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Relationships between proto-oncogene expression and apoptosis induced by anticancer drugs in human prostate tumor
B K Sinha1, H Yamazaki, H M Eliot
1Biochemical and Molecular Pharmacology Section, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Abstract:
A variant of human prostate PC3 cells, isolated from PC3 cells, was shown to be significantly resistant (> 10-fold) to several clinically active anticancer drugs, including VP-16 and cisplatin. Previous studies showed that resistance to these drugs was not due to expression of the mdr1 gene, or modifications in topoisomerases but may have resulted from high expressions of certain proto-oncogenes (Yamazaki et al. (1994) Biochim. Biophys. Acta 1226, 89-96). Flow cytometry, DNA gel electrophoresis and northern blot analysis were used to further characterize drug responses in sensitive and resistant cells. Treatment of the sensitive PC3 cells with VP-16 and CDDP resulted in accumulation of cells in S and G2, and G1 and S phases, respectively, and caused significant degradation of the genomic DNA into internucleosomal sized DNA fragments, indicating apoptosis. In contrast, resistant PC3 cells showed little or no DNA fragmentation. Resistant PC3(R) cells expressed 2-3-fold more bcl2 protein than the parental PC3 cells, and overexpressed c-myc, c-jun and H-ras mRNA compared to sensitive cells. Treatment with VP-16 or CDDP significantly induced c-myc mRNA levels in sensitive PC3 cells. H-ras message was not affected by either VP-16 or CDDP treatment in PC3 cells. These studies, taken together, suggest that a differential susceptibility to apoptosis and chemosensitivity may be related to altered levels of bcl2 and/or oncogene overexpression in PC3(R) cells.
Insights
Prostate cancer cells resistant to chemotherapy show altered apoptosis due to increased bcl2 and oncogene expression. This suggests new therapeutic targets for overcoming drug resistance in prostate cancer.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Biology
Background:
- Prostate cancer PC3 cells exhibit significant resistance (>10-fold) to anticancer drugs like VP-16 and cisplatin.
- Previous research indicated that drug resistance was not linked to mdr1 gene expression or topoisomerase modifications.
- High expression of certain proto-oncogenes was suggested as a potential cause for drug resistance in these cells.
Purpose of the Study:
- To characterize drug responses in sensitive versus resistant prostate cancer PC3 cells.
- To investigate the role of apoptosis and oncogene expression in chemoresistance.
- To explore potential mechanisms underlying drug resistance in PC3 cells.
Main Methods:
- Flow cytometry was employed to analyze cell cycle progression.
- DNA gel electrophoresis was used to detect DNA fragmentation indicative of apoptosis.
- Northern blot analysis quantified gene expression levels of bcl2, c-myc, c-jun, and H-ras.
Main Results:
- Sensitive PC3 cells underwent apoptosis (DNA fragmentation) upon treatment with VP-16 and CDDP, accumulating in specific cell cycle phases.
- Resistant PC3(R) cells showed minimal DNA fragmentation, indicating resistance to apoptosis.
- PC3(R) cells overexpressed bcl2 protein and c-myc, c-jun, and H-ras mRNA compared to sensitive cells; VP-16/CDDP induced c-myc in sensitive cells.
Conclusions:
- Differential susceptibility to apoptosis and chemosensitivity in PC3(R) cells correlates with altered bcl2 protein levels.
- Overexpression of oncogenes like c-myc and c-jun may contribute to the chemoresistant phenotype.
- These findings suggest that bcl2 and oncogene expression are key factors in prostate cancer drug resistance.