Abstract
Protein kinase CK2 is a tetrameric enzyme composed of two catalytic (alpha and/or alpha') subunits and two regulatory (beta) subunits. Because CK2beta is synthesized in excess of CK2alpha, we hypothesized that formation of CK2beta homodimers precedes the incorporation of the catalytic subunits of CK2 into complexes. To test this hypothesis, we cotransfected cells with two epitope-tagged variants of CK2beta. The results of these cotransfection studies demonstrate that interactions between two CK2beta subunits take place in the absence of CK2alpha. Together with results from previous biosynthetic labeling studies, these results suggest that formation of CK2beta homodimers occurs before incorporation of catalytic subunits of CK2 into CK2 complexes. We also cotransfected Cos-7 cells with a deletion fragment of CK2beta (i.e. Myc-beta1-166) together with full-length hemagglutinin (HA)-tagged CK2beta and/or CK2alpha'. Although complexes between Myc-beta1-166 and HA-beta were readily detected, we obtained no evidence of direct interactions between Myc-beta1-166 and HA-CK2alpha'. These results suggest that residues within the N-terminal 166 amino acids of CK2beta are sufficient for interactions between CK2beta subunits, whereas the C-terminal domain of CK2beta is required for complex formation with the catalytic subunits of CK2. Finally, we observed that expression of full-length HA-beta promotes phosphorylation of Myc-beta1-166 by HA-CK2alpha'.
Highlights
Protein kinase CK21 is a protein serine/threonine kinase involved in various aspects of cellular regulation [1,2,3,4]
We hypothesized that formation of complexes between CK2 subunits precedes the incorporation of catalytic subunits into tetrameric complexes
The 12CA5 antibodies do not react with Myc-CK2 (B and C, lane 4) and the 9E10 antibodies do not react with HA-CK2 (B and D, lane 2)
Summary
Protein kinase CK21 (formerly known as casein kinase II) is a protein serine/threonine kinase involved in various aspects of cellular regulation [1,2,3,4]. CK2 appears to mediate the activating effects of compounds such as polyamines that may have a role in regulating CK2 in cells [19, 20] Overall, these results suggest that CK2 is a critical mediator of the cellular functions of CK2. In recent studies using the yeast two-hybrid system, we and others demonstrated that CK2 has the ability to interact with CK2␣ or with CK2, whereas CK2␣ is only able to interact with CK2 [21,22,23] These results suggested that interactions between two  subunits are responsible for bringing two ␣: dimers into active tetrameric complexes. Our results suggest that deletion mutants of CK2 such as CK21– 166 offer new strategies for controlling the functions of CK2 in cells by altering the subunit composition of CK2 in cells in a manner that prevents formation of intact tetrameric CK2 complexes
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