Cellular actions of insulin-like growth factor binding proteins

The insulin-like growth factors (IGFs), insulin-like growth factor binding proteins (IGFBPs), and the IGFBP proteases are involved in the regulation o f somatic growth and cellular proliferation both in vivo and in vitro. IGFs are potent mitogenic agents whose actions are determined by the availabili ty of free IGFs to interact with the IGF receptors. IGFBPs comprise a famil y of proteins that bind IGFs with high affinity and specificity and thereby regulate Icf-dependent actions. IGFBPs have recently emerged as Icf-indepe ndent regulators of cell growth. Various IGFBP association proteins as well as cleavage of IGFBPs by specific proteases modulate levels of free IGFs a nd IGFBPs. The ubiquity and complexity of the IGF axis promise exciting dis coveries and applications for the future.