Scatchard analyses of the binding of transforming growth factor-β (TGFβ) to membranes from rat ventral prostate revealed the presence of high affinity (Kd = 140 pM) saturable binding sites for [125I]TGFβ. The binding of [125I]TGFβto prostatic membranes, while displaced in the presence of excess unlabeled TGFβ, is unaffected by epidermal growth factor, nerve growth factor, fibroblast growth factor, or insulin, indicating the specificity of binding. Affinity labeling of these membrane receptors by covalent attachment to [125I]TGFβ with bis-(sulfosuccinimidyl) suberate and subsequent electrophoretic analysis of the labeled complexes revealed the specific binding of [125I] TGFβ to a macromolecule that predominantly migrates as a 260,000 mol wt band in 7.5% acrylarnide gels. Castration-induced androgen deprivation produced a significant increase in [125I] TGFβ binding to prostatic membranes with no apparent change in the affinity of membrane receptors for TGFβ. TGFβ receptor levels per total gland increased approximately 2-fold by 3 days after castration, reached a peak value by day 4, and then declined during the subsequent 10 days. Androgen administration to 4- day castrated animals decreased the number of TGFβ receptors to a value similar to that in the intact controls. These results demonstrate the presence of specific binding sites for TGFβ in the rat ventral prostate. Furthermore, the TGFβ receptor levels seem to be under negative androgenic regulation, indicating a potential role for this growth factor in the mechanism of activation of castration-induced death of androgen-dependent epithelial cells in the ventral prostate.
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