Ecto‑protein kinase CK2, the neglected form of CK2 (Review)

Abstract

Ecto-protein kinases, including protein kinase CK2 (former name, casein kinase 2), have been the focus of research for more than 30 years. At the beginning of the ecto-kinase research their identification was performed with substrates and inhibitors whose specificity under the current knowledge was rather limited. Since all currently known ecto-kinases, including ecto-CK2, have intracellular counterparts, one has to exclude that an ecto-localization originates from intracellular counterparts after cell damage. Protein kinase CK2 is involved in cellular key processes such as cell cycle progression, inhibition of apoptosis, DNA damage repair, differentiation and many other processes. CK2 is composed of two catalytic CK2α or CK2α' subunits and two non-catalytic CK2β subunits. Progress in the ecto-kinase and in particular ecto-CK2 studies was made with the use of transfected tagged CK2 subunits, which allowed to follow their individual transport and localization on the cell surface after transfection. Furthermore, immunofluorescence studies with antibodies against CK2 subunits as well as affinity chromatography with a binding partner of CK2 subunits have improved ecto-kinase research. The use of new and more specific inhibitors as well as of substrates, which do not cross the plasma membrane, have further improved the specificity for ecto-CK2. From the various substrates of ecto-CK2, it can be concluded that ecto-CK2 plays a role in Alzheimer disease, cell adhesion, platelet aggregation, immune response and cellular signalling. New tools and techniques, to study ecto-CK2 activity, are required to identify new substrates and thereby new functional implications for ecto-CK2.

A proteomics analysis of CK2β(−/−) C2C12 cells provides novel insights into the biological functions of the non‐catalytic β subunit

“…The CK2β (−/−) cells also provide a suitable model to check if the β subunit is required for the export of CK2 to give rise to a pool of ecto‐CK2 whose existence has been known for a long time, but whose role is still obscure . The presence of CK2 catalytic subunits has been monitored in the conditioned medium of C2C12 cells either wild‐type or CK2β (−/−) and CK2α/α′ (−/−) .…”

Advances in the Biology of Seed and Vegetative Storage Proteins Based on Two-Dimensional Electrophoresis Coupled to Mass Spectrometry

“…However, it is assumed that the interplay of protein kinases, protein phosphatases and phytohormones participates in the signaling and metabolic networks that control the phosphorylation/dephosphorylation levels of storage proteins. The CK2 protein is a Ser/Thr kinase presents in all eukaryotes and has pleiotropic effects; it is also involved in the regulation of multiple plant growth and development processes and ABA signalling [ 136 , 137 , 138 ]. Irar et al [ 126 ] used 2-DE-based maps for the phosphoproteome profiling of heat-stable proteins from Arabidopsis dry seeds and phosphoaffinity chromatography for phosphoprotein enrichment.…”

Biochemical and cellular mechanism of protein kinase CK2 inhibition by deceptive curcumin

“…This fraction of CK2, localized at the external side of plasma membrane, has been shown not to affect cellular proliferation, but to promote migration of cancerous cells then enhancing their invasive and metastatic potential . In this context, additional interest is provided by disease‐sustaining roles recently proposed for ecto‐CK2 also in Alzheimer and parasitic diseases .…”