CK2 signaling in androgen-dependent and -independent prostate cancer

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.

Protein kinase CK2 in development and differentiation

Among the human kinomes, protein kinase CK2 (formerly termed casein kinase II) is considered to be essential, as it is implicated in the regulation of various cellular processes. Experiments with pharmacological inhibitors of the kinase activity of CK2 provide evidence that CK2 is essential for development and differentiation. Therefore, the present review addresses the role of CK2 during embryogenesis, neuronal, adipogenic, osteogenic and myogenic differentiation in established model cell lines, and in embryonic, neural and mesenchymal stem cells. CK2 kinase activity appears to be essential in the early stages of differentiation, as CK2 inhibition at early time points generally prevents differentiation. In addition, the present review reports on target proteins of CK2 in embryogenesis and differentiation.

Regulation of cellular proliferation in acute lymphoblastic leukemia by Casein Kinase II (CK2) and Ikaros

The IKZF1 gene encodes the Ikaros protein, a zinc finger transcriptional factor that acts as a master regulator of hematopoiesis and a tumor suppressor in leukemia. Impaired activity of Ikaros is associated with the development of high-risk acute lymphoblastic leukemia (ALL) with a poor prognosis. The molecular mechanisms that regulate Ikaros' function as a tumor suppressor and regulator of cellular proliferation are not well understood. We demonstrated that Ikaros is a substrate for Casein Kinase II (CK2), an oncogenic kinase that is overexpressed in ALL. Phosphorylation of Ikaros by CK2 impairs Ikaros' DNA-binding ability, as well as Ikaros' ability to regulate gene expression and function as a tumor suppressor in leukemia. Targeting CK2 with specific inhibitors restores Ikaros' function as a transcriptional regulator and tumor suppressor resulting in a therapeutic, anti-leukemia effect in a preclinical model of ALL. Here, we review the genes and pathways that are regulated by Ikaros and the molecular mechanisms through which Ikaros and CK2 regulate cellular proliferation in leukemia.

Phosphoproteome Integration Reveals Patient-Specific Networks in Prostate Cancer

We used clinical tissue from lethal metastatic castration-resistant prostate cancer (CRPC) patients obtained at rapid autopsy to evaluate diverse genomic, transcriptomic, and phosphoproteomic datasets for pathway analysis. Using Tied Diffusion through Interacting Events (TieDIE), we integrated differentially expressed master transcriptional regulators, functionally mutated genes, and differentially activated kinases in CRPC tissues to synthesize a robust signaling network consisting of druggable kinase pathways. Using MSigDB hallmark gene sets, six major signaling pathways with phosphorylation of several key residues were significantly enriched in CRPC tumors after incorporation of phosphoproteomic data. Individual autopsy profiles developed using these hallmarks revealed clinically relevant pathway information potentially suitable for patient stratification and targeted therapies in late stage prostate cancer. Here, we describe phosphorylation-based cancer hallmarks using integrated personalized signatures (pCHIPS) that shed light on the diversity of activated signaling pathways in metastatic CRPC while providing an integrative, pathway-based reference for drug prioritization in individual patients.

Protein kinase CK2 is widely expressed in follicular, Burkitt and diffuse large B-cell lymphomas and propels malignant B-cell growth

Serine-threonine kinase CK2 is highly expressed and pivotal for survival and proliferation in multiple myeloma, chronic lymphocytic leukemia and mantle cell lymphoma. Here, we investigated the expression of α catalytic and β regulatory CK2 subunits by immunohistochemistry in 57 follicular (FL), 18 Burkitt (BL), 52 diffuse large B-cell (DLBCL) non-Hodgkin lymphomas (NHL) and in normal reactive follicles. In silico evaluation of available Gene Expression Profile (GEP) data sets from patients and Western blot (WB) analysis in NHL cell-lines were also performed. Moreover, the novel, clinical-grade, ATP-competitive CK2-inhibitor CX-4945 (Silmitasertib) was assayed on lymphoma cells. CK2 was detected in 98.4% of cases with a trend towards a stronger CK2α immunostain in BL compared to FL and DLBCL. No significant differences were observed between Germinal Center B (GCB) and non-GCB DLBCL types. GEP data and WB confirmed elevated CK2 mRNA and protein levels as well as active phosphorylation of specific targets in NHL cells. CX-4945 caused a dose-dependent growth-arresting effect on GCB, non-GCB DLBCL and BL cell-lines and it efficiently shut off phosphorylation of NF-κB RelA and CDC37 on CK2 target sites. Thus, CK2 is highly expressed and could represent a suitable therapeutic target in BL, FL and DLBCL NHL.

CK2-NCoR signaling cascade promotes prostate tumorigenesis

The aberrant expressions of casein kinase 2 (CK2) was found in prostate cancer patient and cell lines, but little is known of the detailed mechanisms implicated in prostate tumorigenesis. In this study, we report that both CK2 activity and CK2-mediated NCoR phosphorylation are significantly elevated in the androgen-independent prostate cancer cell line DU145 and PC-3 compared with RWPE1 and LNCaP cells. Increased phosphorylation inversely correlates with the mRNA level of the NCoR-regulated gene, interferon-γ-inducible protein 10 (IP-10). CK2 inhibition abrogated NCoR phosphorylation, IP-10 transcriptional repression, and the invasion activity of PC-3 cells. Inhibition of the CK2-NCoR network significantly reduced in vivo PC-3 cell tumorigenicity, likely due to transcriptional derepression of IP-10. Clinicopathological analyses revealed that increased CK2-mediated NCoR phosphorylation significantly correlates with poor survival among prostate cancer patients. These findings elucidate a CK2-modulated oncogenic cascade in prostate tumorigenesis.

Regulation of the proapoptotic functions of prostate apoptosis response-4 (Par-4) by casein kinase 2 in prostate cancer cells

The proapoptotic protein, prostate apoptosis response-4 (Par-4), acts as a tumor suppressor in prostate cancer cells. The serine/threonine kinase casein kinase 2 (CK2) has a well-reported role in prostate cancer resistance to apoptotic agents or anticancer drugs. However, the mechanistic understanding on how CK2 supports survival is far from complete. In this work, we demonstrate both in rat and humans that (i) Par-4 is a new substrate of the survival kinase CK2 and (ii) phosphorylation by CK2 impairs Par-4 proapoptotic functions. We also unravel different levels of CK2-dependent regulation of Par-4 between species. In rats, the phosphorylation by CK2 at the major site, S124, prevents caspase-mediated Par-4 cleavage (D123) and consequently impairs the proapoptotic function of Par-4. In humans, CK2 strongly impairs the apoptotic properties of Par-4, independently of the caspase-mediated cleavage of Par-4 (D131), by triggering the phosphorylation at residue S231. Furthermore, we show that human Par-4 residue S231 is highly phosphorylated in prostate cancer cells as compared with their normal counterparts. Finally, the sensitivity of prostate cancer cells to apoptosis by CK2 knockdown is significantly reversed by parallel knockdown of Par-4. Thus, Par-4 seems a critical target of CK2 that could be exploited for the development of new anticancer drugs.

Activation of protein kinase CK2 attenuates FOXO3a functioning in a PML-dependent manner: implications in human prostate cancer

Protein kinase CK2 (also known as Caseine Kinase II) is an ubiquitous Ser/Thr protein kinase present in both the nucleus and cytoplasm of cells, targeting several key enzymes, growth factor receptors, transcription factors and cytoskeletal proteins. It is not only a key player in regulating cellular growth and proliferation, but also behaves as a potent suppressor of apoptosis. CK2 has been frequently found to be deregulated (mostly hyperactivated) in all cancers, prostate cancer being prominent of them. In the recent past, tumor suppressor PML (promyelocytic leukemia) has been shown to be a target of phosphorylation by CK2. This phosphorylation promotes the ubiquitin-mediated proteasomal degradation of PML thereby effectively curbing its role as a tumor suppressor. Among many others, PML has also been established to mediate its tumor suppressive role by mitigating the inactivation of active AKT (pAKT) inside the nucleus by assembling a dephosphorylating platform for nuclear pAKT. One of the immediate consequences, of this inactivation is the stabilization of FOXO3a, another well-established tumor suppressor, inside the nucleus and its downstream activities. Here, we propose a novel signaling axis apexed by deregulated CK2, dismantling the association of PML and PHLPP2 (we also report PHLPP2 to be a novel interacting partner of PML inside the nucleus), ultimately leading to the inactivation and nuclear exclusion of FOXO3a, thereby downregulating p21/p27/Bim in which degradation of PML and the concomitant stabilization of pAKT plays a cardinal part.

Casein kinase 2 inhibition attenuates androgen receptor function and cell proliferation in prostate cancer cells

BACKGROUND

Casein kinase 2 (CK2) is constitutively active with dual specificity and exists as a hetero-tetrameric complex of α, α', and β subunits. Its aberrant expression and elevated activity have been linked to many human cancers, including prostate cancer. As an effort to develop new chemotherapy for prostate cancers, in this study, we tested the effects of tetra-bromo-cinnamic acid (TBCA), a newly synthetic CK2-selective CK2 inhibitor, on androgen receptor (AR) transactivation, cell proliferation, and viability in multiple prostate cancer cell lines.

METHODS

We utilized a comprehensive approach of a newly synthetic CK2-selective inhibitor TBCA, plus gene-specific siRNAs in multiple cell-based assays to further understand the role of CK2 in AR signaling. Alamar-blue-based cell growth assay, flow cytometry for cell cycle distribution, Luciferase report gene assay for AR transactivation, and immuno-fluorescent approach for AR nuclear localization as well as quantitative PCR assay for AR-mediated gene expression were utilized. The significance of the differences between treatment and control was analyzed using the SPSS software (SPSS, Chicago, IL).

RESULTS

Our data revealed that TBCA reduced cell proliferation and caused G2/M cell cycle arrest in a dose-dependent manner. Further analysis demonstrated that TBCA blocked AR nuclear translocation and gene expression. To confirm the target specificity, we used gene-specific siRNAs for both CK2α and CK2α' subunits, and the results suggested that both CK2 catalytic subunits are involved in androgen-stimulated AR nuclear translocation and AR-mediated gene expression in prostate cancer cells.

CONCLUSIONS

CK2 subunits α and α' are likely involved in AR signaling, and TBCA might be useful in the management of prostate cancers as a chemo-preventive agent in the future.

CK2 regulates ATF4 and CHOP transcription within the cellular stress response signalling pathway

Protein kinase CK2 is an ubiquitously expressed serine/threonine kinase. The protein levels along with CK2 activity are highly elevated in tumour cells where it protects cells from apoptosis. Accordingly, inhibition of CK2 is known to induce programmed cell death, making it a promising target for cancer therapy. Analysis of the different behaviour of hormone sensitive LNCaP cells and hormone refractory PC-3 cells after CK2 inhibition revealed CHOP ((C/EBP)-homologous protein) induction and therefore probably ER stress as crucial for apoptosis in the LNCaP cells. In the present study we investigated which promoter element of the CHOP promoter is responsible for its induction. ER stress can be generated by the accumulation of unfolded proteins, by depletion of amino acids or by oxidative stress. ER stress induces specific signalling pathways. In order to analyse which pathway might be activated by CK2 inhibition we started to analyse the activation of the different CHOP promoter elements. By using mutated reporter constructs of the CHOP promoter, it turned out that the amino acid response element (AARE) is the most prominent element for CHOP induction after CK2 inhibition. The ER stress element, however, proves to be less crucial, and along with the AP-1 binding site, they do not seem to play any role. Further we found an up-regulation of the transcription factor ATF4 after CK2 inhibition. ATF4 is involved in ER stress signalling through the AARE, which further supports our finding that CK2 inhibition provokes an amino acid induced response pathway.

Protein B23/nucleophosmin/numatrin nuclear dynamics in relation to protein kinase CK2 and apoptotic activity in prostate cells

Protein B23/nucleophosmin/numatrin (B23) is a key nucleolar/nuclear matrix-associated protein required for cell growth-related functions, such as rRNA synthesis. Protein kinase CK2 (CK2) (formerly casein kinase 2, a protein Ser/Thr kinase signal that is involved in cell growth and cell death) mediates phosphorylation of B23, thereby influencing its functional activity. Here we have delineated the dynamics of B23 and its link to CK2 status in response to altered growth stimuli and induction of apoptosis in cultured prostate cells and in rat prostate cells in vivo. Our studies employing PC-3 and ALVA-41 prostate cancer cells demonstrated colocalization of CK2 and B23 in the nucleus. Further, CK2 and B23 underwent coordinate modulation in the nucleus related to their nucleocytoplasmic shuttling in response to induction of apoptotic activity in cells caused by downregulation of CK2 or by treatment with other apoptosis-inducing agents. These alterations in nuclear association of B23 occurred in the absence of a significant change in the level of cytoplasmic B23. Similar studies in the in vivo model of rat prostate epithelial cells subjected to androgen deprivation (that resulted in loss of nuclear CK2 and induction of apoptosis) demonstrated dynamic modulation of nuclear matrix-associated B23 without a significant change in its cytoplasmic level. These changes were reversed by androgen-mediated growth response in the prostate. Our results suggest that CK2-mediated phosphorylation of B23 is essential for its retention in the nucleus and that coordinated nuclear localization of B23 and CK2 is dynamically regulated in response to altered growth status in the cell.

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.

Regulation of cell proliferation and survival: convergence of protein kinases and caspases

Intricate networks of protein kinases are intimately involved in the regulation of cellular events related to cell proliferation and survival. In addition to protein kinases, cells also contain networks of proteases including aspartic-acid directed caspases organized in cascades that play a major role in the regulation of cell survival through their involvement in the initiation and execution phases of apoptosis. Perturbations in regulatory protein kinase and caspase networks induce alterations in cell survival and frequently accompany transformation and tumorigenesis. Furthermore, recent studies have documented that caspases or their substrates are subject to phosphorylation in cells illustrating a potential convergence of protein kinase and caspase signaling pathways. Interestingly, a number of caspase substrates are protected from cleavage when they are phosphorylated at sites that are adjacent to caspase cleavage sites. While it is theoretically possible that many distinct protein kinases could protect proteins from caspase-mediated cleavage, protein kinase CK2 is of particular interest because acidic amino acids, including aspartic acid residues that are recognized by caspases, are its dominant specificity determinants.

Nanocapsule-delivered Sleeping Beauty mediates therapeutic Factor VIII expression in liver sinusoidal endothelial cells of hemophilia A mice

Liver sinusoidal endothelial cells are a major endogenous source of Factor VIII (FVIII), lack of which causes the human congenital bleeding disorder hemophilia A. Despite extensive efforts, gene therapy using viral vectors has shown little success in clinical hemophilia trials. Here we achieved cell type-specific gene targeting using hyaluronan- and asialoorosomucoid-coated nanocapsules, generated using dispersion atomization, to direct genes to liver sinusoidal endothelial cells and hepatocytes, respectively. To highlight the therapeutic potential of this approach, we encapsulated Sleeping Beauty transposon expressing the B domain-deleted canine FVIII in cis with Sleeping Beauty transposase in hyaluronan nanocapsules and injected them intravenously into hemophilia A mice. The treated mice exhibited activated partial thromboplastin times that were comparable to those of wild-type mice at 5 and 50 weeks and substantially shorter than those of untreated controls at the same time points. Further, plasma FVIII activity in the treated hemophilia A mice was nearly identical to that in wild-type mice through 50 weeks, while untreated hemophilia A mice exhibited no detectable FVIII activity. Thus, Sleeping Beauty transposon targeted to liver sinusoidal endothelial cells provided long-term expression of FVIII, without apparent antibody formation, and improved the phenotype of hemophilia A mice.

Protein kinase CK2 in health and disease: CK2: a key player in cancer biology

Elevated levels of protein kinase CK2 (formerly casein kinase 2 or II) have long been associated with increased cell growth and proliferation both in normal and cancer cells. The ability of CK2 to also act as a potent suppressor of apoptosis offers an important link to its involvement in cancer since deregulation of both cell proliferation and apoptosis are among the key features of cancer cell biology. Dysregulated CK2 may impact both of these processes in cancer cells. All cancers that have been examined show increased CK2 expression, which may also relate to prognosis. The extensive involvement of CK2 in cancer derives from its impact on diverse molecular pathways controlling cell proliferation and cell death. Downregulation of CK2 by various approaches results in induction of apoptosis in cultured cell and xenograft cancer models suggesting its potential as a therapeutic target.

Histone deacetylases: salesmen and customers in the post-translational modification market

HDACs (histone deacetylases) are enzymes that remove the acetyl moiety from N-epsilon-acetylated lysine residues in histones and non-histone proteins. In recent years, it has turned out that HDACs themselves are also subject to post-translational modification. Such structural alterations can determine the stability, localization, activity and protein-protein interactions of HDACs. This subsequently affects the modification of their substrates and the co-ordination of cellular signalling networks. Intriguingly, physiologically relevant non-histone proteins are increasingly found to be deacetylated by HDACs, and aberrant deacetylase activity contributes to several severe human diseases. Targeting the catalytic activity of these enzymes and their post-translational modifications are therefore attractive targets for therapeutical intervention strategies. To achieve this ambitious goal, details on the molecular mechanisms regulating post-translational modifications of HDACs are required. This review summarizes aspects of the current knowledge on the biological role and enzymology of the phosphorylation, acetylation, ubiquitylation and sumoylation of HDACs.

Impact of protein kinase CK2 on inhibitor of apoptosis proteins in prostate cancer cells

We have previously demonstrated that protein kinase CK2 is a potent suppressor of apoptosis in cells subjected to diverse mediators of apoptosis. The process of apoptosis involves a complex series of molecules localized in various cellular compartments. Among the various proteins that modulate apoptotic activity are inhibitors of apoptosis proteins (IAPs) which are elevated in cancers and have been proposed to block caspase activity. We have examined the impact of CK2 signal on these proteins in prostate cancer cells. Cellular IAPs demonstrate distinct localization and responsiveness to altered CK2 expression or activity in the cytoplasmic and nuclear matrix fractions. Modulation of cellular CK2 by various approaches impacts on cellular IAPs such that inhibition or downregulation of CK2 results in reduction in these proteins. Further, IAPs are also reduced when cells are treated with sub-optimal concentrations of chemical inhibitors of CK2 combined with low or sub-optimal levels of apoptosis-inducing agents (such as etoposide) suggesting that downregulation of CK2 sensitizes cells to induction of apoptosis which may be related to attenuation of IAPs. Decreased IAP protein levels in response to apoptotic agents such as TNFalpha or TRAIL were potently blocked upon forced overexpression of CK2 in cells. Together, our results suggest that one of the modes of CK2-mediated modulation of apoptotic activity is via its impact on cellular IAPs.

Poly(malic acid) nanoconjugates containing various antibodies and oligonucleotides for multitargeting drug delivery

Nanoconjugates are emerging as promising drug-delivery vehicles because of their multimodular structure enabling them to actively target discrete cells, pass through biological barriers and simultaneously carry multiple drugs of various chemical nature. Nanoconjugates have matured from simple devices to multifunctional, biodegradable, nontoxic and nonimmunogenic constructs, capable of delivering synergistically functioning drugs in vivo. This review mainly concerns the Polycefin family of natural-derived polymeric drug-delivery devices as an example. This type of vehicle is built by hierarchic conjugation of functional groups onto the backbone of poly(malic acid), an aliphatic polyester obtained from the microorganism Physarum polycephalum. Particular Polycefin variants target human brain and breast tumors implanted into animals specifically and actively and could be detected easily by noninvasive imaging analysis. Delivery of antisense oligonucleotides to a tumor-specific angiogenic marker using Polycefin resulted in significant inhibition of tumor angiogenesis and increase of animal survival.

Phosphorylation of liver X receptor alpha selectively regulates target gene expression in macrophages

Dysregulation of liver X receptor alpha (LXRalpha) activity has been linked to cardiovascular and metabolic diseases. Here, we show that LXRalpha target gene selectivity is achieved by modulation of LXRalpha phosphorylation. Under basal conditions, LXRalpha is phosphorylated at S198; phosphorylation is enhanced by LXR ligands and reduced both by casein kinase 2 (CK2) inhibitors and by activation of its heterodimeric partner RXR with 9-cis-retinoic acid (9cRA). Expression of some (AIM and LPL), but not other (ABCA1 or SREBPc1) established LXR target genes is increased in RAW 264.7 cells expressing the LXRalpha S198A phosphorylation-deficient mutant compared to those with WT receptors. Surprisingly, a gene normally not expressed in macrophages, the chemokine CCL24, is activated specifically in cells expressing LXRalpha S198A. Furthermore, inhibition of S198 phosphorylation by 9cRA or by a CK2 inhibitor similarly promotes CCL24 expression, thereby phenocopying the S198A mutation. Thus, our findings reveal a previously unrecognized role for phosphorylation in restricting the repertoire of LXRalpha-responsive genes.

Mass spectrometry analysis of a protein kinase CK2beta subunit interactome isolated from mouse brain by affinity chromatography

CK2, an acronym derived from the misnomer "casein kinase 2", denotes a ubiquitous and extremely pleiotropic Ser/Thr protein kinase, the holoenzyme of which is composed of two catalytic (alpha and/or alpha') and two noncatalytic beta subunits acting as a docking platform and the multifarious functions of which are still incompletely understood. By combining affinity chromatography and mass spectrometry, we have identified 144 mouse brain proteins that associate with immobilized CK2beta. A large proportion (60%) of the identified proteins had been previously reported to be functionally related to CK2, and a similar proportion have been classified as phosphoproteins with approximately half of these having the features of CK2 targets. A large number of the identified proteins ( approximately 40%) either are nuclear or shuttle between the nucleus and cytoplasm, and the biggest functional classes of CK2beta interactors are committed to protein synthesis and degradation (32 proteins) and RNA/DNA interaction (20 proteins). Also well represented are the categories of cytoskeletal/structural proteins (19), trafficking proteins (17), and signaling proteins (14). The identified proteins are examined in relation to their functions and potential as targets and/or regulators of CK2, disclosing in some cases unanticipated links between this kinase and a variety of biochemical events.

Protein kinase CK2 modulates apoptosis induced by resveratrol and epigallocatechin-3-gallate in prostate cancer cells

Resveratrol and epigallocatechin-3-gallate (EGCG) are important candidates as chemopreventive agents by virtue of their ability to induce apoptosis in cancer cells. Casein kinase 2 (CK2) is a ubiquitous protein ser/thr kinase that plays diverse roles in cell proliferation and apoptosis. We have previously shown that overexpression of CK2 suppresses apoptosis induced by a variety of agents, whereas down-regulation of CK2 sensitizes cells to induction of apoptosis. We therefore investigated whether or not CK2 played a role in resveratrol and EGCG signaling in androgen-sensitive (ALVA-41) and androgen-insensitive (PC-3) prostate cancer cells. Resveratrol- and EGCG-induced apoptosis is associated with a significant down-regulation of CK2 activity and protein expression in both the ALVA-41 and PC-3 cells. Overexpression of CK2alpha protected prostatic cancer cells against resveratrol- and EGCG-induced apoptosis. Relatively low doses (10 mumol/L) of resveratrol and EGCG induced a modest proliferative response in cancer cells that could be switched to cell death by moderate inhibition of CK2. These findings characterize, for the first time, the effects of polyphenolic compounds on CK2 signaling in androgen-sensitive and androgen-insensitive prostatic carcinoma cells and suggest that resveratrol and EGCG may mediate their cellular activity, at least in part, via their targeting of CK2. Further, the data hint at the potential of using these polyphenols alongside CK2 inhibitors in combination chemotherapy.

Nuclear localization of protein kinase CK2 catalytic subunit (CK2alpha) is associated with poor prognostic factors in human prostate cancer

Many genomic abnormalities have been identified in various subsets of prostate cancer, but until now, few genes have been associated with the progression of this cancer. High activity of protein serine/threonine kinase CK2 has been observed in various solid tumours and this alteration has been linked both to growth-related functions and to suppression of cellular apoptosis. Here, we provide the first evidence for a strong association between a nuclear localization of CK2alpha, evaluated by immunohistochemistry, and poor prognostic factors in a retrospective cohort of 131 human prostate adenocarcinomas. Nuclear CK2alpha localization is significantly correlated with higher Gleason score, more locally advanced disease (cT3-T4) and more perineural or lymphatic invasion (p<0.0019 to 0.046). In contrast, despite a strong trend, no significant relationship was found between higher initial PSA and nuclear CK2alpha localization. Thus, this previously undescribed molecular heterogeneity is the first step in defining CK2 as both a potential biomarker and a promising target in human prostate cancer.

Parathyroid hormone-related protein (PTHrP) inhibits mitochondrial-dependent apoptosis through CK2

Over the past decade, parathyroid hormone-related protein (PTHrP) has been identified as a key survival factor for cells subjected to apoptotic stimuli. Its anti-apoptotic activity has been attributed to nuclear accumulation of the intact protein, or a synthetic peptide corresponding to its nuclear targeting sequence (NTS), which promotes rapid exit of nutrient deprived cells from the cell cycle. Intracellular PTHrP also inhibited apoptosis by blocking tumor necrosis factor alpha (TNFalpha)-induced apoptosis by blocking signaling from the "death receptor" and preventing damage to the mitochondrial membrane. In both cases, the anti-apoptotic activity was significantly reduced in the presence of a nuclear deficient form of PTHrP with a (88)K/E K/E.K/I(91) mutation in the NTS. The current work was undertaken to determine the mechanism by which nuclear PTHrP blocked mitochondrial-mediated apoptosis. Using sub-cellular fractionation and functional assays we showed that pre-treatment of HEK293 cells with exogenous NTS peptide before inducing apoptosis with TNFalpha was as effective as expression of the full-length protein in inhibiting apoptosis. Inhibition of apoptosis was associated with increased expression of protein kinase casein kinase 2 (CK2) and in sustained CK2 accumulation and activity in the nuclear fraction. In primary chondrogenic cells harvested from the limb buds of PTHrP(+/-) and PTHrP(-/-) embryonic mice, there was a dose-dependent decrease in CK2 expression and activity that correlated with increased susceptibility to apoptosis. Taken together the results indicate that nuclear accumulation of PTHrP effectively inhibits mitochondrial-mediated apoptosis through regulation of the expression, activity, and sub-cellular trafficking of CK2.

Intracellular hydrogen peroxide production is an upstream event in apoptosis induced by down-regulation of casein kinase 2 in prostate cancer cells

We have shown previously that down-regulation of CK2 activity (protein kinase CK2, formerly casein kinase 2) by employing its inhibitors apigenin or 4,5,6,7-tetrabromobenzotriazole promotes apoptosis in prostatic carcinoma cells. In an effort to define the downstream mediators of this action, we show that cell apoptosis observed on down-regulation of CK2 is preceded by intracellular generation of hydrogen hydroxide (H2O2) in various normal and cancer cells. In this regard, both androgen-dependent ALVA-41 and androgen-independent PC-3 cells treated with 80 micromol/L apigenin or 4,5,6,7-tetrabromobenzotriazole or with antisense CK2alpha oligonucleotide or small interfering RNA respond similarly to down-regulation of CK2. Interestingly, whereas chemical inhibitors of CK2 elicited H2O2 production in both cancer and noncancer cells, the antisense CK2alpha-mediated down-regulation of CK2 showed significant H2O2 production in cancer cells but had minimal effect in noncancer cells. The basis of this key difference is unclear at present, but this observation may have implications for the therapeutic potential of antisense CK2 oligonucleotide in cancer therapy. The H2O2 production induced by antisense CK2alpha was associated with robust caspase-3 activity, nuclear factor-kappaB nuclear translocation, cytochrome c release, and subsequent DNA fragmentation in prostate cancer cells (ALVA-41 and PC-3). These findings describe, for the first time, a relationship between CK2 and reactive oxygen species, such that CK2 inhibition leads to production of intracellular H2O2, which may serve as a downstream mediator of apoptosis in cancer cells.