Distinctive regulation of the functional linkage between the human cation-independent mannose 6-phosphate receptor and GTP-binding proteins by insulin-like growth factor II and mannose 6-phosphate.
The rat insulin-like growth factor II (IGF-II) receptor develops transmembrane signaling functions by directly coupling to a guanine nucleotide-binding protein (G protein) having a 40-kDa alpha subunit, Gi-2, whereas recent studies have indicated that the IGF-II receptor is a molecule identical to the cation-independent mannose 6-phosphate receptor (CI-MPR), a receptor implicated in lysosomal enzyme sorting. In this study, by using vesicles reconstituted with the clonal human CI-MPR and G proteins, we indicated that the CI-MPR could stimulate guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) binding and GTPase activities of Gi proteins in response to IGF-II. The stimulatory effect of IGF-II on Gi-2 depended on the reconstituted amount of the CI-MPR; it could not be found in vesicles reconstituted with Gi-2 alone; and it was also observed on Gi-1 reconstituted with the CI-MPR in phospholipid vesicles. Of interest, such stimulatory effect was not reproduced by Man-6-P in CI-MPR vesicles reconstituted with either G protein. Furthermore, the affinity for Man-6-P-mediated beta-glucuronidase binding to several kinds of native cell membranes was not reduced by 100 microM GTP gamma S. Instead, however, Man-6-P dose-dependently inhibited IGF-II-induced Gi-2 activation with an IC50 of 6 microM in vesicles reconstituted with the CI-MPR and Gi-2. The action of 100 nM IGF-II was completely abolished by 1 mM Man-6-P. Such an inhibitory effect of Man-6-P was reproduced by 4000 times lower concentrations of beta-glucuronidase or similar concentrations of fructose 1-phosphate, but not by mannose or glucose 6-phosphate. These results indicate that the human CI-MPR has two distinct signaling functions that positively or negatively regulate the activity of Gi-2 in response to the binding of IGF-II or Man-6-P.
Murayama
Y
Y
Fourth Department of Internal Medicine, University of Tokyo School of Medicine, Japan.
Okamoto
T
T
Ogata
E
E
Asano
T
T
Iiri
T
T
Katada
T
T
Ui
M
M
Grubb
J H
JH
Sly
W S
WS
Nishimoto
I
I
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005966:Glucuronidase / Q000037:antagonists & inhibitors / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D007700:Kinetics; D007739:L Cells / Q000378:metabolism; D008360:Mannosephosphates / Q000378:metabolism / Q000494:pharmacology*; D051379:Mice; D008954:Models, Biological; D011485:Protein Binding; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D008360:Mannosephosphates; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C027693:mannose-6-phosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D007335:Insulin-Like Growth Factor II; D005966:Glucuronidase; D019204:GTP-Binding Proteins