Activation of Osteoblast Insulin-like Growth Factor-II/ Cation-Independent Mannose-6-phosphate Receptors by Specific Phosphorylated Sugars and Antibodies Induce Insulin-like Growth Factor-II Effects

The phosphorylated monosaccharide, mannose-6-phosphate (M6P), causes a dose-dependent stimulation of alkaline phosphatase production by osteoblasts. The concentrations tested ranged from 0.1 to 30 mM. A maximal effect was reproducibly seen at 10-30 mM, and represented a 30% stimulation over control cells. Glucose-6-phosphate and fructose-1-phosphate also stimulated osteoblast alkaline phosphatase production, but not to the same extent as M6P. Sugar residues such as mannose, mannose-1-phosphate, and fructose-6-phosphate had no effect. The stimulatory effect of M6P is similar to that seen with insulin-like growth factor II(IGF-II). However, increasing doses of IGF-II did not further stimulate or add to the effect of 10 mM M6P. These data indicate that the mechanism for the transduction of the stimulatory signal may be similar for both IGF-II and M6P. They do not address, however, the possibility of separate or similar binding sites for the two agents. A specific polyclonal antibody to the IGF-II/cation-independent mannose-6-phosphate receptor (IGF-II/CI-MPR) elicits the same effects as M6P and IGF-II in these bone cells. Non-immune serum used as a control does not have any effect. These results suggest that activation of the osteoblast IGF-II/CI-MPR by either M6P or a specific antibody can evoke a biological response similar to that observed with IGF-II.