Protein kinase CK2: analysis of its role in acute myeloid leukemia and conditional KO in mouse hematopoiesis

Hematopoiesis is a tightly controlled, hierarchically organized developmental process whereby hematopoietic stem cells (HSC) give rise to highly specialized, differentiated blood cells. HSC are characterized by the capacity of both self-renewing and differentiating in downstream committed hematopoietic progenitor cells. In vertebrates, hematopoiesis in embryonic and fetal life occurs in primitive hematopoietic organs whereas in the adult organism the definitive site of blood cell production is the bone marrow (BM). HSC are quiescent cells that reside most of the time in G0-G1 phases of the cell cycle, dividing during their lifespan as much as it is needed to maintain their own pool and give rise to committed precursors. Leukemia formation is characterized by the block of this process and accumulation of immature cells in the bone marrow and peripheral blood. In particular, acute myeloid leukaemia (AML) is characterized by the accumulation of large numbers of abnormal cells that fail to differentiate into functional mature blood cells. Leukemic blasts have a limited, exhaustible proliferative potential, suggesting that, in order to maintain leukemia growth, a small subpopulation of leukemic stem cells (LSCs) must display an inexhaustible proliferative capacity and self-renewal potential. No definitive proof of LSCs was available, however, until Dick and colleagues showed that the engraftment of NOD/SCID mice with primary AML samples could only be accomplished using cells that were phenotypically similar to normal hematopoietic stem cells (HSCs) by expressing CD34 and lacking markers of lineage commitment such as CD38 . HSCs and LSCs share common features: self-renewal, the capacity to differentiate, resistance to apoptosis, and limitless proliferative potential. The pathway regulating these functional properties can be categorized into self-renewal, developmental, and miscellaneous pathways, each of which is governed by a distinct set of critical genes that have emerged from molecular profiling and can be associated with stemness. In particular Wingless (Wnt)/β catenin and PI3K/AKT pathways are crucial for the control of both HSCs and LSCs biology, because they regulate proliferation, self renewal and differentiation of HSCs and they are involved in maintenance of LSCs. Phosphorylation is one of the molecular mechanism responsible for the signal transduction modulation of these two pathways and some molecules belonging to these pathways are phosphorylated by serin-threonin kinase CK2. Thus, this protein can have an important role in the biology of both HSCs and LSCs. CK2 is a pleiotropic and constitutive activated kinase, which has a tetrameric structure composed by two alpha catalytic subunits and two beta regulatory subunits, but these two components can work also separately. CK2 is essential for cell survival and proliferation, and is more and more evident its involvement in various aspects of tumor transformation. High levels of CK2 are found in different tumor type such as breast, lung, kidney cancer and also blood cancer. CK2 promotes the activity of proto-oncogenes (c-myc, C-Jun, A-Raf), drives cell cycle progression, stimulates beta-catenin activity, inhibits the onco-suppressors p53, PML and PTEN, and it can exert an anti-apoptotic effect through the inhibition of caspase activity. For this reasons, the principal aim of our research project is obtaining experimental evidence of a role of CK2 in normal hematopoiesis and in LSCs through the analysis of AML cell lines and samples collected from patients, and of a conditional knockout mouse model for CK2β in the hematopoietic system. As far as the role of CK2 in the hematopoiesis is concerned, our conditional KO mouse model for CK2β in the hematopoietic compartment, demonstrate that the regulatory subunit of CK2 has an important role in hematopoiesis. In particular, the KO of CK2β induces an impairment in hematopoiesis, especially in erythropoiesis. However, CK2β KO seems not to influence the HSCs pool but instead the hematopoietic progenitors. As far as the analysis of LSCs from AML samples, our analysis performed both on AML samples derive from patients and on Kasumi-1 cell line demonstrated that CK2 does not affect the Wnt/ β catenin and HH pathways, whereas it is able to modulate the PI3K/AKT pathway. Moreover, we have demonstrated that CK2 is important in LSCs survival as its inhibition increases the apoptosis and potentiates the effects of Daunorubicin, a drug currently used for AML treatment in clinic. Taken together, all our results indicate that CK2 possesses an important role both in hematopoiesis and in the biology of LSCs

Protein kinase CK2: analysis of its role in acute myeloid leukemia and conditional KO in mouse hematopoiesis

Hematopoiesis is a tightly controlled, hierarchically organized developmental process whereby hematopoietic stem cells (HSC) give rise to highly specialized, differentiated blood cells. HSC are characterized by the capacity of both self-renewing and differentiating in downstream committed hematopoietic progenitor cells. In vertebrates, hematopoiesis in embryonic and fetal life occurs in primitive hematopoietic organs whereas in the adult organism the definitive site of blood cell production is the bone marrow (BM). HSC are quiescent cells that reside most of the time in G0-G1 phases of the cell cycle, dividing during their lifespan as much as it is needed to maintain their own pool and give rise to committed precursors. Leukemia formation is characterized by the block of this process and accumulation of immature cells in the bone marrow and peripheral blood. In particular, acute myeloid leukaemia (AML) is characterized by the accumulation of large numbers of abnormal cells that fail to differentiate into functional mature blood cells. Leukemic blasts have a limited, exhaustible proliferative potential, suggesting that, in order to maintain leukemia growth, a small subpopulation of leukemic stem cells (LSCs) must display an inexhaustible proliferative capacity and self-renewal potential. No definitive proof of LSCs was available, however, until Dick and colleagues showed that the engraftment of NOD/SCID mice with primary AML samples could only be accomplished using cells that were phenotypically similar to normal hematopoietic stem cells (HSCs) by expressing CD34 and lacking markers of lineage commitment such as CD38 . HSCs and LSCs share common features: self-renewal, the capacity to differentiate, resistance to apoptosis, and limitless proliferative potential. The pathway regulating these functional properties can be categorized into self-renewal, developmental, and miscellaneous pathways, each of which is governed by a distinct set of critical genes that have emerged from molecular profiling and can be associated with stemness. In particular Wingless (Wnt)/β catenin and PI3K/AKT pathways are crucial for the control of both HSCs and LSCs biology, because they regulate proliferation, self renewal and differentiation of HSCs and they are involved in maintenance of LSCs. Phosphorylation is one of the molecular mechanism responsible for the signal transduction modulation of these two pathways and some molecules belonging to these pathways are phosphorylated by serin-threonin kinase CK2. Thus, this protein can have an important role in the biology of both HSCs and LSCs. CK2 is a pleiotropic and constitutive activated kinase, which has a tetrameric structure composed by two alpha catalytic subunits and two beta regulatory subunits, but these two components can work also separately. CK2 is essential for cell survival and proliferation, and is more and more evident its involvement in various aspects of tumor transformation. High levels of CK2 are found in different tumor type such as breast, lung, kidney cancer and also blood cancer. CK2 promotes the activity of proto-oncogenes (c-myc, C-Jun, A-Raf), drives cell cycle progression, stimulates beta-catenin activity, inhibits the onco-suppressors p53, PML and PTEN, and it can exert an anti-apoptotic effect through the inhibition of caspase activity. For this reasons, the principal aim of our research project is obtaining experimental evidence of a role of CK2 in normal hematopoiesis and in LSCs through the analysis of AML cell lines and samples collected from patients, and of a conditional knockout mouse model for CK2β in the hematopoietic system. As far as the role of CK2 in the hematopoiesis is concerned, our conditional KO mouse model for CK2β in the hematopoietic compartment, demonstrate that the regulatory subunit of CK2 has an important role in hematopoiesis. In particular, the KO of CK2β induces an impairment in hematopoiesis, especially in erythropoiesis. However, CK2β KO seems not to influence the HSCs pool but instead the hematopoietic progenitors. As far as the analysis of LSCs from AML samples, our analysis performed both on AML samples derive from patients and on Kasumi-1 cell line demonstrated that CK2 does not affect the Wnt/ β catenin and HH pathways, whereas it is able to modulate the PI3K/AKT pathway. Moreover, we have demonstrated that CK2 is important in LSCs survival as its inhibition increases the apoptosis and potentiates the effects of Daunorubicin, a drug currently used for AML treatment in clinic. Taken together, all our results indicate that CK2 possesses an important role both in hematopoiesis and in the biology of LSCs.L'ematopoiesi è un processo fisiologico, finemente e strettamente controllato, attraverso il quale si ha la produzione di tutte le cellule mature del sangue a partire da una piccola popolazione di cellule staminali, denominate cellule staminali ematopoietiche (HSC). Le HSC si caratterizzano per la loro capacità di auto-rinnovarsi e di differenziare in cellule progenitrici maggiormente differenziate. Nei vertebrati, l'ematopoiesi viene suddivisa in primitiva e definitiva: la prima avviene negli organi ematopoietici primitivi, mentre la seconda risiede nel midollo osseo delle ossa lunghe. Le HSC sono cellule quiescenti, che per la maggior parte della loro vita si trovano nello stadio G0/G1 del ciclo cellulare, dividendosi solamente lo stretto necessario per auto mantenersi e per dare origine ai progenitori in grado poi di differenziare nelle cellule ematiche mature. La formazione di una leucemia è caratterizzata dal blocco di questo processo e dall'accumulo di cellule immature nel midollo osseo e nel sangue periferico. In particolare la leucemia mieloide acuta (AML) si caratterizza per l'accumulo di un gran numero di cellule anomale (blasti) incapaci di completare il processo di differenziamento in cellule mature del sangue. I blasti leucemici si caratterizzano per la loro limitata capacità proliferativa, e questo suggerisce che, per mantenere la crescita del clone leucemico, sia necessaria la presenza di una piccola popolazione di cellule in grado di auto rinnovarsi e proliferare. Questa popolazione viene definita come cellule staminali leucemiche (LSC). La prova definitiva dell'esistenza delle LSC è stata fornita dagli studi condotti da Jonh Dick e colleghi in un modello di xenotrapianto in topi NOD/SCID, nei quali venivano introdotte cellule derivate da pazienti affetti da AML e aventi un fenotipo simile alle HSC normali (queste cellule infatti esprimono sulla loro superficie il marcatore CD34 ma mancano del marker CD38 e di tutti i marcatori di linea, come le cellule staminali ematopoietiche normali). HSC e LSC posseggono caratteristiche comuni, quali la capacità di auto- rinnovarsi (self-renewal), di differenziare, di resistere all'apoptosi e un potenziale di proliferazione illimitato. Tutte queste proprietà funzionali sono regolate a livello molecolare da molteplici vie del segnale, che vengono generalmente raggruppate nelle seguenti categorie: vie del segnale del self-renewal, dello sviluppo e miscellanei, ciascuno dei quali è controllato da un set distinto di geni il cui ruolo nel controllo e mantenimento della staminalità è stato determinato con una serie di studi di profiling molecolare. Tra queste vie del segnale, le vie di Wnt/ β catenina, Hedgehog e PI3K/AKT posseggono un ruolo cruciale nel controllo della biologia sia delle LSC che delle HSC, dato che sono coinvolte nella regolazione dei processi di proliferazione, auto rinnovamento e differenziamento. Uno dei meccanismi molecolari responsabile della modulazione della trasduzione del segnale di queste vie è la fosforilazione, e alcune molecole appartenenti a queste vie sono fosforilate dalla proteina chinasi CK2. Quindi questa proteina potrebbe rivestire un ruolo importante nella biologia sia delle HSC e delle LSC. CK2 è una serin- treonin chinasi pleiotropica e costitutivamente attiva, che possiede una struttura tetramerica, composta da due subunità α ad attività catalitica e da due subunità β con attività regolatoria, ma questi due componenti possono lavorare anche indipendentemente l'una dall'altra. CK2 è essenziale per la sopravvivenza cellulare e proliferazione, ed è sempre più evidente il suo coinvolgimento in vari aspetti della formazione neoplastica. Infatti, elevati livelli di CK2 sono stati riscontrati in vari tipi di tumore, come il tumore al seno, al polmone, al rene ed ematologici. CK2 infatti promuove l'attività di proto-oncogeni (c-myc, C-Jun, A-Raf), regola la progressione del ciclo cellulare, stimola l'attività di β catenina , inibisce gli onco-soppressori p53, PML e PTEN e può esercitare un effetto anti-apoptotico attraverso l'inibizione delle caspasi. Con il presente progetto di dottorato abbiamo pertanto cercato di ottenere prove sperimentali del ruolo svolto da CK2 sia nell'ematopoiesi normale, mediante lo studio di un modello murino di KO condizionale di CK2β nel tessuto ematopoietico, che nella condizione patologica di leucemia mieloide acuta, mediante lo studio di 10 casi di pazienti affetti da AML e con l'ausilio della linea cellulare Kasumi-1. Per quanto concerne lo studio del ruolo di CK2 nell'ematopoiesi normale, il nostro modello di KO condizionale per CK2β nell'intero sistema ematopoietico ci ha permesso di determinare il ruolo fondamentale che tale proteina riveste in tale processo. In particolare il KO per CK2β ha un fenotipo letale, in quanto la mancanza di CK2β causa un grave deficit dell'ematopoiesi, in particolare nel processo di eritropoiesi. Tuttavia, Tra le popolazioni analizzate solo i progenitori ematopoietici sembrano risentire del KO di CK2β, mentre le HSC non sembrano subire alterazioni nei topi KO. Per quanto riguarda invece lo studio del ruolo di CK2 nelle cellule staminali leucemiche, l'analisi affettuata sia su campioni prelevati da pazienti affetti da LMA che sulla linea cellulare Kasumi-1 ha evidenziato come CK2 sia in grado di modulare l'attività della via del segnale di PI3K/AKT, mentre le vie di Hedgehog e Wnt/ β catenina non sembrano influenzate in modo rilevante da CK2. Inoltre, studi condotti combiando l'inibitore di CK2, CX-4945, da solo o in combinazione con Daunorubicina (un chemioterapico correntemente usato nella terapia della LMA), ha evidenziato come la mancanza dell'attività di CK2, non solo aumenti il tasso di apoptosi nelle LSC ma sia in grado di potenziare l'effetto citotossico della Daunorubicina, rendendole maggiormente sensibili all'azione del farmaco. Concludendo, i risultati elencati sopra dimostrano come CK2 possegga un ruolo essenziale sia nell'ematopoiesi che nella biologia delle LSC

Analysis of Wnt and Hedgehog Pathways Regulating Protein Kinases CK1 and CK2 in Acute Myeloid Leukemia Cells and Stem Cells: Correlation with the Expression of Wnt and Hedgehog Targets and Biological and Clinical Features

Background. Leukemia stem cells (LSC) constitute the reservoir of acute and chronic leukemias, from which the relapse of the disease takes origin. The Wnt/\u3b2catenin and the Hedgehog (Hh) signaling pathways regulate the balance between self-renewal and commitment of both normal hematopoietic stem cells (HSC) and LSC. Serine-Threonine protein kinases CK1 and CK2 phosphorylate members of Wnt and Hh and are therefore potential regulators of HSC and LSC biology; however, their function in HSC and LSC is unknown. Purpose. In the present work we have investigated the mRNA and protein levels of CK1 and CK2 in acute myeloid leukemia (AML) blasts and LSC isolated from patients. We have also integrated the expression data of CK1 and CK2 with the expression data of Wnt and Hh signaling pathways gene targets and with biological and clinical parameters of a group of AML patients and cell lines. We also tested the effects on the growth of AML blasts of CK1 and CK2 small chemical inhibitors. The aim of this study was to gain insights into the function of these pivotal protein kinases and on their expression levels relative to biological, clinical and prognostic variables that dictate the outcome of AML patients. Methods. mRNA was extracted from HSC and FACS-sorted LSC (as defined as Lineage- CD34+ CD38- CD123+ CD90+); proteins were obtained from the bulk of blasts from fifteen AML patients. Quantitative RT-PCR was employed to assess mRNA levels of: CK1\u3b1, CK1\u3b3, CK2\u3b1 (catalytic) and CK2\u3b2 (regulatory subunit); Lef1, FoxO1, FoxO3, CyclinD1 (Wnt targets); Ptch, Gli1, Gli2, Gli3, Bmi1 (Hh targets); western blot analysis was performed to determine CK1\u3b1, CK2\u3b1, CK2\u3b2, p53, phospho-Ser529 NF-\u3baB and phospho-Ser13 Cdc37 (two direct CK2 target sites) protein levels. Normal CD34+ bone marrow cells were used as controls. CK2 chemical inhibitors (CX4945 and tTBB) were assayed on LSC and AML cells. Results. CK1\u3b1, CK2\u3b1 and CK2\u3b2 mRNA and proteins were found overexpressed in LSC and in AML blasts. CK1\u3b3 mRNA levels were barely detectable. Notably, some AML cases displayed low levels of CK2\u3b2 but high levels of CK2\u3b1, indicating a possible CK2\u3b2-independent function of CK2\u3b1. FoxO1, FoxO3 mRNAs were found upregulated while Lef1 and CyclinD1 ones were found slightly and Axin2 one strongly diminished, respectively. Ptch, Smo, Gli1, Gli2 and Gli3 mRNAs were unchanged or reduced, while we observed a strong upregulation of that of Bmi1. A correlation between the overexpression of CK1\u3b1 and CK2 and high-risk cytogenetic groups was observed. Also, in most of CK2\u3b1 high-expressing cases, TP53 was found downregulated, while phospho-Ser529 p65 upregulated. Importantly, inhibition of CK2 with selective compounds caused AML cell and LSC growth arrest, a restoration of TP53 and a downregulation of phospho-Ser529-NF-kB p65 and phospho-Ser13 Cdc37 protein levels. Conclusions. The present study is the first to report on the expression of CK1 and CK2 kinases in normal HSC and LSC. CK1 (\u3b1) and CK2 (\u3b1 and \u3b2) mRNA and protein levels were higher in LSC (especially from high risk groups) than in HSC. CK1\u3b3 mRNA levels were low. Wnt and Hh pathways genes were differentially upregulated pointing to a gene specific LSC-associated function. Moreover, our data with CK2 inhibitors suggest that CK2 could be a suitable therapeutic target to eradicate residual AML LSCs. Future research will assess more in depth the in vivo functional role of CK1 and CK2 in HSC and LSC

CK2 Kinase Inhibitors Display Anti-Myeloma Effects and Antagonize Osteoclast Activity in Models of Multiple Myeloma Bone Marrow Microenvironment

Background. Multiple myeloma (MM) plasma cell growth in the bone marrow (BM) microenvironment is fueled by survival signals delivered by the surrounding non-malignant cells (stromal and other types) and through contacts with the extracelllar matrix. Interactions of MM cells with osteoclasts and osteoblasts generate a milieu, in which bone resorption and bone loss occur more rapidly than bone deposition. Novel agents, such as bortezomib and lenalidomide, which target the MM BM microenvironment, have shown unprecedented anti-myeloma efficacy in part due to their ability to somewhat revert these microenvironmental alterations. However, often resistance occurs also to novel drugs and the disease progresses. We have described that targeting protein kinase CK2 with chemical inhibitors or RNA interference causes MM cell death, increases the sensitivity to chemotherapeutics and compromises the NF-\u3baB and STAT3 activity (Piazza FA et al. 2006, Blood; 108: 1698). We also found that CK2 inhibitors synergize with Hsp90 inhibitors (Manni S et al. 2012, Clinical Cancer Res; 18: 1888) and bortezomib (Manni S et al., Blood (2011 ASH Annual Meeting Abstracts); 118; 1849) in inducing MM cell death. Moreover, a phase I clinical trial is ongoing in USA (ID: NCT01199718) testing the oral CK2 inhibitor CX4945 (Cylene Pharmaceuticals, CA, USA) in MM patients. Purpose. We investigated whether and how CK2 inhibition with ATP-competitive CX4945 and tTBB inhibitors could affect the growth of MM cells and of osteoprogenitors in models of BM microenvironemnt. The aim of the study was to provide further insights into the mechanism of action of CK2 inhibitors also in the MM microenvironment, in particular on the stromal cell-mediated MM cell survival and on the unbalanced bone metabolism. We ultimately aimed at generating original data useful for the design of novel rational combination therapies incorporating CK2 inhibitors in the therapy of MM and of MM-bone disease. Methods. MM plasma cells from patients and MM cell lines were cultured in the presence of BM stromal cells obtained from MM patients or BM stromal cell lines or in the presence of osteoclasts. ATP-competitive CK2 inhibitors were added to the co-cultures or to cultures of osteoblast cell lines or progenitors. Cell growth was evaluated with different means and signaling pathways were studied in MM plasma cells and in the stromal cells. NF-\u3baB target gene expression and DNA binding was tested with microplate arrays. For osteoclast generation, CD14+ peripheral blood monocytes were stimulated in alpha-MEM medium with 10% FBS plus RANKL (60ng/ml) plus M-CSF (25ng/ml) for 28 days; early-osteoblasts colonies were obtained from BM cells stimulated under appropriate conditions. Results. CK2 inhibition with CX4945 or tTBB caused apoptosis of MM cells (either freshly isolated from patients or cell lines) cultured on patient-derived mesenchymal stromal cells (MSC) or on the BM stromal cell line HS-5. The inhibitors did not significantly affect MSC viability. A reduction of NF-\u3baB activity evaluated in MM cells was found upon CK2 inhibition, with a parallel reduction of the production of NF-\u3baB-dependent cytokines. When assayed on osteoprogenitors, CX4945 displayed an inhibitory effect on osteoclast formation from CD14+ monocytes even at low concentrations (1 \u3bcM up to 7 \u3bcM, comparable with the effects of zolendronate 1 \u3bcM), whereas it inhibited the formation of osteoblasts from BM colonies at day 14 at fairly higher concentrations (>5 \u3bcM). Moreover, CX4945 inhibited osteoblast proliferation at even higher concentration (>7.5 \u3bcM). The anti-myeloma effect of CK2 inhibitors was present also when MM cells (INA-6 cell line) were cultured in the presence of osteoclasts generated from CD14+ monocytes. Conclusions. Our study shows that inhibition of CK2 could profoundly affect the growth of MM cells in models of BM microenvironment while substantially sparing the normal cellular stromal counterparts and osteoblasts and suggests that CK2 inhibitors could be exploited to target the hyperactivity of osteoclast seen in MM bone disease

Protein kinase CK2\u3b2 regulates peripheral B cell development

Serine-threonine kinase CK2 is involved in oncogenesis of B-cell derived tumors chronic lymphocytic leukemia and multiple myeloma. To gain insights into its role in B-lymphocytes, we generated CK2\u3b2 conditional knockout mice in B-cells. Non B-cell lineages were normal in CD19-CRE CK2\u3b2flox/flox mice. In the bone marrow, CD19-CRE CK2\u3b2flox/flox mice displayed a reduction of B-cells and the B220high IgMhigh recirculating population was found dramatically reduced. B-cell progenitors were apparently not affected by CK2\u3b2 loss. On the contrary, B220+ CD19+ B-cells in peripheral blood, lymph-nodes, spleen and peritoneal cavity were markedly reduced. However, splenic IgDlow IgMhigh B-cell subset was reduced whereas we observed an increase of the IgDhigh IgMlow population, indicating an imbalance between the frequency of follicular (FO) and marginal zone (MZ) B-cells. Detailed FO and MZ B-cell populations analysis showed that FO B-cells were reduced by approximately 35-40% (from 72% to 45%), whereas MZ B-cells were increased up to three folds (from 8.5% to 23%). Histological analysis of CD19-CRE CK2\u3b2flox/flox spleens revealed a reduction of the size of follicles, absence of spontaneous germinal centers and an expansion of the interfollicular-marginal zone areas. In vitro class switch recombination assays demonstrated a moderate impairment in IgG1 and IgG3 class switch. In vitro cell cycle analysis experiments suggested an impairment in G1-S and S-G2 transition of CD19-CRE CK2\u3b2flox/flox B cells. Results of in vivo experiments testing T-cell dependent and T-cell independent responses will be described. Our study places CK2\u3b2 as a novel regulator of B-lymphocyte development and survival

Inhibition of protein kinase CK2 with the clinical-grade small ATP-competitive compound CX-4945 or by RNA interference unveils its role in acute myeloid leukemia cell survival, p53-dependent apoptosis and daunorubicin-induced cytotoxicity

Background The involvement of protein kinase CK2 in sustaining cancer cell survival could have implications also in the resistance to conventional and unconventional therapies. Moreover, CK2 role in blood tumors is rapidly emerging and this kinase has been recognized as a potential therapeutic target. Phase I clinical trials with the oral small ATP-competitive CK2 inhibitor CX-4945 are currently ongoing in solid tumors and multiple myeloma. Methods We have analyzed the expression of CK2 in acute myeloid leukemia and its function in cell growth and in the response to the chemotherapeutic agent daunorubicin We employed acute myeloid leukemia cell lines and primary blasts from patients grouped according to the European LeukemiaNet risk classification. Cell survival, apoptosis and sensitivity to daunorubicin were assessed by different means. p53-dependent CK2-inhibition-induced apoptosis was investigated in p53 wild-type and mutant cells. Results CK2\u3b1 was found highly expressed in the majority of samples across the different acute myeloid leukemia prognostic subgroups as compared to normal CD34+ hematopoietic and bone marrow cells. Inhibition of CK2 with CX-4945, K27 or siRNAs caused a p53-dependent acute myeloid leukemia cell apoptosis. CK2 inhibition was associated with a synergistic increase of the cytotoxic effects of daunorubicin. Baseline and daunorubicin-induced STAT3 activation was hampered upon CK2 blockade. Conclusions These results suggest that CK2 is over expressed across the different acute myeloid leukemia subsets and acts as an important regulator of acute myeloid leukemia cell survival. CK2 negative regulation of the protein levels of tumor suppressor p53 and activation of the STAT3 anti-apoptotic pathway might antagonize apoptosis and could be involved in acute myeloid leukemia cell resistance to daunorubicin