Inhibition of protein kinase CK2 expression and activity blocks tumor cell growth.
ABSTRACT Protein kinase CK2 (CK2) is a highly conserved and ubiquitous serine/threonine kinase. It is a multifunctional and pleiotropic protein kinase implicated in the regulation of cell proliferation, survival, and differentiation. Deregulation of CK2 is observed in a wide variety of tumors. It has been the focus of intensive research efforts to establish the cause-effect relationship between CK2 and neoplastic growth. Here, we further validate the role of CK2 in cancer cell growth using siRNA approach. We also screened a library of more than 200,000 compounds and identified several molecules, which inhibit CK2 with IC(50) < 1 microM. The binding mode of a representative compound with maize CK2 was determined. In addition, the cellular activity of the compounds was demonstrated by their inhibition of phosphorylation of PTEN Ser370 in HCT116 cells. Treatment of a variety of cancer cell lines with the newly identified CK2 inhibitor significantly blocked cell growth with IC(50)s as low as 300 nM.
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ABSTRACT: CK2 (formerly termed "casein kinase 2") is a ubiquitous, highly pleiotropic and constitutively active Ser/Thr protein kinase whose implication in neoplasia, cell survival, and virus infection is supported by an increasing number of arguments. Here an updated inventory of 307 CK2 protein substrates is presented. More than one-third of these are implicated in gene expression and protein synthesis as being either transcriptional factors (60) or effectors of DNA/RNA structure (50) or translational elements. Also numerous are signaling proteins and proteins of viral origin or essential to virus life cycle. In comparison, only a minority of CK2 targets (a dozen or so) are classical metabolic enzymes. An analysis of 308 sites phosphorylated by CK2 highlights the paramount relevance of negatively charged side chains that are (by far) predominant over any other residues at positions n+3 (the most crucial one), n+1, and n+2. Based on this signature, it is predictable that proteins phosphorylated by CK2 are much more numerous than those identified to date, and it is possible that CK2 alone contributes to the generation of the eukaryotic phosphoproteome more so than any other individual protein kinase. The possibility that CK2 phosphosites play some global role, e.g., by destabilizing alpha helices, counteracting caspase cleavage, and generating adhesive motifs, will be discussed.The FASEB Journal 04/2003; 17(3):349-68. · 5.70 Impact Factor
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ABSTRACT: Protein kinase CK2 (formerly casein kinase II) is a highly conserved and ubiquitous serine/threonine kinase that is composed of two catalytic subunits (CK2alpha and/or CK2alpha') and two CK2beta regulatory subunits. CK2 has many substrates in cells, and key roles in yeast cell physiology have been uncovered by introducing subunit mutations. Gene-targeting experiments have demonstrated that in mice, the CK2beta gene is required for early embryonic development, while the CK2alpha' subunit appears to be essential only for normal spermatogenesis. We have used homologous recombination to disrupt the CK2alpha gene in the mouse germ line. Embryos lacking CK2alpha have a marked reduction in CK2 activity in spite of the presence of the CK2alpha' subunit. CK2alpha(-/-) embryos die in mid-gestation, with abnormalities including open neural tubes and reductions in the branchial arches. Defects in the formation of the heart lead to hydrops fetalis and are likely the cause of embryonic lethality. Thus, CK2alpha appears to play an essential and uncompensated role in mammalian development.Molecular and cellular biology 02/2008; 28(1):131-9. · 6.06 Impact Factor
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ABSTRACT: Human casein kinase II (CKII) is a ubiquitous and multipotential Ser/Thr kinase involved in the regulation of cell growth and differentiation. Biochemically, two characteristics are particularly notable; first, the tetrameric composition of two catalytic subunits (alpha and/or alpha') and two regulatory subunits (beta); second, the autophosphorylation of the holoenzyme at the N-terminus of CKII beta, suspected to be involved in tuning of the kinase activity. Whether CKII alpha and CKII alpha' reconstitute comparably with CKII beta to form holoenzyme is unclear. For a systematic investigation, the complete set of recombinant CKII subunits and of autophosphorylation mutants of CKII beta were expressed in Escherichia coli and comparative reconstitutions carried out. At 1:1 molar ratio, CKII beta stimulated both catalytic subunits roughly fivefold with phosvitin as a substrate. The level of activity reached with both of the reconstituted CKII isoforms was of the same order of magnitude as that of holoenzyme isolated from human placenta. It was also similar to a recombinant alpha 2 beta 2 holoenzyme whose expression had been attained in E. coli with a bicistronic construct containing the coding regions of CKII beta and CKII alpha in a tandem arrangement. Both Ser2 and Ser3 were identified as the autophosphorylation sites; replacement of one of these with Ala by oligonucleotide-mediated site-directed mutagenesis influenced only the extent of CKII beta autophosphorylation, replacement of both resulted in a loss of autophosphorylation. Despite these differences, the stimulatory effect of all the CKII beta mutants was comparable both to each other and to that of wild-type CKII beta. This was also obtained when substrates other than phosvitin were employed such as tubulin, or upstream-binding factor (UBF). However, the degree of stimulation was substrate specific and ranged from 2-5-fold with no major differences between CKII alpha and CKII alpha' stimulation. Calmodulin phosphorylation by both CKII alpha and CKII alpha' was decreased similarly by CKII beta and the CKII beta mutants. Proteins such as cAMP-responsive-element-binding protein (CREB), HPV16 E7 or Jun were not phosphorylated by either catalytic subunit but became substrates of both in the presence of CKII beta or CKII beta mutants. The data suggest that CKII alpha and CKII alpha' form similar CKII holoenzymes and that the tuning of holoenzyme activity is independent of the autophosphorylation status of CKII beta.European Journal of Biochemistry 03/1994; 220(1):263-73. · 3.58 Impact Factor