title: Proteasome components with reciprocal expression to that of the MHC-encoded LMP proteins.
abstract: BACKGROUND
  Intracellular proteins are processed into small peptides that bind HLA class I molecules of the major histocompatibility complex (MHC) in order to be presented to T lymphocytes. The proteasome, a multi-subunit protease, has recently been implicated in the generation of these peptides. Two genes encoding proteasome subunits, LMP2 and LMP7, are tightly linked to the TAP peptide transport loci in the class II region of the human MHC. Inclusion of the LMP subunits may alter proteasome activity, biasing it towards the production of peptides with carboxyl termini appropriate for binding HLA class I molecules. Nevertheless, mutant cells that lack the LMP genes are able to process and present antigens at the cell surface at similar levels to wild-type cells. These results raise questions about the role of the proteasome, and in particular of the LMP subunits, in antigen processing.
  
  
  RESULTS
  We have cloned the genes encoding a new proteasome subunit, MB1, which is closely related to LMP7, and that encoding a second subunit, Delta, which is closely related to LMP2. Expression of the MB1 and delta genes is reciprocal to that of the LMP genes: MB1 and delta are up-regulated in mutant cell lines lacking LMPs and down-regulated in the presence of gamma-interferon. The MB1 and delta genes are found to be located on chromosomes 14 and 17, respectively, raising interesting evolutionary questions about how the LMP genes independently became incorporated into the MHC.
  
  
  CONCLUSIONS
  We suggest that the subtle phenotype of LMP-deficient cell lines results from the compensatory expression in these lines of two other proteasome subunits, MB1 and Delta.
authors: Human Immunogenetics Laboratory, Imperial Cancer Research Fund, Holborn, London, UK.
authors: M P
authors: MP
authors: Belich
authors: R J
authors: RJ
authors: Glynne
authors: G
authors: G
authors: Senger
authors: D
authors: D
authors: Sheer
authors: J
authors: J
authors: Trowsdale
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002460:Cell Line; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics; D005786:Gene Expression Regulation; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007371:Interferon-gamma / Q000494:pharmacology; D008285:Major Histocompatibility Complex; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics*; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000235:genetics*; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D009097:Multienzyme Complexes; D011506:Proteins; D012333:RNA, Messenger; C071313:LMP-2 protein; D007371:Interferon-gamma; D003546:Cysteine Endopeptidases; C077436:LMP7 protein; D046988:Proteasome Endopeptidase Complex