The chick embryo fibroblast cation-independent mannose 6-phosphate receptor is functional and immunologically related to the mammalian insulin-like growth factor-II (IGF-II)/man 6-P receptor but does not bind IGF-II

• Published in: Endocrinology (Philadelphia) Vol. 128; no. 2; p. 1177
• Main Authors: Yang, Y W, Robbins, A R, Nissley, S P, Rechler, M M
• Format: Journal Article
• Language: English
• Published: United States 01.02.1991
• Subjects: Animals; Cations - pharmacology; Cells, Cultured; Chick Embryo - metabolism; Fibroblasts - enzymology; Fibroblasts - metabolism; Insulin-Like Growth Factor II - metabolism; Mammals - metabolism; Mannosephosphates - metabolism; Mannosephosphates - pharmacology; Precipitin Tests; Receptor, IGF Type 2; Receptors, Cell Surface - immunology; Receptors, Cell Surface - metabolism; Receptors, Somatomedin; Somatomedins - metabolism
• ISSN: 0013-7227
• DOI: 10.1210/endo-128-2-1177

The insulin-like growth factor-II (IGF-II)/Mannose 6-P receptor (Man 6-P) is a multifunctional receptor that binds two unrelated ligands, IGF-II and lysosomal enzymes that contain Man 6-P recognition markers. Although this receptor has been extensively characterized in mammalian cells, binding of radiolabeled IGF-II to this receptor in avian cells and tissues has not been reported. In the present study, we demonstrate that chick embryo fibroblasts (CEFs) bind and internalize lysosomal enzymes in a Man 6-P-inhibitable fashion, and possess a protein immunologically related to the mammalian IGF-II/Man 6-P receptor that binds lysosomal enzymes with Man 6-P recognition markers but does not bind IGF-II. 1) When lysates of biosynthetically labeled CEFs were affinity-purified on beta-galactosidase-Sepharose, an approximately 250 kilodalton protein was observed in the Man 6-P eluate but not in the Glc 1-P or mannose eluates, that was precipitated by antisera to purified rat and bovine IGF-II/Man 6-P receptors, but not by nonimmune serum. 2) When CEFs were incubated with [35S]proteins enriched in lysosomal enzymes, Man 6-P inhibited binding (0 C) and uptake (34 C) in a dose-dependent fashion. Binding was unchanged in the absence of divalent cations. At low sugar concentrations, binding and uptake were inhibited selectively by Man 6-P and the conformationally similar sugar phosphate, Fru 1-P, a specificity similar to that of mammalian cation-independent Man 6-P receptors. 3) When affinity-purified lysates from biosynthetically labeled CEFs were incubated with antiserum to the rat IGF-II/Man 6-P receptor, a 245 kilodalton protein was immunoprecipitated from lysates that had been affinity purified on beta-galactosidase-Sepharose but not after purification on IGF-II-Sepharose. By contrast, a truncated IGF-II/Man 6-P receptor, presumably internalized from the fetal bovine serum used to feed the cells, was purified from lysates of unlabeled CEFs on IGF-II-Sepharose. Thus, CEFs possess a cation-independent Man 6-P receptor that is similar in size and immunological reactivity to the mammalian IGF-II/Man 6-P receptor, and binds and internalizes lysosomal enzymes but, unlike the mammalian receptor, does not bind IGF-II.