Treatment of Jurkat cells with specific inhibitors of protein kinase CK2 induces apoptosis. Here we provide evidence that the antiapoptotic effect of CK2 can be at least partially mediated by upregulation of the Akt/PKB pathway. Such a conclusion is based on the following observations: (1) inhibition of CK2 by cell treatment with two structurally unrelated CK2 inhibitors induces downregulation of Akt/PKB, as judged from decreased phosphorylation of its physiological targets, and immunoprecipitate kinase assay; (2) similar results are observed upon reduction of CK2 catalytic subunit by the RNA-interference technique; (3) Akt/PKB Ser129 is phosphorylated by CK2 in vitro and in vivo; (4) such a phosphorylation of activated Akt/PKB correlates with a further increase in catalytic activity. These data disclose an unanticipated mechanism by which constitutive phosphorylation by CK2 may be required for maximal activation of Akt/PKB.

CK2 (casein kinase 2) is a very pleiotropic serine/threonine protein kinase whose abnormally high constitutive activity has often been correlated to pathological conditions with special reference to neoplasia. The two most widely used cell permeable CK2 inhibitors, TBB (4,5,6,7-tetrabromo-1H-benzotriazole) and DMAT (2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole), are marketed as quite specific CK2 blockers. In the present study we show, by using a panel of approx. 80 protein kinases, that DMAT and its parent compound TBI (or TBBz; 4,5,6,7-tetrabromo-1H-benzimidazole) are potent inhibitors of several other kinases, with special reference to PIM (provirus integration site for Moloney murine leukaemia virus)1, PIM2, PIM3, PKD1 (protein kinase D1), HIPK2 (homeodomain-interacting protein kinase 2) and DYRK1a (dual-specificity tyrosine-phosphorylated and -regulated kinase 1a). In contrast, TBB is significantly more selective toward CK2, although it also inhibits PIM1 and PIM3. In an attempt to improve selectivity towards CK2 a library of 68 TBB/TBI-related compounds have been tested for their ability to discriminate between CK2, PIM1, HIPK2 and DYRK1a, ending up with seven compounds whose efficacy toward CK2 is markedly higher than that toward the second most inhibited kinase. Two of these, K64 (3,4,5,6,7-pentabromo-1H-indazole) and K66 (1-carboxymethyl-2-dimethylamino-4,5,6,7-tetrabromo-benzimidazole), display an overall selectivity much higher than TBB and DMAT when tested on a panel of 80 kinases and display similar efficacy as inducers of apoptosis.

Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) is a moderately potent and poorly selective inhibitor of protein kinase CK2, one of the most pleiotropic serine/threonine protein kinases, implicated in neoplasia and in other global diseases. By virtual screening of the MMS (Molecular Modeling Section) database, we have now identified quinalizarin (1,2,5,8-tetrahydroxyanthraquinone) as an inhibitor of CK2 that is more potent and selective than emodin. CK2 inhibition by quinalizarin is competitive with respect to ATP, with a Ki value of approx. 50 nM. Tested at 1 microM concentration on a panel of 75 protein kinases, quinalizarin drastically inhibits only CK2, with a promiscuity score (11.1), which is the lowest ever reported so far for a CK2 inhibitor. Especially remarkable is the ability of quinalizarin to discriminate between CK2 and a number of kinases, notably DYRK1a (dual-specificity tyrosine-phosphorylated and -regulated kinase), PIM (provirus integration site for Moloney murine leukaemia virus) 1, 2 and 3, HIPK2 (homeodomain-interacting protein kinase-2), MNK1 [MAPK (mitogen-activated protein kinase)-interacting kinase 1], ERK8 (extracellular-signal-regulated kinase 8) and PKD1 (protein kinase D 1), which conversely tend to be inhibited as drastically as CK2 by commercially available CK2 inhibitors. The determination of the crystal structure of a complex between quinalizarin and CK2alpha subunit highlights the relevance of polar interactions in stabilizing the binding, an unusual characteristic for a CK2 inhibitor, and disclose other structural features which may account for the narrow selectivity of this compound. Tested on Jurkat cells, quinalizarin proved able to inhibit endogenous CK2 and to induce apoptosis more efficiently than the commonly used CK2 inhibitors TBB (4,5,6,7-tetrabromo-1H-benzotriazole) and DMAT (2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole).

The rs4374383 AA genotype, associated with lower intrahepatic expression of MERTK, is protective against F2-F4 fibrosis in patients with NAFLD. The mechanism may involve modulation of HSC activation.

Casein kinase 2 (CK2) is a ubiquitous cellular serine-threonine kinase that regulates relevant biologic processes, many of which are dysregulated in malignant plasma cells. Here we investigated its role in multiple myeloma (MM). Analysis of MM cell lines and highly purified malignant plasma cells in patients with MM revealed higher protein and CK2 activity levels than in controls (normal in vitro-generated polyclonal plasma cells and B lymphocytes). The inhibition of CK2 with specific synthetic compounds or by means of RNA interference caused a cytotoxic effect on MM plasma cells that could not be overcome by IL-6 or IGF-I and that was associated with the activation of extrinsic and intrinsic caspase cascades. CK2 blockage lowered the sensitivity threshold of MM plasma cells to the cytotoxic effect of melphalan. CK2 inhibition also resulted in impaired IL-6-dependent STAT3 activation and in decreased basal and TNF-α-dependent IκBα degradation and NF-κB-driven transcription. Our data show that CK2 was involved in the pathophysiology of MM, suggesting that it might play a crucial role in controlling survival and sensitivity to chemotherapeutics of malignant plasma cells.

No abstract

Abnormally high constitutive activity of protein kinase CK2, levels of which are elevated in a variety of tumours, is suspected to underlie its pathogenic potential. The most widely employed CK2 inhibitor is 4,5,6,7-tetrabromobenzotriazole (TBB), which exhibits a comparable efficacy toward another kinase, DYRK1 a. Here we describe the development of a new class of CK2 inhibitors, conceptually derived from TBB, which have lost their potency toward DYRK1 a. In particular, tetrabromocinnamic acid (TBCA) inhibits CK2 five times more efficiently than TBB (IC50 values 0.11 and 0.56 microM, respectively), without having any comparable effect on DYRK1 a (IC50 24.5 microM) or on a panel of 28 protein kinases. The usefulness of TBCA for cellular studies has been validated by showing that it reduces the viability of Jurkat cells more efficiently than TBB through enhancement of apoptosis. Collectively taken, the reported data support the view that suitably derivatized tetrabromobenzene molecules may provide powerful reagents for dissecting the cellular functions of CK2 and counteracting its pathogenic potentials.

Purpose: Protein kinase CK2 promotes multiple myeloma cell growth by regulating critical signaling pathways. CK2 also modulates proper HSP90-dependent client protein folding and maturation by phosphorylating its co-chaperone CDC37. Because the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) is central in myeloma pathogenesis, we tested the hypothesis that the CK2/CDC37/HSP90 axis could be involved in UPR in myeloma cells.Experimental Design: We analyzed CK2 activity upon ER stress, the effects of its inactivation on the UPR pathways and on ER stress-induced apoptosis. The consequences of CK2 plus HSP90 inhibition on myeloma cell growth in vitro and in vivo and CK2 regulation of HSP90-triggered UPR were determined.Results: CK2 partly localized to the ER and ER stress triggered its kinase activity. CK2 inhibition reduced the levels of the ER stress sensors IRE1a and BIP/GRP78, increased phosphorylation of PERK and EIF2a, and enhanced ER stress-induced apoptosis. Simultaneous inactivation of CK2 and HSP90 resulted in a synergic anti-myeloma effect (combination index ¼ 0.291) and in much stronger alterations of the UPR pathways as compared with the single inhibition of the two molecules. Cytotoxicity from HSP90 and CK2 targeting was present in a myeloma microenvironment model, on plasma cells from patients with myeloma and in an in vivo mouse xenograft model. Mechanistically, CK2 inhibition led to a reduction of IRE1a/HSP90/CDC37 complexes in multiple myeloma cells.Conclusions: Our results place CK2 as a novel regulator of the ER stress/UPR cascades and HSP90 function in myeloma cells and offer the groundwork to design novel combination treatments for this disease.