Treatment of U937 cells with bufalin induces the translocation of casein kinase 2 and modulates the activity of topoisomerase II prior to the induction of apoptosis.
The treatment of human leukemia U937 cells with 10(-8) M bufalin in the absence of serum resulted in the immediate translocation of casein kinase 2 (CK 2) from the cytoplasm to the nucleus, as determined by confocal laser-scanning microscopy. Concomitantly, the activity of topoisomerase (topo) II, as determined by monitoring activities specific to this enzyme such as DNA relaxation, DNA decatenation, and topo II-mediated DNA cleavage, was enhanced. The activity reached a maximum after 3 h and then decreased markedly after treatment with bufalin for 9 h. The amount of a complex of CK 2 and topo IIalpha in U937 cells was estimated by immunoprecipitation with antibodies raised against subunits of CK 2 and against topo IIalpha. The amount increased just after the start of treatment with bufalin and reached a maximum at 6 h. The results suggest that the topo IIalpha in the complex might have been phosphorylated by the translocated CK 2 and that the topo activity was stimulated by such phosphorylation. Apoptotic U937 cells with fragmented nuclei were observed between 9 and 12 h after the start of treatment using 10(-8) M bufalin. Therefore, it appears that the bufalin signal was transmitted to the nucleus by the translocation of CK 2, which formed a complex with topo IIalpha and modulated the activity of this enzyme, leading to the induction of apoptosis.
Watabe
M
M
Laboratory of Biological Chemistry, School of Pharmaceutical Sciences, Showa University, Tokyo, Japan.
Nakajo
S
S
Yoshida
T
T
Kuroiwa
Y
Y
Nakaya
K
K
D017209:Apoptosis / Q000187:drug effects*; D001692:Biological Transport; D002018:Bufanolides / Q000494:pharmacology*; D047390:Casein Kinase II; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004278:DNA, Superhelical / Q000032:analysis; D006801:Humans; D007938:Leukemia / Q000201:enzymology* / Q000473:pathology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D014407:Tumor Cells, Cultured
D002018:Bufanolides; D004278:DNA, Superhelical; D012333:RNA, Messenger; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D004250:DNA Topoisomerases, Type II; C022777:bufalin