Bcl10 and MALT1, Independent Targets of Chromosomal Translocation in MALT Lymphoma, Cooperate in a Novel NF-κB Signaling Pathway
ABSTRACT At least two distinct recurrent chromosomal translocations have been implicated in the pathogenesis of MALT lymphoma. The first, t(1;14), results in the transfer of the entire Bcl10 gene to chromosome 14 wherein Bcl10 expression is inappropriately stimulated by the neighboring Ig enhancer. The second, t(11;18), results in the synthesis of a novel fusion protein, API2-MALT1. Until now, no common mechanism of action has been proposed to explain how the products of these seemingly unrelated translocations may contribute to the same malignant process. We show here that Bcl10 and MALT1 form a strong and specific complex within the cell, and that these proteins synergize in the activation of NF-kappaB. The data support a mechanism of action whereby Bcl10 mediates the oligomerization and activation of the MALT1 caspase-like domain. This subsequently activates the IKK complex through an unknown mechanism, setting in motion a cascade of events leading to NF-kappaB induction. Furthermore, the API2-MALT1 fusion protein also strongly activates NF-kappaB and shows dependence upon the same downstream signaling factors. We propose a model whereby both the Bcl10.MALT1 complex and the API2-MALT1 fusion protein activate a common downstream signaling pathway that originates with the oligomerization-dependent activation of the MALT1 caspase-like domain.
- SourceAvailable from: Stephen Weeks
[Show abstract] [Hide abstract]
- "Lucas et al.  reported that co-expression of BCL10 resulted in strong MALT1 oligomerization and activation of an NF-κB reporter in 293T cells . We and others had demonstrated that co-expression of BCL10 with MALT1 in 293T cells triggers MALT1 protease activity and cleavage of its substrates A20 and BCL10 , . "
ABSTRACT: Mucosa-associated lymphoid tissue 1 (MALT1) controls antigen receptor-mediated signalling to nuclear factor κB (NF-κB) through both its adaptor and protease function. Upon antigen stimulation, MALT1 forms a complex with BCL10 and CARMA1, which is essential for initial IκBα phosphorylation and NF-κB nuclear translocation. Parallel induction of MALT1 protease activity serves to inactivate negative regulators of NF-κB signalling, such as A20 and RELB. Here we demonstrate a key role for auto-proteolytic MALT1 cleavage in B- and T-cell receptor signalling. MALT1 cleavage occurred after Arginine 149, between the N-terminal death domain and the first immunoglobulin-like region, and did not affect its proteolytic activity. Jurkat T cells expressing an un-cleavable MALT1-R149A mutant showed unaltered initial IκBα phosphorylation and normal nuclear accumulation of NF-κB subunits. Nevertheless, MALT1 cleavage was required for optimal activation of NF-κB reporter genes and expression of the NF-κB targets IL-2 and CSF2. Transcriptome analysis confirmed that MALT1 cleavage after R149 was required to induce NF-κB transcriptional activity in Jurkat T cells. Collectively, these data demonstrate that auto-proteolytic MALT1 cleavage controls antigen receptor-induced expression of NF-κB target genes downstream of nuclear NF-κB accumulation.PLoS ONE 08/2014; 9(8):e103774. DOI:10.1371/journal.pone.0103774 · 3.23 Impact Factor
[Show abstract] [Hide abstract]
- "The protease MALT1 (also known as paracaspase) plays a central role in the antigen receptor-mediated activation of lymphocytes and the pathogenesis of human diffuse large B-cell lymphoma (DLBCL) of the activated B-cell (ABC) subtype , . In resting naïve lymphocytes, MALT1 is present in its catalytically inactive form, constitutively associated with the adaptor protein BCL10 , . Upon antigen receptor triggering, MALT1 and BCL10 form a complex with the scaffold protein CARMA1 (also known as CARD11) ,  that promotes the activation of the transcription factor nuclear factor kappa B (NF-κB). "
ABSTRACT: The mucosa-associated lymphoid tissue protein-1 (MALT1, also known as paracaspase) is a protease whose activity is essential for the activation of lymphocytes and the growth of cells derived from human diffuse large B-cell lymphomas of the activated B-cell subtype (ABC DLBCL). Crystallographic approaches have shown that MALT1 can form dimers via its protease domain, but why dimerization is relevant for the biological activity of MALT1 remains largely unknown. Using a molecular modeling approach, we predicted Glu 549 (E549) to be localized within the MALT1 dimer interface and thus potentially relevant. Experimental mutation of this residue into alanine (E549A) led to a complete impairment of MALT1 proteolytic activity. This correlated with an impaired capacity of the mutant to form dimers of the protease domain in vitro, and a reduced capacity to promote NF-κB activation and transcription of the growth-promoting cytokine interleukin-2 in antigen receptor-stimulated lymphocytes. Moreover, this mutant could not rescue the growth of ABC DLBCL cell lines upon MALT1 silencing. Interestingly, the MALT1 mutant E549A was unable to undergo monoubiquitination, which we identified previously as a critical step in MALT1 activation. Collectively, these findings suggest a model in which E549 at the dimerization interface is required for the formation of the enzymatically active, monoubiquitinated form of MALT1.PLoS ONE 08/2013; 8(8):e72051. DOI:10.1371/journal.pone.0072051 · 3.23 Impact Factor
[Show abstract] [Hide abstract]
- "These include t[14;18] [q32;q21] involving IGH and MALT1, t[11;18] [q21;q21] involving API2 and MALT1, t[1;14] [p22;q32] involving Bcl-10 and IGH, and t[3;14] [p14;q32] involving FOXP1 and IGH . All of these, except the translocation involving FOXP1, lead to formation or up-regulation of proteins (API2-MALT1, MALT1 and bcl-10) that ultimately target the NF-κBA20 gene by stimulating cell proliferation and survival  . "
ABSTRACT: The aetiology of OAL is undefined, although much attention has been recently focused on determining whether OAL is caused by an autoimmune disorder, chronic antigenic stimulation or both. It is becoming evident that infectious agents underlying chronic eye infection, as Chlamydia, may play a role in ocular lymphomagenesis. The high prevalence of Chlamydophila psittaci in patients with OAL has suggested a potential oncogenic role for its tendency to cause chronic and persistent infections, although it has been documented an evident geographical variability and response to antibiotic treatment. For C. pneumoniae, the findings so far obtained are very limited not only for identification in OAL but also for the specific treatment with antibiotics. The recent molecular and cultural evidence of C. trachomatis in patients with OAL, seems to suggest that also this pathogen may contribute to pathogenesis of such lymphoma. The potential appli- cation of bacteria-eradicating therapy at local and systemic level may ultimately result in safer and more efficient therapeutic option for patients affected by these malignancies. Moreover, a close collaboration between experts in oph- thalmology, infectious diseases and hematology will help, in the future, to effectively manage this disease. This review attempts to weigh the currently available evidence regarding the role that Chlamydia play in development of OAL and focuses on patients with OAL observed at our Institution.Journal of Cancer Therapy 03/2013; 4(02):662-677. DOI:10.4236/jct.2013.42082