Protein Kinase CK2 Is Inhibited by Human Nucleolar Phosphoprotein p140 in an Inositol Hexakisphosphate-dependent Manner

Abstract

Protein kinase CK2 is a ubiquitous protein kinase that can phosphorylate various proteins involved in central cellular processes, such as signal transduction, cell division, and proliferation. We have shown that the human nucleolar phosphoprotein p140 (hNopp140) is able to regulate the catalytic activity of CK2. Unphosphorylated hNopp140 and phospho-hNopp140 bind to the regulatory and catalytic subunits of CK2, respectively, and the interaction between hNopp140 and CK2 was prevented by inositol hexakisphosphate (InsP6). Phosphorylation of α-casein, genimin, or human phosphatidylcholine transfer protein-like protein by CK2 was inhibited by hNopp140, and InsP6 recovered the suppressed activity of CK2 by hNopp140. These observations indicated that hNopp140 serves as a negative regulator of CK2 and that InsP6 stimulates the activity of CK2 by blocking the interaction between hNopp140 and CK2. Protein kinase CK2 is a ubiquitous protein kinase that can phosphorylate various proteins involved in central cellular processes, such as signal transduction, cell division, and proliferation. We have shown that the human nucleolar phosphoprotein p140 (hNopp140) is able to regulate the catalytic activity of CK2. Unphosphorylated hNopp140 and phospho-hNopp140 bind to the regulatory and catalytic subunits of CK2, respectively, and the interaction between hNopp140 and CK2 was prevented by inositol hexakisphosphate (InsP6). Phosphorylation of α-casein, genimin, or human phosphatidylcholine transfer protein-like protein by CK2 was inhibited by hNopp140, and InsP6 recovered the suppressed activity of CK2 by hNopp140. These observations indicated that hNopp140 serves as a negative regulator of CK2 and that InsP6 stimulates the activity of CK2 by blocking the interaction between hNopp140 and CK2. The protein kinase CK2, formerly known as casein kinase II, is a serine/threonine protein kinase that has been found in virtually all tissues and cell lines and is responsible for the phosphorylation of more than 300 cellular proteins (1Meggio F. Pinna L.A. FASEB J. 2003; 17: 349-368Crossref PubMed Scopus (1126) Google Scholar). The cellular function of CK2 is related to essential processes such as cell cycle, proliferation, or signal transduction since the proteins phosphorylated by CK2 are involved in DNA replication and transcription, translation, and signal transduction (2Henriksson M. Luscher B. Adv. Cancer Res. 1996; 68: 109-182Crossref PubMed Google Scholar, 5Lin A. Frost J. Deng T. Smeal T. al-Alawi N. Kikkawa U. Hunter T. Brenner D. Karin M. Cell. 1992; 70: 777-789Abstract Full Text PDF PubMed Scopus (317) Google Scholar). Although the activity of CK2 is observed ubiquitously, unregulated CK2 has been correlated with cell transformation. Elevated levels of CK2 have been observed in transformed cells (6Boldyreff B. Meggio F. Pinna L.A. Issinger O.G. Biochem. Biophys. Res. Commun. 1992; 188: 228-234Crossref PubMed Scopus (54) Google Scholar, 7Ahmed K. Cell. Mol. Biol. Res. 1994; 40: 1-11PubMed Google Scholar) and a wide variety of tumors (8Tawfic S. Yu S. Wang H. Faust R. Davis A. Ahmed K. Histol. Histopathol. 2001; 16: 573-582PubMed Google Scholar). Additionally, expression of the catalytic subunit of CK2 in transgenic mice as well as the altered expression of CK2 in p53 deficiency conditions have been shown to induce lymphomas (9Seldin D.C. Leder P. Science. 1995; 267: 894-897Crossref PubMed Scopus (364) Google Scholar, 10Landesman-Bollag E. Channavajhala P.L. Cardiff R.D. Seldin D.C. Oncogene. 1998; 16: 2965-2974Crossref PubMed Scopus (148) Google Scholar), suggesting that CK2 plays a role in neoplastic growth (8Tawfic S. Yu S. Wang H. Faust R. Davis A. Ahmed K. Histol. Histopathol. 2001; 16: 573-582PubMed Google Scholar). In addition, the recognition of many viral proteins as targets of CK2 indicates that CK2-dependent activation of viral proteins may be essential to the viral life cycle (11Pinna L.A. Meggio F. Prog. Cell Cycle Res. 1997; 3: 77-97Crossref PubMed Scopus (316) Google Scholar). Because of the involvement of CK2 in these processes, CK2 is considered a potential target for anti-neoplastic and anti-infectious agents (12Sarno S. Moro S. Meggio F. Zagotto G. Dal Ben D. Ghisellini P. Battistutta R. Zanotti G. Pinna L.A. Pharmacol. Ther. 2002; 93: 159-168Crossref PubMed Scopus (155) Google Scholar). CK2 is a holoenzyme that consists of two catalytic subunits (α or α′) and two regulatory subunits (β). The crystal structure of the CK2 holoenzyme (α2β2) showed that the two catalytic subunits each interact with a central dimer formed by the regulatory subunits and make no direct contact with one another (13Niefind K. Guerra B. Ermakowa I. Issinger O.G. EMBO J. 2001; 20: 5320-5331Crossref PubMed Scopus (346) Google Scholar). The regulatory subunit dimer appears to regulate CK2 activity either by direct modulation of the activity of catalytic subunit (14Guerra B. Boldyreff B. Sarno S. Cesaro L. Issinger O.G. Pinna L.A. Pharmacol. Ther. 1999; 82: 303-313Crossref PubMed Scopus (87) Google Scholar, 15Cochet C. Chambaz E.M. J. Biol. Chem. 1983; 258: 1403-1406Abstract Full Text PDF PubMed Google Scholar) or by altering the substrate specificity of the catalytic subunit (16Meggio F. Boldyreff B. Marin O. Pinna L.A. Issinger O.G. Eur. J. Biochem. 1992; 204: 293-297Crossref PubMed Scopus (136) Google Scholar). The regulatory machinery controlling CK2 in the cell is poorly understood. The cellular activity of CK2 appears to be independent of either the typical secondary messengers or phosphorylation (17Guerra B. Issinger O.G. Electrophoresis. 1999; 20: 391-408Crossref PubMed Scopus (366) Google Scholar). Several proteins that could interact with CK2 and affect the activity of the enzyme have been identified. Among these proteins, the FACT (facilitates chromatin transcription) complex (3Keller D.M. Zeng X. Wang Y. Zhang Q.H. Kapoor M. Shu H. Goodman R. Lozano G. Zhao Y. Lu H. Mol. Cell. 2001; 7: 283-292Abstract Full Text Full Text PDF PubMed Scopus (259) Google Scholar, 18Keller D.M. Lu H. J. Biol. Chem. 2002; 277: 50206-50213Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar) and Pin1 (a peptidylprolyl isomerase) (19Messenger M.M. Saulnier R.B. Gilchrist A.D. Diamond P. Gorbsky G.J. Litchfield D.W. J. Biol. Chem. 2002; 277: 23054-23064Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar) were shown to modulate CK2 substrate specificity. In addition, the tumor suppressor adenomatous polyposis coli (APC) 2The abbreviations used are: APC, adenomatous polyposis coli; InsP6, d-myo-inositol 1,2,3,4,5,6-hexakisphosphate; InsP4, d-myo-inositol 1,3,4,5-tetrakisphosphate; InsP5, d-myo-inositol 1,2,3,4,5-pentakisphosphate; h-, human; GST, glutathione S-transferase; PBS, phosphate-buffered saline; PCTP, phosphatidylcholine transfer protein. binds to the catalytic subunit of CK2 and suppresses CK2 activity (20Homma M.K. Li D. Krebs E.G. Yuasa Y. Homma Y. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 5959-5964Crossref PubMed Scopus (56) Google Scholar). Small molecules that can regulate CK2 activity have also been characterized. Polyanions, such as heparin, inhibit CK2 (21Tuazon P.T. Traugh J.A. Adv. Second Messenger Phosphoprotein Res. 1991; 23: 123-164PubMed Google Scholar), where as polycations, such as spermine or polylysine, moderately activate the enzyme (22Leroy D. Heriche J.K. Filhol O. Chambaz E.M. Cochet C. J. Biol. Chem. 1997; 272: 20820-20827Abstract Full Text Full Text PDF PubMed Scopus (93) Google Scholar, 23Sarno S. Marin O. Meggio F. Pinna L.A. Biochem. Biophys. Res. Commun. 1993; 194: 83-90Crossref PubMed Scopus (21) Google Scholar). Recently, highly phosphorylated forms of inositols were shown to regulate the activity of CK2. Inositol hexakisphosphate (InsP6) stimulated the catalytic activity of CK2 in cell extracts or in partially purified fraction of CK2 by 2-3-fold but failed to activate purified recombinant CK2 (24Solyakov L. Cain K. Tracey B.M. Jukes R. Riley A.M. Potter B.V. Tobin A.B. J. Biol. Chem. 2004; 279: 43403-43410Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar), suggesting that the cell extracts contain an unidentified negative regulator whose inhibitory activity was blocked by InsP6. One of the proteins that can interact with CK2 is hNopp140, a nucleolar phosphoprotein (25Kim Y.K. Jin Y. Vukoti K.M. Park J.K. Kim E.E. Lee K.J. Yu Y.G. Protein Expression Purif. 2003; 31: 260-264Crossref PubMed Scopus (10) Google Scholar). It can be highly phosphorylated by CK2, and the cellular function of hNopp140 is related to both the biogenesis of the nucleolus and the cell cycle (26Meier U.T. Blobel G. Cell. 1992; 70: 127-138Abstract Full Text PDF PubMed Scopus (341) Google Scholar). In this study we investigated the interaction between hNopp140 and CK2 and demonstrated that hNopp140 could negatively regulate the catalytic activity of CK2. Furthermore, we showed that InsP6 abolished the negative regulation of CK2 by hNopp140. These findings provide insight into the roles of hNopp140 and phosphoinositides in CK2 regulation. Materials—Protein kinase CK2 was purchased from New England Biolabs (Ipswich, MA). d-myo-Inositol 1,2,3,4,5,6-hexakisphosphate (InsP6), d-myo-inositol 1,3,4,5-tetrakisphosphate (InsP4), d-myo-inositol 1,2,3,4,5-pentakisphosphate (InsP5), d-myo-inositol 1,2,3,4,5,6-hexakissulfate, and α-casein were obtained from Calbiochem and Sigma, respectively. Polyclonal antibodies against hNopp140 were prepared from mice immunized with purified hNopp140. Anti-GST, anti-CK2α, and anti-CK2β antibodies were obtained from Santa Cruz Biotechnology. All other consumables were of reagent grade. Plasmid Construction and Protein Purification—Recombinant hNopp140 was expressed in Escherichia coli BL21(DE3) and purified as previously described (25Kim Y.K. Jin Y. Vukoti K.M. Park J.K. Kim E.E. Lee K.J. Yu Y.G. Protein Expression Purif. 2003; 31: 260-264Crossref PubMed Scopus (10) Google Scholar). The DNA fragments encoding human CK2α and CK2β subunits were amplified by PCR from the pT7-CK2α and pT7-CK2β plasmids, respectively, which were kindly provided by Prof. Young-Seuk Bae (Kyungpook National University). The amplified DNA fragments were inserted into the cloning sites of the pGEX-4T1 vector, producing GST-CK2α and GST-CK2β, in which CK2α or CK2β was fused at the C terminus of GST. The plasmids were then transformed into E. coli DH5α, and the expression of GST-CK2α or GST-CK2β was induced using 0.5 mm isopropyl-β-d-thiogalactopyranoside for 3 h at 37°C in LB medium containing 100 μg/ml ampicillin. Harvested E. coli cells were lysed using a micro fluidizer, and cell debris was removed by centrifugation at 15,000 × g for 20 min. The crude extract was loaded onto a GST-agarose column, and bound proteins were eluted with 20 mm reduced glutathione in PBS (137 mm NaCl, 27 mm KCl, 10 mm sodium phosphate, 2 mm potassium phosphate, pH 7.4). For preparation of CK2α or CK2β, the isolated GST-CK2α or GST-CK2β was cleaved with thrombin, and CK2α or CK2β were further purified by anion exchange chromatography using a Mono Q column (Amersham Biosciences). The cDNA encoding human genimin or PCTP-like protein was amplified by PCR from a human fetal brain cDNA library and inserted into the NdeI and EcoRI cloning sites (New England Biolabs) of pET28a (Novagen) or the HindIII and XhoI cloning sites of the pET21a vector (Novagen) to generate an expression vector for geminin or PCTP-like protein, respectively. The expressions of recombinant His-tagged geminin or PCTP-like protein in E. coli BL21(DE3) were induced using 1 mm isopropyl-β-d-thiogalactopyranoside, and the expressed proteins were purified using nickel nitrilotriacetic acid affinity chromatography. Protein Phosphorylation—CK2-mediated protein phosphorylation assays were performed by incubating 6 μg of substrate protein with 15 units of CK2 in 20 μl of reaction buffer (20 mm Tris-HCl, 50 mm KCl, 10 mm MgCl2, 2.5 mm ATP, pH 7.5) containing 1 μm [γ-32P]ATP (100 cpm pmol-1) at 30 °C for20 min. To prepare phospho-hNopp140, purified recombinant hNopp140 was incubated with CK2 in 100 μl of reaction buffer at 30 °C for 16 h. Quantification of the protein bands detected by autoradiography was performed using FUJIX BAS 2000 phosphorimaging (Fuji, Japan). GST Pulldown Assay—Unphosphorylated hNopp140 or phospho-hNopp140 (2 μg) were mixed with 1 μg GST-CK2α and/or GST-CK2β in PBST (PBS containing 0.1% Tween 20) at 4 °C for 2 h, then further incubated with 20 μl of GST-agarose beads (50% suspension) (Peptron, Korea). After washing the beads 5 times with PBST, the proteins bound to the resin were eluted by adding 2× SDS-PAGE sample buffer and separated by SDS-PAGE. The proteins on the gel were transferred onto a polyvinylidene difluoride membrane. The membrane was blocked with 5% nonfat dried milk for 1 h, reacted with 0.2 μg/ml mouse anti-hNopp140 antibodies in PBST for 1 h, and then incubated with 0.1 μg/ml sheep anti-mouse IgG conjugated to horseradish peroxidase for 1 h. After successive washes with PBST, immunoblots were visualized using an enhanced chemiluminescence system (Pierce) as described in the manufacturer's instruction manual. Cell Culture and cDNA encoding hNopp140, by and was into the expression vector to generate which expressed a hNopp140 with a at the For cells were in and in medium with fetal cells were with DNA mixed with the reagent to the manufacturer's were h cells were lysed in buffer mm Tris-HCl, mm NaCl, 1 mm and pH for 2 h at 4 and cell debris was removed by centrifugation at × g for 30 min. The cell was incubated with 1 μg of anti-hNopp140 antibodies in buffer at 4 °C for 2 h. After with protein Cruz for 2 h, the was for 10 and the was After washing the beads times with the proteins bound to the beads were eluted by adding SDS-PAGE sample buffer and separated by SDS-PAGE. in the gel were transferred onto a polyvinylidene difluoride membrane and visualized with antibodies using an (Pierce) as described in the manufacturer's hNopp140 the of of hNopp140 on the catalytic activity of CK2 was in using α-casein as a Phosphorylation of α-casein by the CK2 holoenzyme was reduced as the of hNopp140 The activity of CK2 to of the in the of an of hNopp140 and further to of in the of μm hNopp140 Because hNopp140 is a substrate of CK2 (26Meier U.T. Blobel G. Cell. 1992; 70: 127-138Abstract Full Text PDF PubMed Scopus (341) Google Scholar), the inhibitory activity of phospho-hNopp140 was to the of that be by the of hNopp140 as an shown in and phospho-hNopp140 is as in the activity of CK2 as hNopp140. The inhibitory activity of hNopp140 on CK2 was also using a regulator of DNA replication Cell. 1998; 93: Full Text Full Text PDF PubMed Scopus Google Scholar) and a substrate of CK2 M. E. F. Pinna L.A. R. Biochem. Biophys. Res. Commun. 2004; PubMed Scopus Google Scholar). shown in recombinant geminin was phosphorylated by CK2, and the CK2-dependent phosphorylation was reduced in the of hNopp140 the inhibitory of hNopp140 was than with α-casein as between hNopp140 and CK2 by the interaction between hNopp140 and CK2, of the catalytic and regulatory subunits of CK2, GST-CK2α or GST-CK2β, respectively, to phospho-hNopp140 or hNopp140 was GST-CK2α was incubated with hNopp140 and with glutathione phospho-hNopp140 with In GST-CK2β was able to bind phospho-hNopp140 but bind to hNopp140 These that hNopp140 to the subunits of CK2 on phosphorylation phospho-hNopp140 binds to and hNopp140 binds to Because hNopp140 is highly phosphorylated in cell extracts (26Meier U.T. Blobel G. Cell. 1992; 70: 127-138Abstract Full Text PDF PubMed Scopus (341) Google Scholar), hNopp140 bind to the catalytic subunit of CK2 and catalytic To hNopp140 could affect the of CK2 the interaction between CK2α and GST-CK2β was in the of hNopp140. of the two subunits of CK2 was by of CK2α with GST-CK2β and In the of hNopp140, the of CK2α bound to GST-CK2β was and failed to the interaction between CK2α and GST-CK2β These that hNopp140 was able to the of CK2 the of CK2 by hNopp140 be to reduced of substrate proteins to the of CK2 or a to a The of CK2 by hNopp140 by CK2-dependent phosphorylation of PCTP-like protein was shown to be by an unidentified and the CK2 activity was stimulated in the of inositol such as InsP6 (24Solyakov L. Cain K. Tracey B.M. Jukes R. Riley A.M. Potter B.V. Tobin A.B. J. Biol. Chem. 2004; 279: 43403-43410Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). To inositol could the activity of CK2 by hNopp140, the activity of CK2 in the of inositol InsP4, InsP5, InsP6, and d-myo-inositol was using α-casein or human PCTP-like protein as α-casein was used as InsP6 the activity of CK2 in the of hNopp140 the reduced activity of CK2 by hNopp140 was recovered as the of InsP6 and the inhibitory activity of hNopp140 was no observed at 10 μm or of InsP6 The of various inositol to the CK2 activity by hNopp140 were further using α-casein as It was found that InsP6 the inositol showed InsP4, InsP5, or d-myo-inositol showed The inhibitory of hNopp140 and the activity of inositol on the CK2-dependent phosphorylation of human PCTP-like protein were with purified recombinant protein. The phosphorylation of PCTP-like protein by CK2 was reduced in the of hNopp140 and The reduced activity of CK2 by hNopp140 was in the of μm InsP6. In InsP4, d-myo-inositol showed on the CK2 activity the reduced CK2-dependent phosphorylation of geminin by hNopp140 was also stimulated by InsP6 the of various inositol were observed to the of the phosphorylation in the or of hNopp140 These indicated that InsP6 CK2 by the activity of CK2 by hNopp140, and the regulatory of hNopp140 was well to the unidentified cellular that CK2 in (24Solyakov L. Cain K. Tracey B.M. Jukes R. Riley A.M. Potter B.V. Tobin A.B. J. Biol. Chem. 2004; 279: 43403-43410Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). InsP6 the between hNopp140 and The affinity of hNopp140 to CK2 and the of CK2 activity that InsP6 the interaction between hNopp140 and CK2. The of InsP6 on this interaction was by the of hNopp140 bound to GST-CK2α or GST-CK2β in the or of InsP6 using a GST with GST-CK2α the proteins were incubated in the of μm InsP6 In the of hNopp140 to GST-CK2β was reduced by InsP6. We further the of InsP6 on the interaction between hNopp140 and CK2 in cell extracts by using anti-hNopp140 antibodies and using antibodies or anti-hNopp140 proteins in the cell extract were with anti-hNopp140 antibodies in the or of InsP6, of hNopp140 were observed the of CK2α with hNopp140 to of the in the of μm InsP6 These that InsP6 stimulated the activity of CK2 by blocking the interaction between hNopp140 and In this study we have shown that hNopp140 can bind to and negatively regulate CK2. InsP6 was shown to hNopp140 CK2 by blocking the interaction between hNopp140 and CK2. Li D. U.T. G. Krebs E.G. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar) showed that mouse in extracts of cells bound to the regulatory subunit of CK2 and that a CK2α with In the study hNopp140 with both subunits of CK2 on the phosphorylation of hNopp140. CK2α with the highly phosphorylated of hNopp140 and CK2β with the The affinity between mouse and CK2α in cell extracts could be to a of phosphorylation of mouse mouse and human have for CK2 subunits on of of hNopp140 to CK2 reduced the catalytic activity of CK2 and the of hNopp140 of CK2 on the Phosphorylation of PCTP-like protein or α-casein by CK2 was inhibited by hNopp140 suggesting that the of hNopp140 may the substrate proteins to to the of CK2. the other was that the phosphorylation of the acid by CK2 was by hNopp140 D. U.T. G. Krebs E.G. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). The reduced inhibitory of hNopp140 on CK2-dependent phosphorylation of substrate may be to the highly which could be more to the hNopp140 appears to the of a of substrate proteins such as α-casein or PCTP-like protein (24Solyakov L. Cain K. Tracey B.M. Jukes R. Riley A.M. Potter B.V. Tobin A.B. J. Biol. Chem. 2004; 279: 43403-43410Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar) to the CK2 but to affect the of or such as the The interaction between hNopp140 and CK2 was by InsP6. Inositol such as InsP6 are found in cells in D. A. J. Biol. Chem. Full Text PDF PubMed Google Scholar, Biochem. Biophys. Res. Commun. PubMed Scopus Google Scholar). Although the of inositol are poorly are in of cell regulation such as A. C. B. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: PubMed Scopus Google Scholar), DNA A. Yu H. E. K. 2002; PubMed Scopus Google Scholar), and chromatin Biol. 2003; PubMed Scopus Google Scholar). Furthermore, the cellular of InsP6 at the cell cycle J. Biochem. J. 2004; PubMed Scopus Google Scholar), that InsP6 has an role in cell cycle the cellular levels of InsP6 cell division, CK2 may from hNopp140 and The of InsP6 in cells E. F. K. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar) and the of CK2 activity in cells the regulation of CK2 by InsP6 and hNopp140 cell Tobin and (24Solyakov L. Cain K. Tracey B.M. Jukes R. Riley A.M. Potter B.V. Tobin A.B. J. Biol. Chem. 2004; 279: 43403-43410Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar) demonstrated the of an negative regulator of CK2. In InsP6 the catalytic activity of purified CK2 but stimulated CK2 activity 2-3-fold the enzyme been by unidentified cellular (24Solyakov L. Cain K. Tracey B.M. Jukes R. Riley A.M. Potter B.V. Tobin A.B. J. Biol. Chem. 2004; 279: 43403-43410Abstract Full Text Full Text PDF PubMed Scopus (44) Google Scholar). These of the negative regulator are well in with of hNopp140, (25Kim Y.K. Jin Y. Vukoti K.M. Park J.K. Kim E.E. Lee K.J. Yu Y.G. Protein Expression Purif. 2003; 31: 260-264Crossref PubMed Scopus (10) Google Scholar). that CK2 forms a complex with hNopp140 at of InsP6, and the activity of CK2 is reduced with that of CK2. in this or can be phosphorylated by CK2. of CK2 may be responsible for the and observed in We also hNopp140 could negatively regulate the CK2-dependent phosphorylation of proteins other than PCTP-like protein using a regulator of DNA replication Cell. 1998; 93: Full Text Full Text PDF PubMed Scopus Google Scholar) and a substrate of CK2 M. E. F. Pinna L.A. R. Biochem. Biophys. Res. Commun. 2004; PubMed Scopus Google Scholar). PCTP-like protein, the phosphorylation of geminin by CK2 was inhibited by hNopp140 the reduced phosphorylation was by InsP6 that the of CK2 activity by hNopp140 on the of substrate It be that inositol such as could phosphorylate hNopp140 in a A. R. A.M. Science. 2004; PubMed Scopus Google Scholar). of hNopp140 with the of InsP6 on the activity of CK2 by hNopp140 a regulation of inositol on the cellular function of hNopp140. Recently, the protein was as a negative regulator of CK2. binds CK2 and the catalytic activity of CK2 (20Homma M.K. Li D. Krebs E.G. Yuasa Y. Homma Y. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 5959-5964Crossref PubMed Scopus (56) Google Scholar). with fragments of and CK2 that a at the C terminus of APC, which consists of inhibited CK2. Although the CK2 regulatory of and hNopp140 are both negative of CK2, showed no It is that both hNopp140 and the CK2 regulatory of have a of and may to CK2. the inhibited the phosphorylation of suggesting that regulation of CK2 from that of hNopp140. In we have hNopp140 as an negative regulator of CK2. The regulation of CK2 by InsP6 and hNopp140 could the of CK2 activity from to highly regulatory phosphorylation of a of CK2 than all CK2 of CK2 whose phosphorylation is by hNopp140 the of hNopp140 on regulation of CK2.