Serum proteolysis of IGFBP-3.

Insulin-like growth factor (IGF) bioavailability is modulated by a family of six IGF binding proteins (IGFBPs) that binds IGF with affinities similar to that of the type 1 IGF receptor. Proteolytic degradation of IGFBP-3, the major serum IGFBP, was first reported in pregnancy serum and suggested to be an additional mechanism involved in the regulation of IGF bioavailability. In this paper, the presence of serum IGFBP-3 proteolysis and its potential role in the regulation of IGF bioavailability is discussed partly in view of our recent finding of IGFBP-3 proteolysis by the tissue plasminogen activator (tPA)-plasminogen-plasmin system in human serum.