Repressing the Activity of Protein Kinase CK2 Releases the Brakes on Mitochondria-Mediated Apoptosis in Cancer Cells

Execution of the mitochondrial death signaling is paramount to an effective response of cancer cells to chemotherapeutic intervention. Therefore, factors that inhibit the engagement of the mitochondrial amplification pathway, such as the expression of the anti-apoptotic proteins of the Bcl2 family or inactivation of inducers of mitochondrial permeability, play a critical role in the acquisition of the resistant phenotype. Protein kinase CK2 (CK2) is a ubiquitous serine/threonine kinase that is highly conserved in eukaryotic cells. This multifunctional protein kinase has been shown to impact cell growth and proliferation, as numerous growth-related proteins are substrates of CK2. More importantly, experimental evidence linking increased expression and activity of the kinase to human cancers, underscores the relevance of CK2 biology to cellular transformation and carcinogenesis. Of note, among the many cellular substrates of CK2 are proteins involved in the efficient execution of the mitochondria-dependent cell death signaling, such as Bid, caspase-2, ARC and others. Supporting this, recent reports have demonstrated that genetic manipulation of CK2 expression as well as pharmacological inhibition of its enzymatic activity sensitizes cancer cells to apoptotic stimuli. Due to the critical regulatory role that this kinase plays in cell fate determination in cancer cells, there is a tremendous increase in activity geared at the development of CK2-specific therapies. Here we provide a brief review of CK2-mediated inhibition of mitochondrial death signaling in cancer cells and its implications for the design of novel target specific therapeutic strategies.