title: The predominant secreted protein of transformed murine fibroblasts carries the lysosomal mannose 6-phosphate recognition marker.
abstract: We have found that the major excreted protein (MEP) of transformed mouse fibroblasts, a phosphoglycoprotein of Mr = 35,000, carries the mannose 6-phosphate recognition marker. MEP secreted by Kirsten virus-transformed NIH 3T3 cells binds to a purified preparation of lysosomal enzyme phosphomannosyl receptor, and this binding is specifically inhibited by mannose 6-phosphate. 32Pi introduced into MEP by metabolic labeling of intact cells is exclusively associated with asparagine-linked oligosaccharides as indicated by sensitivity to endohexosaminidase H. Labeling studies utilizing [2-3H]mannose indicate that approximately one-fifth of the mannose residues of MEP are phosphorylated. Comparative studies of the synthesis, secretion, and uptake of MEP and the lysosomal enzyme beta-galactosidase indicate that MEP made by Kirsten virus-transformed NIH 3T3 cells is not handled in the same manner as are other lysosomal enzymes. MEP may be an unusual lysosomal protein, or both.
mesh_terms: D000818:Animals; D056668:Cathepsin L; D002403:Cathepsins; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases; D010450:Endopeptidases; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D006596:Hexosaminidases; D006600:Hexosephosphates / Q000378:metabolism* / Q000494:pharmacology*; D007708:Kirsten murine sarcoma virus / Q000235:genetics*; D008247:Lysosomes / Q000378:metabolism*; D008360:Mannosephosphates / Q000378:metabolism* / Q000494:pharmacology*; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D051379:Mice; D009844:Oligosaccharides / Q000032:analysis; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000378:metabolism*; D009053:Sarcoma Viruses, Murine / Q000235:genetics*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D006600:Hexosephosphates; D008360:Mannosephosphates; D009844:Oligosaccharides; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; C027693:mannose-6-phosphate; D006596:Hexosaminidases; D001616:beta-Galactosidase; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D056668:Cathepsin L; C534278:Ctsl protein, mouse