Caspase 8 mediated apoptotic cell death induced by β-sheet forming polyalanine peptides

Sustainable Nanoparticles from Stephania glabra and Analysis of Their Anticancer Potential on 2D and 3D Models of Prostate Cancer

In pursuit of a novel effective treatment for prostate cancer, methanolic extract of Stephania glabra tubers (Sg-ME) was utilized to fabricate silver (Sg-AgNP), copper oxide (Sg-CuONP), and silver-copper bimetallic nanoparticles (Sg-BNP). The characterization of the nanoparticles confirmed spherical shape with average diameters of 30.72, 32.19, and 25.59 nm of Sg-AgNP, Sg-CuONP, and Sg-BNP, respectively. Interestingly, these nanoparticles exhibited significant cytotoxicity toward the prostate cancer (PC3) cell line while being non-toxic toward normal cells. The nanoparticles were capable of inducing apoptosis in PC3 cells by enhancing reactive oxygen species (ROS) generation and mitochondrial depolarization. Furthermore, the shrinkage of 3D prostate tumor spheroids was observed after 4 days of treatment with these green nanoparticles. The 3D model system was less susceptible to nanoparticles as compared to the 2D model system. Sg-BNP showed the highest anticancer potential on 2D and 3D prostate cancer models.

Usnic acid induced changes in biomolecules and their association with apoptosis in squamous carcinoma (A-431) cells: A flow cytometry, FTIR and DLS spectroscopic study

Many natural products induce apoptotic cell death in cancer cells, though studies on their interactions with macromolecules are limited. For the first time, this study demonstrated the cytotoxic potential of usnic acid (UA) against squamous carcinoma (A-431) cells and the associated changes in cell surface proteins, lipids and DNA by attenuated total reflection- fourier transform infrared spectroscopy (ATR-FTIR) and dynamic light scattering (DLS) spectroscopic studies. The IC₅₀ for UA was 98.9 µM after treatment of A-431 cells for 48 h, while the IC₅₀ reduced to 39.2 µM after 72 h of incubation time. UA induced oxidative stress in treated cells as confirmed by DCFHDA flow cytometry assay, depletion in reduced glutathione and increase in lipid peroxidation. The oxidative stress resulted in conformation change in amide I, amide II protein bands and DNA as observed by ATR-FTIR in UA treated A-431 cells. Shift in secondary structures of proteins from α helix to β sheets and structural changes in DNA was observed in UA treated A-431 cells. An increase in the band intensity of phospholipids, increased distribution of lipid and change in membrane potential was noted in UA treated cells, which was confirmed by externalization of phosphatidylserine to the outer membrane by annexin V-FITC/PI assay. Increase in mitochondrial membrane potential, cell cycle arrest at G0/G1 phase by flow cytometry and activation of caspase-3/7 dependent proteins confirmed the UA induced apoptosis in treated A-431 cells. FTIR and DLS spectroscopy confirmed the changes in biomolecules after UA treatment, which were associated with apoptosis, as observed by flow cytometry.

Apoptosis induction in lung and prostate cancer cells through silver nanoparticles synthesized from Pinus roxburghii bioactive fraction

The current study was carried out to synthesize silver nanoparticles (AgNPs) via bioactive fraction of Pinus roxburghii needles using a simple, cost-effective, and eco-friendly green chemistry method. As butanol fraction of P. roxburghii exhibited maximum anticancer activity on lung adenocarcinomas (A549) as compared to other fractions therefore, butanol fraction was used to synthesize silver nanoparticles (PNb-AgNPs). The characterization studies by UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED) confirmed the synthesis of the nanoparticles. The field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) analysis showed the spherical structure of nanoparticles with an average diameter of approximately 80 nm. Interestingly, PNb-AgNPs exhibited significant cytotoxicity towards both A549 and prostatic small cell carcinomas (PC-3) with IC₅₀ values of 11.28 ± 1.28 μg/ml and 56.27 ± 1.17 μg/ml, respectively, while lacking toxicity against normal human breast epithelial cells (fR2) and human peripheral blood lymphocytes (PBL). Further, enhanced reactive oxygen species generation, mitochondrial depolarization, apoptotic cell population (sub-G1) and DNA fragmentation observed in cancer cells were treated with PNb-AgNPs. Apoptosis was demonstrated by caspase-3 and PARP-1 activation in PNb-AgNPs-pretreated cancer cells. These results strongly suggest that PNb-AgNPs are capable of inducing cancer cell death and could act as a therapeutic nanoformulation for cancer.

Ethanolic extract of leaf of Dillenia pentagyna reduces in-vitro cell migration and induces intrinsic pathway of apoptosis via downregulation of NF-κβ in human NSCLC A549 cells

Despite the advancement of the pharmaceutical industry, medicinal plants are still a reliable source of traditional medicines to cure a number of diseases. Various parts of Dillenia pentagyna are used in traditional medicine in India for treatment of various disorders including cancers, but detailed mechanisms are still unknown. Dried leaves of D. pentagyna were extracted with ethanol and termed as an ethanolic extract of leaves of D. pentagyna (EELDP). Our aim was to elucidate the role of EELDP in in-vitro cell migration and apoptosis in highly metastatic human lung adenocarcinoma A549 cells. We measured cell viability and in-vitro cell migration in three different human cancer cells A549, HeLa and U2OS treated with EELDP (0-0.6 mg/mL). However, A549 cells showed higher sensitivity to EELDP treatment. Hence we studied several key markers of metastasis and apoptosis pathway in A549 cells treated with EELDP. EELDP treatment significantly reduced in-vitro cell migration, wound healing, expression and activity of MMP-2, MMP-9 via reduction of nuclear factor kappa Beta (NF-κβ). EELDP also reduced vimentin, N-cadherin and increased claudin-1. The intrinsic pathway of apoptosis was triggered by EELDP via the NF-κβ pathway through the increase of the Bax to Bcl₂ ratio, leading to the fall of mitochondrial membrane potential and subsequently induced release of cytochrome c, activation of caspase-3 followed by nuclear fragmentation in A549 cells. Furthermore, we observed change of a few markers of metastasis and apoptosis in other two cell types HeLa and U2OS treated with EELDP. These data implicate that the effect of EELDP is not cell-specific. Since only 0.1 mg/mL EELDP significantly reduces in-vitro cell migration and increases apoptosis, the active compound(s) present in EELDP is very much potent to control highly metastatic cancer.

An in vitro analysis of the rat C6 glioma cells to elucidate the linear alkylbenzene sulfonate induced oxidative stress and consequent G2/M phase cell cycle arrest and cellular apoptosis

Linear alkylbenzene Sulphonate (LAS) is the anionic surfactant component of globally consumed detergents. Exposure of sub-inhibitory fractions viz., 1/10th (T1), 1/5th (T2), and 1/2.5th (T3) of IC₅₀ for 48 h, of LAS (5 μM, 10 μM, and 20 μM, respectively) to viable C6 glioma cells of rat, besides imparting morphological alterations leads to gross cytotoxicity. Expression of the damaged DNA coupled with cleaved PARP (p < 0.05; p < 0.01 and p < 0.001) were recorded for T1, T2 and T3, respectively. Subsequently, the cell cycle at G2/M check point was significantly arrested (p < 0.05 for T1 and T2; p < 0.01 for T3). The flow cytometric analysis reveals the initiation of apoptosis in C6 cells as is evident by a significant increase (p < 0.01 for T1, p < 0.001 for T2, and T3) in the intake of annexin-V, the calcium dependent apoptotic phospholipid binding protein. Moreover, significantly increased reactive oxygen species (ROS) (p < 0.05; p < 0.01 and p < 0.001) after 6 h of exposure for all the three sets, registered a declining trend (P < 0.001) when T3 cells were co-treated with N-acetyl cysteine (NAC). Furthermore, the significant attenuation (p < 0.01) of expression of the cleaved PARP and a consequent decrease (p < 0.05) in the cell cycle arrest at G2/M phase after scavenging ROS induced oxidative stress by treating C6 cells with NAC clearly evinces that LAS induced apoptosis is mediated by intracellular ROS. Thus, these findings provide a tangible basis for further investigations including in vivo studies, to unravel the molecular mechanism involved in ROS mediated and LAS induced cytotoxic manifestations.

One-dimensional poly(L-lysine)-block-poly(L-threonine) assemblies exhibit potent anticancer activity by enhancing membranolysis

Herein, we report the oncolytic activity of cationic, one-dimensional (1D) fibril assemblies formed from coil-sheet poly(L-lysine)-block-poly(L-threonine) (PLL-b-PLT) block copolypeptides for cancer therapy. The 1D fibril assemblies can efficiently interact with negatively charged cellular and mitochondrial membranes via electrostatic interactions, leading to necrosis via membrane lysis and apoptosis via the mitochondria-lytic effect. The concept is analogous to that of 1D drug carriers that exhibit enhanced cell penetration. In comparison to free PLL chains, PLL-b-PLT fibril assemblies exhibit selective cytotoxicity toward cancer cells, low hemolysis activity, enhanced membranolytic activity, and a different apoptosis pathway, which may be due to differences in the peptide-membrane interactions. Antitumor studies using a metastatic LL2 lung carcinoma model indicate that the fibril assemblies significantly inhibited tumor growth, improved survival in tumor-bearing mice and suppressed lung metastasis without obvious body weight loss. An additive efficacy was also observed for treatment with both PLL-b-PLT and cisplatin. These results support the feasibility of using 1D fibril assemblies as potential apoptotic anticancer therapeutics.

STATEMENT OF SIGNIFICANCE

We report that cationic, one-dimensional (1D) fibril assemblies formed by coil-sheet poly(L-lysine)-block-poly(L-threonine) (PLL-b-PLT) block copolypeptides exhibited potent anticancer activity by enhancing membranolysis. The 1D fibril assemblies can efficiently interact with negatively charged cellular and mitochondrial membranes via electrostatic interactions, leading to necrosis via membrane lysis and apoptosis via mitochondria-lytic effect. Moreover, the fibril assemblies exhibited low hemolytic activity and selective cytotoxicity toward cancer cell, which is advantageous as compared to PLL and most antimicrobial/anticancerous peptides. This study provides a new concept of using cationic, 1D fibril assemblies for cancer therapy.

Cardamonin, a chalcone, inhibits human triple negative breast cancer cell invasiveness by downregulation of Wnt/β-catenin signaling cascades and reversal of epithelial-mesenchymal transition

Cardamonin (CD), an active chalconoid, has shown potent anticancer effects in preclinical studies; however, the effect and underlying mechanism of CD for the treatment of triple negative breast cancer (TNBC) is unclear. This study aims to examine the cytotoxic effects of CD and investigate the underlying mechanism in human TNBC cells. The results show that CD exhibits cytotoxicity by inducing apoptosis and cell cycle arrest in TNBC cells via modulation of Bcl-2, Bax, cyt-C, cleaved caspase-3, and PARP. We find that CD significantly increases expression of the epithelial marker E-cadherin, while reciprocally decreasing expression of mesenchymal markers such as snail, slug, and vimentin in BT-549 cells. In parallel with epithelial-mesenchymal transition (EMT) reversal, CD down regulates invasion and migration of BT-549 cells. CD markedly reduces stability and nuclear translocation of β-catenin, accompanied with downregulation of β-catenin target genes. Using the TopFlash luciferase reporter assay, we reveal CD as a specific inhibitor of the Wnt3a-induced signaling. These results suggest the involvement of the Wnt/β-catenin signaling in the CD-induced EMT reversion of BT-549 cells. Notably, CD restores the glycogen synthase kinase-3β (GSK3β) activity, required for β-catenin destruction via the proteasome-mediated system, by inhibiting the phosphorylation of GSK3β by Akt. These occurrences ultimately lead to the blockage of EMT and the invasion of TNBC cells. Further antitumor activity of CD was tested in 4T1 (TNBC cells) induced tumor and it was found that CD significantly inhibited the tumor volume at dose of 5 mg/kg-treated mice. © 2016 BioFactors, 43(2):152-169, 2017.

In vitro and in vivo antitumor effects of the Egyptian scorpion Androctonus amoreuxi venom in an Ehrlich ascites tumor model

Scorpion venom is a highly complex mixture of about 100-700 different components, where peptides are the major constituents with various biological and pharmacological properties including anticancer activities. In this study, anticancer efficacy of the venom of the Egyptian scorpion Androctonus amoreuxi has been evaluated. In vitro, the human breast cancer MCF-7 cell line was treated with the venom and the IC50 was estimated. In vivo studies, Ehrlich ascites carcinoma (EAC) cells were inoculated into CD-1 mice intraperitoneally to form liquid tumor or subcutaneously to form solid tumor and then treated with intraperitoneal injection with venom (0.22 mg/kg) every other day. The total tumor cells in the ascitic fluid and the size of the solid tumor were assessed after 14 and 30 days, respectively. In addition, the mean survival time (MST), body weight, tumor volume, PCV, viability of tumor cells, CBC, AST, ALP, creatinine, oxidative stress biomarkers (GSH, MDA, PCC), tumor marker Ki67, growth factor VEGF and caspase-3 were measured in normal control, EAC control and venom-treated groups (n = 6). Treatment with venom induced anti-tumor effects against liquid and in solid tumors as indicated by a significant (P < 0.05) reduction in tumor volume/size, count of viable EAC cells, expression of Ki67 and VEGF as well as by remarkable increases in MST and caspase-3 expression as compared to non-treated group. Interestingly, the venom restored the altered hematological and biochemical parameters of tumor-bearing animals and significantly increased their life span. These data indicate to (1) the cytotoxic potential effects of A. amoreuxi on tumor cells via anti-proliferative, apoptotic and anti-angiogenic activities; (2) opening a new avenue for further studies on the anti-cancer effects of this agent.

Carbon ion beam triggers both caspase-dependent and caspase-independent pathway of apoptosis in HeLa and status of PARP-1 controls intensity of apoptosis

High linear energy transfer (LET) carbon ion beam (CIB) is becoming very promising tool for various cancer treatments and is more efficient than conventional low LET gamma or X-rays to kill malignant or radio-resistant cells, although detailed mechanism of cell death is still unknown. Poly (ADP-ribose) polymerase-1 (PARP-1) is a key player in DNA repair and its inhibitors are well-known as radio-sensitizer for low LET radiation. The objective of our study was to find mechanism(s) of induction of apoptosis by CIB and role of PARP-1 in CIB-induced apoptosis. We observed overall higher apoptosis in PARP-1 knocked down HeLa cells (HsiI) compared with negative control H-vector cells after irradiation with CIB (0-4 Gy). CIB activated both intrinsic and extrinsic pathways of apoptosis via caspase-9 and caspase-8 activation respectively, followed by caspase-3 activation, apoptotic body, nucleosomal ladder formation and sub-G1 accumulation. Apoptosis inducing factor translocation into nucleus in H-vector but not in HsiI cells after CIB irradiation contributed caspase-independent apoptosis. Higher p53 expression was observed in HsiI cells compared with H-vector after exposure with CIB. Notably, we observed about 37 % fall of mitochondrial membrane potential, activation of caspase-9 and caspase-3 and mild activation of caspase-8 without any detectable apoptotic body formation in un-irradiated HsiI cells. We conclude that reduction of PARP-1 expression activates apoptotic signals via intrinsic and extrinsic pathways in un-irradiated cells. CIB irradiation further intensified both intrinsic and extrinsic pathways of apoptosis synergistically along with up-regulation of p53 in HsiI cells resulting overall higher apoptosis in HsiI than H-vector.

Russell's viper venom affects regulation of small GTPases and causes nuclear damage

Russell's viper with its five sub-species is found throughout the Indian subcontinent. Its venom is primarily hemotoxic. However, its envenomation causes damage to several physiological systems. The present work was aimed to study the dose and time dependent cytotoxic effects of Russell's viper venom (RVV) on human A549 cells grown in vitro. Time dependent changes have been observed in cellular morphology following exposure to RVV. Presence of stress granules, rounding-off of the cells, and formation of punctate structure and loss of cell-cell contact characterized the cellular effects. Fluorescence microscopic studies revealed that apoptotic cell population increased on exposure to RVV. Further to understand the mechanism of these effects, status of small GTPase (smGTPases) expression were studied by Western blot and RT-PCR; as smGTPases play pivotal roles in deciding the cellular morphology, polarity, cell movement and overall signaling cascade. It was shown for the first time that expression patterns of Rac, Rho and CDC42 genes are altered on exposure to RVV. Similarly, significant difference in the expression pattern of HSP70 and p53 at the mRNA levels were noted. Our results confirmed that RVV induces apoptosis in A549 cells; this was further confirmed by AO/EtBr staining as well as caspase-3 assay. All experiments were compared using RVV unexposed cells. We propose for the first time that RVV induces morphological changes in human A549 cells through modulation of smGTPase expression and affects the cellular-nuclear architecture which in turn interferes in proliferation and migration of these cells along with apoptosis.

Anticancer effect of celastrol on human triple negative breast cancer: possible involvement of oxidative stress, mitochondrial dysfunction, apoptosis and PI3K/Akt pathways

Signaling via the phosphatidylinositol-3 kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) is crucial for divergent physiological processes including transcription, translation, cell-cycle progression and apoptosis. The aim of work was to elucidate the anti-cancer effect of celastrol and the signal transduction pathways involved. Cytotoxic effect of celastrol was assessed by MTT assay on human triple negative breast cancer cells (TNBCs) and compared with that of MCF-7. Apoptosis induction was determined by AO/EtBr staining, mitochondrial membrane potential by JC-1, Annexin binding assays and modulation of apoptotic proteins and its effect on PI3K/Akt/mTOR pathway by western blotting. Celastrol induced apoptosis in TNBC cells, were supported by DNA fragmentation, caspase-3 activation and PARP cleavage. Meanwhile, celastrol triggered reactive oxygen species production with collapse of mitochondrial membrane potential, down-regulation of Bcl-2 and up-regulation of Bax expression. Celastrol effectively decreased PI3K 110α/85α enzyme activity, phosphorylation of Akt(ser473) and p70S6K1 and 4E-BP1. Although insulin treatment increased the phosphorylation of Akt(ser473), p70S6K1, 4E-BP1, celastrol abolished the insulin mediated phosphorylation. It clearly indicates that celastrol acts through PI3k/Akt/mTOR axis. We also found that celastrol inhibited the Akt/GSK3β and Akt/NFkB survival pathway. PI3K/Akt/mTOR inhibitor, PF-04691502 and mTOR inhibitor rapamycin enhanced the apoptosis-inducing effect of celastrol. These data demonstrated that celastrol induces apoptosis in TNBC cells and indicated that apoptosis might be mediated through mitochondrial dysfunction and PI3K/Akt signaling pathway.

Piperlongumine, an alkaloid causes inhibition of PI3 K/Akt/mTOR signaling axis to induce caspase-dependent apoptosis in human triple-negative breast cancer cells

The phosphatidylinositol 3-kinase (PI3 K)/Akt/mammalian target of rapamycin (mTOR) signaling axis plays a central role in cell proliferation, growth and survival under physiological conditions. However, aberrant PI3 K/Akt/mTOR signaling has been implicated in many human cancers, including human triple negative breast cancer. Therefore, dual inhibitors of PI3 K/Akt and mTOR signaling could be valuable agents for treating breast cancer. The objective of this study was to investigate the effect of piperlongumine (PPLGM), a natural alkaloid on PI3 K/Akt/mTOR signaling, Akt mediated regulation of NF-kB and apoptosis evasion in human breast cancer cells. Using molecular docking studies, we found that PPLGM physically interacts with the conserved domain of PI3 K and mTOR kinases and the results were comparable with standard dual inhibitor PF04691502. Our results demonstrated that treatment of different human triple-negative breast cancer cells with PPLGM resulted in concentration- and time-dependent growth inhibition. The inhibition of cancer cell growth was associated with G1-phase cell cycle arrest and down-regulation of the NF-kB pathway leads to activation of the mitochondrial apoptotic pathway. It was also found that PPLGM significantly decreased the expression of p-Akt, p70S6K1, 4E-BP1, cyclin D1, Bcl-2, p53 and increased expression of Bax, cytochrome c in human triple-negative breast cancer cells. Although insulin treatment increased the phosphorylation of Akt (Ser473), p70S6K1, 4E-BP1, PPLGM abolished the insulin mediated phosphorylation, it clearly indicates that PPLGM acts through PI3 k/Akt/mTOR axis. Our results suggest that PPLGM may be an effective therapeutic agent for the treatment of human triple negative breast cancer.

Boswellia ovalifoliolata abrogates ROS mediated NF-κB activation, causes apoptosis and chemosensitization in Triple Negative Breast Cancer cells

The present study was aimed to evaluvate the apoptogenic potential of ethanolic extract of leaves from Boswellia ovalifoliolata (BL EthOH) and to unravel the molecular mechanisms implicated in apoptosis of Triple Negative Breast Cancer (TNBC) cells. BL EthOH was cytotoxic against TNBC cells like MDA-MB-231 and MDA-MB-453 with IC₅₀ concentrations 67.48 ± 5.45 and 70.03 ± 4.76 μg/ml, respectively. Apoptotic studies showed that BL EthOH was able to induce apoptosis and western blot studies demonstrated that BL EthOH significantly decreased the Phospho-NF-κB (ser536), PCNA, anti-apoptotic protein Bcl-2 expression and increased the expression of pro-apoptotic protein Bax, in MDA-MB-231 and MDA-MB-453 cell lines when compared with untreated cells. Besides, BL EthOH has synergistic chemosensitizing effects on TNBC cells and increased the cytotoxicity of doxorubicin and cisplatin.

Functional and structural analysis of the conserved EFhd2 protein

EFhd2 is a novel protein conserved from C. elegans to H. sapiens. This novel protein was originally identified in cells of the immune and central nervous systems. However, it is most abundant in the central nervous system, where it has been found associated with pathological forms of the microtubule-associated protein tau. The physiological or pathological roles of EFhd2 are poorly understood. In this study, a functional and structural analysis was carried to characterize the molecular requirements for EFhd2's calcium binding activity. The results showed that mutations of a conserved aspartate on either EF-hand motif disrupted the calcium binding activity, indicating that these motifs work in pair as a functional calcium binding domain. Furthermore, characterization of an identified single-nucleotide polymorphisms (SNP) that introduced a missense mutation indicates the importance of a conserved phenylalanine on EFhd2 calcium binding activity. Structural analysis revealed that EFhd2 is predominantly composed of alpha helix and random coil structures and that this novel protein is thermostable. EFhd2's thermo stability depends on its N-terminus. In the absence of the N-terminus, calcium binding restored EFhd2's thermal stability. Overall, these studies contribute to our understanding on EFhd2 functional and structural properties, and introduce it into the family of canonical EF-hand domain containing proteins.

Stress-inducible caspase substrate TRB3 promotes nuclear translocation of procaspase-3

Pseudokinase TRB3 is a stress-inducible nuclear protein, which has recently been shown to be involved in ER stress-induced apoptosis. However, it remains unclear how TRB3 contributes to the process. We recently demonstrated that TRB3 was cleaved by caspase-3 (CASP3) in vitro and also in apoptosis-induced cells. Thus, we investigate the role of TRB3 cleavage in the apoptotic process to address the above question. Overexpression studies revealed that the cleavage of TRB3 promoted CASP3/7 activation and apoptosis. In contrast, the anti-apoptotic effects were found under TRB3 non-cleavable conditions, such as ER stress, and also when the CASP3/7 activation was enhanced by knockdown of endogenous TRB3 expression. Interestingly, nuclear translocation of procaspase-3 (proCASP3) was observed in cells either overexpressing TRB3 or under tunicamycin-induced ER stress. Although forced cytoplasmic expression of proCASP3 enhanced apoptosis significantly, its nuclear expression did not produce any pro-apoptotic effect, suggesting that nuclear distribution of proCASP3 is not critical for the execution of apoptosis. Thus, TRB3 might prevent cytoplasmic activation of CASP3 by promoting proCASP3 entry into the nucleus, and thereby inhibit apoptosis. Taken together, our results suggest that TRB3, through its own cleavage, functions as a molecular switch between the cell survival and apoptotic pathways under stressful conditions.

Mangiferin, a dietary xanthone protects against mercury-induced toxicity in HepG2 cells

Mercury is one of the noxious heavy metal environmental toxicants and is a cause of concern for human exposure. Mangiferin (MGN), a glucosylxanthone found in Mangifera indica, reported to have a wide range of pharmacological properties. The objective of this study was to evaluate the cytoprotective potential of MGN, against mercury chloride (HgCl(2) ) induced toxicity in HepG2 cell line. The cytoprotective effect of MGN on HgCl(2) induced toxicity was assessed by colony formation assay, while antiapoptotic effect by fluorescence microscopy, flow cytometric DNA analysis, and DNA fragmentation pattern assays. Further, the cytoprotective effect of MGN against HgCl(2) toxicity was assessed by using biochemical parameters like reduced glutathione (GSH), glutathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT) by spectrophotometrically, mitochondrial membrane potential by flowcytometry and the changes in reactive oxygen species levels by DCFH-DA spectrofluoremetric analysis. A significant increase in the surviving fraction was observed with 50 μM of MGN administered two hours prior to various concentrations of HgCl(2) . Further, pretreatment of MGN significantly decreased the percentage of HgCl(2) induced apoptotic cells. Similarly, the levels of ROS generated by the HgCl(2) treatment were inhibited significantly (P < 0.01) by MGN. MGN also significantly (P < 0.01) inhibited the HgCl(2) induced decrease in GSH, GST, SOD, and CAT levels at all the post incubation intervals. Our study demonstrated the cytoprotective potential of MGN, which may be attributed to quenching of the ROS generated in the cells due to oxidative stress induced by HgCl(2) , restoration of mitochondrial membrane potential and normalization of cellular antioxidant levels.

Length-dependent aggregation of uninterrupted polyalanine peptides

Polyalanine (polyA) is the third-most prevalent homopeptide repeat in eukaryotes, behind polyglutamine and polyasparagine. Abnormal expansion of the polyA repeat is linked to at least nine human diseases, and the disease mechanism likely involves enhanced length-dependent aggregation. Because of the simplicity of its side chain, polyA has been a favorite target of computational studies, and because of their tendency to fold into α-helix, peptides containing polyA-rich domains have been a popular experimental subject. However, experimental studies on uninterrupted polyA are very limited. We synthesized polyA peptides containing uninterrupted sequences of 7 to 25 alanines (A7 to A25) and characterized their length-dependent conformation and aggregation properties. The peptides were primarily disordered, with a modest component of α-helix that increased with increasing length. From measurements of mean distance spanned by the polyA segment, we concluded that physiological buffers are neutral solvents for shorter polyA peptides and poor solvents for longer peptides. At moderate concentration and near-physiological temperature, polyA assembled into soluble oligomers, with a sharp transition in oligomer physical properties between A19 and A25. With A19, oligomers were large, contained only a small fraction of the total peptide mass, and slowly grew into loose clusters, while A25 rapidly and completely assembled into small stable oligomers of ~7 nm radius. At high temperatures, A19 assembled into fibrils, but A25 precipitated as dense, micrometer-sized particles. A comparison of these results to those obtained with polyglutamine peptides of similar design sheds light on the role of the side chain in regulating conformation and aggregation.

A yeast model for polyalanine-expansion aggregation and toxicity

Polyalanine expansions can result in aggregation and cause cytotoxicity. We have created the first yeast model of polyalanine-expansion aggregation and toxicity using the poly(Ade)-binding protein Pab1.

Nine human disorders result from the toxic accumulation and aggregation of proteins with expansions in their endogenous polyalanine (polyA) tracts. Given the prevalence of polyA tracts in eukaryotic proteomes, we wanted to understand the generality of polyA-expansion cytotoxicity by using yeast as a model organism. In our initial case, we expanded the polyA tract within the native yeast poly(Adenine)-binding protein Pab1 from 8A to 13A, 15A, 17A, and 20A. These expansions resulted in increasing formation of Pab1 inclusions, insolubility, and cytotoxicity that correlated with the length of the polyA expansion. Pab1 binds mRNA as part of its normal function, and disrupting RNA binding or altering cytoplasmic mRNA levels suppressed the cytotoxicity of 17A-expanded Pab1, indicating a requisite role for mRNA in Pab1 polyA-expansion toxicity. Surprisingly, neither manipulation suppressed the cytotoxicity of 20A-expanded Pab1. Thus longer expansions may have a different mechanism for toxicity. We think that this difference underscores the potential need to examine the cytotoxic mechanisms of both long and short expansions in models of expansion disorders.

Single homopolypeptide chains collapse into mechanically rigid conformations

Huntington's disease is linked to the insertion of glutamine (Q) in the protein huntingtin, resulting in polyglutamine (polyQ) expansions that self-associate to form aggregates. While polyQ aggregation has been the subject of intense study, a correspondingly thorough understanding of individual polyQ chains is lacking. Here we demonstrate a single molecule force-clamp technique that directly probes the mechanical properties of single polyQ chains. We have made polyQ constructs of varying lengths that span the length range of normal and diseased polyQ expansions. Each polyQ construct is flanked by the I27 titin module, providing a clear mechanical fingerprint of the molecule being pulled. Remarkably, under the application of force, no extension is observed for any of the polyQ constructs. This is in direct contrast with the random coil protein PEVK of titin, which readily extends under force. Our measurements suggest that polyQ chains form mechanically stable collapsed structures. We test this hypothesis by disrupting polyQ chains with insertions of proline residues and find that their mechanical extensibility is sensitive to the position of the proline interruption. These experiments demonstrate that polyQ chains collapse to form a heterogeneous ensemble of conformations that are mechanically resilient. We further use a heat-annealing molecular dynamics protocol to extensively search the conformation space and find that polyQ can exist in highly mechanically stable compact globular conformations. The mechanical rigidity of these collapsed structures may exceed the functional ability of eukaryotic proteasomes, resulting in the accumulation of undigested polyQ sequences in vivo.

Polyalanine tracts directly induce the release of cytochrome c, independently of the mitochondrial permeability transition pore, leading to apoptosis

In recent years, several novel types of disorder caused by the expansion of triplet repeats in specific genes have been characterized; in the "polyalanine diseases", these expanded repeats result in proteins with aberrantly elongated polyalanine tracts. In this study, we fused expanded polyalanine tracts to yellow fluorescent protein to examine their physical interaction with mitochondria. Tracts containing more than 23 alanine repeats were found to physically associate with mitochondria, strongly suggesting that an interaction between polyalanine tracts and mitochondria is a contributing factor in the pathology of polyalanine diseases. Furthermore, in in vitro experiments, polyalanine tracts induced release of cytochrome c from mitochondria and caspase-3 activation, independently of the mitochondrial permeability transition pore. These results suggest that oligomerized polyalanine tracts might induce the rupture of the mitochondrial membrane, the subsequent release of cytochrome c, and apoptosis. This novel mechanism for polyalanine tract cytotoxicity might be common to the pathogenesis of all polyalanine diseases. Further investigation of this mechanism might aid the development of therapies for these diseases.

Amyloid peptides and proteins in review

Amyloids are filamentous protein deposits ranging in size from nanometres to microns and composed of aggregated peptide beta-sheets formed from parallel or anti-parallel alignments of peptide beta-strands. Amyloid-forming proteins have attracted a great deal of recent attention because of their association with over 30 diseases, notably neurodegenerative conditions like Alzheimer's, Huntington's, Parkinson's, Creutzfeldt-Jacob and prion disorders, but also systemic diseases such as amyotrophic lateral sclerosis (Lou Gehrig's disease) and type II diabetes. These diseases are all thought to involve important conformational changes in proteins, sometimes termed misfolding, that usually produce beta-sheet structures with a strong tendency to aggregate into water-insoluble fibrous polymers. Reasons for such conformational changes in vivo are still unclear. Intermediate aggregated state(s), rather than precipitated insoluble polymeric aggregates, have recently been implicated in cellular toxicity and may be the source of aberrant pathology in amyloid diseases. Numerous in vitro studies of short and medium length peptides that form amyloids have provided some clues to amyloid formation, with an alpha-helix to beta-sheet folding transition sometimes implicated as an intermediary step leading to amyloid formation. More recently, quite a few non-pathological amyloidogenic proteins have also been identified and physiological properties have been ascribed, challenging previous implications that amyloids were always disease causing. This article summarises a great deal of current knowledge on the occurrence, structure, folding pathways, chemistry and biology associated with amyloidogenic peptides and proteins and highlights some key factors that have been found to influence amyloidogenesis.

Cell killing, nuclear damage and apoptosis in Chinese hamster V79 cells after irradiation with heavy-ion beams of (16)O, (12)C and (7)Li

Chinese hamster V79 cells were exposed to high LET (linear energy transfer) (16)O-beam (625keV/mum) radiation in the dose range of 0-9.83Gy. Cell survival, micronuclei (MN), chromosomal aberrations (CA) and induction of apoptosis were studied as a follow up of our earlier study on high LET radiations ((7)Li-beam of 60keV/mum and (12)C-beam of 295keV/mum) as well as (60)Co gamma-rays. Dose dependent decline in surviving fraction was noticed along with the increase of MN frequency, CA frequency as well as percentage of apoptosis as detected by nuclear fragmentation assay. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was also increased in a dose dependent manner. Additionally, expression of tyrosine kinase lck-1 gene, which plays an important role in response to ionizing radiation induced apoptosis, was increased with the increase of radiation doses and also with incubation time. The present study showed that all the high LET radiations were generally more effective in cell killing and inflicting other cytogenetic damages than that of low LET gamma-rays. The dose response curves revealed that (7)Li-beam was most effective in cell killing as well as inducing other nuclear damages followed by (12)C, (16)O and (60)Co gamma-rays, in that order. The result of this study may have some application in biological dosimetry for assessment of genotoxicity in heavy ion exposed subjects and in determining suitable doses for radiotherapy in cancer patients where various species of heavy ions are now being generally used.

The subunit CSN6 of the COP9 signalosome is cleaved during apoptosis

The COP9 signalosome is a large multiprotein complex that consists of eight subunits termed CSN1-CSN8. The diverse functions of the COP9 complex include regulation of several important intracellular pathways, including the ubiquitin/proteasome system, DNA repair, cell cycle, developmental changes, and some aspects of immune responses. Nod1 is also thought to be an important cytoplasmic receptor involved in innate immune responses. It detects specific motifs of bacterial peptidoglycan, and this results in activation of multiple signaling pathways and changes in cell function. In this report, we performed a yeast two-hybrid screening and discovered that Nod1 interacts with several components of the COP9 signalosome through its CARD domain. Moreover, we observed that activation of the Nod1 apoptotic pathway leads to specific cleavage of the subunit CSN6. This cleavage is concomitant with caspase processing and generates a short amino-terminal peptide of 3 kDa. A complete inhibition of this cleavage was achieved in the presence of the broad spectrum pharmacological inhibitor of apoptosis, Z-VAD. Furthermore, overexpression of CLARP, a specific caspase 8 inhibitor, completely blocked cleavage of CSN6. Taken together, these results suggest a critical role of caspase 8 in the processing of CSN6. Moreover, these findings suggest that CSN6 cleavage may result in modifications of functions of the COP9 complex that are involved in apoptosis.

Genotoxic effects in M5 cells and Chinese hamster V79 cells after exposure to 7Li-beam (LET=60 keV/microm) and correlation of their survival dynamics to nuclear damages and cell death

Chinese hamster V79 cell and a cell strain M5, derived from V79 cells and reported to be relatively resistant to gamma-ray, hydrogen peroxide, and N-methyl-N-nitro-N-nitrosoguanidine (MNNG; a potent human carcinogen), were exposed to high LET (7)Li-beam (LET=60 keV/microm) at approximately 90% confluent state in the dose range of 0-1 Gy. Effects of (7)Li-beam exposure on cell survival, micronuclei induction (MN), chromosomal aberrations (CA) and apoptosis were compared in both the cell lines. A dose-dependent decline in survival for both the cell lines was noted, relatively less in M5 cells (mostly p<0.01) indicating greater radio-resistance in this strain. The MN, CA and apoptosis increased in a dose-dependent manner in both V79 and M5 cells. Significant differences in various other parameters between these two cell lines were also noted. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was much higher in V79 cells. A good correlation between the reduction of the surviving fractions and the increase in frequencies of MN or CA or apoptosis was noted for both the cell lines.

Geldanamycin promotes nuclear localisation and clearance of PHOX2B misfolded proteins containing polyalanine expansions

Polyalanine expansions in the PHOX2B gene have been detected in the vast majority of patients affected with congenital central hypoventilation syndrome, a neurocristopathy characterized by absence of adequate control of breathing, especially during sleep, with decreased sensitivity to hypoxia and hypercapnia. The correlation between length of the alanine expanded tracts and severity of congenital central hypoventilation syndrome respiratory phenotype has been confirmed by length-dependent cytoplasmic PHOX2B retention with formation of aggregates. To deepen into the molecular mechanisms mediating the effects of PHOX2B polyalanine expansions, we have set up experiments aimed at assessing the fate of cells characterized by PHOX2B polyalanine aggregates. In particular, we have observed that activation of the heat shock response by the drug geldanamycin is efficient both in preventing formation and in inducing clearance of PHOX2B pre-formed polyalanine aggregates in COS-7 cells expressing PHOX2B-GFP fused proteins, and ultimately also in rescuing the PHOX2B ability to transactivate the Dopamine-beta-Hydroxilase promoter. In addition, we have demonstrated elimination of PHOX2B mutant proteins by the proteasome and autophagy, two cellular mechanisms already been involved in the clearance of proteins containing expanded polyglutamine and polyalanine tracts. Moreover, our data suggest that geldanamycin effects on PHOX2B aggregates may be also mediated by the proteasome pathway. Finally, analysis of cellular toxicity due to polyalanine aggregates has confirmed the occurrence of cell apoptosis consequent to expression of PHOX2B carrying the longest expanded alanine tract and shown that geldanamycin can delay cell progression toward the most advanced apoptotic stages.

pH-dependent self-assembly of polyalanine peptides

Polyalanine expansions in the nuclear RNA-binding protein PABP2 induce misfolding and aggregation of the protein into insoluble inclusions in muscle tissues and cell nuclei, leading to the disease oculopharyngeal muscular dystrophy (OPMD). We have explored the effect of solvent conditions and alanine repeat number on the propensity of fibril formation in this protein deposition disease. Three peptides mimicking the N-terminal polyalanine segment of PABP2, having the generic sequence Ac-Lys-Met-(Ala)(n)-Gly-Tyr with n = 7, 11, and 17 (referred to as 7-ala, 11-ala, and 17-ala, respectively), were synthesized and their conformational properties studied as a function of pH. In strongly alkaline medium (pH >10), the two longer peptides (11-ala and 17-ala, but not 7-ala) showed remarkable enhancement of beta-sheet content and formed fibrils after incubation for 1-2 weeks at room temperature. Fluorescence studies suggested that tyrosyl radicals produced at high pH cross-linked to form dityrosine, which provided added stabilization for fibril growth. The kinetic progress curves for fibril formation, obtained by ThT fluorescence assay, showed exponential increase with time after an initial quiescent period (lag time) and an eventual saturation phase, all of which are indicative of a nucleation-controlled polymerization mechanism for fibrillation. Hierarchical self-assembly of the peptides led to the formation of striking fractal-shaped growth patterns on substrates, raising the possibility of designing novel materials using these peptides.

Induction of apoptosis in cells expressing exogenous Hippi, a molecular partner of huntingtin-interacting protein Hip1

To decipher the pathway of apoptosis induction downstream to caspase-8 activation by exogenous expression of Hippi, an interactor of huntingtin-interacting protein Hip1, we studied apoptosis in HeLa and Neuro2A cells expressing GFP-tagged Hippi. Nuclear fragmentation, caspase-1, caspase-8, caspase-9/caspase-6 and caspase-3 activation were increased significantly in Hippi expressing cells. Cleavage of Bid, release of cytochrome c and apoptosis inducing factor (AIF) from mitochondria were also increased in GFP-Hippi expressing cells. It was observed that caspase-1 and caspase-8 activation was earlier than caspase-3 activation and nuclear fragmentation. Expression of caspase-1, caspase-3 and caspase-7 was increased while anti-apoptotic gene Bcl-2 and mitochondrial genes ND1 and ND4 were reduced in Hippi expressing cells. Besides, the expression SDHA and SDHB, nuclear genes, subunits of mitochondrial complex II were decreased in GFP-Hippi expressing cells. Taken together, we concluded that Hippi expression induced apoptosis by releasing AIF and cytochrome c from mitochondria, activation of caspase-1 and caspase-3, and altering the expression of apoptotic genes and genes involved in mitochondrial complex I and II.

Cytoplasmic targeting of mutant poly(A)-binding protein nuclear 1 suppresses protein aggregation and toxicity in oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive eyelid drooping, swallowing difficulties and proximal limb weakness. The autosomal dominant form of this disease is caused by a polyalanine expansion from 10 to 12-17 residues, located at the N-terminus of the poly(A)-binding protein nuclear 1 (PABPN1). A distinct pathological hallmark of OPMD is the presence of filamentous intranuclear aggregates in patients' skeletal muscle cells. Wildtype PABPN1 protein is expressed ubiquitously and was shown to be mostly concentrated in discrete nuclear domains called 'speckles'. Using an established cell- culture model, we show that most mutant PABPN1- positive (alanine expanded form) intranuclear aggregates are structures distinct from intranuclear speckles. In contrast, the promyelocytic leukaemia protein, a major component of nuclear bodies, strongly colocalized to intranuclear aggregates of mutant PABPN1. Wildtype PABPN1 can freely shuttle between the nucleus and cytoplasm. We determined whether the nuclear environment is necessary for mutant PABPN1 inclusion formation and cellular toxicity. This was achieved by inactivating the mutant PABPN1 nuclear localization signal and by generating full-length mutant PABPN1 fused to a strong nuclear export sequence. A green fluorescence protein tag inserted at the N-terminus of both wildtype PABPN1 (ala10) and mutant PABPN1 (ala17) proteins allowed us to visualize their subcellular localization. Targeting mutant PABPN1 to the cytoplasm resulted in a significant suppression of both intranuclear aggregates formation and cellular toxicity, two histological consequences of OPMD. Our results indicate that the nuclear localization of mutant PABPN1 is crucial to OPMD pathogenesis.

Benzamide and 4-amino 1,8 naphthalimide treatment inhibit telomerase activity by down-regulating the expression of telomerase associated protein and inhibiting the poly(ADP-ribosyl)ation of telomerase reverse transcriptase in cultured cells

To test the role of poly(ADP-ribose) polymerase on the telomerase activity, we determined the telomerase activity in leukemic cells K562 treated with benzamide and 4-amino 1,8 naphthalimide (NAP), the inhibitors of PARP. We observed that both the agents inhibited telomerase activity in a dose-dependent manner. The doses of benzamide and NAP that inhibited telomerase activity to 50% of untreated control cells were 10.7 +/- 0.6 mm and 200 +/- 7 microm, respectively. Benzamide treatment (10 mm) inhibited telomerase activity in a time-dependent manner. We also tested the ability of benzamide to inhibit the telomerase activity in Chinese hamster V79 cells and observed similar inhibition of the telomerase activity. Expression of telomerase reverse transcriptase (TERT) and telomerase RNA component, detected by RT-PCR, remained unaltered by treatment with benzamide or NAP. On the contrary, the expression of telomerase associated protein (TEP1/TP1), as detected by RT-PCR and western blot analysis, was reduced by both the agents. Further, in K562 cells, immunoprecipitation with the anti-TERT IgG and probed anti-poly (ADP-ribose) IgG revealed that TERT was poly(ADP-ribosyl)ated in the physiological condition of cell growth and such poly(ADP-ribosyl)ation was inhibited by benzamide treatment. Decrease in TEP1/TP1 expression and poly(ADP-ribosyl)ation of TERT were correlated with the inhibition of PARP activity by benzamide, indicating that PARP had a role in telomerase activity through poly(ADP-ribosyl)ation of TERT and down-regulation of TEP1/TP1.

Poly-(L-alanine) expansions form core β-sheets that nucleate amyloid assembly

Expansion to a total of 11-17 sequential alanine residues from the normal number of 10 in the polyadenine-binding protein nuclear-1 (PABPN1) results in formation of intranuclear, fibrillar inclusions in skeletal muscle and hypothalamic neurons in adult-onset, dominantly inherited oculopharyngeal muscular dystrophy (OPMD). To understand the role that homopolymeric length may play in the protein misfolding that leads to the inclusions, we analyzed the self-assembly of synthetic poly-(L-alanine) peptides having 3-20 residues. We found that the conformational transition and structure of polyalanine (polyAla) assemblies in solution are not only length-dependent but also are determined by concentration, temperature, and incubation time. No beta-sheet complex was detected for those peptides characterized by n < 8, where n is number of alanine residues. A second group of peptides with 7 < n < 15 showed varying levels of complex formation, while for those peptides having n > 15, the interconversion process from the monomeric to the beta-sheet complex was complete under any of the tested experimental conditions. Unlike the typical tinctorial properties of amyloid fibrils, polyalanine fibrils did not show fluorescence with thioflavin T or apple-green birefringence with Congo red; however, like amyloid, X-ray diffraction showed that the peptide chains in these fibrils were oriented normal to the fibril axis (i.e., in the cross-beta arrangement). Neighboring beta-sheets are quarter-staggered in the hydrogen-bonding direction such that the alanine side-chains were closely packed in the intersheet space. Strong van der Waals contacts between side-chains in this arrangement likely account for the high stability of the macromolecular fibrillar complex in solution over a wide range of temperature (5-85 degrees C), and pH (2-10.5), and its resistance to denaturant (< 8 M urea) and to proteases (protease K, trypsin). We postulate that a similar stabilization of an expanded polyalanine stretch could form a core beta-sheet structure that mediates the intermolecular association of mutant proteins into fibrillar inclusions in human pathologies.

Functional insights from the distribution and role of homopeptide repeat-containing proteins

Expansion of "low complex" repeats of amino acids such as glutamine (Poly-Q) is associated with protein misfolding and the development of degenerative diseases such as Huntington's disease. The mechanism by which such regions promote misfolding remains controversial, the function of many repeat-containing proteins (RCPs) remains obscure, and the role (if any) of repeat regions remains to be determined. Here, a Web-accessible database of RCPs is presented. The distribution and evolution of RCPs that contain homopeptide repeats tracts are considered, and the existence of functional patterns investigated. Generally, it is found that while polyamino acid repeats are extremely rare in prokaryotes, several eukaryote putative homologs of prokaryote RCP-involved in important housekeeping processes-retain the repetitive region, suggesting an ancient origin for certain repeats. Within eukarya, the most common uninterrupted amino acid repeats are glutamine, asparagines, and alanine. Interestingly, while poly-Q repeats are found in vertebrates and nonvertebrates, poly-N repeats are only common in more primitive nonvertebrate organisms, such as insects and nematodes. We have assigned function to eukaryote RCPs using Online Mendelian Inheritance in Man (OMIM), the Human Reference Protein Database (HRPD), FlyBase, and Wormpep. Prokaryote RCPs were annotated using BLASTp searches and Gene Ontology. These data reveal that the majority of RCPs are involved in processes that require the assembly of large, multiprotein complexes, such as transcription and signaling.

Muscle-fiber apoptosis in neuromuscular diseases

Muscle-fiber loss is a characteristic of many progressive neuromuscular disorders. Over the past decade, identification of a growing number of apoptosis-associated factors and events in pathological skeletal muscle provided increasing evidence that apoptotic cell-death mechanisms account significantly for muscle-fiber atrophy and loss in a wide spectrum of neuromuscular disorders. It became obvious that there is not one specific pathway for muscle fibers to undergo apoptotic degradation. In contrast, certain neuromuscular diseases seem to involve characteristic expression patterns of apoptosis-related factors and pathways. Furthermore, there are some characteristics of muscle-fiber apoptosis that rely on the muscle fiber itself as an extremely specified cell type. Multinucleated muscle fibers with successive muscle-fiber segments controlled by individual nuclei display some specifics different from apoptosis of mononucleated cells. This review focuses on the expression patterns of apoptosis-associated factors in different primary and secondary neuromuscular disorders and gives a synopsis of current knowledge.

Heat shock proteins and neuromuscular disease

The heat shock proteins are families of proteins with known activities that include chaperoning nascent peptides within the cell and cytoprotection. Most work on the nervous system has related to the role of heat shock proteins in neuroprotection from either hypoxic-ischemic or traumatic injury. The role of these proteins during normal physiological activity and injury is still under investigation. Heat shock proteins in neuromuscular disease have been investigated to some extent but were largely neglected until recently. The goal of this review is to summarize the evidence linking heat shock proteins with neuromuscular disease and to provide some insight into the roles or functions of these proteins in disease states.

Patterns of cell death triggered in two different cell lines by HypF-N prefibrillar aggregates

The finding that aggregates of disease-unrelated proteins can induce cell death indicates that proteins may act as potential toxins. Cells experiencing toxic protein aggregates often display modifications of the redox status and ion balance, eventually leading to apoptosis; however, in some cases, tissue and cultured cell types die with features of necrosis. To elucidate the pathways leading to such different outcomes, we studied the biochemical features of death in H-END and NIH/3T3 cells exposed to prefibrillar aggregates of a disease-unrelated protein. The two types of cells died by apoptosis and necrosis, respectively. The pattern of caspase and proapoptotic factor activation was investigated together with the extent of mitochondria impairment and the energy load in either cell line. Our data depict a scenario where the events related to the extrinsic pathway of apoptosis are the same in the two cell lines, the difference in the final outcome being related to the extent of mitochondria derangement, possibly due to the different ability of the cells to counteract ion homeostasis impairment.

Induction of apoptosis by benzamide and its inhibition by aurin tricarboxylic acid (ATA) in Chinese hamster V79 cells

To investigate the effect of benzamide and nicotinamide, well known inhibitors of poly(ADP-ribose) polymerase, in Chinese hamster V79 cells at the physiological condition of cell growth, we have tested the ability of the inhibitors to induce apoptosis. Apoptosis was detected by nuclear fragmentation, nucleosomal ladder formation, cytochrome-c release from the mitochondria and caspase-3 activation. Benzamide treatment alone increased nuclear fragmentation in dose (2.5-10 mM) and time (4-48 h)-dependent manner. Such treatment also increased nucleosomal ladders. However, 5 mM benzamide pre-treatment inhibited the nucleosomal ladders induced by gamma-irradiation indicating the role of poly(ADP-ribose) polymerase was different in irradiated cells and in un-irradiated cells. Release of cytochrome-c from the mitochondria and caspase-3 activity were also increased by such treatment. Treatment with 200 microM of aurin tricarboxylic acid (ATA), an inhibitor of DNases, inhibited the nucleosomal ladders induced by benzamide or gamma-irradiation without changing the cytochrome-c release or caspase-3 activation. This result showed that ATA inhibited the nucleosomal ladders possibly by inhibiting DNase(s) involved in apoptosis.

Trichomonas vaginalis-induced apoptosis in RAW264.7 cells is regulated through Bcl-xL, but not Bcl-2

The purpose of this study was to determine whether anti-apoptotic proteins of the Bcl-2 family such as Bcl-2 and Bcl-x(L), proteins that confer resistance to apoptotic death from some stimuli, block apoptotic cell death in RAW264.7 cells upon treatment with Trichomonas vaginalis. In this study, the expression level of Bcl-2 was unchanged throughout the course of apoptotic cell death, and overexpressed Bcl-2 did not prevent release of cytochrome c, the significant change of the membrane potential, activation of caspases, and PARP cleavage in T. vaginalis-treated RAW264.7 cells. On the other hand, Bcl-x(L)expression was decreased after T. vaginalis treatment accompanied with Bax activation. Furthermore, we showed that release of mitochondrial cytochrome c, cleavage of caspase-9 and PARP during apoptosis in T. vaginalis-treated RAW264.7 cells were considerably diminished by transfection with overexpressed Bcl-x(L), and overexpressed Bcl-x(L)could inhibit T. vaginalis-induced apoptosis in RAW264.7 cells. In addition, interestingly, pre-treatment with caspase inhibitors, Boc-D-FMK and Z-DEVD-FMK, significantly abolished T. vaginalis-induced down-regulation of Bcl-x(L), suggesting that caspase-3 may play a pivotal role in the process of apoptosis as well as the down-regulation of Bcl-x(L)by T. vaginalis. Therefore, these results suggest that T. vaginalis-induced apoptosis in RAW264.7 cells can occur via a Bcl-x(L)-dependent apoptotic mechanism.