Oxygen consumption is particularly elevated in cardiac cells as they are equipped with a large number of mitochondria and high levels of respiratory chain components. Consequently, production of reactive oxygen species (ROS) is tightly controlled as an imbalance in redox reactions can lead to irreversible cellular damage. siRNA-mediated down-regulation of protein kinase CK2 has been implicated in the accumulation of ROS in cells. The present study was undertaken in order to investigate the role of CK2 in redox homeostasis in cardiomyoblasts. We found that inhibition or silencing of CK2 causes elevated levels of ROS, notably superoxide radical, and this is accompanied by suppression of NF-κB transcriptional activity and mitochondrial dysfunction. We show that CK2 regulates the expression of manganese superoxide dismutase, the enzyme catalyzing the dismutation of superoxide, in cancer cells but not in cardiomyoblasts. Furthermore, we report evidence that impaired expression of CK2 results in destabilization of the Bcl-2 mammalian homolog Bcl-xL, which is known to stabilize the mitochondrial membrane potential, through a mechanism involving disruption of the chaperone function of heat shock protein 90. Analysis of differential mRNA expression related to oxidative stress revealed that CK2 silencing caused a statistically significant deregulation of four genes associated with the oxidative damage, i.e., Fmo2, Ptgs1, Dhcr24, and Ptgs2. Overall, the results reported here are consistent with the notion that CK2 plays a role in conferring protection against oxidative stress by positively regulating pro-survival signaling molecules and the protein folding machinery in cardiomyoblasts.
CK2 ROS NF-κB/RelA Bcl-xL HSP-90 Cardiomyoblasts
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The authors would like to thank Dr. Olaf-Georg Issinger (University of Southern Denmark) for critically reading the manuscript; Dr. David W. Litchfield (University of Western Ontario) for the generous gift of the RS3.22 cell line; Dr. Tuula Kallunki (Danish Cancer Society) for providing the Bcl-xL viral vector; Dr. Phillip Hallenborg (University of Southern Denmark) for expertise in establishing Bcl-xL-overexpressing cardiomyoblasts; and Tina H. Svenstrup for technical assistance. We thank the Drug Synthesis and Chemistry Branch, Developmental Therapeutics Program, NCI, USA, for providing us with viable samples. This work was supported by the Danish Council for Independent Research-Natural Sciences (Grant 1323-00212A to B. Guerra).
Supplementary material Fig. S1 Analysis of Bcl-xL overexpression in cardiomyoblasts. H9c-2 cells transduced with Bcl-xL-encoding viral particles were transfected with scramble siRNA or siRNA against the individual catalytic subunits of CK2 as indicated in the figure. Whole cell lysates were analyzed employing antibodies against the indicated proteins. (TIFF 484 kb)
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