Home > Insulin-like growth factor
The insulin-like growth factors (IGFs) are polypeptides with high sequence similarity to insulin. They can trigger the same cellular responses as insulin, including mitogenesis in cell culture. IGF-II is thought to be a primary growth factor required for early development while IGF-I expression is seen in later life. 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. Insulin-like growth factor 1 (IGF-1) is mainly secreted by the liver as a result of stimulation by growth hormone (hGH). Almost every cell in the human body is affected by IGF-1, especially cells in muscle, cartilage, bone, liver, kidney, nerves, skinThis article is about skin in the biological sense. For other uses of skin see skin (computing) and skinhead. Regarding exposure of the skin to be seen by others, or prevention of this, see nudity, nudism, modesty, clothing. Fruits such as oranges also ha, and lungs. In addition to the insulin-like effects, IGF-1 can also regulate cell growthThe term cell growth is used in two different ways in biology. When used in the context of reproduction of living cells the phrase "cell growth" is shorthand for the idea of "growth in cell numbers by means of cell reproduction. During cell reproduction o and development, especially in nerve cells, as well as cellular DNADeoxyribonucleic acid DNA is a nucleic acid which carries genetic instructions for the biological development of all cellular forms of life and many viruses. DNA is sometimes referred to as the molecule of heredity as it is inherited and used to propagate synthesis.
IGF-II is secreted by the brain, kidney, pancreasThe pancreas is a retroperitoneal organ that serves two functions: exocrine it produces pancreatic juice containing digestive enzymes endocrine it produces several important hormones Anatomy The pancreas is a retroperitoneal organ located posterior to the and muscle in mammalsSubclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorp. It is more specific in action than IGF-1. In adult humans it is found at 600 times the concentration of insulin.
IGF-1 and IGF-II are regulated by a family of genes known as the IGF-Binding Proteins. These proteins help to modulate IGF action in complex ways that involve both inhibiting IGF action by preventing binding to the IGF-1 receptor as well as promoting IGF action possibly through aiding in delivery to the receptor and increasing IGF half-life. Currently, there are 6 characterized IGF Binding Proteins (IGFBP1-6). While non IGF-mediating functions have been proposed for many of these proteins, conclusive evidence has yet to be shown.
Studies of recent interest show that the IGF axis play an important role in agingIn biology, senescence is the state or process of aging. For the social, cultural, and economic aspects see ageing. The word senescence is derived from the Latin word senex meaning "old man" or "old age. Cellular senescence is a phenomena where isolated c. Nematodes, fruit-fly and other organisms have an increased life span when the gene equivalent to the mammalian IGF is knocked out. Clearly the IGF/Insulin axis has an ancient evolutionary origin. Other studies are beginning to uncover the important role the IGF's play in diseases such as cancer and diabetes, showing for instance that IGF-1 stimulates growth of both prostate and breast cancer cells. 1-3 Researchers are not in complete agreement about the degree of cancer risk that IGF-1 poses.
Further work is required to determine the main receptors used by these growth factors to elicit their effects. Currently the IGF's are known to bind the insulin receptor, IGF-1 receptor, IGF-2 receptor, the insulin-related receptor and possible other receptors. IGF-1 and IGF-2 strongly bind to and activate the IGF-1 receptor, with weaker binding and action occurring through insulin receptors. The IGF-2 receptor only binds IGF-2 and acts as a "clearance receptor" - it activates no intracellular signalling pathways, functioning only as an IGF-2 sequestering agent and preventing IGF-2 signalling.
IGF-1 is present in milk, especially when the cow has been treated with bovine growth hormone.
See insulin-like growth factor 1.
