Loss of XIAP facilitates switch to TNFα-induced necroptosis in mouse neutrophils.

Neutrophils are essential players in the first-line defense against invading bacteria and fungi. Besides its antiapoptotic role, the inhibitor of apoptosis protein (IAP) family member X-linked IAP (XIAP) has been shown to regulate innate immune signaling. Whereas the role of XIAP in innate signaling pathways is derived mostly from work in macrophages and dendritic cells, it is not known if and how XIAP contributes to these pathways in neutrophils. Here we show that in response to bacterial lipopolysaccharides (LPS), mouse neutrophils secreted considerable amounts of tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β) and, in accordance with earlier reports, XIAP prevented LPS-induced hypersecretion of IL-1β also in neutrophils. Interestingly, and in contrast to macrophages or dendritic cells, Xiap-deficient neutrophils were insensitive to LPS-induced cell death. However, combined loss of function of XIAP and cIAP1/-2 resulted in rapid neutrophil cell death in response to LPS. This cell death occurred by classical apoptosis initiated by a TNFα- and RIPK1-dependent, but RIPK3- and MLKL-independent, pathway. Inhibition of caspases under the same experimental conditions caused a shift to RIPK3-dependent cell death. Accordingly, we demonstrate that treatment of neutrophils with high concentrations of TNFα induced apoptotic cell death, which was fully blockable by pancaspase inhibition in wild-type neutrophils. However, in the absence of XIAP, caspase inhibition resulted in a shift from apoptosis to RIPK3- and MLKL-dependent necroptosis. Loss of XIAP further sensitized granulocyte-macrophage colony-stimulating factor (GM-CSF)-primed neutrophils to TNFα-induced killing. These data suggest that XIAP antagonizes the switch from TNFα-induced apoptosis to necroptosis in mouse neutrophils. Moreover, our data may implicate an important role of neutrophils in the development of hyperinflammation and disease progression of patients diagnosed with X-linked lymphoproliferative syndrome type 2, which are deficient in XIAP

SMAC mimetics promote NIK-dependent inhibition of CD4+ TH17 cell differentiation

Second mitochondria-derived activator of caspase (SMAC) mimetics (SMs) are selective antagonists of the inhibitor of apoptosis proteins (IAPs), which activate noncanonical NF-κB signaling and promote tumor cell death. Through gene expression analysis, we found that treatment of CD4+ T cells with SMs during T helper 17 (TH17) cell differentiation disrupted the balance between two antagonistic transcription factor modules. Moreover, proteomics analysis revealed that SMs altered the abundance of proteins associated with cell cycle, mitochondrial activity, and the balance between canonical and noncanonical NF-κB signaling. Whereas SMs inhibited interleukin-17 (IL-17) production and ameliorated TH17 cell–driven inflammation, they stimulated IL-22 secretion. Mechanistically, SM-mediated activation of NF-κB–inducing kinase (NIK) and the transcription factors RelB and p52 directly suppressed Il17a expression and IL-17A protein production, as well as the expression of a number of other immune genes. Induction of IL-22 production correlated with the NIK-dependent reduction in cMAF protein abundance and the enhanced activity of the aryl hydrocarbon receptor. Last, SMs also increased IL-9 and IL-13 production and, under competing conditions, favored the differentiation of naïve CD4+ T cells into TH2 cells rather than TH17 cells. These results demonstrate that SMs shape the gene expression and protein profiles of TH17 cells and inhibit TH17 cell–driven autoimmunity

BRD9 is a druggable component of interferon-stimulated gene expression and antiviral activity

Interferon (IFN) induction of IFN-stimulated genes (ISGs) creates a formidable protective antiviral state. However, loss of appropriate control mechanisms can result in constitutive pathogenic ISG upregulation. Here, we used genome-scale loss-of-function screening to establish genes critical for IFN-induced transcription, identifying all expected members of the JAK-STAT signaling pathway and a previously unappreciated epigenetic reader, bromodomain-containing protein 9 (BRD9), the defining subunit of non-canonical BAF (ncBAF) chromatin-remodeling complexes. Genetic knockout or small-molecule-mediated degradation of BRD9 limits IFN-induced expression of a subset of ISGs in multiple cell types and prevents IFN from exerting full antiviral activity against several RNA and DNA viruses, including influenza virus, human immunodeficiency virus (HIV1), and herpes simplex virus (HSV1). Mechanistically, BRD9 acts at the level of transcription, and its IFN-triggered proximal association with the ISG transcriptional activator, STAT2, suggests a functional localization at selected ISG promoters. Furthermore, BRD9 relies on its intact acetyl-binding bromodomain and unique ncBAF scaffolding interaction with GLTSCR1/1L to promote IFN action. Given its druggability, BRD9 is an attractive target for dampening ISG expression under certain autoinflammatory conditions

Correction: TNFR2 induced priming of the inflammasome leads to a RIPK1-dependent cell death in the absence of XIAP.

The original version of this article contained an error in the name of one of the co-authors (Erika Owsley). This has been corrected in the PDF and HTML versions

TWEAK-FN14 signaling induces lysosomal degradation of a cIAP1–TRAF2 complex to sensitize tumor cells to TNFα

Synthetic inhibitor of apoptosis (IAP) antagonists induce degradation of IAP proteins such as cellular IAP1 (cIAP1), activate nuclear factor κB (NF-κB) signaling, and sensitize cells to tumor necrosis factor α (TNFα). The physiological relevance of these discoveries to cIAP1 function remains undetermined. We show that upon ligand binding, the TNF superfamily receptor FN14 recruits a cIAP1–Tnf receptor-associated factor 2 (TRAF2) complex. Unlike IAP antagonists that cause rapid proteasomal degradation of cIAP1, signaling by FN14 promotes the lysosomal degradation of cIAP1–TRAF2 in a cIAP1-dependent manner. TNF-like weak inducer of apoptosis (TWEAK)/FN14 signaling nevertheless promotes the same noncanonical NF-κB signaling elicited by IAP antagonists and, in sensitive cells, the same autocrine TNFα-induced death occurs. TWEAK-induced loss of the cIAP1–TRAF2 complex sensitizes immortalized and minimally passaged tumor cells to TNFα-induced death, whereas primary cells remain resistant. Conversely, cIAP1–TRAF2 complex overexpression limits FN14 signaling and protects tumor cells from TWEAK-induced TNFα sensitization. Lysosomal degradation of cIAP1–TRAF2 by TWEAK/FN14 therefore critically alters the balance of life/death signals emanating from TNF-R1 in immortalized cells

TNFR2 induced priming of the inflammasome leads to a RIPK1-dependent cell death in the absence of XIAP.

The pediatric immune deficiency X-linked proliferative disease-2 (XLP-2) is a unique disease, with patients presenting with either hemophagocytic lymphohistiocytosis (HLH) or intestinal bowel disease (IBD). Interestingly, XLP-2 patients display high levels of IL-18 in the serum even while in stable condition, presumably through spontaneous inflammasome activation. Recent data suggests that LPS stimulation can trigger inflammasome activation through a TNFR2/TNF/TNFR1 mediated loop in xiap-/- macrophages. Yet, the direct role TNFR2-specific activation plays in the absence of XIAP is unknown. We found TNFR2-specific activation leads to cell death in xiap-/- myeloid cells, particularly in the absence of the RING domain. RIPK1 kinase activity downstream of TNFR2 resulted in a TNF/TNFR1 cell death, independent of necroptosis. TNFR2-specific activation leads to a similar inflammatory NF-kB driven transcriptional profile as TNFR1 activation with the exception of upregulation of NLRP3 and caspase-11. Activation and upregulation of the canonical inflammasome upon loss of XIAP was mediated by RIPK1 kinase activity and ROS production. While both the inhibition of RIPK1 kinase activity and ROS production reduced cell death, as well as release of IL-1β, the release of IL-18 was not reduced to basal levels. This study supports targeting TNFR2 specifically to reduce IL-18 release in XLP-2 patients and to reduce priming of the inflammasome components

Characterization of the apoptotic response of human leukemia cells to organosulfur compounds

Background: Novel therapeutic agents that selectively induce tumor cell death are urgently needed in the clinical management of cancers. Such agents would constitute effective adjuvant approaches to traditional chemotherapy regimens. Organosulfur compounds (OSCs), such as diallyl disulfide, have demonstrated anti-proliferative effects on cancer cells. We have previously shown that synthesized relatives of dysoxysulfone, a natural OSC derived from the Fijian medicinal plant, Dysoxylum richi, possess tumor-specific antiproliferative effects and are thus promising lead candidates. Methods: Because our structure-activity analyses showed that regions flanking the disulfide bond mediated specificity, we synthesized 18 novel OSCs by structural modification of the most promising dysoxysulfone derivatives. These compounds were tested for anti-proliferative and apoptotic activity in both normal and leukemic cells. Results: Six OSCs exhibited tumor-specific killing, having no effect on normal bone marrow, and are thus candidates for future toxicity studies. We then employed mRNA expression profiling to characterize the mechanisms by which different OSCs induce apoptosis. Using Gene Ontology analysis we show that each OSC altered a unique set of pathways, and that these differences could be partially rationalized from a transcription factor binding site analysis. For example, five compounds altered genes with a large enrichment of p53 binding sites in their promoter regions (p < 0.0001). Conclusions: Taken together, these data establish OSCs derivatized from dysoxysulfone as a novel group of compounds for development as anti-cancer agents

Cellular IAPs inhibit a cryptic CD95-induced cell death by limiting RIP1 kinase recruitment

cIAPs keep RIP1 from getting to the DISC complex and complex II; when cIAPs are repressed, signaling is modulated by the cFLIP isoform

Genomic, Pathway Network, and Immunologic Features Distinguishing Squamous Carcinomas

This integrated, multiplatform PanCancer Atlas study co-mapped and identified distinguishing molecular features of squamous cell carcinomas (SCCs) from five sites associated with smokin

Pan-cancer Alterations of the MYC Oncogene and Its Proximal Network across the Cancer Genome Atlas

Although theMYConcogene has been implicated incancer, a systematic assessment of alterations ofMYC, related transcription factors, and co-regulatoryproteins, forming the proximal MYC network (PMN),across human cancers is lacking. Using computa-tional approaches, we define genomic and proteo-mic features associated with MYC and the PMNacross the 33 cancers of The Cancer Genome Atlas.Pan-cancer, 28% of all samples had at least one ofthe MYC paralogs amplified. In contrast, the MYCantagonists MGA and MNT were the most frequentlymutated or deleted members, proposing a roleas tumor suppressors.MYCalterations were mutu-ally exclusive withPIK3CA,PTEN,APC,orBRAFalterations, suggesting that MYC is a distinct onco-genic driver. Expression analysis revealed MYC-associated pathways in tumor subtypes, such asimmune response and growth factor signaling; chro-matin, translation, and DNA replication/repair wereconserved pan-cancer. This analysis reveals insightsinto MYC biology and is a reference for biomarkersand therapeutics for cancers with alterations ofMYC or the PMN