Abstract
Prosaposin is the precursor of four lysosomal saposins that promote the degradation of glycosphingolipids (GSLs) by acidic hydrolases. GSLs contain a hydrophobic ceramide moiety, which acts as a membrane anchor, and a hydrophilic oligosaccharide chain that faces the lumen of the Golgi apparatus and extracellular spaces. By using fumonisin B1, PDMP and D609, we tested the hypothesis that sphingolipids mediate the transport of prosaposin to the lysosomes. Fumonisin B1 interferes with the synthesis of ceramide, PDMP blocks the formation of glucosylceramide and D609 blocks the formation of sphingomyelin. Fumonisin B1 produced a 59–85% decrease in the density of gold particles in the lysosomes of CHO and NRK cells immunolabeled with anti-prosaposin antibody, and a 55% reduction in the lysosomes of CHO cells stably transfected with an expression vector containing a human prosaposin cDNA. To examine whether the mannose 6-phosphate receptor pathway was affected by this treatment, NRK and CHO cells treated or not with fumonisin B1 were labeled with anti-cathepsin A antibody. The results showed no significant differences in labeling of the lysosomes, suggesting that the effect of fumonisin B1 was specific. When fumonisin B1 and D609 were added to the media of transfected CHO cells, a decrease in immunofluorescence with anti-prosaposin antibody was observed by confocal microscopy. PDMP did not cause any reduction in immunoreactivity, indicating that sphingolmyelin appears to be involved in this process.▪In conclusion, our data support the hypothesis that sphingolipids, possibly sphingomyelin, are involved in the transport of prosaposin to the lysosomes.—Lefrancois, S., L. Michaud, M. Potier, S. Igdoura, and C. R. Morales. Role of sphingolipids in the transport of prosaposin to the lysosomes. J. Lipid Res. 1999. 40: 1593–1603.
Highlights
Prosaposin is the precursor of four lysosomal saposins that promote the degradation of glycosphingolipids (GSLs) by acidic hydrolases
GSLs contain a hydrophobic ceramide moiety, which acts as a membrane anchor, and a hydrophilic oligosaccharide chain, that faces the lumen of the Golgi apparatus and extracellular spaces [1]
Quantitative analysis of electron micrographs taken from Normal rat kidney (NRK) cells reacted with anti-prosaposin antibody demonstrated a decrease in density of colloidal gold labeling of 59% in the lysosomes of fumonisin B1-treated cells as compared to the non-treated NRK cells (Figs. 1b, 1c and Fig. 2)
Summary
Prosaposin is the precursor of four lysosomal saposins that promote the degradation of glycosphingolipids (GSLs) by acidic hydrolases. By using fumonisin B1, PDMP and D609, we tested the hypothesis that sphingolipids mediate the transport of prosaposin to the lysosomes. According to the first model, lysosomal hydrolases acquire a large pre-formed oligosaccharide side chain within the endoplasmic reticulum [3]. These proteins are transported to the Golgi apparatus where they are tagged with the M6P recognition signal and translocated to the lysosomes [7,8,9,10,11]. Proteins that are delivered to the lysosomal compartment by this mechanism display certain characteristics These proteins have a high number of Nlinked sialylated oligosaccharides on their luminal domain, a single membrane-spanning domain and a short C-terminal tail of about 10 or more amino acid residues extending in the cytoplasm [5]. Lysosomal acid phosphatase (LAP) which shares many of these characteristics has 7 or 8 N-linked oligosaccharides, a single trans-membrane do-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
