Adaptation of proteasome composition in inflammatory response - the impact of the hybridproteasome
Final Report Abstract
The molecular mechanisms and cellular consequences of PA28α/β function are poorly understood. Using in vitro as well as in vivo models for induction of inflammatory response pathway upon TLR receptor engagement (ligands for TLR4 and TLR3) or viral infection (CVB3), we investigated cellular responses such as cell viability, the degradation capacity of proteasome complexes as mirrored by the abundance of oxidant-damaged and K48-ubiquitinated proteins as well as the antigen processing machinery with respect to the abundance of PA28-bound proteasome complexes. Since both the iproteasome and PA28 complexes are upregulated during inflammation, as a model for hybridproteasome PA28-20S-PA700 complex formation we generated mice lacking both intact iproteasome formation (LMP7-/-) as well as PA28αβ expression. Since PA28α/β complexes can associate with s-proteasome and i-proteasome 20S core particles resulting in the formation of PA28- capped 20S and PA700-20S proteasome complexes, we speculated that in addition to the iproteasome also the function of the s-proteasome 20S core particle might be influenced by association with PA28 in vivo. Overall, we obtained experimental evidence of facilitated antigen processing in the presence of both i-proteasomes and PA28 and an influence of the PA28 complex on the viral replication machinery. Facilitated liberation of the CVB3 epitope P3D2170-2177 within the context of epitope-harboring peptide processing by PA28-capped 20S proteasomes was also supportive for a biological function of PA28α/β during viral myocarditis. Moreover, our studies indicate that both PA28 and i-proteasome formation represent adaptor pathways to clear cells from protein aggregates. We found that hybridproteasome formation equips cells with more powerful protein degradation machineries that contribute to lower abundance of insoluble, putatively toxic protein aggregates. Nevertheless, these biochemical observations in cell culture models did not directly translate into a substantial alteration of cellular viability nor were they mirrored by exacerbated pathology e.g. upon LPS injection or infection of PA28-/- mice with a cardiotropic variant of CoxsackievirusB3. In vitro findings on PA28α/β-mediated viral replication were not corroborated by in vivo infection studies that investigated CVB3 myocarditis in PA28α/β-/- mice. Other than reported for cytokine-inducible immunoproteasome formation, PA28α/β is most likely not a prerequisite for coping with CVB3 myocarditis in C57BL/6 mice. In conclusion, the constitutive or induced formation of additional proteasome isoforms such as i- or hybridproteasomes is important to maintain the cellular protein homeostasis and to compensate for inflammatory protein damage. In this context, some of our moderate in vivo effects can be explained by upregulation of ß5 as a compensatory mechanism for ß5i/LMP7 deficiency. Thus, there are additional pathways that contribute to the protein homeostasis network that remain to be determined.
Publications
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Dysfunction in protein clearance by the proteasome: impact on autoinflammatory diseases, Seminars in Immunopathology 2015, 37, 323-33
Brehm A, Krüger E
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The availability of the cardio-protective pattern recognition molecule Pentraxin3 is controlled by the immunoproteasome. European Journal of Immunology 2015; 46(3):619-633
Paeschke A, Possehl A, Klingel K, Voss M, Voss K, Kespohl M, Sauter M, Overkleeft HS, Althof N, Garlanda C, Voigt A
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Inhibition of chymotryptic-like standard proteasome activity exacerbates doxorubicin-induced cytotoxicity in primary cardiomyocytes. Toxicology. 2016; 353-354:34-47
Spur EM, Althof N, Respondek D, Klingel K, Heuser A, Overkleeft HS, Voigt A
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TCF11/Nrf1-Mediated Induction of Proteasome Expression Prevents Cytotoxicity by Rotenone. Antioxid Redox Signal 2016, 25, 870-885
Sotzny F, Schormann E, Kühlewindt I, Koch A, Brehm A, Goldbach-Mansky R, Gilling KE, Krüger, E
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PA28 modulates antigen processing and viral replication during coxsackievirus B3 infection. PLoS One. 2017, 9;12(3):e0173259
Respondek D, Voss M, Kühlewindt I, Klingel K, Krüger E, Beling A
