Phosphorylation regulates the stability of the regulatory CK2β subunit

Abstract

Protein kinase CK2 is a protein serine/threonine kinase that exhibits elevated expression in a number of cancers and displays oncogenic activity in mice. The regulatory CK2b subunit has a central role in assembly of functional tetrameric CK2 complexes where it participates in modulation of catalytic activity and substrate speci®city. Since overexpression of CK2b results in elevated levels of CK2 activity, we investigated the molecular mechanisms that control its degradation since perturbations in these pathways could contribute to elevated CK2 in cancer. In this study, we demonstrate that CK2b is degraded by a proteasome-dependent pathway and that it is ubiquitinated. We have also investigated the role of phosphorylation and a putative destruction box in regulating its stability in cells. Importantly, replacement of three serine residues within the autophosphorylation site of CK2b with glutamic acid residues resulted in a signi®cant decrease in its degradation indicating that autophosphorylation is involved in regulating its stability. Notably, although the autophosphorylation site of CK2b is remarkably conserved between species, this is the ®rst functional role ascribed to this site. Furthermore, based on these results, we speculate that alterations in the phosphorylation or dephosphorylation of the regulatory CK2b subunit could underlie the elevated expression of CK2 that is observed in cancer cells.

The Rice CK2 Kinase Regulates Trafficking of Phosphate Transporters in Response to Phosphate Levels

“…In addition, phosphomimicking in the human CK2b subunit enhances its stability (Zhang et al, 2002). In line with this result, we found that rice CK2b3 contains a related "destruction" box (YDYALDLILD) in the analogous position (amino acids 139 to 148), and abundance of CK2b3 was reduced when it was dephosphorylated in Pi-starved plants.…”

“…Treatment with MG132 (10 mM), a 26S proteasome inhibitor, blocked the CK2b3 decline but not the reduction in phosphorylation ( Figure 2D), indicative of protein degradation dependent on the ubiquitin/26S proteasome pathway. CK2b subunits that fail to form complexes with catalytic subunits are rapidly degraded (Zhang et al, 2002). In this context, the reduced accumulation of CK2b3 we observed under Pi starvation suggested that unphosphorylated CK2b3 may display decreased binding affinity with CK2a3 to form a stable holoenzyme.…”

Modulation of human checkpoint kinase Chk1 by the regulatory β-subunit of protein kinase CK2

“…Moreover, transfection with Chk1 alone leads to an increase of endogenous CK2b ( Figure 2a, lane 2). It is known that CK2b degradation is mediated by the proteosome (Zhang et al, 2002). The fact that coexpression of CK2b with Chk1 leads to enhanced CK2b expression, might indicate a protective role of Chk1 with respect to CK2b degradation via the proteosome pathway.…”

Site-Directed Mutagenesis in the Research of Protein Kinases - The Case of Protein Kinase CK2

“…Moreover, CK2 is physiologically expressed at a higher level than CK2 , and the excess of the regulatory subunit is rapidly ubiquitinated and degraded in a proteasomedependent manner (Luscher & Litchfield, 1994;Zhang et al, 2002). To protect CK from the degradation machinery and to stabilize it, six surface-exposed lysine residues were mutated to arginine (French et al, 2007).…”