title: Insulin-like growth factor-II/mannose 6-phosphate receptor is incapable of activating GTP-binding proteins in response to mannose 6-phosphate, but capable in response to insulin-like growth factor-II.
abstract: We previously reported that insulin-like growth factor-II (IGF-II) stimulates both calcium influx and DNA synthesis by acting on the cell surface IGF-II receptor (IGF-IIR) in a manner sensitive to pertussis toxin, and recently demonstrated that IGF-II binding to the IGF-IIR gives rise to functional changes of purified Gi-2, a GTP-binding protein (G protein) in phospholipid vesicles as well as in broken cell membranes. On the other hand, a variety of evidence indicates that the IGF-IIR binds mannose 6-phosphate (man6P) with high affinity probably at a receptor extracellular region different from the IGF-II-binding site. In the present study, we examined whether man6P stimulation of the IGF-IIR evokes the activation of Gi-2 in phospholipid vesicles and in native cell membranes. In vesicles reconstituted with purified rat IGF-IIR and bovine Gi-2, man6P did not stimulate GDP dissociation from Gi-2 even in concentrations up to 10 mM, while IGF-II dose-dependently facilitated GDP release from Gi-2 with an EC50 of 6 nM. The stimulatory effect of IGF-II was not observed in vesicles reconstituted with Gi-2 alone. In addition, also in a native environment of cell membranes, man6P did not affect an endogenous 40-kDa protein or exogenously added purified Gi-2 as assessed with reduction of the pertussis toxin-catalyzed ADP-ribosylation. These results indicate that the IGF-IIR does not activate Gi-like proteins upon man6P binding in phospholipid vesicles and in native cellular membranes, whereas the receptor activates Gi-like proteins upon IGF-II binding in both environments. Thus, we postulate that the IGF-IIR dissimilarly responds to the two structurally unrelated ligands, IGF-II and man6P, in the linkage function with G proteins.
authors.affiliation: Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Okamoto
authors.forename: I
authors.initials: I
authors.lastname: Nishimoto
authors.forename: Y
authors.initials: Y
authors.lastname: Murayama
authors.forename: Y
authors.initials: Y
authors.lastname: Ohkuni
authors.forename: E
authors.initials: E
authors.lastname: Ogata
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006600:Hexosephosphates / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D008360:Mannosephosphates / Q000378:metabolism*; D008567:Membranes, Artificial; D051379:Mice; D008807:Mice, Inbred BALB C; D051381:Rats; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
chemical_list: D006600:Hexosephosphates; D008360:Mannosephosphates; D008567:Membranes, Artificial; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D006153:Guanosine Diphosphate; C027693:mannose-6-phosphate; D007335:Insulin-Like Growth Factor II; D019204:GTP-Binding Proteins