Abstract 6986: Oncogenic CARD11 enhances marginal zone B cell survival by potentiating the non-canonical NF-κB pathway

Abstract Dysregulation of antigen receptor-mediated signaling contributes to the oncogenesis of lymphoid malignancies. The activated B cell-like (ABC) subtype of Diffuse Large B cell Lymphoma (DLBCL) is characterized by receptor-independent constitutive activation of the canonical nuclear factor-kappaB (NF-κB) pathway, which is essential for the proliferation and survival of tumor cells. Caspase recruitment domain-containing protein 11 (CARD11) is a scaffolding protein that regulates B and T cell receptor signaling to canonical NF-κB activation downstream for adaptive immune response. Oncogenic gain-of-function (GOF) CARD11 mutations bypass normal pathway regulation and result in a hyperactive CARD11 that signals constitutively. Although present in ~10% of human ABC-DLBCL biopsies, we do not have a complete mechanistic understanding of how CARD11 GOF mutations drive abnormal B cell proliferation to cause lymphoma. We generated a mouse expressing the DLBCL-associated GOF mutation C49Y from the endogenous CARD11 locus. GOF CARD11 was sufficient to specifically drive B cell expansion in the mice with no significant effect on CD4+ or CD8+ T cells or NK cells. Quantification of splenic lymphocytes revealed that CARD11C49Y/C49Y mice had ~5-fold more splenic B cells when compared to CARD11+/+ mice and ~13-fold more marginal zone (MZ) B cells. CARD11C49Y/C49Y MZ B cells proliferated and survived much better than CARD11+/+ following stimulation with αIgM and importantly exhibited significant survivability prior to stimulation. Bulk mRNA sequencing revealed genes uniquely dysregulated in CARD11C49Y/C49Y MZ B cells including those associated with non-canonical NF-κB pathway signaling. CARD11C49Y/C49Y MZ B cells exhibited elevated levels of the p100 precursor NF-kB subunit leading to enhanced production of nuclear p52 following BAFF treatment. CARD11C49Y/C49Y MZ B cells also exhibited elevated levels of TRAF2, TRAF3 and cIAP1/2, components of a complex that degrades the NIK kinase that is responsible in normal cells for inducing p100 processing. Our results reveal an unexpected ability of CARD11 GOF mutants to potentiate the non-canonical NF-κB pathway through p100 accumulation, which likely contributes to the dysregulated B cell expansion observed in DLBCL cases that harbor CARD11 GOF variants. Citation Format: Anushka Ghosh, Joel Pomerantz. Oncogenic CARD11 enhances marginal zone B cell survival by potentiating the non-canonical NF-κB pathway abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6986.