PA28 and the proteasome immunosubunits play a central and independent role in the production of MHC class I-binding peptides in vivo

Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, The Netherlands.
European Journal of Immunology (Impact Factor: 4.03). 04/2011; 41(4):926-35. DOI: 10.1002/eji.201041040
Source: PubMed


Proteasomes play a fundamental role in the processing of intracellular antigens into peptides that bind to MHC class I molecules for the presentation of CD8(+) T cells. Three IFN-γ-inducible catalytic proteasome (immuno)subunits as well as the IFN-γ-inducible proteasome activator PA28 dramatically accelerate the generation of a subset of MHC class I-presented antigenic peptides. To determine whether these IFN-γ-inducible proteasome components play a compounded role in antigen processing, we generated mice lacking both PA28 and immunosubunits β5i/LMP7 and β2i/MECL-1. Analyses of MHC class I cell-surface levels ex vivo demonstrated that PA28 deficiency reduced the production of MHC class I-binding peptides both in cells with and without immunosubunits, in the latter cells further decreasing an already diminished production of MHC ligands in the absence of immunoproteasomes. In contrast, the immunosubunits but not PA28 appeared to be of critical importance for the induction of CD8(+) T-cell responses to multiple dominant Influenza and Listeria-derived epitopes. Taken together, our data demonstrate that PA28 and the proteasome immunosubunits use fundamentally different mechanisms to enhance the supply of MHC class I-binding peptides; however, only the immunosubunit-imposed effects on proteolytic epitope processing appear to have substantial influence on the specificity of pathogen-specific CD8(+) T-cell responses.

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Available from: E.J.A.M. Sijts, Oct 04, 2015
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    • "The subunit replacements and the association of the 11S regulator to at least one end of the 20S core alter the cleavage pattern of the proteasome, optimizing the generation of small peptides for loading on the groove of MHC class I molecules [25]–[27]. These changes are also related to increase the production of immunogenic peptides compared to standard proteasome [28], [29]. "
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    ABSTRACT: Generally, Trypanosoma cruzi infection in human is persistent and tends to chronicity, suggesting that the parasite evade the immune surveillance by down regulating the intracellular antigen processing routes. Within the MHC class I pathway, the majority of antigenic peptides are generated by the proteasome. However, upon IFN-γ stimulation, the catalytic constitutive subunits of the proteasome are replaced by the subunits β1i/LMP2, β2i/MECL-1 and β5i/LMP7 to form the immunoproteasome. In this scenario, we analyzed whether the expression and activity of the constitutive and the immunoproteasome as well as the expression of other components of the MHC class I pathway are altered during the infection of HeLa cells with T. cruzi. By RT-PCR and two-dimensional gel electrophoresis analysis, we showed that the expression and composition of the constitutive proteasome is not affected by the parasite. In contrast, the biosynthesis of the β1i, β2i, β5i immunosubunits, PA28β, TAP1 and the MHC class I molecule as well as the proteasomal proteolytic activities were down-regulated in infected-IFN-γ-treated cell cultures. Taken together, our results provide evidence that the protozoan T. cruzi specifically modulates its infection through an unknown posttranscriptional mechanism that inhibits the expression of the MHC class I pathway components.
    PLoS ONE 04/2014; 9(4):e95977. DOI:10.1371/journal.pone.0095977 · 3.23 Impact Factor
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    • "However, this speculation still needs further investigation. It was thought that PA28a/b complexes have a role of activating proteasomes to generate the antigenic peptides presented by MHC class I molecules [27] [32]. Therefore, interfering effect of Naa10p on PA28-regulated chymotrypsin-like proteasome activity might impair tumor antigenic peptides presentation, or shift the repertoire of tumor-associated antigens presented by MHC class I, which may result in cells escaping from immunosurveillance and malignant transformation. "
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    ABSTRACT: N-α-acetyltransferase 10 protein (Naa10p) regulates various pathways associated with cancer cell proliferation, metastasis, apoptosis and autophagy. However, its role in protein quality control is unknown. Here, we report that Naa10p is physically associated with proteasome activator 28β (PA28β). Naa10p also interacts with PA28α in a PA28β-dependent manner. Naa10p negatively regulates PA28-dependent chymotrypsin-like proteasome activity in cancer cells and in a cell-free system reconstituted with purified proteins, which was not related to 26S proteasome. Acetyltransferase activity of Naa10p isn't required for its effect on chymotrypsin-like proteasome activity. Therefore, our data reveal that Naa10p suppresses 28S proteasome activity through interaction with PA28β. STRUCTURED SUMMARY OF PROTEIN INTERACTIONS: Naa10pphysically interactswithPS28alphaandPS28 betabyanti bait coimmunoprecipitation(View Interaction:1,2).
    FEBS letters 04/2013; 587(11). DOI:10.1016/j.febslet.2013.04.016 · 3.17 Impact Factor
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    • "The decrease of Pcmt1 by PCP therefore concurs with the observed upregulation of Mapk1. Proteasome activator subunit 1 (Psme1 or PA28alpha) is a part of the protein degradation process and the production of antigenic peptides [38]. Psme1 also enhances degradation of oxidized proteins and is protective against apoptosis induced by oxidative stress [39]. "
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