The insulin-like growth factors

"The insulin-like growth factors (IGF-I and IGF-II) are single-chain polypeptides with structural homology to proinsulin. They regulate proliferation and differentiation of a multitude of cell types and are capable of exerting insulin-like metabolic effects. Unlike insulin, they are produced by most tissues of the body and are abundant in the circulation. Thus the IGFs have the potential to act via endocrine as well as autocrine andlor paracrine mechanisms. The IGFs exert their effects at the cellular level by interacting with the Type-I IGF receptor (IGF-I receptor). They also bind to the Type II1mannose- 6-phosphate receptor (IGF-II receptor) and insulin receptors, as well as high affinity binding proteins (IGFBPs). Like the IGFs, the IGFBPs are produced by multiple cell types and have been shown to modulate IGF bioactivity. The recent availability of cDNA probes and antibodies for the IGFs, IGF receptors, and IGFBPs has led to a substantial increase in published studies of IGF physiology. This review attempts to integrate recent information regarding coordinate regulation and function of the IGFs, their receptors, and IGFBPs.