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.
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.
Yang
Y W
YW
Molecular, Cellular and Nutritional Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Robbins
A R
AR
Nissley
S P
SP
Rechler
M M
MM
D000818:Animals; D002412:Cations / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo / Q000378:metabolism*; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D008322:Mammals / Q000378:metabolism*; D008360:Mannosephosphates / Q000378:metabolism / Q000494:pharmacology; D011233:Precipitin Tests; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism
D002412:Cations; D008360:Mannosephosphates; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; C027693:mannose-6-phosphate; D007335:Insulin-Like Growth Factor II