title: Novel dipeptide aldehydes are proteasome inhibitors and block the MHC-I antigen-processing pathway.
abstract: Class I MHC (MHC-I) molecules present peptides derived from Ag that are processed in the cytosol. The proteasome is a multicatalytic protease complex that is present in the cytosol and has been implicated in cytosolic Ag processing. Novel dipeptide aldehydes were designed, synthesized, and demonstrated to specifically inhibit the chymotrypsin-like protease activity of isolated proteasomes, but produced relatively little inhibition of cathepsin B, a vacuolar cysteine protease. The inhibitors were membrane permeable and inhibited intracellular cleavage of a membrane-permeable fluorogenic substrate of the chymotrypsin-like proteasome activity. When a model Ag, OVA, was introduced into the cytoplasm of M12.B6 murine B cells by electroporation, the proteasome inhibitors blocked its processing for subsequent presentation by MHC-I molecules. The inhibitors had little effect on class II MHC processing of exogenous Ag. The potencies of different inhibitors for blockade of MHC-I Ag processing correlated directly with their potencies for inhibition of the chymotrypsin-like proteasome activity. In contrast, conventional inhibitors of vacuolar cysteine proteases (e.g., leupeptin and benzyloxycarbonyl-Phe-Ala-CHN2) had little effect on MHC-I processing or the chymotryspin-like activity of isolated proteasomes. These results directly demonstrate that inhibition of proteasome activity blocks MHC-I Ag processing, confirming a role for proteasomes in this pathway. Moreover, they suggest that the chymotrypsin-like activity of the proteasome may be of major importance to the cytosolic processing of at least some Ag.
authors.affiliation: Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: C V
authors.initials: CV
authors.lastname: Harding
authors.forename: J
authors.initials: J
authors.lastname: France
authors.forename: R
authors.initials: R
authors.lastname: Song
authors.forename: J M
authors.initials: JM
authors.lastname: Farah
authors.forename: S
authors.initials: S
authors.lastname: Chatterjee
authors.forename: M
authors.initials: M
authors.lastname: Iqbal
authors.forename: R
authors.initials: R
authors.lastname: Siman
mesh_terms: D000447:Aldehydes / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects*; D002918:Chymotrypsin / Q000502:physiology; D003546:Cysteine Endopeptidases / Q000187:drug effects* / Q000502:physiology; D004151:Dipeptides / Q000494:pharmacology*; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000187:drug effects* / Q000502:physiology; D046988:Proteasome Endopeptidase Complex
chemical_list: D000447:Aldehydes; D004151:Dipeptides; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D009097:Multienzyme Complexes; D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex