The rate of internalization of the mannose 6-phosphate/insulin-like growth factor II receptor is enhanced by multivalent ligand binding.
The cation-independent mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF-II receptor) undergoes constitutive endocytosis, mediating the internalization of two unrelated classes of ligands, mannose 6-phosphate (Man-6-P)-containing acid hydrolases and insulin-like growth factor II (IGF-II). To determine the role of ligand valency in M6P/IGF-II receptor-mediated endocytosis, we measured the internalization rates of two ligands, beta-glucuronidase (a homotetramer bearing multiple Man-6-P moieties) and IGF-II. We found that beta-glucuronidase entered the cell approximately 3-4-fold faster than IGF-II. Unlabeled beta-glucuronidase stimulated the rate of internalization of 125I-IGF-II to equal that of 125I-beta-glucuronidase, but a bivalent synthetic tripeptide capable of occupying both Man-6-P-binding sites on the M6P/IGF-II receptor simultaneously did not. A mutant receptor with one of the two Man-6-P-binding sites inactivated retained the ability to internalize beta-glucuronidase faster than IGF-II. Thus, the increased rate of internalization required a multivalent ligand and a single Man-6-P-binding site on the receptor. M6P/IGF-II receptor solubilized and purified in Triton X-100 was present as a monomer, but association with beta-glucuronidase generated a complex composed of two receptors and one beta-glucuronidase. Neither IGF-II nor the synthetic peptide induced receptor dimerization. These results indicate that intermolecular cross-linking of the M6P/IGF-II receptor occurs upon binding of a multivalent ligand, resulting in an increased rate of internalization.
York
S J
SJ
Division of Hematology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Arneson
L S
LS
Gregory
W T
WT
Dahms
N M
NM
Kornfeld
S
S
D019281:Dimerization; D004705:Endocytosis; D005966:Glucuronidase / Q000378:metabolism*; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007700:Kinetics; D008024:Ligands; D011485:Protein Binding; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D017451:Receptors, Somatomedin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D007457:Iodine Radioisotopes; D008024:Ligands; D017527:Receptor, IGF Type 2; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins; D007335:Insulin-Like Growth Factor II; D005966:Glucuronidase