CK2ß-regulated signaling controls B cell differentiation and function.

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 ß regulatory subunit of CK2. CK2ßKO 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 CK2ßKO 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 CK2ßKO 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 CK2ß 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 CK2ßKO mice suggesting the importance of the ß 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.

CX-4945, a Selective Inhibitor of Casein Kinase 2, Synergizes with B Cell Receptor Signaling Inhibitors in Inducing Diffuse Large B Cell Lymphoma Cell Death.

BACKGROUND: Approximately one third of Diffuse Large B cell Lymphomas (DLBCL) are refractory or relapse. Novel therapeutic approaches under scrutiny include inhibitors of B-cell receptor (BCR) signaling. Protein kinase CK2 propels survival, proliferation and stress response in solid and hematologic malignancies and promotes a "non-oncogene addiction" phenotype. Whether this kinase regulates BCR signaling, being a suitable pharmacological target in DLBCL, is unknown. OBJECTIVE: The objective was to establish if CK2 controls DLBCL cell survival and the BCR signaling, to check if the combination of CK2 inhibitor CX-4945 and BCR blockers Ibrutinib and Fostamatinib is more effectively cytotoxic for DLBCL cells than the single agents and to survey the changes in signaling molecules downstream BCR upon CK2 inhibition. METHOD: A panel of GC and ABC DLBCL cells was treated with CX-4945 and Fostamatinib or Ibrutinib. BCR signaling was assayed by intracellular Ca++ measurement and looking at the phosphorylation of signaling molecules. The effects on cell survival were assessed by flow cytometry, western blot and MTT assays. RESULTS: CK2 inhibition with CX-4945 causes DLBCL cell death. CX-4945 impaired AKT phosphorylation and intracellular Ca++ mobilization upon BCR engagement. The CK2 inhibitor acted synergistically with either the SYK inhibitor Fostamatinib or the BTK inhibitor Ibrutinib in inducing DLBCL cell death. CX-4945 was equally effective in GC and ABC DLBCL subtypes as well as in "double hit" DLBCL cell lines. CONCLUSION: These findings suggest a role for CK2 downstream of the BCR in controlling survival pathways crucial for cell growth of different DLBCL subtypes. Also, the use of CX-4945 in combination with BCR signaling blockers could represent a novel rational therapeutic approach in the DLBCL.

Protein kinase CK2 inhibition down modulates the NF-κB and STAT3 survival pathways, enhances the cellular proteotoxic stress and synergistically boosts the cytotoxic effect of bortezomib on multiple myeloma and mantle cell lymphoma cells.

CK2 is a pivotal pro-survival protein kinase in multiple myeloma that may likely impinge on bortezomib-regulated cellular pathways. In the present study, we investigated CK2 expression in multiple myeloma and mantle cell lymphoma, two bortezomib-responsive B cell tumors, as well as its involvement in bortezomib-induced cytotoxicity and signaling cascades potentially mediating bortezomib resistance. In both tumors, CK2 expression correlated with that of its activated targets NF-κB and STAT3 transcription factors. Bortezomib-induced proliferation arrest and apoptosis were significantly amplified by the simultaneous inhibition of CK2 with two inhibitors (CX-4945 and K27) in multiple myeloma and mantle cell lymphoma cell lines, in a model of multiple myeloma bone marrow microenvironment and in cells isolated from patients. CK2 inhibition empowered bortezomib-triggered mitochondrial-dependent cell death. Phosphorylation of NF-κB p65 on Ser529 (a CK2 target site) and rise of the levels of the endoplasmic reticulum stress kinase/endoribonuclease Ire1α were markedly reduced upon CK2 inhibition, as were STAT3 phospho Ser727 levels. On the contrary, CK2 inhibition increased phospho Ser51 eIF2α levels and enhanced the bortezomib-dependent accumulation of poly-ubiquitylated proteins and of the proteotoxic stress-associated chaperone Hsp70. Our data suggest that CK2 over expression in multiple myeloma and mantle cell lymphoma cells might sustain survival signaling cascades and can antagonize bortezomib-induced apoptosis at different levels. CK2 inhibitors could be useful in bortezomib-based combination therapies.

Protein kinase CK2 protects multiple myeloma cells from ER stress-induced apoptosis and from the cytotoxic effect of HSP90 inhibition through regulation of the unfolded protein response.

PURPOSE: Protein kinase CK2 promotes multiple myeloma cell growth by regulating critical signaling pathways. CK2 also modulates proper HSP90-dependent client protein folding and maturation by phosphorylating its co-chaperone CDC37. Because the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) is central in myeloma pathogenesis, we tested the hypothesis that the CK2/CDC37/HSP90 axis could be involved in UPR in myeloma cells. EXPERIMENTAL DESIGN: We analyzed CK2 activity upon ER stress, the effects of its inactivation on the UPR pathways and on ER stress-induced apoptosis. The consequences of CK2 plus HSP90 inhibition on myeloma cell growth in vitro and in vivo and CK2 regulation of HSP90-triggered UPR were determined. RESULTS: CK2 partly localized to the ER and ER stress triggered its kinase activity. CK2 inhibition reduced the levels of the ER stress sensors IRE1α and BIP/GRP78, increased phosphorylation of PERK and EIF2α, and enhanced ER stress-induced apoptosis. Simultaneous inactivation of CK2 and HSP90 resulted in a synergic anti-myeloma effect (combination index = 0.291) and in much stronger alterations of the UPR pathways as compared with the single inhibition of the two molecules. Cytotoxicity from HSP90 and CK2 targeting was present in a myeloma microenvironment model, on plasma cells from patients with myeloma and in an in vivo mouse xenograft model. Mechanistically, CK2 inhibition led to a reduction of IRE1α/HSP90/CDC37 complexes in multiple myeloma cells. CONCLUSIONS: Our results place CK2 as a novel regulator of the ER stress/UPR cascades and HSP90 function in myeloma cells and offer the groundwork to design novel combination treatments for this disease.