Differential induction of etoposide-mediated apoptosis in human leukemia HL-60 and K562 cells.
Etoposide (VP-16) is one of several DNA-damaging agents that induce subcellular structural changes associated with apoptosis. VP-16 exerts its DNA-damaging and cytotoxic effects subsequent to interference with DNA topoisomerase II activity. VP-16 also stimulates c-jun and c-fos mRNA expression in some cell lines, including human leukemia K562 and HL-60 cells. To compare the temporal relationship between drug-induced c-jun expression and apoptosis, we examined cell morphology, cell viability, DNA integrity, and c-jun induction during VP-16 treatment of K562 and HL-60 cells. VP-16 (10 microM)-induced internucleosomal DNA damage and nuclear fragmentation were readily apparent within 6 hr in HL-60 cells but were absent in K562 cells treated for up to 24 hr. Some internucleosomal DNA damage was observed in K562 cells but only after treatment with 100 microM VP-16 for 24 hr. In contrast, VP-16-induced DNA single-strand breaks, VP-16-induced topoisomerase II/DNA covalent complex formation, and VP-16-mediated growth inhibition were similar in K562 and HL-60 cells. Also, the time course of VP-16-induced c-jun mRNA expression was comparable for both K562 and HL-60 cell lines. Western blot analysis of whole-cell lysates showed that Bcl-2 protein levels were 13-fold greater in HL-60 cells than in K562 cells. Thus, the resistance of VP-16-treated K562 cells to apoptosis was not attributable to protection by Bcl-2. Furthermore, the relatively high levels of Bcl-2 in HL-60 cells were not sufficient to protect these cells against apoptosis. Together, our results indicate that the temporal coupling of VP-16-induced DNA damage, c-jun expression, and apoptosis is cell type specific and suggest that different signaling pathways for apoptosis are operating in these two human leukemia cell lines.
Ritke
M K
MK
Department of Pharmacology, University of Pittsburgh School of Medicine, Pennsylvania 15261.
Rusnak
J M
JM
Lazo
J S
JS
Allan
W P
WP
Dive
C
C
Heer
S
S
Yalowich
J C
JC
D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000187:drug effects; D004249:DNA Damage; D005047:Etoposide / Q000494:pharmacology*; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000187:drug effects; D016762:Genes, fos; D016758:Genes, jun; D006801:Humans; D007938:Leukemia; D011518:Proto-Oncogene Proteins / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D014407:Tumor Cells, Cultured
D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D005047:Etoposide; D004247:DNA