Protein kinase CK2 impact on intracellular calcium homeostasis in prostate cancer.

Protein kinase CK2 plays multiple roles in cell function in normal and disease states. CK2 is elevated in numerous types of cancer cells, and CK2 suppression of apoptosis represents a key link to the cancer cell phenotype. CK2 regulation of cell survival and death involves diverse processes, and our previous work suggested that mitochondrial machinery is a key locus of this function. One of the earliest responses of prostate cells to inhibition of CK2 is a change in mitochondrial membrane potential, possibly associated with Ca2+ signaling. Thus, in the present work, we investigated early impact of CK2 on intracellular Ca2+ dynamics. Three prostate cancer (PCa) cell lines, PC3-LN4, C4-2B, and 22Rv1, were studied. PCa cells were treated with the CK2 small molecule inhibitors 4,5,6,7-tetrabrombenzotriazole and CX-4945 followed by analysis of Ca2+ levels in various cellular compartments over time. The results showed dose-dependent loss in cytosolic Ca2+ levels starting within 2 min and reaching maximal loss within 5-10 min. There was a concomitant increase in Ca2+ in the endoplasmic reticulum (ER) and mitochondrial compartments. The results suggest that inhibition of CK2 activity results in a rapid movement of Ca2+ out of the cytosol and into the ER and mitochondria, which may be among the earliest contributory factors for induction of apoptosis in cells subjected to inhibition of CK2. In cells with death-inducing levels of CK2 inhibition, total cellular Ca2+ levels dropped at 2 h post-treatment. These novel observations represent a potential mechanism underlying regulation of cell survival and death by CK2 activity.