Disulphide reduction alters the immunoreactivity and increases the affinity of insulin-like growth-factor-I receptors in human placenta.
We previously identified two forms of the insulin-like growth-factor-I (IGF-I) receptor in human placenta: a lower-affinity form reactive with an autoantiserum (B-2) to the insulin receptor and a higher-affinity non-immunoreactive form [Jonas & Harrison (1985) J. Biol. Chem. 260, 2288-2294]. Evidence is now presented that the lower-affinity immunoreactive forms are convertible into higher-affinity non-immunoreactive forms via reduction of receptor disulphide bonds. Treatment of placental membranes with increasing concentrations of dithiothreitol (DTT): (1) converted native Mr-290 000 heterotetrameric IGF-I receptors into Mr-180 000 dimers (determined by chemical cross-linking of 125I-IGF-I with disuccinimidyl suberate); (2) increased 125I-IGF-I binding, owing to an increase in receptor affinity; and (3) abolished the reactivity of Triton-solubilized IGF-I receptors with antiserum B-2 and transformed the curvilinear plot of IGF-I binding to a linear form. In isolated complexes between receptor and B-2 antibody, DTT increased 125I-IGF-I binding and released a single class of higher affinity IGF-I receptors of Mr 180,000. Thus DTT-treated IGF-I receptors have similar properties to the higher-affinity non-immunoreactive forms of the native receptor, except that reduced dimeric forms are not detected by cross-linking of 125I-IGF-I to native membranes. Cleavage of the inter-dimeric disulphide bonds is therefore not a prerequisite for higher-affinity binding or loss of immunoreactivity. These observations suggest that the thiol redox state of the IGF-I receptor in vivo is an important determinant of receptor conformation and therefore of the biological responses to IGF-I.
D002462:Cell Membrane / Q000378:metabolism; D011232:Chemical Precipitation; D003432:Cross-Linking Reagents; D004229:Dithiothreitol / Q000494:pharmacology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010084:Oxidation-Reduction; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013388:Succinimides
D003432:Cross-Linking Reagents; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013388:Succinimides; D004229:Dithiothreitol; C019358:disuccinimidyl suberate