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. MATERIALS AND 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. CONCLUSION: 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.
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. MATERIALS AND 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. CONCLUSION: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.