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Camptothecin and its derivatives induce expression of the c-jun protooncogene in human myeloid leukemia cells
S Kharbanda1, E Rubin, H Gunji
1Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
Abstract:
We have recently demonstrated that certain camptothecin derivatives are effective agents in the treatment of human tumor xenografts in nude mice. While camptothecin and its derivatives are recognized as inhibitors of topoisomerase I, little is known about the effects of these agents on specific gene expression, particularly genes involved in growth control. The c-jun early response gene codes for a leucine zipper transcription factor. The present studies demonstrate that 20(S)-camptothecin, 9-amino-20(S)-camptothecin, and 9-nitro-20(S)-camptothecin inhibit the growth of human U-937 myeloid leukemia cells and induce expression of the c-jun gene. c-jun transcripts were increased at 3 h and reached a maximum at 6 h of drug exposure. We also demonstrate that the induction of c-jun gene expression by these agents occurs at the transcriptional level. H7, a nonselective inhibitor of protein kinase C, completely blocked c-jun expression in 20(S)-camptothecin-treated cells, while another protein kinase inhibitor, HA1004, had no detectable effect. Similar findings were obtained for other leucine zipper encoding genes, including jun-B. These results suggest that 20(S)-camptothecin, 9-amino-20(S)-camptothecin, and 9-nitro-20(S)-camptothecin activate a cellular response involving the induction of early response genes. Finally, we demonstrate that induction of c-jun expression occurs in association with internucleosomal DNA fragmentation, a characteristic of programmed cell death.
Insights
Certain camptothecin derivatives inhibit leukemia cell growth and induce c-jun gene expression. This cellular response, involving early response genes and protein kinase C, is linked to programmed cell death.
Area of Science:
- Molecular Biology
- Cancer Research
- Pharmacology
Background:
- Camptothecin derivatives are effective in treating human tumor xenografts.
- Camptothecins are known topoisomerase I inhibitors, but their effect on gene expression, especially growth control genes, is not well understood.
- The c-jun gene encodes a leucine zipper transcription factor involved in cellular regulation.
Purpose of the Study:
- To investigate the effects of specific camptothecin derivatives on gene expression in human myeloid leukemia cells.
- To determine if camptothecin derivatives induce the expression of early response genes, such as c-jun.
- To elucidate the mechanism of c-jun gene induction and its relation to programmed cell death.
Main Methods:
- Treatment of human U-937 myeloid leukemia cells with 20(S)-camptothecin, 9-amino-20(S)-camptothecin, and 9-nitro-20(S)-camptothecin.
- Analysis of c-jun gene expression levels over time using transcript analysis.
- Investigation of the role of protein kinase C (PKC) using inhibitors H7 and HA1004.
- Assessment of internucleosomal DNA fragmentation as an indicator of programmed cell death.
Main Results:
- Camptothecin derivatives inhibited U-937 cell growth and significantly increased c-jun gene expression.
- c-jun transcript levels rose by 3 hours and peaked at 6 hours post-treatment, indicating transcriptional regulation.
- Protein kinase C inhibition by H7 blocked c-jun induction, while HA1004 had no effect, suggesting a role for PKC.
- Induction of c-jun expression correlated with internucleosomal DNA fragmentation, a hallmark of apoptosis.
- Similar effects were observed for other leucine zipper genes, including jun-B.
Conclusions:
- 20(S)-camptothecin, 9-amino-20(S)-camptothecin, and 9-nitro-20(S)-camptothecin trigger a cellular response characterized by early response gene induction.
- The induction of c-jun and jun-B genes by these camptothecin derivatives is mediated transcriptionally and involves protein kinase C.
- Camptothecin-induced c-jun expression is associated with programmed cell death, suggesting a potential mechanism for their anti-cancer activity.