Insulin-like growth factor binding protein 3 (IGFBP-3), is a protein that in humans is encoded by the IGFBP3 gene. IGFBP-3 is one of six IGF binding proteins (IGFBP-1 to IGFBP-6) that have highly conserved structures and bind IGF-1 and IGF-2 with high affinity. IGFBP-3 is the main IGF transport protein in the bloodstream. It interacts with cell-surface proteins, affecting cell signaling from outside the cell or after internalization, and also enters the cell nucleus where it binds to nuclear hormone receptors and other ligands.
Based on cell growth experiments, animal cancer models, and epidemiological studies, it appears that IGFBP-3 functions as a low-penetrance tumor suppressor gene. Dysregulation of IGFBP-3 has been implicated in many cancers. Serum levels of IGFBP-3 can be used to screen for growth hormone deficiency. Serum levels of IGFBP-3 are decreased in AIDS, uncontrolled diabetes mellitus, trauma, and severe burns.