Insulin-like growth factor binding proteins

The insulin-like growth factors (IGFs) are proteins with high sequence similarity to insulin. IGFs are part of a complex system that cells use to communicate with their physiologic environment. This complex system (often referred to as the IGF "axis") consists of two cell-surface receptors (IGF1R and IGF2R), two ligands (Insulin-like growth factor 1 (IGF-1) and Insulin-like growth factor 2 (IGF-2)), a family of six high-affinity IGF-binding proteins (IGFBP-1 to IGFBP-6), as well as associated IGFBP degrading enzymes, referred to collectively as proteases.

The IGF "axis" is also commonly referred to as the Growth Hormone/IGF-1 Axis. Insulin-like growth factor 1 (IGF-1, or sometimes with Roman Numeral as IGF-I) is mainly secreted by the liver as a result of stimulation by growth hormone (GH). IGF-1 is important for both the regulation of normal physiology, as well as a number of pathological states, including cancer. The IGF axis has been shown to play roles in the promotion of cell proliferation and the inhibition of cell death (apoptosis). Insulin-like growth factor 2 (IGF-2, or sometimes with Roman Numeral as IGF-II) is thought to be a primary growth factor required for early development while IGF-1 expression is required for achieving maximal growth. Gene knockout studies in mice have confirmed this, though other animals are likely to regulate the expression of these genes in distinct ways. While IGF-2 may be primarily fetal in action it is also essential for development and function of organs such as the brain, liver, and kidney.

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