Increased expression of bone morphogenetic protein-7 in bone metastatic prostate cancer

Prostate cancer frequently metastasizes to bone. The skeletal metastases of prostate cancer origin are osteoblastic rather than osteolytic. Recently, the expression of bone morphogenetic proteins (BMPs) in prostate cancer cell lines was detected. The present study indicated the existence of BMP-7 in normal prostate tissue, but its function has not been clarified. The mechanism by which prostate cancer causes osteoblastic metastasis is not clear. We investigated the expression of BMP-7 and -6 in normal and metastatic bone tissues to clarify the biological relationship between the expression of BMPs and bone metastasis in prostatic cancer.

Six samples of normal bone tissue and nine samples of bone metastasis tissue were collected during the autopsies of six patients with prostate cancer. Total RNA was extracted from these samples. After reverse transcription (RT) of the RNA samples, the expression of BMP-6 and -7 in each sample was measured by the real-time quantitative polymerase chain reaction (PCR). Glyceraldehyde phosphate dehydrogenase (GAPDH) was used as an internal standard.

Although the expression of BMP-7 was detected in five out of seven (71%) metastatic bone lesions of prostate cancer, it was not detected in normal bone tissues. The expression level of BMP-7 was significantly higher in metastatic bone lesions than in normal bone (P < 0.05). There was no significant difference between the level of expression of BMP-6 in metastatic bone lesions from prostate cancer and the level in normal bone tissue (P = 0.81).

These results suggest that high expression of BMP-7 in metastatic bone lesions of prostate cancer is related to osteoblastic metastasis. BMP-7 in the bone metastasis tissue indicates that the cells expressing BMP-7 probably originated from the prostate, because we have detected high expression of BMP-7 in the prostate. Prostate 54: 268-274, 2003.