DNA topoisomerase II inhibitor, etoposide, induces p21WAF1/CIP1 through down-regulation of c-Myc in K562 cells.
BACKGROUND
Anticancer agents modulate gene expression and these changes are essential for tumor cell killing. To investigate the mechanism by which etoposide acts as an anticancer agent, the relationship between p21WAF1/CIP1 (p21) and c-Myc was studied.


METHODS
K562 cells with and without ectopic c-Myc expression were studied. Apoptosis was detected using propidium iodide and Hoechst 33342 double staining. The c-Myc and p21 levels were studied by RT-PCR and immunoblot. The p21 promoter (from -205 to +67) was investigated by the luciferase reporter gene assay.


RESULTS
Ectopic c-Myc-expressing K562 (K562/c-Myc) cells showed more extensive apoptosis than K562 cells after continuous exposure to 200 microM etoposide for 24 hours. During this treatment, p21 expression was not observed in K562/c-Myc cells, and the expression of c-Myc and p21 was mutually exclusive. Etoposide activated the p21 promoter in a concentration-dependent manner, and etoposide-induced luciferase activity was suppressed by co-transfection of c-Myc.


CONCLUSIONS
p21 promoter activity was repressed by c-Myc in proliferating K562 cells, and detoposide-induced down-regulation of c-Myc released this suppression, resulting in the induction of p21.
Horiguchi-Yamada
Junko
J
Department of Oncology, Institute of DNA Medicine, Jikei University School of Medicine, 3-25-8 Nishi-Shinbashi, Minato-ku, Tokyo 105-8461, Japan. jhydoidm@jikei.ac.jp
Fukumi
Sachiko
S
Saito
Shinobu
S
Nakayama
Ritsuko
R
Iwase
Satsuki
S
Yamada
Hisashi
H
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001483:Base Sequence; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D016259:Genes, myc / Q000187:drug effects / Q000235:genetics; D006801:Humans; D020014:K562 Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis* / Q000235:genetics; D059005:Topoisomerase II Inhibitors; D014158:Transcription, Genetic / Q000187:drug effects
D000972:Antineoplastic Agents, Phytogenic; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D016271:Proto-Oncogene Proteins c-myc; D059005:Topoisomerase II Inhibitors; D005047:Etoposide