Blockade of transforming growth factor-β signaling suppresses progression of androgen-independent human prostate cancer in nude mice

We investigated the role of transforming growth factor-β (TGF-β) signaling in the growth and metastasis of PC-3MM2 human prostate cancer cells. Highly metastatic PC-3MM2 human prostate cancer cells were engineered to constitutively overexpress a dominant-negative type II TGF-β receptor (DNR). Transfection of DNR had minimal direct effects on cell growth and attenuated TGF-β-induced cell growth inhibition and TGF-β1 production. There were no discernable differences in tumorigenicity (tumor incidence) among PC-3MM2 variants when the cells were implanted into the prostates of nude mice. Growth rate and metastatic incidence of DNR-engineered PC-3MM2 cells, however, were significantly reduced. Most cells in the control tumors were positively stained by an antibody to proliferation cell nuclear antigen and very few cells were stained by terminal deoxynucleotidyl transferase - mediated nick-end labeling (TUNEL). In sharp contrast, tumors formed by PC-3MM2-DNR cells contained fewer proliferation cell nuclear antigen - positive cells and many more TUNEL-positive cells. Staining with antibody against CD31 showed that control tumors contained more blood vessels than PC-3MM2-DNR tumors. Expression of interleukin-8 (IL-8) in tumors formed by PC-3MM2 cells was significantly reduced as revealed by both Northern blotting and ELISA. Finally, transfection of antisense IL-8 cDNA significantly reduced IL-8 production by PC-3MM2 cells and antisense IL-8-transfected PC-3MM2 cells grew slower in comparison with parental and control vector-transfected cells. Taken together, our data suggest that TGF-β signaling, by regulating IL-8 expression in tumor cells and hence tumor angiogenesis, is critical for progressive growth of PC-3MM2 cells in the prostate of nude mice.