Volume 406, Issue 3-4 - HIGHLIGHT: 9th International Conference on Protein Kinase CK2

In the early days of CK2 research, it was already published that the affinity of CK2 for its substrate casein was affected by insulin. Subsequent to the discovery of inhibitors of CK2 kinase activity, it was shown that CK2 has an influence on hormones that regulate glucose homeostasis and on enzymes that influence glucose metabolism in pancreatic islet cells as well as in hormone-sensitive target cells. This regulation includes the influence on transcription factors and thereby, gene expression, as well as direct modulation of the catalytic activity. The used CK2 inhibitors, especially the older ones, show a broad range of specificity, selectivity and off-target effects. Recently applied methods to down-regulate the expression of individual CK2 subunits using siRNA or CRISPR/Cas9 technology have contributed to the improvement of specificity. It was shown that inhibition of CK2 kinase activity or knock-down or knock-out of CK2α leads to an elevated synthesis and secretion of insulin in pancreatic β-cells and a down-regulation of the synthesis and secretion of glucagon from pancreatic α-cells. In the present review CK2-dependent molecular mechanisms will be addressed which contribute to the maintenance of glucose homeostasis.

Human papillomaviruses are causative agents in around 5 % of all cancers, and in a number of other human diseases. While prophylactic vaccines will alleviate the HPV disease burden on future generations, there are currently no therapeutic anti-viral strategies for combating HPV infections or lesions. HPV induce the proliferation of infected epithelial cells and modulate the host differentiation response, and both of these controls are required for a successful viral life cycle. Enhanced understanding of viral-host interactions during the viral life cycle will identify potential novel anti-viral strategies for therapeutic development. This minireview will summarize the critical role of the host enzyme CK2 in regulating the function of the viral proteins E1, E2 and E7; such control makes CK2 a critical enzyme for regulating HPV life cycles. Therapeutic strategies blocking CK2 function to combat HPV infections and treat HPV diseases will be described.

Proteome-wide scale in a dose- and time-depending setting is crucial to fully understand the pharmacological mechanism of anticancer drugs as well as identification of candidates for drug response biomarkers. Here, we investigated the effect of the CIGB-300 anticancer peptide at IC 50 and IC 80 doses during 1 and 4 h of treatment on the squamous lung cancer cell (NCI-H226) proteome. An overwhelming dose-dependent inhibitory effect with minor up-regulated proteins was observed by increasing CIGB-300 dose level. Functional enrichment was also CIGB-300 dose-dependent with common or exclusively regulated proteins in each dose and time settings. A protein core involving small molecule biosynthesis, aldehyde metabolism and metabolism of nucleobases was regulated irrespectively to the dose or the treatment time. Importantly, a group of proteins linked to NSCLC tumor biology, poor clinical outcome and some Protein Kinase CK2 substrates, were significantly regulated by treating with both CIGB-300 doses. Likewise, we observed a consistent downregulation of different proteins that had been already reported to be inhibited by CIGB-300 in lung adenocarcinoma and acute myeloid leukemia. Overall, our proteomics-guided strategy based on time and drug dose served to uncover novel clues supporting the CIGB-300 cytotoxic effect and also to identify putative pharmacodynamic biomarkers in NSCLC.

Protein kinase CK2 (casein kinase 2) mainly exists as heterotetrameric holoenzyme with two catalytic subunits (CK2α or CK2α′) bound to a homodimer of non-catalytic subunits (CK2β). With CSNK2A1 and CSNK2A2 , the human genome contains two paralogs encoding catalytic CK2 subunits. Both gene products, called CK2α and CK2α′, strongly interact with CK2β. An earlier report that CK2α′ has a lower CK2β affinity than CK2α is confirmed via isothermal titration calorimetry in this study. Furthermore, we show with a fluorescence-anisotropy assay that a CK2β-competitive peptide binds less strongly to CK2α′ than to CK2α. The reason for the reduced affinity of CK2α′ to CK2β and CK2β competitors is puzzling: both isoenzymes have identical amino acid compositions at their CK2β interfaces, but the β4β5 loop, a component of this interface, is conformationally less adaptable in CK2α′ than in CK2α due to intramolecular constraints. To release these constraints, we constructed a CK2α′ mutant that was equalized to CK2α at the backside of the β4β5 loop. Concerning thermostability, affinity to CK2β or CK2β competitors and 3D-structure next to the β4β5 loop, this CK2α′ mutant is more similar to CK2α than to its own wild-type, suggesting a critical role of the β4β5 loop adaptability for CK2β affinity.

This study introduces a novel, rapid assay to measure CK2α activity in Escherichia coli cell lysates. By fusing CK2α with the fluorescent protein mScarlet it was possible to quantify CK2α concentration directly in lysates. We used the dose-dependent increase of CK2α activity after addition of CK2β 1-193 to determine the dissociation constants ( K D ) of the CK2α/CK2β-interaction. As a first trial, activity and affinity of the variant CK2α R191Q to CK2β 1-193 was investigated using the developed assays. This mutation in the CSNK2A1 gene, encoding CK2α is related to the Okur-Chung Neurodevelopmental Syndrome (OCNDS). Apparent K D values of 13 nM for the CK2α R191Q /CK2β interaction and 7.4 nM for the CK2α/CK2β interaction were determined using nonlinear regression. Uncertainties with regards to the concentration of both binding partners were propagated through the entire process of nonlinear regression by Monte Carlo simulations. This way, accuracy confidence intervals of the K D -values were derived. This resulted in 96.4 % confidence that the accurate K D -values of the CK2α-CK2β and CK2α R191Q -CK2β interactions were different. The results suggest potential disruptions in oligomeric assembly caused by the R191Q mutation.

Protein kinase CK2 is a promising therapeutic target, especially in oncology. Over the years, various inhibitors have been developed, with polyhalogenated scaffolds emerging as a particularly effective class. Halogens like bromine and chlorine enhance inhibitor stability by forming additional interactions within the ATP pocket. Among halogenated scaffolds, benzotriazole and benzimidazole have led to potent molecules such as 4,5,6,7-tetrabromo-1 H -benzotriazole (IC 50 = 300 nM) and 4,5,6,7-tetrabromo-2-(dimethylamino)benzimidazole (IC 50 = 140 nM). Modifications, including 4,5,6-tribromo-7-ethyl-1 H -benzotriazole (IC 50 = 160 nM), further improved activity. Changing scaffolds while retaining halogens has enabled design of new inhibitors. Flavonols, dibenzofuranones, and the indeno[1,2- b ]indole scaffold are key examples. Halogenation of the reference molecule 5-isopropyl-5,6,7,8-tetrahydroindeno[1,2- b ]indole-9,10-dione ( 4b , IC 50 = 360 nM) significantly boosted potency. The study focused on introducing four halogens, yielding to the compound 1,2,3,4-tetrabromo-5-isopropyl-5,6,7,8-tetrahydroindeno[1,2- b ]indole-9,10-dione ( MC11 ), with an IC 50 of 16 nM. Co-crystallography revealed how bromine atoms enhance binding, and MC11 demonstrated strong in cellulo activity, particularly against leukemic cell lines like IPC-Bcl2.

Poirier-Bienvenu neurodevelopmental syndrome is a neurodevelopmental disorder associated with de novo variants of the CSNK2B gene, characterized by intellectual disability, developmental delay, frequent seizures and more. While the majority of variants are nonsense variants leading to abortion of protein translation and no or truncated CK2β, many pathogenic missense variants also exist. We investigated the effect of four variants on CK2 holoenzyme formation and activity. We show that variants in the Zinc-finger region leads to reduced protein stability and altered subcellular localization. The instability is partly mediated by proteasomal and lysosomal degradation. We further show that homodimerization of these CK2β variants (p.Arg111Pro, p.Cys137Phe), localized within the Zinc-finger domain, is significantly reduced, while CK2α binding appears not affected. Other variants, p.Asp32Asn and p.Arg86Cys, did not affect stability or CK2β/α binding. For these mutants, the key to understanding the pathological mechanism may depend on external factors, such as altered protein–protein interaction. We conclude that Zinc-finger domain variants appear to destabilize the protein and affect holoenzyme formation, effectively reducing the pool of competent holoCK2. In the context of POBINDS, our findings suggest that Zinc-finger domain variants are likely to affect cells similarly to truncating and splicing variants with reduced translation of full-length CK2β.