Novel mechanism of drug resistance to proteasome inhibitors in multiple myeloma

Multiple myeloma(MM) is a cancer caused by uncontrolled proliferation of antibody-secreting plasma cells in bone marrow, which represents the second most common hematological malignancy. MM is a highly heterogeneous disease and can be classified into a spectrum of subgroups based on their molecular and cytogenetic abnormalities. In the past decade, novel therapies, especially, the first-in-class proteasome inhibitor bortezomib, have been revolutionary for the treatment of MM patients. Despite these remarkable achievements, myeloma remains incurable with a high frequency of patients suffering from a relapse, due to drug resistance. Mutation in the proteasome β5-subunit(PSMB5) was found in a bortezomib-resistant cell line generated via long-term coculture with increasing concentrations of bortezomib in 2008, but their actual implication in drug resistance in the clinic has not been reported until recently. A recent study discovered four resistance-inducing PSMB5 mutations from a relapsed MM patient receiving prolonged bortezomib treatment. Analysis of the dynamic clonal evolution revealed that two subclones existed at the onset of disease, while the other two subclones were induced. Protein structural modeling and functional assays demonstrated that all four mutations impaired the binding of bortezomib to the 20 S proteasome, conferring different degrees of resistance. The authors further demonstrated two potential approaches to overcome drug resistance by using combination therapy for targeting proteolysis machinery independent of the 20 S proteasome.

Proteasome inhibitor treatment in alcoholic liver disease

Oxidative stress, generated by chronic ethanol consumption, is a major cause of hepatotoxicity and liver injury. Increased production of oxygen-derived free radicals due to ethanol metabolism by CYP2E1 is principally located in the cytoplasm and in the mitochondria, which does not only injure liver cells, but also other vital organs, such as the heart and the brain. Therefore, there is a need for better treatment to enhance the antioxidant response elements. To date, there is no established treatment to attenuate high levels of oxidative stress in the liver of alcoholic patients. To block this oxidative stress, proteasome inhibitor treatment has been found to significantly enhance the antioxidant response elements of hepatocytes exposed to ethanol. Recent studies have shown in an experimental model of alcoholic liver disease that proteasome inhibitor treatment at low dose has cytoprotective effects against ethanol-induced oxidative stress and liver steatosis. The beneficial effects of proteasome inhibitor treatment against oxidative stress occurred because antioxidant response elements （glutathione peroxidase 2, superoxide dismutase 2, glutathione synthetase, glutathione reductase, and GCLC） were upregulated when rats fed alcohol were treated with a low dose of PS-34Z （Bortezomib, Velcade）. This is an important finding because proteasome inhibitor treatment up-regulated reactive oxygen species removal and glutathione recycling enzymes, while ethanol feeding alone down-regulated these antioxidant elements. For the first time, it was shown that proteasome inhibition by a highly specific and reversible inhibitor is different from the chronic ethanol feeding-induced proteasome inhibition. As previously shown by our group, chronic ethanol feeding causes a complex dysfunction in the ubiquitin proteasome pathway, which affects the proteasome system, as well as the ubiquitination system. The beneficial effects of proteasome inhibitor treatment in alcoholic liver disease are related to proteasome inhibitor reversibility and the rebound of proteasome activity 72 h post PS-341 administration.

Anti-tumor Action and Clinical Application of Proteasome Inhibitor

Ubiquitin-proteasome pathway mediates the degradation of cell protein, and cell cycle, gene translation and expression, antigen presentation and inflammatory development. Proteasome inhibitor can inhibit growth and proliferation of tumor cell, induce apoptosis and reverse multipledrug resistance of tumor cell, increase the sensitivity of other chemotherapeutic drugs and radiotherapy, and is a novel class of potent anti-tumor agents.

Is 26S proteasome non-ATPase regulatory subunit 6 a potential molecular target for intrahepatic cholangiocarcinoma?

In this editorial we comment on the article by Tang et al published in the recent issue of World Journal of Hepatology.Drug therapy of intrahepatic cholangiocarcinoma(iCCA)poses an enormous challenge since only a small proportion of patients demonstrate beneficial responses to therapeutic agents.Thus,there has been a sustained search for novel molecular targets for iCCA.The study by Tang et al evaluated the role of 26S proteasome non-ATPase regulatory subunit 6(PSMD6),a 19S regulatory subunit of the proteasome,in human iCCA cells and specimens.The authors employed clustered regularly interspaced short palindromic repeat(CRISPR)knockout screening technology integrated with the computational CERES algorithm,and analyzed the human protein atlas(THPA)database and tissue microarrays.The results show that PSMD6 is a gene essential for the proliferation of 17 iCCA cell lines,and PSMD6 protein was overexpressed in iCCA tissues without a significant correlation with the clinicopathological parameters.The authors conclude that PSMD6 may play a promoting role in iCCA.The major limitations and defects of this study are the lack of detailed information of CRISPR knockout screening,in vivo experiments,and a discussion of plausible mechanistic cues,which,therefore,dampen the significance of the results.Further studies are required to verify PSMD6 as a molecular target for developing novel therapeutics for iCCA.In addition,the editorial article summarizes the latest advances in molecular targeted drugs and recently emerging immunotherapy in the clinical management of iCCA,development of proteasome inhibitors for cancer therapy,and advantages of CRISPR screening technology,computational methods,and THPA database as experimental tools for fighting cancer.We hope that these comments may provide some clues for those engaged in the field of basic and clinical research into iCCA.

The Apoptosis of Bovine Lens Epithelial Cells Induced by Proteasome Inhibitor MG132

To investigate the effect of proteasome inhibitor MG132 on the apoptosis of bovine lens epithelial cells （BLECs）, the cells were treated with MG132 at different concentrations for12, 24 and 36 h. The cell viability was analyzed by MTT assay and the effect of MG132 on the apoptosis of BLECs was assessed by flow cytometry （FCM）. The results showed that after treatment for the same period, the inhibitory effect of MG132 on BLECs proliferation was enhanced with the increment of the concentration of MG132 （0, 2, 5, 10, μmol/L） （P〈0.05）. The 50% inhibiting concentration （IC50） was 2.03 μmol/L when the BLECs were treated with MG132 for 36 h. MG132 also induced the apop- tosis of BLECs obviously. FCM showed that the apoptosis index of the cells treated by MG132 at 2 μmol/L for 12 h was （20.24±1.51）%, and that of the control was （0.98±0.20）% respectively （P〈0.01, n=3）. It was concluded that MG132 could lead to apoptosis of BLECs. The decrease of proteasome activity may play an important role in the formation and development of cataract.

Experimental Study on the Mechanism of Reversal of Leukemia Multidrug Resistance by Proteasome Inhibitor Bortezomib

OBJECTIVE In this study, we applied multidrug resistant leukemia cell line expressing mdr1-mRNA to observe changes in mdr1-mRNA, the P-gp, cell cycle and apoptosis before and after bortezomib was used, in order to explore the mechanism of reversal of leukemia multidrug resistance by the proteasome inhibitor bortezomib.METHODS Flow cytometry （FCM） was used to detect the intracellular drug concentration, expression of P-gp, cell apoptosis and cell cycle status of K562/DNR cells before and a er treatment with different concentrations of bortezomib. Fluorescence quantitative PCR was applied to detect the mdr1-mRNA expression in K562/DNR and K562/S cells.RESULTS Bortezomib could increase the intracellular DNR content in K562/DNR cells, but showed no e. ect in K562/S cells.5-100 nmol/L bortezomib could significantly reduce the P-gp/mdr1-mRNA expression in K562/DNR cells in vitro, and showed a dose-dependent effect. There was a statistically significant di. erence （P 〈 0.05） between di. erent concentration groups and the control group. P-gp/mdr1-mRNA expression was negatively correlated with cell apoptosis （r = -0.912 and P 〈 0.01）. After treatment with different concentrations of bortezomib for 24 h,K562/DNR cells in G2 ＋ M phases were significantly increased,while cells in G0 ＋ G1 phases and S phase were significantly decreased, accompanied by an increased apoptotic rate.CONCLUSION Bortezomib can induce G0 ＋ G1 phase to G2 ＋ M phase, and thereby enhance the chemosensitivity of leukemia, and may also reverse the multidrug resistance in leukemia mediated by P-gp overexpression encoded by mdr1 gene. This confi rms that bortezomib can reverse leukemia multidrug resistance at the levels of nucleic acid and protein molecules.

26S proteasome inhibitors inhibit dexamethasone-dependent increase of tyrosine aminotransferase and tryptophan 2,3-dioxygenase mRNA levels in primary cultured rat hepatocytes

Dexamethasone (Dex), a ligand for transcriptional enhancement of tyrosine aminotransferase (TAT) and tryptophan 2,3-dioxygenase (TO) genes, (100 nM) maximally increased these mRNA levels at 12 h and 7 h in primary cultured rat hepatocytes and the nuclear fraction, respectively. Lactacystin (5 μM) and epoxomicin (0.5 μM), 26S proteasome inhibitors, significantly suppressed the Dex-dependent maximum increase of TAT and TO mRNA levels in the cells and the nuclear fraction. Electrophoretic mobility shift assay demonstrated that lactacystin did not affect binding of glucocorticoid receptor to glucocorticoid responsive element. Furthermore, lactacystin did not affect the activation of GRE luciferase reporter by Dex transfected to the cells. The results demonstrate that 26S proteasome is positively involved in the Dex-dependent increase of TAT and TO mRNA levels in the cells and suggest that the mechanism of action of 26S proteasome may be degradation of some RNase(s), which breaks down TAT and TO mRNAs.

Synthetic protease inhibitor-induced inclusions in PC12 cells Potential proteomic characterization of six subunits in the 26S proteasome

Proteasome dysfunction during dopaminergic degeneration induces proteolytic stress, and is a contributing factor for the onset and formation of Lewy bodies. Results from our previous studies showed that synthetic proteasome inhibitor-induced inclusions in PC12 cells contained six subunits in the 26S proteasome. In the present study, mass spectrometry analysis of single protein spots resolved by two-dimensional gel electrophoresis and identified by bioinformatic analysis of peptide mass fingerprint （PMF） data were performed to comprehensively characterize the proteomic profile of the proteasome subunits. Results showed that six subunits in the 26S proteasome were characterized through accurate assignment by PMF data-specific protein identification in protein databases. Additionally, identification of one of the proteasome subunits was further confirmed using a subunit-specific antibody against non-adenosine triphosphatase subunit 11 of the 19S regulatory particle. Results suggest that the potential proteomic profile of six subunits in the 26S proteasome could be established from proteasome inhibitor-induced inclusions in PC12 cells.

Medicinal chemistry strategies towards the development of non-covalent SARS-CoV-2 Mpro inhibitors

The main protease(M^(pro))of SARS-CoV-2 is an attractive target in anti-COVID-19 therapy for its high conservation and major role in the virus life cycle.The covalent M^(pro)inhibitor nirmatrelvir(in combination with ritonavir,a pharmacokinetic enhancer)and the non-covalent inhibitor ensitrelvir have shown efficacy in clinical trials and have been approved for therapeutic use.Effective antiviral drugs are needed to fight the pandemic,while non-covalent M^(pro)inhibitors could be promising alternatives due to their high selectivity and favorable druggability.Numerous non-covalent M^(pro)inhibitors with desirable properties have been developed based on available crystal structures of M^(pro).In this article,we describe medicinal chemistry strategies applied for the discovery and optimization of non-covalent M^(pro)inhibitors,followed by a general overview and critical analysis of the available information.Prospective viewpoints and insights into current strategies for the development of non-covalent M^(pro)inhibitors are also discussed.

Discovery and characterization of novel potent non-covalent small molecule inhibitors targeting papain-like protease from SARS-CoV-2

To the Editor:The papain-like protease(PL^(pro)),as one of the most important proteases of SARS-CoV-2,has emerged as a highly promising target protein,its inhibitor probably holds dual potentials,namely blocking the cleavage of viral polyprotein and intercepting the deubiquitination and deISGylation functions to restore antiviral immunity1.

Histone deacetylase inhibitor MS-275 alone or combined with bortezomib or sorafenib exhibits strong antiproliferative action in human cholangiocarcinoma cells

AIM: To investigate the antiproliferative effect of the histone deacetylase (HDAC) inhibitor MS-275 on cholangiocarcinoma cells alone and in combination with conventional cytostatic drugs (gemcitabine or doxorubicin) or the novel anticancer agents sorafenib or bortezomib. METHODS: Two human bile duct adenocarcinoma cell lines (EGI-1 and TFK-1) were studied. Crystal violet staining was used for detection of cell number changes. Cytotoxicity was determined by measuring the release of the cytoplasmic enzyme lactate dehydrogenase (LDH). Apoptosis was determined by measuring the enzyme activity of caspase-3. Cell cycle status reflected by the DNA content was detected by flow cytometry.RESULTS: MS-275 treatment potently inhibited the proliferation of EGI-1 and TFK-1 cholangiocarcinoma cells by inducing apoptosis and cell cycle arrest. MS-275-induced apoptosis was characterized by activation of caspase-3, up-regulation of Bax and down-regulation of Bcl-2. Cell cycle was predominantly arrested at the G1/S checkpoint, which was associated with induction of the cyclin-dependent kinase inhibitor p21Waf/CIP1. Furthermore, additive anti-neoplastic effects were observed when MS-275 treatment was combined with gemcitabine or doxorubicin, while combination with the multi-kinase inhibitor sorafenib or the proteasome inhibitor bortezomib resulted in overadditive anti-neoplastic effects.CONCLUSION: The growth of human cholangiocarcinoma cells can be potently inhibited by MS-275 alone or in combination with conventional cytostatic drugs or new, targeted anticancer agents.

Cell cycle arrest effect of compound YSY-01A, a new proteasome inhibitor, on HT-29 cells in vitro

Compound YSY-01A, a recently synthesized proteasome inhibitor, has shown potent growth-inhibitory effect on tumor cells in previous researches. However, the mechanism of its inhibitory effects, especially on cell cycle, remains largely unclear. This study aims to evaluate the correlation between cell cycle arrest effect of YSY-01A and its anti-cancer effect, and to probe the possible molecular mechanisms for its effects on human colorectal adenocarcinoma cells HT-29. The results suggested that YSY-01A significantly （P0.05） inhibited cellular proliferation of HT-29 cells in a time and concentration-dependent manner. Furthermore, YSY-01A suppressed the G 2 /M transition of HT-29 cells, whereas the mitotic inhibitor paclitaxel induced M phase accumulation. Further investigation revealed that YSY-01A significantly （P0.05） up-regulated the expression levels of a series of cell cycle related protein, such as cyclin B1, Wee1, p-cdc2 （Tyr15）, p53, p21, and p27. The HT-29 cells only exhibited typical cytotoxic symptom when YSY-01A concentration reached 0.5 μM （P0.05）, which was above the dose we used in the mechanism research. In conclusion, YSY-01A showed remarkable anti-cancer activity on HT-29 cells, and its molecular mechanisms are related to G 2 /M cell cycle transition arrest.

Cell cycle arrest effect of compound YSY-01A, a new proteasome inhibitor,on SK-OV-3 cells

Compound YSY-01A, a recently synthesized proteasome inhibitor, has shown potent growth-inhibitory effect on tumor cells in previous researches. However, the mechanism of its inhibitory effects, especially on cell cycle, remains largely unclear. This study aimed to evaluate the correlation between cell cycle arrest effect of YSY-01A and its anti-cancer effect, and to probe the possible molecular mechanisms for its effects on human ovarian cancer SK-OV-3 cells. The results suggested that YSY-01A significantly （P〈0.05） inhibited cellular proliferation of SK-OV-3 cells in a concentration-dependent and time-dependent manner. Furthermore, YSY-01A induced a G2/M cell cycle arrest of SK-OV-3 cells. Further investigation revealed that YSY-01A significantly （P〈0.05） changed the expression levels of a series of cell cycle related protein, such as cyclin B1, cdc2, and p-cdc2 （T14）. Meanwhile, YSY-01A could inhibit the TNF-a-induced NF-kB nuclear translocation and lead to the increase of 1kBa as well as the decrease of IKK and Gadd45a In conclusion, YSY-01A showed remarkable anti-cancer activity on SK-OV-3 cells, and its molecular mechanisms were related to G2/M cell cycle arrest.

Effects of compound YSY-01A, a novel proteasome inhibitor, on MGC-803 cells and its related mechanism

As a novel proteasome inhibitor, remarkable proliferation inhibitory effect of compound YSY-01A was shown on tumor cells in previous studies. However, few studies has reported its effect on gastric cancer and related mechanism. We evaluated the anti-proliferative effect of compound YSY-01A using MGC-803 cells and its anti-tumor effect using xenograft nu-BALB/c mouse model. Cell proliferation inhibition was assessed by SRB assay. Related protein expression levels were determined by Western blot assay. We observed that the compound YSY-01A had a significant proliferation inhibitory effect on MGC-803 cells in vitro. Experiment in vivo showed that the compound YSY-01A had a remarkable growth inhibitory effect on MGC-803 cells xenograft tumor when it was used either alone or in combination with the conventional chemotherapeutic agent 5-fluorouracil （5-FU）. Furthermore, YSY-01A and 5-FU had a synergistic effect on xenograft tumor. Results of molecular experiment showed that the compound YSY-01A had a remarkable inhibitory effect on TNF-c~ and IFN induced NF-KB nuclear translocation. At the same time, the compound YSY-01A could reduce the expression of IKK-~, IL-I~ and iNOS, while it significantly enhanced the expression of COX-2 in MGC-803 ceils. Taken together, compound YSY-01A had an impressive tumor inhibitory effect, and it worked in NF-KB-related pathway, suggesting that the compound YSY-01A was an effective therapeutic drug for patients with gastric cancer. Higher tumor cell growth inhibition after the treatment in a combination with 5-FU indicated that combining YSY-01A with 5-FU might be more effective for displaying tumor cell growth inhibitory effects on gastric cancer cells.

Study on the dipeptide vinyl sulfonamide derivatives as proteasome inhibitor

On the basis of the Michael-addition mechanism of classical proteasome inhibitors, six dipeptide vinyl sulfonamide and dipeptide vinyl sulfonate derivatives were designed and synthesized. Moreover, an efficient method for the synthesis of g-amino vinyl sulfonamides, key intermediates to the target molecules, was developed via the Wittig-Horner reaction of peptide aldehyde with Wittig reagents derived from methanesulfonamides.

Effects and mechanism of proteasome inhibitor YSY01--A alone or in combination with cisplatin against A549 cells in vitro

YSY01-A, as a novel proteasome inhibitor, has shown remarkable proliferation inhibitory effect on certain types of tumor cells. However, few studies have reported its effect on non-small cell lung cancer （NSCLC）, and its underlying mechanism remains unknown. In our present study, we aimed to figure out the inhibitory effects as well as the mechanism of proteasome inhibitor YSY01-A against A549 cells both individually and in combination with cisplatin. A549 cell proliferation inhibition was assessed by SRB assay. Its related protein expression levels were determined by western blot assay. Moreover, the change of intracellular cisplatin accumulation was examined by ICP-MS assay. The results suggested that YSY01-A significantly （P〈0.001） inhibited the proliferation of A549 cells （IC50 was 36.2 nM for 72 h） in a concentration-dependent and time-dependent manner. Compared with the negative control group, YSY01-A （60 nM, 48 h） down-regulated PI3K/Akt pathway in A549 cells by increasing the expression level of PTEN （P〈0.01）, and decreasing the expression level of PI3K （P〈0.001） and p-Akt/Akt （P〈0.001）. When combined with cisplatin, YSY01-A of different concentrations （5, 10, 20 nM） could significantly increase the inhibition effects on A549 cells compared with the cisplatin alone treatment, showing a synergistic effect. At the same time, YSY01-A could remarkably block the cisplatin-induced down-regulation of hCTR1 in a concentration-dependent manner and increase cisplatin uptake from 2.01 to 2.47 fold （P〈0.001）. In conclusion, compound YSY01-A could significantly inhibit proliferation of NSCLC A549 cells, showing a strong synergistic effect when combined with cisplatin. Down-regulation of PI3K/Akt pathway might be the mechanism of inhibitory effect of YSY0 l-A, and the combination with cisplatin might increase the expression of CTR1 and intracellular cisplatin accumulation.

Comparison and discovery of potential non-covalent CD38 inhibitors by virtual screening strategy based on natural substrates and known inhibitors

As a type II or III transmembrane glycoprotein, human CD38 is ubiquitously expressed in all mammalian tissues. CD38 is a multi-functional enzyme and a member of the ADP-ribosyl cyclase family, and it catalyzes nicotinamide adenine dinucleotide （NAD^＋） and nicotinamide adenine dinucleotide phosphate （NADP＋） to two distinct Ca^2＋ messengers as follows： cyclic ADP-ribose （cADPR） and nicotinic acid adenine dinucleotide phosphate （NAADP）, respectively. Moreover, both cADPR and NAADP mediate mobilization of intracellular Ca^2＋ targeting endoplasmic stores and the lysosomes, respectively. In this study, we combined ligand-based and structure-based virtual screening strategies to compare the inhibitor discovery efficacy based on natural substrates and the known inhibitors. The similarity queries towards SPECS database were carried out using ROCS and EON modules of OpenEye software. The hits were further docked to CD38 using AutoDock 4.05 program. In addition, ADME studies were also processed considering solubility in water and membrane permeability. Finally, we identified 17 compotmds-based on natural substrates and 10 compounds based on known inhibitor models. The results showed that the known inhibitor H2-based model was more efficient in virtual screening of CD38 non-covalent inhibitors.

A new proteasome inhibitor YSY-01A induced autophagy in PC-3M cells

YSY-01A has shown proliferation inhibitory activity to certain types of tumor cells by inhibiting proteasome. How- ever, its effect on autophagy, which is related with the ubiquitin proteasome pathway （UPP）, remains unclear. Our study aimed to find out its effect on autophagy and possible molecular mechanisms. The results suggested that YSY-0 l A significantly （P〈0.001） inhibited proliferation of PC-3M cells （IC50 was 287 nM for 48 h） in a concentration-dependent and time-dependent manner. YSY-01A （100 nM, 3 h） also induced autophagy in PC-3M ceils through increasing the expression of P53 （P〈0.001）, Beclin-1 （P〈0.001） and LC3 （P〈0.001）, and decreasing the expression of p-roTOR （P〈0.001） as compared with the negative control group. Autophagy stayed at a final stage in PC-3M cells after treated with YSY-01A （400 nM） for 12 h. Meanwhile inhibition of autophagy with chloroquine increased the sensitivity to YSY-01A in PC-3M cells. In conclusion, YSY-01A showed high proliferation inhibitory activity of PC-3M cells and it could induce autophagy in PC-3M cells. Inhibiting autophagy increased the cytotoxic activity of YSY-01A in PC-3M cells.

蛋白酶体抑制剂MG132对慢性缺氧致小鼠记忆损伤的作用及其机制

目的探讨蛋白酶体抑制剂MG132对慢性缺氧所致小鼠记忆功能损伤的作用及其机制。方法(1)利用低氧工作站构建小鼠中脑多巴胺能神经元MN9D细胞缺氧损伤模型。将MN9D细胞分为常氧组及缺氧12 h、24 h和48 h组,观察缺氧对MN9D细胞中酪氨酸羟化酶(TH)、泛素的K48链(Ub-K48)和Ub-K63表达的影响;将MN9D细胞分为常氧组、缺氧组、缺氧+MG132(25、50、100、200)μmol/L组,观察MG132对缺氧细胞中上述蛋白表达的影响。(2)利用低压舱建立低压缺氧小鼠记忆功能损伤模型。将C57小鼠随机分为常氧组、缺氧3 d组、缺氧21 d组,每组10只,观察低压低氧对小鼠中脑黑质致密部(SNc)TH、Ub-K48和Ub-K63表达的影响;将小鼠随机分为常氧组、缺氧21 d组、缺氧21 d+MG132组,每组8只,观察MG132对缺氧所致小鼠空间记忆损伤的影响。(3)采用Western blotting检测不同缺氧时长及MG132预处理再低氧处理的MN9D细胞中TH、Ub-K48和Ub-K63的蛋白表达水平;采用新物体识别测试检测各组小鼠记忆功能,免疫荧光染色检测SNc区TH阳性免疫反应面积百分比,Western blotting检测小鼠SNc区TH、Ub-K48和Ub-K63表达水平。结果(1)与常氧组比较,缺氧24 h组MN9D细胞中Ub-K48和Ub-K63表达水平增高(P<0.05),TH表达水平降低(P<0.05);各缺氧组Ub-K48/TH和Ub-K63/TH表达水平均增高(P<0.05)。与缺氧组比较,缺氧+MG132100μmol/L组和缺氧+MG132200μmol/L组MN9D细胞中Ub-K48/TH和Ub-K63/TH表达水平降低(P<0.05)。(2)与常氧组比较,缺氧3 d组和缺氧21 d组小鼠中脑SNc区TH表达水平降低(P<0.001),Ub-K48/TH和Ub-K63/TH表达水平升高(P<0.05);缺氧21 d组小鼠新物体识别指数降低(P<0.01),SNc区多巴胺能神经元TH阳性免疫反应面积百分比降低(P<0.05)。与缺氧21 d组比较,缺氧21 d+MG132组小鼠新物体识别指数升高(P<0.01)。结论蛋白酶体抑制剂MG132可改善慢性缺氧所致小鼠记忆损伤,其机制可能与抑制Ub-K48和Ub-K63,上调多巴胺能神经元TH表达有关。

The role of proteasomes in tumorigenesis

Protein homeostasis is the basis of normal life activities,and the proteasomefamily plays an extremely important function in this process.The proteasome 2os is a concentric circle structure with twoαrings and twoβrings overlapped.The proteasome 2os can perform both ATP-dependent and non-ATP-dependent ubiquitination proteasome degradation by binding to various subunits(such as 19S,11S,and 200 PA),which is performed by its active subunitβ1,β2,andβ5.The proteasome can degrade misfolded,excess proteins tomaintain homeostasis.At the same time,it can be utilized by tumors to degrade over-proliferate and unwanted proteins to support their growth.Proteasomes can affect the development of tumors from several aspects including tumor signaling pathways such as NF-kB and p53,cell cycle,immune regulation,and drug resistance.Proteasome-encoding genes have been found to be overexpressed in a variety of tumors,providing a potential novel target for cancer therapy.In addition,proteasome inhibitors such as bortezomib,carfilzomib,and ixazomib have been put into clinical application as the first-line treatment of multiple myeloma.More and more studies have shown that it also has different therapeutic effects in other tumors such as hepatocellular carcinoma,non-small cell lung cancer,glioblastoma,and neuroblastoma.However,proteasome inhibitors are not much effective due to their tolerance and singleness in other tumors.Therefore,further studies on their mechanisms of action and drug interactions are needed to investigate their therapeutic potential.