title: HLA-DM interactions with intermediates in HLA-DR maturation and a role for HLA-DM in stabilizing empty HLA-DR molecules.
abstract: Major histocompatibility complex (MHC) class II-positive cell lines which lack HLA-DM expression accumulate class II molecules associated with residual invariant (I) chain fragments (class II-associated invariant chain peptides [CLIP]). In vitro, HLA-DM catalyzes CLIP dissociation from class II-CLIP complexes, promoting binding of antigenic peptides. Here the physical interaction of HLA-DM with HLA-DR molecules was investigated. HLA-DM complexes with class II molecules were detectable transiently in cells, peaking at the time when the class II molecules entered the MHC class II compartment. HLA-DR alpha beta dimers newly released from I chain, and those associated with I chain fragments, were found to associate with HLA-DM in vivo. Mature, peptide-loaded DR molecules also associated at a low level. These same species, but not DR-I chain complexes, were also shown to bind to purified HLA-DM molecules in vitro. HLA-DM interaction was quantitatively superior with DR molecules isolated in association with CLIP. DM-DR complexes generated by incubating HLA-DM with purified DR alpha beta CLIP contained virtually no associated CLIP, suggesting that this superior interaction reflects a prolonged HLA-DM association with empty class II dimers after CLIP dissociation. Incubation of peptide-free alpha beta dimers in the presence of HLA-DM was found to prolong their ability to bind subsequently added antigenic peptides. Stabilization of empty class II molecules may be an important property of HLA-DM in facilitating antigen processing.
authors.affiliation: Howard Hughes Medical Institute, Yale University School of Medicine, Section of Immunobiology, New Haven, Connecticut 06510, USA.
authors.forename: L K
authors.initials: LK
authors.lastname: Denzin
authors.forename: C
authors.initials: C
authors.lastname: Hammond
authors.forename: P
authors.initials: P
authors.lastname: Cresswell
mesh_terms: D000595:Amino Acid Sequence; D002461:Cell Line, Transformed; D019281:Dimerization; D006681:HLA-D Antigens / Q000096:biosynthesis / Q000276:immunology*; D006684:HLA-DR Antigens / Q000276:immunology*; D015803:HLA-DR3 Antigen / Q000096:biosynthesis / Q000737:chemistry / Q000276:immunology*; D000949:Histocompatibility Antigens Class II; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000276:immunology; D011485:Protein Binding; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: C416189:H2-M antigens; D006681:HLA-D Antigens; C084245:HLA-DM antigens; D006684:HLA-DR Antigens; D015803:HLA-DR3 Antigen; D000949:Histocompatibility Antigens Class II; D010446:Peptide Fragments