IGFBP-2, also known as IGFBP-2, is an insulin-like growth factor-binding protein (IGFBP). IGFBPs prolong the half-life of the IGFs, control bioavailability, activity, and distribution of insulin-like growth factor (IGF) throμgh high-affinity IGFBP/IGF complexes. Six high-affinity IGF-binding proteins (IGFBP-1 to-6) have been identified. The six IGFBPs are structurally related but encoded by distinct genes. IGFBPs have a high affinity for IGFs. Some members of the IGFBP family have been consistently shown to inhibit IGF actions by preventing them from gaining access to the IGF receptors, while others potentiate IGF actions by facilitating the ligand-receptor interaction. IGFBP-2 is overexpressed in many malignancies and is often correlated with an increasingly malignant status of the tumor, pointing to the potential involvement of IGFBP-2 in tumorigenesis. It contains 1 IGFBP N-terminal domain and 1 thyroglobulin type-1 domain. It inhibits IGF-mediated growth and developmental rates.
Mouse Insulin-like growth factor-binding protein 5(IGFBP-5) belongs to the superfamily of insulin-like growth factor (IGF) binding proteins. It contains 1 IGFBP N-terminal domain and 1 thyroglobulin type-1 domain. Mouse IGFBP-5 shows 97% aa sequence identity with those of human and rat IGFBP-5. It is expressed mostly in kidney, uterus and gastrocnemius muscle. It also expressed by fibroblasts, myoblasts and osteoblasts, making it the predominant IGFBP found in bone extracts. IGFBP-5 has a strong affinity for hydroxyapatite, allowing it to bind to bone cells. When bound to extracelluar matrix, IGFBP-5 is protected from proteolysis and potentiates IGF activity, but when it is soluble, IGFBP-5 is cleaved to a biologically inactive 21 kDa fragment. IGF-binding proteins prolong the half-life of the IGFs and have been shown to either inhibit or stimulate the growth promoting effects of the IGFs on cell culture. They alter the interaction of IGFs with their cell surface receptors.
Insulin-like growth factor binding protein 6 (IGFBP6) is a 24-kDa protein that binds insulin-like growth factor 1 (IGF-1) and IGF-2 with high affinity and inhibits IGF action in vitro. The Insulin-like growth factor-binding protein also known as IGFBP serves as a carrier protein for Insulin-like growth factor 1. IGFBPs are clearly distinct but are sharing regions with strong homology. All members of the IGFBP family bind IGF-I and IGF-II with about equal affinity. Insulin-like growth factor (IGF) binding proteins (IGFBPs) have been shown to either inhibit or enhance the action of IGF, or act in an IGF-independent manner in the prostate. IGF-binding protein-4 (IGFBP-4) inhibits IGF-I action in vitro and is the most abundant IGFBP in the rodent arterial wall. IGFBP6 is directly downregulated by the beta-catenin/TCF complex in desmoid tumors, and imply a role for the IGF axis in the proliferation of desmoid tumors. There is mounting evidence that the structure of the IGFBP proteins plays a key role in the regulation of IGF bioavailability, by modulating its molecular size, capillary membrane permeability, target tissue specificity, cell membrane adherence and IGF affinity.
Insulin-like growth factors (IGFs) comprise a family of endocrine, paracrine and autocrine polypeptides consisting of the ligands IGF1 and IGF2, two receptors (IGF1R, IGF2R), at least 6 IGF-binding proteins (IGFBPs) and IGFBP proteases. Among the binding proteins, IGFBP6 is unique because of its N-terminal disulfide linkages and its marked binding preference for IGF2. It is a potent inhibitor of the interaction between IGF2 and its receptor IGF1R, thus preventing major functions of IGF2, such as induction of proliferation, differentiation, cell adhesion, or colony formation. In particular, IGFBP-6 inhibited the growth of neuroblastoma and rhabdomyosarcoma xenografts. GFBP-6 is expressed in many tissues, including lung, liver, gut and the central nervous system.
The superfamily of insulin-like growth factor (IGF) binding proteins include the six high-affinity IGF binding proteins (IGFBP) and at least four additional low-affinity binding proteins referred to as IGFBP related proteins (IGFBP-rP). All IGFBP superfamily members are cysteine-rich proteins with an conserved cysteine residues, which are clustered in the amino-and carboxy-terminal thirds of the molecule. IGFBPs modulate the biological activities of IGF proteins. Some IGFBPs may also have intrinsic bioactivity that is independent of their ability to bind IGF proteins. Post-translational modifications of IGFBPs, including glycosylation, phosphorylation and proteolysis, have been shown to modify the affinities of the binding proteins to IGF. Mouse IGFBP-6 cDNA encodes a 238 amino acid (aa) residue precursor protein with an a putative 25 aa residue signal peptide that is processed to generate the 213 aa residue mature protein that is O-glycosylated. Mouse and Human IGFBP-6 share 73% amino acid similarity. Mouse and rat IGFBP-6 share 94% amino acid similarity and the Mouse IGFBP-6 has a 9 amino acid insertion compared to the rat homolog. IGFBP-6 is expressed in ovarian, testicular, muscle, heart and lung tissues in the adult Mouse. IGFBP-6 was not detected in total RNA from a whole Mouse embryo.
Insulin like growth factor binding protein 7 (IGFBP7) is a member of the IGFBP family. It has been identified in colorectal adenocarcinoma (CRC) cell lines. The Insulin-like growth factor-binding protein also known as IGFBP serves as a carrier protein for Insulin-like growth factor 1. IGFBPs are clearly distinct but are sharing regions with strong homology. All members of the IGFBP family bind IGF-I and IGF-II with about equal affinity. Insulin-like growth factor (IGF) binding proteins (IGFBPs) have been shown to either inhibit or enhance the action of IGF, or act in an IGF-independent manner in the prostate. IGFBP7 could inhibit cell growth, decrease soft agar colony formation activity and induce apoptosis in RKO and SW620 cells. There is mounting evidence that the structure of the IGFBP proteins plays a key role in the regulation of IGF bioavailability, by modulating its molecular size, capillary membrane permeability, target tissue specificity, cell membrane adherence and IGF affinity.
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