Mannose-6-phosphate enhances cross-linking efficiency between insulin-like growth factor-II (IGF-II) and IGF-II/mannose-6-phosphate receptors in membranes.

Abstract

Endogenous and exogenous phosphomannosyl ligands inhibit binding of insulin-like growth factor-II (IGF-II) to the IGF-II/mannose-6-phosphate receptor (IGF-II/Man-6-P receptor). In the present study, the mechanism of this antagonism was examined using a [125I]IGF-II cross-linking assay with disuccinimidyl suberate in cell membranes. Treatment with 5 mM Man-6-P enhanced [125I]IGF-II cross-linking to the receptor. The magnitude of the Man-6-P enhancement differed depending on the source of the membranes, ranging from a 30% increase in JEG-3 human choriocarcinoma up to a 560% increase in B16-F1 mouse melanoma. Man-6-P stimulated [125I]IGF-II-receptor cross-linking in H-35 hepatoma membranes by about 80%, even at concentrations of labeled IGF-II (greater than or equal to 10 nM) that nearly saturated the receptors. Thus, in addition to its effect on IGF-II-binding affinity, Man-6-P caused a 1.5- to 2-fold increase in cross-linking efficiency within the IGF-II-receptor complex. Furthermore, Man-6-P enhanced [125I]IGF-II cross-linking to the H-35 receptor by a constant (approximately 80%) increment 1) when the cross-linking reaction was conducted in buffers of different pH over the range 6.8-8.0, or 2) using cross-linking agents differing in spacer arm length from 6.4-16.1 A. Washing membranes before assay with either Man-6-P (pH 7.4) or 0.5 M NaCl (pH 4.5) reduced the subsequent Man-6-P enhancement of [125I]IGF-II-receptor cross-linking, suggesting that this phenomenon was actually due to displacement of inhibitory phosphomannosyl ligands bound endogenously to the Man-6-P sites of the receptor. In support of this hypothesis, Man-6-P produced a minimal (8-14%) enhancement of [125I]IGF-II-receptor cross-linking in membranes from I-cell fibroblasts lacking such phosphomannosyl ligands. Thus, phosphomannosyl ligands bound to the IGF-II/Man-6-P receptor decrease both IGF-II-binding affinity and IGF-II-receptor cross-linking efficiency. Membrane-associated receptors appear to exist in experimentally and perhaps functionally distinct populations, depending on occupancy of the Man-6-P-binding sites.

• Authors: R G MacDonald
• Journal: Endocrinology (Endocrinology) Vol. 128 Issue 1 Pg. 413-21 (Jan 1991) ISSN: 0013-7227 [Print] United States
• PMID: 1846107 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Cross-Linking Reagents
• Mannosephosphates
• Receptor, IGF Type 2
• Receptors, Cell Surface
• Receptors, Somatomedin
• mannose-6-phosphate
• Insulin-Like Growth Factor II

Topics

• Animals
• Cell Line
• Cross-Linking Reagents
• Humans
• Insulin-Like Growth Factor II (metabolism)
• Kinetics
• Mannosephosphates (metabolism, pharmacology)
• Molecular Weight
• Receptor, IGF Type 2
• Receptors, Cell Surface (drug effects, isolation & purification, metabolism)
• Receptors, Somatomedin