Regulation of glycosylation of Lamp-1 in the bovine renal epithelial cell line NBL-1 by changes in the concentration of extracellular phosphate.
We have identified the bovine renal homologue of Lamp-1 (lysosomal-associated membrane glycoprotein 1). It has very similar physical characteristics to other Lamp-1 proteins from a wide variety of tissues and species. Partial sequence analysis has shown it to be 61% identical with human Lamp-1 and about 50% identical with rat and mouse Lamp-1. The extent of glycosylation of bovine Lamp-1 alters in response to changes in the concentration of extracellular phosphate. Bovine renal epithelial cells (NBL-1) grown in normal or phosphate-starved medium contain Lamp-1 of 120 kDa. However, if cells are grown in medium containing 8-10 mM phosphate, they contain Lamp-1 of only 100 kDa. The core protein and mRNA levels have been shown to remain constant under both conditions. Therefore the only conclusion is that the extent of Lamp-1 glycosylation must be changing in response to the extracellular concentration of phosphate. Unlike Carlsson and Fukuda [(1990) J. Biol. Chem. 265, 20488-20495], who showed that the human Lamp-1 protein contained polylactosaminoglycan residues, we have been unable to demonstrate the partial deglycosylation of bovine Lamp-1 by endo-beta-galactosidase. This enzyme removes polylactosaminoglycan groups from glycoproteins, and therefore indicates that the carbohydrate structure of bovine Lamp-1 is probably different from that of other Lamp-1 proteins. At present the physiological importance of bovine renal Lamp-1 and the changes in its extent of glycosylation are unknown. In this paper we postulate that Lamp-1 may be involved in the cycling of plasma-membrane proteins to the lysosome. This is based on the finding that the only other known effect of high extracellular phosphate on NBL-1 cells is to cause a decrease in the Vmax. of plasma-membrane-associated Na(+)-dependent phosphate transport [Helps and McGivan (1991) Eur. J. Biochem. 200, 797-803].
Helps
C R
CR
Department of Biochemistry, School of Medical Sciences, University Walk, Bristol, U.K.
McGivan
J D
JD
D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D001345:Autoradiography; D001483:Base Sequence; D001693:Biological Transport, Active; D015152:Blotting, Northern; D015153:Blotting, Western; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002846:Chromatography, Affinity; D017931:DNA Primers / Q000737:chemistry; D003720:Densitometry; D004591:Electrophoresis, Polyacrylamide Gel; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D007668:Kidney / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
D015703:Antigens, CD; D017931:DNA Primers; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D010710:Phosphates