Project description:293T were transfected with plasmids expressing DNA-dependent activator of IFN-regulatory factors (DAI) or retinoic acid-inducible gene 1 (RIG-I). Transfected cells were subsequently infected with influenza A/Puerto Rico/8/34 virus for 12 hours. Cell extract was subjected to FLAG Ab beads, washed, and retained. RNA was sequenced using the Illumina TruSeq Stranded Total RNA Library kit. The input sample represents total RNA from vector-infected cells.
Project description:Influenza A virus (IAV) is an RNA virus that is cytotoxic to most cell types in which it replicates. IAV activates the host kinase RIPK3, which induces cell death via parallel pathways of necroptosis, driven by the pseudokinase MLKL, and apoptosis, dependent on the adaptor proteins RIPK1 and FADD. How IAV activates RIPK3 remains unknown. We report that DAI (ZBP1/DLM-1), previously implicated as a cytoplasmic DNA sensor, is essential for RIPK3 activation by IAV. Upon infection, DAI recognizes IAV genomic RNA, associates with RIPK3, and is required for recruitment of MLKL and RIPK1 to RIPK3. Cells lacking DAI or containing DAI mutants deficient in nucleic acid binding are resistant to IAV-triggered necroptosis and apoptosis. DAI-deficient mice fail to control IAV replication and succumb to lethal respiratory infection. These results identify DAI as a link between IAV replication and RIPK3 activation and implicate DAI as a sensor of RNA viruses.
Project description:Necroptosis is a programmed lytic cell death involving active cytokine production and plasma membrane rupture through distinct signaling cascades. However, it remains challenging to delineate this inflammatory cell death pathway at specific signaling nodes with spatiotemporal accuracy. To address this challenge, we developed an optogenetic system, termed Light-activatable Receptor-Interacting Protein Kinase 3 or La-RIPK3, to enable ligand-free, optical induction of RIPK3 oligomerization. La-RIPK3 activation dissects RIPK3-centric lytic cell death through the induction of RIPK3-containing necrosome, which mediates cytokine production and plasma membrane rupture. Bulk RNA-Seq analysis reveals that RIPK3 oligomerization results in partially overlapped gene expression compared to pharmacological induction of necroptosis. However, La-RIPK3 activates a group of genes likely regulated by RIPK3 kinase-independent processes. Using patterned light stimulation delivered by a spatial light modulator, we demonstrate precise spatiotemporal control of necroptosis in La-RIPK3-transduced HT-29 cells. Optogenetic control of proinflammatory lytic cell death could lead to the development of innovative experimental strategies to finetune the immune landscape for disease intervention.
Project description:Pathogen recognition receptors and TNF superfamily members engage Receptor Interacting Serine/threonine Kinase-3 (RIPK3) to activate programmed cell death, including MLKL-mediated necroptosis and caspase-8-dependent apoptosis. However, the post-translational control of RIPK3 signalling is not fully understood. Using mass-spectrometry, we identified a novel ubiquitylation site on murine RIPK3 beyond the RIP homotypic interaction motif (RHIM) on K469. Complementation of RIPK3-deficient cells with a Ripk3K469R mutant demonstrated that the decoration of RIPK3 K469 by ubiquitin limits both RIPK3-mediated caspase-8 activation and apoptotic killing, in addition to RIPK3 autophosphorylation and MLKL-mediated necroptosis. Unexpectedly, the overall ubiquitylation of mutant RIPK3K469R was enhanced, which largely resulted from additional RIPK3 ubiquitylation on K359. Loss of RIPK3 K359 ubiquitylation reduced RIPK3K469R hyper-ubiquitylation and limited the ability of Ripk3K469R/K469R to trigger enhanced killing. Ripk3K469R/K469R mice challenged with Salmonella displayed increased bacterial loads in the spleen and liver, with reduced IFN serum levels. Therefore, RIPK3 K469 ubiquitylation can function to prevent RIPK3 ubiquitylation on alternate lysine residues, which otherwise promote RIPK3 oligomerization and consequent cell death signalling.
Project description:We show that RIPK1, a key mediator of cell death and inflammation, senses the abundance of methionine and its metabolite, S-adenosylmethionine (SAM), to dictate cell survival and death.
Project description:Astrocyte activation is a common feature of neurodegenerative diseases. However, the ways in which dying neurons influence the activity of astrocytes is poorly understood. RIPK3 signaling has recently been described as a key regulator of neuroinflammation, but whether this kinase mediates astrocytic responsiveness to neuronal death has not yet been studied. Here, we used the MPTP model of Parkinson’s disease to show that activation of astrocytic RIPK3 drives dopaminergic cell death and axon damage. Transcriptomic profiling revealed that astrocytic RIPK3 promoted gene expression associated with neuroinflammation and movement disorders, and this coincided with significant engagement of DAMP signaling. Using human cell culture systems, we show that factors released from dying neurons signal through RAGE to induce RIPK3-dependent astrocyte activation. These findings highlight a mechanism of neuron-glia crosstalk in which neuronal death perpetuates further neurodegeneration by engaging inflammatory astrocyte activation via RIPK3.
Project description:Receptor-interacting protein kinase 3 (RIPK3) is the primary regulator of necroptotic cell death. RIPK3 expression is often silenced in various cancer cells, which suggests that it may have tumor suppressor properties. However, the exact mechanism by which RIPK3 negatively regulates cancer development and progression remains unclear. This report indicates that RIPK3 acts as a potent regulator of homeostatic proliferation of CD4+CD8+ double-positive (DP) thymocytes. Abnormal proliferation of RIPK3-deficient DP thymocytes occurs independently of the well-known role for RIPK3 in necroptosis (upstream of MLKL activation), and is associated with an incidental thymic mass, likely thymic hyperplasia. In addition, Ripk3-null mice developed increased thymic tumor formation accompanied by reduced host survival in the context of a N-ethyl-N-nitrosourea (ENU)-induced tumor model. Moreover, RIPK3 deficiency in p53-null mice promoted thymic lymphoma development via upregulated ERK signaling, which correlated with markedly reduced survival rates. Mechanistically, lymphocyte-specific protein tyrosine kinase (LCK) activates RIPK3, which in turn leads to increases in the phosphatase activity of protein phosphatase 2 (PP2A), thereby suppressing hyper-activation of ERK in DP thymocytes. Overall, these findings suggest that a RIPK3-PP2A-ERK signaling axis regulates DP thymocyte homeostasis and may provide a potential therapeutic target to improve thymic lymphoma therapies.
Project description:Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a well-known inducer of apoptosis via formation of the primary death-inducing signaling complex (TRAIL-DISC) at the level of membrane death receptors (DR4 and DR5) which recruit successively FADD and caspase-8. TRAIL can also induce necroptosis when caspases are inhibited. Necroptosis is a regulated cell death dependent on the formation of a cytosolic necrosome complex which includes RIPK1, RIPK3 and MLKL proteins. Elucidating the molecular mechanisms involved in TRAIL-induced necroptosis might provide new insights into the TRAIL death signaling pathway. Here, we report the analysis by mass spectrometry of endogenous RIPK3-dependent necrosome complex constituents upon necroptosis induced by TRAIL/z-VAD/Birinapant (TzB) in HT29 cells. Besides characterization of RIPK1, RIPK3, MLKL, FADD, caspase-8, we find TRIM21 as a new constituent of the necrosome complex. Moreover RIPK1, RIPK3, MLKL, P-MLKL, FADD, caspase-8 and TRIM21 are also found associated to the native TRAIL-DISC upon TzB stimulation showing initiation of the necrotic pathway at the level of TRAIL death receptors in HT29 cells. Finally, TRIM21 may positively modulate necroptosis induction by downregulating NF-kB activation.
Project description:Ptpn6 is a cytoplasmic phosphatase that functions to prevent autoimmune disease and IL-1R-dependent caspase-1-independent inflammatory disease. Conditional deletion of Ptpn6 in neutrophils (Ptpn6∆PMN) is sufficient to initiate IL-1R-dependent cutaneous inflammatory disease, but the source of IL-1 and the mechanisms behind IL-1 release remain unclear. Here, we investigated the mechanisms controlling IL-1α/β release from neutrophils by inhibiting caspase-8-dependent apoptosis and Ripk1/Ripk3/Mlkl-regulated necroptosis. Loss of Ripk1 accelerated disease onset, whereas combined deletion of caspase-8 and either Ripk3 or Mlkl strongly protected Ptpn6∆PMN mice. Ptpn6∆PMN neutrophils displayed increased p38-dependent Ripk1-independent IL-1 and TNF production, and were prone to cell death. Together, these data emphasize dual functions for Ptpn6 in the negative regulation of p38 MAP kinase activation to control TNF and IL-1α/β transcription, and in maintaining Ripk1 function to prevent caspase-8- and Ripk3/Mlkl-dependent cell death and concomitant IL-1α/β release.