Insulin-like Growth Factor-Binding Protein 3 (IGF-BP3) belongs to the IGFBP family, which are all cysteinerich proteins with conserved cysteine and have an IGFBP domain and a thyroglobulin type-I domain. Mature human IGF-BP3 contains 264 a.a. with three potential N-linked and two potential O-linked glycosylation sites. It is expressed by most tissues and has higher levels during extrauterine life and peak during puberty. The expression of IGF-BP3 in fibroblasts is stimulated by mitogenic growth factors such as Bombesin, Vasopressin, PDGF, and EGF. The protein forms a ternary complex with IGF-I or II and acid-labile subunit. In this form, it circulates in the plasma, prolonging the half-life of IGFs and altering their interaction with cell surface receptors. Decreased plasma levels of IGF-BP3 often happen during the progression of prostate cancer from benign to metastatic disease.
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