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NLRP3-independent inflammasome activation by proteasome inhibitors

Journal Contribution - Journal Abstract Conference Contribution


Proteasome inhibitors (PIs) such as Bortezomib (BTZ) have revolutionized multiple myeloma (MM) treatment. However, their efficacy is limited by the emergence of drug resistance and treatment-limiting side effects, including peripheral neuropathy and lymphopenia. Treatment resistance in MM has been demonstrated to be promoted by an NLRP3 inflammasome-mediated innate immune response to MM-associated proteins. Thus, we set out to investigate the impact of PI treatment on innate immune cytokine production.

Materials and Methods

The PIs BTZ, marizomib, epoxomicin and onx-0914 were applied to a variety of inflammasome-competent human immortalized and primary cells, including the cell line THP-1 (monocytic), primary human peripheral blood mononuclear cells (PBMC), M-CSF or ascites-derived macrophages, keratinocytes, and epithelial cells. Inflammasome activation was characterized via Interleukin-1b (IL-1β) release in cellular supernatants (ELISA, all cell types) and ASC-speck formation using an ASC-GFP reporter cell line (THP-1). To characterize the contribution of Nod-like receptor pyrin domain-containing protein 3 (NLRP3) and caspase-1 (CASP-1) to inflammasome formation, NLRP3 and CASP-1-deficient THP1 cells were generated using CRISPR/Cas9-mediated genome engineering, and NLRP3 and caspase-1 were pharmacologically inhibited using MCC-950 (Invitrogen) and VX-765 (Invivogen).


We report PI-mediated activation of the inflammasome in all cells tested. Treatment with PI induced secretion of IL-1b by THP1 cells and PBMC with an EC50 that was similar to the IC50 in BTZ-sensitive, but not BTZ-resistant, KMS-11 MM cells. We observed hallmarks of canonical inflammasome activation such as the formation of ASC specks in PI-exposed cells. Moreover, pharmacological inhibition of caspase-1 with VX-765 or genetic caspase-1 deficiency abrogated IL-1b. A variety of inflammatory stimuli, including soluble proteins secreted by MM cells, induce inflammasome formation via activation of NLRP3, the only inflammasome receptor currently targetable by a small molecule and investigated in clinical trials. Surprisingly, neither genetic ablation of NLRP3 in THP-1 cells nor MCC-950 treatment of PBMC inhibited IL-1b signaling following BTZ exposure.


Here, we identify PIs as activators of the inflammasome. In contrast to previously identified myeloma-intrinsic mechanisms leading to inflammasome assembly, PI-mediated IL-1b secretion was independent of NLRP3. Further investigation will include the identification of the receptor mediating BTZ-driven inflammasome assembly in order to identify mechanisms of action that may be amenable to therapeutic intervention.
Journal: Blood
ISSN: 0006-4971
Issue: Supplement 1
Volume: 140
Pages: 3125
Publication year:2022