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Query: UNIPROT:P06889 (Mol)
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The protein kinase CK2 is composed of two catalytic alpha- or alpha'- and two regulatory beta-subunits. In mammalian cells there is ample evidence for the presence of individual CK2 subunits beside the holoenzyme. By immunofluorescence studies using peptide antibodies which allow us to detect the CK2alpha-, alpha'- and beta-subunits we found all three subunits to be co-localized with a 58 KDa Golgi protein which is specific for the Golgi complex. Subfractionation studies using dog pancreas cells revealed the presence of all three subunits of CK2 at the smooth endoplasmic reticulum (sER)/Golgi fraction whereas the rough endoplasmic reticulum (rER) harboured only the catalytic alpha- and alpha'-subunits. We found that the microsomal preparation from dog pancreas cells contained CK2 which phosphorylated a CK2 specific synthetic peptide and which was heparin sensitive. Furthermore, we could immunoprecipitate the CK2alpha-subunit that exhibited a kinase activity which phosphorylated a CK2 specific substrate and which was heparin sensitive. Protease digestion experiments revealed that the CK2 subunits were located on the cytosolic side of the rER and the sER/Golgi complex. Thus, we could demonstrate an asymmetric distribution of the CK2 subunits at the rER and sER/Golgi complex. Since the CK2alpha- and alpha'-subunits exhibit a substrate specificity which is different from the CK2 holoenzyme one might speculate that the asymmetric distribution of the CK2 holoenzyme and the CK2 catalytic subunits may have regulatory functions.
Mol Cell Biochem 2001 Nov
PMID:Localization of individual subunits of protein kinase CK2 to the endoplasmic reticulum and to the Golgi apparatus. 1182 77

We have generated fusion proteins between the subunits of CK2 and GFP and characterized their behaviour in living cells. The expressed fusion proteins were functional and interacted with endogenous CK2. Imaging of NIH3T3 cells expressing low level of GFP-CK2alpha or GFP-CK2beta showed that both proteins were mostly nuclear in interphase. Both CK2 subunits contain nuclear localization domains that target them independently to the nucleus. Once in the nucleus, both subunits diffused rapidly in the nucleoplasm. In mitotic cells, CK2 subunits were dispersed throughout the cytoplasm and were not associated to chromatin. Our data are compatible with the idea that each subunit can translocate individually to the nucleus to interact with each other or with important cellular partners. Understanding the molecular mechanisms which regulate the dynamic localization of CK2 subunits will be of central importance.
Mol Cell Biochem 2001 Nov
PMID:Visualization and molecular analysis of nuclear import of protein kinase CK2 subunits in living cells. 1182 78

D. melanogaster CK2 (DmCK2) is a highly conserved protein kinase that is composed of catalytic, alpha, and regulatory, beta, subunits associated as an alpha2beta2 heterotetramer. In order to analyze the functions of CK2 in this metazoan model, we have used the two hybrid approach to identify interacting proteins. One of these cDNAs, DmA24, encodes a novel polypeptide with no homologs in GenBank, and is notable in that it contains a bipartite nuclear localization signal and two sites for phosphorylation by CK2. In situ hybridization to polytene chromosomes indicates that the DmA24 gene is located at the 61 D interval of chromosome II a region that also harbors 3 additional genes with similar structure. DmA24p interacts with DmCK2alpha, but not with DmCK2beta, demonstrating that this interaction is specific for the catalytic subunit of CK2. In addition, the protein is phosphorylated by the holoenzyme purified from Drosophila embryos. These studies identify DmA24p as a potentially new physiological partner of DmCK2. In addition, we also report the results of a large-scale screen that has identified a new set of DmCK2-interacting proteins. Most notable among these are Surf6, a nucleolar protein involved in RNA processing, and Spalt, a homeotic protein.
Mol Cell Biochem 2001 Nov
PMID:Identification and characterization of proteins that interact with Drosophila melanogaster protein kinase CK2. 1182 79

Drosophila melanogaster protein kinase CK2 (DmCK2) is a Ser/Thr protein kinase composed of catalytic alpha and regulatory beta subunits associated as an alpha2beta2 heterotetramer. Using the two hybrid system, we have screened a Drosophila embryo cDNA library in order to identify proteins that interact with DmCK2alpha. One of these cDNAs encodes a novel previously undescribed zinc-finger protein, which we call ZFP47. ZFP47 interacts with DmCK2alpha but not with DmCK2beta, indicating that this interaction is specific for the catalytic subunit of CK2. In situ hybridization to polytene chromosomes indicates that the corresponding gene is located at the 72A interval of chromosome III. Sequence analysis indicates that ZFP47 contains a consensus site for phosphorylation by CK2, 4 C1H1-type zinc-fingers, and a bipartite nuclear localization signal. Consistent with the prediction of a site for phosphorylation by CK2, we demonstrate that ZFP47 is phosphorylated by CK2 purified from Drosophila embryos. These studies demonstrate that ZFP47 is a new physiological partner and substrate of CK2.
Mol Cell Biochem 2001 Nov
PMID:A gene located at 72A in Drosophila melanogaster encodes a novel zinc-finger protein that interacts with protein kinase CK2. 1182 80

The papillomavirus E1 protein is essential for viral DNA replication, and phosphorylation of E1 appears to regulate protein function and DNA replication. Serine 584 of bovine papillomavirus E1 is in a conserved motif resembling a CK2 consensus site, and is phosphorylated by CK2 in vitro. Mutation of serine 584 to alanine eliminates replication of the viral genome in transient replication assays. Wild-type and mutant E1 proteins were expressed from recombinant baculoviruses and used to assess biochemical functions of the amino acid 584 substitution. Helicase enzyme activity, E1 binding to the viral E2 protein and to cellular DNA polymerase alpha-primase were all unaffected in the mutant protein. Binding of E1 to viral replication origin DNA sequences was reduced in the mutant, but not eliminated. The carboxyl-terminal region of the protein appears to play a role in regulating E1 function, and adds to a complex picture emerging for papillomavirus DNA replication control.
J Mol Biol 2002 Feb 22
PMID:Functional analysis of a carboxyl-terminal phosphorylation mutant of the bovine papillomavirus E1 protein. 1186 20

CK2 is a highly conserved protein kinase with growth-promoting and oncogenic properties. It is known to activate RNA polymerase III (PolIII) transcription in Saccharomyces cerevisiae and is shown here to also exert a potent effect on PolIII in mammalian cells. Peptide and chemical inhibitors of CK2 block PolIII transcription in human cell extracts. Furthermore, PolIII transcription in mammalian fibroblasts is decreased significantly when CK2 activity is compromised by chemical inhibitors, antisense oligonucleotides, or kinase-inactive mutants. Coimmunoprecipitation and cofractionation show that endogenous human CK2 associates stably and specifically with the TATA-binding protein-containing factor TFIIIB, which brings PolIII to the initiation site of all class III genes. Serum stimulates TFIIIB phosphorylation in vivo, an effect that is diminished by inhibitors of CK2. Binding to TFIIIC2 recruits TFIIIB to most PolIII promoters; this interaction is compromised specifically by CK2 inhibitors. The data suggest that CK2 stimulates PolIII transcription by binding and phosphorylating TFIIIB and facilitating its recruitment by TFIIIC2. CK2 also activates PolI transcription in mammals and may therefore provide a mechanism to coregulate the output of PolI and PolIII. CK2 provides a rare example of an endogenous activity that operates on the PolIII system in both mammals and yeasts. Such evolutionary conservation suggests that this control may be of fundamental importance.
Mol Cell Biol 2002 Jun
PMID:CK2 forms a stable complex with TFIIIB and activates RNA polymerase III transcription in human cells. 1199 11

Caspases play a central role in apoptosis, but their activity is under the control of caspase-inhibiting proteins. A characteristic of caspase-inhibiting proteins is direct caspase binding. It is yet unknown how the localization of caspase-inhibiting proteins is regulated and whether there are upstream signals controlling their function. Here we report that the function of ARC is regulated by protein kinase CK2. ARC at threonine 149 is phosphorylated by CK2. This phosphorylation targets ARC to mitochondria. ARC is able to bind to caspase-8 only when it is localized to mitochondria but not to the cytoplasm. Our results reveal a molecular mechanism by which a caspase-inhibiting protein requires phosphorylation in order to prevent apoptosis.
Mol Cell 2002 Aug
PMID:Phosphorylation by protein kinase CK2: a signaling switch for the caspase-inhibiting protein ARC. 1219 71

Fragile X syndrome is caused by loss of FMR1 protein expression. FMR1 binds RNA and associates with polysomes in the cytoplasm; thus, it has been proposed to function as a regulator of gene expression at the posttranscriptional level. Posttranslational modification of FMR1 had previously been suggested to regulate its activity, but no experimental support for this model has been reported to date. Here we report that FMR1 in Drosophila melanogaster (dFMR1) is phosphorylated in vivo and that the homomer formation and the RNA-binding activities of dFMR1 are modulated by phosphorylation in vitro. Identification of a protein phosphorylating dFMR1 showed it to be Drosophila casein kinase II (dCKII). dCKII directly interacts with and phosphorylates dFMR1 in vitro. The phosphorylation site in dFMR1 was identified as Ser406, which is highly conserved among FMR1 family members from several species. Using mass spectrometry, we established that Ser406 of dFMR1 is indeed phosphorylated in vivo. Furthermore, human FMR1 (hFMR1) is also phosphorylated in vivo, and alteration of the conserved Ser500 in hFMR1 abolishes phosphorylation by CKII in vitro. These studies support the model that the biological functions of FMR1, such as regulation of gene expression, are likely regulated by its phosphorylation.
Mol Cell Biol 2002 Dec
PMID:Casein kinase II phosphorylates the fragile X mental retardation protein and modulates its biological properties. 1244 64

Protein kinase CKII (CKII) is required for progression through the cell division cycle. We recently reported that the beta subunit of protein kinase CKII (CKIIbeta) associates with CKBBP1 that contains the Ring-H2 finger motif in the yeast two-hybrid system. We demonstrate here that the Ring-H2 finger-disrupted mutant of CKBBP1 does not interact with purified CKIIbeta in vitro, which shows that the Ring-H2 finger motif is critical for direct interaction with CKIIbeta. The CKII holoenzyme is efficiently co-precipitated with the wild-type CKBBP1, but not with the Ring-H2 finger-disrupted CKBBP1, from whole cell extracts when epitope-tagged CKBBP1 is transiently expressed in HeLa cells. Disruption of the Ring-H2 finger motif does not affect the cellular localization of CKBBP1 in HeLa cells. The increased expression of either the wild-type CKBBP1 or Ring-H2 finger-disrupted CKBBP1 does not modulate the protein or the activity levels of CKII in HeLa cells. However, the stable expression of Ring-H2 finger-disrupted CKBBP1 in HeLa cells suppresses cell proliferation and causes the accumulation of the G1/G0 peak of the cell cycle. The Ring-H2 finger motif is required for maximal CKBBP1 phosphorylation by CKII, suggesting that the stable binding of CKBBP1 to CKII is necessary for its efficient phosphorylation. Taken together, these results suggest that the complex formation of CKIIbeta with CKBBP1 and/or CKII-mediated CKBBP1 phosphorylation is important for the G1/S phase transition of the cell cycle.
J Biochem Mol Biol 2002 Nov 30
PMID:The Ring-H2 finger motif of CKBBP1/SAG is necessary for interaction with protein kinase CKII and optimal cell proliferation. 1247 May 99

Protein kinase CK2 is a ubiquitous protein kinase implicated in proliferation and cell survival. Its regulatory beta subunit, CK2beta, which is encoded by a single gene in mammals, has been suspected of regulating other protein kinases. In this work, we show that knockout of the CK2beta gene in mice leads to postimplantation lethality. Mutant embryos were reduced in size at embryonic day 6.5 (E6.5). They did not exhibit signs of apoptosis but did show reduced cell proliferation. Mutant embryos were resorbed at E7.5. In vitro, CK2beta(-/-) morula development stopped after the blastocyst stage. Attempts to generate homozygous embryonic stem (ES) cells failed. By using a conditional knockout approach, we show that lack of CK2beta is deleterious for mouse ES cells and primary embryonic fibroblasts. This is in contrast to what occurs with yeast cells, which can survive without functional CK2beta. Thus, our study demonstrates that in mammals, CK2beta is essential for viability at the cellular level, possibly because it acquired new functions during evolution.
Mol Cell Biol 2003 Feb
PMID:Disruption of the regulatory beta subunit of protein kinase CK2 in mice leads to a cell-autonomous defect and early embryonic lethality. 1252 96


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