Sigma-1 receptor regulates mitophagy in dopaminergic neurons and contributes to dopaminergic protection.

Mitochondria are essential for neuronal survival and function, and mitochondrial dysfunction plays a critical role in the pathological development of Parkinson's disease (PD). Mitochondrial quality control is known to contribute to the survival of dopaminergic (DA) neurons, with mitophagy being a key regulator of the quality control system. In this study, we show that mitophagy is impaired in the substantia nigra pars compacta (SNc) of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. Treatment with the sigma-1 receptor (Sig 1R) agonist 2-morpholin-4-ylethyl 1-phenylcyclohexane-1-carboxylate (PRE-084) reduced loss of DA neurons, restored motor ability and MPTP-induced damage to mitophagy activity in the SNc of PD-like mice. Additionally, knockdown of Sig 1R in SH-SY5Y DA cells inhibited mitophagy and enhanced 1-methyl-4-phenylpyridinium ion (MPP+) neurotoxicity, whereas application of the Sig 1R selective agonist SKF10047 promoted clearance of damaged mitochondria. Moreover, knockdown of Sig 1R in SH-SY5Y cells resulted in decreased levels of p-ULK1 (Unc-51 Like Autophagy Activating Kinase 1) (Ser555), p-TBK1 (TANK Binding Kinase 1) (Ser172), p-ubiquitin (Ub) (Ser65), Parkin recruitment, and stabilization of PTEN-induced putative kinase 1 (PINK1) in mitochondria. The present data provide the first evidence for potential roles of PINK1/Parkin in Sig 1R-modulated mitophagy in DA neurons.

Docosahexaenoic Acid, a Potential Treatment for Sarcopenia, Modulates the Ubiquitin-Proteasome and the Autophagy-Lysosome Systems.

One of the characteristic features of aging is the progressive loss of muscle mass, a nosological syndrome called sarcopenia. It is also a pathologic risk factor for many clinically adverse outcomes in older adults. Therefore, delaying the loss of muscle mass, through either boosting muscle protein synthesis or slowing down muscle protein degradation using nutritional supplements could be a compelling strategy to address the needs of the world's aging population. Here, we review the recently identified properties of docosahexaenoic acid (DHA). It was shown to delay muscle wasting by stimulating intermediate oxidative stress and inhibiting proteasomal degradation of muscle proteins. Both the ubiquitin-proteasome and the autophagy-lysosome systems are modulated by DHA. Collectively, growing evidence indicates that DHA is a potent pharmacological agent that could improve muscle homeostasis. Better understanding of cellular proteolytic systems associated with sarcopenia will allow us to identify novel therapeutic interventions, such as omega-3 polyunsaturated fatty acids, to treat this disease.

Endocytic sorting and downregulation of the M2 acetylcholine receptor is regulated by ubiquitin and the ESCRT complex.

Cholinergic dysfunction plays a critical role in a number of disease states, and the loss of functional muscarinic acetylcholine receptors plays a key role in disease pathogenesis. Therefore, preventing receptor downregulation would maintain functional receptor number, and be predicted to alleviate symptoms. However, the molecular mechanism(s) underlying muscarinic receptor downregulation are currently unknown. Here we demonstrate that the M2 muscarinic receptor undergoes rapid lysosomal proteolysis, and this lysosomal trafficking is facilitated by ubiquitination of the receptor. Importantly, we show that this trafficking is driven specifically by ESCRT mediated involution. Critically, we provide evidence that disruption of this process leads to a re-routing of the trafficking of the M2 receptor away from the lysosome and into recycling pathway, and eventually back to the plasma membrane. This study is the first to identify the process by which the M2 muscarinic acetylcholine receptor undergoes endocytic sorting, and critically reveals a regulatory checkpoint that represents a target to pharmacologically increase the number of functional muscarinic receptors within the central nervous system.

A20 protects cells from TNF-induced apoptosis through linear ubiquitin-dependent and -independent mechanisms.

The cytokine TNF promotes inflammation either directly by activating the MAPK and NF-κB signaling pathways, or indirectly by triggering cell death. A20 is a potent anti-inflammatory molecule, and mutations in the gene encoding A20 are associated with a wide panel of inflammatory pathologies, both in human and in the mouse. Binding of TNF to TNFR1 triggers the NF-κB-dependent expression of A20 as part of a negative feedback mechanism preventing sustained NF-κB activation. Apart from acting as an NF-κB inhibitor, A20 is also well-known for its ability to counteract the cytotoxic potential of TNF. However, the mechanism by which A20 mediates this function and the exact cell death modality that it represses have remained incompletely understood. In the present study, we provide in vitro and in vivo evidences that deletion of A20 induces RIPK1 kinase-dependent and -independent apoptosis upon single TNF stimulation. We show that constitutively expressed A20 is recruited to TNFR1 signaling complex (Complex I) via its seventh zinc finger (ZF7) domain, in a cIAP1/2-dependent manner, within minutes after TNF sensing. We demonstrate that Complex I-recruited A20 protects cells from apoptosis by stabilizing the linear (M1) ubiquitin network associated to Complex I, a process independent of its E3 ubiquitin ligase and deubiquitylase (DUB) activities and which is counteracted by the DUB CYLD, both in vitro and in vivo. In absence of linear ubiquitylation, A20 is still recruited to Complex I via its ZF4 and ZF7 domains, but this time protects the cells from death by deploying its DUB activity. Together, our results therefore demonstrate two distinct molecular mechanisms by which constitutively expressed A20 protect cells from TNF-induced apoptosis.

The ubiquitin-proteasome system is necessary for the replication of duck Tembusu virus.

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that has caused massive economic losses to the duck industry in China. The cellular factors required for DTMUV replication have been poorly studied. The ubiquitin-proteasome system (UPS), the major intracellular proteolytic pathway, mediates diverse cellular processes, including endocytosis and signal transduction, which may be involved in the entry of virus. In the present study, we explored the interplay between DTMUV replication and the UPS in BHK-21 cells and found that treatment with proteasome inhibitor (MG132 and lactacystin) significantly decreased the DTMUV progency at the early infection stage. We further revealed that inhibition of the UPS mainly occurs on the level of viral protein expression and RNA transcription. In addition, using specific siRNAs targeting ubiquitin reduces the production of viral progeny. In the presence of MG132 the staining for the envelope protein of DTMUV was dramatically reduced in comparison with the untreated control cells. Overall, our observations reveal an important role of the UPS in multiple steps of the DTMUV infection cycle and identify the UPS as a potential drug target to modulate the impact of DTMUV infection.

A patent review of the ubiquitin ligase system: 2015-2018.

INTRODUCTION: Ubiquitin-proteasome system (UPS) has been validated as a novel anticancer drug target in the past 20 years. The UPS contains two distinct steps: ubiquitination of a substrate protein by ubiquitin activating enzyme (E1), ubiquitin conjugating enzyme (E2), and ubiquitin ligase (E3), and substrate degradation by the 26S proteasome complex. The E3 enzyme is the central player in the ubiquitination step and has a wide range of specific substrates in cancer cells, offering great opportunities for discovery and development of selective drugs. Areas covered: This review summarizes the recent advances in small molecule inhibitors of E1s, E2s, and E3s, with a focus on the latest patents (from 2015 to 2018) of E3 inhibitors and modulators. Expert opinion: One strategy to overcome limitations of current 20S proteasome inhibitors is to discover inhibitors of the upstream key components of the UPS, such as E3 enzymes. E3s play important roles in cancer development and determine the specificity of substrate ubiquitination, offering novel target opportunities. E3 modulators could be developed by rational design, natural compound or library screening, old drug repurposes, and application of other novel technologies. Further understanding of mechanisms of E3-substrate interaction will be essential for discovering and developing next-generation E3 inhibitors as effective anticancer drugs.

Structures of REV1 UBM2 Domain Complex with Ubiquitin and with a Small-Molecule that Inhibits the REV1 UBM2-Ubiquitin Interaction.

REV1 is a DNA damage tolerance protein and encodes two ubiquitin-binding motifs (UBM1 and UBM2) that are essential for REV1 functions in cell survival under DNA-damaging stress. Here we report the first solution and X-ray crystal structures of REV1 UBM2 and its complex with ubiquitin, respectively. Furthermore, we have identified the first small-molecule compound, MLAF50, that directly binds to REV1 UBM2. In the heteronuclear single quantum coherence NMR experiments, peaks of UBM2 but not of UBM1 are significantly shifted by the addition of ubiquitin, which agrees to the observation that REV1 UBM2 but not UBM1 is required for DNA damage tolerance. REV1 UBM2 interacts with hydrophobic residues of ubiquitin such as L8 and L73. NMR data suggest that MLAF50 binds to the same residues of REV1 UBM2 that interact with ubiquitin, indicating that MLAF50 can compete with the REV1 UBM2-ubiquitin interaction orthosterically. Indeed, MLAF50 inhibited the interaction of REV1 UBM2 with ubiquitin and prevented chromatin localization of REV1 induced by cisplatin in U2OS cells. Our results structurally validate REV1 UBM2 as a target of a small-molecule inhibitor and demonstrate a new avenue to targeting ubiquitination-mediated protein interactions with a chemical tool.

Therapeutic Strategies against Epstein-Barr Virus-Associated Cancers Using Proteasome Inhibitors.

Epstein-Barr virus (EBV) is closely associated with several lymphomas (endemic Burkitt lymphoma, Hodgkin lymphoma and nasal NK/T-cell lymphoma) and epithelial cancers (nasopharyngeal carcinoma and gastric carcinoma). To maintain its persistence in the host cells, the virus manipulates the ubiquitin-proteasome system to regulate viral lytic reactivation, modify cell cycle checkpoints, prevent apoptosis and evade immune surveillance. In this review, we aim to provide an overview of the mechanisms by which the virus manipulates the ubiquitin-proteasome system in EBV-associated lymphoid and epithelial malignancies, to evaluate the efficacy of proteasome inhibitors on the treatment of these cancers and discuss potential novel viral-targeted treatment strategies against the EBV-associated cancers.

JS-K, a nitric oxide pro-drug, regulates growth and apoptosis through the ubiquitin-proteasome pathway in prostate cancer cells.

BACKGROUND: In view of the fact that JS-K might regulate ubiquitin E3 ligase and that ubiquitin E3 ligase plays an important role in the mechanism of CRPC formation, the goal was to investigate the probable mechanism by which JS-K regulates prostate cancer cells. METHODS: Proliferation inhibition by JS-K on prostate cancer cells was examined usingCCK-8 assays. Caspase 3/7 activity assays and flow cytometry were performed to examine whether JS-K induced apoptosis in prostate cancer cells. Western blotting and co-immunoprecipitation analyses investigated JS-K's effects on the associated apoptosis mechanism. Real time-PCR and Western blotting were performed to assess JS-K's effect on transcription of specific AR target genes. Western blotting was also performed to detect Siah2 and AR protein concentrations and co-immunoprecipitation to detect interactions of Siah2 and AR, NCoR1 and AR, and p300 and AR. RESULTS: JS-K inhibited proliferation and induced apoptosis in prostate cancer cells. JS-K increased p53 and Mdm2 concentrations and regulated the caspase cascade reaction-associated protein concentrations. JS-K inhibited transcription of AR target genes and down-regulated PSA protein concentrations. JS-K inhibited Siah2 interactions and also inhibited the ubiquitination of AR. With further investigation, JS-K was found to stabilize AR and NCoR1 interactions and diminish AR and p300 interactions. CONCLUSIONS: The present results suggested that JS-K might have been able to inhibit proliferation and induce apoptosis via regulation of the ubiquitin-proteasome degradation pathway, which represented a promising platform for the development of new compounds for PCa treatments.

Aß40 Reduces P-Glycoprotein at the Blood-Brain Barrier through the Ubiquitin-Proteasome Pathway.

Failure to clear amyloid-ß (Aß) from the brain is in part responsible for Aß brain accumulation in Alzheimer's disease (AD). A critical protein for clearing Aß across the blood-brain barrier is the efflux transporter P-glycoprotein (P-gp) in the luminal plasma membrane of the brain capillary endothelium. P-gp is reduced at the blood-brain barrier in AD, which has been shown to be associated with Aß brain accumulation. However, the mechanism responsible for P-gp reduction in AD is not well understood. Here we focused on identifying critical mechanistic steps involved in reducing P-gp in AD. We exposed isolated rat brain capillaries to 100 nm Aß40, Aß40, aggregated Aß40, and Aß42. We observed that only Aß40 triggered reduction of P-gp protein expression and transport activity levels; this occurred in a dose- and time-dependent manner. To identify the steps involved in Aß-mediated P-gp reduction, we inhibited protein ubiquitination, protein trafficking, and the ubiquitin-proteasome system, and monitored P-gp protein expression, transport activity, and P-gp-ubiquitin levels. Thus, exposing brain capillaries to Aß40 triggers ubiquitination, internalization, and proteasomal degradation of P-gp. These findings may provide potential therapeutic targets within the blood-brain barrier to limit P-gp degradation in AD and improve Aß brain clearance. SIGNIFICANCE STATEMENT: The mechanism reducing blood-brain barrier P-glycoprotein (P-gp) in Alzheimer's disease is poorly understood. In the present study, we focused on defining this mechanism. We demonstrate that Aß40 drives P-gp ubiquitination, internalization, and proteasome-dependent degradation, reducing P-gp protein expression and transport activity in isolated brain capillaries. These findings may provide potential therapeutic avenues within the blood-brain barrier to limit P-gp degradation in Alzheimer's disease and improve Aß brain clearance.

Arsenic trioxide induces programmed cell death through stimulation of ER stress and inhibition of the ubiquitin-proteasome system in human sarcoma cells.

Sarcoma is a rare form of cancer that differs from the much more common carcinomas because it occurs in a distinct type of tissue. Many patients of sarcoma have poor response to chemotherapy and an increased risk for local recurrence. Arsenic trioxide (ATO) is used to treat certain types of leukemia. Recently, data have revealed that ATO induces sarcoma cell death in several types of solid tumor cell lines. In the present study, we investigated whether ATO induces cancer cell death and elucidated the underlying anti-cancer mechanisms. Our results showed that ATO caused concentration- and time-dependent cell death in human osteosarcoma and fibrosarcoma cells. The types of cell death that were induced by ATO were primarily autophagy and apoptosis. Furthermore, ATO activated p38, JNK and AMPK and inhibited the Akt/mTOR signaling pathways. Specifically, we found that ATO induced endoplasmic reticulum (ER) stress and suppressed proteasome activation in two types of sarcoma cell lines. However, the level of proteasome inhibition in osteosarcoma cells was lower than in fibrosarcoma cells. Thus, we used combined treatment with ATO and a proteasome inhibitor to examine the antitumor activity in fibrosarcoma cells. The data indicated showed that the combination treatment of ATO and MG132 (a proteasome inhibitor) resulted in synergistic cytotoxicity. In a fibrosarcoma xenograft mouse model, the combined treatment significantly reduced tumor progression. Immunohistochemical studies revealed that combined treatment induced autophagy and apoptosis. In summary, our results suggest a potential clinical application of ATO in sarcoma therapy and that combined treatment with a proteasome inhibitor can increase the therapeutic efficacy.

Activation of the ubiquitin-proteasome system against arsenic trioxide cardiotoxicity involves ubiquitin ligase Parkin for mitochondrial homeostasis.

Parkin is an E3 ubiquitin ligase involved in the elimination of damaged mitochondria. Ubiquitination of mitochondrial substrates by Parkin results in proteasomal as well as lysosomal degradation of mitochondria, the latter of which is executed by the autophagy machinery and is called as mitophagy (mitochondrial autophagy). The aim of this study is to examine the possible role of Parkin against cardiotoxicity elicited by arsenic trioxide (ATO) exposure in HL-1 mouse atrial cardiomyocytes. HL-1 cells were administered 1-10µM ATO for up to 24h, and the involvements of apoptosis, and the ubiquitin-proteasome and autophagy-lysosome systems (UPS and ALS) were examined. ATO dose-dependently reduced mitochondrial membrane potentials (ΔΨm) in HL-1 cells, indicating that ATO works as a mitochondrial toxin in these cells. Apoptosis was evident in cells exposed to more than 6µM ATO for 24h. Levels of Parkin in mitochondria-rich fractions were increased, suggesting the recruitment of Parkin to mitochondria. Ubiquitination of the voltage-dependent anion channel1 (VDAC1), a substrate of Parkin, was also proved by immunoprecipitation. Accumulation of ubiquitinated proteins including both K48- and K63-lineages was observed in HL-1 cells after ATO exposure, implying an increased demand for proteasomal as well as lysosomal degradation of cellular proteins. Although UPS was activated by ATO as proved by increased proteasomal activity, only slight activation of the ALS marker LC3 was observed, suggesting differential reactions of UPS and ALS to ATO toxicity. The abrogation of UPS by the proteasome inhibitor bortezomib significantly sensitized HL-1 cells to ATO toxicity, showing the contribution of UPS to the maintenance of cellular homeostasis during ATO exposure. Taken together, our results reveal the activation of Parkin as well as UPS during ATO exposure in HL-1 cardiomyocytes, which contributes to the maintenance of mitochondrial as well as cellular homeostasis.

Cetuximab inhibits oral squamous cell carcinoma invasion and metastasis via degradation of epidermal growth factor receptor.

Cetuximab (Erbitux, C225) is a chimeric monoclonal antibody that binds to the extracellular domain of epidermal growth factor receptor (EGFR), inhibiting tumor growth, invasion, angiogenesis and metastasis. However, the mechanisms underlying the effect of Cetuximab in human oral squamous cell carcinoma (OSCC) remain unclear. Here, we report that Cetuximab modulates EGFR protein stability through the ubiquitin/proteasome pathway, resulting in the inhibition of human OSCC growth. Cetuximab significantly inhibited the migration and invasion of human OSCC cells by blocking epithelial/mesenchymal transition (EMT) and the AKT and ERK pathways. Furthermore, Cetuximab-inhibited cell growth by modulating the expression of integrin ß5. Taken together, these results provide novel insights into the mechanism of Cetuximab action and suggest potential therapeutic strategies for OSCC.

General aspects and recent advances on bacterial protein toxins.

Bacterial pathogens produce protein toxins to influence host-pathogen interactions and tip the outcome of these encounters toward the benefit of the pathogen. Protein toxins modify host-specific targets through posttranslational modifications (PTMs) or noncovalent interactions that may inhibit or activate host cell physiology to benefit the pathogen. Recent advances have identified new PTMs and host targets for toxin action. Understanding the mechanisms of toxin action provides a basis to develop vaccines and therapies to combat bacterial pathogens and to develop new strategies to use toxin derivatives for the treatment of human disease.

Mitochondrial dysfunction precedes other sub-cellular abnormalities in an in vitro model linked with cell death in Parkinson's disease.

Dysfunction of mitochondria, the ubiquitin proteasome system (UPS), and lysosomes are believed to contribute to the pathogenesis of Parkinson's disease (PD). If it were possible to rescue functionally compromised, but still viable neurons early in the disease process, this would slow the rate of neurodegeneration. Here, we used a catecholaminergic neuroblastoma cell line (SH-SY5Y) as a model of susceptible neurons in PD. To identify a target early in the cell death process that was common to all neurodegenerative processes linked with PD, cells were exposed to toxins that mimic cell death mechanisms associated with PD. The sub-cellular abnormalities that occur shortly after toxin exposure were determined. 3 h of exposure to either naphthazarin, to inhibit lysosomal function, Z-Ile-Glu(OBu(t))-Ala-Leu-H (PSI), to inhibit the UPS, or rotenone, to inhibit mitochondrial complex I, caused depolarisation of the mitochondrial membrane potential (2.5-fold, twofold, and 4.6-fold change, respectively compared to vehicle), suggesting impaired mitochondrial function. Following 24 h exposure to the same toxins, UPS and lysosomal function were also impaired, and ubiquitin levels were increased. Thus, following exposure to toxins that mimic three important, but disparate cell death mechanisms associated with PD, catecholaminergic cells initially experience mitochondrial dysfunction, which is then followed by abnormalities in UPS and lysosomal function. Thus, mitochondrial dysfunction is an early event in cell stress. We suggest that, in patients with PD, the surviving cells of the substantia nigra pars compacta are most susceptible to mitochondrial impairment. Thus, targeting the mitochondria may be useful for slowing the progression of neurodegeneration in PD.

ß-cell dysfunctional ERAD/ubiquitin/proteasome system in type 2 diabetes mediated by islet amyloid polypeptide-induced UCH-L1 deficiency.

OBJECTIVE: The islet in type 2 diabetes is characterized by ß-cell apoptosis, ß-cell endoplasmic reticulum stress, and islet amyloid deposits derived from islet amyloid polypeptide (IAPP). Toxic oligomers of IAPP form intracellularly in ß-cells in humans with type 2 diabetes, suggesting impaired clearance of misfolded proteins. In this study, we investigated whether human-IAPP (h-IAPP) disrupts the endoplasmic reticulum-associated degradation/ubiquitin/proteasome system. RESEARCH DESIGN AND METHODS: We used pancreatic tissue from humans with and without type 2 diabetes, isolated islets from h-IAPP transgenic rats, isolated human islets, and INS 832/13 cells transduced with adenoviruses expressing either h-IAPP or a comparable expression of rodent-IAPP. Immunofluorescence and Western blotting were used to detect polyubiquitinated proteins and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) protein levels. Proteasome activity was measured in isolated rat and human islets. UCH-L1 was knocked down by small-interfering RNA in INS 832/13 cells and apoptosis was evaluated. RESULTS: We report accumulation of polyubiquinated proteins and UCH-L1 deficiency in ß-cells of humans with type 2 diabetes. These findings were reproduced by expression of oligomeric h-IAPP but not soluble rat-IAPP. Downregulation of UCH-L1 expression and activity to reproduce that caused by h-IAPP in ß-cells induced endoplasmic reticulum stress leading to apoptosis. CONCLUSIONS: Our results indicate that defective protein degradation in ß-cells in type 2 diabetes can, at least in part, be attributed to misfolded h-IAPP leading to UCH-L1 deficiency, which in turn further compromises ß-cell viability.

The ubiquitin-proteasome system is inhibited by p53 protein expression in human ovarian cancer cells.

The ubiquitin-proteasome system (UPS) and autophagy provide major cellular pathways for protein degradation. Since the p53 pathway controls autophagy, we investigated whether p53 regulates UPS in ovarian tumour cell lines. A reporter cell line (SKOV3-EGFPu) was established to measure UPS function against a constant genetic background. Transient expression of either wild type or mutant p53 in SKOV3-EGFPu cells reduced UPS activity as compared to vector control. These results, together with those from endogenous p53 expression in seven ovarian cancer cell lines, suggest that expression of both wild-type and mutant p53 protein impairs UPS function. Thus, p53 expression may regulate protein homeostasis by down-regulating UPS function in response to cellular stress.

Effects of combined gamma-irradiation and metal (Al+Cd) exposures in Atlantic salmon (Salmo salar L.).

These experiments were designed to investigate transcriptional effects in Atlantic salmon (Salmo salar) after exposure in vivo to ionizing gamma radiation combined with subtoxic levels of aluminum (Al) and cadmium (Cd). Juvenile fish (35 g) in freshwater with or without Al and Cd (255 microg Al/L + 6 microg Cd/L) were exposed to a 75 mGy dose of gamma-irradiation, and induced responses were compared to those of controls. The transcriptional levels of eight genes encoding proteins known to respond to stress in fish were quantified in liver of fish exposed for 5 h to gamma radiation, to Al and Cd or to the combination of Al, Cd and gamma radiation. The studied genes were caspase 3B, caspase 6A, caspase 7, p53 (apoptosis), glutathione reductase (GR), phospholipid hydroperoxide glutathione peroxidase (GSH-Px), (oxidative stress), metallothionein (MT-A) (metal stress) and ubiquitin (Ubi) (protein degradation). The results showed that gamma-irradiation alone induced significant upregulation of caspase 6A, GR, GSH-Px, MT-A and Ubi compared to the control group, while 5 h exposure to Al+Cd alone did not induce any of the studied genes compared to the control. No significant upregulation of the series of investigated genes could be observed in fish exposed to gamma-irradiation in combination with Al+Cl. In conclusion, the results suggest that the presence of Al+Cd in the water counteracted the gamma-irradiation effect by modifying the transcription of genes encoding proteins involved in the defense mechanisms against free radicals in the cells.

Targeting the ubiquitin proteasome pathway for the treatment of septic shock in patients.

Endotoxic shock is a serious systemic inflammatory response to an external biological stressor. The responsiveness of NF-kappaB is built upon rapid protein modification and degradation involving the ubiquitin proteasome pathway. Using transgenic mice, we have obtained in vivo evidence that interference with this pathway can alleviate the symptoms of toxic shock. We posit that administration of proteasome inhibitors may enhance the survival of patients with septic shock.