Tonic B-Cell-Receptor Signaling in the Germinal Center B-Cell Type of Diffuse Large B-Cell Lymphoma

Multiple types of B-cell lymphoma respond clinically to BTK inhibition, reflecting their dependence on B-cell receptor signaling. The germinal center B-cell subtype of diffuse large B-cell lymphoma resists BTK inhibition, but we found that B-cell receptor elimination in cell lines of this lymphoma type reduced their size and proliferation. Their B-cell receptor signals in a “tonic”, antigen-independent manner, requiring SYK, CD19, and phosphorylation of a specific tyrosine residue in the CD79A immunoreceptor tyrosine-based activation motif domain. The effect of B-cell receptor elimination or inhibition in these lines is proportional to their B-cell receptor surface density and its relative contribution to AKT activity, on which these lines uniformly depend, and is rescued by spontaneous or induced loss of PTEN protein. Biomarker-guided targeting of tonic B-cell receptor signaling may improve treatment of germinal center B-cell lymphoma. Total RNA was extracted from BCR KO cells isolated by FACS sorting 4-7 days after electroporation with chimeric Cas9/gRNA plasmids targeting Ig Heavy hypervariable or constant regions. 2-4 differennt KO replicates were compared to 1-2 replicates of GFP+ FACS sorted cells that had been electroporated in parallel with empty px458 plasmid.