Roles of insulin-like growth factor (IGF) binding proteins in regulating IGF actions.
The insulin-like growth factor (IGF) system is an evolutionarily conserved signaling pathway that is composed of two IGF ligands, two IGF receptors, and six IGF binding proteins. Studies in a variety of species suggest that the IGF signaling system plays a fundamental role in regulating embryonic growth and differentiation as well as in maintaining homeostasis in the adults. In extracellular fluids, IGFs are present in a complex with an IGF-binding protein (IGFBP). These IGFBPs are traditionally thought to function as carrier proteins and regulate circulating IGF turnover, transport, and distribution. Locally expressed IGFBPs can also inhibit and/or potentiate IGF activities. Recent studies have shown that some IGFBPs, in particular IGFBP-3 and -5, possess intrinsic biological activities and can act through IGF-independent mechanisms. In this article, we provide a brief overview of our current understanding of the IGF signaling system with particular reference to IGFBPs.
Duan
Cunming
C
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA. cduan@umich.edu
Xu
Qijin
Q
D000818:Animals; D005399:Fishes; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins / Q000494:pharmacology / Q000502:physiology*; D013002:Somatomedins / Q000502:physiology*
D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins