CK2 (Casein Kinase 2), also known as Protein Kinase CK2, is a constitutively active serine/threonine protein kinase that represents one of the most versatile and ubiquitous protein kinases in eukaryotic cells. Unlike many protein kinases that require activation by second messengers or phosphorylation, CK2 is constitutively active and phosphorylates over 300 known substrates involved in diverse cellular processes including transcription, translation, cell cycle progression, cell survival, and signal transduction[1].
CK2 exists as a tetrameric holoenzyme composed of two catalytic subunits (α or α') and two regulatory β subunits. The regulatory β subunit enhances substrate specificity, modulates activity, and targets the enzyme to specific cellular compartments. CK2 is unique among protein kinases for its preference for clusters of acidic residues surrounding the phosphorylation site (S/T-X-X-E/D/pS/pT), and for its ability to utilize both ATP and GTP as phosphoryl donors[2].
The dysregulation of CK2 has been implicated in multiple diseases, including Alzheimer's disease (where it phosphorylates tau protein promoting aggregation), several cancers, and inflammatory conditions. Its central role in cell survival and proliferation makes CK2 an attractive therapeutic target, with clinical trials of CK2 inhibitors ongoing in oncology.
CK2 has a distinctive tetrameric structure:
Structural organization:
The CK2 catalytic subunit has a typical protein kinase fold with distinctive features[3]:
The β subunit serves multiple functions:
CK2 has unique substrate preferences[4]:
Consensus motif: S/T-X-X-D/E/pS/pT
Substrate diversity:
CK2 phosphorylates numerous transcription factors[5]:
Nuclear receptors:
Other TFs:
CK2 regulates translation machinery:
CK2 is essential for cell cycle progression[6]:
CK2 participates in multiple signaling pathways[7]:
CK2 promotes cell survival through multiple mechanisms[12]:
CK2 phosphorylatestau protein at multiple AD-relevant sites[14]:
Target sites:
Consequences:
CK2 affects APP processing[15]:
CK2 alterations in AD neurons:
CK2 as therapeutic target in AD[16]:
CK2 shows alterations in PD brains[17]:
CK2 may play roles in ALS[18]:
CK2 is frequently upregulated in cancer[19]:
Clinical inhibitors:
CK2 localizes to mitochondria[21]:
CK2 participates in autophagy regulation[22]:
Clinical development:
Selectivity issues:
Neuroprotective approaches:
CK2 (Casein Kinase 2) is a constitutively active serine/threonine protein kinase with diverse functions in transcription, translation, cell cycle, and cell survival. Its phosphorylation of tau protein at aggregation-promoting sites makes it relevant to Alzheimer's disease pathogenesis. CK2 also intersects with multiple signaling pathways (Wnt, PI3K/Akt, NF-κB, mTOR) and promotes cell survival. The enzyme is frequently upregulated in cancer, and CK2 inhibitors are in clinical development. In neurodegenerative diseases, CK2 dysregulation contributes to pathological protein phosphorylation and neuronal dysfunction. While direct CK2 inhibitors have been challenging to develop due to selectivity issues, they represent a potential therapeutic approach.
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Pinna LA. A history of protein kinase CK2. Cellular and Molecular Biology. 2002. ↩︎
Niefind K, et al. Active site conformation of CK2. EMBO Journal. 2000. ↩︎
Meggio F, Pinna LA. The CK2 substrate database. Cellular and Molecular Life Sciences. 2003. ↩︎
Janus P, et al. CK2 regulates transcription factors. Cellular Signalling. 2011. ↩︎
Sturgill TW, et al. Cell cycle regulation by CK2. Current Opinion in Cell Biology. 2008. ↩︎
Allende JE, Allende CC. CK2 in signal transduction. Trends in Biochemical Sciences. 1995. ↩︎
Tremblay F, et al. CK2 and Wnt signaling. Journal of Cell Science. 2012. ↩︎
Paronetto MK, et al. CK2 intersects with PI3K/Akt pathway. Oncogene. 2006. ↩︎
Wang D, et al. CK2 and NF-κB signaling. Journal of Molecular Medicine. 2012. ↩︎
Aceto L, et al. CK2 and mTOR signaling. Molecular Cell. 2012. ↩︎
Ahmed K, et al. CK2 in apoptosis and cell survival. Cell Death and Differentiation. 2008. ↩︎
Meek DW, Anderson CW. CK2 phosphorylates p53. Cell Cycle. 2009. ↩︎
Brotwer J, et al. CK2 phosphorylates tau and promotes aggregation. Journal of Biological Chemistry. 2000. ↩︎
Akiyama H, et al. CK2 phosphorylates APP and affects amyloidogenesis. Journal of Neuroscience. 2003. ↩︎
Liu Y, et al. CK2 in Alzheimer's disease. Journal of Alzheimer's Disease. 2015. ↩︎
J酵母 M, et al. CK2 alterations in Parkinson's disease. Brain Research. 2004. ↩︎
Browne RM, et al. CK2 in motor neuron disease. Experimental Neurology. 2004. ↩︎
Ruzzene M, et al. CK2 in cancer progression. Molecular Cancer Research. 2012. ↩︎
Chua MM, et al. CK2 inhibitors in clinical development. Oncotarget. 2017. ↩︎
Tavid MM, et al. CK2 at mitochondria. Biochimica et Biophysica Acta. 2013. ↩︎
Liu J, et al. CK2 in autophagy. Autophagy. 2011. ↩︎