Purified hybrid insulin/insulin-like growth factor-I receptors bind insulin-like growth factor-I, but not insulin, with high affinity

Abstract

Hybrid insulin/insulin-like growth factor-I (IGF-I) receptors have previously been described in human placenta, but it has not been possible to study their properties in the presence of classical insulin receptors and type I IGF receptors. To facilitate the purification of hybrids, we produced an anti-peptide monoclonal antibody IGFR 1-2, directed against the C-terminal peptide of the type I IGF receptor beta-subunit. The antibody bound native human and rat type I IGF receptors, and reacted specifically with the beta-subunit on immunoblots. Solubilized placental microsomal membranes were depleted of classical type I IGF receptors by incubation with an immobilized monoclonal antibody IGFR 24-55, which reacts well with type I receptors but very poorly with hybrid receptors. Residual hybrid receptors were then isolated by incubation with immobilized antibody IGFR 1-2, and recovered by elution with excess of synthetic peptide antigen. Binding properties of hybrids were compared with those of immuno-affinity-purified insulin receptors and type I IGF receptors, by using the radioligands 125I-IGF-I and 125I-insulin. Hybrids bound approx. 20 times as much 125I-IGF-I as 125I-insulin at tracer concentrations (approx. 0.1 nM). The binding of 125I-insulin, but not 125I-IGF-I, to hybrids increased after treatment with dithiothreitol to reduce disulphide bonds between the alpha-subunits. Hybrids behaved very similarly to type I receptors with respect to the inhibition of 125I-IGF-I binding by unlabelled IGF-I and insulin. By contrast, the affinity of hybrids for insulin was approx. 10-fold lower than that of classical insulin receptors, as assessed by inhibition of 125I-insulin binding by unlabelled hormone. It is concluded that the properties of insulin receptors, but not IGF receptors, are markedly affected by assembly as hybrid compared with classical structures, and that hybrids are more likely to be responsive to IGF-I than insulin under physiological conditions.

Partial rescue of in vivo insulin signalling in skeletal muscle by impaired insulin clearance in heterozygous carriers of a mutation in the insulin receptor gene

“…This partial rescue of the action of insulin on glucose storage and in vivo insulin signalling by impaired insulin clearance is likely to involve an effect of higher insulin levels on the fraction of fully functional (wt/wt) insulin receptors. Additionally, insulin levels of ∼1,300 pmol/l may be enough to overcome the ∼10-fold lower affinity of insulin for IGF-I and insulin/IGF-I hybrid receptors and evoke signalling through these receptors [24]. Reports of an increased number of insulin/IGF-I hybrid receptors in muscle of patients with chronic hyperinsulinaemia [25,26] provide further support for a potential compensatory action of insulin through the IGF-I receptors in patients with mutant INSR.…”

Changes in insulin and IGF-I receptor expression during differentiation of human preadipocytes

“…Hybrid receptors consisting of one αβ-subunit from the IGF-IR and one αβ-subunit from the IR occur and functions mainly as an IGF-IR with approximately 20-fold higher affinity for IGF-I than for insulin (18). Insulin/IGF-I hybrid receptors have been found in several different human tissues, as muscle, fat, kidney (19) and human cell types, including different breast cancer cells (20) and endothelial cells (21,22).…”

Construction of antibody/insulin receptor chimera for growth induction of mammalian cells

“…It is interesting that only IR and insulin-like growth factor-1 receptor (IGF-1R) adopt such complex structures in the extracellular domain for regulating the signaling (Ullrich et al 1986). Previously, it was reported that IR and IGF-1R can form an IR/IGF-1R hybrid receptor (HR) which is activated by IGF-1/2 (Soos et al 1990(Soos et al , 1993. Of note, IGF-1/2 induces proliferation not only in normal cells but also in cancer cells such as breast and thyroid carcinomas, where HR formation has been confirmed Pandini et al 1999).…”