Beta-actin is required for mitochondria clustering and ROS generation in TNF-induced, caspase-independent cell death

Poxvirus A51R proteins regulate microtubule stability and antagonize a cell-intrinsic antiviral response

Numerous viruses alter host microtubule (MT) networks during infection, but how and why they induce these changes is unclear in many cases. We show that the vaccinia virus (VV)-encoded A51R protein is a MT-associated protein (MAP) that directly binds MTs and stabilizes them by both promoting their growth and preventing their depolymerization. Furthermore, we demonstrate that A51R-MT interactions are conserved across A51R proteins from multiple poxvirus genera, and highly conserved, positively charged residues in A51R proteins mediate these interactions. Strikingly, we find that viruses encoding MT interaction-deficient A51R proteins fail to suppress a reactive oxygen species (ROS)-dependent antiviral response in macrophages that leads to a block in virion morphogenesis. Moreover, A51R-MT interactions are required for VV virulence in mice. Collectively, our data show that poxviral MAP-MT interactions overcome a cell-intrinsic antiviral ROS response in macrophages that would otherwise block virus morphogenesis and replication in animals.

Transcription Factor Driven Gene Regulation in COVID-19 Patients

SARS-CoV-2 and its many variants have caused a worldwide emergency. Host cells colonised by SARS-CoV-2 present a significantly different gene expression landscape. As expected, this is particularly true for genes that directly interact with virus proteins. Thus, understanding the role that transcription factors can play in driving differential regulation in patients affected by COVID-19 is a focal point to unveil virus infection. In this regard, we have identified 19 transcription factors which are predicted to target human proteins interacting with Spike glycoprotein of SARS-CoV-2. Transcriptomics RNA-Seq data derived from 13 human organs are used to analyse expression correlation between identified transcription factors and related target genes in both COVID-19 patients and healthy individuals. This resulted in the identification of transcription factors showing the most relevant impact in terms of most evident differential correlation between COVID-19 patients and healthy individuals. This analysis has also identified five organs such as the blood, heart, lung, nasopharynx and respiratory tract in which a major effect of differential regulation mediated by transcription factors is observed. These organs are also known to be affected by COVID-19, thereby providing consistency to our analysis. Furthermore, 31 key human genes differentially regulated by the transcription factors in the five organs are identified and the corresponding KEGG pathways and GO enrichment are also reported. Finally, the drugs targeting those 31 genes are also put forth. This in silico study explores the effects of transcription factors on human genes interacting with Spike glycoprotein of SARS-CoV-2 and intends to provide new insights to inhibit the virus infection.

Structural and functional diversity of mitochondria in vestibular/cochlear hair cells and vestibular calyx afferents

Mitochondria supply energy in the form of ATP to drive a plethora of cellular processes. In heart and liver cells, mitochondria occupy over 20% of the cellular volume and the major need for ATP is easily identifiable - i.e., to drive cross-bridge recycling in cardiac cells or biosynthetic machinery in liver cells. In vestibular and cochlear hair cells the overall cellular mitochondrial volume is much less, and mitochondria structure varies dramatically in different regions of the cell. The regional demands for ATP and cellular forces that govern mitochondrial structure and localization are not well understood. Below we review our current understanding of the heterogeneity of form and function in hair cell mitochondria. A particular focus of this review will be on regional specialization in vestibular hair cells, where large mitochondria are found beneath the cuticular plate in close association with the striated organelle. Recent findings on the role of mitochondria in hair cell death and aging are covered along with potential therapeutic approaches. Potential avenues for future research are discussed, including the need for integrated computational modeling of mitochondrial function in hair cells and the vestibular afferent calyx.

Eriodictyol mediated selective targeting of the TNFR1/FADD/TRADD axis in cancer cells induce apoptosis and inhibit tumor progression and metastasis

While the anti-inflammatory activities of Eriodictyol, a plant-derived flavonoid is well-known, reports on its anti-cancer efficacy and selective cytotoxicity in cancer cells are still emerging. However, little is known regarding its mechanism of selective anti-cancer activities. Here, we show the mechanism of selective cytotoxicity of Eriodictyol towards cancer cells compared to normal cells. Investigation reveals that Eriodictyol significantly upregulates TNFR1 expression in tumor cells (HeLa and SK-RC-45) while sparing the normal cells (HEK, NKE and WI-38), which display negligible TNFR1 expression, irrespective of the absence or presence of Eriodictyol. Further investigation of the molecular events reveal that Eriodictyol induces apoptosis through expression of the pro-apoptotic DISC components leading to activation of the caspase cascade. In addition, CRISPR-Cas9 mediated knockout of TNFR1 completely blocks apoptosis in HeLa cells in response to Eriodictyol, confirming that Eriodictyol induced cancer cell apoptosis is indeed TNFR1-dependent. Finally, in vivo data demonstrates that Eriodictyol not only impedes tumor growth and progression, but also inhibits metastasis in mice implanted with 4T1 breast cancer cells. Thus, our study has identified Eriodictyol as a compound with high selectivity towards cancer cells through TNFR1 and suggests that it can be further explored for its prospect in cancer therapeutics.

Housekeeping Proteins in Meat Quality Research: Are They Reliable Markers for Internal Controls in Western Blot? A Mini Review

Advancements in technology and analytical methods enable researchers to explore the biochemical events that cause variation in meat quality. Among those, western blot techniques have been successfully used in identifying and quantifying the key proteins that have critical functions in the development of meat quality. Housekeeping proteins, like β-actin, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and tubulins are often used as internal controls in western blots to normalize the abundance of the protein of interest. However, there are increasing concerns about using housekeeping proteins for western blot normalization, as these proteins do not demonstrate any loading differences above the relatively small total protein loading amounts of 10μg. In addition, the interaction between these housekeeping proteins and programmed cell death processes highlights the concerns about using the housekeeping protein as the internal control in meat quality research. Moreover, recent proteomic research has indicated that the abundance of some housekeeping proteins, like β-actin, GAPDH, and tubulin, can be altered by preslaughter stress, dietary supplementation, sex, slaughter method, genotype, breed, aging period, muscle type, and muscle portion. Furthermore, these housekeeping proteins could have differential expression in meat with differing color stability, tenderness, and water holding capacity. Therefore, this review aims to examine the realities of using housekeeping proteins as the loading control in meat quality research and introduce some alternative methods that can be used for western blot normalization.

Miro1 functions as an inhibitory regulator of MFN at elevated mitochondrial Ca2+ levels

Mitochondria function as an integrated network that moves along the microtubules within cells and changes the morphology through membrane fusion and fission events. Mitofusin (MFN) mediates membrane tethering and subsequent fusion of the mitochondrial outer membrane. Understanding the regulatory mechanisms of MFN function is critical to tackling the pathology related to mitochondrial network imbalance. Here, we reveal a novel inhibitory mechanism of MFN-mediated fusion by mitochondrial Rho GTPase (Miro1) in response to elevated mitochondrial Ca²⁺ concentration ([Ca²⁺ ]_m ). We showed that elevated [Ca²⁺ ]_m prevents the fusion between mitochondria forming the outer membrane tether by ectopically expressing MFN. Lowering [Ca²⁺ ]_m by treating cells with an inhibitor of mitochondrial calcium uniporter or knocking down Miro1/2 induces more fused networks. Miro1 interacts with MFN as supported by co-immunoprecipitation and protein association identified by proximity labeling proteomics. It suggests that Miro1 functions as a Ca²⁺ -sensor and inhibits MFN function at elevated [Ca²⁺ ]_m. Miro1 EF-hand mutant has a compromised inhibitory effect, which reiterates Ca²⁺ -modulated regulation. Dysregulated Ca²⁺ -handling and mitochondrial network imbalance are highly relevant in the pathology of cancers, cardiovascular, and neurodegenerative diseases. Miro1 functions as a coordinated Ca²⁺ -responder by pausing mitochondrial transport while reducing network fusion and cooperating with Drp1-mediated fission. It likely prevents the detrimental effect of Ca²⁺ _m overload and facilitates mitophagy. Our finding reveals a novel regulation of mitochondrial network dynamics responding to [Ca²⁺ ]_m through the interplay of Miro1 and MFN. Modulation of Miro1 and MFN interaction is a potential intervention to promote network homeostasis.

Melatonin Treatment Improves Renal Fibrosis via miR-4516/SIAH3/PINK1 Axis

Dysregulation in mitophagy, in addition to contributing to imbalance in the mitochondrial dynamic, has been implicated in the development of renal fibrosis and progression of chronic kidney disease (CKD). However, the current understanding of the precise mechanisms behind the pathogenic loss of mitophagy remains unclear for developing cures for CKD. We found that miR-4516 is downregulated and its target SIAH3, an E3 ubiquitin protein ligase that reduces PINK1 accumulation to damaged mitochondria, is upregulated in the renal cortex of CKD mice. Here, we demonstrated that melatonin injection induces miR-4516 expression and suppresses SIAH3, and promotes PINK1/Parkin-mediated mitophagy. Furthermore, we demonstrated that melatonin injection attenuates the pathological features of CKD by improving mitochondrial homeostasis. Our data supports that mitochondrial autophagy regulation by activating miR-4516/SIAH3/PINK1 mitophagy signaling axis can be a viable new strategy for treating CKD.

Major ascaroside pheromone component asc-C5 influences reproductive plasticity among isolates of the invasive species pinewood nematode

Pheromones are communication chemicals and regulatory signals used by animals and represent unique tools for organisms to mediate behaviors and make "decisions" to maximize their fitness. Phenotypic plasticity refers to the innate capacity of a species to tolerate a greater breadth of environmental conditions across which it adapts to improve its survival, reproduction, and fitness. The pinewood nematode, Bursaphelenchus xylophilus, an invasive nematode species, was accidentally introduced from North America into Japan, China, and Europe; however, few studies have investigated its pheromones and phenotypic plasticity as a natural model. Here, we demonstrated a novel phenomenon, in which nematodes under the condition of pheromone presence triggered increased reproduction in invasive strains (JP1, JP2, CN1, CN2, EU1, and EU2), while it simultaneously decreased reproduction in native strains (US1 and US2). The bidirectional effect on fecundity, mediated by presence/absence of pheromones, is henceforth termed pheromone-regulative reproductive plasticity (PRRP). We further found that synthetic ascaroside asc-C5 (ascr#9), the major pheromone component, plays a leading role in PRRP and identified 2 candidate receptor genes, Bxydaf-38 and Bxysrd-10, involved in perceiving asc-C5. These results suggest that plasticity of reproductive responses to pheromones in pinewood nematode may increase its fitness in novel environments following introduction. This opens up a new perspective for invasion biology and presents a novel strategy of invasion, suggesting that pheromones, in addition to their traditional roles in chemical signaling, can influence the reproductive phenotype among native and invasive isolates. In addition, this novel mechanism could broadly explain, through comparative studies of native and invasive populations of animals, a potential underlying factor behind of the success of other biological invasions.

Melatonin Suppresses Renal Cortical Fibrosis by Inhibiting Cytoskeleton Reorganization and Mitochondrial Dysfunction through Regulation of miR-4516

Renal fibrosis, a major risk factor for kidney failure, can lead to chronic kidney disease (CKD) and is caused by cytoskeleton reorganization and mitochondrial dysfunction. In this study, we investigated the potential of melatonin treatment to reduce renal fibrosis by recovering the cytoskeleton reorganization and mitochondrial dysfunction. We found that miR-4516 expression was downregulated in the renal cortex of CKD mice and P-cresol-treated TH1 cells. Decreased miR-4516 expression stimulated cytoskeleton reorganization and mitochondrial dysfunction, and induced renal fibrosis. Melatonin treatment suppressed fibrosis by inhibiting cytoskeleton reorganization and restoring mitochondrial function via increased miR-4516 expression. More specifically, melatonin treatment increased miR-4516 expression while decreasing ITGA9 expression, thereby inhibiting cytoskeleton reorganization. In addition, increased expression of miR-4516 by melatonin treatment reduced ROS formation and restored mitochondrial function. These findings suggest that melatonin may be a promising treatment for patients with CKD having renal fibrosis. Moreover, regulation of miR-4516 expression may be a novel strategy for the treatment of renal fibrosis.

Role of Mitochondria-Cytoskeleton Interactions in the Regulation of Mitochondrial Structure and Function in Cancer Stem Cells

Despite the promise of cancer medicine, major challenges currently confronting the treatment of cancer patients include chemoresistance and recurrence. The existence of subpopulations of cancer cells, known as cancer stem cells (CSCs), contributes to the failure of cancer therapies and is associated with poor clinical outcomes. Of note, one of the recently characterized features of CSCs is augmented mitochondrial function. The cytoskeleton network is essential in regulating mitochondrial morphology and rearrangement, which are inextricably linked to its functions, such as oxidative phosphorylation (OXPHOS). The interaction between the cytoskeleton and mitochondria can enable CSCs to adapt to challenging conditions, such as a lack of energy sources, and to maintain their stemness. Cytoskeleton-mediated mitochondrial trafficking and relocating to the high energy requirement region are crucial steps in epithelial-to-mesenchymal transition (EMT). In addition, the cytoskeleton itself interplays with and blocks the voltage-dependent anion channel (VDAC) to directly regulate bioenergetics. In this review, we describe the regulation of cellular bioenergetics in CSCs, focusing on the cytoskeleton-mediated dynamic control of mitochondrial structure and function.

Simultaneous Inhibition of BCR-ABL1 Tyrosine Kinase and PAK1/2 Serine/Threonine Kinase Exerts Synergistic Effect against Chronic Myeloid Leukemia Cells

Tyrosine kinase inhibitors (TKIs) revolutionized the treatment of chronic myeloid leukemia in the chronic phase (CML-CP). However, it is unlikely that they can completely “cure” the disease. This might be because some subpopulations of CML-CP cells such as stem and progenitor cells are resistant to chemotherapy, even to the new generation of TKIs. Therefore, it is important to look for new methods of treatment to improve therapeutic outcomes. Previously, we have shown that class I p21-activated serine/threonine kinases (PAKs) remained active in TKI-naive and TKI-treated CML-CP leukemia stem and early progenitor cells. In this study, we aimed to determine if simultaneous inhibition of BCR-ABL1 oncogenic tyrosine kinase and PAK1/2 serine/threonine kinase exert better anti-CML effect than that of individual treatments. PAK1 was inhibited by small-molecule inhibitor IPA-3 (p21-activated kinase inhibitor III), PAK2 was downregulated by specific short hairpin RNA (shRNA), and BCR-ABL1 tyrosine kinase was inhibited by imatinib (IM). The studies were conducted by using (i) primary CML-CP stem/early progenitor cells and normal hematopoietic counterparts isolated from the bone marrow of newly diagnosed patients with CML-CP and from healthy donors, respectively, (ii) CML-blast phase cell lines (K562 and KCL-22), and (iii) from BCR-ABL1-transformed 32Dcl3 cell line. Herein, we show that inhibition of the activity of PAK1 and/or PAK2 enhanced the effect of IM against CML cells without affecting the normal cells. We observed that the combined use of IM with IPA-3 increased the inhibition of growth and apoptosis of leukemia cells. To evaluate the type of interaction between the two drugs, we performed median effect analysis. According to our results, the type and strength of drug interaction depend on the concentration of the drugs tested. Generally, combination of IM with IPA-3 at the 50% of the cell kill level (EC50) generated synergistic effect. Based on our results, we hypothesize that IM, a BCR-ABL1 tyrosine kinase inhibitor, combined with a PAK1/2 inhibitor facilitates eradication of CML-CP cells.

Paternal Exposure to Environmental Chemical Stress Affects Male Offspring's Hepatic Mitochondria

Preconceptional paternal exposures may affect offspring's health, which cannot be explained by mutations in germ cells, but by persistent changes in the regulation of gene expression. Therefore, we investigated whether pre-conceptional paternal exposure to benzo[a]pyrene (B[a]P) could alter the offspring's phenotype. Male C57BL/6 mice were exposed to B[a]P by gavage for 6 weeks, 3× per week, and were crossed with unexposed BALB-c females 6 weeks after the final exposure. The offspring was kept under normal feeding conditions and was sacrificed at 3 weeks of age. Analysis of the liver proteome by 2D-gel electrophoresis and mass spectrometry indicated that proteins involved in mitochondrial function were significantly downregulated in the offspring of exposed fathers. This down-regulation of mitochondrial proteins was paralleled by a reduction in mitochondrial DNA copy number and reduced activity of citrate synthase and β-hydroxyacyl-CoA dehydrogenase, but in male offspring only. Surprisingly, analysis of hepatic mRNA expression revealed a male-specific up-regulation of the genes, whose proteins were downregulated, including Aldh2 and Ogg1. This discrepancy could be related to several selected microRNA (miRNA)'s that regulate the translation of these proteins; miRNA-122, miRNA-129-2-5p, and miRNA-1941 were upregulated in a gender-specific manner. Since mitochondria are thought to be a source of intracellular reactive oxygen species, we additionally assessed oxidatively-induced DNA damage. Both 8-hydroxy-deoxyguanosine and malondialdehyde-dG adduct levels were significantly reduced in male offspring of exposed fathers. In conclusion, we show that paternal exposure to B[a]P can regulate mitochondrial metabolism in offspring, which may have profound implications for our understanding of health and disease risk inherited from fathers.

Increase in proapoptotic activity of inhibitory PAS domain protein via phosphorylation by MK2

Inhibitory PAS domain protein (IPAS) is a bifunctional protein that downregulates hypoxic gene expression and exerts proapoptotic activity by preventing prosurvival activity of Bcl-x_L and its related factors. Proapoptotic activity of IPAS is attenuated by the activation of the PINK1-Parkin pathway, and involved in neuronal degeneration in an experimental mouse model of Parkinson's disease. The current study shows that phosphorylation of IPAS at Ser184 by MAPK-activated protein kinase 2 (MK2 or MAPKAPK2) enhances the proapoptotic function of IPAS. Perinuclear clustering of mitochondria and activation of caspase-3 caused by the transient expression of EGFP-IPAS were increased by UVB irradiation. The C-terminal region of IPAS mediated the UVB susceptibility of IPAS. Increase in IPAS-induced mitochondrial clustering by UVB was completly inhibited by the p38 MAPK inhibitor SB203580. Mass spectrometry analysis of UVB-activated IPAS identified several phosphorylation sites in the C-terminal region containing p38 MAPK consensus phosphorylation sites at Ser219 and Ser223, and an MK2 consensus site at Ser184. Although mutations of Ser219 and Ser223 to Ala did not suppress the UVB-induced mitochondrial clustering, replacement of Ser184 with Ala blocked it. A phosphomimetic substitution at Ser184 enhanced mitochondrial clustering and activation of caspase-3 without UVB exposure. Furthermore, binding affinity to Bcl-x_L was increased by the mutation. Treatment of PC12 cells with CoCl₂ caused activation of MK2 and mitochondrial clustering. IPAS-dependent cell death induced by CoCl₂ in PC12 cells was decreased by the treatment with the MK2 inhibitor MK2 inhibitor III and by siRNA-directed silencing of MK2.

Altered redox mitochondrial biology in the neurodegenerative disorder fragile X-tremor/ataxia syndrome: use of antioxidants in precision medicine

A 55-200 expansion of the CGG nucleotide repeat in the 5'-UTR of the fragile X mental retardation 1 gene (FMR1) is the hallmark of the triplet nucleotide disease known as the "premutation" as opposed to those with >200 repeats, known as the full mutation or fragile X syndrome. Originally, premutation carriers were thought to be free of phenotypic traits; however, some are diagnosed with emotional and neurocognitive issues and, later in life, with the neurodegenerative disease fragile X-associated tremor/ataxia syndrome (FXTAS). Considering that mitochondrial dysfunction has been observed in fibroblasts and post-mortem brain samples from carriers of the premutation, we hypothesized that mitochondrial dysfunction-derived ROS may result in cumulative oxidative-nitrative damage. Fibroblasts from premutation carriers (n=31, all FXTAS-free except 8), compared to age- and sex-matched controls (n=25), showed increased mitochondrial ROS production, impaired Complex I activity, lower expression of MIA40 (rate-limiting step of the redox-regulated mitochondrial-disulfide-relay-system), increased mtDNA deletions, and increased biomarkers of lipid and protein oxidative-nitrative damage. Most of the outcomes were more pronounced in FXTAS-affected individuals. Significant recovery of mitochondrial mass and/or function was obtained with superoxide or hydroxyl radicals' scavengers, a glutathione peroxidase analog, or by overexpressing MIA40. The effects of ethanol (a hydroxyl radical scavenger) were deleterious, while others (by N-acetyl-cysteine, quercetin and epigallocatechin-3-gallate) were outcome- and/or carrier-specifics. The use of antioxidants in the context of precision medicine is discussed with the goal of improving mitochondrial function in carriers with the potential of decreasing the morbidity and/or delaying FXTAS onset.

Methylmercury-induced developmental toxicity is associated with oxidative stress and cofilin phosphorylation. Cellular and human studies

Environmental exposure to methylmercury (MeHg) during development is of concern because it is easily incorporated in children's body both pre- and post-natal, it acts at several levels of neural pathways (mitochondria, cytoskeleton, neurotransmission) and it causes behavioral impairment in child. We evaluated the effects of prolonged exposure to 10-600nM MeHg on primary cultures of mouse cortical (CCN) and of cerebellar granule cells (CGC) during their differentiation period. In addition, it was studied if prenatal MeHg exposure correlated with altered antioxidant defenses and cofilin phosphorylation in human placentas (n=12) from the INMA cohort (Spain). Exposure to MeHg for 9days in vitro (DIV) resulted in protein carbonylation and in cell death at concentrations ≥200nM and ≥300nM, respectively. Exposure of CCN and CGC to non-cytotoxic MeHg concentrations for 5 DIV induced an early concentration-dependent decrease in cofilin phosphorylation. Furthermore, in both cell types actin was translocated from the cytosol to the mitochondria whereas cofilin translocation was found only in CGC. Translocation of cofilin and actin to mitochondria in CGC occurred from 30nM MeHg onwards. We also found an increased expression of cortactin and LIMK1 mRNA in CGC but not in CCN. All these effects were prevented by the antioxidant probucol. Cofilin phosphorylation was significantly decreased and a trend for decreased activity of glutathione reductase and glutathione peroxidase was found in the fetal side of human placental samples from the highest (20-40μg/L) MeHg-exposed group when compared with the low (<7μg/L) MeHg-exposed group. In summary, cofilin dephosphorylation and oxidative stress are hallmarks of MeHg exposure in both experimental and human systems.

Premutation in the Fragile X Mental Retardation 1 (FMR1) Gene Affects Maternal Zn-milk and Perinatal Brain Bioenergetics and Scaffolding

Fragile X premutation alleles have 55–200 CGG repeats in the 5′ UTR of the FMR1 gene. Altered zinc (Zn) homeostasis has been reported in fibroblasts from >60 years old premutation carriers, in which Zn supplementation significantly restored Zn-dependent mitochondrial protein import/processing and function. Given that mitochondria play a critical role in synaptic transmission, brain function, and cognition, we tested FMRP protein expression, brain bioenergetics, and expression of the Zn-dependent synaptic scaffolding protein SH3 and multiple ankyrin repeat domains 3 (Shank3) in a knock-in (KI) premutation mouse model with 180 CGG repeats. Mitochondrial outcomes correlated with FMRP protein expression (but not FMR1 gene expression) in KI mice and human fibroblasts from carriers of the pre- and full-mutation. Significant deficits in brain bioenergetics, Zn levels, and Shank3 protein expression were observed in the Zn-rich regions KI hippocampus and cerebellum at PND21, with some of these effects lasting into adulthood (PND210). A strong genotype × age interaction was observed for most of the outcomes tested in hippocampus and cerebellum, whereas in cortex, age played a major role. Given that the most significant effects were observed at the end of the lactation period, we hypothesized that KI milk might have a role at compounding the deleterious effects on the FMR1 genetic background. A higher gene expression of ZnT4 and ZnT6, Zn transporters abundant in brain and lactating mammary glands, was observed in the latter tissue of KI dams. A cross-fostering experiment allowed improving cortex bioenergetics in KI pups nursing on WT milk. Conversely, WT pups nursing on KI milk showed deficits in hippocampus and cerebellum bioenergetics. A highly significant milk type × genotype interaction was observed for all three-brain regions, being cortex the most influenced. Finally, lower milk-Zn levels were recorded in milk from lactating women carrying the premutation as well as other Zn-related outcomes (Zn-dependent alkaline phosphatase activity and lactose biosynthesis—whose limiting step is the Zn-dependent β-1,4-galactosyltransferase). In premutation carriers, altered Zn homeostasis, brain bioenergetics and Shank3 levels could be compounded by Zn-deficient milk, increasing the risk of developing emotional and neurological/cognitive problems and/or FXTAS later in life.

Methyl methanesulfonate induces necroptosis in human lung adenoma A549 cells through the PIG-3-reactive oxygen species pathway

Methyl methanesulfonate (MMS) is an alkylating agent that can induce cell death through apoptosis and necroptosis. The molecular mechanisms underlying MMS-induced apoptosis have been studied extensively; however, little is known about the mechanism for MMS-induced necroptosis. Therefore, we first established MMS-induced necroptosis model using human lung carcinoma A549 cells. It was found that, within a 24-h period, although MMS at concentrations of 50, 100, 200, 400, and 800 μM can induce DNA damage, only at higher concentrations (400 and 800 μM) MMS treatment lead to necroptosis in A549 cells, as it could be inhibited by the specific necroptotic inhibitor necrostatin-1, but not the specific apoptotic inhibitor carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone (Z-VAD-fmk). MMS-induced necroptosis was further confirmed by the induction of the necroptosis biomarkers including the depletion of cellular NADH and ATP and leakage of LDH. This necroptotic cell death was also concurrent with the increased expression of p53, p53-induced gene 3 (PIG-3), high mobility group box-1 protein (HMGB1), and receptor interaction protein kinase (RIP) but not the apoptosis-associated caspase-3 and caspase-9 proteins. Elevated reactive oxygen species (ROS) level was also involved in this process as the specific ROS inhibitor (4-amino-2,4-pyrrolidine-dicarboxylic acid (APDC)) can inhibit the necroptotic cell death. Interestingly, knockdown of PIG-3 expression by small interfering RNA (siRNA) treatment can inhibit the generation of ROS. Taken together, these results suggest that MMS can induce necroptosis in A549 cells, probably through the PIG-3-ROS pathway.

Beyond TLR Signaling—The Role of SARM in Antiviral Immune Defense, Apoptosis & Development

SARM (Sterile alpha and armadillo motif-containing protein) is the recently identified TIR domain-containing cytosolic protein. Classified as a member of the TLR adaptor family, the multiple locations and functions of SARM (sometimes playing opposing roles), provoke an enigma on its biology. Although originally assumed to be a member of the TLR adaptor family (functioning as a negative regulator of TLR signaling pathway), latest findings indicate that SARM regulates signaling differently from other TLR adaptor proteins. Recent studies have highlighted the significant functional role of SARM in mediating apoptosis and antiviral innate immune response. In this review, we provide an update on the evolutionary conservation, spatial distribution, and regulated expression of SARM to highlight its diverse functional roles. The review will summarize findings on the known interacting partners of SARM and provide analogy on how they add new dimensions to the current understanding on the multifaceted roles of SARM in antiviral activities and apoptotic functions. In addition, we provide a future perspective on the roles of SARM in differentiation and development, with substantial emphasis on the molecular insights to its mechanisms of action.

The Gβγ-Src signaling pathway regulates TNF-induced necroptosis via control of necrosome translocation

Formation of multi-component signaling complex necrosomes is essential for tumor necrosis factor α (TNF)-induced programmed necrosis (also called necroptosis). However, the mechanisms of necroptosis are still largely unknown. We isolated a TNF-resistant L929 mutant cell line generated by retrovirus insertion and identified that disruption of the guanine nucleotide-binding protein γ 10 (Gγ10) gene is responsible for this phenotype. We further show that Gγ10 is involved in TNF-induced necroptosis and Gβ2 is the partner of Gγ10. Src is the downstream effector of Gβ2γ10 in TNF-induced necroptosis because TNF-induced Src activation was impaired upon Gγ10 knockdown. Gγ10 does not affect TNF-induced activation of NF-κB and MAPKs and the formation of necrosomes, but is required for trafficking of necrosomes to their potential functioning site, an unidentified subcellular organelle that can be fractionated into heterotypic membrane fractions. The TNF-induced Gβγ-Src signaling pathway is independent of RIP1/RIP3 kinase activity and necrosome formation, but is required for the necrosome to function.

RNF13 protein regulates endoplasmic reticulum stress induced apoptosis in dopaminergic SH-SY5Y cells by enhancing IRE1α stability

Any interruption in the folding capacity of endoplasmic reticulum (ER) may result in inducing ER stress which would initiate an adaptive signaling mechanism called Unfolded Protein Response (UPR) in order to restore homeostasis, failing to which would initiate signaling pathway leading to death of the cell. Finding new mediators could help better understand the molecular mechanisms of ER stress-induced apoptosis. Our lab initiated a genetic screen method using retroviral insertion mutation system to look for genes whose inactivation would confer resistance to apoptosis. In our previous findings, Ring finger protein 13 (RNF13) was identified whose down-regulation conferred survival against ER stress-induced apoptosis. Our previous results also showed important role of RNF13 in apoptotic signaling in 293T cells as a result of strong RNF13-IRE1α interaction. In current study, using SH-SY5Y cells, overexpression of RNF13 in apoptosis assays and RT-PCR analysis has shown to induce apoptosis as well as splicing of X-box binding Protein 1 (XBP1) confirming its role in ER stress mediated cell death in this cell line as well. Western blot analysis has revealed that overexpression of both N-terminal as well as C-terminal tagged RNF13 resulted in activation of c-Jun N-terminal kinase (JNK) in SH-SY5Y cells. Our co-immunoprecipitation assays in SH-SY5Y cells also showed a strong interaction of RNF13 with IRE1α. Finally, Cycloheximide chase experiment exhibited that RNF13-IRE1α interaction increased the stability of IRE1α. Altogether, our data suggest that RNF13 may act as an important regulator of IRE1α, mediating ER stress-mediated apoptosis in neuroblastoma SH-SY5Y cells.

HTS by NMR of combinatorial libraries: a fragment-based approach to ligand discovery

Fragment-based ligand design (FBLD) approaches have become more widely used in drug discovery projects from both academia and industry, and are even often preferred to traditional high-throughput screening (HTS) of large collection of compounds (>10(5)). A key advantage of FBLD approaches is that these often rely on robust biophysical methods such as NMR spectroscopy for detection of ligand binding, hence are less prone to artifacts that too often plague the results from HTS campaigns. In this article, we introduce a screening strategy that takes advantage of both the robustness of protein NMR spectroscopy as the detection method, and the basic principles of combinatorial chemistry to enable the screening of large libraries of fragments (>10(5) compounds) preassembled on a common backbone. We used the method to identify compounds that target protein-protein interactions.

Actin polymerization negatively regulates p53 function by impairing its nuclear import in response to DNA damage

Actin, one of the most evolutionarily conservative proteins in eukaryotes, is distributed both in the cytoplasm and the nucleus, and its dynamics plays important roles in numerous cellular processes. Previous evidence has shown that actin interacts with p53 and this interaction increases in the process of p53 responding to DNA damage, but the physiological significance of their interaction remains elusive. Here, we show that DNA damage induces both actin polymerization and p53 accumulation. To further understand the implication of actin polymerization in p53 function, cells were treated with actin aggregation agent. We find that the protein level of p53 decrease. The change in p53 is a consequence of the polymeric actin anchoring p53 in the cytoplasm, thus impairing p53 nuclear import. Analysis of phosphorylation and ubiquitination of p53 reveals that actin polymerization promotes the p53 phosphorylation at Ser315 and reduces the stabilization of p53 by recruiting Aurora kinase A. Taken together, our results suggest that the actin polymerization serves as a negative modulator leading to the impairment of nuclear import and destabilization of p53. On the basis of our results, we propose that actin polymerization might be a factor participating in the process of orchestrating p53 function in response to DNA damage.

Genomic instability may originate from imatinib-refractory chronic myeloid leukemia stem cells

Genomic instability is a hallmark of chronic myeloid leukemia in chronic phase (CML-CP) resulting in BCR-ABL1 mutations encoding resistance to tyrosine kinase inhibitors (TKIs) and/or additional chromosomal aberrations leading to disease relapse and/or malignant progression. TKI-naive and TKI-treated leukemia stem cells (LSCs) and leukemia progenitor cells (LPCs) accumulate high levels of reactive oxygen species (ROS) and oxidative DNA damage. To determine the role of TKI-refractory LSCs in genomic instability, we used a murine model of CML-CP where ROS-induced oxidative DNA damage was elevated in LSCs, including quiescent LSCs, but not in LPCs. ROS-induced oxidative DNA damage in LSCs caused clinically relevant genomic instability in CML-CP-like mice, such as TKI-resistant BCR-ABL1 mutations (E255K, T315I, H396P), deletions in Ikzf1 and Trp53, and additions in Zfp423 and Idh1. Despite inhibition of BCR-ABL1 kinase, imatinib did not downregulate ROS and oxidative DNA damage in TKI-refractory LSCs to the levels detected in normal cells, and CML-CP-like mice treated with imatinib continued to accumulate clinically relevant genetic aberrations. Inhibition of class I p21-activated protein kinases by IPA3 downregulated ROS in TKI-naive and TKI-treated LSCs. Altogether, we postulate that genomic instability may originate in the most primitive TKI-refractory LSCs in TKI-naive and TKI-treated patients.

Low-dose etoposide-treatment induces endoreplication and cell death accompanied by cytoskeletal alterations in A549 cells: Does the response involve senescence? The possible role of vimentin

Background

Senescence in the population of cells is often described as a program of restricted proliferative capacity, which is manifested by broad morphological and biochemical changes including a metabolic shift towards an autophagic-like response and a genotoxic-stress related induction of polyploidy. Concomitantly, the cell cycle progression of a senescent cell is believed to be irreversibly arrested. Recent reports suggest that this phenomenon may have an influence on the therapeutic outcome of anticancer treatment. The aim of this study was to verify the possible involvement of this program in the response to the treatment of the A549 cell population with low doses of etoposide, as well as to describe accompanying cytoskeletal alterations.

Methods

After treatment with etoposide, selected biochemical and morphological parameters were examined, including: the activity of senescence-associated ß-galactosidase, SAHF formation, cell cycle progression, the induction of p21^{Cip1/Waf1/Sdi1} and cyclin D1, DNA strand breaks, the disruption of cell membrane asymmetry/integrity and ultrastructural alterations. Vimentin and G-actin cytoskeleton was evaluated both cytometrically and microscopically.

Results and conclusions

Etoposide induced a senescence-like phenotype in the population of A549 cells. Morphological alterations were nevertheless not directly coupled with other senescence markers including a stable cell cycle arrest, SAHF formation or p21^{Cip1/Waf1/Sdi1} induction. Instead, a polyploid, TUNEL-positive fraction of cells visibly grew in number. Also upregulation of cyclin D1 was observed. Here we present preliminary evidence, based on microscopic analyses, that suggest a possible role of vimentin in nuclear alterations accompanying polyploidization-depolyploidization events following genotoxic insults.

RNF13, a RING finger protein, mediates endoplasmic reticulum stress-induced apoptosis through the inositol-requiring enzyme (IRE1α)/c-Jun NH2-terminal kinase pathway

Disturbance of homeostasis at endoplasmic reticulum (ER) causes stress to cells that in turn triggers an adaptive signaling pathway termed unfolded protein response for the purpose of restoring normal cellular physiology or initiating signaling events leading to apoptosis. Identification of those genes that are involved in the unfolded protein response-mediated apoptotic signaling pathway would be valuable toward elucidating the molecular mechanism underlying the relationship between ER stress and apoptosis. We initiated a genetic screen by using the retroviral insertion mutation system to search for genes whose inactivation confers resistance to apoptosis induction by staurosporine. Using this approach, RING finger protein 13 (RNF13) was identified. Interestingly, RNF13 is highly enriched in ER. RNF13 knockdown cells are resistant to apoptosis and JNK activation triggered by ER stress. Conversely, overexpression of RNF13 induces JNK activation and caspase-dependent apoptosis. The RING and transmembrane domains of RNF13 are both required for its effects on JNK activation and apoptosis. Moreover, systematic analysis of the involvement of individual signaling components in the ER stress pathway using knockdown approach reveals that RNF13 acts upstream of the IRE1α-TRAF2 signaling axis for JNK activation and apoptosis. Finally, RNF13 co-immunoprecipitates with IRE1α, and the intact RING domain is also required for mediating its interaction. Together, our data support a model that RNF13 is a critical mediator for facilitating ER stress-induced apoptosis through the activation of the IRE1α-TRAF2-JNK signaling pathway.

Mycoepoxydiene, a fungal polyketide inhibits MCF-7 cells through simultaneously targeting p53 and NF-κB pathways

Mycoepoxydiene (MED) is a cytotoxic polyketide that is isolated from the marine fungal strain Diaporthe sp. HLY-1, which is associated with mangroves; however, the mechanism of action of MED remains unknown. Here, we report the molecular mechanisms of apoptosis activation and growth inhibition induced by MED in MCF-7 cells. The present results show that MED induces DNA damage through the production of reactive oxygen species (ROS), which resulted in the phosphorylation of H2AX and the activation of the Ataxia telangiectasia mutated kinase (ATM) and p53 signaling pathways. In addition, MED increases the accumulation of IκBα and enhances the association between IKKγ and Hsp27 via the activation of Hsp27, which eventually resulted in the inhibition of TNF-α-induced NF-κB transactivation. Therefore, we conclude that MED inhibits MCF-7 cells by simultaneously activating p53 to induce apoptosis and suppressing NF-κB to disrupt cell proliferation. Because small molecules having both of these effects are rare, further exploration of MED as an antitumor lead compound is needed.

Antibody-induced nonapoptotic cell death in human lymphoma and leukemia cells is mediated through a novel reactive oxygen species-dependent pathway

Monoclonal antibodies (mAbs) have revolutionized the treatment of B-cell malignancies. Although Fc-dependent mechanisms of mAb-mediated tumor clearance have been extensively studied, the ability of mAbs to directly evoke programmed cell death (PCD) in the target cell and the underlying mechanisms involved remain under-investigated. We recently demonstrated that certain mAbs (type II anti-CD20 and anti-HLA DR mAbs) potently evoked PCD through an actin-dependent, lysosome-mediated process. Here, we reveal that the induction of PCD by these mAbs, including the type II anti-CD20 mAb GA101 (obinutuzumab), directly correlates with their ability to produce reactive oxygen species (ROS) in human B-lymphoma cell lines and primary B-cell chronic lymphocytic leukemia cells. ROS scavengers abrogated mAb-induced PCD indicating that ROS are required for the execution of cell death. ROS were generated downstream of mAb-induced actin cytoskeletal reorganization and lysosome membrane permeabilization. ROS production was independent of mitochondria and unaffected by BCL-2 overexpression. Instead, ROS generation was mediated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. These findings provide further insights into a previously unrecognized role for NADPH oxidase-derived ROS in mediating nonapoptotic PCD evoked by mAbs in B-cell malignancies. This newly characterized cell death pathway may potentially be exploited to eliminate malignant cells, which are refractory to conventional chemotherapy and immunotherapy.

Cytoprotective effect of γ-tocopherol against tumor necrosis factor α induced cell dysfunction in L929 cells

The antioxidant vitamin γ-tocopherol exerts protective and anti-inflammatory effects in various models of critical illness. The combination of actinomycin D and tumor necrosis factor α (TNFα) in the immortalized fibroblast cell line L929 is a well-established method to model pro-inflammatory cytotoxicity in cultured cells in vitro. The present study had two aims. First, we wished to characterize the contribution of reactive oxygen species (ROS) to the cell dysfunction and this commonly used model system of cell death. Second, we wished to investigate the effects of γ-tocopherol on this response. Cells were exposed to actinomycin D (0.5 µg/ml) + TNFα (100 pg/ml) in the absence or presence of 1 h of γ-tocopherol pre-treatment. The earliest change that was detected in our system in response to TNFα was an increase in mitochondrial oxidant production, already apparent at 45 min. Changes in glycolysis and oxidative phosphorylation parameters were already apparent at 2 h, as detected by the Seahorse Biosciences XF24 Flux Analyzer. By 6 h, a slight decrease in Cell Index was detected by impedance-based analysis, employing an electronic sensor array system (XCelligence). At the same time, a slight decrease in cell viability was detected by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) method, along with a significant increase in lactate dehydrogenase (LDH) release into the culture medium, and a detectable degree of mitochondrial membrane depolarization. Between 12 and 24 h, the cell viability (already at a low level) further declined, which coincided with a secondary, marked decline in the mitochondrial membrane potential. Pre-treatment of the cells with γ-tocopherol (10-300 µM) provided a significant protection against all of the functional alterations induced by actinomycin D and TNFα. The current study provides direct evidence that reactive oxidant formation plays an important role in the current experimental model of cell dysfunction, and demonstrates the protective effects of the potent endogenous antioxidant vitamin, γ-tocopherol. The mechanisms described in the current study may, in part, contribute to the protective effects of γ-tocopherol in various models of critical illness.

TNF-α treatment alters Mfn2 expression and mitochondrial morphology and function in hepatic LO2 cells

AIM: To investigate the influence of treatment with tumor necrosis factor-alpha (TNF-α) on the expression of mitofusin 2 (Mfn2) and mitochondrial morphology and function in hepatic LO2 cells.

METHODS: After pEGFP-Mfn2 plasmid was transfected into LO2 cells with Lipofectamine 2000, transfected LO2 cells were incubated with TNF-α for 12 h. The expression of Mfn2 mRNA and protein was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot, respectively. MitoTracker Mitochondrion-Selective Probes were used to detect the changes in mitochondrial morphology. ATP synthesis and reactive oxygen species (ROS) production were measured to assess mitochondrial function.

RESULTS: RT-PCR and Western blot analyses showed that Mfn2 was highly expressed in LO2 cells. After treatment of LO2 cells with TNF-α, Mfn2 expression was significantly suppressed (0.279 ± 0.026 vs 0.742 ± 0.018; 0.196 ± 0.024 vs 0.580 ± 0.011, P < 0.05), ATP level decreased (2.00 µmol/g ± 0.15 µmol/g vs 5.81 µmol/g ± 0.31 µmol/g, P < 0.05), ROS production increased (80.68 ± 4.02 vs 65.44 ± 3.47, P < 0.05), and the normal tubular network of mitochondria was fragmented into short rods or spheres when compared to control cells. In contrast, these changes were not significant in Mfn2-transfected LO2 cells.

CONCLUSION: TNF-α treatment may alter mitochondrial morphology and impair mitochondrial function by decreasing the expression of Mfn2 in hepatic LO2 cells.

Superoxide is the major reactive oxygen species regulating autophagy

Autophagy is involved in human diseases and is regulated by reactive oxygen species (ROS) including superoxide (O(2)(*-)) and hydrogen peroxide (H(2)O(2)). However, the relative functions of O(2)(*-) and H(2)O(2) in regulating autophagy are unknown. In this study, autophagy was induced by starvation, mitochondrial electron transport inhibitors, and exogenous H(2)O(2). We found that O(2)(*-) was selectively induced by starvation of glucose, L-glutamine, pyruvate, and serum (GP) whereas starvation of amino acids and serum (AA) induced O(2)(*-) and H(2)O(2). Both types of starvation induced autophagy and autophagy was inhibited by overexpression of SOD2 (manganese superoxide dismutase, Mn-SOD), which reduced O(2)(*-) levels but increased H(2)O(2) levels. Starvation-induced autophagy was also inhibited by the addition of catalase, which reduced both O(2)(*-) and H(2)O(2) levels. Starvation of GP or AA also induced cell death that was increased following treatment with autophagy inhibitors 3-methyladenine, and wortamannin. Mitochondrial electron transport chain (mETC) inhibitors in combination with the SOD inhibitor 2-methoxyestradiol (2-ME) increased O(2)(*-) levels, lowered H(2)O(2) levels, and increased autophagy. In contrast to starvation, cell death induced by mETC inhibitors was increased by 2-ME. Finally, adding exogenous H(2)O(2) induced autophagy and increased intracellular O(2)(*-) but failed to increase intracellular H(2)O(2). Taken together, these findings indicate that O(2)(*-) is the major ROS-regulating autophagy.

Death by committee: organellar trafficking and communication in apoptosis

Apoptosis proceeds through a set of evolutionarily conserved processes that co-ordinate the elimination of damaged or unneeded cells. This program of cell death is carried out by organelle-directed regulators, including the Bcl-2 proteins, and ultimately executed by proteases of the caspase family. Although the biochemical mechanisms of apoptosis are increasingly understood, the underlying cell biology orchestrating programmed cell death remains enigmatic. In this review, we summarize the current understanding of Bcl-2 protein regulation and caspase activation while examining cell biological mechanisms and consequences of apoptotic induction. Organellar contributions to apoptotic induction include death receptor endocytosis, mitochondrial and lysosomal permeabilization, endoplasmic reticulum calcium release and fragmentation of the Golgi apparatus. These early apoptotic events are accompanied by stabilization of the microtubule cytoskeleton and translocation of organelles to the microtubule organizing center. Together, these phenomena establish a model of apoptotic induction whereby a cytoskeletal-dependent coalescence and 'scrambling' of organelles in the paranuclear region co-ordinates apoptotic communication, caspase activation and cell death.

Mitochondrial DNA base excision repair and mitochondrial DNA mutation in human hepatic HuH-7 cells exposed to stavudine

The mitochondrial toxicity of nucleoside reverse transcriptase inhibitors (NRTIs) is due to the inhibition of mitochondrial DNA (mtDNA) polymerase gamma (Pol gamma), resulting in a blockade of mtDNA replication and subsequent disruption of cellular energetics. Because mtDNA Pol gamma is not only involved in mtDNA replication but also responsible for mtDNA repair, we hypothesize that mitochondrial oxidative stress leads to changes in the balance between mtDNA repair and mutation following stavudine (d4T) treatment. However, the mechanisms underlying how changes in mtDNA base excision repair (mtBER) lead to mtDNA mutation remain unclear. To test this hypothesis, total mitochondrial repair capability, different steps of mtBER, mtDNA mutations in D-loop, and oxidative stress were all assessed in cultured HuH-7 human hepatoblast cells treated with d4T for 2 weeks. Assessment by denaturing Southern blotting and quantitative PCR revealed that d4T significantly reduced in vivo repair of H(2)O(2) damaged mtDNA in HuH-7 cells. d4T reduced total in vitro mtBER and DNA Pol gamma capability, but did not affect mtDNA oxoguanine glycosylase and apurinic/apyrimidinic endonuclease activity in HuH-7 cells. In addition, d4T treatment is associated with a significant increase in the frequency of mtDNA mutations in HuH-7 cells. In conclusion, d4T treatment reduces mtBER and contributes mechanistically to NRTI-induced mtDNA mutation. These events may potentially be associated with some diseases linked to mtDNA mutation.

TNF-induced mitochondrial damage: a link between mitochondrial complex I activity and left ventricular dysfunction

Mitochondrial damage is implicated in the progression of cardiac disease. Considerable evidence suggests that proinflammatory cytokines induce oxidative stress and contribute to cardiac dysfunction. This study was conducted to determine whether a TNF-induced increase in superoxide (O(2)(*)(-)) contributes to mitochondrial damage in the left ventricle (LV) by impairing respiratory complex I activity. We employed an electron paramagnetic resonance (EPR) method to measure O(2)(*)(-) and oxygen consumption in mitochondrial respiratory complexes, using an oxygen label. Adult male Sprague-Dawley rats were divided into four groups: control, TNF treatment (ip), TNF+ apocynin (APO; 200 micromol/kg bw, orally), and TNF+ Tempol (Temp; 300 micromol/kg bw, orally). TNF was injected daily for 5 days. Rats were sacrificed, LV tissue was collected, and mitochondria were isolated for EPR studies. Total LV ROS production was significantly higher in TNF animals than in controls; APO or Temp treatment ameliorated TNF-induced LV ROS production. Total mitochondrial ROS production was significantly higher in the TNF and TNF+ APO groups than in the control and TNF+ Temp groups. These findings suggest that TNF alters the cellular redox state, reduces the expression of four complex I subunits by increasing mitochondrial O(2)(*)(-) production and depleting ATP synthesis, and decreases oxygen consumption, thereby resulting in mitochondrial damage and leading to LV dysfunction.

Internalisation of uncross-linked rituximab is not essential for the induction of caspase-independent killing in Burkitt lymphoma cell lines

Characterising the mechanisms underpinning caspase-independent programmed cell death (CI-PCD) induction by uncross-linked rituximab in B-cells may positively impact upon the treatment of disease states in which the classical apoptotic pathway is disabled. The necessity of rituximab internalisation for CI-PCD induction was investigated by flow cytometry and confocal microscopy in human BL cell lines with (e.g. Mutu I) and without (Mutu III) susceptibility to rituximab-induced killing. Flow cytometry demonstrated small, significant and similar amounts of rituximab internalisation by Mutu I cells after 1, 2, 4 and 24 h (p < 0.03, n = 5) and Mutu III cells after 0.5, 2, 4 and 24 h (p < 0.05, n = 4). Confocal microscopy confirmed this. Cytochalasin B and latrunculin A significantly inhibited rituximab-induced CI-PCD (p < or = 0.04, n = 6 and p = 0.01, n = 6, respectively) and internalisation (p = 0.02, n = 5 and p = 0.0002, n = 6, respectively) in Mutu I cells, but confocal microscopy showed no correlation between internalised rituximab and phosphatidylserine exposure. We conclude that rituximab internalisation is not essential for CI-PCD induction in BL cell lines.

Mitochondrial shuttling of CAP1 promotes actin- and cofilin-dependent apoptosis

Mitochondria play a central role in regulating apoptosis by releasing proapoptotic contents such as cytochrome c, and generating reactive oxygen species (ROS). Early in apoptosis, proteins translocate to mitochondria to promote the release of their contents. Here, we show that the actin- and cofilin-interacting protein CAP1 has a role in apoptosis. When we induced apoptosis, CAP1 rapidly translocated to the mitochondria independently of caspase activation. Translocation was proapoptotic because CAP1-knockdown cells were resistant to apoptosis inducers. Overexpression of wild-type CAP1 did not stimulate apoptosis on its own, but stimulated cofilin-induced apoptosis. Apoptosis induction required a mitochondrial-targeting domain, localized in the N-terminus and also the actin-binding domain in the C-terminus. Taken together, these studies suggest that CAP1 provides a direct link from the actin cytoskeleton to the mitochondria by functioning as an actin shuttle.

Influence of increased adiposity on mitochondrial-associated proteins of the rat colon: a proteomic and transcriptomic analysis

Epidemiological studies report obesity to be an important risk factor influencing colon pathologies, yet mechanism(s) are unknown. Recent studies have shown significant elevation of insulin, leptin and triglycerides associated with increased adipose tissue. In situ hybridisation studies have located insulin, leptin and adiponectin receptor expression in the colon epithelia. The influence of increased adiposity and associated deregulation of insulin and adipokines on regulation of the colon epithelium is unknown. Altered adipokine and insulin signalling associated with obesity has an impact on mitochondrial function and mitochondrial dysfunction is increasingly recognised as a contributing factor in many diseases. Proteomics and transcriptomics are potentially powerful methods useful in elucidating the mechanisms whereby obesity increases risk of colon diseases as observed epidemiologically. This study investigated colon mitochondrial-associated protein profiles and corresponding gene expression in colon in response to increased adiposity in a rat model of diet induced obesity. Increased adiposity in diet-induced obese sensitive rats was found to be associated with altered protein expression of 69 mitochondrial-associated proteins involved in processes associated with calcium binding, protein folding, energy metabolism, electron transport chain, structural proteins, protein synthesis and degradation, redox regulation, and transport. The changes in these mitochondrial protein profiles were not correlated with changes at the gene expression level assessed using real-time PCR arrays.

Differential protein expression following low temperature culture of suspension CHO-K1 cells

Background

To ensure maximal productivity of recombinant proteins (rP) during production culture it is typical to encourage an initial phase of rapid cell proliferation to achieve high biomass followed by a stationary phase where cellular energies are directed towards production of rP. During many such biphasic cultures, the initial phase of rapid cell growth at 37°C is followed by a growth arrest phase induced through reduction of the culture temperature. Low temperature induced growth arrest is associated with many positive phenotypes including increased productivity, sustained viability and an extended production phase, although the mechanisms regulating these phenotypes during mild hypothermia are poorly understood.

Results

In this study differential protein expression in suspension CHO-K1 cells was investigated following a reduction of the culture temperature from 37°C to 31°C in comparison to standard batch culture maintained at 37°C using 2D-DIGE (Fluorescence 2-D Difference Gel Electrophoresis) and mass spectrometry (MS). There is only limited proteomic analysis of suspension-grown CHO cells describing a direct comparison of temperature shifted versus non-temperature shifted cultures using 2D-DIGE. This investigation has enabled the identification of temperature-dependent as well as temperature-independent proteomic changes. 201 proteins were observed as differentially expressed following temperature shift, of which 118 were up regulated. Of the 53 proteins identified by MALDI-ToF MS, 23 were specifically differentially expressed upon reduction of the culture temperature and were found related to a variety of cellular functions such as regulation of growth (HNRPC), cap-independent translation (EIF4A), apoptosis (importin-α), the cytoskeleton (vimentin) and glycoprotein quality control (alpha glucosidase 2).

Conclusion

These results indicate the extent of the temperature response in CHO-K1 cells and suggest a number of key regulatory proteins and pathways that are involved in modulating the response of cells to mild hypothermia. Regulation of these identified proteins and pathways could be useful for future approaches to engineer CHO cells for improved recombinant protein production.

A proteomic analysis of allograft rejection in rats after liver transplantation

In order to understand the allograft rejection in orthotopic liver transplantation (OLT), an allograft rejection rat model was established and studied by proteomic approach. The protein expression profiles of liver tissues were acquired by fluorescence two-dimensional difference gel electrophoresis (2D DIGE) that incorporated a pooled internal standard and reverse fluorescent labeling method. The expression levels of 27 protein spots showed significant changes in acute rejection rats. Among these spots, 19 were identified with peptide mass fingerprinting using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) after tryptic in-gel digestion. The results of the present paper could be helpful for our better understanding of allograft rejection in organ transplantation.

Conserved actin cysteine residues are oxidative stress sensors that can regulate cell death in yeast

Actin's functional complexity makes it a likely target of oxidative stress but also places it in a prime position to coordinate the response to oxidative stress. We have previously shown that the NADPH oxidoreductase Oye2p protects the actin cytoskeleton from oxidative stress. Here we demonstrate that the physiological consequence of actin oxidation is to accelerate cell death in yeast. Loss of Oye2p leads to reactive oxygen species accumulation, activation of the oxidative stress response, nuclear fragmentation and DNA degradation, and premature chronological aging of yeast cells. The oye2Delta phenotype can be completely suppressed by removing the potential for formation of the actin C285-C374 disulfide bond, the likely substrate of the Oye2p enzyme or by treating the cells with the clinically important reductant N-acetylcysteine. Because these two cysteines are coconserved in all actin isoforms, we theorize that we have uncovered a universal mechanism whereby actin helps to coordinate the cellular response to oxidative stress by both sensing and responding to oxidative load.

Can electrons travel through actin microfilaments and generate oxidative stress in retinol treated Sertoli cell?

In early reports our research group has demonstrated that 7 microM retinol (vitamin A) treatment leads to many changes in Sertoli cell metabolism, such as up-regulation of antioxidant enzyme activities, increase in damage to biomolecules, abnormal cellular division, pre-neoplasic transformation, and cytoskeleton conformational changes. These effects were observed to be dependent on the production of reactive oxygen species (ROS), suggesting extra-nuclear (non-genomic) effects of retinol metabolism. Besides 7 microM retinol treatment causing oxidative stress, we have demonstrated that changes observed in cytoskeleton of Sertoli cells under these conditions were protective, and seem to be an adaptive phenomenon against a pro-oxidant environment resulting from retinol treatment. We have hypothesized that the cytoskeleton can conduct electrons through actin microfilaments, which would be a natural process necessary for cell homeostasis. In the present study we demonstrate results correlating retinol metabolism, actin architecture, mitochondria physiology and ROS, in order to demonstrate that the electron conduction through actin microfilaments might explain our results. We believe that electrons produced by retinol metabolism are dislocated through actin microfilaments to mitochondria, and are transferred to electron transport chain to produce water. When mitochondria capacity to receive electrons is overloaded, superoxide radical production is increased and the oxidative stress process starts. Our results suggested that actin cytoskeleton is essential to oxidative stress production induced by retinol treatment, and electrons conduction through actin microfilaments can be the key of this correlation.

Cytotoxic T Lymphocytes Induce Caspase-Dependent and -Independent Cell Death in Neuroblastomas in a MHC-Nonrestricted Fashion

The MHC class I- restricted processing and presentation pathway is frequently nonfunctional in tumor cells; therefore, the direct targeting of tumor cells by CTLs may be difficult, if at all possible, to achieve. We used neuroblastoma (NB), which represents a striking example of a tumor with an impaired MHC class I pathway, as a model to study bystander effects of activated T lymphocytes on tumor cells. We found that NB cell lines are susceptible to killing by differentiated CD8(+) CTL clones in a MHC class I-nonrestricted manner that involves two programs of cell death distinguished on the basis of different kinetics, sensitivities to caspase inhibitors, and cytokine-blocking reagents. The "early" death exhibited characteristic features of apoptosis, whereas the "delayed" caspase-independent death exhibited features associated with necrosis and was partially inhibited by TNF-alpha-blocking and prevented by overexpression of Bcl-2 or Bcl-x(L). Our data reveal a previously unappreciated complexity of death pathways induced in tumor cells by immune activation and suggest that redirecting nonspecific effector CTLs to even a small proportion of NB cells or activating CTLs in a tumor's proximity may have therapeutic effects in patients with NB.

Necrosis, a well-orchestrated form of cell demise: signalling cascades, important mediators and concomitant immune response

Necrosis has long been described as a consequence of physico-chemical stress and thus accidental and uncontrolled. Recently, it is becoming clear that necrotic cell death is as well controlled and programmed as caspase-dependent apoptosis, and that it may be an important cell death mode that is both pathologically and physiologically relevant. Necrotic cell death is not the result of one well-described signalling cascade but is the consequence of extensive crosstalk between several biochemical and molecular events at different cellular levels. Recent data indicate that serine/threonine kinase RIP1, which contains a death domain, may act as a central initiator. Calcium and reactive oxygen species (ROS) are main players during the propagation and execution phases of necrotic cell death, directly or indirectly provoking damage to proteins, lipids and DNA, which culminates in disruption of organelle and cell integrity. Necrotically dying cells initiate pro-inflammatory signalling cascades by actively releasing inflammatory cytokines and by spilling their contents when they lyse. Unravelling the signalling cascades contributing to necrotic cell death will permit us to develop tools to specifically interfere with necrosis at certain levels of signalling. Necrosis occurs in both physiological and pathophysiological processes, and is capable of killing tumour cells that have developed strategies to evade apoptosis. Thus detailed knowledge of necrosis may be exploited in therapeutic strategies.

The increase in mitochondrial association with actin precedes Bax translocation in apoptosis

Accumulating evidence indicates the potential role of actin cytoskeleton in facilitating the mitochondrial recruitment of various pro-apoptotic proteins from the cytosol to initiate apoptosis. In the present paper, we report the observation of the increase in mitochondrial association of actin in early apoptosis. Using cell fractionation and Western blot analysis, we found that mitochondrial accumulation of beta-actin occurred before the mitochondrial insertion of Bax and release of cytochrome c in apoptosis. The mitochondrial accumulation of beta-actin was observed with various apoptotic stimuli in various cell lines, suggesting that this is a general apoptotic phenomenon in mammalian systems. Using fluorescence microscopy, we have shown that an apoptotic induction triggered the reorganization of the F-actin (filamentous actin) network with an increase in the association with mitochondria, which was observed before mitochondrial fission and nuclear condensation. Perhaps actin could contribute to the initiation of apoptosis by enabling cytosolic pro-apoptotic proteins to be carried to mitochondria by the cytoskeleton-driven trafficking system.

The relationship between mitochondrial shape and function and the cytoskeleton

Mitochondria are crucial organelles for life and death of the cell. They are prominent players in energy conversion and integrated signaling pathways including regulation of Ca2+ signals and apoptosis. Their functional versatility is matched by their morphological plasticity and by their high mobility, allowing their transport at specialized cellular sites. This transport occurs by interactions with a variety of cytoskeletal proteins that also have the ability to influence shape and function of the organelle. A growing body of evidence suggests that mitochondria use cytoskeletal proteins as tracks for their movement; in turn, mitochondrial morphology and function is regulated via mostly uncharacterized pathways, by the cytoskeleton.