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Altered apoptotic gene expression and acquired apoptotic resistance in cadmium-transformed human prostate epithelial
William E Achanzar1, Mukta M Webber, Michael P Waalkes
1Inorganic Carcinogenesis Section, National Cancer Institute at National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Background:
Cadmium is a suspected prostatic carcinogen, although the underlying mechanisms are unclear. To investigate these mechanisms, we performed molecular comparisons between the cadmium-transformed prostate epithelial cell line CTPE and the nontumorigenic parental line RWPE-1.
Methods:
Gene expression patterns were compared by using cDNA arrays, RNase protection assays, and Western blots. Apoptosis was analyzed by using flow cytometry to quantify apoptotic nuclei and an enzyme-linked immunosorbent assay method to measure DNA fragmentation. Caspase-3 activity was measured colorimetrically.
Results:
Among the genes down-regulated in CTPE cells were those encoding several members of the caspase family of apoptotic proteases as well as the apoptotic regulator Bax. Ribonuclease protection assays confirmed global down-regulation of caspase gene expression in CTPE. Decreased Bax expression in CTPE was confirmed by Western blots, which also revealed increased expression of anti-apoptotic Bcl-2. Consistent with these changes, CTPE cells exhibited increased resistance to apoptosis induced by cadmium, cisplatin, and etoposide. CTPE cells also exhibited lower caspase-3 activity vs. RWPE-1 after etoposide treatment.
Conclusions:
CTPE cells exhibited altered expression of important apoptotic regulators as well as resistance to several apoptotic stimuli. We hypothesize that acquired apoptotic resistance may be a key aspect of cadmium-induced malignant transformation of prostate epithelial cells and that this may contribute to both tumor initiation and the acquisition of aggressive characteristics subsequent to tumor formation.
Insights
Cadmium exposure may lead to prostate cancer by altering apoptotic regulators, causing resistance to cell death. This resistance is a key factor in malignant transformation and tumor progression.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Cadmium is a suspected carcinogen for the prostate, but its mechanisms are not fully understood.
- Molecular differences between cadmium-transformed (CTPE) and normal (RWPE-1) prostate cells were investigated.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying cadmium-induced prostate carcinogenesis.
- To compare gene expression and apoptotic responses in cadmium-transformed prostate cells.
Main Methods:
- Gene expression profiling using cDNA arrays, RNase protection assays, and Western blots.
- Apoptosis analysis via flow cytometry and ELISA for DNA fragmentation.
- Measurement of caspase-3 activity.
Main Results:
- Down-regulation of pro-apoptotic genes (caspases, Bax) and up-regulation of anti-apoptotic gene (Bcl-2) in CTPE cells.
- CTPE cells showed increased resistance to apoptosis induced by cadmium, cisplatin, and etoposide.
- Reduced caspase-3 activity was observed in CTPE cells post-etoposide treatment.
Conclusions:
- Altered expression of apoptotic regulators and resistance to apoptosis are characteristic of cadmium-transformed prostate cells.
- Acquired apoptotic resistance is hypothesized to be crucial for cadmium-induced prostate cancer initiation and progression.
- This resistance may contribute to tumor aggressiveness.