title: Insulin-like growth factor binding to the atypical insulin receptors of a human lymphoid-derived cell line (IM-9).
abstract: The cells of the IM-9 human lymphocyte-derived line contain a sub-population of insulin-binding sites whose immunological and hormone-binding characteristics closely resemble those of the atypical insulin-binding sites of human placenta. These binding sites, which have moderately high affinity for multiplication-stimulating activity [MSA, the rat homologue of insulin-like growth factor (IGF) II] and IGF-I, are identified on IM-9 cells by 125I-MSA binding. They account for approximately 30% of the total insulin-receptor population, and do not react with a monoclonal antibody to the type I IGF receptor (alpha IR-3). The relative concentrations of unlabelled insulin, MSA and IGF-I required to displace 50% of 125I-MSA from these binding sites (1:4.7:29 respectively) are maintained for cells, particulate membranes, Triton-solubilized membranes precipitated either by poly(ethylene glycol) or a polyclonal antibody (B-10) to the insulin receptor, and receptors purified by insulin affinity chromatography. Because the atypical insulin/MSA-binding sites outnumber the type I IGF receptors in IM-9 cells by approximately 10-fold, they also compete with the latter receptors for 125I-IGF-I binding. Thus 125I-IGF-I binding to IM-9 cells is inhibited by moderately low concentrations of insulin (relative potency ratios for insulin compared with IGF-I are approx. 1/14 to 1/4) and is partially displaced (65-80%) by alpha IR-3. When type I IGF receptors are blocked by alpha IR-3 or removed by B-10 immunoprecipitation or insulin affinity chromatography, the hormone-displacement patterns for 125I-IGF-I binding resemble those of the atypical insulin/MSA-binding sites.
authors.affiliation: Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria, Australia.
authors.forename: H A
authors.initials: HA
authors.lastname: Jonas
authors.forename: A J
authors.initials: AJ
authors.lastname: Cox
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002846:Chromatography, Affinity; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008214:Lymphocytes / Q000378:metabolism*; D010920:Placenta; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D012995:Solubility; D013002:Somatomedins / Q000378:metabolism*
chemical_list: D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin