Spontaneous aggregation and novel signalosome organization of BENTA-associated gain-of-function CARD11 mutants in lymphocytes. (IRM5P.641)

Abstract

Abstract We recently described BENTA (B cell Expansion with NF-kB and T cell Anergy), a novel lymphoproliferative disorder caused by germline, gain-of-function mutations in the lymphocyte-specific scaffolding protein CARD11. Normally, antigen receptor (AgR) stimulation induces CARD11 phosphorylation to evoke an active conformation that nucleates a signalosome incorporating BCL10, MALT1, and other proteins required for IkB kinase (IKK) activation and NF-κB nuclear translocation. However, ectopic expression of CARD11 mutants triggers constitutive NF-kB activity in B and T cell lines without AgR stimulation. Here we show that these CARD11 mutants form large, cytosolic protein aggregates with a novel substructure, dubbed mCADS (Mutant CARD11 Dependent Shells). Endogenous mCADS are also detected in B cell lymphomas harboring similar CARD11 mutations. In contrast, WT CARD11 cannot form mCADS -/+ AgR stimulation. Only MALT1 and phospho-IKK are stably colocalized with mCADS, indicative of active, sustained signaling. Surprisingly, mCADS formation requires interaction with BCL10 but not NEMO (IKKg). Our results suggest that gain-of-function CARD11 mutants spontaneously assemble into an active, highly-ordered signalosome that is structurally and functionally distinct from WT CARD11, regardless of AgR ligation. The unique structure and composition of mCADS may represent a novel therapeutic target for treating BENTA or lymphoma without disrupting normal AgR-induced NF-kB activation.