Administration Of Proteasome Inhibitors Research Articles

Peripheral Neuropathy During Concomitant Administration of Proteasome Inhibitors and Factor Xa Inhibitors: Identifying the Likelihood of Drug-Drug Interactions.

Backgrounds: Proteasome inhibitors (PI) cause toxic peripheral neuropathy (PN), which is one of the dose-limiting adverse events of these treatments. Recent preclinical studies find that factor Xa inhibitor (FXaI), rivaroxaban, promotes PN in animals receiving oxaliplatin. Cancer patients can receive combined therapy of PI and FXaI. This study aimed to identify and characterize the interaction signals for the concomitant use of PI and FXaI resulting in PN. Methods: Reports from the United States FDA Adverse Event Reporting System (FAERS) were extracted from the first quarter of 2004 to the first quarter of 2020 for analysis. The Standardized Medical Dictionary for Regulatory Activities (MedDRA) query was used to identify PN cases. We conducted an initial disproportionality investigation to detect PN adverse event signals associated with the combined use of PI and FXaI by estimating a reporting odds ratio (ROR) with a 95% confidence interval (CI). The adjusted RORs were then analyzed by logistic regression analysis (adjusting for age, gender, and reporting year), and additive/multiplicative models were performed to further confirm the findings. Additionally, subset data analysis was performed on the basis of a single drug of PI and FXaI. Results: A total of 159,317 adverse event reports (including 2,822 PN reports) were included. The combined use of PI and FXaI was associated with a higher reporting of PN (RORadj = 7.890, 95%CI, 5.321–11.698). The result remained significant based on additive/multiplicative methods. The observed association was consistent in the analysis restricted to all specific PI agents (bortezomib and ixazomib) and FXaI (rivaroxaban), except apixaban. Conclusion: Analysis of FAERS data identified reporting associations of PN in the combined use of PI and FXaI, suggesting the need for more robust preclinical and clinical studies to elucidate the relationship.

Primary anti-infective prophylaxis during routine treatment of lymphoma in the United States: A large real-world cohort analysis.

268 Background: While infectious complications contribute to considerable morbidity and mortality in patients with cancer, most scenarios lack evidence to guide optimal anti-infective prophylaxis (AIP). We evaluated a large real-world dataset to identify baseline utilization and factors associated with AIP in patients with non-Hodgkin lymphoma (NHL) treated in the US-community setting. Methods: Using the nationwide Flatiron Health de-identified electronic health record-derived database (from ≈ 280 US cancer clinics), we selected patients treated prior to 7/1/2020 with 1) R-CHOP for DLBCL, 2) bendamustine and rituximab (BR) for CLL/SLL, or 3) ibrutinib for CLL/SLL. We limited our analysis to patients treated by providers with documented prescribing of guideline recommended anti-viral prophylaxis (ppx) during proteasome inhibitor administration to ≥1 multiple myeloma patient. Our main outcome was the documented use of primary AIP defined as anti-viral and/or pneumocystis jiroveci (PJP) ppx within +/- 14 days of treatment initiation. We also report the delayed documented AIP use from day 15 to 60. We applied separate multivariable logistic regression models to each setting to examine the associations of patient-level characteristics with primary AIP (including age, sex, race, region, insurance, ECOG, year of treatment initiation). Results: A total of 3,142 (R-CHOP for DLBCL), 2,180 (BR for CLL/SLL), and 3,590 (ibrutinib for CLL/SLL) patients were included, with median age of 69, 69, and 72 years, respectively. Primary AIP was most common during BR for CLL/SLL, with 16.8% receiving any AIP (antiviral 15.6%, PJP 7.3%). Primary AIP was used in 10.5% of DLBCL patients initiating R-CHOP (antiviral 7.6%, PJP 5.6%), with the lowest utilization of AIP during ibrutinib for CLL/SLL (any 6.4%, antiviral 5.6%, PJP 2.6%). In the delayed setting, an additional 4-6% and 2-5% received viral and PJP ppx, respectively. Across all three of our multivariable analyses, higher provider rate of anti-viral ppx during proteosome inhibitor administration in MM, residing in the Midwest (vs. Northeast), and more recent treatment initiation were associated with greater odds of AIP. Other patient characteristics (age, race, ECOG) were less consistently associated with AIP across models. Furthermore, C-statistics were <0.7 in all three models (0.660-0.685), suggesting suboptimal discrimination for AIP based on patient-level characteristics alone. Conclusions: We observed low utilization of primary AIP during treatment in three common NHL settings that lack clear consensus on AIP. Variation was not well explained by measured patient characteristics, and future studies should consider provider and system attributes. Ultimately, robust evidence generation (e.g. pragmatic clinical trials) and quality improvement measures are needed to optimize ppx during routine lymphoma management.

Indoxyl Sulfate Promotes Macrophage IL-1β Production by Activating Aryl Hydrocarbon Receptor/NF-κ/MAPK Cascades, but the NLRP3 inflammasome Was Not Activated.

In chronic kidney disease (CKD) patients, accumulation of uremic toxins is associated with cardiovascular risk and mortality. One of the hallmarks of kidney disease-related cardiovascular disease is intravascular macrophage inflammation, but the mechanism of the reaction with these toxins is not completely understood. Macrophages differentiated from THP-1 cells were exposed to indoxyl sulfate (IS), a representative uremic toxin, and changes in inflammatory cytokine production and intracellular signaling molecules including interleukin (IL)-1, aryl hydrocarbon receptor (AhR), nuclear factor (NF)-κ, and mitogen-activated protein kinase (MAPK) cascades as well as the NLRP3 inflammasome were quantified by real-time PCR, Western blot analysis, and enzyme-linked immunosorbent assay. IS induced macrophage pro-IL-1β mRNA expression, although mature IL-1 was only slightly increased. IS increased AhR and the AhR-related mRNA expression; this change was suppressed by administration of proteasome inhibitor. IS promoted phosphorylation of NF-κB p65 and MAPK enzymes; the reaction and IL-1 expression were inhibited by BAY11-7082, an inhibitor of NF-κB. In contrast, IS decreased NLRP3 and did not change ASC, pro-caspase 1, or caspase-1 activation. IS-inducing inflammation in macrophages results from accelerating AhR-NF-κB/MAPK cascades, but the NLRP3 inflammasome was not activated. These reactions may restrict mature IL-1β production, which may explain sustained chronic inflammation in CKD patients.

Morphological Changes within the Rat Lateral Ventricle after the Administration of Proteasome Inhibitors.

The broad variety of substances that inhibit the action of the ubiquitin-proteasome system (UPS)—known as proteasome inhibitors—have been used extensively in previous studies, and they are currently frequently proposed as a novel form of cancer treatment and as a protective factor in intracerebral hemorrhage treatment. The experimental data on the safest route of proteasome inhibitor administration, their associated side effects, and the possible ways of minimizing these effects have recently become a very important topic. The aim of our present study was to determine the effects of administering of MG-132, lactacystin and epoxomicin, compounds belonging to three different classes of proteasome inhibitors, on the ependymal walls of the lateral ventricle. Observations were made 2 and 8 weeks after the intraventricular administration of the studied substances dissolved in dimethyl sulfoxide (DMSO) into the lateral ventricle of adult Wistar rats. Qualitative and quantitative analysis of brain sections stained with histochemical and inmmunofluorescence techniques showed that the administration of proteasome inhibitors caused a partial occlusion of the injected ventricle in all of the studied animals. The occlusion was due to ependymal cells damage and subsequent ependymal discontinuity, which caused direct contact between the striatum and the lateral nuclei of the septum, mononuclear cell infiltration and the formation of a glial scar between these structures (with the activation of astroglia, microglia and oligodendroglia). Morphologically, the ubiquitin-positive aggregates corresponded to aggresomes, indicating impaired activity of the UPS and the accumulation and aggregation of ubiquitinated proteins that coincided with the occurrence of glial scars. The most significant changes were observed in the wall covering the striatum in animals that were administered epoxomicin, and milder changes were observed in animals administered lactacystin and MG-132. Interestingly, DMSO administration also caused damage to some of the ependymal cells, but the aggresome-like structures were not formed. Our results indicate that all of the studied classes of proteasome inhibitors are detrimental to ependymal cells to some extent, and may cause severe changes in the ventricular system. The safety implications of their usage in therapeutic strategies to attenuate intracerebral hemorrhagic injury and in brain cancer treatment will require further studies.

Local application of a proteasome inhibitor enhances fracture healing in rats.

The ubiquitin/proteasome system plays an important role in regulating the activity of osteoblast precursor cells. Proteasome inhibitors (PSIs) have been shown to stimulate the differentiation of osteoblast precursor cells and to promote bone formation. This raises the possibility that PSIs might be useful for enhancing fracture healing. In this study, we examined the effect of the local administration of PSI on fracture repair in rats. The effects of treatment on the healing of a fractured femur were assessed based on radiographs, micro-computed tomography (μCT) analysis, biomechanical testing, and histological analysis. PSI enhanced osteogenic differentiation in bone marrow- and periosteum-derived mesenchymal progenitor cells in vitro. Moreover, the local administration of PSI in vivo promoted fracture healing in rats, as demonstrated by an increased fracture callus volume in radiographs at 2 weeks post-fracture, and improved radiographic scores. By week 4, PSI treatment had enhanced biomechanical strength and mineral density in the callus as assessed using bending tests, and μCT, respectively. Histological sections demonstrated that PSI treatment accelerated endochondral ossification during the early stages of fracture repair. Although further investigations are necessary to assess its clinical use, the local administration of PSIs might be a novel, and effective therapeutic approach for fracture repair.

Abstract 3523: Targeting FOXM1 in pancreatic cancer

Abstract Pancreatic cancer (PC) is one of the deadliest malignancies of our time. The limited treatment options necessitate the identification of novel therapeutic targets and strategies. FOXM1 is overexpressed in many different human malignancies including PC and it contributes to multiple aspects of tumorigenesis. In addition, emerging data indicates that FOXM1 might contribute to drug resistance. Therefore, we hypothesized that targeting FOXM1 could interfere with PC development and sensitize pancreatic tumor cells to apoptosis induced by anticancer drugs. The goal of this study was to explore the potential of targeting FOXM1 in pancreatic cancer. First, we examined how FOXM1 knockdown by RNA interference (RNAi) may affect the tumorigenecity of MIA PaCa-2 highly aggressive human pancreatic cancer cell line. Depletion of FOXM1 inhibited the colony forming ability of the PC cells in anchorage-dependent and independent conditions. In addition, we found that FOXM1 knockdown strongly impaired the ability of PC cells to induce xenograft tumors in nude mice. Second, we explored the potential anticancer properties of Simoycin A and thiostrepton and other known FOXM1/proteasome inhibitors against PC in culture and in xenograft mouse models. We demonstrate that FOXM1/proteasome inhibitors efficiently inhibited the growth of multiple human PC cell lines in low micromolar concentrations, repressed the protein expression of FOXM1 and also induced potent cell death in PC cells. In addition, we show that FOXM1/proteasome inhibitors reduced tumor growth in vivo, in a xenograft model of PC. Third, recent emerging data suggest that targeting cancer by combination treatment offers a more efficient therapeutic approach. Combination treatment improves efficacy, lowers the dose needed for effect and also overcomes drug resistance. Consequently, we evaluated targeting FOXM1 in combination with DNA-damage and oxidative stress. We found that FOXM1 knockdown by RNAi or suppression by proteasome inhibitors inhibits long-term survival and sensitizes PC cells to cell death induced by DNA-damage and by oxidative stress. In addition, we found that ROS inhibitor N-acetyl-L-cysteine antagonizes the activity of proteasome inhibitors by direct interaction with them and it is the first compound that acts as inhibitor of proteasome inhibitors. Overall, our findings suggest that targeting FOXM1 alone or in combination with DNA-damage or oxidative stress could offer an effective therapeutic approach against PC. According to our data, administration of proteasome inhibitors in combination with ROS inducers/DNA damaging agents represents an innovative treatment strategy, which would utilize integral properties of cancer cells in order to specifically eliminate them. Further work is needed to verify that our preclinical results should warrant clinical trials. Citation Format: Marianna Halasi, Andrei L. Gartel. Targeting FOXM1 in pancreatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3523. doi:10.1158/1538-7445.AM2014-3523

Reactive oxygen species/neddylation is a novel pathway of transforming growth factor‐β‐induced smooth muscle cell differentiation (952.2)

Smooth muscle cell (SMC) differentiation is an essential process in cardiovascular development. SMCs can be differentiated from pluripotent mesenchymal progenitors by transforming Growth Factor‐β (TGF‐β) while ubiquitin‐mediated protein degradation blocks SMC differentiation. Neural precursor cell‐Expressed Developmentally Down‐regulated 8 (NEDD8), a member in ubiquitin family, promotes protein stability and prevents protein degradation by conjugating to target proteins. We found that NEDD8/neddylation is essential for TGF‐β‐induced SMC differentiation. NEDD8 protein is increased during TGF‐β‐induced SMC differentiation and conjugates to smooth muscle α‐actin (α‐SMA). Blockade of neddylation by neddylation inhibitor (MLN‐4924) or NEDD8 short hairpin interfering RNA significantly inhibited the expression of α‐SMA and calponin (CNN) in TGF‐β‐treated cells. We found that reactive oxygen species (ROS) attenuation by SOD2 overexpression blocked TGF‐β‐induced NEDD8 conjugation to α‐SMA. SOD2 appeared to block neddylation through inhibiting expression of Casitas B‐lineage lymphoma (c‐Cbl), suggesting that ROS/c‐Cbl mediates TGF‐β‐mediated neddylation of α‐SMA and CNN. NEDD8/neddylation appears to enhance α‐SMA and CNN stability and prevent proteasome‐mediated degradation because administration of proteasome inhibitor (MG‐132) significantly inhibited α‐SMA and CNN protein degradation in neddylation‐depleted cells. Taken together, our study demonstrates that NEDD8‐mediated neddylation through ROS/c‐Cbl is a novel molecular event critical for TGF‐β‐induced SMC differentiation.Grant Funding Source: NIH‐R01

Detrimental Effect of the Proteasome Inhibitor, Bortezomib in Bacterial Superantigen- and Lipopolysaccharide-induced Systemic Inflammation

Bacterial superantigen (BSAg)-induced toxic shock syndrome (TSS) and bacterial lipopolysaccharide (LPS)-induced shock are characterized by severe systemic inflammation. As nuclear factor kappaB (NF kappaB) plays an important role in inflammation and bortezomib, a proteasome inhibitor widely used in cancer chemotherapy, is a potent inhibitor of NF kappaB activation, we evaluated the therapeutic and prophylactic use of bortezomib in these conditions using murine models. Bortezomib prophylaxis significantly reduced serum levels of many cytokines and chemokines induced by BSAg. However, at 3 hours, serum level of TNF-a, an important cytokine implicated in TSS, was significantly reduced but not abolished. At 6 hours, there was no difference in the serum TNF-a levels between bortezomib treated and untreated mice challenged with staphylococcal enterotoxin B (SEB). Paradoxically, all mice treated with bortezomib either before or after BSAg challenge succumbed to TSS. Neither bortezomib nor BSAg was lethal if given alone. Serum biochemical parameters and histopathological findings suggested acute liver failure as the possible cause of mortality. Liver tissue from SEB-challenged mice treated with bortezomib showed a significant reduction in NF kappaB activation. Because NF kappaB-dependent antiapoptotic pathways protect hepatocytes from TNF-alpha-induced cell death, inhibition of NF kappaB brought forth by bortezomib in the face of elevated TNF-alpha levels caused by BSAg or LPS is detrimental.

Proteasome inhibition modulates kinase activation in neural cells: Relevence to ubiquitination, ribosomes, and survival

In this study we examined whether established signal transduction cascades, p44/42 mitogen-activated protein kinase (ERK1/2) and Jun N-terminal kinases (JNK) pathways, are altered in N2a neural cells in response to proteasome inhibition. Additionally, we sought to elucidate the relative contribution of these signal transduction pathways to the multiple downstream effects of proteasome inhibition. Our data indicate that ERK1/2 and JNK are activated in response to proteasome inhibition. Washout of proteasome inhibitor (MG132) results in an enhancement of ERK1/2 activation and amelioration of JNK activation. Treatment with an established MAPK inhibitor resulted in an increase in proteasome inhibitor toxicity, and incubation with JNK inhibitor was observed to attenuate proteasome inhibitor toxicity significantly. Subsequent studies demonstrated that inhibition of ERK1/2 and JNK activity does not alter the gross increase in ubiquitinated protein following proteasome inhibitor administration. Similarly, ERK1/2 and JNK activity do not appear to play a role in the disruption of polysomes following proteasome inhibitor administration in neural cells. Together these data indicate that ERK1/2 and JNK activation may play differential roles in modulating neurochemical disturbances and neurotoxicity induced by proteasome inhibition.

B372 Peripheral Neuropathy Associated with Administration of Proteasome Inhibitors Is Mechanism Based

B372 Peripheral Neuropathy Associated with Administration of Proteasome Inhibitors Is Mechanism Based

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-κB 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.

Effect of an experimental proteasome inhibitor on the cytoskeleton, cytosolic protein turnover, and induction in the neuronal cells in vitro

GT-1 murine neuronal cells exposed to an experimental proteasome inhibitor (EPI) for 24 h showed increased cell death via a non-apoptotic mechanism, as assessed by TUNEL and DNA fragmentation assays. Immunofluorescence staining demonstrated that EPI induced reorganization and relocation of non-ubiquinated actin microfilaments and microtubules to the perinuclear region in EPI treated cells. Immunohistochemistry analysis also demonstrated that other non-cytoskeletal proteins became ubiquitinated and/or upregulated including ubiquitin and other stress proteins. Perinuclear-centrosomal accumulation of γ-tubulin and vimentin, key components of aggresomes, was observed in the EPI treated cells. Biochemical analysis indicated that EPI-induced accumulation of ubiquitinated protein aggregates in GT-1 cells was detergent – and mechanical – disruption resistant, a feature of aggresomes. Similar results were observed in GT-1 cells treated with lactacystin, a prototypical proteasome inhibitor, which is structurally dissimilar to EPI indicating a pharmacologic effect. In conclusion, EPI causes cytoskeletal reorganization and accumulation of diverse ubiquitinated and non-ubiquitinated proteins in the perinuclear region and potentially overloads the endoplasmic reticulum—dependent quality control mechanism. These processes acting alone, or in combination, are hypothesized to affect axonal transport or other aspects of cellular homeostasis and thus, represent events potentially relevant to the development of peripheral neuropathy associated with administration of proteasome inhibitors in nonclinical studies.

Abstract 257: Oxidative Stress Induces Endothelial Dysfunction: Role of Ubiquitin-Proteasome System

Endothelial Nitric oxide (NO) production is dependent on adequate cellular tetrahydrobiopterin (BH 4 ), a key cofactor for endothelial NO syntheses (eNOS). Reduction of BH 4 levels is reported in diseased vessels and plays a causal role in the development of eNOS uncoupling. However, the mechanisms that lead to BH 4 reduction are not entirely understood. Here we report that angiotensin-II (Ang II) reduced tetrahydrobiopterin (BH 4 ) and eNOS uncoupling by peroxynitrite ONOO − )-triggered proteasome activation. Compared to control, exposure of human umbilical vein endothelial cells (HUVEC) to angiotensin II (Ang II, 100nM) for 6h significantly decreased the levels of total biopterins (BH 4 plus BH 2 ) and BH 4 (−22.0 4.6%, n= 3, p<0.01), indicating decreased synthesis of biopterins. In parallel, Ang II but not vehicle significantly reduced the levels of GTP-cyclohydrolase (GTPCH), a rate-limiting enzyme for de novo synthesis of biopterins, and dihydrofolate reductase (DHFR), a crucial enzyme for BH 4 recycle from BH 2 . Ang II but not vehicle significantly increased the 26S proteasome activity. In addition, administration of proteasome inhibitors, MG132, abolished the Ang II-induced reduction of both GTPCH and DHFR. While Ang II significantly increased O 2 − , the scavenging of O 2 − by Tempol (SOD mimetic), or inhibition of NOS with N -nitro-L-arginine methyl ester hydrochloride (L-NAME) (1mM) significantly attenuated Ang II-induced both 26S proteasome activation and the reduction of both GTPCH and DHFR, suggesting that Ang II via endogenous ONOO − causes 26S proteasome-dependent degradation of both GTPCH and DHFR. Moreover, inhibition of NAD(P)H oxidase with either apocynin or by overexpression of p67 phox -dominant negative mutants ablated Ang II-induced proteasome activation and degradation of both GTPCH and DHFR. Finally, treatment of mice aorta ex vivo with MG132 (0.5 μM for 1h followed by Ang II for 12h) reversed the Ang II-induced reduction of GTPCH, DHFR and BH 4 , and increased acetylcholine-induced endothelium-dependent relaxation. We conclude that Ang II activates NAD(P)H oxidase to release O 2 . − and ONOO − , which activate 26S proteasome resulting in increased degradation of both GTPCH and DHFR, two key enzymes in controlling the levels of BH 4 .

Effects of systemic PSI administration on catecholaminergic cells in the brain, adrenal medulla and carotid body in Wistar rats

Traditional Parkinson's disease models in rats have several disadvantages. A promising alternative in terms of a more physiological model was proposed by McNaught et al. [McNaught, K.S., Perl, D.P., Brownell, A.L., Olanow, C.W., 2004. Systemic exposure to proteasome inhibitors causes a progressive model of Parkinson’s disease. Ann. Neurol. 56, 149–162.] inhibiting the proteasomal protein degradation in vivo where they observed in Sprague–Dawley rats distinct symptoms of Parkinson's disease, a typical slow progredient loss of dopaminergic neurons in the substantia nigra and a lack of dopaminergic afferences in the striatum. We administered to Wistar rats a synthetic proteasome inhibitor (PSI) analogous to the published method. Locomotor changes were analysed by a footprint test. Brain slices containing the substantia nigra and the striatum were stained immunohistochemically against tyrosine hydroxylase, neuronal nuclei antigen, glial fibrillary acidic protein, α-synuclein and microglia. Standard histological stainings (haematoxylin eosin or Nissl) were also performed. The proteasome inhibitor effect on the glomerular layer of the olfactory bulb, the adrenal medulla and the carotid body was examined. We observed no PSI-induced motor deficits and loss of tyrosine hydroxylase immunoreactivity in the substantia nigra or the striatum. However, we detected a distinct increase of tyrosine hydroxylase immunoreactivity in the glomerular layer of the olfactory bulb and in the adrenal medulla. Our results fall in line with reports of other research groups which failed to reproduce the original report, but here for the first time McNaughts model could not be reproduced in Wistar rats. The observed effects on the olfactory bulb and peripheral catecholaminergic organs speak for an impermeability of the blood brain barrier for PSI.

Proteasome inhibition increases DNA and RNA oxidation in astrocyte and neuron cultures

Increased levels of nucleic acid oxidation have been described as part of normal brain aging and have been demonstrated to occur in multiple neurological disorders. The basis for increased nucleic acid oxidation in each of these conditions is presently unknown. Proteasome inhibition occurs in a host of neurodegenerative conditions and likely contributes to increased levels of oxidative damage and neurotoxicity. In the present study we demonstrate for the first time the ability of proteasome inhibition to increase the level of nucleic acid oxidation in primary neuron and astrocyte cultures. Administration of proteasome inhibitors (MG262, MG115) at concentrations that do not induce neuron death in the first 24 h of treatment, dramatically increase the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 8-hydroxyguanosine (8OHG) immunoreactivity in both cell types. Neurons underwent larger increases in nucleic acid oxidation compared to astrocyte cultures. While both DNA and RNA oxidation were observed following proteasome inhibition, RNA appeared to undergo a greater degree of oxidation than DNA. Both 18S and 28S ribosomal RNA were dramatically decreased following proteasome inhibition. Interestingly, an accumulation of unprocessed and/or cross-linked RNA species was observed following proteasome inhibition. Taken together, these data indicate the ability of proteasome inhibition to increase the levels of nucleic acid oxidation in both neurons and astrocytes, and suggest that proteasome inhibition may have deleterious effects on transcription and translation in both neurons and glia.

Polyglutamine Expansion, Protein Aggregation, Proteasome Activity, and Neural Survival

Huntington's disease (HD) is one of eight established triplet repeat neurodegenerative disorders, which are collectively caused by the genetic expansion of polyglutamine repeats. While the mechanism(s) by which polyglutamine expansion causes neurodegeneration in each of these disorders is being intensely investigated, the underlying cause of polyglutamine toxicity has not been fully elucidated. A number of studies have focused on the potential role of protein aggregation and disruption of the proteasome proteolytic pathway in polyglutamine-mediated neurodegeneration. However, at present it is not clear whether polyglutamine-mediated protein aggregation is sufficient to induce cell death, nor has it been clearly determined whether proteasome inhibition precedes, coincides, or occurs as the result of the formation of polyglutamine-associated protein aggregation. To address these important components of polyglutamine toxicity, in the present study we utilized neural SH-SY5Y cells stably transfected with polyglutamine-green fluorescent protein constructs to examine the effects of polyglutamine expansion on protein aggregation, proteasome activity, and neural cell survival. Data from the present study demonstrate that polyglutamine expansion does not dramatically impair proteasome activity or elevate protein aggregate formation under basal conditions, but does significantly impair the ability of the proteasome to respond to stress, and increases stress-induced protein aggregation following stress, all in the absence of neural cell death.