title: Saposin C-LBPA interaction in late-endosomes/lysosomes.
abstract: Acidic phospholipids and saposins associations are involved in the degradation process of glycosphingolipids/sphingolipids in late endosomes/lysosomes. In this report, we showed the colocalization of saposin C and lysobisphosphatidic acid (LBPA) in human fibroblasts by using cytoimmunofluorescence analysis. This colocalization pattern was not seen with other saposins. Large numbers of saposins A, B, and D illustrated the staining patterns that differ from LBPA. In addition, ingested anti-LBPA antibody altered the location of saposin C in human wild-type fibroblasts. In vitro assays demonstrated that saposin C at nM concentrations induced membrane fusion of LBPA containing phospholipid vesicles. Under the same condition, other saposins had no fusion induction on these vesicles. These results suggested a specific interaction between saposin C and LBPA. Total saposin-deficient fibroblasts showed a massive accumulation of multivesicular bodies (MVBs) by electron microscopic analysis. No significant increase of MVBs was found in saposins A and B deficient cells. Interestingly, the accumulated MVBs were significantly reduced by loading saposin C alone into the total saposin-deficient cells. Therefore, we propose that saposin C-LBPA interaction plays a role in the regulation of MVB formation in cells.
authors.affiliation: Division and Program in Human Genetics, Children's Hospital Research Foundation, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, USA.
authors.forename: Zhengtao
authors.initials: Z
authors.lastname: Chu
authors.forename: David P
authors.initials: DP
authors.lastname: Witte
authors.forename: Xiaoyang
authors.initials: X
authors.lastname: Qi
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D011992:Endosomes / Q000378:metabolism* / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006801:Humans; D066298:In Vitro Techniques; D008081:Liposomes; D008246:Lysophospholipids / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism* / Q000648:ultrastructure; D008561:Membrane Fusion; D051379:Mice; D008854:Microscopy, Electron; D050178:Monoglycerides; D011498:Protein Precursors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D049231:Saposins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D008081:Liposomes; D008246:Lysophospholipids; D050178:Monoglycerides; D011498:Protein Precursors; D049231:Saposins; C012786:bis(monoacylglyceryl)phosphate