title: Biosynthesis and processing of the type II insulin-like growth factor receptor in H-35 hepatoma cells.
abstract: The biosynthesis and post-translational processing of the insulin-like growth factor II (IGF-II) receptor has been studied in H-35 hepatoma cells using a specific polyclonal anti-receptor immunoglobulin preparation. Cells were pulse-labeled with [35S]methionine followed by incubation with excess unlabeled methionine (chase). Gel electrophoresis of the immunoadsorbed receptors shows that the receptor is first synthesized as a 245-kDa precursor which is transformed to the mature 250-kDa form with a half-time of about 2 h. The 245-kDa precursor could also be labeled biosynthetically with [3H]mannose, only one-half of which was ultimately found associated with the 250-kDa product. Neuraminidase converts the 250-kDa receptor species to a 245-kDa form. Whereas the 250-kDa receptor is insensitive to detectable cleavage by endoglycosidase H, digestion of the 245-kDa species with this enzyme produces a 232-kDa form. A similar 232-kDa receptor species accumulates in H-35 cells incubated with tunicamycin (2 micrograms/ml). This tunicamycin-induced aglyco-receptor is not further processed to the 250-kDa form. Monensin (50 nM) blocks receptor processing at the 245-kDa stage. Endoglycosidase H treatment of the monensin-induced 245-kDa species indicates that this is a mixture of partially processed precursors having equivalent Mr. No evidence was obtained for the presence of O-linked oligosaccharides on the IGF-II receptor. The IGF-II binding activity of the three different biosynthetic forms of the receptor was assessed by affinity cross-linking of 125I-IGF-II to the receptors using disuccinimidyl suberate. Both the mature 250-kDa receptor and the neuraminidase-digested 245-kDa form specifically bound 125-I-IGF-II. However, the 232-kDa aglyco-receptor had no detectable IGF-II binding activity using this method. In summary, these studies show: 1) that the H-35 cell IGF-II receptor is synthesized first as a 245-kDa precursor having 4-6 high-mannose oligosaccharide side chains, 2) processing of the receptor oligosaccharides by mannose removal and terminal sialylation converts the 245-kDa precursor to the 250-kDa mature product which has been previously identified as the functional receptor in the plasma membrane, 3) the apparent molecular mass of the receptor in the absence of N-glycosylation is 232-kDa, and 4) glycosylation of the IGF-II receptor is required for the acquisition of IGF-II binding activity.
authors.forename: R G
authors.initials: RG
authors.lastname: MacDonald
authors.forename: M P
authors.initials: MP
authors.lastname: Czech
mesh_terms: D000818:Animals; D002460:Cell Line; D006026:Glycoside Hydrolases; D007700:Kinetics; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D008715:Methionine / Q000378:metabolism; D008970:Molecular Weight; D011499:Protein Processing, Post-Translational; D051381:Rats; D011956:Receptors, Cell Surface / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013462:Sulfur Radioisotopes
chemical_list: D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013462:Sulfur Radioisotopes; D008715:Methionine; D006026:Glycoside Hydrolases; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase