Fig. 1

IGF, insulin, and their receptors. IGF can be secreted by the liver, cancer cells, and macrophages, while insulin is secreted by pancreatic β cells. IGF-IR may heterodimerize with InsR-A or InsR-B and then forms a hybrid receptor. Whereas IGFBPs usually act as serum reservoirs for IGFs, IGFBP7, in particular, may compete with IGFs to bind to IGF-IR and inhibit the activation of IGF-IR. GH, growth hormone