Our previous work has highlighted the regulatory role of intracellular reactive oxygen species (ROS) in cellular response to apoptotic stimuli. Using a variety of models we showed that a slight increase in intracellular superoxide anion inhibited death signaling and/or promoted cell survival in tumor cells, whereas an increase in intracellular hydrogen peroxide facilitated death execution via acidification of the cytosolic milieu. It has been reported that inhibition of Casein Kinase II (CK2) with antisense siRNA is a potent inducer of apoptosis in cancer cells but not in normal cells. In this regard, the apoptotic inducing effect is attributed to the catalytic activity of the enzyme, which phosphorylates pro-apoptotic proteins to inhibit their function(s). We investigated the role of intracellular redox status in the death inhibitory effect of CK2 and in the pro-apoptotic activity of CK2 inhibition. We provide evidence that inhibition of CK2 activity via pharmacological or genetic approaches in a variety of cell lines (CEM, Jurkat, HCT116, and HeLa) induces caspase 2 and 3 activation, translocation of cytochrome c and subsequent DNA fragmentation. CK2 inhibition-induced apoptotic cell death is not blocked by the anti-apoptotic protein Bcl-2 or by the absence of the tumor suppressor p53. Interestingly, inhibition of CK2 activity induces an increase in intracellular hydrogen peroxide and blocking this by transfection with the hydrogen peroxide scavenger, catalase, neutralized death signaling. Data is also presented to illustrate that increasing the expression of the different subunits of CK2 resulted in an increase in intracellular superoxide anion in a subunit-dependent manner, which inhibits apoptotic cell death induced by common chemotherapeutic drugs, vincristine and daunorubicin. These data suggest that survival and death signaling induced by CK2 or its inhibition, respectively, in a variety of systems involve divergent signaling by intracellular ROS. In summary, decreasing CK2 activity increases intracellular hydrogen peroxide creating an intracellular environment conducive for death execution, whereas increasing CK2 activity increases intracellular superoxide creating an intracellular environment non-conducive for death execution. Taken together, these data provide novel pathways involved in CK2 biology with implications for effective drug design against drug resistance tumors.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA