CK2β-regulated signaling controls B cell differentiation and function

Abstract

Serine-Threonine kinase CK2 supports malignant B-lymphocyte growth but its role in B-cell development and activation is largely unknown. Here, we describe the first B-cell specific knockout (KO) mouse model of the β regulatory subunit of CK2. CK2βKO mice present an increase in marginal zone (MZ) and a reduction in follicular B cells, suggesting a role for CK2 in the regulation of the B cell receptor (BCR) and NOTCH2 signaling pathways. Biochemical analyses demonstrate an increased activation of the NOTCH2 pathway in CK2βKO animals, which sustains MZ B-cell development. Transcriptomic analyses indicate alterations in biological processes involved in immune response and B-cell activation. Upon sheep red blood cells (SRBC) immunization CK2βKO mice exhibit enlarged germinal centers (GCs) but display a limited capacity to generate class-switched GC B cells and immunoglobulins. In vitro assays highlight that B cells lacking CK2β have an impaired signaling downstream of BCR, Toll-like receptor, CD40, and IL-4R all crucial for B-cell activation and antigen presenting efficiency. Somatic hypermutations analysis upon 4-Hydroxy-3-nitrophenylacetyl hapten conjugated to Chicken Gamma Globulin (NP-CGG) evidences a reduced NP-specific W33L mutation frequency in CK2βKO mice suggesting the importance of the β subunit in sustaining antibody affinity maturation. Lastly, since diffuse large B cell lymphoma (DLBCL) cells derive from GC or post-GC B cells and rely on CK2 for their survival, we sought to investigate the consequences of CK2 inhibition on B cell signaling in DLBCL cells. In line with the observations in our murine model, CK2 inactivation leads to signaling defects in pathways that are essential for malignant B-lymphocyte activation.

CK2β Regulates Hematopoietic Stem Cell Biology and Erythropoiesis

“…Thus, a combination of alterations in cell viability and in differentiation programs could determine the CK2β KO phenotype such as the reduced cellularity of fetal livers. To note, KO embryos also displayed reduction in B mature (B220 + CD19 + ) cells with expansion in percentages of immature pre/pro B population, data that support our previous finding obtained in the Csnk2b fl/fl / CD19 +/Cre KO mouse model 35 . The depletion of mature erythroid compartment (Ter119 + ) in CK2β KO embryos is another cause of reduced fetal liver cellularity.…”

“…Since literature has also widely reported the key role of CK2 in embryogenesis, 32–34 we hypothesized that this kinase might also be essential for the ontogenesis of blood cells. In a recent article published by our group, we have demonstrated the importance of CK2 in B cell commitment towards follicular fate and in the germinal center reaction using mice bearing loxP‐flanked CK2β alleles and expressing the Cre recombinase under the control of the CD19 promoter 35 . In the present work, we crossed the same model of loxP mice with animals expressing the Cre recombinase under the control of the Vav1 promoter, thereby achieving CK2β KO in all the hematopoietic cells.…”

“…To note, KO embryos also displayed reduction in B mature (B220 + CD19 + ) cells with expansion in percentages of immature pre/pro B population, data that support our previous finding obtained in the Csnk2b fl/fl / CD19 +/Cre KO mouse model. 35 The depletion of mature erythroid compartment (Ter119 + ) in CK2β KO embryos is another cause of reduced fetal liver cellularity. We discovered stage-dependent erythroid functions for CK2β.…”

“…In a recent article published by our group, we have demonstrated the importance of CK2 in B cell commitment towards follicular fate and in the germinal center reaction using mice bearing loxP-flanked CK2β alleles and expressing the Cre recombinase under the control of the CD19 promoter. 35 In the present work, we crossed the same model of loxP mice with animals expressing the Cre recombinase under the control of the Vav1 promoter, thereby achieving CK2β KO in all the hematopoietic cells. We focused the analysis on the HSPC and erythroid compartments.…”

Protein kinase CK2α is overexpressed in classical hodgkin lymphoma, regulates key signaling pathways, PD-L1 and may represent a new target for therapy

“…Of interest, our group has recently reported the first B-cell specific knockout mouse of CK2β, showing NOTCH2-mediated increase of marginal zone B cells and a decrease of follicular B cells ( 16 ). In addition, B cells lacking CK2β have an impaired signaling downstream to the B-cell receptor, toll-like receptor and CD40 ( 16 ).…”