Association of intestinal inflammation and permeability markers with clinical manifestations of Parkinson's disease

INTRODUCTION

Intestinal inflammation and gut microbiota dysbiosis can stimulate degeneration of dopaminergic neurons and development of Parkinson's disease (PD) via the gut-brain axis in certain patients.

METHODS

In a case-control study, fecal markers of intestinal inflammation and permeability were measured using the ELISA method in PD patients and healthy controls. Motor and nonmotor symptoms were assessed using the Movement Disorder Society (MDS) Unified PD Rating Scale, Hoehn & Yahr scale, MDS Non-Motor Symptom Scale, Scales for Outcomes in PD - Autonomic Dysfunction, PD Sleep Scale - 2, Montreal Cognitive Assessment, Beck Anxiety Inventory, and Beck Depression Inventory-II. A correlation was established between the intestinal inflammation and permeability markers and PD symptoms.

RESULTS

Higher levels of beta-defensin 2, zonulin and lactoferrin were recorded in PD patients compared to controls. Calprotectin and secretory immunoglobulin A showed no significant differences. Regression analysis indicated the roles of beta-defensin 2 and lactoferrin in predicting PD likelihood. Calprotectin yielded positive correlations with disease duration, depression, motor fluctuations, and gastrointestinal symptoms; beta defensin 2 with thermoregulation; and secretory immunoglobulin A with depression. Secretory immunoglobulin A showed negative correlation with age and age at disease onset, while zonulin showed negative correlation with the MDS Unified PD Rating Scale total score.

CONCLUSIONS

Fecal markers differed in PD patients compared to controls and correlated with age, disease duration, and some nonmotor symptoms. Future studies should identify the subgroups of PD patients that are likely to develop intestinal inflammation.

Immunomodulatory effects and improved outcomes with cisplatin- versus carboplatin-based chemotherapy plus atezolizumab in urothelial cancer

In metastatic urothelial cancer (mUC), cisplatin versus carboplatin leads to durable disease control in a subset of patients. The IMvigor130 trial reveals more favorable effects with atezolizumab combined with gemcitabine and cisplatin (GemCis) versus gemcitabine and carboplatin (GemCarbo). This study investigates the immunomodulatory effects of cisplatin as a potential explanation for these observations. Our findings indicate that improved outcomes with GemCis versus GemCarbo are primarily observed in patients with pretreatment tumors exhibiting features of restrained adaptive immunity. In addition, GemCis versus GemCarbo ± atezolizumab induces transcriptional changes in circulating immune cells, including upregulation of antigen presentation and T cell activation programs. In vitro experiments demonstrate that cisplatin, compared with carboplatin, exerts direct immunomodulatory effects on cancer cells, promoting dendritic cell activation and antigen-specific T cell killing. These results underscore the key role of immune modulation in cisplatin's efficacy in mUC and highlight the importance of specific chemotherapy backbones in immunotherapy combination regimens.

Simultaneous substrate and ubiquitin modification recognition by bispecific antibodies enables detection of ubiquitinated RIP1 and RIP2

Ubiquitination is a posttranslational modification that is crucial for the dynamic regulation of diverse signaling pathways. To enhance our understanding of ubiquitination-mediated signaling, we generated a new class of bispecific antibodies that combine recognition of ubiquitination substrates and specific polyubiquitin linkages. RIP1-K63 and RIP1-linear (Lin) linkage polyubiquitin bispecific antibodies detected linkage-specific ubiquitination of the proinflammatory kinase RIP1 in cells and in tissues and revealed RIP1 ubiquitination by immunofluorescence. Similarly, ubiquitination of the RIP1-related kinase RIP2 with K63 or linear linkages was specifically detected with the RIP2-K63 and RIP2-Lin bispecific antibodies, respectively. Furthermore, using the RIP2-K63 and RIP2-Lin bispecific antibodies, we found prominent K63-linked and linear RIP2 ubiquitination in samples from patients with ulcerative colitis and Crohn's disease. We also developed a bispecific antibody (K63-Lin) that simultaneously recognizes K63-linked and linear ubiquitination of components of various signaling pathways. Together, these bispecific antibodies represent a new class of reagents with the potential to be developed for the detection of inflammatory biomarkers.

Inhibition of RIP1 improves immune reconstitution and reduces GVHD mortality while preserving graft-versus-leukemia effects

Graft-versus-host disease (GVHD) remains the major cause of morbidity and nonrelapse mortality (NRM) after hematopoietic cell transplantation (HCT). Inflammatory cytokines mediate damage to key GVHD targets such as intestinal stem cells (ISCs) and also activate receptor interacting protein kinase 1 (RIP1; RIPK1), a critical regulator of apoptosis and necroptosis. We therefore investigated the role of RIP1 in acute GVHD using samples from HCT patients, modeling GVHD damage in vitro with both human and mouse gastrointestinal (GI) organoids, and blocking RIP1 activation in vivo using several well-characterized mouse HCT models. Increased phospho-RIP1 expression in GI biopsies from patients with acute GVHD correlated with tissue damage and predicted NRM. Both the genetic inactivation of RIP1 and the RIP1 inhibitor GNE684 prevented GVHD-induced apoptosis of ISCs in vivo and in vitro. Daily administration of GNE684 for 14 days reduced inflammatory infiltrates in three GVHD target organs (intestine, liver, and spleen) in mice. Unexpectedly, GNE684 administration also reversed the marked loss of regulatory T cells in the intestines and liver during GVHD and reduced splenic T cell exhaustion, thus improving immune reconstitution. Pharmacological and genetic inhibition of RIP1 improved long-term survival without compromising the graft-versus-leukemia (GVL) effect in lymphocytic and myeloid leukemia mouse models. Thus, RIP1inhibition may represent a nonimmunosuppressive treatment for GVHD.

cIAPs control RIPK1 kinase activity-dependent and -independent cell death and tissue inflammation

Cellular inhibitor of apoptosis proteins (cIAPs) are RING-containing E3 ubiquitin ligases that ubiquitylate receptor-interacting protein kinase 1 (RIPK1) to regulate TNF signalling. Here, we established mice simultaneously expressing enzymatically inactive cIAP1/2 variants, bearing mutations in the RING domains of cIAP1/2 (cIAP1/2 mutant RING, cIAP1/2MutR ). cIap1/2MutR/MutR mice died during embryonic development due to RIPK1-mediated apoptosis. While expression of kinase-inactive RIPK1D138N rescued embryonic development, Ripk1D138N/D138N /cIap1/2MutR/MutR mice developed systemic inflammation and died postweaning. Cells expressing cIAP1/2MutR and RIPK1D138N were still susceptible to TNF-induced apoptosis and necroptosis, implying additional kinase-independent RIPK1 activities in regulating TNF signalling. Although further ablation of Ripk3 did not lead to any phenotypic improvement, Tnfr1 gene knock-out prevented early onset of systemic inflammation and premature mortality, indicating that cIAPs control TNFR1-mediated toxicity independent of RIPK1 and RIPK3. Beyond providing novel molecular insights into TNF-signalling, the mouse model established in this study can serve as a useful tool to further evaluate ongoing therapeutic protocols using inhibitors of TNF, cIAPs and RIPK1.

A phase I, randomized, ascending-dose study to assess safety, pharmacokinetics, and activity of GDC-8264, a RIP1 inhibitor, in healthy volunteers

Receptor-interacting protein 1 (RIP1) is a key regulator of multiple signaling pathways that mediate inflammatory responses and cell death. RIP1 kinase activity mediates apoptosis and necroptosis induced by tumor necrosis factor (TNF)-α, Toll-like receptors, and ischemic tissue damage. RIP1 has been implicated in several human pathologies and consequently, RIP1 inhibition may represent a therapeutic approach for diseases dependent on RIP1-mediated inflammation and cell death. GDC-8264 is a potent, selective, and reversible small molecule inhibitor of RIP1 kinase activity. This phase I, randomized, placebo-controlled, double-blinded trial examined safety, pharmacokinetics (PKs), and pharmacodynamics (PDs) of single- (5-225 mg) and multiple- (50 and 100 mg once daily, up to 14 days) ascending oral doses of GDC-8264 in healthy volunteers, and also tested the effect of food on the PKs of GDC-8264. All adverse events in GDC-8264-treated subjects in both stages were mild. GDC-8264 exhibited dose-proportional increases in systemic exposure; the mean terminal half-life ranged from 10-13 h, with limited accumulation on multiple dosing (accumulation ratio [AR] ~ 1.4); GDC-8264 had minimal renal excretion at all doses. A high-fat meal had no significant effect on the PKs of GDC-8264. In an ex vivo stimulation assay of whole blood, GDC-8264 rapidly and completely inhibited release of CCL4, a downstream marker of RIP1 pathway activation, indicating a potent pharmacological effect. Based on PK-PD modeling, the GDC-8264 half-maximal inhibitory concentration for the inhibition of CCL4 release was estimated to be 0.58 ng/mL. The favorable safety, PKs, and PDs of GDC-8264 support its further development for treatment of RIP1-driven diseases.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

XIAP deletion sensitizes mice to TNF-induced and RIP1-mediated death

XIAP is a caspase-inhibitory protein that blocks several cell death pathways, and mediates proper activation of inflammatory NOD2-RIP2 signaling. XIAP deficiency in patients with inflammatory diseases such as Crohn's disease, or those needing allogeneic hematopoietic cell transplantation, is associated with a worse prognosis. In this study, we show that XIAP absence sensitizes cells and mice to LPS- and TNF-mediated cell death without affecting LPS- or TNF-induced NF-κB and MAPK signaling. In XIAP deficient mice, RIP1 inhibition effectively blocks TNF-stimulated cell death, hypothermia, lethality, cytokine/chemokine release, intestinal tissue damage and granulocyte migration. By contrast, inhibition of the related kinase RIP2 does not affect TNF-stimulated events, suggesting a lack of involvement for the RIP2-NOD2 signaling pathway. Overall, our data indicate that in XIAP's absence RIP1 is a critical component of TNF-mediated inflammation, suggesting that RIP1 inhibition could be an attractive option for patients with XIAP deficiency.

XIAP promotes melanoma growth by inducing tumour neutrophil infiltration

Elevated expression of the X‐linked inhibitor of apoptosis protein (XIAP) has been frequently reported in malignant melanoma suggesting that XIAP renders apoptosis resistance and thereby supports melanoma progression. Independent of its anti‐apoptotic function, XIAP mediates cellular inflammatory signalling and promotes immunity against bacterial infection. The pro‐inflammatory function of XIAP has not yet been considered in cancer. By providing detailed in vitro analyses, utilising two independent mouse melanoma models and including human melanoma samples, we show here that XIAP is an important mediator of melanoma neutrophil infiltration. Neutrophils represent a major driver of melanoma progression and are increasingly considered as a valuable therapeutic target in solid cancer. Our data reveal that XIAP ubiquitylates RIPK2, involve TAB1/RIPK2 complex and induce the transcriptional up‐regulation and secretion of chemokines such as IL8, that are responsible for intra‐tumour neutrophil accumulation. Alteration of the XIAP‐RIPK2‐TAB1 inflammatory axis or the depletion of neutrophils in mice reduced melanoma growth. Our data shed new light on how XIAP contributes to tumour growth and provides important insights for novel XIAP targeting strategies in cancer.

Primary Amine Tethered Small Molecules Promote the Degradation of X-Linked Inhibitor of Apoptosis Protein

We hypothesized that the proximity-driven ubiquitylation of E3-interacting small molecules could affect the degradation of E3 ubiquitin ligases. A series of XIAP BIR2 domain-binding small molecules was modified to append a nucleophilic primary amine. This modification transforms XIAP binders into inducers of XIAP degradation. The degradation of XIAP is E1- and proteasome-dependent, dependent on the ligase function of XIAP, and is rescued by subtle modifications of the small molecule that would obviate ubiquitylation. We demonstrate in vitro ubiquitylation of the small molecule that is dependent on its interaction with XIAP. Taken together, these results demonstrate the designed ubiquitylation of an engineered small molecule and a novel approach for the degradation of E3 ubiquitin ligases.

Genetic inactivation of RIP1 kinase activity in rats protects against ischemic brain injury

RIP1 kinase-mediated inflammatory and cell death pathways have been implicated in the pathology of acute and chronic disorders of the nervous system. Here, we describe a novel animal model of RIP1 kinase deficiency, generated by knock-in of the kinase-inactivating RIP1(D138N) mutation in rats. Homozygous RIP1 kinase-dead (KD) rats had normal development, reproduction and did not show any gross phenotypes at baseline. However, cells derived from RIP1 KD rats displayed resistance to necroptotic cell death. In addition, RIP1 KD rats were resistant to TNF-induced systemic shock. We studied the utility of RIP1 KD rats for neurological disorders by testing the efficacy of the genetic inactivation in the transient middle cerebral artery occlusion/reperfusion model of brain injury. RIP1 KD rats were protected in this model in a battery of behavioral, imaging, and histopathological endpoints. In addition, RIP1 KD rats had reduced inflammation and accumulation of neuronal injury biomarkers. Unbiased proteomics in the plasma identified additional changes that were ameliorated by RIP1 genetic inactivation. Together these data highlight the utility of the RIP1 KD rats for target validation and biomarker studies for neurological disorders.

Cell death pathways: intricate connections and disease implications

Various forms of cell death have been identified over the last decades with each relying on a different subset of proteins for the activation and execution of their respective pathway(s). In addition to the three best characterized pathways-apoptosis, necroptosis, and pyroptosis-other forms of regulated cell death including autophagy-dependent cell death (ADCD), mitochondrial permeability transition pore (MPTP)-mediated necrosis, parthanatos, NETosis and ferroptosis, and their relevance for organismal homeostasis are becoming better understood. Importantly, it is increasingly clear that none of these pathways operate alone. Instead, a more complex picture is emerging with many pathways sharing components and signaling principles. Finally, a number of cell death regulators are implicated in human diseases and represent attractive therapeutic targets. Therefore, better understanding of physiological and mechanistic aspects of cell death signaling should yield improved reagents for addressing unmet medical needs.

Impaired RIPK1 ubiquitination sensitizes mice to TNF toxicity and inflammatory cell death

Receptor-interacting protein 1 (RIP1; RIPK1) is a key regulator of multiple signaling pathways that mediate inflammatory responses and cell death. TNF-TNFR1 triggered signaling complex formation, subsequent NF-κB and MAPK activation and induction of cell death involve RIPK1 ubiquitination at several lysine residues including Lys376 and Lys115. Here we show that mutating the ubiquitination site K376 of RIPK1 (K376R) in mice activates cell death resulting in embryonic lethality. In contrast to Ripk1K376R/K376R mice, Ripk1K115R/K115R mice reached adulthood and showed slightly higher responsiveness to TNF-induced death. Cell death observed in Ripk1K376R/K376R embryos relied on RIPK1 kinase activity as administration of RIPK1 inhibitor GNE684 to pregnant heterozygous mice effectively blocked cell death and prolonged survival. Embryonic lethality of Ripk1K376R/K376R mice was prevented by the loss of TNFR1, or by simultaneous deletion of caspase-8 and RIPK3. Interestingly, elimination of the wild-type allele from adult Ripk1K376R/cko mice was tolerated. However, adult Ripk1K376R/cko mice were exquisitely sensitive to TNF-induced hypothermia and associated lethality. Absence of the K376 ubiquitination site diminished K11-linked, K63-linked, and linear ubiquitination of RIPK1, and promoted the assembly of death-inducing cellular complexes, suggesting that multiple ubiquitin linkages contribute to the stability of the RIPK1 signaling complex that stimulates NF-κB and MAPK activation. In contrast, mutating K115 did not affect RIPK1 ubiquitination or TNF stimulated NF-κB and MAPK signaling. Overall, our data indicate that selective impairment of RIPK1 ubiquitination can lower the threshold for RIPK1 activation by TNF resulting in cell death and embryonic lethality.

Ubiquitination in the regulation of inflammatory cell death and cancer

The ubiquitin system is complex, multifaceted, and is crucial for the modulation of a vast number of cellular processes. Ubiquitination is tightly regulated at different levels by a range of enzymes including E1s, E2s, and E3s, and an array of DUBs. The UPS directs protein degradation through the proteasome, and regulates a wide array of cellular processes including transcription and epigenetic factors as well as key oncoproteins. Ubiquitination is key to the dynamic regulation of programmed cell death. Notably, the TNF signaling pathway is controlled by competing ubiquitin conjugation and deubiquitination, which governs both proteasomal degradation and signaling complex formation. In the inflammatory response, ubiquitination is capable of both activating and dampening inflammasome activation through the control of either protein stability, complex formation, or, in some cases, directly affecting receptor activity. In this review, we discuss the enzymes and targets in the ubiquitin system that regulate fundamental cellular processes regulating cell death, and inflammation, as well as disease consequences resulting from their dysregulation. Finally, we highlight several pre-clinical and clinical compounds that regulate ubiquitin system enzymes, with the aim of restoring homeostasis and ameliorating diseases.

Immunoblot Analysis of the Regulation of TNF Receptor Family-Induced NF-κB Signaling by c-IAP Proteins

Proper maintenance of organismal homeostasis, development, and immune defense requires precise regulation of survival and signaling pathways. Inhibitor of apoptosis (IAP) proteins are evolutionarily conserved regulators of cell death and immune signaling that impact numerous cellular processes. Although initially characterized as inhibitors of apoptosis, the ubiquitin ligase activity of IAP proteins is critical for modulating various signaling pathways (e.g., NF-κB, MAPK) and cell survival. Cellular IAP1 and 2 regulate the pro-survival canonical NF-κB pathway by ubiquitinating RIP1 and themselves thus enabling recruitment of kinase (IKK) and E3 ligase (LUBAC) complexes. On the other hand, c-IAP1 and c-IAP2 are negative regulators of noncanonical NF-κB signaling by promoting ubiquitination and consequent proteasomal degradation of the NF-κB-inducing kinase NIK. Here we describe the involvement of c-IAP1 and c-IAP2 in NF-κB signaling and provide detailed methodology for examining functional roles of c-IAPs in these pathways.

Genetic inactivation of RIP1 kinase does not ameliorate disease in a mouse model of ALS

RIP1 kinase is proposed to play a critical role in driving necroptosis and inflammation in neurodegenerative disorders, including Amyotrophic Lateral Sclerosis (ALS). Preclinical studies indicated that while pharmacological inhibition of RIP1 kinase can ameliorate axonal pathology and delay disease onset in the mutant SOD1 transgenic (SOD1-Tg) mice, genetic blockade of necroptosis does not provide benefit in this mouse model. To clarify the role of RIP1 kinase activity in driving pathology in SOD1-Tg mice, we crossed SOD1-Tgs to RIP1 kinase-dead knock-in mice, and measured disease progression using functional and histopathological endpoints. Genetic inactivation of the RIP1 kinase activity in the SOD1-Tgs did not benefit the declining muscle strength or nerve function, motor neuron degeneration or neuroinflammation. In addition, we did not find evidence of phosphorylated RIP1 accumulation in the spinal cords of ALS patients. On the other hand, genetic inactivation of RIP1 kinase activity ameliorated the depletion of the neurotransmitter dopamine in a toxin model of dopaminergic neurodegeneration. These findings indicate that RIP1 kinase activity is dispensable for disease pathogenesis in the SOD1-Tg mice while inhibition of kinase activity may provide benefit in acute injury models.

Regulation of Cell Death and Immunity by XIAP

X-chromosome-linked inhibitor of apoptosis protein (XIAP) controls cell survival in several regulated cell death pathways and coordinates a range of inflammatory signaling events. Initially identified as a caspase-binding protein, it was considered to be primarily involved in blocking apoptosis from both intrinsic as well as extrinsic triggers. However, XIAP also prevents TNF-mediated, receptor-interacting protein 3 (RIPK3)-dependent cell death, by controlling RIPK1 ubiquitylation and preventing inflammatory cell death. The identification of patients with germline mutations in XIAP (termed XLP-2 syndrome) pointed toward its role in inflammatory signaling. Indeed, XIAP also mediates nucleotide-binding oligomerization domain-containing 2 (NOD2) proinflammatory signaling by promoting RIPK2 ubiquitination within the NOD2 signaling complex leading to NF-κB and MAPK activation and production of inflammatory cytokines and chemokines. Overall, XIAP is a critical regulator of multiple cell death and inflammatory pathways making it an attractive drug target in tumors and inflammatory diseases.

Ubiquitin Ligases cIAP1 and cIAP2 Limit Cell Death to Prevent Inflammation

Cellular inhibitor of apoptosis proteins cIAP1 and cIAP2 ubiquitinate nuclear factor κB (NF-κB)-inducing kinase (NIK) to suppress non-canonical NF-κB signaling and substrates such as receptor interacting protein kinase 1 (RIPK1) to promote cell survival. We investigate how these functions contribute to homeostasis by eliminating cIap2 from adult cIap1-deficient mice. cIAP1 and cIAP2 (cIAP1/2) deficiency causes rapid weight loss and inflammation, with aberrant cell death, indicated by cleaved caspases-3 and -8, prevalent in intestine and liver. Deletion of Casp8 and Ripk3 prevents this aberrant cell death, reduces the inflammation, and prolongs mouse survival, whereas Ripk3 loss alone offers little benefit. Residual inflammation in mice lacking cIap1/2, Casp8, and Ripk3 is reduced by inhibition of NIK. Loss of Casp8 and Mlkl (mixed lineage kinase domain-like), but not Mlkl loss alone, also prevents cIAP1/2-deficient mice from dying around embryonic day 11. Therefore, a major function of cIAP1/2 in vivo is to suppress caspase-8-dependent cell death.

The kinase IRAK4 promotes endosomal TLR and immune complex signaling in B cells and plasmacytoid dendritic cells

The dysregulation of multiple signaling pathways, including those through endosomal Toll-like receptors (TLRs), Fc gamma receptors (FcγR), and antigen receptors in B cells (BCR), promote an autoinflammatory loop in systemic lupus erythematosus (SLE). Here, we used selective small-molecule inhibitors to assess the regulatory roles of interleukin-1 receptor (IL-1R)-associated kinase 4 (IRAK4) and Bruton's tyrosine kinase (BTK) in these pathways. The inhibition of IRAK4 repressed SLE immune complex- and TLR7-mediated activation of human plasmacytoid dendritic cells (pDCs). Correspondingly, the expression of interferon (IFN)-responsive genes (IRGs) in cells and in mice was positively regulated by the kinase activity of IRAK4. Both IRAK4 and BTK inhibition reduced the TLR7-mediated differentiation of human memory B cells into plasmablasts. TLR7-dependent inflammatory responses were differentially regulated by IRAK4 and BTK by cell type: In pDCs, IRAK4 positively regulated NF-κB and MAPK signaling, whereas in B cells, NF-κB and MAPK pathways were regulated by both BTK and IRAK4. In the pristane-induced lupus mouse model, inhibition of IRAK4 reduced the expression of IRGs during disease onset. Mice engineered to express kinase-deficient IRAK4 were protected from both chemical (pristane-induced) and genetic (NZB/W_F1 hybrid) models of lupus development. Our findings suggest that kinase inhibitors of IRAK4 might be a therapeutic in patients with SLE.

The Balance of TNF Mediated Pathways Regulates Inflammatory Cell Death Signaling in Healthy and Diseased Tissues

Tumor necrosis factor alpha (TNF; TNFα) is a critical regulator of immune responses in healthy organisms and in disease. TNF is involved in the development and proper functioning of the immune system by mediating cell survival and cell death inducing signaling. TNF stimulated signaling pathways are tightly regulated by a series of phosphorylation and ubiquitination events, which enable timely association of TNF receptors-associated intracellular signaling complexes. Disruption of these signaling events can disturb the balance and the composition of signaling complexes, potentially resulting in severe inflammatory diseases.

Atypical presentation and pathogenesis of a macaque lymphocryptoviral-associated B-cell lymphoma in a cynomolgus monkey

We report the unique pathogenesis and presentation of a rapidly progressive B-cell lymphoma in a 3-year-old female cynomolgus monkey on day 50 of a 13-week toxicity study. Clinical pathology evaluation revealed a marked leukocytosis with bicytopenia. A serum protein electrophoresis was consistent with monoclonal gammopathy. The architecture of the lymph node, spleen, and thymus were variably effaced by neoplastic cells, which also infiltrated other tissues. Immunohistochemistry of the affected tissues confirmed a predominant population of CD20+, CD79a+, CD3-, CD68-, and CD34-neoplastic cells. The full data best support a diagnosis of Stage V lymphoma. Nextgen sequencing and negative prestudy serology results suggested a recent infection by macaque lymphocryptovirus (mLCV) with a unique transcriptional profile comparable with a rarely observed direct LCV infection model. This infection model might be associated with a temporary lack of an LCV antigen-specific cytotoxic T-cell adaptive immune response. Consistent with the established mechanisms of LCV-related lymphoproliferation, MYC and BCL2L11 gene expression were increased and decreased, respectively. While there was no overt immunosuppression, immunophenotyping revealed the index animal had a relatively low NK cell count, which further decreased by >50% on day 24 of the study. In addition to the temporary lack of adaptive immunity, the low NK cell counts were suggestive of an impaired innate immunity to control the virally-transformed cells and the subsequent unchecked lymphoproliferation. To our knowledge, this is the first report of a Stage V lymphoma with a unique pathogenesis in an otherwise immunocompetent cynomolgus monkey.

RIP1 kinase activity is critical for skin inflammation but not for viral propagation

Receptor interacting protein kinase 1 (RIP1) is a critical effector of inflammatory responses and cell death activation. Cell death pathways regulated by RIP1 include caspase‐dependent apoptosis and caspase‐independent necroptosis. The kinase activity of RIP1 has been associated with a number of inflammatory, neurodegenerative, and oncogenic diseases. In this study, we use the RIP1 kinase inhibitor GNE684 to demonstrate that RIP1 inhibition can effectively block skin inflammation and immune cell infiltrates in livers of Sharpin mutant (Cpdm; chronic proliferative dermatitis) mice in an interventional setting, after disease onset. On the other hand, genetic inactivation of RIP1 (RIP1 KD) or ablation of RIP3 (RIP3 KO) or MLKL (MLKL KO) did not affect testicular pathology of aging male mice. Likewise, infection with vaccinia virus or with mouse gammaherpesvirus MHV68 resulted in similar viral clearance in wild‐type, RIP1 KD, and RIP3 KO mice. In summary, this study highlights the benefits of inhibiting RIP1 in skin inflammation, as opposed to its lack of relevance for testicular longevity and the response to certain viral infections.

The Indian cobra reference genome and transcriptome enables comprehensive identification of venom toxins

Snakebite envenoming is a serious and neglected tropical disease that kills ~100,000 people annually. High-quality, genome-enabled comprehensive characterization of toxin genes will facilitate development of effective humanized recombinant antivenom. We report a de novo near-chromosomal genome assembly of Naja naja, the Indian cobra, a highly venomous, medically important snake. Our assembly has a scaffold N50 of 223.35 Mb, with 19 scaffolds containing 95% of the genome. Of the 23,248 predicted protein-coding genes, 12,346 venom-gland-expressed genes constitute the ‘venom-ome’ and this included 139 genes from 33 toxin families. Among the 139 toxin genes were 19 ‘venom-ome-specific toxins’ (VSTs) that showed venom-gland-specific expression, and these probably encode the minimal core venom effector proteins. Synthetic venom reconstituted through recombinant VST expression will aid in the rapid development of safe and effective synthetic antivenom. Additionally, our genome could serve as a reference for snake genomes, support evolutionary studies and enable venom-driven drug discovery.

Analysis of a near-chromosomal genome assembly and transcriptome profiling of the Indian cobra identifies genes expressed in the venom glands. These data should help develop a new antivenom.

Potent and selective inhibitors of receptor-interacting protein kinase 1 that lack an aromatic back pocket group

Receptor-interacting protein kinase 1 (RIPK1), a key component of the cellular necroptosis pathway, has gained recognition as an important therapeutic target. Pharmacologic inhibition or genetic inactivation of RIPK1 has shown promise in animal models of disease ranging from acute ischemic conditions, chronic inflammation, and neurodegeneration. We present here a class of RIPK1 inhibitors that is distinguished by a lack of a lipophilic aromatic group present in most literature inhibitors that typically occupies a hydrophobic back pocket of the protein active site. Despite not having this ubiquitous feature of many known RIPK1 inhibitors, we were able to obtain compounds with good potency, kinase selectivity, and pharmacokinetic properties in rats. The use of the lipophilic yet metabolically stable pentafluoroethyl group was critical to balancing the potency and properties of optimized analogs.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Smac mimetic induces cell death in a large proportion of primary acute myeloid leukemia samples, which correlates with defined molecular markers

Apoptosis is deregulated in most, if not all, cancers, including hematological malignancies. Smac mimetics that antagonize Inhibitor of Apoptosis (IAP) proteins have so far largely been investigated in acute myeloid leukemia (AML) cell lines; however, little is yet known on the therapeutic potential of Smac mimetics in primary AML samples. In this study, we therefore investigated the antileukemic activity of the Smac mimetic BV6 in diagnostic samples of 67 adult AML patients and correlated the response to clinical, cytogenetic and molecular markers and gene expression profiles. Treatment with cytarabine (ara-C) was used as a standard chemotherapeutic agent. Interestingly, about half (51%) of primary AML samples are sensitive to BV6 and 21% intermediate responsive, while 28% are resistant. Notably, 69% of ara-C-resistant samples show a good to fair response to BV6. Furthermore, combination treatment with ara-C and BV6 exerts additive effects in most samples. Whole-genome gene expression profiling identifies cell death, TNFR1 and NF-κB signaling among the top pathways that are activated by BV6 in BV6-sensitive, but not in BV6-resistant cases. Furthermore, sensitivity of primary AML blasts to BV6 correlates with significantly elevated expression levels of TNF and lower levels of XIAP in diagnostic samples, as well as with NPM1 mutation. In a large set of primary AML samples, these data provide novel insights into factors regulating Smac mimetic response in AML and have important implications for the development of Smac mimetic-based therapies and related diagnostics in AML.

Targeting Cell Death Pathways for Therapeutic Intervention in Kidney Diseases

Precise regulation of cell death and survival is essential for proper maintenance of organismal homeostasis, development, and the immune system. Deregulated cell death can lead to developmental defects, neuropathies, infections, and cancer. Kidney diseases, especially acute pathologies linked to ischemia-reperfusion injury, are among illnesses that profoundly are affected by improper regulation or execution of cell death pathways. Attempts to develop medicines for kidney diseases have been impacted by the complexity of these pathologies given the heterogeneous patient population and diverse etiologies. By analyzing cell death pathways activated in kidney diseases, we attempt to differentiate their importance for these pathologies with a goal of identifying those that have more profound impact and the best therapeutic potential. Although classic apoptosis still might be important, regulated necrosis pathways including necroptosis, ferroptosis, parthanatos, and mitochondrial permeability transition-associated cell death play a significantly role in kidney diseases, especially in acute kidney pathologies. Although targeting receptor-interacting protein 1 kinase appears to be the best therapeutic strategy, combination with inhibitors of other cell death pathways is likely to bring superior benefit and possible cure to patients suffering from kidney diseases.

Diverse ubiquitin linkages regulate RIP kinases-mediated inflammatory and cell death signaling

Members of the RIP kinase family are key regulators of inflammation and cell death signaling implicated in maintaining immune responses and proper tissue homeostasis. Increasing evidence points to post-translational modifications of RIP1, RIP2 and RIP3 as being critical for regulating their function. Ubiquitination and the E3 ligases, such as inhibitors of apoptosis (IAP) proteins and LUBAC, that direct substrate selectivity as well as the deubiquitinating enzymes, such as A20 and OTULIN, that reverse these modifications dictate the outcome of RIP kinase signaling. Perturbation of the tightly regulated RIP1, RIP2 and RIP3 ubiquitination can lead to signaling disbalance in TNF, TLR and NOD1/2-controlled pathways and result in severe human pathologies. In this review, we focus on the biological function of ubiquitin-modifying enzymes in the context of RIP1, RIP2 and RIP3 signaling. We also discuss the impact of deregulated ubiquitin networks in RIP1, RIP2 and RIP3 signaling pathways on human health.

The kinase TPL2 activates ERK and p38 signaling to promote neutrophilic inflammation

Tumor progression locus 2 (TPL2; also known as MAP3K8) is a mitogen-activated protein kinase (MAPK) kinase kinase (MAP3K) that phosphorylates the MAPK kinases MEK1 and MEK2 (MEK1/2), which, in turn, activate the MAPKs extracellular signal-regulated kinase 1 (ERK1) and ERK2 (ERK1/2) in macrophages stimulated through the interleukin-1 receptor (IL-1R), Toll-like receptors (TLRs), or the tumor necrosis factor receptor (TNFR). We describe a conserved and critical role for TPL2 in mediating the effector functions of neutrophils through the activation of the p38 MAPK signaling pathway. Gene expression profiling and functional studies of neutrophils and monocytes revealed a MEK1/2-independent branch point downstream of TPL2 in neutrophils. Biochemical analyses identified the MAPK kinases MEK3 and MEK6 and the MAPKs p38α and p38δ as downstream effectors of TPL2 in these cells. Genetic ablation of the catalytic activity of TPL2 or therapeutic intervention with a TPL2-specific inhibitor reduced the production of inflammatory mediators by neutrophils in response to stimulation with the TLR4 agonist lipopolysaccharide (LPS) in vitro, as well as in rodent models of inflammatory disease. Together, these data suggest that TPL2 is a drug target that activates not only MEK1/2-dependent but also MEK3/6-dependent signaling to promote inflammatory responses.

Coordinated ubiquitination and phosphorylation of RIP1 regulates necroptotic cell death

Proper regulation of cell death signaling is crucial for the maintenance of homeostasis and prevention of disease. A caspase-independent regulated form of cell death called necroptosis is rapidly emerging as an important mediator of a number of human pathologies including inflammatory bowel disease and ischemia–reperfusion organ injury. Activation of necroptotic signaling through TNF signaling or organ injury leads to the activation of kinases receptor-interacting protein kinases 1 and 3 (RIP1 and RIP3) and culminates in inflammatory cell death. We found that, in addition to phosphorylation, necroptotic cell death is regulated by ubiquitination of RIP1 in the necrosome. Necroptotic RIP1 ubiquitination requires RIP1 kinase activity, but not necroptotic mediators RIP3 and MLKL (mixed lineage kinase-like). Using immunoaffinity enrichment and mass spectrometry, we profiled numerous ubiquitination events on RIP1 that are triggered during necroptotic signaling. Mutation of a necroptosis-related ubiquitination site on RIP1 reduced necroptotic cell death and RIP1 ubiquitination and phosphorylation, and disrupted the assembly of RIP1 and RIP3 in the necrosome, suggesting that necroptotic RIP1 ubiquitination is important for maintaining RIP1 kinase activity in the necrosome complex. We also observed RIP1 ubiquitination in injured kidneys consistent with a physiological role of RIP1 ubiquitination in ischemia–reperfusion disease. Taken together, these data reveal that coordinated and interdependent RIP1 phosphorylation and ubiquitination within the necroptotic complex regulate necroptotic signaling and cell death.

Identification of RIP1 as a critical mediator of Smac mimetic-mediated sensitization of glioblastoma cells for Drozitumab-induced apoptosis

This study aims at evaluating the combination of the tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL)-receptor 2 (TRAIL-R2)-specific antibody Drozitumab and the Smac mimetic BV6 in preclinical glioblastoma models. To this end, the effect of BV6 and/or Drozitumab on apoptosis induction and signaling pathways was analyzed in glioblastoma cell lines, primary glioblastoma cultures and glioblastoma stem-like cells. Here, we report that BV6 and Drozitumab synergistically induce apoptosis and reduce colony formation in several glioblastoma cell lines (combination index<0.1). Also, BV6 profoundly enhances Drozitumab-induced apoptosis in primary glioblastoma cultures and glioblastoma stem-like cells. Importantly, BV6 cooperates with Drozitumab to suppress tumor growth in two glioblastoma in vivo models including an orthotopic, intracranial mouse model, underlining the clinical relevance of these findings. Mechanistic studies reveal that BV6 and Drozitumab act in concert to trigger the formation of a cytosolic receptor-interacting protein (RIP) 1/Fas-associated via death domain (FADD)/caspase-8-containing complex and subsequent activation of caspase-8 and -3. BV6- and Drozitumab-induced apoptosis is blocked by the caspase inhibitor zVAD.fmk, pointing to caspase-dependent apoptosis. RNA interference-mediated silencing of RIP1 almost completely abolishes the BV6-conferred sensitization to Drozitumab-induced apoptosis, indicating that the synergism critically depends on RIP1 expression. In contrast, both necrostatin-1, a RIP1 kinase inhibitor, and Enbrel, a TNFα-blocking antibody, do not interfere with BV6/Drozitumab-induced apoptosis, demonstrating that apoptosis occurs independently of RIP1 kinase activity or an autocrine TNFα loop. In conclusion, the rational combination of BV6 and Drozitumab presents a promising approach to trigger apoptosis in glioblastoma, which warrants further investigation.

Immunoaffinity enrichment coupled to quantitative mass spectrometry reveals ubiquitin-mediated signaling events

Ubiquitination is one of the most prevalent posttranslational modifications in eukaryotic cells, with functional importance in protein degradation, subcellular localization and signal transduction pathways. Immunoaffinity enrichment coupled with quantitative mass spectrometry enables the in-depth characterization of protein ubiquitination events at the site-specific level. We have applied this strategy to investigate cellular response triggered by two distinct type agents: small molecule inhibitors of the tumor-associated kinases MEK and PI3K or the pro-inflammatory cytokine IL-17. Temporal profiling of protein ubiquitination events across a series of time points covering the biological response permits interrogation of signaling through thousands of quantified proteins, of which only a subset display significant and physiologically meaningful regulation. Distinctive clusters of residues within proteins can display distinct temporal patterns attributable to diverse molecular functions, although the majority of differential ubiquitination appears as a coordinated response across the modifiable residues present within an individual substrate. In cells treated with a combination of MEK and PI3K inhibitors, we found differential ubiquitination of MEK within the first hour after treatment and a series of mitochondria proteins at later time points. In the IL-17 signaling pathway, ubiquitination events on several signaling proteins including HOIL-1 and Tollip were observed. The functional relevance of these putative IL-17 mediators was subsequently validated by knockdown of HOIL-1, HOIP and TOLIP, each of which decreased IL-17-stimulated cytokine production. Together, these data validate proteomic profiling of protein ubiquitination as a viable approach for identifying dynamic signaling components in response to intracellular and extracellular perturbations.

Necroptosis: Pathway diversity and characteristics

Regulated cell death is a physiological process that controls organismal homeostasis. Deregulation of cell death can lead to the development of a number of human diseases and tissue damage. Apoptosis is a best-known model of caspase-dependent regulated cell death, but recently necroptosis has garnered a lot of attention as a form of regulated cell death not mediated by caspases. Different stimuli can trigger necroptosis, and all of them converge at the activation of the protein kinase RIP3 (receptor-interacting protein 3) and the pseudokinase MLKL (mixed lineage kinase domain-like). Necroptosis activation relies on the unique protein-interaction motif RHIM (RIP homology interaction motif). Different RHIM-containing proteins (RIP1, DAI and TRIF) transduce necroptotic signals from the cell death trigger to the cell death mediators RIP3-MLKL. RIP1 has a particularly important and complex role in necroptotic cell death regulation ranging from cell death activation to inhibition, often in a cell type and context dependent fashion.

Roles of c-IAP proteins in TNF receptor family activation of NF-κB signaling

Precise regulation of survival and signaling pathways is essential for proper maintenance of organismal homeostasis, development, and immune defense. Inhibitor of apoptosis (IAP) proteins are evolutionarily conserved regulators of cell death and immune signaling that impact numerous cellular processes. Initially characterized as inhibitors of apoptosis, the ubiquitin ligase activity of IAP proteins is critical for modulating various signaling pathways (e.g., NF-κB, MAPK) and cellular fate. Cellular IAP1 and IAP2 regulate the pro-survival canonical NF-κB pathway by ubiquitinating RIP1 and enabling recruitment of kinase (IKK) and E3 ligase (LUBAC) complexes. On the other hand, c-IAP1 and c-IAP2 are negative regulators of noncanonical NF-κB signaling by promoting ubiquitination and consequent degradation of the NF-κB-inducing kinase NIK. In this article, we describe the involvement of c-IAP1 and c-IAP2 in NF-κB signaling and provide detailed methodology for examining how c-IAPs exert their functional roles.

Ubiquitination in disease pathogenesis and treatment

Ubiquitination is crucial for a plethora of physiological processes, including cell survival and differentiation and innate and adaptive immunity. In recent years, considerable progress has been made in the understanding of the molecular action of ubiquitin in signaling pathways and how alterations in the ubiquitin system lead to the development of distinct human diseases. Here we describe the role of ubiquitination in the onset and progression of cancer, metabolic syndromes, neurodegenerative diseases, autoimmunity, inflammatory disorders, infection and muscle dystrophies. Moreover, we indicate how current knowledge could be exploited for the development of new clinical therapies.

Activity of protein kinase RIPK3 determines whether cells die by necroptosis or apoptosis

Receptor-interacting protein kinase 1 (RIPK1) and RIPK3 trigger pro-inflammatory cell death termed "necroptosis." Studies with RIPK3-deficient mice or the RIPK1 inhibitor necrostatin-1 suggest that necroptosis exacerbates pathology in many disease models. We engineered mice expressing catalytically inactive RIPK3 D161N or RIPK1 D138N to determine the need for the active kinase in the whole animal. Unexpectedly, RIPK3 D161N promoted lethal RIPK1- and caspase-8-dependent apoptosis. In contrast, mice expressing RIPK1 D138N were viable and, like RIPK3-deficient mice, resistant to tumor necrosis factor (TNF)-induced hypothermia. Cells expressing RIPK1 D138N were resistant to TNF-induced necroptosis, whereas TNF-induced signaling pathways promoting gene transcription were unperturbed. Our data indicate that the kinase activity of RIPK3 is essential for necroptosis but also governs whether a cell activates caspase-8 and dies by apoptosis.

IAP family of cell death and signaling regulators

Inhibitor of apoptosis (IAP) proteins interface with, and regulate a large number of, cell signaling pathways. If there is a common theme to these pathways, it is that they are involved in the development of the immune system, immune responses, and unsurprisingly, given their name, cell death. Beyond that it is difficult to discover an underlying logic because sometimes IAPs are required to inhibit or prevent signaling, whereas in other cases they are required for signaling to take place. In whatever role they play, they are recruited into signaling complexes and function as ubiquitin E3 ligases, via their RING domains. This review discusses IAP regulation of signaling pathways and focuses on the mammalian IAPs, XIAP, c-IAP1, and c-IAP2, with a particular emphasis on techniques and methods that were used to uncover their roles. We also provide a perspective on targeting IAP proteins for therapeutic intervention and methods used to define the clinical relevance of IAP proteins.

The Role of Ubiquitination in TWEAK-Stimulated Signaling

Tumor necrosis factor superfamily ligands and receptors are responsible for development, immunity, and homeostasis of metazoan organisms. Thus, it is not surprising that signals emanating from these receptors are tightly regulated. Binding of TNF-related weak inducer of apoptosis (TWEAK) to its cognate receptor, FN14, triggers the assembly of receptor-associated signaling complex, which allows the activation of canonical and non-canonical nuclear factor kappa B (NF-κB) as well as mitogen-activated protein kinase signaling pathways. Ubiquitin ligases cellular inhibitor of apoptosis 1 and 2 (c-IAP1 and 2) and adaptor proteins TNFR-associated factors 2 and 3 (TRAF2 and TRAF3) are crucial for the regulation of TWEAK signaling as they facilitate the recruitment of distal signaling components including IKK and linear ubiquitin chain assembly complex complexes. At the same time c-IAP1/2, together with TRAF2 and TRAF3, promote constitutive ubiquitination and proteasomal degradation of NF-κB inducing kinase (NIK) – a kinase with critical role in the activation of non-canonical NF-κB signaling. While c-IAP1/2 mediated ubiquitination allows the activation of TWEAK-stimulated canonical NF-κB signaling, these E3 ligases are negative regulators of non-canonical signaling. TWEAK stimulation prompts the recruitment of c-IAP1/2 as well as TRAF2 and TRAF3 to the FN14 signaling complex leading to c-IAP1/2 autoubiquitination and degradation, which stabilizes NIK and allows subsequent phosphorylation of IKKα and partial proteasomal processing of p100 to activate gene expression. Recent studies have revealed that the spatio-temporal pattern of TWEAK-stimulated ubiquitination is a carefully orchestrated process involving several substrates that are modified by different ubiquitin linkages. Understanding the significance of ubiquitination for TWEAK signaling is important for the overall understanding of TWEAK biology and for the design of therapeutics that can be used in the treatment of human pathologies that are driven by TWEAK/FN14 expression and activity.

A senescence-inflammatory switch from cancer-inhibitory to cancer-promoting mechanism

Senescence, perceived as a cancer barrier, is paradoxically associated with inflammation, which promotes tumorigenesis. Here, we characterize a distinct low-grade inflammatory process in stressed epithelium that is related to para-inflammation; this process either represses or promotes tumorigenesis, depending on p53 activity. Csnk1a1 (CKIα) downregulation induces a senescence-associated inflammatory response (SIR) with growth arrest in colorectal tumors, which loses its growth control capacity in the absence of p53 and instead, accelerates growth and invasiveness. Corresponding processes occur in CKIα-deleted intestinal organoids, assuming tumorigenic transformation properties ex vivo, upon p53 loss. Treatment of organoids and mice with anti-inflammatory agents suppresses the SIR and prevents p53-deficient organoid transformation and mouse carcinogenesis. SIR/para-inflammation suppression may therefore constitute a key mechanism in the anticarcinogenic effects of nonsteroidal anti-inflammatory drugs.

The inhibitor of apoptosis (IAP) proteins are critical regulators of signaling pathways and targets for anti-cancer therapy

Cell death regulation is vital for maintenance of homeostasis and proper development of multicellular organisms. Inhibitor of apoptosis (IAP) proteins are implicated in multiple ways in cell death regulation, ranging from inhibition of apoptosis and necrosis to the regulation of cell cycle and inflammation. Due to their prominent ability to control cell death and elevated expression in a variety of cancer cell types, IAP proteins are attractive targets for the development of novel anti-cancer treatments. The most widely used strategy for targeting IAP proteins is based on mimicking the natural IAP antagonist, SMAC/DIABLO. IAP antagonists are currently being tested in humans and they were designed for anti-cancer therapy but they could potentially also be considered for treatments of the immune system disorders. In this manuscript we will review the functional roles of IAP proteins, specifically of c-IAP1, c-IAP2, ML-IAP and XIAP, and evaluate IAP targeting strategies for disease treatments. This article is part of a Special Issue entitled "Apoptosis: Four Decades Later".

Abstract SY06-01: Targeting IAP proteins for the treatment of cancer

Evasion of cell death is a characteristic feature of human cancers and represents a key cause of resistance to current treatment approaches. Therefore, reactivation of cell death programs in cancer cells is a promising strategy to overcome treatment resistance, one of the major unsolved problems in clinical oncology. Inhibitor of apoptosis (IAP) protein family members block cell death in response to diverse stimuli and are expressed at elevated levels in the majority of human malignancies, which makes them attractive targets for developing a novel class of cancer therapeutics. We have designed small-molecule IAP antagonists (smac mimetics) that bind with high affinities to select baculovirus IAP repeat (BIR) domains of IAPs resulting in a dramatic induction of c IAP auto-ubiquitination activity and rapid proteasomal degradation. IAP antagonists inhibit tumor growth in vivo as single agents and in combination with a number of anti-tumor agents. Using several different proteomic approaches we have discovered novel binding partners for IAP proteins and determined the spatial and temporal pattern of endogenous IAP-mediated ubiquitination during proliferative, apoptotic and necrotic signaling. The differential expression levels and posttranslational modifications of identified proteins will be used to build diagnostic profiles for the treatment with IAP antagonists. These compounds can be used in the treatment of malignancies in which IAP expression contributes to tumor progression and resistance to conventional chemotherapeutic agents.

Citation Format: Domagoj Vucic. Targeting IAP proteins for the treatment of cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr SY06-01. doi:10.1158/1538-7445.AM2013-SY06-01

OTUB1 modulates c-IAP1 stability to regulate signalling pathways

The cellular inhibitor of apoptosis (c-IAP) proteins are E3 ubiquitin ligases that are critical regulators of tumour necrosis factor (TNF) receptor (TNFR)-mediated signalling. Through their E3 ligase activity c-IAP proteins promote ubiquitination of receptor-interaction protein 1 (RIP1), NF-κB-inducing kinase (NIK) and themselves, and regulate the assembly of TNFR signalling complexes. Consequently, in the absence of c-IAP proteins, TNFR-mediated activation of NF-κB and MAPK pathways and the induction of gene expression are severely reduced. Here, we describe the identification of OTUB1 as a c-IAP-associated deubiquitinating enzyme that regulates c-IAP1 stability. OTUB1 disassembles K48-linked polyubiquitin chains from c-IAP1 in vitro and in vivo within the TWEAK receptor-signalling complex. Downregulation of OTUB1 promotes TWEAK- and IAP antagonist-stimulated caspase activation and cell death, and enhances c-IAP1 degradation. Furthermore, knockdown of OTUB1 reduces TWEAK-induced activation of canonical NF-κB and MAPK signalling pathways and modulates TWEAK-induced gene expression. Finally, suppression of OTUB1 expression in zebrafish destabilizes c-IAP (Birc2) protein levels and disrupts fish vasculature. These results suggest that OTUB1 regulates NF-κB and MAPK signalling pathways and TNF-dependent cell death by modulating c-IAP1 stability.