Hyperphosphorylation as a defense mechanism to reduce TDP-43 aggregation

Several neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitinated inclusions (FTLD-U) are characterized by inclusion bodies formed by TDP-43 (TDP). We established cell and transgenic Drosophila models expressing TDP carboxyl terminal fragment (ND251 and ND207), which developed aggregates recapitulating important features of TDP inclusions in ALS/FTLD-U, including hyperphosphorylation at previously reported serine^{403,404,409,410} residues, polyubiquitination and colocalization with optineurin. These models were used to address the pathogenic role of hyperphosphorylation in ALS/FTLD-U. We demonstrated that hyperphosphorylation and ubiquitination occurred temporally later than aggregation in cells. Expression of CK2α which phosphorylated TDP decreased the aggregation propensity of ND251 or ND207; this effect could be blocked by CK2 inhibitor DMAT. Mutation of serines^{379,403,404,409,410} to alanines (S5A) to eliminate phosphorylation increased the aggregation propensity and number of aggregates of TDP, but mutation to aspartic acids (S5D) or glutamic acids (S5E) to simulate hyperphosphorylation had the opposite effect. Functionally, ND251 or ND207 aggregates decreased the number of neurites of Neuro2a cells induced by retinoic acid or number of cells by MTT assay. S5A mutation aggravated, but S5E mutation alleviated these cytotoxic effects of aggregates. Finally, ND251 or ND251S5A developed aggregates in neurons, and salivary gland of transgenic Drosophila, but ND251S5E did not. Taken together, our data indicate that hyperphosphorylation may represent a compensatory defense mechanism to stop or prevent pathogenic TDP from aggregation. Therefore, enhancement of phosphorylation may serve as an effective therapeutic strategy against ALS/FTLD-U.

Systemic administration of antisense oligonucleotides simultaneously targeting CK2α and α' subunits reduces orthotopic xenograft prostate tumors in mice

CK2 is a highly conserved, ubiquitous, signal responsive protein serine/threonine kinase. CK2 promotes cell proliferation and suppresses apoptosis, and increased CK2 expression is observed in all cancers examined. We previously reported that direct injection of antisense (AS) CK2α phosphorothioate oligonucleotides (PTO) into xenograft prostate tumors in mice significantly reduced tumor size. Downregulation of CK2α in tumor cells in vivo appeared to result in overexpression of CK2α' protein. This suggested that in cancer cells downregulation of CK2α might be compensated by CK2α' in vivo, prompting us to design a bispecific (bs) AS PTO (bs-AS-CK2) targeting both catalytic subunits. bs-AS-CK2 reduced CK2α and α' protein expression, decreased cell proliferation, and induced apoptosis in cultured cells. Biodistribution studies of administered bs-AS-CK2 oligonucleotide demonstrated its presence in orthotopic prostate xenograft tumors. High dose injections of bs-AS-CK2 resulted in no damage to normal liver or prostate, but induced extensive cell death in tumor tissue. Intraperitoneal treatment with bs-AS-CK2 PTO decreased orthotopic tumor size and downregulated both CK2 mRNA and protein expression. Tumor reduction was accomplished using remarkably low doses and was improved by dividing the dose using a multi-day schedule. Decreased expression of the key signaling pathway proteins NF-κB p65 and AKT was also observed. We propose that the molecular downregulation of CK2 through bispecific targeting of the two catalytic subunits may be uniquely useful for therapeutic elimination of tumors.

Interactions between subunits of protein kinase CK2 and their protein substrates influences its sensitivity to specific inhibitors

Five isoforms of CK2 may exist simultaneously in yeast cells: free catalytic subunits CK2α', CK2α and three holoenzymatic structures composed of αα'ββ', α(2)ββ' and α'(2)ββ'. Each isolated and purified form exhibits properties typical for CK2, but they differ in substrate specificity as well as in sensitivity to specific modulators. All five isoforms of protein kinase CK2 from Saccharomyces cerevisiae were examined for their binding capacity with ATP/GTP and two commonly used ATP-competitive inhibitors TBB and TBI. Enzymes were tested with protein substrates differently interacting with CK2 subunits: Elf1, Fip1, Svf1, P2B and synthetic peptide. Obtained results show that K(m) for ATP varies from 2.4-53 μM for Elf1/CK2α' and Svf1/CK2α, respectively. Similar differences can be seen in case when GTP was used as phosphate donor. The inhibitory effect depends on composition of CK2/substrate complexes. Highest sensitivity to TBB shows all complexes containing αα'ββ' isoform with K (i) values between 0.2 and 1.1 μM. The prospect that TBB and TBI could be utilized to discriminate between different molecular forms of CK2 in yeast cells was examined. Both inhibitors, TBB as well as TBI, decreases cell growth to extents devoting interactions with different CK2 isoforms present in the cell but the presence of β/β'-dimer has a high importance towards sensitivity. Conceivably, a given inhibitor concentration can inhibit only selected CK2-mediated processes in the cell.

Multisite-directed inhibitors of protein kinase CK2: new challenges

New 4,5,6,7-tetrabromo benzotriazole derivatives have been synthesized, and their activities against CK2 have been tested. A click chemistry approach based on the copper-catalyzed azide-alkyne cycloaddition has been utilized to connect benzotriazoles, which efficiently interact with the ATP-binding site, to other subunits designed to simultaneously bind to the active and the substrate-binding sites of the enzyme. Docking studies allowed us to identify key interactions between CK2 and the designed ligands, which will be useful to optimize this series of multisite-directed inhibitors.

Enzymatic activity with an incomplete catalytic spine: insights from a comparative structural analysis of human CK2α and its paralogous isoform CK2α'

Eukaryotic protein kinases are fundamental factors for cellular regulation and therefore subject of strict control mechanisms. For full activity a kinase molecule must be penetrated by two stacks of hydrophobic residues, the regulatory and the catalytic spine that are normally well conserved among active protein kinases. We apply this novel spine concept here on CK2α, the catalytic subunit of protein kinase CK2. Homo sapiens disposes of two paralog isoforms of CK2α (hsCK2α and hsCK2α'). We describe two new structures of hsCK2α constructs one of which in complex with the ATP-analog adenylyl imidodiphosphate and the other with the ATP-competitive inhibitor 3-(4,5,6,7-tetrabromo-1H-benzotriazol-1-yl)propan-1-ol. The former is the first hsCK2α structure with a well defined cosubstrate/magnesium complex and the second with an open β4/β5-loop. Comparisons of these structures with existing CK2α/CK2α' and cAMP-dependent protein kinase (PKA) structures reveal: in hsCK2α' an open conformation of the interdomain hinge/helix αD region that is critical for ATP-binding is found corresponding to an incomplete catalytic spine. In contrast hsCK2α often adopts the canonical, PKA-like version of the catalytic spine which correlates with a closed conformation of the hinge region. HsCK2α can switch to the incomplete, non-canonical, hsCK2α'-like state of the catalytic spine, but this transition apparently depends on binding of either ATP or of the regulatory subunit CK2β. Thus, ATP looks like an activator of hsCK2α rather than a pure cosubstrate.

CK2 inhibitors increase the sensitivity of HSV-1 to interferon-β

Herpes simplex virus type 1 (HSV-1) requires the activities of cellular kinases for efficient replication. The host kinase, CK2, has been shown or is predicted to modify several HSV-1 proteins and has been proposed to affect one or more steps in the viral life cycle. Furthermore, potential cellular and viral substrates of CK2 are involved in antiviral pathways and viral counter-defenses, respectively, suggesting that CK2 regulates these processes. Consequently, we tested whether pharmacological inhibitors of CK2 impaired HSV-1 replication, either alone or in combination with the cellular antiviral factor, interferon-β (IFN-β). Our results indicate that the use of CK2 inhibitors results in a minor reduction in HSV-1 replication but enhanced the inhibitory effect of IFN-β on replication. This effect was dependent on the HSV-1 E3 ubiquitin ligase, infected cell protein 0 (ICP0), which impairs several host antiviral responses, including that produced by IFN-β. Inhibitors of CK2 did not, however, impede the ability of ICP0 to induce the degradation of two cellular targets: the promyelocytic leukemia protein (PML) and the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Notably, this effect was only apparent for HSV-1, as the CK2 inhibitors did not enhance the antiviral effect of IFN-β on either vesicular stomatitis virus or adenovirus type 5. Thus, our data suggest that the activity of CK2 is required for an early function during viral infection that assists the growth of HSV-1 in IFN-β-treated cells.

The serine 814 of TRPC6 is phosphorylated under unstimulated conditions

TRPC are nonselective cation channels involved in calcium entry. Their regulation by phosphorylation has been shown to modulate their routing and activity. TRPC6 activity increases following phosphorylation by Fyn, and is inhibited by protein kinase G and protein kinase C. A previous study by our group showed that TRPC6 is phosphorylated under unstimulated conditions in a human embryonic kidney cells line (HEK293). To investigate the mechanism responsible for this phosphorylation, we used a MS/MS approach combined with metabolic labeling and showed that the serine at position 814 is phosphorylated in unstimulated cells. The mutation of Ser(814) into Ala decreased basal phosphorylation but did not modify TRPC6 activity. Even though Ser(814) is within a consensus site for casein kinase II (CK2), we showed that CK2 is not involved in the phosphorylation of TRPC6 and does not modify its activity. In summary, we identified a new basal phosphorylation site (Ser(814)) on TRPC6 and showed that CK2 is not responsible for the phosphorylation of this site.

Treatment of cultured human astrocytes and vascular endothelial cells with protein kinase CK2 inhibitors induces early changes in cell shape and cytoskeleton

Ubiquitous protein kinase CK2 is a key regulator of cell migration, proliferation and tumor growth. CK2 is abundant in retinal astrocytes, and its inhibition suppresses retinal neovascularization in a mouse retinopathy model. In human astrocytes, CK2 co-distributes with GFAP-containing intermediate filaments, which implies its association with cytoskeleton. Contrary to astrocytes, CK2 is co-localized in microvascular endothelial cells (HBMVEC) with microtubules and actin stress fibers, but not with vimentin-containing intermediate filaments. Specific CK2 inhibitors (TBB, TBI, TBCA and DMAT) and nine novel CK2 inhibiting compounds (TID43, TID46, Quinolone-7, Quinolone-39, FNH28, FNH62, FNH64, FNH68 and FNH74) were tested at 10-200 μM for their ability to induce morphological alterations in cultured human astrocytes (HAST-40), and HBMVEC (For explanation of the inhibitor names, see "Methods" section). CK2 inhibitors caused dramatic changes in shape of cultured cells with effective inhibitor concentrations between 50 and 100 μM. Attached cells retracted, acquired shortened processes, and eventually rounded up and detached. CK2 inhibitor-induced morphological alterations were completely reversible and were not blocked by caspase inhibition. However, longer treatment or higher inhibitor concentration did cause apoptosis. The speed and potency of the CK2 inhibitors effects on cell shape and adhesion were inversely correlated with serum concentration. Western analyses showed that TBB and TBCA elicited a significant (about twofold) increase in the activation of p38 and ERK1/2 MAP kinases that may be involved in cytoskeleton regulation. This novel early biological cell response to CK2 inhibition may underlie the anti-angiogenic effect of CK2 suppression in the retina.

Restricted growth of U-type infectious haematopoietic necrosis virus (IHNV) in rainbow trout cells may be linked to casein kinase II activity

Previously, we demonstrated that a representative M genogroup type strain of infectious haematopoietic necrosis virus (IHNV) from rainbow trout grows well in rainbow trout-derived RTG-2 cells, but a U genogroup type strain from sockeye salmon has restricted growth, associated with reduced genome replication and mRNA transcription. Here, we analysed further the mechanisms for this growth restriction of U-type IHNV in RTG-2 cells, using strategies that assessed differences in viral genes, host immune regulation and phosphorylation. To determine whether the viral glycoprotein (G) or non-virion (NV) protein was responsible for the growth restriction, four recombinant IHNV viruses were generated in which the G gene of an infectious IHNV clone was replaced by the G gene of U- or M-type IHNV and the NV gene was replaced by NV of U- or M-type IHNV. There was no significant difference in the growth of these recombinants in RTG-2 cells, indicating that G and NV proteins are not major factors responsible for the differential growth of the U- and M-type strains. Poly I:C pretreatment of RTG-2 cells suppressed the growth of both U- and M-type IHNV, although the M virus continued to replicate at a reduced level. Both viruses induced type 1 interferon (IFN1) and the IFN1 stimulated gene Mx1, but the expression levels in M-infected cells were significantly higher than in U-infected cells and an inhibitor of the IFN1-inducible protein kinase PKR, 2-aminopurine (2-AP), did not affect the growth of U- or M-type IHNV in RTG-2 cells. These data did not indicate a role for the IFN1 system in the restricted growth of U-type IHNV in RTG-2 cells. Prediction of kinase-specific phosphorylation sites in the viral phosphoprotein (P) using the NetPhosK program revealed differences between U- and M-type P genes at five phosphorylation sites. Pretreatment of RTG-2 cells with a PKC inhibitor or a p38MAPK inhibitor did not affect the growth of the U- and M-type viruses. However, 100 μm of the casein kinase II (CKII) inhibitor, 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB), reduced the titre of the U type 8.3-fold at 24 h post-infection. In contrast, 100 μm of the CKII inhibitor reduced the titre of the M type only 1.3-fold at 48 h post-infection. Our data suggest that the different growth of U- and M-type IHNV in RTG-2 cells may be linked to a differential requirement for cellular protein kinases such as CKII for their growth.

Phosphoinositide 3-kinase induced activation and cytoskeletal translocation of protein kinase CK2 in protease activated receptor 1-stimulated platelets

CK2 is a highly conserved protein kinase involved in several cellular events. CK2 is expressed in platelets but its role in platelet activation remains poorly understood. In the present study, we tested the hypothesis that CK2 plays a role in platelet activation, particularly in the PAR1-dependent signal transduction pathway. The effect of CK2 and PI 3-kinase inhibitors on aggregation of platelets, activation of GPIIb/IIIa, activation and translocation of CK2 was examined. Platelets were incubated with the cell permeable CK2 inhibitors, DRB, DMAT and TBB and stimulated with the PAR1-AP (SFLLRNP). CK2 inhibitors showed the specific inhibitory pattern of platelet aggregation, characterized by a primary phase of aggregation followed by progressive disaggregation. CK2 inhibitors suppressed the activation of GPIIb/IIIa. PAR1-AP induced two-fold increase in CK2 activity and stimulated the translocation of CK2 from Triton X-100-soluble to -insoluble fraction. Preincubation of platelets with the PI 3-kinase inhibitor, wortmannin or LY294002, impaired PAR1-AP-induced aggregation of platelets. PAR1-AP-induced increase in CK2 activity and translocation of CK2 were inhibited by these treatments. Taken together, the present study demonstrated, for the first time, that PI 3-kinase-CK2 pathway plays an important role in the mechanism of PAR1-dependent platelet aggregation.

Synthesis and proapoptotic properties of new casein kinase II inhibitors

Casein kinase II (CK2) is the most pleiotropic of all protein kinases with more than 300 substrates implicated in a wide variety of cellular functions as signal transduction, proliferation and cell survival. Increased levels of CK2 has been demonstrated in a number of cancers, where it regulates the activity of various oncoproteins and tumor suppressor proteins. Therefore, CK2 inhibitors could be considered as potential anticancer drugs in monotherapy or in combination with known cytostatics. In this study, we examined proapoptotic activity of new strong CK2 inhibitor - 4,5,6,7-tetraiodobenzimidazole (TIBI) (IC50 = 38 nM) as well as new derivatives of 4,5,6,7-tetrabromobenzimidazole and 4,5,6,7-tetraiodobenzimidazole. All the tested compounds induced apoptosis and cytostatic effects in the promyelocytic leukemia cell line (HL-60). The proapoptotic effect was concentration and time dependent. The changes of the mitochondrial membrane potential and cell cycle progression were also observed.

Inhibition of CK2{alpha} and PI3K/Akt synergistically induces apoptosis of CD34+CD38- leukaemia cells while sparing haematopoietic stem cells

BACKGROUND/AIM

The CD34(+)CD38(-) leukaemia cell population contains leukaemia stem cells (LSCs) responsible for treatment failure in acute myeloid leukaemia (AML) and, thus, novel therapies are required to eradicate LSCs without harming healthy haematopoietic stem cells (HSC).

MATERIALS AND METHODS

The present study evaluated the effects of co-treatment with LY294002 (a PI3K/Akt inhibitor) and apigenin (a CK2 inhibitor) (LY/Api) at subtoxic concentrations on leukaemia cell lines and primary AML cells.

RESULTS

LY/Api synergistically induced apoptosis in leukaemia cells, especially CD34(+)CD38(-) leukaemia cells. However, these effects were negligible in HSCs. LY/Api-induced apoptosis was accompanied by activation of caspase cascades and disruption of mitochondrial membrane potential. Caspase inhibitor or Akt overexpression abrogated this synergistic induction in apoptosis by LY/Api. LY/Api also led to remarkable down-regulation of anti-apoptotic proteins including Bcl-xL and NF-κB in CD34(+)CD38(-) leukaemia cells, but not in healthy hematopoietic stem cells.

CONCLUSION

Inhibition of both CK2 and PI3K/Akt pathways may be a promising LSCs-targeted therapeutic strategy for AML.

CK2 phosphorylation of Pdx-1 regulates its transcription factor activity

The duodenal homeobox-1 protein Pdx-1 is one of the regulators for the transcription of the insulin gene. Pdx-1 is a phosphoprotein, and there is increasing evidence for the regulation of some of its functions by phosphorylation. Here, we asked whether protein kinase CK2 might phosphorylate Pdx-1 and how this phosphorylation could be implicated in the functional regulation of Pdx-1. We used fragments of Pdx-1 as well as phosphorylation mutants for experiments with protein kinase CK2. Transactivation was measured by reporter assays using the insulin promoter. Our data showed that Pdx-1 is phosphorylated by protein kinase CK2 at amino acids thr(231) and ser(232), and this phosphorylation was implicated in the regulation of the transcription factor activity of Pdx-1. Furthermore, inhibition of protein kinase CK2 by specific inhibitors led to an elevated release of insulin from pancreatic beta-cells. Thus, these findings identify CK2 as a novel mediator of the insulin metabolism.

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.

CK2 modulation of NF-kappaB, TP53, and the malignant phenotype in head and neck cancer by anti-CK2 oligonucleotides in vitro or in vivo via sub-50-nm nanocapsules

PURPOSE

The aim of this study is to investigate the expression of CK2 subunits and CK2 effects on NF-kappaB-mediated and TP53-mediated signal activation and gene expression, the malignant phenotype, and chemosensitivity in head and neck squamous cell carcinoma (HNSCC) in vitro and in vivo.

EXPERIMENTAL DESIGN

Protein expression of CK2 subunits was investigated by Western blot and immunohistochemistry. CK2 subunits were knocked down by small interfering RNA, and NF-kappaB activation was examined using DNA binding, Western blot, and luciferase reporter assays. Gene expression was measured by quantitative reverse transcription-PCR. Cell growth, survival, motility, and sensitivity to cisplatin were measured by MTT, flow cytometry, and migration assays. In vivo targeting of CK2alpha/alpha' in HNSCC xenograft models was achieved using anti-CK2alpha/alpha' oligodeoxynucleotide encapsulated in sub-50-nm tenfibgen nanocapsules.

RESULTS

CK2 subunit proteins were overexpressed in HNSCC lines and tissues. Knockdown of CK2 subunits differentially inhibited IkappaBalpha degradation, NF-kappaB nuclear localization, phosphorylation, DNA binding, and reporter activity. CK2 subunits modulated gene expression and the malignant phenotype involved in cell cycle and migration, whereas CK2alpha is critical to promote proliferation, antiapoptosis, and cisplatin resistance in vitro. Furthermore, in vivo delivery of anti-CK2alpha/alpha' oligodeoxynucleotide nanocapsules significantly suppressed tumor growth in HNSCC xenograft models, in association with modulation of CK2 and NF-kappaB regulated molecules, TP53 family proteins, and induction of apoptosis.

CONCLUSIONS

Our study reveals a novel role of CK2 in coregulating NF-kappaB activation, TP53/p63 expression, and downstream gene expression. Downregulation of CK2 in HNSCC models in vitro and in vivo shows antitumor effects as well as sensitization to cisplatin.

p53 is dispensable for the induction of apoptosis after inhibition of protein kinase CK2

BACKGROUND

Protein kinase CK2 is a ubiquitously expressed heterotetramer consisting of two catalytic alpha/alpha' and two regulatory beta subunits. Expression of CK2 is highly elevated in tumor cells where it protects cells from apoptosis. A variety of different compounds were tested as inhibitors of protein kinase CK2 in order to find new therapy strategies. To analyze the role of p53 in the response to CK2 inhibition we used one of the most specific CK2 inhibitors available, TBB, in different prostate cancer cell lines.

METHODS

We treated prostate cancer cells with the CK2 inhibitor TBB and determined its effect on CK2 activity by an in vitro phosphorylation assay and its effect on viability by an MTT assay. Furthermore, we analyzed changes in the expression of p53 and PARP cleavage by Western Blot analysis.

RESULTS

Inhibition of CK2 by TBB led to a decrease in cell viability and apoptosis in two cell lines which express wild-type p53 whereas two other cell lines expressing mutant or no p53 failed to show signs of apoptosis. Moreover, cell lines expressing wild-type p53 showed an increase of the amount of p53 and of its transactivation efficiency. However, down-regulation of p53 by RNAi showed that p53 is not necessary for the induction of apoptosis.

CONCLUSIONS

Wild-type p53 is not necessary for the induction of apoptosis by TBB in prostate cancer cells.

The p53-p21(Cip1/WAF1) pathway is necessary for cellular senescence induced by the inhibition of protein kinase CKII in human colon cancer cells

We have previously shown that the down-regulation of protein kinase CKII activity is tightly associated with cellular senescence of human fibroblast IMR-90 cells. Here, we examined the roles of p53 and p21(Cip1/WAF1) in senescence development induced by CKII inhibition using wild-type, isogenic p53-/- and isogenic p21-/- HCT116 human colon cancer cell lines. A senescent marker appeared after staining for senescence-associated beta-galactosidase activity in wild-type HCT116 cells treated with CKII inhibitor or CKIIalpha siRNA, but this response was almost abolished in p53- or p21(Cip1/WAF1)-null cells. Increased cellular levels of p53 and p21(Cip1/WAF1) protein occurred with the inhibition of CKII. CKII inhibition upregulated p53 and p21(Cip1/WAF1) expression at post-transcriptional level and transcription level, respectively. RB phosphorylation significantly decreased in cells treated with CKII inhibitor. Taken together, this study shows that the activation of the p53-p21(Cip1/WAF1) pathway acts as a major mediator of cellular senescence induced by CKII inhibition.

Requirement for nuclear factor kappa B signalling in the interleukin-1-induced expression of the CCAAT/enhancer binding protein-delta gene in hepatocytes

Elevated circulating levels of acute phase proteins (APP) are associated with inflammation and inflammatory disorders such as cardiovascular disease. APP are mainly synthesised by hepatocytes and their transcription is induced by pro-inflammatory cytokines such as interleukin-1 (IL-1). The molecular mechanisms underlying the IL-1-induced expression of key transcription factors implicated in the regulation of APP are poorly understood. We have investigated this aspect using the CCAAT/enhancer binding protein-delta (C/EBPdelta) as a model gene. IL-1 induced the expression of C/EBPdelta mRNA and protein in the human hepatoma Hep3B cell line, a widely employed model system for studies on cytokine signalling in relation to the expression of APP. The IL-1-mediated induction of C/EBPdelta expression was attenuated in the presence of pharmacological inhibitors against c-Jun N-terminal kinase (JNK) (curcumin and SP600125), casein kinase 2 (CK2) (apigenin) and nuclear factor-kappaB (NF-kappaB) (NF-kappaB activation inhibitor). RNA interference assays showed significant attenuation of the IL-1-induced expression of C/EBPdelta following knockdown of the p50 and p65 subunits of NF-kappaB. IL-1 induced NF-kappaB DNA binding and activation by this transcription factor and this was attenuated by curcumin and apigenin. Taken together, these results suggest a potentially crucial role for NF-kappaB in the IL-1-induced expression of C/EBPdelta, and thereby downstream APP genes regulated by this transcription factor.

Protein kinase CK2 in health and disease: Structural bases of protein kinase CK2 inhibition

Protein kinase CK2 is involved in many fundamental aspects of normal cell life, but it is also able to establish favourable conditions for tumorigenesis. CK2 is elevated in various cancers, it is a potent suppressor of apoptosis, it strongly promotes cell survival, it strengthens the multi-drug resistant phenotype and can be considered a valuable drug target for cancer therapy. In this review, the structural bases of CK2 inhibition deduced from the analysis of crystal structures of CK2alpha-inhibitor complexes are presented and discussed. The best ATP-competitive inhibitors show an adequate hydrophobic character, an excellent shape complementarity with the unique active site of CK2, and the ability to establish polar interactions with both the hinge region and the positive electrostatic area near the conserved water W1 and the Lys68-Glu81 salt bridge. The state of the art of non-ATP-competitive inhibitors is also presented.

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.

Safety and preliminary efficacy data of a novel casein kinase 2 (CK2) peptide inhibitor administered intralesionally at four dose levels in patients with cervical malignancies

BACKGROUND

Cervical cancer is now considered the second leading cause of death among women worldwide, and its incidence has reached alarming levels, especially in developing countries. Similarly, high grade squamous intraepithelial lesion (HSIL), the precursor stage for cervical cancer, represents a growing health problem among younger women as the HSIL management regimes that have been developed are not fully effective. From the etiological point of view, the presence of Human Papillomavirus (HPV) has been demonstrated to play a crucial role for developing cervical malignancies, and viral DNA has been detected in 99.7% of cervical tumors at the later stages. CIGB-300 is a novel cyclic synthetic peptide that induces apoptosis in malignant cells and elicits antitumor activity in cancer animal models. CIGB-300 impairs the Casein Kinase (CK2) phosphorylation, by targeting the substrate's phosphoaceptor domain. Based on the perspectives of CIGB-300 to treat cancer, this "first-in-human" study investigated its safety and tolerability in patients with cervical malignancies.

METHODS

Thirty-one women with colposcopically and histologically diagnosed microinvasive or pre-invasive cervical cancer were enrolled in a dose escalating study. CIGB-300 was administered sequentially at 14, 70, 245 and 490 mg by intralesional injections during 5 consecutive days to groups of 7 - 10 patients. Toxicity was monitored daily until fifteen days after the end of treatment, when patients underwent conization. Digital colposcopy, histology, and HPV status were also evaluated.

RESULTS

No maximum-tolerated dose or dose-limiting toxicity was achieved. The most frequent local events were pain, bleeding, hematoma and erythema at the injection site. The systemic adverse events were rash, facial edema, itching, hot flashes, and localized cramps. 75% of the patients experienced a significant lesion reduction at colposcopy and 19% exhibited full histological regression. HPV DNA was negative in 48% of the previously positive patients. Long term follow-up did not reveal recurrences or adverse events.

CONCLUSION

CIGB 300 was safe and well tolerated. This is the first clinical trial where a drug has been used to target the CK2 phosphoaceptor domain providing an early proof-of-principle of a possible clinical benefit.

Over-expression of phospholipase D isozymes down-regulates protein kinase CKII activity via proteasome-dependent CKIIbeta degradation in NIH3T3 cells

Over-expression of phospholipase D (PLD) 1 or PLD2 down-regulated CKII activity in NIH3T3 cells. The same results were found with catalytically inactive mutants of PLD isozymes, indicating that the catalytic activity of PLD is not required for PLD-mediated CKII inhibition. Consistent with this, 1-butanol did not alter CKII activity. The reduction in CKII activity in PLD-over-expressing NIH3T3 cells was due to reduced protein level, but not mRNA level, of the CKIIbeta subunit. This PLD-induced CKIIbeta degradation was mediated by ubiquitin-proteasome machinery, but MAP kinase and mTOR were not involved in CKIIbeta degradation. PLD isozymes interacted with the CKIIbeta subunit. Immunocyto-chemical staining revealed that PLD and CKIIbeta colocalize in the cytoplasm of NIH3T3 cells, especially in the perinuclear region. PLD binding to CKIIbeta inhibited CKIIbeta autophosphory-lation, which is known to be important for CKIIbeta stability. In summary, the current data indicate that PLD isozymes can down-regulate CKII activity through the acceleration of CKIIbeta degradation by ubiquitin-proteasome machinery.

Structure of human protein kinase CK2 alpha 2 with a potent indazole-derivative inhibitor

Casein kinase 2 (CK2) is a serine/threonine kinase that functions as a heterotetramer composed of two catalytic subunits (CK2alpha1 or CK2alpha2) and two regulatory subunits (CK2beta). The two isozymes CK2alpha1 and CK2alpha2 play distinguishable roles in healthy subjects and in patients with diseases such as cancer, respectively. In order to develop novel CK2alpha1-selective inhibitors, the crystal structure of human CK2alpha2 (hCK2alpha2) complexed with a potent CK2alpha inhibitor which binds to the active site of hCK2alpha2 was determined and compared with that of human CK2alpha1. While the two isozymes exhibited a high similarity with regard to the active site, the largest structural difference between the isoforms occurred in the beta4-beta5 loop responsible for the CK2alpha-CK2beta interface. The top of the N-terminal segment interacted with the beta4-beta5 loop via a hydrogen bond in hCK2alpha2 but not in hCK2alpha1. Thus, the CK2alpha-CK2beta interface is a likely target candidate for the production of selective CK2alpha1 inhibitors.