μM MG132 Research Articles

Abstract PO4-18-03: Combined Treatment with Pyrotinib and Chrysin Synergistically Improve the Autophagy Level in HER2-Positive Breast Cancer by Regulating the miR-16-5p/ZBTB16/G6PD Axis

Abstract Human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) has been the most challenging subtype of BC, which consists of 20% of BC with an apparent correlation with poor prognosis. Despite that pyrotinib, a new HER2 inhibitor, has led to dramatic improvements in prognosis outcome, the efficacy of pyrotinib as monotherapy remain largely restricted due to its acquired resistance. Therefore, we aim at identifying a potent antitumor drug incorporated with pyrotinib for amplifying therapeutic efficacy for treating HER2-positive BC. Here, we reported a novel incorporation of pyrotinib in combination with chrysin, and explored its antitumor efficacy and the underlying mechanisms on HER2+ breast cancer. We determined that pyrotinib combined with chrysin yielded a potent synergistic effect to induce apoptosis and inhibit BT-474 and SK-BR-3 tumor cells, and suppressed in vivo tumor growth in tumor-bearing mice models. This may be mechanistically attributed to the induction of enhanced endoplasmic reticulum stress to increase the autophagy level. Furthermore, it was demonstrated that the combined treatment with pyrotinib and chrysin induced ubiquitination and G6PD degradation by regulating zinc finger and BTB/POZ domain-containing family protein 16 (ZBTB16) in tumorigenesis of BC. Besides, we identified that miR-16-5p is a potential upstream regulatory target of ZBTB16. Blocking miR-16-5p overexpression could inhibit HER2-positive tumorigenesis and significantly potentiate the efficacy of pyrotinib in combination with chrysin. Together, these findings demonstrate the utility of combined treatment with pyrotinib and chrysin as a potential option in the target treatment of HER2-positive BC through an unrecognized miR-16-5p/ZBTB16/G6PD axis. The miR-16-5p/ZBTB16/G6PD axis plays a crucial role in the pyrotinib plus chrysin-enabled anti HER2-positive BC Fig.1 a Cell viability of SK-BR-3 cells received various treatments. b Detection of cell cycle arrest of SK-BR-3 cells after various treatments. c Schematic diagram of the established protocol of the animal models. Photograph of resected tumor tissues, tumor volume (d), and tumor weight (e) of mice in different treatment groups during the whole testing period. f H&E, Ki67, and Tunel immunohistochemical staining of tumor sections of mice in various treatment groups. g Autophagy flux of SK-BR-3 cells labeled with mRFP-GFP-LC3 in the different treatment groups. h Expression level of ER stress markers in SK-BR-3 cells after various treatments via RT-qPCR and western blot. *P <0.05, compared with control group (DMSO), #P <0.05, compared with chrysin group, & P<0.05, compared with pyrotinib group. i Western blot analysis of the expression of G6PD in different treatment groups. j Fluorescence images of SK-BR-3 cells subjected to G6PD overexpression for the detection of autophagy level. k Ubibrowser database predicting the E3 ubiquitin ligases that may be involved in the regulation of G6PD ubiquitination. l Western blot analysis of G6PD protein half-life in SK-BR-3 cells with ZBTB16 silence. Cells were co-incubated with cycloheximide (CHX, 50μg/ml) for the indicated time. m Determination of the ubiquitination of G6PD in cells pretreated with 10 μM MG-132 for 3 h. Cells were transfected with ubiquitin after different treatments. The ubiquitinated G6PD was subjected to immunoprecipitation before western blot with ubiquitin antibody. n Dual-luciferase report verifying the targeting of ZBTB16 and miR-16-5p. o Transmission electron microscopy images of autophagosomes of tumors in various treatment groups (× 20000). p Immunohistochemical staining images of tumor slices for the determination of G6PD. q Schematic diagram for the underlying mechanism of pyrotinib combined chrysin against HER2-positive BC. Citation Format: Ting Luo, Xiaorong Zhong, Ping He, Dan Zheng, Yan Cheng, Kunrui Zhu. Combined Treatment with Pyrotinib and Chrysin Synergistically Improve the Autophagy Level in HER2-Positive Breast Cancer by Regulating the miR-16-5p/ZBTB16/G6PD Axis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-18-03.

The Ubiquitin-Proteasome System Participates in Sperm Surface Subproteome Remodeling during Boar Sperm Capacitation.

Sperm capacitation is a complex process endowing biological and biochemical changes to a spermatozoon for a successful encounter with an oocyte. The present study focused on the role of the ubiquitin-proteasome system (UPS) in the remodeling of the sperm surface subproteome. The sperm surface subproteome from non-capacitated and in vitro capacitated (IVC) porcine spermatozoa, with and without proteasomal inhibition, was selectively isolated. The purified sperm surface subproteome was analyzed using high-resolution, quantitative liquid chromatography-mass spectrometry (LC-MS) in four replicates. We identified 1680 HUGO annotated proteins, out of which we found 91 to be at least 1.5× less abundant (p < 0.05) and 141 to be at least 1.5× more abundant (p < 0.05) on the surface of IVC spermatozoa. These proteins were associated with sperm capacitation, hyperactivation, metabolism, acrosomal exocytosis, and fertilization. Abundances of 14 proteins were found to be significantly different (p < 0.05), exceeding a 1.5-fold abundance between the proteasomally inhibited (100 µM MG132) and vehicle control (0.2% ethanol) groups. The proteins NIF3L1, CSE1L, NDUFB7, PGLS, PPP4C, STK39, and TPRG1L were found to be more abundant; while BPHL, GSN, GSPT1, PFDN4, STYXL1, TIMM10, and UBXN4 were found to be less abundant in proteasomally inhibited IVC spermatozoa. Despite the UPS having a narrow range of targets, it modulated sperm metabolism and binding by regulating susceptible surface proteins. Changes in CSE1L, PFDN4, and STK39 during in vitro capacitation were confirmed using immunocytochemistry, image-based flow cytometry, and Western blotting. The results confirmed the active participation of the UPS in the extensive sperm surface proteome remodeling that occurs during boar sperm capacitation. This work will help us to identify new pharmacological mechanisms to positively or negatively modulate sperm fertilizing ability in food animals and humans.

Proteasome inhibitor MG132 enhances the sensitivity of human OSCC cells to cisplatin via a ROS/DNA damage/p53 axis.

Cis-diamine-dichloroplatinum II (cisplatin, CDDP) is a key chemotherapeutic regimen in the treatment of oral squamous cell carcinoma (OSCC). However, the therapeutic efficacy of cisplatin in OSCC may be hampered by chemoresistance. Therefore, the development of novel combination therapy strategies to overcome the limitations of CDDP is of great importance. The proteasome inhibitor MG132 exhibits anti-cancer properties against various types of cancer. However, our knowledge of its anti-cancer effects in combination with CDDP in OSCC cells remains limited. In the current study, the synergetic effects of MG132 and CDDP were evaluated in the human CAL27 OSCC cell line. CAL27 cells were treated with CDDP alone or in combination with MG132. The results showed that MG132 significantly reduced cell viability in a dose-dependent manner. Additionally, cell viability was significantly reduced in CAL27 cells treated with 0.2 µM MG132 and 2 µM CDDP compared with cells treated with MG132 or CDDP alone. In addition, MG132 significantly enhanced the CDDP-induced generation of intracellular reactive oxygen species and DNA damage in OSCC cells. Furthermore, treatment with CDDP or MG132 alone notably inhibited colony formation and proliferation of OSCC cells. However, co-treatment of OSCC cells with MG132 and CDDP further hampered colony formation and proliferation compared with cells treated with either MG132 or CDDP alone. Finally, in cells co-treated with MG132 and CDDP, the expression of p53 was markedly elevated and the p53-mediated apoptotic pathway was further activated compared with cells treated with MG132 or CDDP alone, as shown by the enhanced cell apoptosis, Bax upregulation, and Bcl-2 downregulation. Overall, the results of the current study support the synergistic anti-cancer effects of a combination of MG132 and CDDP against OSCC, thus suggesting that the combination of MG132 and CDDP may be a promising therapeutic strategy for the management of OSCC.

Modulatory effect of MG-132 proteasomal inhibition on boar sperm motility during in vitro capacitation.

A series of biochemical and biophysical changes during sperm capacitation initiates various signaling pathways related to protein phosphorylation leading to sperm hyperactivation, simultaneously with the regulation of proteasomal activity responsible for protein degradation and turnover. Our study aimed to unveil the role of the proteasome in the regulation of boar sperm motility, hyperactivated status, tyrosine phosphorylation, and total protein ubiquitination. The proteolytic activity of the 20S proteasomal core was inhibited by MG-132 in concentrations of 10, 25, 50, and 100 μM; and monitored parameters were analyzed every hour during 3 h of in vitro capacitation (IVC). Sperm motility and kinematic parameters were analyzed by Computer Assisted Sperm Analysis (CASA) during IVC, showing a significant, negative, dose-dependent effect of MG-132 on total and progressive sperm motility (TMOT, PMOT, respectively). Furthermore, proteasomal inhibition by 50 and 100 μM MG-132 had a negative impact on velocity-based kinematic sperm parameters (VSL, VAP, and VCL). Parameters related to the progressivity of sperm movement (LIN, STR) and ALH were the most affected by the highest inhibitor concentration (100 μM). Cluster analysis revealed that the strongest proteasome-inhibiting treatment had a significant effect (p ≤ 0.05) on the hyperactivated sperm subpopulation. The flow cytometric viability results proved that reduced TMOT and PMOT were not caused by disruption of the integrity of the plasma membrane. Neither the protein tyrosine phosphorylation profile changes nor the accumulation of protein ubiquitination was observed during the course of capacitation under proteasome inhibition. In conclusion, inhibition of the proteasome reduced the ability of spermatozoa to undergo hyperactivation; however, there was no significant effect on the level of protein tyrosine phosphorylation and accumulation of ubiquitinated proteins. These effects might be due to the presence of compensatory mechanisms or the alteration of various ubiquitin-proteasome system-regulated pathways.

Proteasome- and Calpain-Mediated Proteolysis, but Not Autophagy, Is Required for Leucine-Induced Protein Synthesis in C2C12 Myotubes.

Muscle protein synthesis and proteolysis are tightly coupled processes. Given that muscle growth is promoted by increases in net protein balance, it stands to reason that bolstering protein synthesis through amino acids while reducing or inhibiting proteolysis could be a synergistic strategy in enhancing anabolism. However, there is contradictory evidence suggesting that the proper functioning of proteolytic systems in muscle is required for homeostasis. To add clarity to this issue, we sought to determine if inhibiting different proteolytic systems in C2C12 myotubes in conjunction with acute and chronic leucine treatments affected markers of anabolism. In Experiment 1, myotubes underwent 1-h, 6-h, and 24-h treatments with serum and leucine-free DMEM containing the following compounds (n = 6 wells per treatment): (i) DMSO vehicle (CTL), (ii) 2 mM leucine + vehicle (Leu-only), (iii) 2 mM leucine + 40 μM MG132 (20S proteasome inhibitor) (Leu + MG132), (iv) 2 mM leucine + 50 μM calpeptin (calpain inhibitor) (Leu + CALP), and (v) 2 mM leucine + 1 μM 3-methyladenine (autophagy inhibitor) (Leu + 3MA). Protein synthesis levels significantly increased (p < 0.05) in the Leu-only and Leu + 3MA 6-h treatments compared to CTL, and levels were significantly lower in Leu + MG132 and Leu + CALP versus Leu-only and CTL. With 24-h treatments, total protein yield was significantly lower in Leu + MG132 cells versus other treatments. Additionally, the intracellular essential amino acid (EAA) pool was significantly greater in 24-h Leu + MG132 treatments versus other treatments. In a follow-up experiment, myotubes were treated for 48 h with CTL, Leu-only, and Leu + MG132 for morphological assessments. Results indicated Leu + MG132 yielded significantly smaller myotubes compared to CTL and Leu-only. Our data are limited in scope due to the utilization of select proteolysis inhibitors. However, this is the first evidence to suggest proteasome and calpain inhibition with MG132 and CALP, respectively, abrogate leucine-induced protein synthesis in myotubes. Additionally, longer-term Leu + MG132 treatments translated to an atrophy phenotype. Whether or not proteasome inhibition in vivo reduces leucine- or EAA-induced anabolism remains to be determined.

Effects of a proteasome inhibitor on the riboflavin production in Ashbya gossypii.

Effects of a proteasome inhibitor, MG-132, on the riboflavin production in Ashbya gossypii were investigated to elucidate the relationship of the riboflavin production with flavoprotein homeostasis. The addition of MG-132 to the liquid medium reduced the specific riboflavin production by 79% in A. gossypii at 25μM after 24h. The addition of the inhibitor also caused the accumulation of reactive oxygen species and ubiquitinated proteins. These results indicated that MG-132 works in A. gossypii without any genetic engineering and reduces riboflavin production. In the presence of 25μM MG-132, specific NADH dehydrogenase activity was increased by 1.4-fold compared to DMSO, but specific succinate dehydrogenase (SDH) activity was decreased to 52% compared to DMSO. Additionally, the amount of AgSdh1p (ACR052Wp) was also reduced. Specific riboflavin production was reduced to 22% when 20mM malonate, a SDH inhibitor, was added to the culture medium. The riboflavin production in heterozygous AgSDH1gene-disrupted mutant (AgSDH1-/+ ) was reduced to 63% compared to that in wild type. MG-132 suppresses the riboflavin production and SDH activity in A. gossypii. SDH is one of the flavoproteins involved in the riboflavin production in A. gossypii. This study shows that MG-132 has a negative influence on the riboflavin production and SDH activity in A. gossypii and leads to the elucidation of the connection of the riboflavin production with flavoproteins.

USP42 protects ZNRF3/RNF43 from R-spondin-dependent clearance and inhibits Wnt signalling.

The tumour suppressors RNF43 and ZNRF3 play a central role in development and tissue homeostasis by promoting the turnover of the Wnt receptors LRP6 and Frizzled (FZD). The stem cell growth factor R‐spondin induces auto‐ubiquitination and membrane clearance of ZNRF3/RNF43 to promote Wnt signalling. However, the deubiquitinase stabilising ZNRF3/RNF43 at the plasma membrane remains unknown. Here, we show that the USP42 antagonises R‐spondin by protecting ZNRF3/RNF43 from ubiquitin‐dependent clearance. USP42 binds to the Dishevelled interacting region (DIR) of ZNRF3 and stalls the R‐spondin‐LGR4‐ZNRF3 ternary complex by deubiquitinating ZNRF3. Accordingly, USP42 increases the turnover of LRP6 and Frizzled (FZD) receptors and inhibits Wnt signalling. Furthermore, we show that USP42 functions as a roadblock for paracrine Wnt signalling in colon cancer cells and mouse small intestinal organoids. We provide new mechanistic insights into the regulation R‐spondin and conclude that USP42 is crucial for ZNRF3/RNF43 stabilisation at the cell surface.

The Synergistic Effects for Apoptosis of Propolis Extracts and MG-132 on HeLa Ovarian Cancer Cell Line and Its Molecular Mechanism

In this study, we investigated the synergistic effect of apoptosis of propolis extract and MG-132 on HeLa ovarian cancer cells. The cytotoxicity of MG-132 and propolis was confirmed on dose-dependent manner. The LD<SUB>50</SUB> values of MG-132 and propolis showed at 10 μM and 100 μg/mL, respectively. Based on this concentration, in order to investigate the synergistic effect, the apoptosis effect of the mixture of low concentration of MG-132 and propolis extract was confirmed. The concentration of the mixture determined 0.5 μM MG-132 and 10 μg/mL and 25 μg/mL of propolis extracts. Cytotoxicity was measured after treating HeLa cells with a mixture of MG-132 and propolis extract. HeLa cells survived at least 90% in 0.5 μM of MG-132 and 25 μg/mL of propolis. However, it survived less than 80% when treated with a MG-132 and propolis extract. We investigated the level of expression of apoptosis-related proteins by Western blotting. When apoptosis stimulation occurred, apoptosis marker proteins PARP and caspase-3 produced 70 kDa and 19 kDa fragment, respectively. Treatment with a mixture of MG-132 and propolis extract produced PARP and caspase-3, but a single treatment did not. In the treatment of MG-132 and propolis extract, ubiquitination as another apoptosis molecule was expressed very strongly. In the mixture of MG-132 and propolis extract, the apoptosis molecule as well as proliferation protein expression level was changed. JAK showed digested fragments in mixture treatment group. Thus, the interaction of the mixture of MG-132 and propolis extract can induce apoptosis stimulation, and protein expression levels related to apoptosis and proliferation in cells are changed. Mixture of the two molecules could show potential as a cancer treatment.

Combining Live Cell Imaging with Cellular Impedance to Monitor Apoptotic Cell Death in Real Time

Although apoptosis can be tracked using various biomarker‐based assays, these typically require multiple manual handling steps and only yield endpoint measurements. Requiring just a cell seeding step and a drug addition step, we used the Agilent xCELLigence RTCA eSight to continuously monitor drug‐mediated apoptosis over the course of multiple days. Providing a direct and objective assessment of cell number, cell size, cell‐substrate attachment strength, and cell barrier function, impedance biosensors embedded within the base of eSight microplates quantitatively track early (cell shrinkage) to late (fragmentation) apoptotic events with high analytical sensitivity. Concurrently, eSight captures live cell images in brightfield and three fluorescence channels (red, green, and blue), providing an orthogonal readout of the apoptosis process. By combining the strengths of real‐time impedance monitoring (simplicity, analytical sensitivity, and objectivity) with that of live cell imaging (specificity of the readout), eSight increases the information richness of the apoptosis assay without increasing the workload. Importantly, the drug EC50 values determined using these two approaches are nearly identical, suggesting that eSight can simultaneously provide both the primary and secondary (confirmatory) readouts for apoptosis studies.Corroborating the impedance response with live cell images. Image panels demonstrate the progression of apoptosis 20 and 40 hours after treating A549‐Blue cells with 5.5 μm MG132. White arrows denote large membrane blebs that contain phosphatidylserine in their outer leaflet.Figure 1Multiplex monitoring of apoptosis in real‐time: combining readouts from cellular impedance and live cell imaging.Figure 2

Proteasome inhibition creates a chromatin landscape favorable to RNA Pol II processivity

Proteasome inhibition creates a chromatin landscape favorable to RNA Pol II processivity

Ubiquitin-proteasome system participates in the de-aggregation of spermadhesins and DQH protein during boar sperm capacitation.

We studied the participation of the ubiquitin-proteasome system (UPS) in spermadhesin release during in vitro capacitation (IVC) of domestic boar spermatozoa. At ejaculation, boar spermatozoa acquire low molecular weight (8-16 kDa) seminal plasma proteins, predominantly spermadhesins, aggregated on the sperm surface. Due to their arrangement, such aggregates are relatively inaccessible to antibody labeling. As a result of de-aggregation and release of the outer layers of spermadhesins from the sperm surface during IVC, antibody labeling becomes feasible in the capacitated spermatozoa. In vivo, the capacitation-induced shedding of spermadhesins from the sperm surface is associated with the release of spermatozoa from the oviductal sperm reservoir. We took advantage of this property to perform image-based flow cytometry to study de-aggregation and shedding of boar spermadhesins (AQN, AWN, PSP protein families) and boar DQH (BSP1) sperm surface protein which induces higher fluorescent intensity in capacitated vs ejaculated spermatozoa. Addition of a proteasomal inhibitor (100 µM MG132) during IVC significantly reduced fluorescence intensity of all studied proteins (P < 0.05) compared to vehicle control IVC. Western blot detection of spermadhesins did not support their retention during IVC with proteasomal inhibition (P > 0.99) but showed the accumulation of DQH (P = 0.03) during IVC, compared to vehicle control IVC. Our results thus demonstrate that UPS participates in the de-aggregation of spermadhesins and DQH protein from the sperm surface during capacitation, with a possible involvement in sperm detachment from the oviductal sperm reservoir and/or sperm-zona pellucida interactions. The activity of sperm UPS modulates de-aggregation of boar spermadhesins and DQH sperm surface protein/binder of sperm1 (BSP1) during the sperm capacitation.

Proteasome Inhibitor MG132 Enhances Cisplatin-Induced Apoptosis in Osteosarcoma Cells and Inhibits Tumor Growth.

Although cisplatin has been shown to be an integral part of chemotherapy regimen in osteosarcoma (OS) treatment, toxicity issues and chemoresistance have hindered therapeutic development for OS. Exploring novel combination therapy methods is needed to circumvent the limitations of cisplatin alone. The proteasome inhibitor MG132 has shown antitumor effects in many solid tumors. However, little is known about its effects in combination with cisplatin in OS cells. In this study, we examined the effects of MG132 in combination with cisplatin in human OS cells (MG-63 and HOS). MG132 and cisplatin were applied to OS cells, respectively or jointly. The results demonstrated that MG132 markedly inhibited cell viability in a dose- and time-dependent manner, whereas viability of osteoblast cells was not affected, suggesting a selective toxicity of MG132 to cancerous cells. Mechanistically, MG132 arrested cells in the G2/M phase in association with increased p21waf1 and induced cell apoptosis, which was accompanied by cleaved PARP. In addition to its apoptotic effect alone, MG132 significantly enhanced cisplatin-induced apoptosis in OS cells. Furthermore, cell viability of the combined application of 10 μM MG132 and 5 μg/ml cisplatin was markedly inhibited compared to that of the individual application. These events were accompanied by the downregulation of NF-κB, mitochondrial antiapoptotic protein Bcl-xL, and PI3K/Akt, which play a key role in cell survival. Finally, combination treatment of MG132 and cisplatin showed more antiproliferative effect than the single treatment in OS xenograft models. In summary, we concluded that MG132 interacted synergistically with cisplatin, which raised the possibility that combining the two drugs may represent a novel strategy in OS.

Proteasome Inhibition Increases the Efficiency of Lentiviral Vector-Mediated Transduction of Trabecular Meshwork.

PurposeTo determine if proteasome inhibition using MG132 increased the efficiency of FIV vector–mediated transduction in human trabecular meshwork (TM)-1 cells and monkey organ-cultured anterior segments (MOCAS).MethodsTM-1 cells were pretreated for 1 hour with 0.5% dimethyl sulfoxide (DMSO; vehicle control) or 5 to 50 μM MG132 and transduced with FIV.GFP (green fluorescent protein)– or FIV.mCherry-expressing vector at a multiplicity of transduction (MOT) of 20. At 24 hours, cells were fixed and stained with antibodies for GFP, and positive cells were counted, manually or by fluorescence-activated cell sorting (FACS). Cells transduced with FIV.GFP particles alone were used as controls. The effect of 20 μM MG132 treatment on high- and low-dose (2 × 107 and 0.8 × 107 transducing units [TU], respectively) FIV.GFP transduction with or without MG132 was also evaluated in MOCAS using fluorescence microscopy. Vector genome equivalents in cells and tissues were quantified by quantitative (q)PCR on DNA.ResultsIn the MG132 treatment groups, there was a significant dose-dependent increase in the percentage of transduced cells at all concentrations tested. Vector genome equivalents were also increased in TM-1 cells treated with MG132. Increased FIV.GFP expression in the TM was also observed in MOCAS treated with 20 μM MG132 and the high dose of vector. Vector genome equivalents were also significantly increased in the MOCAS tissues. Increased transduction was not seen with the low dose of virus.ConclusionsProteasome inhibition increased the transduction efficiency of FIV particles in TM-1 cells and MOCAS and may be a useful adjunct for delivery of therapeutic genes to the TM by lentiviral vectors.

Maintained MPF Level after Oocyte Vitrification Improves Embryonic Development after IVF, but not after Somatic Cell Nuclear Transfer.

Levels of maturation-promoting factor (MPF) in oocytes decline after vitrification, and this decline has been suggested as one of the main causes of low developmental competence resulting from cryoinjury. Here, we evaluated MPF activity in vitrified mouse eggs following treatment with caffeine, a known stimulator of MPF activity, and/or the proteasome inhibitor MG132. Collected MII oocytes were vitrified and divided into four groups: untreated, 10 mM caffeine (CA), 10 μM MG132 (MG), and 10 mM caffeine +10 μM MG132 (CA+MG). After warming, the MPF activity of oocytes and their blastocyst formation and implantation rates in the CA, MG, and CA+MG groups were much higher than those in the untreated group. However, the cell numbers in blastocysts did not differ among groups. Analysis of the effectiveness of caffeine and MG132 for improving somatic cell nuclear transfer (SCNT) technology using cryopreserved eggs showed that supplementation did not improve the blastocyst formation rate of cloned mouse eggs. These results suggest that maintaining MPF activity after cryopreservation may have a positive effect on further embryonic development, but is unable to fully overcome cryoinjury. Thus, intrinsic factors governing the developmental potential that diminish during oocyte cryopreservation should be explored.

Endoplasmic reticulum oxidase 1α is critical for collagen secretion from and membrane type 1-matrix metalloproteinase levels in hepatic stellate cells

Upon liver injury, excessive deposition of collagen from activated hepatic stellate cells (HSCs) is a leading cause of liver fibrosis. An understanding of the mechanism by which collagen biosynthesis is regulated in HSCs will provide important clues for practical anti-fibrotic therapy. Endoplasmic reticulum oxidase 1α (ERO1α) functions as an oxidative enzyme of protein disulfide isomerase, which forms intramolecular disulfide bonds of membrane and secreted proteins. However, the role of ERO1α in HSCs remains unclear. Here, we show that ERO1α is expressed and mainly localized in the endoplasmic reticulum in human HSCs. When HSCs were transfected with ERO1α siRNA or an ERO1α shRNA-expressing plasmid, expression of ERO1α was completely silenced. Silencing of ERO1α expression in HSCs markedly suppressed their proliferation but did not induce apoptosis, which was accompanied by impaired secretion of collagen type 1. Silencing of ERO1α expression induced impaired disulfide bond formation and inhibited autophagy via activation of the Akt/mammalian target of rapamycin signaling pathway, resulting in intracellular accumulation of collagen type 1 in HSCs. Furthermore, silencing of ERO1α expression also promoted proteasome-dependent degradation of membrane type 1-matrix metalloproteinase (MT1-MMP), which stimulates cell proliferation through cleavage of secreted collagens. The inhibition of HSC proliferation was reversed by treatment with MT1-MMP-cleaved collagen type 1. The results suggest that ERO1α plays a crucial role in HSC proliferation via posttranslational modification of collagen and MT1-MMP and, therefore, may be a suitable therapeutic target for managing liver fibrosis.

Loss of ΔNp63α promotes mitotic exit in epithelial cells.

Volume 585, Issue 17, Pages 2720–2726, First published online: 3 August 2011 https://doi.org/10.1016/j.febslet.2011.07.030 In this paper by Hau et al. [1], there are errors in Fig. 4B concerning the western blots of HA (Cdc20), and HA (Cdh1). The western blots of HA (Cdc20) and HA (Cdh1) were erroneously used as the western blots for Actin and ΔNp63α expression respectively. The corrected figure 4B is shown below. These mistakes do not alter the conclusion that APC/CCdh1 targets ΔNp63α for degradation during mitosis. Fig. 4B. 293 cells were cotransfected with ΔNp63α and either with HA-cdc20 (upper panel) or HA-cdh1 (lower panel) expressing vectors. The cells were treated with 10 μg·mL−1 cycloheximide (CHX) and harvested according to the time specified. For the rescue experiment, 10 μm MG132 was added 1 h before addition of cycloheximide. Cell extract was prepared and subjected to immunoblot with anti-HA (12CA5) and anti-p63 (4A4) antibodies.

Effects of MG132 on the in vitro development and epigenetic modification of Debao porcine somatic cell nuclear transfer embryos

The present study was undertaken to examine the effect of MG132, a proteasome inhibitor, on the in vitro development, zygotic genome activation (ZGA) and epigenetic modification of Debao porcine somatic cell nuclear transfer (SCNT) embryos. Treatment of oocytes with 1 μM MG132 from 30 h to 42 h of maturation and SCNT embryos with 5 μM MG132 for 2 h after fusion resulted in higher blastocyst yield (36.5%) of SCNT embryos compared with the control group (11.0%). The ZGA of SCNT embryos at 2- and 4-cell stages was also enhanced by MG132 treatment through altering the RNA pol II status and increasing the expression of eIF3A and TFIIA. Meanwhile, MG132 treatment also resulted in increase of inner cell mass (ICM) and trophectoderm (TE) and total cell numbers and decrease of apoptotic cell numbers of SCNT blastocysts. Expression of BCL-2, OCT4, NANOG and CDX2 in SCNT blastocysts developed from SCNT embryos and oocytes treated with MG132 was increased significantly (P < 0.01), while the expression of pro-apoptotic BAX gene was suppressed significantly (P < 0.01). In addition, MG132 treatment not only affected the expression patterns of H3K9 acetylation, H3K4 and H3K9 trimethylation, but also regulated the relative expression of SMYD3, ASH2L, KDM5B, HAT1, HDAC1 and HDAC2 of Debao porcine SCNT embryos. These results demonstrate that MG132 treatment can improve the developmental potential of Debao porcine SCNT embryos through regulating the expression of genes related to histone acetylation and the processes of ZGA.

Partial inhibition of the ubiquitin–proteasome system ameliorates cardiac dysfunction following ischemia–reperfusion in the presence of high glucose

BackgroundAcute hyperglycemia co-presenting with myocardial infarction (in diabetic and non-diabetic individuals) is often associated with a poor prognosis. Although acute hyperglycemia induces oxidative stress that can lead to dysregulation of the ubiquitin–proteasome system (UPS), it is unclear whether increased/decreased UPS is detrimental with ischemia–reperfusion under such conditions. As our earlier data implicated the UPS in cardiac damage, we hypothesized that its inhibition results in cardioprotection with ischemia–reperfusion performed under conditions that simulate acute hyperglycemia.MethodsEx vivo rat heart perfusions were performed with Krebs–Henseleit buffer containing 33 mM glucose vs. controls (11 mM glucose) for 60 min stabilization, followed by 20 min global ischemia and 60 min reperfusion ± 5 µM lactacystin and 10 µM MG-132, respectively. The UPS inhibitors were added during the first 20 min of the reperfusion phase and various cardiac functional parameters evaluated. In parallel experiments, infarct sizes were assessed following 20 min regional ischemia and 120 min reperfusion ± each of the respective UPS inhibitors (added during reperfusion). Heart tissues were collected and analyzed for markers of oxidative stress, UPS activation, inflammation and autophagy.ResultsThe proteasome inhibitor doses and treatment duration here employed resulted in partial UPS inhibition during the reperfusion phase. Both lactacystin and MG-132 administration resulted in cardioprotection in our experimental system, with MG-132 showing a greater effect. The proteasome inhibitors also enhanced cardiac superoxide dismutase protein levels (SOD1, SOD2), attenuated pro-inflammatory effects and caused an upregulation of autophagic markers.ConclusionsThis study established that partial proteasome inhibition elicits cardioprotection in hearts exposed to ischemia–reperfusion with acute simulated hyperglycemia. These data reveal that protease inhibition triggered three major protective effects, i.e. (a) enhancing myocardial anti-oxidant defenses, (b) attenuating inflammation, and (c) increasing the autophagic response. Thus the UPS emerges as a unique therapeutic target for the treatment of ischemic heart disease under such conditions.

Prolonged High Glucose Treatment Increased Orai1 Protein Expression through Inhibition of Lysosomal Pathway in Human Mesangial Cells

The Orai1‐mediated store operated calcium entry (SOCE) is associated with many physiological and pathological processes in a variety of cells, including glomerular mesangial cells (MCs). We have previously demonstrated that prolonged treatment of MCs with high glucose (HG) significantly increased Orai1 expression at protein level, but not at mRNA level. These findings suggest that a post‐transcriptional mechanism(s) contributes to the HG effect. The aim of the present study was to identify if proteosomal and/or lysosomal pathways were involved in the increased abundance of Orai1 protein in response to HG. Cultured human MCs were with and without treatment with 10 μM MG132 (an inhibitor of proteosomal pathway) or 10 mM ammonium chloride (an inhibitor of lysosomal pathway) in the presence of normal glucose (NG, 5.6 mM) or HG (25 mM) for 6 days. Western blots of the whole cell lysates were conducted to evaluate Orai1 expression level. We found that both MG132 and ammonium chloride increased abundance of Orai1 protein in MCs incubated with NG. The MG132 response was further increased by HG treatment. However, HG failed to cause additional increase in Orai1 protein expression in ammonium chloride‐treated cells. Furthermore, fura‐2 fluorescence ratiometry study showed that both MG132 and ammonium chloride increased the cyclopiazonic acid (25 μM)‐stimulated SOCE. Simultaneous treatment with HG only enhanced the MG132 response, but not the ammonium chloride response. Taken together, our results indicate that HG increased expression of Orai1protein by inhibiting its degradation through the lysosomal pathway. (Supported by NIH)

Proteasome inhibition-induced downregulation of Akt/GSK-3β pathway contributes to abnormality of tau in hippocampal slice.

Proteasome inhibition can induce abnormal accumulation and phosphorylation of microtubule-associated protein tau. The major function of tau protein is to promote microtubules assembly and stabilization, and abnormal tau protein would disturb its microtubule-binding function. In this study, proteasome inhibitor MG132 was used to treat hippocampal slices to explore the role and mechanism of Akt/glycogen synthase kinase-3β (GSK-3β) in proteasome inhibition-induced tau abnormality. During the culture period, we measure the lactate dehydrogenase (LDH) content to assay the viability of hippocampal slices. Following 2.5 and 5 μM MG132 treatment for 6 h, we detected the expression, phosphorylation modification, and microtubule-binding function of tau protein of slices. We also analyzed the changed activities of glycogen synthase kinase-3β (GSK-3β) and protein kinase B (PKB/Akt) and the level of heat shock protein 90 (Hsp90) in the process. In addition, co-immunoprecipitation was used to investigate the interaction between Akt and Hsp90, Akt and protein phosphatase-2A (PP2A) in the MG132-treated organotypic hippocampal slices. Our results indicated that proteasome inhibition led to degradation obstacles and abnormal phosphorylation of tau protein. The downregulated Akt/GSK-3β signaling pathway might be responsible for the abnormal phosphorylation of tau protein at multiple sites which further reduced the microtubule-binding function of tau protein. Furthermore, proteasome inhibition decreased the binding capacity of Akt-Hsp90 while increased the Akt-PP2A binding ability which mediated Akt inactivity. This current study establishes a hippocampal slice model targeting Akt/GSK-3β signaling pathway to explore the pivotal role of proteasome inhibition in tau pathology.