[Bone morphogenetic protein (BMP) receptors and signal transduction]

BMPs are multifunctional cytokines which regulate cellular proliferation, differentiation, apoptosis of various cell types, including osteoblasts and chondroblasts. These functions are related to various biological functions in vivo; e.g. formation of bone and cartilage, embryogenesis, and organogenesis. BMPs transduce signals through binding to type I and type II receptors with serine/threonine kinase activity. As for type I receptors, BMPs bind to BMP type IA receptor, BMP type IB receptor and activin type I receptor. As for type II receptors, BMPs bind to BMP type II receptor, activin type II receptor and activin type IIB receptor. In the receptor-ligand complexes, type II receptors phosphorylate type I receptors in the GS domain (domain rich in glycine, serine and threonine residues) to activate the latter. The activated type I receptors phosphorylate Smad family, which transduces the signals from cytoplasm into nuclei.