Effects of Amyloid Precursor Protein Overexpression on NF-κB,Rho-GTPase and Pro-Apoptosis Bcl-2 Pathways in Neuronal Cells

Background:Alzheimer’s disease (AD) is a neurodegenerative disorder that causes cognitive dysfunction. Previous studies have suggested that amyloid plaques, mainly comprising of amyloid-beta peptides, play a pivotal role in AD pathophysiology. This study focuses on the evaluation of the effects of amyloid precursor protein (APP) overexpression on NF-κB, Rho-GTPase and Bcl-2 mediated pro-apoptotic pathways in neuronal cells. Methods:A lentiviral transduction system was used to generate SH-SY5Y cells overexpressing APP. Immunoblotting was conducted to determine expression levels of NF-κB, Rho-GTPase, and Bcl-2 family proteins in the APP overexpressed cells.Results:In the NF-κB signaling pathway, APP-overexpressing SH-SY5Y cells showed that there was a reduction of p-NF-κB (p< 0.05) and IKKα. Subsequently, there was upregulation of protein expression of NF-Κb, IKKβ and IκBα. On the other hand, protein expression of RhoC (p< 0.05) and Rac1/2/3 was upregulated as compared to the control group. Meanwhile, a decrease in RhoA, Cdc42 (p< 0.05) and p-Rac1/cdc42 protein levels was observed in the APP-overexpressed group. Lastly, in the pro-apoptotic pathway, the expression of Bcl-2, Bid, Bok and Puma (p< 0.05) was up regulated in the APP-overexpressed group. Downregulation of Bad and Bim expression was observed in the APP-overexpressed as compared to the control group, and Bax expression remained unchanged in the APP-overexpressed group.Conclusion:APP overexpression regulated signaling in the NF-κB, Rho-GTPase and Bcl-2 family pathways in neuronal cells, suggesting that these are involved in promoting neuronal survival and modulating synaptic plasticity in AD. However, further studies are essential to elucidate the APP-mediated mechanism of action.Key Words: Alzheimer’s disease, Amyloid precursor protein, Bcl-2 family proteins, NF-κB, Rho-GTPase     

XPD could suppress growth of HepG2.2.15 and down-regulate the expression of hepatitis B virus x protein through P53 pathway

ObjectivesWe investigated the effects of xeroderma pigmentosum D (XPD) on the growth of hepatoma cells and the expressions of P21, Bax, Bcl-2 and Hepatitis B virus X protein (HBx). In addition, we examined whether XPD affected the aforementioned genes via the P53 pathway.MethodsHuman hepatoma cells (HepG2.2.15) were transfected with XPD expression vector, followed by incubation with Pifithrin-α (P53 inhibitor). By using RT-PCR and Western blotting, the expression levels of XPD, P53, phospho-P53 (ser-15), P21, Bax, Bcl-2 and HBx were detected. The cell cycle and the apoptosis rate were examined with flow cytometry, and the cell viability was detected by MTT.ResultsOver-expression of XPD up-regulated the expressions of P53, phospho-P53 (ser-15), P21 and Bax but down-regulated the expressions of Bcl-2 and HBx. XPD inhibited the viability of HepG2.2.15 and exacerbated the apoptosis. However, the inhibition of P53 by Pifithrin-α abolished the above-mentioned effects of XPD.ConclusionXPD could suppress growth of hepatoma cells, up-regulate the expressions of P21 and Bax, and down-regulate the expressions of Bcl-2 and HBx through the P53 pathway. There may be mutual influences among XPD, P53 and HBx that co-regulate hepatocarcinogenesis.     

Protective Efficacy of Vitamins C and E on p,p′-DDT-Induced Cytotoxicity via the ROS-Mediated Mitochondrial Pathway and NF-κB/FasL Pathway

Dichlorodiphenoxytrichloroethane (DDT) is a known persistent organic pollutant and liver damage toxicant. However, there has been little emphasis on the mechanism underlying liver damage toxicity of DDT and the relevant effective inhibitors. Hence, the present study was conducted to explore the protective effects of vitamin C (VC) and vitamin E (VE) on the cytotoxicity of DDT in HL-7702 cells and elaborate the specific molecular mechanisms. The results demonstrated that p,p′-DDT exposure at over 10 µM depleted cell viability of HL-7702 cells and led to cell apoptotic. p,p′-DDT treatment elevated the level of reactive oxygen species (ROS) generation, induced mitochondrial membrane potential, and released cytochrome c into the cytosol, with subsequent elevations of Bax and p53, along with suppression of Bcl-2. In addition, the activations of caspase-3 and -8 were triggered. Furthermore, p,p′-DDT promoted the expressions of NF-κB and FasL. When the cells were exposed to the NF-κB inhibitor (PDTC), the up-regulated expression of FasL was attenuated. Strikingly, these alterations caused by DDT treatment were prevented or reversed by the addition of VC or VE, and the protective effects of co-treatment with VC and VE were higher than the single supplement with p,p′-DDT. Taken together, these findings provide novel experimental evidences supporting that VC or/and VE could reduce p,p′-DDT-induced cytotoxicity of HL-7702 cells via the ROS-mediated mitochondrial pathway and NF-κB/FasL pathway.     

Bcl-2 and Bax Interact via the BH1–3 Groove-BH3 Motif Interface and a Novel Interface Involving the BH4 Motif

The interaction of Bcl-2 family proteins at the mitochondrial outer membrane controls membrane permeability and thereby the apoptotic program. The anti-apoptotic protein Bcl-2 binds to the pro-apoptotic protein Bax to prevent Bax homo-oligomerization required for membrane permeabilization. Here, we used site-specific photocross-linking to map the surfaces of Bax and Bcl-2 that interact in the hetero-complex formed in a Triton X-100 micelle as a membrane surrogate. Heterodimer-specific photoadducts were detected from multiple sites in Bax and Bcl-2. Many of the interaction sites are located in the Bcl-2 homology 3 (BH3) region of Bax and the BH1–3 groove of Bcl-2 that likely form the BH3-BH1–3 groove interface. However, other interaction sites form a second interface that includes helix 6 of Bax and the BH4 region of Bcl-2. Loss-of-function mutations in the BH3 region of Bax and the BH1 region of Bcl-2 disrupted the BH3-BH1–3 interface, as expected. Surprisingly the second interface was also disrupted by these mutations. Similarly, a loss-of-function mutation in the BH4 region of Bcl-2 that forms part of the second interface also disrupted both interfaces. As expected, both kinds of mutation abolished Bcl-2-mediated inhibition of Bax oligomerization in detergent micelles. Therefore, Bcl-2 binds Bax through two interdependent interfaces to inhibit the pro-apoptotic oligomerization of Bax.     

Dihydromyricetin Reduced Bcl-2 Expression via p53 in Human Hepatoma HepG2 Cells

Dihydromyricetin (DHM) is a major active ingredient of flavonoids compounds. It exhibited anticancer activity and induced apoptosis in human hepatocellular carcinoma HepG2 cells according to our previous data. In this study, we investigated whether p53 is involved in DHM-triggered viability inhibition and apoptosis induction in cancer cells. MTT [3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] assay was employed to evaluate the viability of HepG2 cells after DHM treatment. Meanwhile, p53 small interfering RNA (siRNA) was adopted to silence p53 expression. Protein level of p53 and Bax/Bcl-2 were evaluated by western blot analysis. Cell counting assay showed that DHM inhibited HepG2 cell growth effectively in a time- and dose-dependent manner. P53 expression was significantly increased after DHM treatment, whereas Bcl-2 was reduced potently. Furthermore, after co-treatment with Pifithrin-α (PFT-α, p53 inhibitor), Bcl-2 expression was reversed. The expression of Bax was no significant change, which was also observed after p53 silence. These findings defined and supported a novel function that DHM could induce human hepatocellular carcinoma HepG2 cells apoptosis by up-regulating Bax/Bcl-2 expression via p53 signal pathway.     

The differential expression of apoptosis factors in the alveolar epithelium is redox sensitive and requires NF-kappaB (RelA)-selective targeting

Fetal alveolar type II (fATII) epithelial cells were used to evaluate the role of signaling factors involved in oxidative stress-induced programmed cell death (PCD; apoptosis). Bcl-2, an antiapoptotic proto-oncogene, showed maximum abundance in hypoxia and mild reoxygenation, but declined thereafter. The Bcl-2 counterpart, Bax, which promotes PCD, displayed an increasing logarithmic profile with ascending DeltapO(2) regimen, such that the ratio of Bcl-2/Bax decreased as pO(2) increased. The expression of p53, a cell cycle regulator, paralleled Bax abundance. Pretreatment of fATII cells with l-buthionine-(S,R)-sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in the biosynthesis of glutathione (GSH), enhanced Bax and p53 expression over Bcl-2. The GSH analogue, gamma-glutamylcysteinyl-ethyl ester, down-regulated Bax/p53 abundance but restored that of Bcl-2, thereby increasing Bcl-2/Bax. The antioxidant and GSH precursor N-acetyl-l-cysteine favored Bcl-2 at the expense of Bax/p53, whereas pyrrolidine dithiocarbamate induced Bax against Bcl-2, with mild effect on p53. Sulfasalazine, a potent and specific inhibitor of NF-kappaB, induced Bax at the expense of Bcl-2, in a p53-dependent manner. We conclude that the differential expression of signaling factors involved in PCD in the alveolar epithelium is redox-sensitive and mediated, at least in part, by a negative feedback mechanism transduced by NF-kappaB.     

Smac调控Caspase-3对耐药肺腺癌细胞株生物活性及相关信号的研究

摘要 目的：探讨Smac基因调控Caspase-3表达对紫杉醇耐药肺腺癌细胞株生物活性及经典凋亡信号通路的作用机制。方法：取构建好的耐药A549细胞,将其分为A549细胞（LC）组、A549细胞+Smac-NC（SN）组、A549细胞+Smac抑制剂（SI）组、A549细胞+Smac激动剂（SM）组、A549细胞+Caspase-3-NC（CN）组、A549细胞+Caspase-3抑制剂（CI）组、A549细胞+Caspase-3激动剂（CM）组、A549细胞+Smac激动剂+Caspase-3激动剂（MM）组;Real-time PCR法检测正常肺上皮细胞及4种肺腺癌细胞系中Smac、Caspase-3表达水平,将阴性对照、Smac、Caspase-3类似物转染至紫杉醇耐药肺腺癌细胞株,MTT法检测细胞增殖,流式细胞仪检测细胞凋亡,免疫印迹法检测经典凋亡信号通路表达,并分析Smac与Caspase-3的相关性。结果：肺腺癌细胞系中的Smac、Caspase-3 mRNA表达量显著低于正常肺上皮细胞系BEAS-2B（P＜0.05）,其中A549的Smac、Caspase-3 mRNA值最小（P＜0.05）,因此选取其作为此次实验细胞;LC组与SN组相比,细胞增殖率、凋亡率及Caspase-3、Bcl-2、Bax、Cyto-C蛋白表达基本无差异（P＞0.05）,与SN组相比,SI组细胞凋亡率及Caspase-3、Bax、Cyto-C蛋白表达明显降低（P＜0.05）,增殖率、Bcl-2表达明显升高（P＜0.05）,与SI组相比,SM组细胞凋亡率及Caspase-3、Bax、Cyto-C蛋白表达明显升高（P＜0.05）,增殖率、Bcl-2表达明显降低（P＜0.05）;LC组与CN组相比,细胞增殖率、凋亡率及Caspase-3、Bcl-2、Bax、Cyto-C蛋白表达基本无差异（P＞0.05）,与CN组相比,CI组细胞凋亡率及Caspase-3、Bax、Cyto-C蛋白表达明显降低（P＜0.05）,增殖率、Bcl-2表达明显升高（P＜0.05）,与CI组相比,CM组细胞凋亡率及Caspase-3、Bax、Cyto-C蛋白表达明显升高（P＜0.05）,增殖率、Bcl-2表达明显降低（P＜0.05）;SM组与CM组相比,细胞增殖率、凋亡率及Caspase-3、Bcl-2、Bax、Cyto-C蛋白表达基本无差异（P＞0.05）,与CM组相比,MM组细胞凋亡率及Caspase-3、Bax、Cyto-C蛋白表达明显升高（P＜0.05）,增殖率、Bcl-2表达明显降低（P＜0.05）;Smac与Caspase-3呈现正相关（r=0.470,P=0.002）,组间具有显著差异。结论：Smac基因可显著改善紫杉醇耐药肺腺癌细胞株细胞生物活性,并激活经典凋亡信号通路,其作用机制可能与调控Caspase-3表达有关。     

Long term lithium treatment suppresses p53 and Bax expression but increases Bcl-2 expression. A prominent role in neuroprotection against excitotoxicity

This study was undertaken to investigate the molecular mechanisms underlying the neuroprotective actions of lithium against glutamate excitotoxicity with a focus on the role of proapoptotic and antiapoptotic genes. Long term, but not acute, treatment of cultured cerebellar granule cells with LiCl induces a concentration-dependent decrease in mRNA and protein levels of proapoptotic p53 and Bax; conversely, mRNA and protein levels of cytoprotective Bcl-2 are remarkably increased. The ratios of Bcl-2/Bax protein levels increase by approximately 5-fold after lithium treatment for 5-7 days. Exposure of cerebellar granule cells to glutamate induces a rapid increase in p53 and Bax mRNA and protein levels with no apparent effect on Bcl-2 expression. Pretreatment with LiCl for 7 days prevents glutamate-induced increase in p53 and Bax expression and maintains Bcl-2 in an elevated state. Glutamate exposure also triggers the release of cytochrome c from the mitochondria into the cytosol. Lithium pretreatment blocks glutamate-induced cytochrome c release and cleavage of lamin B1, a nuclear substrate for caspase-3. These results strongly suggest that lithium-induced Bcl-2 up-regulation and p53 and Bax down-regulation play a prominent role in neuroprotection against excitotoxicity. Our results further suggest that lithium, in addition to its use in the treatment of bipolar depressive illness, may have an expanded use in the intervention of neurodegeneration.     

通窍明目IV号对青光眼模型大鼠视神经保护的机制研究

目的:观察不同浓度通窍明目Ⅳ号对青光眼模型大鼠凋亡相关蛋白表达的干预作用。方法:将42只SD大鼠随机分为空白组,模型组,通窍明目4号低、中、高剂量组和神经营养剂组,共计6组,每组7只。经眼球前房角膜缘注射卡波姆复制高眼压模型,成模21天后灌胃给药,给药期4周。采用HE染色观察视网膜形态及视神经节胞、免疫组化法测定BCL-2、Bax、P53蛋白表达,用Western Blot法测定Caspase-3、Caspase-9蛋白表达。结果:与空白组对比,模型组视网膜Bax与p53阳性表达显著升高(P<0.01);与模型组比较,神经营养剂组与通窍明目Ⅳ号高、中剂量组视网膜Bax与p53蛋白的阳性表达显著降低(P<0.01)。与空白组比较,模型组视网膜Bcl-2阳性表达显著降低(P<0.01);与模型组比较,神经营养剂组与通窍明目Ⅳ号各剂量组视网膜Bcl-2的阳性表达有不同程度的提高。模型组大鼠caspase-3、caspase-9的蛋白表达水平均高于空白组(P<0.01);与模型组比较,神经营养剂组与通窍明目Ⅳ号各剂量组大鼠视网膜Caspase3及caspase-9表达水平明显降低(P<0.01)。结论:通窍明目Ⅳ号可能通过下调Bax、P53表达,促进Bcl-2表达升高、抑制Caspase-3、Caspase-9激活凋亡途径,从而对青光眼视神经起到保护作用。     

Roles of Apolipoprotein E (ApoE) and Inducible Nitric Oxide Synthase (iNOS) in Inflammation and Apoptosis in Preeclampsia Pathogenesis and Progression

Objectives

To investigate potential roles of inducible nitric oxide synthase (iNOS) and apolipoprotein (apoE) in inflammation and apoptosis promoting pathological changes in preeclampsia in pregnant mice with apoE and/or iNOS knock out.

Methods

B6.129 mice were crossed to produce WT, apoE^−/−, apoE^+/−, iNOS^−/−, iNOS^+/− and apoE^−/−iNOS^−/− groups. Variants were confirmed by PCR. Serum lipid parameters (triglycerides, TG; total cholesterol, TC; high density lipoprotein, HDL; and low density lipoprotein, LDL), NO levels and placental electronic microscopic ultrastructures were evaluated, and blood pressure (BP), 24-hour urine protein and pregnancy outcomes were recorded for pregnant F1 generation mice. Placental expressions of inflammatory (tumor necrosis factor-α, TNF-α; interleukin-6, IL-6; nuclear factor-κB, NF-κb) and apoptotic markers (Bcl-2 associated X protein, Bax, B-cell lymphoma/leukemia-2, Bcl-2, and Caspase-3) were evaluated via Western blot.

Results

Serum lipids, BP and 24-hour urine protein levels were shown to be significantly higher and parturition and placenta weights were lower in apoE^−/− and apoE^−/−iNOS^−/− groups (p<0.05). NO levels were lower in the apoE^−/−iNOS^−/− group. In addition, inflammatory/apoptosis parameters, including TNF-α, IL-6, NF-κb, Bax, Bcl-2 and Caspase-3 in the apoE^−/−iNOS^−/− group (p<0.01), as well as in the apoE^−/− group (p<0.05), and NF-κB, Bax in iNOS^−/− group (p<0.05) were higher compared with WT group. However, most of the inflammatory/apoptosis parameters in the iNOS^+/− and the apoE^+/− groups (p>0.05) showed no differences. In addition, placenta vascular endothelial and trophoblast cell morphological changes were demonstrated in both the apoE^−/−iNOS^−/− and apoE^−/− groups.

Conclusion

Elevated lipid metabolism and inflammatory/apoptosis parameters suggest a potentially significant role of apoE in preeclampsia pathology, as well as a relationship between iNOS and preeclampsia progression.     

Restoration of p53/miR-34a regulatory axis decreases survival advantage and ensures Bax-dependent apoptosis of non-small cell lung carcinoma cells

Tumor-suppressive miR-34a, a direct target of p53, has been shown to target several molecules of cell survival pathways. Here, we show that capsaicin-induced oxidative DNA damage culminates in p53 activation to up-regulate expression of miR-34a in non-small cell lung carcinoma (NSCLC) cells. Functional analyses further indicate that restoration of miR-34a inhibits B cell lymphoma-2 (Bcl-2) protein expression to withdraw the survival advantage of these resistant NSCLC cells. In such a proapoptotic cellular milieu, where drug resistance proteins are also down-regulated, p53-transactivated Bcl-2 associated X protein (Bax) induces apoptosis via the mitochondrial death cascade. Our results suggest that p53/miR-34a regulatory axis might be critical in sensitizing drug-resistant NSCLC cells.     

p21 promotes ceramide-induced apoptosis and antagonizes the antideath effect of Bcl-2 in human hepatocarcinoma cells

p21, a potent cyclin-dependent kinase inhibitor, has been known to induce cell cycle arrest in response to DNA-damaging agents. Although p21 has been reported to play an important role in the regulation of apoptosis, the postulated role for p21 in apoptosis is still controversial. Previously, we reported that p21 was induced in a p53-independent manner during ceramide-induced apoptosis in human hepatocarcinoma cell lines. In the present study, we investigated the precise role of p21 in ceramide-induced apoptosis in human hepatocarcinoma cells by using a tetracycline-inducible expression system. Overexpression of p21 by itself did not induce apoptosis in p53-deficient Hep3B cells. However, Hep3B/p21 cells were more sensitive to ceramide-induced apoptosis. In these cells, p21 overexpression did not result in G1 arrest. The expression level of Bax was increased in Hep3B/p21 cells treated with ceramide and its expression was more accelerated under the p21-overexpressed condition compared to that of the p21-repressed condition. Overexpression of Bax induced apoptosis in Hep3B cells. On the other hand, the levels of p21 and Bax protein were increased by ceramide in another hepatocarcinoma cell line, SK-Hep-1, while the Bcl-2 protein level was not changed. Overexpression of Bcl-2 not only suppressed apoptosis but also completely prevented induction of p21 and Bax caused by ceramide in SK-Hep-1 cells. Furthermore, overexpression of p21 antagonized the death-protective function of Bcl-2 and upregulated expression of Bax protein. These results suggest that p21 promotes ceramide-induced apoptosis by enhancing the expression of Bax, thereby modulating the molecular ratio of Bcl-2:Bax in human hepatocarcinoma cells.     

缺氧微环境SIRT1亚细胞定位对结直肠癌细胞凋亡的影响及其机制研究

目的:探究缺氧微环境SIRT1亚细胞定位对结直肠癌细胞凋亡的影响及其分子机制。方法:将编码过表达野生型SIRT1以及核定位序列(nuclear localization sequence,NLS)突变型SIRT1(SIRT1NLSmt)的慢病毒载体转染人类结肠癌HCT116细胞株,经嘌呤霉素筛选获得稳定过表达野生型SIRT1细胞株(LV-SIRT1细胞)和细胞质定位的NLS突变型SIRT1细胞株(LV-SIRT1NLSmt细胞),通过观察慢病毒载体编码的SIRT1-GFP融合蛋白的荧光定位,明确稳定转染细胞中外源性SIRT1的亚细胞定位。利用real-time PCR、Western blot法对分离提取的核-质蛋白进行检测,证实外源性SIRT1的表达和亚细胞定位情况。利用CCK-8细胞毒性实验、流式细胞术检测和TUNEL染色比较缺氧(1%O2)处理前后LV-SIRT1和LV-SIRT1NLSmt细胞存活或凋亡情况,Western blot法检测凋亡相关蛋白p53、ac-p53(K382)、Bcl-2、Bax、caspase-3和cleaved caspase-3表达水平。结果:Western blot、real-time PCR和免疫荧光染色结果显示稳定转染细胞均存在外源性SIRT1的过表达,NLS突变可导致SIRT1NLSmt富集于细胞质中;与亲本细胞HCT116和LV-SIRT1NLSmt细胞相比,LV-SIRT1细胞对缺氧的耐受能力最差、细胞凋亡水平最高,凋亡相关蛋白p53、Bax、caspase-3、cleaved caspase-3表达水平显著升高,ac-p53(K382)和Bcl-2表达水平显著下降,且LV-SIRT1细胞的胞核ac-p53下降最为显著。结论:在缺氧微环境中,细胞核定位的SIRT1通过影响p53的去乙酰化水平促进结直肠癌细胞凋亡。     

Mfn2 Affects Embryo Development via Mitochondrial Dysfunction and Apoptosis

BackgroundGrowth factors, energy sources, and mitochondrial function strongly affect embryo growth and development in vitro. The biological role and prospective significance of the mitofusin gene Mfn2 in the development of preimplantation embryos remain poorly understood. Our goal is to profile the role of Mfn2 in mouse embryos and determine the underlying mechanism of Mfn2 function in embryo development.MethodsWe transfected Mfn2-siRNA into 2-cell fertilized eggs and then examined the expression of Mfn2, the anti-apoptotic protein Bcl-2, and the apoptosis-promoting protein Bax by Western blot. Additionally, we determined the blastocyst formation rate and measured ATP levels, mtDNA levels, mitochondrial membrane potential (ΔΨm), and apoptosis in all of the embryos.ResultsThe results indicate that the Mfn2 and Bcl-2 levels were markedly decreased, whereas Bax levels were increased in the T group (embryos transfected with Mfn2-siRNA) compared with the C group (embryos transfected with control-siRNA). The blastocyst formation rate was significantly decreased in the T group. The ATP content and the relative amounts of mtDNA and cDNA in the T group were significantly reduced compared with the C group. In the T group, ΔΨm and Ca²⁺ levels were reduced, and the number of apoptotic cells was increased.ConclusionLow in vitro expression of Mfn2 attenuates the blastocyst formation rate and cleavage speed in mouse zygotes and causes mitochondrial dysfunction, as confirmed by the ATP and mtDNA levels and mitochondrial membrane potential. Mfn2 deficiency induced apoptosis through the Bcl-2/Bax and Ca²⁺ pathways. These findings indicate that Mfn2 could affect preimplantation embryo development through mitochondrial function and cellular apoptosis.