Altered apoptotic gene expression and acquired apoptotic resistance in cadmium-transformed human prostate epithelial cells.
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.
Inorganic Carcinogenesis Section, National Cancer Institute at National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
William E
WE
Achanzar
Mukta M
MM
Webber
Michael P
MP
Waalkes
D017209:Apoptosis / Q000235:genetics*; D002104:Cadmium / Q000494:pharmacology*; D002460:Cell Line; D002461:Cell Line, Transformed; D002945:Cisplatin / Q000506:poisoning; D004351:Drug Resistance; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology; D005047:Etoposide / Q000506:poisoning; D015870:Gene Expression; D006801:Humans; D008297:Male; D011467:Prostate / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*
D002104:Cadmium; D005047:Etoposide; D002945:Cisplatin