Summary Hijacking of the B-cell receptor (BCR) pathway drives chemoresistance in diffuse large B-cell lymphoma (DLBCL). While inhibiting BCR-associated kinases (e.g., ibrutinib) has shown promise in other non-Hodgkin lymphoma subtypes and leukemias, these therapies fail to achieve sustained responses in DLBCL patients. In addition to acquired mutations in the targeted kinases, this disparity is related to the inherent resistance of DLBCL from genetic lesions or up-regulation of non-kinase components that feed into the BCR pathway, such as scaffold and adaptor proteins CARD11 and MYD88. Identifying new strategies to target this oncogenic signaling will advance the knowledge of DLBCL pathobiology and the treatment of patients with this refractory-prone disease. The overall goals of our research program are to provide insight into the deregulation of BCR signaling and develop effective therapeutic approaches to inhibit key molecules in this lymphoma-specific pathway. We recently discovered guanine (G)-rich elements upstream of the CARD11 and MYD88 transcription start sites form G-quadruplex (G4) DNA secondary structures. Stabilization of these structures with small molecules lowered mRNA levels suggesting a regulatory role in gene expression. Furthermore, chromatin immunoprecipitation sequencing (ChIP-seq) revealed CARD11 and MYD88 G4 forming sequences aligned with targeted loci of an enzyme called activation-induced cytidine deaminase (AID), which is implicated in mutation of genes important in DLBCL. Based on this preliminary data, we hypothesize the promoter G4 structures deregulate CARD11 and MYD88 expression via controlling transcription and facilitating mutations, and can serve as targets to silence BCR oncogenic signaling. We will test our hypothesis in the following aims: (1) Identify the mechanism by which the CARD11 and MYD88 promoter G4 structures regulate the BCR pathway, (2) Define the involvement of G4 structures in the mechanism for AID induced CARD11 and MYD88 mutation, and (3) Determine efficacy of silencing CARD11 and MYD88 transcription on tumor growth to develop lead molecules.