Abstract
Nuclear factor kappa B (NF-κB) is a critical transcription factor involved in regulating cell activation, inflammation, and survival. The linear ubiquitin chain assembly complex (LUBAC) which consists of HOIL1, HOIP, and SHARPIN, catalyzes the linear ubiquitination of target proteins—a post-translational modification that is essential for NF-κB activation. Human germline pathogenic variants that dysregulate linear ubiquitination and NF-κB signaling are associated with immunodeficiency and/or autoinflammation including dermatitis, recurrent fevers, systemic inflammation and enteropathy. We previously identified MALT1 paracaspase as a novel negative regulator of LUBAC by proteolytic cleavage of HOIL1. To directly investigate the impact of HOIL1 cleavage activity on the inflammatory response, we employed a stable transduction system to express and directly compare non-cleavable HOIL1 with wild-type HOIL1 in primary HOIL1-deficient patient skin fibroblasts. We discovered that non-cleavable HOIL1 resulted in enhanced NF-κB signaling in response to innate stimuli. Transcriptomics revealed enrichment of inflammation and proinflammatory cytokine-related pathways after stimulation. Multiplexed cytokine assays confirmed a ‘hyperinflammatory’ phenotype in these cells. This work highlights the physiological importance of MALT1-dependent cleavage and modulation of HOIL1 on NF-κB signaling and inflammation, provides a mechanism for the autoinflammation observed in MALT1-deficient patients, and will inform the development of therapeutics that target MALT1 paracaspase and LUBAC function in treating autoinflammatory skin diseases.
Highlights
The transcription factor nuclear factor kB (NF-kB) is a critical mediator of inflammation, immunity and malignancy [1, 2]
To directly investigate the impact of this cleavage event on canonical NF-kB activation and whether inability to cleave heme-oxidized IRP2 ligase 1 (HOIL1) could contribute to the clinical features of MALT1-deficient patients [32, 33, 35], we developed a non-cleavable version of HOIL1 by mutating R165 to lysine
We confirmed that HOIL1 deficiency had direct impact on the cellular stability of linear ubiquitin chain assembly complex (LUBAC) [16, 17], where HOIL1 interacting protein (HOIP) and SHANKassociated RH domain interacting protein (SHARPIN) expression was significantly decreased in the HOIL1-deficient fibroblasts (Figures 1B, C)
Summary
The transcription factor nuclear factor kB (NF-kB) is a critical mediator of inflammation, immunity and malignancy [1, 2]. The study of humans with pathogenic variants affecting key elements of the NF-kB signaling cascade has provided key insights into the biology of this system [3]. Today we know that upon activation, NF-kB drives cellular activation, proliferation, and survival by modulating gene expression, cytokine production and signaling pathways. NF-kB can be induced by diverse innate and adaptive stimuli through the canonical (classical) or noncanonical (alternative) pathways. Major activators of the canonical pathway include signals from pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs), tumor necrosis factor-a (TNF-a), interleukin-1b (IL-1b), and lymphocyte antigen receptor signaling [1]. Non-canonical stimuli [e.g. receptor activator of nuclear factor kappa-B ligand (RANKL)] cooperate with the canonical NF-kB pathway [4]. Given the central role of NF-kB, aberrant activation is associated with various pathological states, including inflammatory diseases, autoimmunity, immunodeficiency, and cancer [2, 5, 6]
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