Abstract A56: Spontaneous aggregation and novel signalosome organization of BENTA-associated gain-of-function CARD11 mutants in lymphocytes

Abstract

Abstract Antigen receptor (AgR)-induced NF-κB activation is a critical determinant of lymphocyte growth and survival. However, constitutive NF-κB activity can drive excessive lymphoproliferation and oncogenesis. We recently described a novel human lymphoproliferative disorder designated as BENTA (B cell Expansion with NF-κB and T cell Anergy), caused by germline gain-of-function mutations in the lymphocyte-specific scaffolding protein CARD11. Similar, somatic CARD11 mutations are found in ~10% of activated B cell-type diffuse large B cell lymphomas (ABC-DLBCL). Normally, AgR ligation converts CARD11 into an active conformation that nucleates a large multi-protein signalosome incorporating BCL10, MALT1, and other components that ultimately facilitate activation of IκB kinase (IKK) and nuclear translocation of NF-κB. We have now identified four different heterozygous CARD11 missense mutations (E134G, G123S, G123D, C49Y) in affected patients. Similar to BENTA patient cells and DLBCL tumors, ectopic expression of each mutant triggers constitutive NF-κB activation in B and T cell lines without AgR stimulation. Using confocal microscopy, we now demonstrate that these CARD11 mutants form large, spontaneous perinuclear aggregates with a novel, shell-like substructure. While BCL10 is largely excluded, other signaling components such as MALT1 and phospho-IκB kinase (IKK) are found within or closely colocalized with CARD11 shells, suggesting these aggregates are sites of active signaling. Our results provide the first evidence that gain-of-function CARD11 mutants assemble into a compartmentalized, active signalosome with a distinct structural organization. Further imaging and biochemical analysis of these aggregates will provide new insights into aberrant CARD11 signaling in BENTA patient lymphocytes and DLBCL tumors harboring active CARD11 mutations. Citation Format: Jeffrey Richard Stinson, Andrew L. Snow. Spontaneous aggregation and novel signalosome organization of BENTA-associated gain-of-function CARD11 mutants in lymphocytes. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr A56.