Abstract
Progression to hormone-refractory disease is a common outcome of human prostate cancer. In this study, we have investigated the basis of androgen insensitivity in the human prostate cancer cell line, PC-3, which was derived from a bone metastasis of a hormone-refractory prostate cancer. PC-3 cells with virtually undetectable (PC-3 AR −) or low (PC-3 AR +) levels of androgen receptor (AR) RNA expression were examined. RNase protection assays demonstrated that the level of AR RNA in PC-3 AR + cells was similar to that in a normal androgen-responsive genital skin fibroblast cell strain. Quantitative immunocytochemical staining of AR in PC-3 AR + cells using antibodies directed against the amino and carboxyl termini of the receptor revealed staining in 30% of cells with either antibody. Furthermore, the level of AR staining in PC-3 AR + cells was higher than in the androgen-responsive breast cancer cell lines ZR-75-1, T47-D, and MCF-7. Despite the expression of AR RNA and protein, PC-3 AR + cell proliferation was unaffected by the presence of 0.1–10 nM mibolerone. Scatchard analysis demonstrated a complete absence of specific [ 3H]dihydrotestosterone ([ 3H]DHT) binding to PC-3 AR + cytosolic extracts, which could not be explained by structural alterations in the AR gene. The sizes of individual AR exons amplified from genomic DNA derived from PC-3 AR + cells were identical to those amplified from normal human cells. Furthermore, sequence analysis did not reveal a mutation in the DNA- or hormone-binding domains of the AR gene in PC-3 AR + cells. These data demonstrate that PC-3 AR + cells express AR RNA and protein of apparently normal structure and, in view of the inability to detect specific ligand binding to the AR, imply the existence of a novel mechanism for the androgen insensitivity of this prostate cancer cell line.
Published Version
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