Copper Modulates the Catalytic Activity of Protein Kinase CK2

Abstract

Casein kinase 2 (CK2) is an evolutionarily conserved serine/threonine kinase implicated in a wide range of cellular functions and known to be dysregulated in various diseases such as cancer. Compared to most other kinases, CK2 exhibits several unusual properties, including dual co-substrate specificity and a high degree of promiscuity with hundreds of substrates described to date. Most paradoxical, however, is its apparent constitutive activity: no definitive mode of catalytic regulation has thus far been identified. Here we demonstrate that copper enhances the enzymatic activity of CK2 both in vitro and in vivo. We show that copper binds directly to CK2, and we identify specific residues in the catalytic subunit of the enzyme that are critical for copper-binding. We further demonstrate that increased levels of intracellular copper result in enhanced CK2 kinase activity, while decreased copper import results in reduced CK2 activity. Taken together, these findings establish CK2 as a copper-regulated kinase and indicate that copper is a key modulator of CK2-dependent signaling pathways.

Metalloallostery and Transition Metal Signaling: Bioinorganic Copper Chemistry Beyond Active Sites

“…[67] Casein kinase 2 (CK2), a kinase responsible for generating 21 % of the phosphoproteome, is similarly modulated by copper (Figure 4a). [68,69] As a final example of cancerrelevant copper metalloallostery beyond kinases, Opazo and Bush showed that copper binds to the E2 ubiquitin-conjugating enzyme D (UBE2D) at a conserved CXXXC motif to promote ubiquitination (Figure 4a). As such, copper plays an important role in protein quality control, which also has implications for neurodegenerative diseases.…”

Copper-Dependent Kinases and Their Role in Cancer Inception, Progression and Metastasis

“…At the same time, Chojnowski and colleagues [ 84 ] investigated if CK2 (also called casein kinase 2 or CKII) could be a putative copper-dependent kinase, using the same strategy of the research groups that demonstrate the presence of copper-binding motifs in ULK1/2 and in PDK1 [ 84 ]. Among other functions, CK2 potentiates oncogenic signaling such as the PI3K/AKT pathway, by phosphorylating AKT at Ser129, thus finalizing its activation through the stabilization of the PDK1-depentent phosphorylation at Thr308 [ 84 ] ( Figure 3 ). By analyzing the homology sequence between CK2α and MEK1, two residues (Met153 and His154) were pinpointed as copper-binding sites.…”

“…By analyzing the homology sequence between CK2α and MEK1, two residues (Met153 and His154) were pinpointed as copper-binding sites. CK2 is a Ser/Thr kinase that has hundreds of physiological substrates, and for this reason, it is responsible for the generation of over the 20% of the human phosphoproteome [ 84 ]. Mammalian CK2 is a tetrameric enzyme composed of two catalytic α subunits and two regulatory β subunits.…”

“…To further investigate the putative interaction between copper and CK2, Chojnowski et al performed an in silico analysis that revealed the presence of two copper-binding sites: one at protein surface and the other in the catalytic pocket [ 84 ]. The authors demonstrated that copper increased CK2 kinase activity as revealed by increased phosphorylation of Jabba, a CK2 substrate.…”

“…Furthermore, in CTR1 -/- MEFs, there was observed a reduction in the phosphorylation of two CK2 substrates, AKT at Ser129 and CDC37 at Ser13. Finally, to demonstrate that CK2 activity depends on copper availability, the authors used a copper ionophore, namely Cu-ATSM (diacetylbis(4-methyl-3-thiosemicarbazonato)copper(II), known to facilitate copper delivery inside cells [ 84 ], and they observed that copper–ATSM was able to enhance CK2 activity, increasing the phosphorylation of its targets.…”