Bone morphogenetic protein-6 expression in normal and malignant prostate.

Bone morphogenetic proteins (BMPs) have multiple biologic functions, including bone formation and embryonic induction. One of these proteins, BMP-6, was reportedly expressed at high levels in human prostate cancers that had also metastasized to bone. This study investigated both BMP-6 mRNA and protein expression in normal and malignant rat and human prostate tissues. BMP-6 was detected in both rat normal prostate and in Dunning rat-prostate adenocarcinoma sublines. The levels of BMP-6 mRNA and protein were similar for normal and malignant rat prostate, regardless of the metastatic potential. Moreover, castration had no apparent effect on BMP-6 production in rat normal ventral prostate, suggesting an androgen-independent gene regulation of this protein. BMP-6 mRNA and protein were also produced by normal and neoplastic human prostate cancer (radical prostatectomy specimens and human carcinoma cell lines DU145 and PC3). BMP-6 mRNA and protein expression, however, was higher in prostate cancer as compared with adjacent normal prostate, with higher-grade tumors (Gleason score of 6 or more) having greater BMP-6 immunostaining than the lower-grade tumors (Gleason score of 4 or less). Taken together, these results suggest that BMP-6 protein expression may serve as a potential marker for prostate cancer but not as a metastatic marker. Moreover, BMP-6 may contribute to prostate neoplastic behavior even in the absence of androgens.