Protein kinase CK2 in mammary gland tumorigenesis

CK2: The master regulator in tumor immune-microenvironment - A crucial target in oncotherapy

A constitutively active serine/threonine kinase, casein kinase 2 (CK2) is involved in several physiological functions, such as DNA repair, apoptosis, and cell cycle control. New research emphasizes how critical CK2 is to the immune system's dysregulation in the tumor immune-microenvironment (TIME). The inhibition of immunological responses, including the downregulation of immune effector cells and the elevation of immunosuppressive proteins that aid in the development of tumor and immune evasion, has been linked to CK2 overexpression. CK2 maintains an immunosuppressive milieu that impedes anti-tumor immunity by encouraging the expressions and activities of immune checkpoint markers, regulating cytokines release, and boosting immune-suppressive cells such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) to maintain immune evasion. It is a promising target for cancer treatment due to its complex role in immune regulation and oncogenic pathways. In this study, we address the therapeutic perspectives of targeting CK2 in oncotherapy and investigate the mechanisms by which it controls immunological responses in the TME. This review, comprehending the function of CK2 in immune suppression can facilitate the creation of innovative treatment approaches aimed at augmenting anti-tumor immunity and enhancing immunotherapy effectiveness.

Nucleolar casein kinase 2 alpha as a prognostic factor in patients with surgically resected early‑stage lung adenocarcinoma

Lung cancer remains a leading cause of global cancer‑related deaths, therefore the identification of prognostic factors for lung cancer is critical. Casein kinase 2 alpha (CK2α) is one of the driver kinases in various cancers, and it was previously demonstrated that CK2α localization was associated with a poor prognosis in invasive breast cancer. In the present study, the importance of CK2α in the nucleolus was explored as a potential prognostic marker for surgically resected early‑stage lung adenocarcinoma. The present study included 118 patients who underwent pulmonary lobectomy between 2014 and 2018 in Fukushima Medical University Hospital (Fukushima, Japan), and in whom CK2α localization in tumor samples was assessed by immunohistochemistry. Patient and tumor characteristics, including pathological stage, histological type and histological grade, were analyzed. Recurrence‑free survival (RFS) and overall survival were evaluated in relation to nucleolar CK2α staining. CK2α staining in the nucleoli was observed in 50.8% of lung adenocarcinoma tumors. Positive nucleolar CK2α staining was independent of pathological stage, histological type and histological grade. Patients with positive nucleolar CK2α staining exhibited significantly worse RFS compared with patients with negative staining. Multivariate analysis identified nucleolar CK2α staining and lymph node metastasis as independent poor prognostic factors. The results of the present study suggested that nucleolar CK2α staining is a novel and independent prognostic factor in surgically resected early‑stage lung adenocarcinoma. These findings indicated the potential of nucleolar CK2α as a predictive biomarker for future recurrence, and a guide to treatment decisions. Further research is required, particularly in understanding the molecular mechanisms linking nucleolar CK2α to recurrence.

Chemoproteomics reveals immunogenic and tumor-associated cell surface substrates of ectokinase CK2α

Foreign epitopes for immune recognition provide the basis of anticancer immunity. Due to the high concentration of extracellular adenosine triphosphate in the tumor microenvironment, we hypothesized that extracellular kinases (ectokinases) could have dysregulated activity and introduce aberrant phosphorylation sites on cell surface proteins. We engineered a cell-tethered version of the extracellular kinase CK2α, demonstrated it was active on cells under tumor-relevant conditions, and profiled its substrate scope using a chemoproteomic workflow. We then demonstrated that mice developed polyreactive antisera in response to syngeneic tumor cells that had been subjected to surface hyperphosphorylation with CK2α. Interestingly, these mice developed B cell and CD4+ T cell responses in response to these antigens but failed to develop a CD8+ T cell response. This work provides a workflow for probing the extracellular phosphoproteome and demonstrates that extracellular phosphoproteins are immunogenic even in a syngeneic system.

Chemoproteomics reveals immunogenic and tumor-associated cell surface substrates of ectokinase CK2α

New epitopes for immune recognition provide the basis of anticancer immunity. Due to the high concentration of extracellular adenosine triphosphate in the tumor microenvironment, we hypothesized that extracellular kinases (ectokinases) could have dysregulated activity and introduce aberrant phosphorylation sites on cell surface proteins. We engineered a cell-tethered version of the extracellular kinase CK2α, demonstrated it was active on cells under tumor-relevant conditions, and profiled its substrate scope using a chemoproteomic workflow. We then demonstrated that mice developed polyreactive antisera in response to syngeneic tumor cells that had been subjected to surface hyperphosphorylation with CK2α. Interestingly, these mice developed B cell and CD4+ T cell responses in response to these antigens but failed to develop a CD8+ T cell response. This work provides a workflow for probing the extracellular phosphoproteome and demonstrates that extracellular phosphoproteins are immunogenic even in a syngeneic system.

Cell cycle-dependent gene networks for cell proliferation activated by nuclear CK2α complexes

Nuclear expression of protein kinase CK2α is reportedly elevated in human carcinomas, but mechanisms underlying its variable localization in cells are poorly understood. This study demonstrates a functional connection between nuclear CK2 and gene expression in relation to cell proliferation. Growth stimulation of quiescent human normal fibroblasts and phospho-proteomic analysis identified a pool of CK2α that is highly phosphorylated at serine 7. Phosphorylated CK2α translocates into the nucleus, and this phosphorylation appears essential for nuclear localization and catalytic activity. Protein signatures associated with nuclear CK2 complexes reveal enrichment of apparently unique transcription factors and chromatin remodelers during progression through the G1 phase of the cell cycle. Chromatin immunoprecipitation-sequencing profiling demonstrated recruitment of CK2α to active gene loci, more abundantly in late G1 phase than in early G1, notably at transcriptional start sites of core histone genes, growth stimulus-associated genes, and ribosomal RNAs. Our findings reveal that nuclear CK2α complexes may be essential to facilitate progression of the cell cycle, by activating histone genes and triggering ribosomal biogenesis, specified in association with nuclear and nucleolar transcriptional regulators.

John N, Zaidi F, Doyle F, Fasullo M. High-throughput screening of the Saccharomyces cerevisiae genome for 2-amino-3-methylimidazo [4,5-f] quinoline resistance identifies colon cancer-associated genes

Heterocyclic aromatic amines (HAAs) are potent carcinogenic agents found in charred meats and cigarette smoke. However, few eukaryotic resistance genes have been identified. We used Saccharomyces cerevisiae (budding yeast) to identify genes that confer resistance to 2-amino-3-methylimidazo[4,5-f] quinoline (IQ). CYP1A2 and NAT2 activate IQ to become a mutagenic nitrenium compound. Deletion libraries expressing human CYP1A2 and NAT2 or no human genes were exposed to either 400 or 800 µM IQ for 5 or 10 generations. DNA barcodes were sequenced using the Illumina HiSeq 2500 platform and statistical significance was determined for exactly matched barcodes. We identified 424 ORFs, including 337 genes of known function, in duplicate screens of the "humanized" collection for IQ resistance; resistance was further validated for a select group of 51 genes by growth curves, competitive growth, or trypan blue assays. Screens of the library not expressing human genes identified 143 ORFs conferring resistance to IQ per se. Ribosomal protein and protein modification genes were identified as IQ resistance genes in both the original and "humanized" libraries, while nitrogen metabolism, DNA repair, and growth control genes were also prominent in the "humanized" library. Protein complexes identified included the casein kinase 2 (CK2) and histone chaperone (HIR) complex. Among DNA Repair and checkpoint genes, we identified those that function in postreplication repair (RAD18, UBC13, REV7), base excision repair (NTG1), and checkpoint signaling (CHK1, PSY2). These studies underscore the role of ribosomal protein genes in conferring IQ resistance, and illuminate DNA repair pathways for conferring resistance to activated IQ.

Blockade of chemo-resistance to 5-FU by a CK2-targeted combination via attenuating AhR-TLS-promoted genomic instability in human colon cancer cells

As highly expressed in several human cancers, Casein Kinase 2 (CK2) is involved in chemotherapy-induced resistance. As a new potent CK2 inhibitor, DN701 is used to overcome chemoresistance through its synergistic antitumor effect with 5-fluorouracil (5-FU). Translesion DNA synthesis (TLS) has drawn our attention because it is associated with the development of chemo-resistance and tumor recurrence. The in vitro biological properties of 5-FU-resistant colon cancer cells revealed that DN701 combined with 5-FU could overcome chemo-resistance via blocking CK2-mediated aryl hydrocarbon receptor (AhR) and TLS-induced DNA damage repair (DDR). Moreover, pharmacologic and genetic inhibitions of AhR potently reduced TLS-promoted genomic instability. The mechanistic studies showed that combined DN701 with 5-FU was investigated to inhibit CK2 expression level and AhR-TLS-REV1 pathway. Meanwhile, DN701 combined with 5-FU could reduce CK2-AhR-TLS genomic instability, thus leading to superior in vivo antitumor effect. The insights provide a rationale for combining DN701 with 5-FU as a therapeutic strategy for patients with colon cancer.

Emodin attenuates high lipid-induced liver metastasis through the AKT and ERK pathways in vitro in breast cancer cells and in a mouse xenograft model

Emodin, a natural anthraquinone derivative, can inhibit lipid synthesis and breast cancer cell proliferation. We previously found that emodin decreased breast cancer liver metastasis via epithelial-to-mesenchymal transition (EMT) inhibition. However, the mechanism through which emodin affects breast cancer liver metastasis in high-fat diet-induced obese and hyperlipidemic mice has not been elucidated. Bioinformatics analysis was used to reveal the potential targets and pathways of emodin. The mouse model of liver metastasis was established by injecting breast cancer cells into the left ventricle in high-fat diet-induced obese mice. The effect of emodin on inhibiting liver metastasis of breast cancer was evaluated by animal experiments. The mechanisms through which emodin inhibits liver metastasis of breast cancer were studied by cell and molecular biological methods. Emodin reduced lipid synthesis by inhibiting the expression of triglyceride (TG) synthesis-related genes, such as fatty acid synthase (Fasn), glycerol-3-phosphate acyltransferase 1 (Gpat1), and stearoyl-CoA desaturase (Scd1), and ultimately reduced liver metastasis in breast cancer. In addition, emodin inhibited breast cancer cell proliferation and invasion through the serine/threonine kinase (AKT) signaling and extracellular-regulated protein kinase (ERK) pathways by interacting with CSNK2A1, ESR1, ESR2, PIM1 and PTP4A3. Our results indicate that emodin may have therapeutic potential in the prevention or treatment of breast cancer liver metastasis.

Circumventing drug resistance through a CK2-targeted combination via attenuating endogenous ahr-TLS-promoted genomic instability in human colorectal cancer cells

As anchoring Casein Kinase 2 (CK2) in several human tumors, DN701 as a novel CK2 inhibitor was applied to reverse chemo-resistance via its antitumor effect synergized with oxaliplatin. Recently, translesion DNA synthesis (TLS) has attracted our attention for its association with chemo-resistance, as demonstrated by previous clinical data. The in vitro cell-based properties supported that oxaliplatin combined with DN701 could reverse drug resistance via blockading CK2-mediated aryl hydrocarbon receptor (AhR) and translesion DNA synthesis (TLS)-induced DNA damage repair. Moreover, pharmacologic or genetic inhibition on REV3L (Protein reversion less 3-like) greatly impaired TLS-induced genomic instability. Mechanistically, combination of oxaliplatin with DN701 was found to inhibit CK2 expression and AhR-TLS-REV3L axis signaling, implying the potential decrease of genomic instability. In addition, the combination of oxaliplatin with DN701 could reduce CK2-AhR-TLS-related genomic instability, leading to potent antitumor effects in vivo. Our study presents an underlying mechanism that DN701 could attenuate tumoral chemo-resistance via decaying CK2-mediated AhR and TLS genomic instability, suggesting a potential cancer chemotherapeutic modality to prolong survival in chemo-resistant patients.

Protein kinase CK2 – diverse roles in cancer cell biology and therapeutic promise

The association of protein kinase CK2 (formerly casein kinase II or 2) with cell growth and proliferation in cells was apparent at early stages of its investigation. A cancer-specific role for CK2 remained unclear until it was determined that CK2 was also a potent suppressor of cell death (apoptosis); the latter characteristic differentiated its function in normal versus malignant cells because dysregulation of both cell growth and cell death is a universal feature of cancer cells. Over time, it became evident that CK2 exerts its influence on a diverse range of cell functions in normal as well as in transformed cells. As such, CK2 and its substrates are localized in various compartments of the cell. The dysregulation of CK2 is documented in a wide range of malignancies; notably, by increased CK2 protein and activity levels with relatively moderate change in its RNA abundance. High levels of CK2 are associated with poor prognosis in multiple cancer types, and CK2 is a target for active research and testing for cancer therapy. Aspects of CK2 cellular roles and targeting in cancer are discussed in the present review, with focus on nuclear and mitochondrial functions and prostate, breast and head and neck malignancies.

CSNK2 in cancer: pathophysiology and translational applications

Protein kinase CSNK2 (CK2) is a pleiotropic serine/threonine kinase frequently dysregulated in solid and hematologic malignancies. To consolidate a wide range of biological and clinically oriented data from this unique kinase in cancer, this systematic review summarises existing knowledge from in vitro, in vivo and pre-clinical studies on CSNK2 across 24 different human cancer types. CSNK2 mRNA transcripts, protein levels and activity were found to be routinely upregulated in cancer, and commonly identified phosphotargets included AKT, STAT3, RELA, PTEN and TP53. Phenotypically, it frequently influenced evasion of apoptosis, enhancement of proliferation, cell invasion/metastasis and cell cycle control. Clinically, it held prognostic significance across 14 different cancers, and its inhibition in xenograft experiments resulted in a positive treatment response in 12. In conjunction with commentary on preliminary studies of CSNK2 inhibitors in humans, this review harmonises an extensive body of CSNK2 data in cancer and reinforces its emergence as an attractive target for cancer therapy. Continuing to investigate CSNK2 will be crucial to advancing our understanding of CSNK2 biology, and offers the promise of important new discoveries scientifically and clinically.

Targeting protein kinase CK2 in the treatment of cholangiocarcinoma

Cholangiocarcinoma (CCA) is a disease with a very poor prognosis and limited treatment options. Although targeted therapies directed towards specific mutations found in CCA are becoming available and are showing great potential, many tumors do not carry actionable mutations and, in those that do, the emergence of drug resistance is a likely consequence of treatment. Therapeutic targeting of enzymes and other proteins that show elevated activity in CCA cells but which are not altered by mutation is a potential strategy for the treatment of target negative and drug-resistant disease. Protein kinase CK2 (CK2) is a ubiquitously expressed kinase that has increased expression and increased activity in a variety of cancer types including CCA. Several potent CK2 inhibitors are in pre-clinical development or under assessment in a variety of clinical trials often in combination with drugs that induce DNA damage. This review outlines the importance of CK2 in CCA and assesses the progress that has been made in the evaluation of CK2 inhibition as a treatment strategy in this disease. Targeting CK2 based on the expression levels or activity of this protein and/or in combination with drugs that induce DNA damage or inhibit cell cycle progression, could be a viable option for tumors that lack actionable mutations, or for tumors that develop resistance to targeted treatments.

Hinge Binder Scaffold Hopping Identifies Potent Calcium/Calmodulin-Dependent Protein Kinase Kinase 2 (CAMKK2) Inhibitor Chemotypes

CAMKK2 is a serine/threonine kinase and an activator of AMPK whose dysregulation is linked with multiple diseases. Unfortunately, STO-609, the tool inhibitor commonly used to probe CAMKK2 signaling, has limitations. To identify promising scaffolds as starting points for the development of high-quality CAMKK2 chemical probes, we utilized a hinge-binding scaffold hopping strategy to design new CAMKK2 inhibitors. Starting from the potent but promiscuous disubstituted 7-azaindole GSK650934, a total of 32 compounds, composed of single-ring, 5,6-, and 6,6-fused heteroaromatic cores, were synthesized. The compound set was specifically designed to probe interactions with the kinase hinge-binding residues. Compared to GSK650394 and STO-609, 13 compounds displayed similar or better CAMKK2 inhibitory potency in vitro, while compounds 13g and 45 had improved selectivity for CAMKK2 across the kinome. Our systematic survey of hinge-binding chemotypes identified several potent and selective inhibitors of CAMKK2 to serve as starting points for medicinal chemistry programs.

Simultaneous CK2/TNIK/DYRK1 inhibition by 108600 suppresses triple negative breast cancer stem cells and chemotherapy-resistant disease

Triple negative breast cancer (TNBC) remains challenging because of heterogeneous responses to chemotherapy. Incomplete response is associated with a greater risk of metastatic progression. Therefore, treatments that target chemotherapy-resistant TNBC and enhance chemosensitivity would improve outcomes for these high-risk patients. Breast cancer stem cell-like cells (BCSCs) have been proposed to represent a chemotherapy-resistant subpopulation responsible for tumor initiation, progression and metastases. Targeting this population could lead to improved TNBC disease control. Here, we describe a novel multi-kinase inhibitor, 108600, that targets the TNBC BCSC population. 108600 treatment suppresses growth, colony and mammosphere forming capacity of BCSCs and induces G2M arrest and apoptosis of TNBC cells. In vivo, 108600 treatment of mice bearing triple negative tumors results in the induction of apoptosis and overcomes chemotherapy resistance. Finally, treatment with 108600 and chemotherapy suppresses growth of pre-established TNBC metastases, providing additional support for the clinical translation of this agent to clinical trials.

Synthesis of Novel Acyl Derivatives of 3-(4,5,6,7-Tetrabromo-1H-benzimidazol-1-yl)propan-1-ols-Intracellular TBBi-Based CK2 Inhibitors with Proapoptotic Properties

Protein kinase CK2 has been considered as an attractive drug target for anti-cancer therapy. The synthesis of N-hydroxypropyl TBBi and 2MeTBBi derivatives as well as their respective esters was carried out by using chemoenzymatic methods. Concomitantly with kinetic studies toward recombinant CK2, the influence of the obtained compounds on the viability of two human breast carcinoma cell lines (MCF-7 and MDA-MB-231) was evaluated using MTT assay. Additionally, an intracellular inhibition of CK2 as well as an induction of apoptosis in the examined cells after the treatment with the most active compounds were studied by Western blot analysis, phase-contrast microscopy and flow cytometry method. The results of the MTT test revealed potent cytotoxic activities for most of the newly synthesized compounds (EC50 4.90 to 32.77 µM), corresponding to their solubility in biological media. We concluded that derivatives with the methyl group decrease the viability of both cell lines more efficiently than their non-methylated analogs. Furthermore, inhibition of CK2 in breast cancer cells treated with the tested compounds at the concentrations equal to their EC50 values correlates well with their lipophilicity since derivatives with higher values of logP are more potent intracellular inhibitors of CK2 with better proapoptotic properties than their parental hydroxyl compounds.

Protein kinase CK2: a potential therapeutic target for diverse human diseases

CK2 is a constitutively active Ser/Thr protein kinase, which phosphorylates hundreds of substrates, controls several signaling pathways, and is implicated in a plethora of human diseases. Its best documented role is in cancer, where it regulates practically all malignant hallmarks. Other well-known functions of CK2 are in human infections; in particular, several viruses exploit host cell CK2 for their life cycle. Very recently, also SARS-CoV-2, the virus responsible for the COVID-19 pandemic, has been found to enhance CK2 activity and to induce the phosphorylation of several CK2 substrates (either viral and host proteins). CK2 is also considered an emerging target for neurological diseases, inflammation and autoimmune disorders, diverse ophthalmic pathologies, diabetes, and obesity. In addition, CK2 activity has been associated with cardiovascular diseases, as cardiac ischemia-reperfusion injury, atherosclerosis, and cardiac hypertrophy. The hypothesis of considering CK2 inhibition for cystic fibrosis therapies has been also entertained for many years. Moreover, psychiatric disorders and syndromes due to CK2 mutations have been recently identified. On these bases, CK2 is emerging as an increasingly attractive target in various fields of human medicine, with the advantage that several very specific and effective inhibitors are already available. Here, we review the literature on CK2 implication in different human pathologies and evaluate its potential as a pharmacological target in the light of the most recent findings.

TMEM2 binds to CSNK2A3 to inhibit HBV infection via activation of the JAK/STAT pathway

To investigate mechanisms that TMEM2 activation inhibits hepatitis B virus (HBV) infection in hepatocarcinoma (HCC) cells, co-immunoprecipitation (Co-IP) and mass spectrometry were used in screening interacting proteins for TMEM2. Levels of casein kinase 2 subunit α3 (CSNK2A3) in HCC cells were found to be inhibited or overexpressed using siRNAs and pcDNA3.1-CSNK2A3, respectively. Effect of CSNK2A3 expression on cell proliferation was analyzed using MTS, while its effect on HBV infection was measured using ddPCR and IHC. Western blotting and JAK inhibitor ruxolitinib were also used to determine whether TMEM2-regulated CSNK2A3 expression and HBV infection were affected by JAK-STAT signaling. Co-IP and mass spectrometry results showed that CSNK2A3 interacts with TMEM2. Moreover, overexpression of CSNK2A3 significantly inhibited cell proliferation, while inhibition of CSNK2A3 promoted proliferation of HCC cells. In addition, overexpression of CSNK2A3 was observed to significantly enhance HBV infection, while siRNA knockdown of CSNK2A3 inhibited HBV infection. Notably, effect of CSNK2A3 overexpression on HBV infection was suppressed by TMEM2 overexpression. Further mechanistic analyses have revealed that TMEM2 could antagonize the effects of CSNK2A3 on cell proliferation and HBV infection via JAK-STAT pathway activation. In conclusion, TMEM2 has been determined to bind to CSNK2A3 to inhibit HBV infection via activation of the JAK-STAT pathway.

Intracellular localization of CK2α as a prognostic factor in invasive breast carcinomas

Overexpression of the ubiquitous protein kinase, CK2α, has been reported in various human cancers. Here, we demonstrate that nuclear and nucleolar CK2α localization in invasive ductal carcinomas of the breast is a reliable predictor of poor prognosis. Cellular localization of CK2α in nuclei and nucleoli was analyzed immunohistochemically using surgical tissue blocks from 112 patients, who had undergone surgery without neoadjuvant chemotherapy. Clinical data collection and median follow-up period were for more than 5 y. In total, 93.8% of patients demonstrated elevated CK2α expression in nuclei and 36.6% of them displayed elevated expression predominantly in nucleoli. Clinicopathological malignancy was strongly correlated with elevated nuclear and nucleolar CK2α expression. Recurrence-free survival was significantly worse (P = .0002) in patients with positive nucleolar CK2α staining. The 5-y survival rate decreased to a roughly 50% in nucleolar CK2α-positive patients of triple-negative (P = .0069) and p Stage 3 (P = .0073) groups. In contrast, no patients relapsed or died in the triple-negative group who exhibited a lack of nucleolar CK2α staining. Evaluation of nucleolar CK2α staining showed a high secondary index with a hazard ratio of 6.629 (P = .001), following lymph node metastasis with a hazard ratio of 14.30 (P = .0008). Multivariate analysis demonstrated that nucleolar CK2α is an independent factor for recurrence-free survival. Therefore, we propose that histochemical evaluation of nucleolar CK2α-positive staining may be a new and robust prognostic indicator for patients who need further treatment. Functional consequences of nucleolar CK2 dysfunction may be a starting point to facilitate development of novel treatments for invasive breast carcinoma.

Preclinical and Clinical Advances of Targeted Protein Degradation as a Novel Cancer Therapeutic Strategy: An Oncologist Perspective

PROteolysis Targeting Chimeras (PROTACs) are a family of heterobifunctional small molecules that specifically target cellular proteins for degradation. Given that their mode of action is distinct from that of small-molecule inhibitors widely used in clinical practice, PROTACs have the potential to improve current cancer therapies. Multiple studies have suggested that PROTACs exhibit enhanced pharmacodynamics and reduced toxicity both in vitro and in vivo compared to clinically relevant small-molecule kinase inhibitors. In addition, PROTACs have been reported to be less prone to mutation-mediated drug resistance in specific disease settings. Since its development in 2001, the field of targeted protein degradation, in which PROTACs are used, has expanded rapidly. However, earlier studies focused on the advancement of the technology itself, while preclinical and clinical data on the disease-modifying effect of PROTACs have only recently been reported. As preclinical and clinical evidence accumulates, the efficacy of PROTACs as targeted therapeutics-distinct from that of small-molecule kinase inhibitors-suggests potential translational benefit in the clinical setting. In this short review, we aim to describe translational potentials of PROTACs. We offer our perspectives as practicing oncologists on the preclinical and clinical data on PROTACs as novel therapeutics for both solid and hematological malignancies.

Knockdown of CSNK2ß suppresses MDA-MB231 cell growth, induces apoptosis, inhibits migration and invasion

Breast cancer is the most common cancer among women worldwide. Among different types of breast cancer known, treatment of triple-negative breast cancer is a major challenge because of its aggressiveness and poor prognosis; thus, identification of specific drivers is required for targeted therapies of breast cancer malignancy. Protein Casein Kinase (CSNK) is a serine/threonine kinase that exists as a tetrameric complex consisting of two catalytic (α and /or α') and two regulatory β subunits. CSNK2β can also function independently without catalytic subunits and exist as a distinct population in cells. This study aims to elucidate the role of Casein Kinase 2β (CSNK2β) gene in cell proliferation, cell cycle, migration and apoptosis of triple-negative breast cancer MDA-MB-231 cells. The silencing of CSNK2β in MDA-MB-231 cells resulted in decreased cell viability and colony formation. Cell cycle analysis showed a significant arrest of cells in G2M phase. Hoechst and CM-H2DCFDA staining showed nuclear condensation and augmented intracellular reactive oxygen species (ROS) production. Furthermore, silencing of CSNK2β in MDA-MB-231 cells modulated the apoptotic machinery- BAX, Bcl-xL, and caspase 3; autophagy machinery-Beclin-1 and LC3-1; and inhibited the vital markers (p-ERK, c-Myc, NF-κB, E2F1, PCNA, p38-α) associated with cell proliferation and DNA replication pathways. In addition, knockdown of CSNK2β also affected the migration potential of MDA-MB-231, as observed in the wound healing and transwell migration assays. Altogether, the study suggests that CSNK2β silencing may offer future therapeutic target in triple-negative breast cancer.

Role of Protein Kinase CK2 in Aberrant Lipid Metabolism in Cancer

Uncontrolled proliferation is a feature defining cancer and it is linked to the ability of cancer cells to effectively adapt their metabolic needs in response to a harsh tumor environment. Metabolic reprogramming is considered a hallmark of cancer and includes increased glucose uptake and processing, and increased glutamine utilization, but also the deregulation of lipid and cholesterol-associated signal transduction, as highlighted in recent years. In the first part of the review, we will (i) provide an overview of the major types of lipids found in eukaryotic cells and their importance as mediators of intracellular signaling pathways (ii) analyze the main metabolic changes occurring in cancer development and the role of oncogenic signaling in supporting aberrant lipid metabolism and (iii) discuss combination strategies as powerful new approaches to cancer treatment. The second part of the review will address the emerging role of CK2, a conserved serine/threonine protein kinase, in lipid homeostasis with an emphasis regarding its function in lipogenesis and adipogenesis. Evidence will be provided that CK2 regulates these processes at multiple levels. This suggests that its pharmacological inhibition combined with dietary restrictions and/or inhibitors of metabolic targets could represent an effective way to undermine the dependency of cancer cells on lipids to interfere with tumor progression.

Flavone inspired discovery of benzylidenebenzofuran-3(2H)-ones (aurones) as potent inhibitors of human protein kinase CK2

In this work, we describe the design, synthesis and SAR studies of 2-benzylidenebenzofuran-3-ones (aurones), a new family of potent inhibitors of CK2. A series of aurones have been synthesized. These compounds are structurally related to the synthetic flavones and showed nanomolar activities towards CK2. Biochemical tests revealed that 20 newly synthesized compounds inhibited CK2 with IC₅₀ values in the nanomolar range. Further property-based optimization of aurones was performed, yielding a series of CK2 inhibitors with enhanced lipophilic efficiency. The most potent compound 12m (BFO13) has CLipE = 4.94 (CLogP = 3.5; IC₅₀ = 3.6 nM) commensurable with the best known inhibitors of CK2.

A RUNX2 stabilization pathway mediates physiologic and pathologic bone formation

The osteoblast differentiation capacity of skeletal stem cells (SSCs) must be tightly regulated, as inadequate bone formation results in low bone mass and skeletal fragility, and over-exuberant osteogenesis results in heterotopic ossification (HO) of soft tissues. RUNX2 is essential for tuning this balance, but the mechanisms of posttranslational control of RUNX2 remain to be fully elucidated. Here, we identify that a CK2/HAUSP pathway is a key regulator of RUNX2 stability, as Casein kinase 2 (CK2) phosphorylates RUNX2, recruiting the deubiquitinase herpesvirus-associated ubiquitin-specific protease (HAUSP), which stabilizes RUNX2 by diverting it away from ubiquitin-dependent proteasomal degradation. This pathway is important for both the commitment of SSCs to osteoprogenitors and their subsequent maturation. This CK2/HAUSP/RUNX2 pathway is also necessary for HO, as its inhibition blocked HO in multiple models. Collectively, active deubiquitination of RUNX2 is required for bone formation and this CK2/HAUSP deubiquitination pathway offers therapeutic opportunities for disorders of inappropriate mineralization.

Comparative analysis of two brine shrimps revealed differential expression pattern and functional characterization of CK2α under bacterial stimulation from different geographical distribution

Understanding how the brine shrimp responds to different geographical populations can provide novel insights on response to bacterial stimulation. In the paper, Artemia sinica from lower altitudes and Artemia parthenogenetica from higher altitudes of the Tibetan Plateau, were used to illustrate different defense against bacteria mechanisms that these organisms used to adapt to different geographical environments. Protein kinase CK2 is a serine/threonine kinase with a multitude of protein substrates. It is a ubiquitous enzyme essential for the viability of eukaryotic cells, where its functions in a variety of cellular processes, including cell cycle progression, apoptosis, transcription, and viral infection. The gene encodes the same mRNA sequence in A. sinica and A. parthenogenetica, named AsCK2α and ApCK2α, respectively. The open reading frame was obtained, a 1047-bp sequence encoding a predicted protein of 349 amino acids. To systematically analyze the expression of AsCK2α and ApCK2α during embryonic development and bacterial challenge, real-time PCR, Western blotting and immunohistochemistry were performed. The results showed that AsCK2α was higher than ApCK2α at different developmental stages. Under bacterial challenge, the expression of ApCK2α was significantly higher than AsCK2α. Protein localization analysis showed that AsCK2α and ApCK2α were mainly distributed in the head and chest. Our research revealed that CK2α plays a vital role in the growth, development and bacterial stimulation of the brine shrimp.

miRNA expression in advanced Algerian breast cancer tissues

Breast cancer is one of the commonest cancers among Algerian females. Compared to Western populations, the median age of diagnosis of breast cancer is much lower in Algeria. The objective of this study is to explore the expression of several miRNAs reported to be deregulated in breast cancer. The miRNAs miR-21, miR-125b, miR-100, miR-425-5p, miR-200c, miR-183 and miR-182 were studied on tumor and normal adjacent Algerian breast tissues using quantitative reverse transcription real time PCR, and the results were analyzed according to clinical characteristics. Compared to the normal adjacent tissues, miR-21, miR-183, miR-182, miR-425-5p and miR-200c were found to be upregulated while miR-100 and miR-125b were insignificantly deregulated. A positive correlation was noted among miR-183, miR-182 and miR-200c and among miR-425-5p, miR-183, miR-200c and miR-21. Further global miRNA microarray profiling studies can aid in finding ethnic specific miRNA biomarkers in the Algerian breast cancer population.

In Depth Analysis of Kinase Cross Screening Data to Identify CAMKK2 Inhibitory Scaffolds

The calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) activates CAMK1, CAMK4, AMPK, and AKT, leading to numerous physiological responses. The deregulation of CAMKK2 is linked to several diseases, suggesting the utility of CAMKK2 inhibitors for oncological, metabolic and inflammatory indications. In this work, we demonstrate that STO-609, frequently described as a selective inhibitor for CAMKK2, potently inhibits a significant number of other kinases. Through an analysis of literature and public databases, we have identified other potent CAMKK2 inhibitors and verified their activities in differential scanning fluorimetry and enzyme inhibition assays. These inhibitors are potential starting points for the development of selective CAMKK2 inhibitors and will lead to tools that delineate the roles of this kinase in disease biology.

PROTACs: great opportunities for academia and industry

Although many kinds of therapies are applied in the clinic, drug-resistance is a major and unavoidable problem. Another disturbing statistic is the limited number of drug targets, which are presently only 20-25% of all protein targets that are currently being studied. Moreover, the focus of current explorations of targets are their enzymatic functions, which ignores the functions from their scaffold moiety. As a promising and appealing technology, PROteolysis TArgeting Chimeras (PROTACs) have attracted great attention both from academia and industry for finding available approaches to solve the above problems. PROTACs regulate protein function by degrading target proteins instead of inhibiting them, providing more sensitivity to drug-resistant targets and a greater chance to affect the nonenzymatic functions. PROTACs have been proven to show better selectivity compared to classic inhibitors. PROTACs can be described as a chemical knockdown approach with rapidity and reversibility, which presents new and different biology compared to other gene editing tools by avoiding misinterpretations that arise from potential genetic compensation and/or spontaneous mutations. PRTOACs have been widely explored throughout the world and have outperformed not only in cancer diseases, but also in immune disorders, viral infections and neurodegenerative diseases. Although PROTACs present a very promising and powerful approach for crossing the hurdles of present drug discovery and tool development in biology, more efforts are needed to gain to get deeper insight into the efficacy and safety of PROTACs in the clinic. More target binders and more E3 ligases applicable for developing PROTACs are waiting for exploration.

Triazol: a privileged scaffold for proteolysis targeting chimeras

Current traditional drugs such as enzyme inhibitors and receptor agonists/antagonists present inherent limitations due to occupancy-driven pharmacology as the mode of action. Proteolysis targeting chimeras (PROTACs) are composed of an E3 ligand, a connecting linker and a target protein ligand, and are an attractive approach to specifically knockdown-targeted proteins utilizing an event-driven mode of action. The length, hydrophilicity and rigidity of connecting linkers play important role in creating a successful PROTAC. Some PROTACs with a triazole linker have displayed promising anticancer activity. This review provides an overview of PROTACs with a triazole scaffold and discusses its structure-activity relationship. Important milestones in the development of PROTACs are addressed and a critical analysis of this drug discovery strategy is also presented.

Kinase Regulation of HOX Transcription Factors

The HOX genes are a group of homeodomain-containing transcription factors that play important regulatory roles in early development, including the establishment of cell and tissue identity. HOX expression is generally reduced in adult cells but is frequently re-established as an early event in tumour formation and supports an oncogenic phenotype. HOX transcription factors are also involved in cell cycle regulation and DNA repair, along with normal adult physiological process including stem cell renewal. There have been extensive studies on the mechanism by which HOX proteins regulate transcription, with particular emphasis on their interaction with cofactors such as Pre-B-cell Leukaemia Homeobox (PBX) and Myeloid Ecotropic Viral Integration Site 1 (MEIS). However, significantly less is known of how the activity of HOX proteins is regulated. There is growing evidence that phosphorylation may play an important role in this context, and in this review, we draw together a number of important studies published over the last 20 years, and discuss the relevance of phosphorylation in the regulation and function of HOX proteins in development, evolution, cell cycle regulation, and cancer.

Protein kinase CK2-dependent aerobic glycolysis-induced lactate dehydrogenase A enhances the migration and invasion of cancer cells

We investigated the intracellular metabolic fluxes of protein kinase CK2-activating (Cα OE) cells and role of lactate dehydrogenase A (LDHA) as a contributor of tumorigenesis after reprogrammed glucose metabolism. Facilitated aerobic glycolysis was confirmed via isotope tracer analysis, in which ¹³C₆-Glc or ¹³C₅-Gln was added to the media, following which metabolites converted from Cα OE cells were identified. We found a greater decrease in cell survival, colony-forming ability, migration, and Cα OE cell invasion under glucose (Glc)-depletion conditions than under glutamine (Gln)-depletion conditions. Cancer cell migration and invasion increased due to LDHA elevation of the altered metabolic axis driven by activated CK2. FX11 treatment and LDHA knockdown suppressed migration and invasion through ROS generation, but this was partially reversed by the antioxidant N-acetylcysteine (NAC). Moreover, LDHA inhibition decreased tumor growth in a mouse xenograft model transplanted with Cα OE cells. Finally, we concluded that LDHA is an excellent metabolic target for tumor therapy, based on CK2α derived aerobic glycolysis.

Lamin A buffers CK2 kinase activity to modulate aging in a progeria mouse model

Defective nuclear lamina protein lamin A is associated with premature aging. Casein kinase 2 (CK2) binds the nuclear lamina, and inhibiting CK2 activity induces cellular senescence in cancer cells. Thus, it is feasible that lamin A and CK2 may cooperate in the aging process. Nuclear CK2 localization relies on lamin A and the lamin A carboxyl terminus physically interacts with the CK2α catalytic core and inhibits its kinase activity. Loss of lamin A in Lmna-knockout mouse embryonic fibroblasts (MEFs) confers increased CK2 activity. Conversely, prelamin A that accumulates in Zmpste24-deficent MEFs exhibits a high CK2α binding affinity and concomitantly reduces CK2 kinase activity. Permidine treatment activates CK2 by releasing the interaction between lamin A and CK2, promoting DNA damage repair and ameliorating progeroid features. These data reveal a previously unidentified function for nuclear lamin A and highlight an essential role for CK2 in regulating senescence and aging.

Novel halogenated pyrido[2,3-a]carbazoles with enhanced aromaticity as potent anticancer and antioxidant agents: rational design and microwave assisted synthesis

Design and synthesis a series of pyrido[2,3-a]carbazoles for their anticancer and antioxidant activity.

Protein kinase CK2 activation is required for transforming growth factor β-induced epithelial-mesenchymal transition

Transforming growth factor β (TGFβ) is overexpressed in advanced cancers and promotes tumorigenesis by inducing epithelial–mesenchymal transition (EMT), which enhances invasiveness and metastasis. Although we previously reported that EMT could be induced by increasing CK2 activity alone, it is not known whether CK2 also plays an essential role in TGFβ‐induced EMT. Therefore, in the present study, we investigated whether TGFβ signaling could activate CK2 and, if so, whether such activation is required for TGFβ‐induced EMT. We found that CK2 is activated by TGFβ treatment, and that activity peaks at 48 h after treatment. CK2 activation is dependent on TGFβ receptor (TGFBR) I kinase activity, but independent of SMAD4. Inhibition of CK2 activation through the use of either a CK2 inhibitor or shRNA against CSNK2A1 inhibited TGFβ‐induced EMT. TGFβ signaling decreased CK2β but did not affect CK2α protein levels, resulting in a quantitative imbalance between the catalytic α and regulatory β subunits, thereby increasing CK2 activity. The decrease in CK2β expression was dependent on TGFBRI kinase activity and the ubiquitin–proteasome pathway. The E3 ubiquitin ligases responsible for TGFβ‐induced CK2β degradation were found to be CHIP and WWP1. Okadaic acid (OA) pretreatment protected CK2β from TGFβ‐induced degradation, suggesting that dephosphorylation of CK2β by an OA‐sensitive phosphatase might be required for CK2 activation in TGFβ‐induced EMT. Collectively, our results suggest CK2 as a therapeutic target for the prevention of EMT and metastasis of cancers.

Chemically induced degradation of CK2 by proteolysis targeting chimeras based on a ubiquitin-proteasome pathway

As a ubiquitous, highly pleiotropic and constitutively active serine/threonine protein kinase, casein kinase 2 (CK2) is closely associated with tumorigenesis by its overexpression in cancer cells. Here we report several proteolysis targeting chimeras (PROTACs) via "click reaction" to connect a CK2 inhibitor (CX-4945) and pomalidomide for degradation of CK2 protein. Among them, compound 2 degraded CK2 in a dose and time-dependent manner, and kept CK2 at a low basal level by recruiting ubiquitin-proteasome system. The degradation of CK2 resulted in the reduced phosphorylation of Akt and the up-regulation of p53. As a CK2 protein degrader, 2 showed the analogous cytotoxicity to CX-4945 but with a quite different mechanism of action from the CK2 inhibitor, hinting that degradation of CK2 proteins by PROTACs is a potential way for cancer treatments.

Function of protein kinase CK2 in thrombus formation

Thrombus formation is dependent on the interaction of platelets, leukocytes and endothelial cells as well as proteins of the coagulation cascade. This interaction is tightly controlled by phospho-regulated pathways involving protein kinase CK2. A growing number of studies have demonstrated an important role of this kinase in the regulation of primary and secondary hemostasis. Inhibition of CK2 downregulates the expression of important adhesion molecules on platelets and endothelial cells, such as glycoprotein (GP)IIb/IIIa, P-selectin, von Willebrand factor and vascular cell adhesion molecule. Moreover, the reduced CK2-dependent phosphorylation of different coagulation factors prevents the conversion of fibrinogen to fibrin. Targeting these mechanisms may open the door for the development of novel anti-thrombotic therapies.

Thiazole- and selenazole-comprising high-affinity inhibitors possess bright microsecond-scale photoluminescence in complex with protein kinase CK2

A previously disclosed protein kinase (PK) CK2-selective inhibitor 4-(2-amino-1,3-thiazol-5-yl)benzoic acid (ATB) and its selenium-containing counterpart (ASB) revealed remarkable room temperature phosphorescence when bound to the ATP pocket of the protein kinase CK2. Conjugation of these fragments with a mimic of CK2 substrate peptide resulted in bisubstrate inhibitors with increased affinity towards the kinase. Attachment of the fluorescent acceptor dye 5-TAMRA to the conjugates led to significant enhancement of intensity of long-lifetime (microsecond-scale) photoluminescence of both sulfur- and selenium-containing compounds. The developed photoluminescent probes make possible selective determination of the concentration of CK2 in cell lysates and characterization of CK2 inhibitors by means of time-gated measurement of photoluminescence.

Role of Transglutaminase 2 in Migration of Tumor Cells and How Mouse Models Fit

A search for the "magic bullet", a molecule, the targeting abilities of which could stop the migration of tumor cells, is currently underway, but remains in the early stages. There are still many unknowns regarding the cell migration. The main approach is the employment of mouse models, that are sources of valuable information, but still cannot answer all of the questions. One of the molecules of interest is Transglutaminase 2 (TG2). It is a well-described molecule involved in numerous pathways and elevated in metastatic tumors. The question remains whether mice and humans can give the same answer considering TG2.

The heat-shock, or HSF1-mediated proteotoxic stress, response in cancer: from proteomic stability to oncogenesis

The heat-shock, or HSF1-mediated proteotoxic stress, response (HSR/HPSR) is characterized by induction of heat-shock proteins (HSPs). As molecular chaperones, HSPs facilitate the folding, assembly, transportation and degradation of other proteins. In mammals, heat shock factor 1 (HSF1) is the master regulator of this ancient transcriptional programme. Upon proteotoxic insults, the HSR/HPSR is essential to proteome homeostasis, or proteostasis, thereby resisting stress and antagonizing protein misfolding diseases and ageing. Contrasting with these benefits, an unexpected pro-oncogenic role of the HSR/HPSR is unfolding. Whereas HSF1 remains latent in primary cells without stress, it becomes constitutively activated within malignant cells, rendering them addicted to HSF1 for their growth and survival. Highlighting the HSR/HPSR as an integral component of the oncogenic network, several key pathways governing HSF1 activation by environmental stressors are causally implicated in malignancy. Importantly, HSF1 impacts the cancer proteome systemically. By suppressing tumour-suppressive amyloidogenesis, HSF1 preserves cancer proteostasis to support the malignant state, both providing insight into how HSF1 enables tumorigenesis and suggesting disruption of cancer proteostasis as a therapeutic strategy. This review provides an overview of the role of HSF1 in oncogenesis, mechanisms underlying its constitutive activation within cancer cells and its pro-oncogenic action, as well as potential HSF1-targeting strategies.This article is part of the theme issue 'Heat shock proteins as modulators and therapeutic targets of chronic disease: an integrated perspective'.

Silencing of casein kinase 2 inhibits PKC‑induced cell invasion by targeting MMP‑9 in MCF‑7 cells

Casein kinase 2 (CK2) is a serine/threonine protein kinase that has been considered to represent an important factor in mammary tumorigenesis. Increased expression of matrix metalloproteinase‑9 (MMP‑9) via nuclear factor‑κB (NF‑κB) activation has been demonstrated to promote breast cancer cell invasion. In the present study, the involvement of CK2 in protein kinase C (PKC) induced cell invasion in MCF‑7 breast cancer cells was investigated as well as the underlying molecular mechanisms. The mRNA and protein levels of MMP‑9 in MCF‑7 cells were investigated using reverse transcription‑quantitative polymerase chain reaction, western blot analyses and a zymography assay. Cell invasiveness was investigated using a Matrigel invasion assay, and it was revealed that small interfering RNA specific for CK2 suppressed PKC induced cell invasion by regulating MMP‑9 expression via activation of the p38 kinase/c‑Jun N‑terminal kinase/NF‑κB pathway. In addition, it was demonstrated that CK2 inhibitors [apigenin (20 µM), emodin (20 µM) or 2‑dimethylamino‑4,5,6,7‑tetrabromo‑1H‑benzimidazole (2 µM)] suppressed PKC induced cell invasion and MMP‑9 expression. The results of the present study suggested that CK2 is an important factor involved in the induction of MCF‑7 breast cancer cell invasion by PKC. Therefore, CK2 may represent novel candidates for therapy intended to inhibit invasion in breast cancer.

Downregulation of protein kinase CK2 activity induces age-related biomarkers in C. elegans

Studies show that a decrease in protein kinase CK2 (CK2) activity is associated with cellular senescence. However, the role of CK2 in organism aging is still poorly understood. Here, we investigated whether protein kinase CK2 (CK2) modulated longevity in Caenorhabditis elegans. CK2 activity decreased with advancing age in the worms. Knockdown of kin-10 (the ortholog of CK2β) led to a short lifespan phenotype and induced age-related biomarkers, including retardation of locomotion, decreased pharyngeal pumping rate, increased lipofuscin accumulation, and reduced resistance to heat and oxidative stress. The long lifespan of age-1 and akt-1 mutants was significantly suppressed by kin-10 RNAi, suggesting that CK2 acts downstream of AGE-1 and AKT-1. Kin-10 knockdown did not further shorten the short lifespan of daf-16 mutant worms but either decreased or increased the transcriptional activity of DAF-16 depending on the promoters of the target genes, indicating that CK2 is an upstream regulator of DAF-16 in C. elegans. Kin-10 knockdown increased production of reactive oxygen species (ROS) in the worms. Finally, the ROS scavenger N-acetyl-L-cysteine significantly counteracts the lifespan shortening and lipofuscin accumulation induced by kin-10 knockdown. Therefore, the present results suggest that age-dependent CK2 downregulation reduces longevity by associating with both ROS generation and the AGE-1-AKT-1-DAF-16 pathway in C. elegans.

Phosphorylation-dependent stabilization of MZF1 upregulates N-cadherin expression during protein kinase CK2-mediated epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a critical process in invasion and metastasis of cancer cells. E-cadherin to N-cadherin switching is considered a molecular hallmark of EMT. Recently, we reported that increased CK2 activity fully induces E-cadherin to N-cadherin switching, but the molecular mechanisms of N-cadherin upregulation are unknown. In this study, we examined how N-cadherin is upregulated by CK2. N-cadherin promoter analysis and ChIP analysis identified and confirmed myeloid zinc finger 1 (MZF1) as an N-cadherin transcription factor. Molecular analysis showed that MZF1 directly interacts with CK2 and is phosphorylated at serine 27. Phosphorylation stabilizes MZF1 and induces transcription of N-cadherin. MZF1 knockdown (MKD) in N-cadherin-expressing cancer cells downregulates N-cadherin expression and reverts the morphology from spindle and fibroblast-like to a rounded, epithelial shape. In addition, we showed that that MKD reduced the motility and invasiveness of N-cadherin-expressing cancer cells. Collectively, these data indicate that N-cadherin upregulation in CK2-mediated E-cadherin to N-cadherin switching is dependent on phosphorylation-mediated MZF1 stabilization. CK2 could be a good therapeutic target for the prevention of metastasis.

Cancer-type dependent expression of CK2 transcripts

A multitude of proteins are aberrantly expressed in cancer cells, including the oncogenic serine-threonine kinase CK2. In a previous report, we found increases in CK2 transcript expression that could explain the increased CK2 protein levels found in tumors from lung and bronchus, prostate, breast, colon and rectum, ovarian and pancreatic cancers. We also found that, contrary to the current notions about CK2, some CK2 transcripts were downregulated in several cancers. Here, we investigate all other cancers using Oncomine to determine whether they also display significant CK2 transcript dysregulation. As anticipated from our previous analysis, we found cancers with all CK2 transcripts upregulated (e.g. cervical), and cancers where there was a combination of upregulation and/or downregulation of the CK2 transcripts (e.g. sarcoma). Unexpectedly, we found some cancers with significant downregulation of all CK2 transcripts (e.g. testicular cancer). We also found that, in some cases, CK2 transcript levels were already dysregulated in benign lesions (e.g. Barrett’s esophagus). We also found that CK2 transcript upregulation correlated with lower patient survival in most cases where data was significant. However, there were two cancer types, glioblastoma and renal cell carcinoma, where CK2 transcript upregulation correlated with higher survival. Overall, these data show that the expression levels of CK2 genes is highly variable in cancers and can lead to different patient outcomes.

A novel allosteric site in casein kinase 2α discovered using combining bioinformatics and biochemistry methods

Casein kinase 2 (CK2) is a highly pleiotropic serine-threonine kinase, which catalyzed phosphorylation of more than 300 proteins that are implicated in regulation of many cellular functions, such as signal transduction, transcriptional control, apoptosis and the cell cycle. On the other hand, CK2 is abnormally elevated in a variety of tumors, and is considered as a promising therapeutic target. The currently available ATP-competitive CK2 inhibitors, however, lack selectivity, which has impeded their development in cancer therapy. Because allosteric inhibitors can avoid the shortcomings of conventional kinase inhibitors, this study was aimed to discover a new allosteric site in CK2α and to investigate the effects of mutations in this site on the activity of CK2α. Using Allosite based on protein dynamics and structural alignment, we predicted a new allosteric site that was partly located in the αC helix of CK2α. Five residues exposed on the surface of this site were mutated to validate the prediction. Kinetic analyses were performed using a luminescent ADP detection assay by varying the concentrations of a peptide substrate, and the results showed that the mutations I78C and I78W decreased CK2α activity, whereas V31R, K75E, I82C and P109C increased CK2α activity. Potential allosteric pathways were identified using the Monte Carlo path generation approach, and the results of these predicted allosteric pathways were consistent with the mutation analysis. Multiple sequence alignments of CK2α with the other kinases in the family were conducted using the ClustalX method, which revealed the diversity of the residues in the site. In conclusion, we identified a new allosteric site in CK2α that can be altered to modulate the activity of the kinase. Because of the high diversity of the residues in the site, the site can be targeted using rational drug design of specific CK2α inhibitors for biological relevance.

Evaluation of protein kinase CK2 as a therapeutic target for squamous cell carcinoma of cats

OBJECTIVE To investigate protein kinase CK2 (CK2) expression in squamous cell carcinoma (SCC) of cats and to examine effects of CK2 downregulation on in vitro apoptosis and viability in SCC. SAMPLE Biopsy specimens of oral mucosa and testis and blood samples from clinically normal cats, biopsy specimens of oral SCC from cats, and feline SCC (SCCF1) and mammary gland carcinoma (K12) cell lines. PROCEDURES Immunohistochemical labeling for CK2α was performed on biopsy specimens. Sequences of the CK2α subunit gene and CK2α' subunit gene in feline blood and feline cancer cell lines were determined by use of PCR and reverse-transcription PCR assays followed by direct Sanger sequencing. Specific small interfering RNAs (siRNAs) were developed for feline CK2α and CK2α'. The SCCF1 cells were treated with siRNA and assessed 72 hours later for CK2α and CK2α' expression and markers of apoptosis (via western blot analysis) and for viability (via 3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium assays). RESULTS CK2α was expressed in all feline oral mucosa samples and 7 of 8 oral SCC samples. Expression of CK2α and CK2α' was successfully downregulated in SCCF1 cells by use of siRNAs, which resulted in decreased viability and induction of apoptosis. CONCLUSIONS AND CLINICAL RELEVANCE In this study, CK2 appeared to be a promising therapeutic target for SCCs of cats. A possible treatment strategy for SCCs of cats would be RNA interference that targets CK2.

Role of protein kinases CK1α and CK2 in multiple myeloma: regulation of pivotal survival and stress-managing pathways

Multiple myeloma (MM) is a malignant tumor of transformed plasma cells. MM pathogenesis is a multistep process. This cancer can occur de novo (rarely) or it can develop from monoclonal gammopathy of undetermined significance (most of the cases). MM can be asymptomatic (smoldering myeloma) or clinically active. Malignant plasma cells exploit intrinsic and extrinsic bone marrow microenvironment-derived growth signals. Upregulation of stress-coping pathways is also instrumental to maintain MM cell growth. The phylogenetically related Ser/Thr kinases CSNK1A1 (CK1α) and CSNK2 (CK2) have recently gained a growing importance in hematologic malignancies arising both from precursors and from mature blood cells. In multiple myeloma, CK1α or CK2 sustain oncogenic cascades, such as the PI3K/AKT, JAK/STAT, and NF-κB, as well as propel stress-related signaling that help in coping with different noxae. Data also suggest that these kinases modulate the delivery of growth factors and cytokines from the bone marrow stroma. The “non-oncogene addiction” phenotype generated by the increased activity of CK1α and CK2 in multiple myeloma contributes to malignant plasma cell proliferation and survival and represents an Achilles’ heel for the activity of small ATP competitive CK1α or CK2 inhibitors.

Protein kinase CK2 inhibition suppresses neointima formation via a proline-rich homeodomain-dependent mechanism

Neointimal hyperplasia is a product of VSMC replication and consequent accumulation within the blood vessel wall. In this study, we determined whether inhibition of protein kinase CK2 and the resultant stabilisation of proline-rich homeodomain (PRH) could suppress VSMC proliferation. Both silencing and pharmacological inhibition of CK2 with K66 antagonised replication of isolated VSMCs. SiRNA-induced knockdown as well as ectopic overexpression of proline-rich homeodomain indicated that PRH disrupts cell cycle progression. Mutation of CK2 phosphorylation sites Ser¹⁶³ and Ser¹⁷⁷ within the PRH homeodomain enabled prolonged cell cycle arrest by PRH. Concomitant knockdown of PRH and inhibition of CK2 with K66 indicated that the anti-proliferative action of K66 required the presence of PRH. Both K66 and adenovirus-mediated gene transfer of S163C:S177C PRH impaired neointima formation in human saphenous vein organ cultures. Importantly, neither intervention had notable effects on cell cycle progression, cell survival or migration in cultured endothelial cells.

Inhibition of protein kinase CK2 sensitizes non-small cell lung cancer cells to cisplatin via upregulation of PML

Non-small cell lung carcinoma (NSCLC), a malignancy of lungs, is very aggressive and usually ends up with a dismal prognosis. Cisplatin (CDDP)-based systemic chemotherapy is the main pharmaceutical approach for treating NSCLC, but its effect is discounted by some hitherto unknown reasons. Thus, this study is dedicated to improving the efficacy of CDDP. Our results show that combining use of CDDP with CK2 siRNA or inhibitor is more efficient in suppressing cancer cell growth and promoting apoptosis than use of CDDP alone. The underlying mechanism is that CDDP has two pathways to go: one is that it directly induces apoptosis and the other is that it activates CK2, which suppresses proapoptosis gene promyelocytic leukemia (PML). In conclusion, inhibiting CK2 can enhance sensitivity of CDDP to NSCLC cancer cells through PML.