Significance of Divergent Expression of Prostaglandin EP4 and EP3 Receptors in Human Prostate Cancer

Abstract

PGE2 has been implicated in prostate cancer tumorigenesis. We hypothesized that abnormal prostaglandin receptor (EPR) expression may contribute to prostate cancer growth. Twenty-six archived radical prostatectomy specimens were evaluated by immunohistochemistry (IHC) and Western blotting for the expression of EP1, EP2, EP3, and EP4. As a corollary, EPR expression in one normal (PZ-HPV7) and four prostate cancer cell lines (CA-HPV10, LNCaP, PC3, and Du145) were assessed by Western blotting. Prostate cancer and normal cell growth were compared in vitro after EPR blockade, siRNA EPR knockdown, or overexpression. EP1, EP2, EP3, and EP4 receptors were detected by IHC in all areas of benign tissue within the clinical prostate cancer specimens. In areas of prostate cancer, EP4 and EP2 were overexpressed in 85% (22 of 26) and 75% (18 of 24) and EP3 expression was reduced in all (26 of 26, 100%) specimens (P < 0.05 vs. benign tissue). EP1 showed no specific differential expression pattern. Increased EP4 and reduced EP3 was confirmed by Western blotting in fresh clinical specimens and in prostate cancer cell lines (CA-HPV10, LNCaP, PC3, and Du145) compared with the normal prostate cell line (PZ-HPV7). EP2 and EP4 siRNA knockdown resulted in reduced in vitro growth and metastasis-related gene expression (MMP9 and Runx2) of prostate cancer lines, and in vitro migration was inhibited by EP4 antagonists. As a corollary, EP3-overexpressing PC3 cells displayed impaired growth in vitro. Human prostate cancer is associated with EP4 and EP2 overexpression and reduced EP3 expression. These data suggest that targeting specific EPR may represent a novel therapeutic approach for prostate cancer.