Davidson S, Yu CH, Steiner A, Ebstein F, Baker PJ, Jarur-Chamy V, Hrovat Schaale K, Laohamonthonkul P, Kong K, Calleja DJ, Harapas CR, Balka KR, Mitchell J, Jackson JT, Geoghegan ND, Moghaddas F, Rogers KL, Mayer-Barber KD, De Jesus AA, De Nardo D, Kile BT, Sadler AJ, Poli MC, Krüger E, Goldbach Mansky R, Masters SL. Protein kinase R is an innate immune sensor of proteotoxic stress via accumulation of cytoplasmic IL-24.
Sci Immunol 2022;
7:eabi6763. [PMID:
35148201 PMCID:
PMC11036408 DOI:
10.1126/sciimmunol.abi6763]
[Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Proteasome dysfunction can lead to autoinflammatory disease associated with elevated type I interferon (IFN-αβ) and NF-κB signaling; however, the innate immune pathway driving this is currently unknown. Here, we identified protein kinase R (PKR) as an innate immune sensor for proteotoxic stress. PKR activation was observed in cellular models of decreased proteasome function and in multiple cell types from patients with proteasome-associated autoinflammatory disease (PRAAS). Furthermore, genetic deletion or small-molecule inhibition of PKR in vitro ameliorated inflammation driven by proteasome deficiency. In vivo, proteasome inhibitor-induced inflammatory gene transcription was blunted in PKR-deficient mice compared with littermate controls. PKR also acted as a rheostat for proteotoxic stress by triggering phosphorylation of eIF2α, which can prevent the translation of new proteins to restore homeostasis. Although traditionally known as a sensor of RNA, under conditions of proteasome dysfunction, PKR sensed the cytoplasmic accumulation of a known interactor, interleukin-24 (IL-24). When misfolded IL-24 egress into the cytosol was blocked by inhibition of the endoplasmic reticulum-associated degradation pathway, PKR activation and subsequent inflammatory signaling were blunted. Cytokines such as IL-24 are normally secreted from cells; therefore, cytoplasmic accumulation of IL-24 represents an internal danger-associated molecular pattern. Thus, we have identified a mechanism by which proteotoxic stress is detected, causing inflammation observed in the disease PRAAS.
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