Mitotic arrest and enhanced nuclear protein phosphorylation in human leukemia K562 cells by okadaic acid, a potent protein phosphatase inhibitor and tumor promoter.
We investigated the effects of the non-phorbol tumor promoter okadaic acid on human leukemia K562 cells. It was found that okadaic acid potently and reversibly inhibited cell growth, with a nearly complete inhibition of thymidine uptake seen at about 10 nM. The cytotoxicity of okadaic acid was characterized by a marked mitotic arrest of the cells exhibiting scattered chromosomes and abnormal anaphase-like structures, a phenomenon distinct from the typical metaphase arrest caused by colchicine. Okadaic acid (10-1,000 nM) greatly stimulated phosphorylation of a number of nuclear proteins in K562 cells. Phosphorylation of many of the same proteins was also stimulated by 12-O-tetradecanoylphorbol-13-O-acetate, a protein kinase C activator. The present findings, consistent with recent reports that okadaic acid is a potent inhibitor of protein phosphatases 1 and 2A (PP1 and PP2A) shown to be essential for normal mitosis, provided evidence for the first time that okadaic acid inhibition of PP1/PP2A resulted in enhanced nuclear protein phosphorylation and subsequent mitotic arrest.
Zheng
B
B
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
Woo
C F
CF
Kuo
J F
JF
D001345:Autoradiography; D002273:Carcinogens; D003078:Colchicine / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004988:Ethers, Cyclic / Q000494:pharmacology*; D006801:Humans; D007938:Leukemia / Q000378:metabolism / Q000473:pathology*; D008938:Mitosis / Q000187:drug effects*; D009687:Nuclear Proteins / Q000378:metabolism*; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D002273:Carcinogens; D004988:Ethers, Cyclic; D009687:Nuclear Proteins; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate; D003078:Colchicine