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.
Achanzar
William E
WE
Inorganic Carcinogenesis Section, National Cancer Institute at National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Webber
Mukta M
MM
Waalkes
Michael P
MP
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