The mannose 6-phosphate/insulin-like growth factor II receptor is a nanomolar affinity receptor for glycosylated human leukemia inhibitory factor

Comparison of the binding properties of non-glycosylated, glycosylated human leukemia inhibitory factor (LIF) and monoclonal antibodies (mAbs) directed at gp190/LIF-receptor beta subunit showed that most of the low affinity (nanomolar) receptors expressed by a variety of cell lines are not due to gp190, These receptors bind glycosylated LIF produced in Chinese hamster ovary cells (CHO LIF) (K-d, = 6.9 nM) but not Escherichia coli-derived LIF or CHO LIF treated with endoglycosidase F, CHO LIF binding to these receptors is neither affected by anti-gp190 mAbs nor by anti-gp130 mAbs and is specifically inhibited by low concentrations of mannose 6-phosphate (Man-6-P) (IC50 = 40 mu M), suggesting that they could be related to Man-B-P receptors, The identity of this LIF binding component with the Man-6-P/insulin-like growth factor-II receptor (Man-6-P/IGFII-R) was supported by several findings. (i) It has a molecular mass very similar to that of the Man-6-P/IGFII-R (270 kDa); (ii) the complex of LIF cross linked to this receptor is immunoprecipitated by a polyclonal anti-Man-6-P/IGFII-R antibody; (iii) this antibody inhibits LIF and IGFII binding to the receptor with comparable efficiencies; (iv) soluble Man-6-P/IGFII-R purified from serum binds glycosylated LIF (K-d = 4.3 nM) but not E. coli LIF. The potential role of Man-6-P/IGFII-R in LIF processing and biological activity is discussed.