Prostate cancer is currently the most common type of
neoplasm found in American men, other than
skin cancer, and is the second leading cause of
cancer death in males. Because cell cycle checkpoint
proteins stabilize the genome, the relationship of one such
protein, Rad9, to
prostate cancer was investigated. We found that four
prostate cancer cell lines (CWR22, DU145, LNCaP, and PC-3), relative to PrEC normal prostate cells, have aberrantly high levels of
Rad9 protein. The 3'-end region of intron 2 of Rad9 in DU145 cells is hypermethylated at CpG islands, and treatment with 5'-aza-2'-deoxycytidine restores near-normal levels of methylation and reduces
Rad9 protein abundance. Southern blot analyses indicate that PC-3 cells contain an amplified Rad9 copy number. Therefore, we provide evidence that Rad9 levels are high in
prostate cancer cells due at least in part to aberrant methylation or gene amplification. The effectiveness of
small interfering RNA to lower
Rad9 protein levels in CWR22, DU145, and PC-3 cells correlated with reduction of tumorigenicity in nude mice, indicating that Rad9 actively contributes to the disease.
Rad9 protein levels were high in 153 of 339 human prostate
tumor biopsy samples examined and detectable in only 2 of 52 noncancerous prostate tissues. There was a strong correlation between
Rad9 protein abundance and
cancer stage.
Rad9 protein level can thus provide a
biomarker for advanced
prostate cancer and is causally related to the disease, suggesting the potential for developing novel diagnostic, prognostic, and therapeutic tools based on detection or manipulation of
Rad9 protein abundance.