Casein kinase 2 regulates both apoptosis and the cell cycle following DNA damage induced by 6-thioguanine.
OBJECTIVE
The purine antimetabolite, 6-thioguanine (6-TG), is an effective drug in the management of acute leukemias. In this study, we analyze the mechanisms of apoptosis associated with 6-TG treatment and casein kinase 2 (CK2 or CKII) in human tumor cells.


METHODS
Small interfering RNA and chemical CK2 inhibitors were used to reduce CK2 activity. Control and CK2 activity-reduced cells were cultured with 6-TG and assessed by flow cytometry to measure apoptosis and cell cycle profiles. Additionally, confocal microscopy was used to assess localization of CK2 catalytic units following 6-TG treatment.


RESULTS
Transfection of small interfering RNA against the CK2 alpha and/or alpha' catalytic subunits results in marked apoptosis of HeLa cells following treatment with 6-TG. Chemical inhibitors of CK2 also induce apoptosis following 6-TG treatment. Apoptosis induced by 6-TG is similarly observed in both mismatch repair-proficient and -deficient HCT116 and HeLa cells. Concomitant treatment with a pan-caspase inhibitor or transfection of apoptosis repressor with caspase recruitment domain markedly suppresses the apoptotic response to DNA damage by 6-TG in the CK2-reduced cells, indicating caspase regulation by CK2. CK2 alpha relocalizes to the endoplasmic reticulum after 6-TG treatment. Additionally, transfection of Cdc2 with a mutation at Ser(39) to Ala, which is the CK2 phosphorylation site, partially inhibits cell cycle progression in G(1) to G(2) phase following 6-TG treatment.


CONCLUSIONS
CK2 is essential for apoptosis inhibition following DNA damage induced by 6-TG, controlling caspase activity.
Yamane
Kazuhiko
K
Department of Radiation Oncology, Case Western Reserve University and University Hospitals of Cleveland, Case Comprehensive Cancer Center, 11100 Euclid Avenue, Cleveland, OH 44106-6068, USA.
Kinsella
Timothy J
TJ
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D047390:Casein Kinase II / Q000235:genetics / Q000494:pharmacology*; D020169:Caspases / Q000187:drug effects / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects* / Q000502:physiology; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006367:HeLa Cells / Q000201:enzymology; D006801:Humans; D034741:RNA, Small Interfering / Q000494:pharmacology; D013866:Thioguanine / Q000494:pharmacology*; D014162:Transfection
D004791:Enzyme Inhibitors; D034741:RNA, Small Interfering; D047390:Casein Kinase II; D020169:Caspases; D013866:Thioguanine