butabindide and epoxomicin

A significant fraction of the HLA-B27-bound peptide repertoire is resistant to proteasome inhibitors. The possible implication of tripeptidyl peptidase II (TPPII) in generating this subset was analyzed by quantifying the surface re-expression of HLA-B*2705 after acid stripping in the presence of two TPPII inhibitors, butabindide and Ala-Ala-Phe-chloromethylketone. Neither decreased HLA-B27 re-expression under conditions in which TPPII activity was largely inhibited. This was in contrast to a significant effect of the proteasome inhibitor epoxomicin. The failure of TPPII inhibition to decrease surface re-expression was not limited to HLA-B27, since it was also observed in several HLA-B27-negative cell lines, including Mel JuSo. Actually, HLA class I re-expression in Mel JuSo cells increased as a function of butabindide concentration, which is consistent with an involvement of TPPII in destroying HLA class I ligands. Inhibition of TPPII with small interfering RNA also failed to decrease the surface expression of HLA class I molecules on 143B cells. Our results indicate that TPPII is dispensable for the generation of proteasome-dependent HLA class I ligands and, without excluding its role in producing some individual epitopes, this enzyme is not involved to any quantitatively significant extent, in generating the proteasome-independent HLA-B27-bound peptide repertoire.

Topics: Acids; Amino Acid Chloromethyl Ketones; Aminopeptidases; Antigen Presentation; Brefeldin A; Cell Line; Cell Line, Tumor; Coumarins; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; Drug Stability; Histocompatibility Antigens Class I; HLA-B27 Antigen; Humans; Hydrogen-Ion Concentration; Indoles; Lymphocytes; Oligopeptides; Proteasome Endopeptidase Complex; RNA Interference; RNA, Small Interfering; Serine Endopeptidases; Serine Proteinase Inhibitors