HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Vielhaber, G. Articles by Sandhoff, K. Search for Related Content PubMed PubMed Citation Articles by Vielhaber, G. Articles by Sandhoff, K. Social Bookmarking                      What's this?

Volume 271, Number 50, Issue of December 13, 1996 pp. 32438-32446
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

---

Biosynthesis, Processing, and Targeting of Sphingolipid Activator Protein (SAP )Precursor in Cultured Human Fibroblasts
MANNOSE 6-PHOSPHATE RECEPTOR-INDEPENDENT ENDOCYTOSIS OF SAP PRECURSOR

(Received for publication, June 3, 1996, and in revised form, September 3, 1996)

Gabriele Vielhaber ^¶ , Robert Hurwitz and Konrad Sandhoff ^¶

From the ^¶ Institut für Organische Chemie und Biochemie, Universität Bonn, D-53121 Bonn, Germany and  Institut für Physiologische Chemie, Universität Bonn, D-53115 Bonn, Germany

Sphingolipid activator proteins (SAPs) are essential cofactors for the lysosomal degradation of glycosphingolipids with short oligosaccharide chains by acidic exohydrolases. SAP-A, -B, -C, and -D derive from proteolysis of a 73-kDa glycoprotein, the SAP precursor. In the present publication, we studied the intracellular transport and the endocytosis of SAP precursor in human skin fibroblasts. Our data indicate that SAP precursor bears phosphate residues on noncomplex carbohydrate chains linked to the SAP-C and the SAP-D domain and sulfate residues on complex carbohydrate chains located within the SAP-A, -C, and possibly the SAP-D domain. Treatment of fibroblasts with either bafilomycin A₁ or 3-methyladenine indicates that proteolytic cleavage of SAP precursor begins as early as in the late endosomes. To determine whether targeting of SAP precursor depends on mannose 6-phosphate residues, we analyzed the processing of SAP precursor in I-cell disease fibroblasts. In these cells nearly normal amounts of newly synthesized SAP-C were found, although secretion of SAP precursor was enhanced 2-3-fold. Moreover, SAP-C could be localized to lysosomal structures by indirect immunofluorescence in normal and in I-cell disease fibroblasts. Mannose 6-phosphate was not found to interfere significantly with endocytosis of SAP precursor. Normal fibroblasts internalized SAP precursor secreted from I-cells nearly as efficiently as the protein secreted from normal cells. To our surprise, deglycosylated SAP precursor was taken up by mannose 6-phosphate receptor double knock out mouse fibroblasts more efficiently than the glycosylated protein. We propose that intracellular targeting of SAP precursor to lysosomes is only partially dependent on mannose 6-phosphate residues, whereas its endocytosis occurs in a carbohydrate-independent manner.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				Y. Sun, D. P. Witte, H. Ran, M. Zamzow, S. Barnes, H. Cheng, X. Han, M. T. Williams, M. R. Skelton, C. V. Vorhees, et al. Neurological deficits and glycosphingolipid accumulation in saposin B deficient mice Hum. Mol. Genet., August 1, 2008; 17(15): 2345 - 2356. [Abstract] [Full Text] [PDF]

				Y. Sun, D. P. Witte, M. Zamzow, H. Ran, B. Quinn, J. Matsuda, and G. A. Grabowski Combined saposin C and D deficiencies in mice lead to a neuronopathic phenotype, glucosylceramide and {alpha}-hydroxy ceramide accumulation, and altered prosaposin trafficking Hum. Mol. Genet., April 15, 2007; 16(8): 957 - 971. [Abstract] [Full Text] [PDF]

				R. S. Kiss, Z. Ma, K. Nakada-Tsukui, E. Brugnera, G. Vassiliou, H. M. McBride, K. S. Ravichandran, and Y. L. Marcel The Lipoprotein Receptor-related Protein-1 (LRP) Adapter Protein GULP Mediates Trafficking of the LRP Ligand Prosaposin, Leading to Sphingolipid and Free Cholesterol Accumulation in Late Endosomes and Impaired Efflux J. Biol. Chem., April 28, 2006; 281(17): 12081 - 12092. [Abstract] [Full Text] [PDF]

				Y. Sun, B. Quinn, D. P. Witte, and G. A. Grabowski Gaucher disease mouse models: point mutations at the acid {beta}-glucosidase locus combined with low-level prosaposin expression lead to disease variants J. Lipid Res., October 1, 2005; 46(10): 2102 - 2113. [Abstract] [Full Text] [PDF]

				Y. Sun, X. Qi, and G. A. Grabowski Saposin C Is Required for Normal Resistance of Acid {beta}-Glucosidase to Proteolytic Degradation J. Biol. Chem., August 22, 2003; 278(34): 31918 - 31923. [Abstract] [Full Text] [PDF]

				H. Hulkova, M. Cervenkova, J. Ledvinova, M. Tochackova, M. Hrebicek, H. Poupetova, A. Befekadu, L. Berna, B.C. Paton, K. Harzer, et al. A novel mutation in the coding region of the prosaposin gene leads to a complete deficiency of prosaposin and saposins, and is associated with a complex sphingolipidosis dominated by lactosylceramide accumulation Hum. Mol. Genet., April 1, 2001; 10(9): 927 - 940. [Abstract] [Full Text] [PDF]

				J. A. Johnston, C. L. Ward, and R. R. Kopito Aggresomes: A Cellular Response to Misfolded Proteins J. Cell Biol., December 28, 1998; 143(7): 1883 - 1898. [Abstract] [Full Text] [PDF]

				Q. Zhao and C. R. Morales Identification of a Novel Sequence Involved in Lysosomal Sorting of the Sphingolipid Activator Protein Prosaposin J. Biol. Chem., August 4, 2000; 275(32): 24829 - 24839. [Abstract] [Full Text] [PDF]