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Mitochondria are increasingly recognized as cellular hubs to orchestrate signaling pathways that regulate metabolism, redox homeostasis, and cell fate decisions. Recent research revealed a role of mitochondria also in innate immune signaling; however, the mechanisms of how mitochondria affect signal transduction are poorly understood. Here, we show that the NF‐κB pathway activated by TNF employs mitochondria as a platform for signal amplification and shuttling of activated NF‐κB to the nucleus. TNF treatment induces the recruitment of HOIP, the catalytic component of the linear ubiquitin chain assembly complex (LUBAC), and its substrate NEMO to the outer mitochondrial membrane, where M1‐ and K63‐linked ubiquitin chains are generated. NF‐κB is locally activated and transported to the nucleus by mitochondria, leading to an increase in mitochondria‐nucleus contact sites in a HOIP‐dependent manner. Notably, TNF‐induced stabilization of the mitochondrial kinase PINK1 furthermore contributes to signal amplification by antagonizing the M1‐ubiquitin‐specific deubiquitinase OTULIN. Overall, our study reveals a role for mitochondria in amplifying TNF‐mediated NF‐κB activation, both serving as a signaling platform, as well as a transport mode for activated NF‐κB to the nuclear. Synopsis: The E3 ubiquitin ligase HOIP is the catalytic component the linear ubiquitin chain assembly complex (LUBAC) that regulates canonical NF‐κB activation in innate immune signaling. This study reports a role of mitochondria in promoting TNF‐induced NF‐κB pathway activation by HOIP‐dependent reshaping of the mitochondrial membrane. LUBAC is recruited to the outer mitochondrial membrane upon TNF receptor activation.Formation of linear or M1‐linked ubiquitin chains enables the assembly of an NF‐κB signaling platform at mitochondria.PINK1 phosphorylates M1‐linked ubiquitin chains, which counteracts their OTULIN‐mediated hydrolysis.Mitochondrial motility facilitates shuttling of activated NF‐κB to the nucleus.TNF increases mitochondria‐ nucleus contact sites in a HOIP‐dependent manner. [ABSTRACT FROM AUTHOR]

The success of cancer immunotherapy is limited to a subset of patients, highlighting the need to identify the processes by which tumors evade immunity. Using CRISPR/Cas9 screening, we reveal that melanoma cells lacking HOIP, the catalytic subunit of LUBAC, are highly susceptible to both NK and CD8+ T‐cell‐mediated killing. We demonstrate that HOIP‐deficient tumor cells exhibit increased sensitivity to the combined effect of the inflammatory cytokines, TNF and IFN‐γ, released by NK and CD8+ T cells upon target recognition. Both genetic deletion and pharmacological inhibition of HOIP augment tumor cell sensitivity to combined TNF and IFN‐γ. Together, we unveil a protective regulatory axis, involving HOIP, which limits a transcription‐dependent form of cell death that engages both intrinsic and extrinsic apoptotic machinery upon exposure to TNF and IFN‐γ. Our findings highlight HOIP inhibition as a potential strategy to harness and enhance the killing capacity of TNF and IFN‐γ during immunotherapy. Synopsis: HOIP protects tumor cells from apoptosis induced by combined TNF and IFN‐γ co‐secreted by NK and CD8+ T cells. HOIP inhibition might thus be a strategy to enhance immunotherapy responses. HOIP limits tumor sensitivity to both NK and CD8+ T cell cytotoxicity.HOIP mediates this activity through protecting against apoptosis induced by combined TNF and IFN‐γ.HOIP limits combined TNF‐ and IFN‐γ‐induced apoptosis, that engages extrinsic and intrinsic apoptotic effectors.HOIP inhibition sensitizes tumor cells to combined TNF and IFN‐γ, and T cell derived co‐culture supernatants. [ABSTRACT FROM AUTHOR]

In recent years, great technological advances have been achieved in the growth of hybrid organic–inorganic perovskites (HOIPs) and these have attracted extensive attention due to their optoelectronic properties, structural tunability and stability. We present here a new two‐dimensional hybrid organic–inorganic perovskite, namely, poly[bis(3‐fluorocyclobutylammonium) [di‐μ‐iodido‐diiodidoplumbate(VI)]], {(C4H9FN)2[PbI4]}n, showing a two‐dimensional reticular layer with the organic cations in the middle of the meshes. The calculated experimental band gap is 2.44 eV and the band gap is calculated as 2.20 eV theoretically, which further suggests the potential of this compound as a semiconductor. [ABSTRACT FROM AUTHOR]

K63- and Met1-linked ubiquitylation are crucial posttranslational modifications for TNF receptor signaling. These non-degradative ubiquitylations are counteracted by deubiquitinases ( DUBs), such as the enzyme CYLD, resulting in an appropriate signal strength, but the regulation of this process remains incompletely understood. Here, we describe an interaction partner of CYLD, SPATA2, which we identified by a mass spectrometry screen. We find that SPATA2 interacts via its PUB domain with CYLD, while a PUB interaction motif ( PIM) of SPATA2 interacts with the PUB domain of the LUBAC component HOIP. SPATA2 is required for the recruitment of CYLD to the TNF receptor signaling complex upon TNFR stimulation. Moreover, SPATA2 acts as an allosteric activator for the K63- and M1-deubiquitinase activity of CYLD. In consequence, SPATA2 substantially attenuates TNF-induced NF-κB and MAPK signaling. Conversely, SPATA2 is required for TNF-induced complex II formation, caspase activation, and apoptosis. Thus, this study identifies SPATA2 as an important factor in the TNF signaling pathway with a substantial role for the effects mediated by the cytokine. [ABSTRACT FROM AUTHOR]

RING-in-between- RING ( RBR) ubiquitin (Ub) ligases are a distinct class of E3s, defined by a RING1 domain that binds E2 Ub-conjugating enzyme and a RING2 domain that contains an active site cysteine similar to HECT-type E3s. Proposed to function as RING/ HECT hybrids, details regarding the Ub transfer mechanism used by RBRs have yet to be defined. When paired with RING-type E3s, E2s perform the final step of Ub ligation to a substrate. In contrast, when paired with RBR E3s, E2s must transfer Ub onto the E3 to generate a E3~Ub intermediate. We show that RBRs utilize two strategies to ensure transfer of Ub from the E2 onto the E3 active site. First, RING1 domains of HHARI and RNF144 promote open E2~Ubs. Second, we identify a Ub-binding site on HHARI RING2 important for its recruitment to RING1-bound E2~Ub. Mutations that ablate Ub binding to HHARI RING2 also decrease RBR ligase activity, consistent with RING2 recruitment being a critical step for the RBR Ub transfer mechanism. Finally, we demonstrate that the mechanism defined here is utilized by a variety of RBRs. [ABSTRACT FROM AUTHOR]

Tumor necrosis factor ( TNF) is a potent cytokine known for its involvement in inflammation, repression of tumorigenesis and activation of immune cells. Consequently, accurate regulation of the TNF signaling pathway is crucial for preventing the potent noxious effects of TNF. These pathological conditions include chronic inflammation, septic shock, cachexia and cancer. The TNF signaling cascade utilizes a complex network of post-translational modifications to control the cellular response following its activation. Next to phosphorylation, the ubiquitination of signaling complex components is probably the most important modification. This process is mediated by a specialist class of enzymes, the ubiquitin ligases. Equally important is the class of dedicated ubiquitin-specific proteases, the deubiquitinases. Together with ubiquitin binding proteins, this ubiquitination-deubiquitination system enables the dynamics of signaling complexes. In TNF signaling, these dynamics translate into the precise regulation of the induction of gene activation or cell death. Here, we review and discuss current knowledge of TNF signaling regulation by the ubiquitin system. [ABSTRACT FROM AUTHOR]