Retention of glucose on oligosaccharide chains linked to the LH/hCG receptor prevents cell surface expression

In the first step of asparagine-linked oligosaccharide chain maturation, te rminal glucose residues are removed from the high mannose oligosaccharide c ore by glucosidases I and II. The role that glucose residues play in traffi cking the luteinizing hormone/human chorionic gonadotropin (LH/hCG) recepto r from the endoplasmic reticulum to the cell surface was investigated. Gluc osidases I and II were inhibited by incubating 293 T cells transiently tran sfected with LH/hCG receptor cDNA with 5 mM 1-deoxynojirimycin (DNJ). DNJ t reatment resulted in a marked reduction in cell surface [I-125]hCG binding. Similar results were obtained from glucosidase I-deficient Lec 23 Chinese hamster ovarian (CHO) cells and wild-type CHO cells that were transiently t ransfected with LH/hCG receptor cDNA Immunoprecipitation followed by Wester n blotting of transfected 293 T cells incubated in the presence or absence of 5 mM DNJ revealed that there is substantially less receptor in DNJ-treat ed cells than in control cells. These results show that the removal of gluc ose residues is necessary for trafficking the LH/hCG receptor to the cell s urface. (C) 2001 Academic Press.