Involvement of reactive oxygen species in apoptosis induced by pharmacological inhibition of protein kinase CK2

Pro-Oxidant Effect of Resveratrol on Human Breast Cancer MCF-7 Cells is Associated with CK2 Inhibition

Casein kinase 2 (CK2) plays a critical role in the proliferation and apoptosis of cancer cells. Resveratrol is a bioactive compound with anticancer and anti-inflammatory effects. This study investigated the pro-oxidant cytotoxic effects of resveratrol in association with the inhibition of CK2 activity on human breast carcinoma cells MCF-7. We showed that resveratrol and TBB, an inhibitor of CK2, decreased cell viability in a concentration dependent manner with an IC₅₀ value of 238 µM and 106 µM after 24 h, of treatment, respectively. Resveratrol and TBB decreased CK2 activity by 1.6 and 1.4-fold, respectively, and both significantly decreased mitochondrial membrane potential. However, only resveratrol increased reactive oxygen species (ROS) levels by 1.7-fold as opposed to TBB, which did not affect ROS levels. Indeed, incubating MCF-7 cells with the antioxidant polyethylene glycol-catalase (PEG-CAT) preserved cell viability from the cytotoxic effects of resveratrol, but not from TBB toxicity. This effect seemed to be related to PEG-CAT ability to prevent CK2 inhibition induced by resveratrol incubation. In conclusion, this study demonstrated that the cytotoxic effect of resveratrol on MCF-7 cells might be associated with its pro-oxidant action, which inhibited CK2 activity, affecting cell viability and mitochondrial function.

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.

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.

Inhibition of Casein Kinase 2 Disrupts Differentiation of Myeloid Cells in Cancer and Enhances the Efficacy of Immunotherapy in Mice

The role of myeloid cells as regulators of tumor progression that significantly impact the efficacy of cancer immunotherapies makes them an attractive target for inhibition. Here we explore the effect of a novel, potent, and selective inhibitor of serine/threonine protein kinase casein kinase 2 (CK2) on modulating myeloid cells in the tumor microenvironment. Although inhibition of CK2 caused only a modest effect on dendritic cells in tumor-bearing mice, it substantially reduced the amount of polymorphonuclear myeloid-derived suppressor cells and tumor-associated macrophages. This effect was not caused by the induction of apoptosis, but rather by a block of differentiation. Our results implicated downregulation of CCAAT-enhancer binding protein-α in this effect. Although CK2 inhibition did not directly affect tumor cells, it dramatically enhanced the antitumor activity of immune checkpoint receptor blockade using anti-CTLA-4 antibody. These results suggest a potential role of CK2 inhibitors in combination therapies against cancer.Significance: These findings demonstrate the modulatory effects of casein kinase 2 inhibitors on myeloid cell differentiation in the tumor microenvironment, which subsequently synergize with the antitumor effects of checkpoint inhibitor CTLA4. Cancer Res; 78(19); 5644-55. ©2018 AACR.

CK2 Molecular Targeting-Tumor Cell-Specific Delivery of RNAi in Various Models of Cancer

Protein kinase CK2 demonstrates increased protein expression relative to non-transformed cells in the majority of cancers that have been examined. The elevated levels of CK2 are involved in promoting not only continued proliferation of cancer cells but also their resistance to cell death; thus, CK2 has emerged as a plausible target for cancer therapy. Our focus has been to target CK2 catalytic subunits at the molecular level using RNA interference (RNAi) strategies to achieve their downregulation. The delivery of oligonucleotide therapeutic agents warrants that they are protected and are delivered specifically to cancer cells. The latter is particularly important since CK2 is a ubiquitous signal that is essential for survival. To achieve these goals, we have developed a nanocapsule that has the properties of delivering an anti-CK2 RNAi therapeutic cargo, in a protected manner, specifically to cancer cells. Tenfibgen (TBG) is used as the ligand to target tenascin-C receptors, which are elevated in cancer cells. This strategy is effective for inhibiting growth and inducing death in several types of xenograft tumors, and the nanocapsule elicits no safety concerns in animals. Further investigation of this therapeutic approach for its translation is warranted.

Protein kinase CK2 inhibition induces cell death via early impact on mitochondrial function

CK2 (official acronym for casein kinase 2 or II) is a potent suppressor of apoptosis in response to diverse apoptotic stimuli-thus its molecular downregulation or activity inhibition results in potent induction of cell death. CK2 downregulation is known to impact mitochondrial apoptotic circuitry but the underlying mechanism(s) remain unclear. Utilizing prostate cancer cell lines subjected to CK2-specific inhibitors which cause loss of cell viability, we have found that CK2 inhibition in cells causes rapid early decrease in mitochondrial membrane potential (Δψm). Cells treated with the CK2 inhibitors TBB (4,5,6,7-tetrabromobenzotriazole) or TBCA (tetrabromocinnamic acid) demonstrate changes in Δψm which become apparent within 2 h, that is, significantly prior to evidence of activation of other mitochondrial apoptotic signals whose temporal expression ensues subsequent to loss of Δψm. Further, we have demonstrated the presence of CK2 in purified mitochondria and it appears that the effect on Δψm evoked by inhibition of CK2 may involve mitochondrial localized CK2. Results also suggest that alterations in Ca(2+) signaling may be involved in the CK2 mediated regulation of Δψm and mitochondrial permeability. Thus, we propose that a key mechanism of CK2 impact on mitochondrial apoptotic circuitry and cell death involves early loss of Δψm which may be a primary trigger for apoptotic signaling and cell death resulting from CK2 inhibition.

Toxicological effect of emodin in mouse testicular gene expression profile

Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) is a herbal medicine extracted from the rhizomes of Rheum palmatum, and is known as an inhibitor of casein kinase II (CK2). The CK2α' knockout mice are known to be male-infertile; however, there have been no reports on the toxicity of emodin in male reproductive organs/tissues. To evaluate the toxicological effects of emodin on differential gene expression profiles of the testis as compared with acrylamide, mice were orally administered emodin and acrylamide for 5 days at a dose of 1000 and 50 mg kg(-1) per day, respectively, and euthanized 24 h after the final administration. Both chemicals induced hypospermatogenesis, eosinophilic change and apoptosis of germ cell. A DNA microarray analysis showed that the IGF-1 receptor signaling was most closely related to the above testicular toxicity induced by emodin, and the RhoA regulation, TGF/WNT and cytoskeletal remodeling, TNFR1 signaling and adenosine A2A receptor signaling were commonly associated with the two chemicals. We selected 36 genes associated with CK2, apoptosis and spermatogenesis and determined their expression by quantitative reverse transcription-polymerase chain reaction (qPCR). Both chemicals perturbed the expression of genes associated with CK2. Genes related to spermatogenesis were also affected, as evidenced by hypospermatogenesis, and eosinophilic change and apoptosis of germ cell. The results suggest that emodin causes testicular toxicity, including apoptosis with related the IGF-1 receptor signaling pathway, and the two chemicals commonly affect CK2, spermatogenesis and sperm motility via four pathways, such as TNFR1 signaling.

Casein Kinase II: an attractive target for anti-cancer drug design

Casein Kinase II (CK2) is a ubiquitous serine/threonine kinase that is highly conserved in eukaryotic cells. CK2 has been shown to impact cell growth and proliferation, as numerous growth-related proteins are substrates of CK2. More importantly, experimental evidence linking increased expression and activity of CK2 to human cancers underscores the relevance of CK2 biology to cellular transformation and carcinogenesis. Due to the critical regulatory role CK2 plays in cell fate determination in cancer cells, there is a tremendous interest in the development of CK2-specific therapies. Supporting this, recent reports have demonstrated that genetic manipulation of CK2 expression as well as pharmacological inhibition of its enzymatic activity sensitizes cancers to apoptotic stimuli. Here we provide a succinct account of the biology of CK2, its cellular substrates, its pro-survival and pro-proliferation activity, and highlight evidence for its involvement in human cancer.

Emergence of protein kinase CK2 as a key target in cancer therapy

Protein kinase CK2, a protein serine/threonine kinase, plays a global role in activities related to cell growth, cell death, and cell survival. CK2 has a large number of potential substrates localized in diverse locations in the cell including, for example, NF-kappaB as an important downstream target of the kinase. In addition to its involvement in cell growth and proliferation it is also a potent suppressor of apoptosis, raising its key importance in cancer cell phenotype. CK2 interacts with diverse pathways which illustrates the breadth of its impact on the cellular machinery of both cell growth and cell death giving it the status of a "master regulator" in the cell. With respect to cancer, CK2 has been found to be dysregulated in all cancers examined demonstrating increased protein expression levels and nuclear localization in cancer cells compared with their normal counterparts. We originally proposed CK2 as a potentially important target for cancer therapy. Given the ubiquitous and essential for cell survival nature of the kinase, an important consideration would be to target it specifically in cancer cells while sparing normal cells. Towards that end, our design of a tenascin based sub-50 nm (i.e., less than 50 nm size) nanocapsule in which an anti-CK2 therapeutic agent can be packaged is highly promising because this formulation can specifically deliver the cargo intracellularly to the cancer cells in vivo. Thus, appropriate strategies to target CK2 especially by molecular approaches may lead to a highly feasible and effective approach to eradication of a given cancer.