title: Biosynthetic transport of a major lysosomal membrane glycoprotein, lamp-1: convergence of biosynthetic and endocytic pathways occurs at three distinctive points.
abstract: We studied the kinetics of the biosynthetic transport of lysosome-associated membrane glycoprotein-1 (lamp-1) to the endocytic compartments in cultured rat hepatocytes. Newly synthesized lamp-1 (NS-lamp-1) was transported to the trans-Golgi from rough endoplasmic reticulum with a half time (t1/2) of 13 min. From the trans-Golgi, at least 25% of NS-lamp-1 was delivered to the cell periphery: to the cell surface and early endosomes with t1/2 s of 32 and 33 min, respectively. A comparison of the kinetics of the biosynthetic transport of lamp-1 to both compartments demonstrated that NS-lamp-1 takes two peripheral routes from the Golgi apparatus; it is delivered to early endosomes directly and after reaching the cell surface. A major portion of NS-lamp-1 follows a direct intracellular pathway to late endosomes (t1/2 = 45 min) and subsequently to lysosomes (t1/2 = 85 min). The kinetic data of the biosynthetic transport to these endocytic vacuoles suggested that a significant fraction of NS-lamp-1 returns to the late endosomes immediately after its arrival at lysosomes and that there is a unique retrograde delivery of NS-lamp-1 from late to early endosomes prior to its transport to lysosomes. Thus, in cultured rat hepatocytes, the lamp-1 biosynthetic and the endocytic pathways converge at the three distinctive points. Late endosomes are centrally situated in the complex biosynthetic route of lamp-1.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University, Hiroshima, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Akasaki
authors.forename: A
authors.initials: A
authors.lastname: Michihara
authors.forename: K
authors.initials: K
authors.lastname: Mibuka
authors.forename: Y
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: H
authors.initials: H
authors.lastname: Tsuji
mesh_terms: D000818:Animals; D000906:Antibodies; D015703:Antigens, CD / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D001345:Autoradiography; D002458:Cell Fractionation / Q000379:methods; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008562:Membrane Glycoproteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism; D008954:Models, Biological; D011205:Povidone; D011499:Protein Processing, Post-Translational; D051381:Rats; D017208:Rats, Wistar; D012822:Silicon Dioxide; D013462:Sulfur Radioisotopes; D013997:Time Factors
chemical_list: D000906:Antibodies; D015703:Antigens, CD; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D013462:Sulfur Radioisotopes; C016039:Percoll; D012822:Silicon Dioxide; D008715:Methionine; D011205:Povidone