Novel role of PKR in inflammasome activation and HMGB1 release

Abstract

The inflammasome regulates the release of caspase activation-dependent cytokines, including interleukin (IL)-1β, IL-18 and high-mobility group box 1 (HMGB1)1,2,3,4,5. By studying HMGB1 release mechanisms, here we identify a role for double-stranded RNA-dependent protein kinase (PKR, also known as EIF2AK2) in inflammasome activation. Exposure of macrophages to inflammasome agonists induced PKR autophosphorylation. PKR inactivation by genetic deletion or pharmacological inhibition severely impaired inflammasome activation in response to double-stranded RNA, ATP, monosodium urate, adjuvant aluminium, rotenone, live Escherichia coli, anthrax lethal toxin, DNA transfection and Salmonella typhimurium infection. PKR deficiency significantly inhibited the secretion of IL-1β, IL-18 and HMGB1 in E. coli-induced peritonitis. PKR physically interacts with several inflammasome components, including NOD-like receptor (NLR) family pyrin domain-containing 3 (NLRP3), NLRP1, NLR family CARD domain-containing protein 4 (NLRC4), absent in melanoma 2 (AIM2), and broadly regulates inflammasome activation. PKR autophosphorylation in a cell-free system with recombinant NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC, also known as PYCARD) and pro-caspase-1 reconstitutes inflammasome activity. These results show a crucial role for PKR in inflammasome activation, and indicate that it should be possible to pharmacologically target this molecule to treat inflammation.

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Figure 1: Role of PKR in pyroptosis-mediated HMGB1 release.
Figure 2: PKR is important for inflammasome activation.
Figure 3: PKR physically interacts with NLRP3 and facilitates inflammasome activation.
Figure 4: PKR regulates NLRP1, AIM2 and NLRC4 inflammasome activation.

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Acknowledgements

We thank H. LaQueta, M. Dancho, M. McCarty, E. Lau, D. Katz and J. Scheinerman for technical assistance. This work was supported in part by grants from the National Institutes of Health (RO1 GM62508 to K.J.T. and DK052539 to G.S.H.). B.L. and S.I.V.-F. are supported by the foundation of Elmezzi Graduate School of Molecular Medicine. T.N. is supported by fellowships from the International Human Frontier Science Program and a Career Development Award from the American Heart Association.

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B.L. and K.J.T. designed the research; B.L., T.N., K.I., D.J.A., J.L., Y.T., P.L., S.I.V.-F. and H.E.-H. performed the experiments; B.L., S.I.V.-F., P.S.O., H.Y., S.S.C., J.R., T.K., D.J.A., G.S.H., U.A. and K.J.T. analysed the results; J.P.-Y.T. and Y.Z. provided important reagents; B.L. made the figures; B.L. and K.J.T. wrote the paper; U.A., H.W., P.S.O., S.S.C. and G.S.H. edited and commented on the manuscripts.

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Correspondence to Ben Lu or Kevin J. Tracey.

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Lu, B., Nakamura, T., Inouye, K. et al. Novel role of PKR in inflammasome activation and HMGB1 release. Nature 488, 670–674 (2012). https://doi.org/10.1038/nature11290

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