Insulin-like growth factor 1 (IGF-1), sometimes called somatomedin C, is a hormone that promotes growth and prevents cell death. It is structurally similar to insulin, as well as to insulin-like growth factor 2 (IGF-2). This hormone is used across the lifespan of a human organism, but becomes most prominent during childhood and adolescence. Many animals—including mammals, birds, and fish—seem to use IGF-1 to regulate cell growth. It is produced in the liver, usually as a consequence of signals from growth hormone.
IGF-1 binds to two types of receptors on the outer surface of cellular membranes: the IGF-1 receptor (IGF1R) and the insulin receptor. Both of these are members of receptor tyrosine kinase (RTK) class II. The primary and unique effects of the hormone take place through IGF1R, which, when activated, triggers a chemical sequence called the AKT pathway. This process, revolving around a protein called AKT, has significant effects on the life and death of the cell. It seems this hormone has the effect of inhibiting programmed cell death. This explains its double-sided role as a stimulus to tissue growth and as an accessory to cancer.
A chemical resemblance to insulin also allows IGF-1 to active the insulin receptor. This protein triggers a process that ultimately causes a cell to take in more glucose from the bloodstream. IGF-1 does not bind to or activate the insulin receptor as effectively as insulin itself.
The effects of the hormone can be modulated by a series of six or seven proteins called insulin-like growth factor binding proteins (IGFBPs). IGFBP-2 and and IGFBP-5 inhibit its effects by preventing it from binding to a cellular receptor. IGFBP-3, the most common of these proteins, prolongs the life of IGF molecules.
Excess of IGF-1 and IGF1R is associated with several types of diseases. Breast and prostate cancers may be caused by a failure of cell death connected to this chemical system. Gigantism and acromegaly, which causes unnatural growth and swelling in the body, may also be connected to an excess of this molecule. Because it is correlated with growth hormone, these problems may result originally from excesses in growth hormone. Doctors suspecting these conditions may take measurements of IGF-1 for diagnostic purposes, since these usually also reflect the production of growth hormone.
Synthetic IGF-1, known as mecasermin, is used as a treatment for hormonal growth deficiency. Several different companies have attempted to create and release versions of this drug, with various levels of scientific and legal success. The hormone is also marketed as a steroid for body-building.
