Murine Ia-associated invariant chain's processing to complex oligosaccharide forms and its dissociation from the I-Ak complex.
The processing of murine invariant chain (Ii) to a cell surface form bearing complex N-linked oligosaccharides has been demonstrated in the B cell lymphoma, AKTB-1b. In addition, the rate of processing of pulse-labeled Ii has been determined relative to its rate of dissociation from the alpha/beta complex of I-Ak. Ii, alpha-, and beta-chains were immunoprecipitated with anti-I-Ak or anti-Ii monoclonal antibodies. The heretofore uncharacterized complex oligosaccharide form of Ii (Ii-c) was identified in gel-purified immunoprecipitates by peptide mapping with reverse-phase HPLC. Ii-c is resistant to deglycosylation by Endo H, which is specific for high-mannose N-linkages, but can be digested with Endo F, a glycosidase capable of cleaving both complex and high-mannose N-linked oligosaccharides. Immunoprecipitation of surface iodinated cells indicates that Ii-c is expressed on the plasma membrane. Pulse-chase metabolic labeling data show that the processing of Ii to Ii-c occurs with a t1/2 of about 120 min. In contrast, the processing of both alpha- and beta-chains of I-Ak to complex forms occurs with a t1/2 of 15 to 20 min. Our data show that Ii-hm begins to dissociate rapidly from the I-Ak complex after 100 to 120 min of chase. Only a small amount (less than 5% on a per mole basis) of Ii-c was found associated with the I-Ak complexes after 300 min of continuous metabolic labeling. These results are consistent with Ii serving as a carrier for Ia antigens as they are transported to the cell surface. In addition, they suggest that the processing of Ii to Ii-c, or a late processing event of the alpha- and beta-chains, such as their sialylation, may be a possible mechanism for inducing the dissociation of Ii from the I-Ak complex.
D000818:Animals; D000954:Antigens, Surface / Q000032:analysis; D001402:B-Lymphocytes / Q000378:metabolism; D001692:Biological Transport; D002236:Carbohydrate Conformation; D014644:Genetic Variation; D006023:Glycoproteins / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000235:genetics*; D007942:Leukemia, Experimental / Q000378:metabolism; D008223:Lymphoma / Q000378:metabolism; D051379:Mice; D008806:Mice, Inbred AKR; D009844:Oligosaccharides / Q000378:metabolism*; D010446:Peptide Fragments; D011499:Protein Processing, Post-Translational; D013347:Subcellular Fractions / Q000378:metabolism; D014357:Trypsin
D000954:Antigens, Surface; D006023:Glycoproteins; D000949:Histocompatibility Antigens Class II; D009844:Oligosaccharides; D010446:Peptide Fragments; D014357:Trypsin