Insulin-like Growth Factor I (IGF-1)

Insulin-like growth factors (IGFs) function as both tissue growth factors and circulating hormones. They actively participate in mammalian development and growth. The IGF family is comprised of insulin and two factors similar to insulin termed IGF-1 and IGF-2. IGF-I and IGF-II are single-chain polypeptides and evolutionarily conserved. The two molecules have 62% homology in their amino acid sequences and their structures resemble the structure of proinsulin. IGFs need a complex system to act, often, it is known as the IGF “axis” system, which should include two IGFs type as IGF-I and IGF-II, two cell-surface receptors such as IGF-receptor type 1 (IGF-1R) and IGF-receptor type 2 (IGF-2R), specific to each IGFs type with tyrosine kinase activity and a family of IGF binding proteins (IGFBPs) . IGFs play an important role in regulating cell proliferation, differentiation, apoptosis, and transformation.