title: Sensitization of tumor cells to Apo2 ligand/TRAIL-induced apoptosis by inhibition of casein kinase II.
abstract: Tumor-cell death can be triggered by engagement of specific death receptors with Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL). Apo2L/TRAIL-induced apoptosis involves caspase-8-mediated cleavage of BID. The active truncated form of BID (tBID) triggers the mitochondrial activation of caspase-9 by inducing the activation of BAK or BAX. Although a broad spectrum of human cancer cell lines express death receptors for Apo2L/TRAIL, many remain resistant to TRAIL/Apo2L-induced death. A variety of human cancers exhibit increased activity of casein kinase II (CK2). Here we demonstrate that CK2 is at the nexus of two signaling pathways that protect tumor cells from Apo2L/TRAIL-induced apoptosis. We find that CK2 inhibits Apo2L/TRAIL-induced caspase-8-mediated cleavage of BID, thereby reducing the formation of tBID. In addition, CK2 promotes nuclear factor kappa B (NF-kappa B)-mediated expression of Bcl-x(L), which sequesters tBID and curtails its ability to activate BAX. Tumor cells with constitutive activation of CK2 exhibit a high Bcl-x(L)/tBID ratio and fail to activate caspase-9 or undergo apoptosis in response to Apo2L/TRAIL. Conversely, reduction of the Bcl-x(L)/tBID ratio by inhibition of CK2 renders such cancer cells sensitive to Apo2L/TRAIL-induced activation of caspase-9 and apoptosis. Using isogenic cancer cell lines that differ only in the presence or absence of either the p53 tumor suppressor or the BAX gene, we show that the enhancement of Apo2L/TRAIL-induced tumor-cell death by CK2 inhibitors requires BAX, but not p53. The identification of CK2 as a key survival signal that protects tumor cells from death-receptor-induced apoptosis could aid the design of Apo2L/TRAIL-based combination regimens for treatment of diverse cancers.
authors.affiliation: The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, The Johns Hopkins University School of Medicine, The Bunting Family-The Family of Jacob and Hilda Blaustein Building For Cancer Research, Baltimore, Maryland 21231-1000, USA.
authors.forename: Rajani
authors.initials: R
authors.lastname: Ravi
authors.forename: Atul
authors.initials: A
authors.lastname: Bedi
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000096:biosynthesis; D047390:Casein Kinase II; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D004357:Drug Synergism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D016328:NF-kappa B / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases