Insulin-like growth factor-I produced by seminal vesicles: relationship to intraepithelial basal cell hyperplasia in the prostate.

PURPOSE This study examined the seminal vesicle fluid (SVF) as a potential local source of insulin-like growth factor-I (IGF-I) in the peripheral zone of the prostate. EXPERIMENTAL DESIGN IGF-I levels in seminal fluid were measured. The levels of the IGF-I receptor (IGF-IR) in its active, phosphorylated form as well as direct downstream targets were examined in the peripheral zone of the prostate. RESULTS In situ, we find that the IGF-IR is activated in the peripheral zone in areas of atrophy, prostatic intraepithelial hyperplasia, and cancer. In addition, immunostaining reveals preferential activation of the IGF-IR in p63-positive cells in areas of intermediate basal cell hyperplasia in the peripheral zone, indicating that prostate progenitor cells are highly sensitive to increases in local IGF-I levels. These areas of basal cell hyperplasia occur at high incidence in the peripheral zone of the prostate. Relatively high levels of IGF-I were identified in SVF. In addition, we find that SVF can stimulate the proliferation of both normal and cancer-derived prostate cells. CONCLUSIONS These results suggest that SVF is a local source of IGF-I that provides chronic stimulation of prostate cells. This chronic stimulation could contribute to the development of prostate cancer in older men.