Altered growth and insulin-like growth factor-binding protein-3 production in PC3 prostate carcinoma cells stably transfected with a constitutively active androgen receptor complementary deoxyribonucleic acid.

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The network of androgen-dependent growth factors regulating the growth and function of normal or neoplastic prostate epithelium is largely unknown. To facilitate studies directed at investigating this issue, androgen receptor-negative (AR-) PC3 prostate carcinoma cells were stably transfected with the expression plasmid CMV3 containing a constitutively active AR construct that is truncated at its hormone-binding domain (CMV-ARCA). The major characteristic of the resulting cell line (PC3-ARCA) was a growth rate approximately 35% slower than that of a control mock-transfected cell line (PC3-Neo). Of the several growth factors known to be present in the prostate, the current studies focused on the insulin-like growth factor (IGF) axis, specifically the IGF-binding proteins (IGFBPs), several of which are known to be abnormally produced by prostate cancer. Northern analysis showed that IGFBP-1 and -5 are not expressed by PC3-ARCA and -Neo cells. Western ligand and immunoblot analysis of medium conditioned by PC3-Neo and PC3-ARCA cells revealed that equal amounts of IGFBP-2, -4, and -6 were secreted. In contrast, IGFBP-3 was undetectable in the conditioned medium of PC3-ARCA cells, but normally produced by the AR- cell line PC3-Neo. IGFBP-3 disappearance from the conditioned medium of PC3-ARCA cells was transcriptionally regulated, as a marked decrement in IGFBP-3 messenger RNA was detected by S1 protection analysis. We investigated the responses of these cells to exogenously added IGF-I, IGF-II, or IGFBP-3. IGF-I and IGF-II stimulated the proliferation of PC3-ARCA cells, but not of PC3-Neo cells. IGFBP-3 had no effect when given alone. When IGFBP-3 was administered together with IGF-I or IGF-II, it further increased the mitogenic response observed in PC3-ARCA cells, but no effect on PC3-Neo cells was observed. In conclusion, our studies suggest that the presence of an active AR modulates the proliferation of transfected PC3 prostate cancer cells, and that this phenomenon occurs at least in part through the regulation of IGFBP-3 production.