Mannose 6-phosphate/insulin-like growth factor II receptor in I-cell disease fibroblasts: increased synthesis and defective regulation of cell surface expression. |
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Authors: | T Braulke S Tippmer U Matzner C Gartung K von Figura |
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Affiliation: | Georg-August-Universit?t, Abt. Biochemie II, G?ttingen, Germany. |
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Abstract: | The amount of mannose 6-phosphate/IGF II receptors in fibroblasts from five I-cell patients was about 2-fold higher than in control fibroblasts. The elevated receptor concentration, which led to a higher binding and uptake of mannose 6-phosphate containing ligands and to a higher binding of IGF II resulted from an increased rate of synthesis, while the stability of the receptor was comparable to that in control fibroblasts. Control fibroblasts respond to mannose 6-phosphate, IGF I, IGF II and tumor promoting phorbol esters with a rapid redistribution of mannose 6-phosphate/IGF II receptors from internal membranes to the cell surface. In I-cell fibroblasts only a moderate increase in cell surface receptors was seen after exposure to these effectors. In contrast to control fibroblasts the treatment of I-cell fibroblasts with lysosomotropic amines failed to affect the mannose 6-phosphate containing ligand binding to the receptor. These data provide evidence for multiple potential regulatory sites in intracellular mannose 6-phosphate/IGF II receptor pathway which differ in control and I-cell fibroblasts. |
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