Heink S, Ludwig D, Kloetzel PM, Kruger EIFN-gamma-induced immune adaptation of the proteasome system is an accelerated and transient response. Proc Natl Acad Sci USA 102(26): 9241-9246

Institute of Biochemistry, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 07/2005; 102(26):9241-6. DOI: 10.1073/pnas.0501711102
Source: PubMed

ABSTRACT Peptide generation by the proteasome is rate-limiting in MHC class I-restricted antigen presentation in response to IFN-gamma. IFN-gamma-induced de novo formation of immunoproteasomes, therefore, essentially supports the rapid adjustment of the mammalian immune system. Here, we report that the molecular interplay between the proteasome maturation protein (POMP) and the proteasomal beta5i subunit low molecular weight protein 7 (LMP7) has a key position in this immune adaptive program. IFN-gamma-induced coincident biosynthesis of POMP and LMP7 and their direct interaction essentially accelerate immunoproteasome biogenesis compared with constitutive 20S proteasome assembly. The dynamics of this process is determined by rapid LMP7 activation and the immediate LMP7-dependent degradation of POMP. Silencing of POMP expression impairs recruitment of both beta5 subunits into the proteasome complex, resulting in decreased proteasome activity, reduced MHC class I surface expression, and induction of apoptosis. Furthermore, our data reveal that immunoproteasomes exhibit a considerably shortened half-life, compared with constitutive proteasomes. In consequence, our studies demonstrate that the cytokine-induced rapid immune adaptation of the proteasome system is a tightly regulated and transient response allowing cells to return rapidly to a normal situation once immunoproteasome function is no longer required.

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Available from: Elke Krüger, Sep 28, 2015
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    • "We stably transfected U2OS cells to express POMP with its wild-type 3 0 UTR or with a mutant 3 0 UTR that contains four base exchanges at each of the two miR-101-binding sites to eliminate base pairing with the miR- 101 seed sequence (Figure S3). The overexpression of POMP only resulted in enhanced mRNA levels, but not protein levels (Figures 3D and 3E), due to previously described feedback regulation of POMP (Heink et al., 2005). When transfected with miR- 101, the cells containing the wild-type construct showed severely reduced POMP levels and increased amounts of ubiquitinated proteins; in contrast, the mutation in the 3 0 UTR was enough to abolish both effects completely (Figure 3F). "
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    ABSTRACT: Proteasome inhibition represents a promising strategy of cancer pharmacotherapy, but resistant tumor cells often emerge. Here we show that the microRNA-101 (miR-101) targets the proteasome maturation protein POMP, leading to impaired proteasome assembly and activity, and resulting in accumulation of p53 and cyclin-dependent kinase inhibitors, cell cycle arrest, and apoptosis. miR-101-resistant POMP restores proper turnover of proteasome substrates and re-enables tumor cell growth. In ERα-positive breast cancers, miR-101 and POMP levels are inversely correlated, and high miR-101 expression or low POMP expression associates with prolonged survival. Mechanistically, miR-101 expression or POMP knockdown attenuated estrogen-driven transcription. Finally, suppressing POMP is sufficient to overcome tumor cell resistance to the proteasome inhibitor bortezomib. Taken together, proteasome activity can not only be manipulated through drugs, but is also subject to endogenous regulation through miR-101, which targets proteasome biogenesis to control overall protein turnover and tumor cell proliferation. Copyright © 2015 Elsevier Inc. All rights reserved.
    Molecular cell 07/2015; 59(2). DOI:10.1016/j.molcel.2015.05.036 · 14.02 Impact Factor
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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
    • "It is not clear whether the upregulation of immunoproteasome levels reflects a compensatory and homeostatic effect after initial downregulation during bortezomib resistance development. Importantly, increased β5i expression can drive incorporation of immunoproteasome subunits into prototypic immunoproteasomes [32] or facilitate assembly in hybrid types of proteasomes (β1 + β2 + β5i and β1i + β2 + β5i) [33]. Conceivably, these hybrid forms could compensate for impaired catalytic activity of constitutive proteasomes assembled with a mutated β5-subunit. "
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    ABSTRACT: Despite encouraging results with the proteasome inhibitor bortezomib in the treatment of hematologic malignancies, emergence of resistance can limit its efficacy, hence calling for novel strategies to overcome bortezomib-resistance. We previously showed that bortezomib-resistant human leukemia cell lines expressed significantly lower levels of immunoproteasome at the expense of constitutive proteasomes, which harbored point mutations in exon 2 of the PSMB5 gene encoding the beta5 subunit. Here we investigated whether up-regulation of immunoproteasomes by exposure to interferon-gamma restores sensitivity to bortezomib in myeloma and leukemia cell lines with acquired resistance to bortezomib. RPMI-8226 myeloma, THP1 monocytic/macrophage and CCRF-CEM (T) parental cells and sub lines with acquired resistance to bortezomib were exposed to Interferon-gamma for 24-48h where after the effects on proteasome subunit expression and activity were measured, next to sensitivity measurements to proteasome inhibitors bortezomib, carfilzomib, and the immunoproteasome selective inhibitor ONX 0914. At last, siRNA knockdown experiments of beta5i and beta1i were performed to identify the contribution of these subunits to sensitivity to proteasome inhibition. Statistical significance of the differences were determined using the Mann-Whitney U test. Interferon-gamma exposure markedly increased immunoproteasome subunit mRNA to a significantly higher level in bortezomib-resistant cells (up to 30-fold, 10-fold, and 6-fold, in beta1i, beta5i, and beta2i, respectively) than in parental cells. These increases were paralleled by elevated immunoproteasome protein levels and catalytic activity, as well as HLA class-I. Moreover, interferon-gamma exposure reinforced sensitization of bortezomib-resistant tumor cells to bortezomib and carfilzomib, but most prominently to ONX 0914, as confirmed by cell growth inhibition studies, proteasome inhibitor-induced apoptosis, activation of PARP cleavage and accumulation of polyubiquitinated proteins. This sensitization was abrogated by siRNA silencing of beta5i but not by beta1i silencing, prior to pulse exposure to interferon-gamma. Downregulation of beta5i subunit expression is a major determinant in acquisition of bortezomib-resistance and enhancement of its proteasomal assembly after induction by interferon-gamma facilitates restoration of sensitivity in bortezomib-resistant leukemia cells towards bortezomib and next generation (immuno) proteasome inhibitors.
    Journal of Hematology & Oncology 01/2014; 7(1):7. DOI:10.1186/1756-8722-7-7 · 4.81 Impact Factor
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