Biosynthesis and glycosylation of the invariant chain associated with HLA-DR antigens.
The biosynthesis and glycosylation of the invariant (I) chain associated with HLA-DR alpha-beta chain complexes has been examined in human B lymphoblastoid cell lines. Two-dimensional polyacrylamide gel electrophoresis of HLA-DR immune precipitates from extracts of metabolically labeled cells demonstrated a processes form of the I chain, called Ip, which consists of a series of spots beginning near the basic I chain spot and ending near the acidic alpha spots. Pulse/chase labeling yielded information on the kinetics of processing of the invariant chain, as well as the finding that the association of Ip with alpha-beta chain complexes appears to be transient. Neuraminidase treatment of immune precipitates confirmed that Ip was a form of the I chain containing up to eight sialic acid residues. Labeling in the presence of tunicamycin suggested the presence of both N-linked and O-linked oligosaccharide units on the invariant chain. This processing pattern does not appear to be an artifact of B cell lines; it was seen in peripheral blood lymphocytes, freshly purified monocytes, and in an interleukin 2-dependent continuous T cell line that expressed HLA-DR. In addition, there appears to be a free pool of the invariant chain and its processed form that is not found associated with DR alpha and beta chains.
D001402:B-Lymphocytes / Q000378:metabolism*; D002478:Cells, Cultured; D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II / Q000502:physiology*; D006801:Humans; D007526:Isoelectric Point; D046911:Macromolecular Substances; D008970:Molecular Weight; D009439:Neuraminidase / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D014415:Tunicamycin / Q000494:pharmacology
D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II; D046911:Macromolecular Substances; D014415:Tunicamycin; D009439:Neuraminidase