Addition of a mannose-6-phosphate-containing oligosaccharide alters cellular processing of low density lipoprotein by parental and LDL-receptor-defective Chinese hamster ovary cells.
Low density lipoprotein (LDL) was chemically modified by the addition of omega-(6-phospho)-tetra(alpha 1-3)mannosyl-(alpha 1-2)mannose (M56P), a phosphorylated oligosaccharide containing a terminal mannose 6-phosphate residue. Uptake and degradation of this modified LDL (M56P-LDL) by Chinese hamster ovary (CHO) cells occurred via the lysosomal enzyme (mannose 6-phosphate) receptor pathway. Cellular processing of M56P-LDL was saturable, specific for the mannose 6-phosphate marker, and occurred with approximately threefold higher affinity than that of native LDL by the LDL receptor pathway. Mannose 6-phosphate receptor activity, as measured by degradation of M56P-LDL, was ninefold lower than the LDL receptor activity. Degradation of M56P-LDL was more sensitive to inhibition by the lysosomotropic agent chloroquine than was degradation of LDL, suggesting differences in the intracellular processing of mannose 6-phosphate-bearing ligands and LDL. Previously isolated CHO cell lines defective in LDL receptor activity resembled parental CHO cells in their ability to process M56P-LDL. The potential use of M56P-LDL in the isolation of cells with pleiotropic mutations affecting receptor-mediated endocytosis is discussed.
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D004587:Electrophoresis, Agar Gel; D005260:Female; D006600:Hexosephosphates / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008360:Mannosephosphates / Q000378:metabolism*; D009844:Oligosaccharides / Q000378:metabolism; D010053:Ovary / Q000378:metabolism; D017527:Receptor, IGF Type 2; D011973:Receptors, LDL / Q000378:metabolism*
D002352:Carrier Proteins; D006600:Hexosephosphates; D008077:Lipoproteins, LDL; D008360:Mannosephosphates; D009844:Oligosaccharides; D017527:Receptor, IGF Type 2; D011973:Receptors, LDL; C027693:mannose-6-phosphate; D002738:Chloroquine; D000469:Alkaline Phosphatase