GDF-9 Promotes the Growth of Prostate Cancer Cells by Protecting Them From Apoptosis

Bone morphogenetic proteins (BMPs) have long been implicated in the process of prostate cancer progression and bone metastasis. This current study investigates the role of GDF-9, a BMP member, in prostate cancer. GDF-9 was over-expressed in PC-3 cells using a mammalian expression construct. Additionally, GDF-9 ribozyme transgenes were generated in order to knock down the expression of GDF-9 in PC-3 and DU-145 cells. These cells were then used in in vitro growth assays in order to determine the effect of GDF-9 on prostate cancer cell growth. Recombinant GDF-9 was also generated and used to treat both cell lines before carrying out further growth assays. Levels of apoptosis were subsequently analyzed using flow cytometry. Cell growth was significantly increased in the GDF-9 over-expressing cells compared to the two controls. The cell growth rate at day 5 was significantly greater in the PC-3(GDF-9exp.) (1,131.1 +/- 79.1%) compared to both PC-3(WT) (563.9 +/- 90.6%) and PC-3(pEF) (763.3 +/- 82.0%), P <= 0.001 versus both controls. The opposite effect was seen in both PC-3 and DU-145 GDF-9 knockdown cells. The PC-3(WT) cells treated with rh-GDF-9 (1.35 +/- 0.28) had a significantly increased absorbance and hence growth rate compared to the untreated PC-3 cells (0.79 +/- 0.05), P=0.026. Finally, flow cytometry and Hoechst 33342 DNA staining demonstrated decreased apoptosis and caspase-3 expression levels in PC-3(GDF-9exp.) cells and rh-GDF-9-treated PC-3(WT) cells. This study shows that GDF-9 can promote the growth rate of both PC-3 and DU-145 cells by protecting the cells from caspase-3-mediated apoptosis, and suggests that GDF-9 may aid in the progression of prostate cancer by acting as a survival factor. J. Cell. Physiol. 225: 529-536, 2010. (C) 2010 Wiley-Liss, Inc.