A candidate targeting molecule of insulin-like growth factor-I receptor for gastrointestinal cancers

Figure 1 The structure, signal transductions, and effects of the type I insulin-like growth factor receptor system. Type I insulin-like growth factor receptor (IGF-IR) is synthesized as a single precursor peptide and then is cleaved into the α-subunit (extracellular domain) and the β-subunit (transmembrane and tyrosine kinase domains). After binding to the ligands (IGF-I and IGF-II), IGF-IR, which is constructed with two α- and two β-chains, turns on its signal transductions via two major pathways, such as mitogen-activated protein kinase (MAPK) and phosphatidylinositide 3-kinase (PI3-K)/Akt, results in survival and mitogenesis. IRS: Insulin receptor substrate; Shc: Src homology and collagen-containing protein; Grb2: Growth factor receptor-bound protein 2; PTEN: Phosphatase and tensin homolog; JAK: Janus kinase; MAPKK: MAPK kinase; MEK: MAPK/ERK kinase; ERK: Extracellular signal-regulated kinase; BAD: Bcl-2-associated death promoter; FOXO: Forkhead box O; GSK3β: Glycogen synthase kinase 3 beta; eIF4E: Eukaryotic translation initiation factor 4E.