Insulin-Like Growth Factor (IGF-1)
IGF-1 is a member of the insulin-like growth factor family with potent mitogenic and metabolic effects. IGF-1 is produced in many cell types, but mainly in the liver and is secreted into the blood, where it circulates bound to one of six IGF-binding proteins (IGFBPs). Of these proteins, IGFBP-3 is present at the highest level in adults, and is responsible for carrying IGF-1 to target tissues and prolonging its half-life in circulation. In contrast, IGFBP-1 is the most important negative regulator of IGF-1. IGF-1 helps regulate metabolism of glucose, fatty acids, cartilage and bone, as well as growth hormone activity. This protein also plays important roles in Alzheimer’s disease and tumor pathogenesis. IGF-1 and IGF-2 share 70% sequence identity.