HLA-A2 molecules in an antigen-processing mutant cell contain signal sequence-derived peptides.
The mutant human cell line T2 is defective in antigen presentation in the context of class I major histocompatibility complex (MHC) molecules, and also in that transfected T2 cells show poor surface expression of exogenous human class I (HLA) alleles. Both defects are thought to lie in the transport of antigenic peptides derived from cytosolic proteins into the endoplasmic reticulum (ER), as peptide-deficient class I molecules might be expected to be either unstable or retained in the ER. The products of several mouse class I (H-2) genes, and the endogenous gene HLA-A2 do, however, reach the surface of T2 cells at reasonable levels although they are non-functional. We report here that, as expected, poorly surface-expressed HLA molecules do not significantly bind endogenous peptides. Surprisingly, H-2 molecules expressed in T2 also lack associated peptides, arguing that 'empty' complexes of mouse class I glycoproteins with human beta 2-microglobulin are neither retained in the ER nor unstable. HLA-A2 molecules, however, do bind high levels of a limited set of endogenous peptides. We have sequenced three of these peptides and find that two, a 9-mer and an 11-mer, are derived from a putative signal sequence (of IP-30, an interferon-gamma-inducible protein), whereas a third, a 13-mer, is of unknown origin. The unusual length of two of the peptides argues that the 9-mers normally associated with HLA-A2 molecules may be generated before their transport from the cytosol rather than in a pre-Golgi compartment. To our knowledge, this is the first report of the isolation of a fragment of a eukaryotic signal peptide generated in vivo.
Wei
M L
ML
Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina 27710.
Cresswell
P
P
D000483:Alleles; D000595:Amino Acid Sequence; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D005805:Genes, MHC Class I; D006680:HLA Antigens; D015234:HLA-A Antigens / Q000235:genetics / Q000302:isolation & purification; D015789:HLA-A2 Antigen / Q000235:genetics*; D015235:HLA-B Antigens / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D008285:Major Histocompatibility Complex; D008969:Molecular Sequence Data; D009154:Mutation; D014162:Transfection
D006680:HLA Antigens; D015234:HLA-A Antigens; D015789:HLA-A2 Antigen; D015235:HLA-B Antigens