT1-induced NF-kappaB signaling. In this report, streptavidin pulldowns of biotinylated API2.MALT1 fusion variants showed that none of the fusion variants interacted with endogenous BCL10; its role in NF-kappaB signaling by API2.MALT1 was further questioned by RNA interference experiments. In contrast, TRAF6 was essential for NF-kappaB activation by all fusion variants, and we identified a novel TRAF6 binding site in the second immunoglobulin domain of MALT1, which enhanced NF-kappaB activation when present in the fusion protein. Furthermore, inclusion of both immunoglobulin domains in API2.MALT1 further enhanced NF-kappaB signaling via intramolecular TRAF6 activation. Finally, binding of TRAF2 to BIR1 contributed to NF-kappaB activation by API2.MALT1, although additional mechanisms involving BIR1-mediated raft association are also important. Taken together, these data reveal distinct mechanisms of NF-kappaB activation by the different API2.MALT1 fusion variants with an essential role for TRAF6.
authors.affiliation: Human Genome Laboratory, Department for Molecular and Developmental Genetics, Flanders Institute for Biotechnology VIB, B-3000 Leuven, Belgium.
authors.forename: Heidi
authors.initials: H
authors.lastname: Noels
authors.forename: Geert
authors.initials: G
authors.lastname: van Loo
authors.forename: Sofie
authors.initials: S
authors.lastname: Hagens
authors.forename: Vicky
authors.initials: V
authors.lastname: Broeckx
authors.forename: Rudi
authors.initials: R
authors.lastname: Beyaert
authors.forename: Peter
authors.initials: P
authors.lastname: Marynen
authors.forename: Mathijs
authors.initials: M
authors.lastname: Baens
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000074018:B-Cell CLL-Lymphoma 10 Protein; D001665:Binding Sites / Q000235:genetics; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics; D002887:Chromosomes, Human, Pair 18 / Q000235:genetics; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000235:genetics / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D018442:Lymphoma, B-Cell, Marginal Zone / Q000235:genetics / Q000378:metabolism*; D000074884:Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 Protein; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D015514:Oncogene Proteins, Fusion; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D015398:Signal Transduction; D047992:TNF Receptor-Associated Factor 2 / Q000235:genetics / Q000378:metabolism; D048029:TNF Receptor-Associated Factor 6 / Q000235:genetics / Q000378:metabolism*; D014178:Translocation, Genetic / Q000235:genetics
chemical_list: C415943:API2-MALT1 fusion protein, human; D048868:Adaptor Proteins, Signal Transducing; D000074018:B-Cell CLL-Lymphoma 10 Protein; C118591:BCL10 protein, human; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C094401:KCNJ6 protein, human; D016328:NF-kappa B; D009363:Neoplasm Proteins; D015514:Oncogene Proteins, Fusion; D047992:TNF Receptor-Associated Factor 2; D048029:TNF Receptor-Associated Factor 6; D020169:Caspases; C400109:MALT1 protein, human; D000074884:Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 Protein