Death by committee: organellar trafficking and communication in apoptosis

Characteristics of Developmental and Epileptic Encephalopathy Associated with PACS2 p.Glu209Lys Pathogenic Variant-Our Experience and Systematic Review of the Literature

BACKGROUND

Developmental and epileptic encephalopathies (DEE) encompass a group of rare diseases with hereditary and genetic causes as well as acquired causes such as brain injuries or metabolic abnormalities. The phosphofurin acidic cluster sorting protein 2 (PACS2) is a multifunctional protein with nuclear gene expression. The first cases of the recurrent c.625G>A pathogenic variant of PACS2 gene were reported in 2018 by Olson et al. Since then, several case reports and case series have been published.

METHODS

We performed a systematic review of the PUBMED and SCOPUS databases using Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Our search parameters included DEE66 with a pathogenic PACS2 gene p.Glu209Lys mutation published cases to which we added our own clinical experience regarding this pathology.

RESULTS

A total of 11 articles and 29 patients were included in this review, to which we added our own experience for a total of 30 patients. There was not a significant difference between sexes regarding the incidence of this pathology (M/F: 16/14). The most common neurological and psychiatric symptoms presented by the patients were: early onset epileptic seizures, delayed global development (including motor and speech delays), behavioral disturbances, limited intellectual capacity, nystagmus, hypotonia, and a wide-based gait. Facial dysmorphism and other organs' involvement were also frequently reported. Brain MRIs evidenced anomalies of the posterior cerebellar fossa, foliar distortion of the cerebellum, vermis hypoplasia, white matter reduction, and lateral ventricles enlargement. Genetic testing is more frequent in children. Only 4 cases have been reported in adults to date.

CONCLUSIONS

It is important to maintain a high suspicion of new pathogenic gene variants in adult patients presenting with a characteristic clinical picture correlated with radiologic changes. The neurologist must gradually recognize the distinct evolving phenotype of DEE66 in adult patients, and genetic testing must become a scenario with which the neurologist attending adult patients should be familiar. Accurate diagnosis is required for adequate treatment, genetic counseling, and an improved long-term prognosis.

Metal organic layers enabled cell surface engineering coupling biomembrane fusion for dynamic membrane proteome profiling

Systematically dissecting the highly dynamic and tightly communicating membrane proteome of living cells is essential for the system-level understanding of fundamental cellular processes and intricate relationship between membrane-bound organelles constructed through membrane traffic. While extensive efforts have been made to enrich membrane proteins, their comprehensive analysis with high selectivity and deep coverage remains a challenge, especially at the living cell state. To address this problem, we developed the cell surface engineering coupling biomembrane fusion method to map the whole membrane proteome from the plasma membrane to various organelle membranes taking advantage of the exquisite interaction between two-dimensional metal-organic layers and phospholipid bilayers on the membrane. This approach, which bypassed conventional biochemical fractionation and ultracentrifugation, facilitated the enrichment of membrane proteins in their native phospholipid bilayer environment, helping to map the membrane proteome with a specificity of 77% and realizing the deep coverage of the HeLa membrane proteome (5087 membrane proteins). Furthermore, membrane N-phosphoproteome was profiled by integrating the N-phosphoproteome analysis strategy, and the dynamic membrane proteome during apoptosis was deciphered in combination with quantitative proteomics. The features of membrane protein N-phosphorylation modifications and many differential proteins during apoptosis associated with mitochondrial dynamics and ER homeostasis were found. The method provided a simple and robust strategy for efficient analysis of membrane proteome, offered a reliable platform for research on membrane-related cell dynamic events and expanded the application of metal-organic layers.

Mitochondrial Trafficking of MLKL, Bak/Bax, and Drp1 Is Mediated by RIP1 and ROS which Leads to Decreased Mitochondrial Membrane Integrity during the Hyperglycemic Shift to Necroptosis

Apoptosis and necroptosis overlap in their initial signaling but diverge to produce non-inflammatory and pro-inflammatory outcomes, respectively. High glucose pushes signaling in favor of necroptosis producing a hyperglycemic shift from apoptosis to necroptosis. This shift depends on receptor-interacting protein 1 (RIP1) and mitochondrial reactive oxygen species (ROS). Here, we show that RIP1, mixed lineage kinase domain-like (MLKL) protein, Bcl-2 agonist/killer (Bak), Bcl-2 associated x (Bax) protein, and dynamin-related protein 1 (Drp1) traffic to the mitochondria in high glucose. RIP1 and MLKL appear in the mitochondria in their activated, phosphorylated states while Drp1 appears in its activated, dephosphorylated state in high glucose. Mitochondrial trafficking is prevented in rip1 KO cells and upon treatment with N-acetylcysteine. Induction of ROS replicated the mitochondrial trafficking seen in high glucose. MLKL forms high MW oligomers in the outer and inner mitochondrial membranes while Bak and Bax form high MW oligomers in the outer mitochondrial membrane in high glucose, suggesting pore formation. MLKL, Bax, and Drp1 promoted cytochrome c release from the mitochondria as well as a decrease in mitochondrial membrane potential in high glucose. These results indicate that mitochondrial trafficking of RIP1, MLKL, Bak, Bax, and Drp1 are key events in the hyperglycemic shift from apoptosis to necroptosis. This is also the first report to show oligomerization of MLKL in the inner and outer mitochondrial membranes and dependence of mitochondrial permeability on MLKL.

Apoptotic stress induces Bax-dependent, caspase-independent redistribution of LINC complex nesprins

The canonical function of Bcl-2 family proteins is to regulate mitochondrial membrane integrity. In response to apoptotic signals the multi-domain pro-apoptotic proteins Bax and Bak are activated and perforate the mitochondrial outer membrane by a mechanism which is inhibited by their interaction with pro-survival members of the family. However, other studies have shown that Bax and Bak may have additional, non-canonical functions, which include stress-induced nuclear envelope rupture and discharge of nuclear proteins into the cytosol. We show here that the apoptotic stimuli cisplatin and staurosporine induce a Bax/Bak-dependent degradation and subcellular redistribution of nesprin-1 and nesprin-2 but not nesprin-3, of the linker of nucleoskeleton and cytoskeleton (LINC) complex. The degradation and redistribution were caspase-independent and did not occur in Bax/Bak double knockout (DKO) mouse embryo fibroblasts (MEFs). Re-expression of Bax in Bax/Bak DKO MEFs restored stress-induced redistribution of nesprin-2 by a mechanism which requires Bax membrane localization and integrity of the α helices 5/6, and the Bcl-2 homology 3 (BH3) domain. We found that nesprin-2 interacts with Bax in close proximity to perinuclear mitochondria in mouse and human cells. This interaction requires the mitochondrial targeting and N-terminal region but not the BH3 domain of Bax. Our results identify nesprin-2 as a Bax binding partner and also a new function of Bax in impairing the integrity of the LINC complex.

Golgi Structure and Function in Health, Stress, and Diseases

The Golgi apparatus is a central intracellular membrane-bound organelle with key functions in trafficking, processing, and sorting of newly synthesized membrane and secretory proteins and lipids. To best perform these functions, Golgi membranes form a unique stacked structure. The Golgi structure is dynamic but tightly regulated; it undergoes rapid disassembly and reassembly during the cell cycle of mammalian cells and is disrupted under certain stress and pathological conditions. In the past decade, significant amount of effort has been made to reveal the molecular mechanisms that regulate the Golgi membrane architecture and function. Here we review the major discoveries in the mechanisms of Golgi structure formation, regulation, and alteration in relation to its functions in physiological and pathological conditions to further our understanding of Golgi structure and function in health and diseases.

Platelet procoagulant phenotype is modulated by a p38-MK2 axis that regulates RTN4/Nogo proximal to the endoplasmic reticulum: utility of pathway analysis

Upon encountering physiological cues associated with damaged or inflamed endothelium, blood platelets set forth intracellular responses to ultimately support hemostatic plug formation and vascular repair. To gain insights into the molecular events underlying platelet function, we used a combination of interactome, pathway analysis, and other systems biology tools to analyze associations among proteins functionally modified by reversible phosphorylation upon platelet activation. While an interaction analysis mapped out a relative organization of intracellular mediators in platelet signaling, pathway analysis revealed directional signaling relations around protein kinase C (PKC) isoforms and mitogen-activated protein kinases (MAPKs) associated with platelet cytoskeletal dynamics, inflammatory responses, and hemostatic function. Pathway and causality analysis further suggested that platelets activate a specific p38-MK2 axis to phosphorylate RTN4 (reticulon-4, also known as Nogo), a Bcl-xl sequestration protein and critical regulator of endoplasmic reticulum (ER) physiology. In vitro, we find that platelets drive a p38-MK2-RTN4-Bcl-xl pathway associated with the regulation of the ER and platelet phosphatidylserine exposure. Together, our results support the use of pathway tools in the analysis of omics data sets as a means to help generate novel, mechanistic, and testable hypotheses for platelet studies while uncovering RTN4 as a putative regulator of platelet cell physiological responses.

KIF3A knockdown sensitizes bronchial epithelia to apoptosis and aggravates airway inflammation in asthma

BACKGROUND

KIF3A expression was decreased in asthmatic child patients and animal. Impaired KIF3A expression resulted in increased Th2 inflammation in mice and apoptosis in renal tubular epithelium and photoreceptor cells. This work aimed to investigate the role of KIF3A in epithelium apoptosis and bronchial inflammation in asthma.

METHODS

After establishment of ovalbumin induced asthma, the mice were infected with KIF3A adenovirus through nasal cavity inhalation. KIF3A expression and apoptosis in epithelia of nasal mucosa and bronchia were determined using qRT-PCR, western blotting, immunohistochemistry and TUNEL staining. The mRNA expression of COX-2, IL-4, IL-5, IL-13, IL-6, IL-10 and TNF-α was also measured. In vitro, human bronchial epithelial cell line 16HBE 14o- was stimulated with IL-4, IL-13 and TNF-α, accompanied by KIF3A knockdown or overexpression using siRNA or KIF3A adenovirus respectively. Apoptosis, mRNA expression of CCL17, CCL26, IL-5 and IL-8, and protein expression of COX-2 and β-catenin were determined using flow cytometry, qRT-PCR and western blotting.

RESULTS

KIF3A expression was reduced in epithelia of nasal mucosa and bronchia of asthmatic mice, and overexpression of KIF3A ameliorated epithelial cell apoptosis and bronchial inflammation in asthmatic mice. In vitro, KIF3A knockdown significantly promoted epithelium apoptosis, facilitated the transcription of CCL17, CCL26, IL-5 and IL-8, and increased the protein levels of COX-2 and β-catenin translocation, whereas overexpression of KIF3A exhibited the opposite effect.

CONCLUSION

KIF3A plays an important role in epithelium apoptosis and bronchial inflammation in asthma, and may be a potential target for asthma treatment.

Caught in the act - protein adaptation and the expanding roles of the PACS proteins in tissue homeostasis and disease

Vertebrate proteins that fulfill multiple and seemingly disparate functions are increasingly recognized as vital solutions to maintaining homeostasis in the face of the complex cell and tissue physiology of higher metazoans. However, the molecular adaptations that underpin this increased functionality remain elusive. In this Commentary, we review the PACS proteins - which first appeared in lower metazoans as protein traffic modulators and evolved in vertebrates to integrate cytoplasmic protein traffic and interorganellar communication with nuclear gene expression - as examples of protein adaptation 'caught in the act'. Vertebrate PACS-1 and PACS-2 increased their functional density and roles as metabolic switches by acquiring phosphorylation sites and nuclear trafficking signals within disordered regions of the proteins. These findings illustrate one mechanism by which vertebrates accommodate their complex cell physiology with a limited set of proteins. We will also highlight how pathogenic viruses exploit the PACS sorting pathways as well as recent studies on PACS genes with mutations or altered expression that result in diverse diseases. These discoveries suggest that investigation of the evolving PACS protein family provides a rich opportunity for insight into vertebrate cell and organ homeostasis.

Caspases rule the intracellular trafficking cartel

During apoptosis, caspases feast on several hundreds of cellular proteins to orchestrate rapid cellular demise. Indeed, caspases are known to get a taste of every cellular process in one way or another, activating some, but most often shutting them down. Thus, it is not surprising that caspases proteolyze proteins involved in intracellular trafficking with particularly devastating consequences for this important process. This review article focuses on how caspases target the machinery responsible for smuggling goods within and outside the cell.

Changes in the Golgi Apparatus of Neocortical and Hippocampal Neurons in the Hibernating Hamster

Hibernating animals have been used as models to study several aspects of the plastic changes that occur in the metabolism and physiology of neurons. These models are also of interest in the study of Alzheimer's disease because the microtubule-associated protein tau is hyperphosphorylated during the hibernation state known as torpor, similar to the pretangle stage of Alzheimer's disease. Hibernating animals undergo torpor periods with drops in body temperature and metabolic rate, and a virtual cessation of neural activity. These processes are accompanied by morphological and neurochemical changes in neurons, which reverse a few hours after coming out of the torpor state. Since tau has been implicated in the structural regulation of the neuronal Golgi apparatus (GA) we have used Western Blot and immunocytochemistry to analyze whether the GA is modified in cortical neurons of the Syrian hamster at different hibernation stages. The results show that, during the hibernation cycle, the GA undergo important structural changes along with differential modifications in expression levels and distribution patterns of Golgi structural proteins. These changes were accompanied by significant transitory reductions in the volume and surface area of the GA elements during torpor and arousal stages as compared with euthermic animals.

Emerging roles of apoptotic microtubules during the execution phase of apoptosis

Apoptosis is a genetically programmed energy-dependent process of cell demise, characterized by specific morphological and biochemical events in which the activation of caspases has an essential role. During apoptosis the cytoskeleton participates actively in characteristic morphological rearrangements of the dying cell. This reorganisation has been assigned mainly to actinomyosin ring contraction, while microtubule and intermediate filaments are depolymerized at early stages of apoptosis. However, recent reports have showed that microtubules are reformed during the execution phase of apoptosis organizing an apoptotic microtubule network (AMN). AMN is organized behind plasma membrane, forming a cortical structure. Apoptotic microtubules repolymerization takes place in many cell types and under different apoptotic inducers. It has been hypothesized that AMN is critical for maintaining plasma membrane integrity and cell morphology during the execution phase of apoptosis. AMN disorganization leads apoptotic cells to secondary necrosis and the release of potential toxic molecules which can damage neighbor cells and promotes inflammation. Therefore, AMN formation during physiological apoptosis or in pathological apoptosis induced by anti-cancer treatments is essential for tissue homeostasis and the prevention of additional cell damage and inflammation.

The energy blockers bromopyruvate and lonidamine lead GL15 glioblastoma cells to death by different p53-dependent routes

The energy metabolism of tumor cells relies on aerobic glycolysis rather than mitochondrial oxidation. This difference between normal and cancer cells provides a biochemical basis for new therapeutic strategies aimed to block the energy power plants of cells. The effects produced by the energy blockers bromopyruvate (3BP) and lonidamine (LND) and the underlying biochemical mechanisms were investigated in GL15 glioblastoma cells. 3BP exerts early effects compared to LND, even though both drugs lead cells to death but by different routes. A dramatic decrease of ATP levels occurred after 1 hour treatment with 3BP, followed by cytochrome c and hexokinase II degradation, and by the decrease of both LC3I/LC3II ratio and p62, markers of an autophagic flux. In addition, Akt(Ser(473)) and p53(Ser(15)/Ser(315)) dephosphorylation occurred. In LND treatment, sustained ATP cellular levels were maintained up to 40 hours. The autophagic response of cells was overcome by apoptosis that was preceded by phosphatidylinositol disappearance and pAkt decrease. This last event favored p53 translocation to mitochondria triggering a p53-dependent apoptotic route, as observed at 48 and 72 hours. Adversely, in 3BP treatment, phospho-p53 dephosphorylation targeted p53 to MDM2-dependent proteolysis, thus channeling cells to irreversible autophagy.

Golgi fragmentation precedes neuromuscular denervation and is associated with endosome abnormalities in SOD1-ALS mouse motor neurons

Background

Fragmentation of stacked cisterns of the Golgi apparatus into dispersed smaller elements is a feature associated with degeneration of neurons in amyotrophic lateral sclerosis (ALS) and some other neurodegenerative disorders. However, the role of Golgi fragmentation in motor neuron degeneration is not well understood.

Results

Here we use a SOD1-ALS mouse model (low-copy Gurney G93A-SOD1 mouse) to show that motor neurons with Golgi fragmentation are retrogradely labeled by intramuscularly injected CTB (beta subunit of cholera toxin), indicating that Golgi fragmentation precedes neuromuscular denervation and axon retraction. We further show that Golgi fragmentation may occur in the absence of and precede two other pathological markers, i.e. somatodendritic SOD1 inclusions, and the induction of ATF3 expression. In addition, we show that Golgi fragmentation is associated with an altered dendritic organization of the Golgi apparatus, does not depend on intact apoptotic machinery, and is facilitated in transgenic mice with impaired retrograde dynein-dependent transport (BICD2-N mice). A connection to altered dynein-dependent transport also is suggested by reduced expression of endosomal markers in neurons with Golgi fragmentation, which also occurs in neurons with impaired dynein function.

Conclusions

Together the data indicate that Golgi fragmentation is a very early event in the pathological cascade in ALS that is associated with altered organization of intracellular trafficking.

Golgin-84-associated Golgi fragmentation triggers tau hyperphosphorylation by activation of cyclin-dependent kinase-5 and extracellular signal-regulated kinase

Tau hyperphosphorylation is a critical event in Alzheimer's disease, in which the neuronal Golgi fragmentation occurs earlier than tau hyperphosphorylation. However, the intrinsic link between Golgi impairment and tau pathology is missing. By electron microscopy and western blotting, we observed in the present study that the neuronal Golgi fragmentation was increased age-dependently with a correlated tau hyperphosphorylation in the brains of C57BL/6 mice aged from 4 to 16 months. Simultaneously, golgin-84 and Golgi reassembly stacking protein 65, 2 important Golgi matrix proteins, were decreased in the brains of elder mice. Further studies in HEK293/tau cells showed that Golgi-disturbing agents, brefeldin A and nocodazole induced tau hyperphosphorylation. Knockdown of golgin-84, not Golgi reassembly stacking protein 65, by small interfering RNA was sufficient to induce tau hyperphosphorylation, while over-expressing golgin-84 arrested the brefeldin A-induced Golgi fragmentation and tau hyperphosphorylation. Finally, we demonstrated that cyclin-dependent kinase-5 and extracellular signal-regulated kinase were activated after golgin-84 knockdown, and simultaneous inhibition of these kinases abolished the golgin-84 deficit-induced tau hyperphosphorylation. These data suggest Golgi fragmentation could be an upstream event triggering tau hyperphosphorylation through golgin-84 deficit-induced activation of cyclin-dependent kinase-5 and extracellular signal-regulated kinase.

Increased neuronal activity fragments the Golgi complex

The Golgi complex is essential for many aspects of cellular function, including trafficking and sorting of membrane and secretory proteins and posttranslational modification by glycosylation. We observed reversible fragmentation of the Golgi complex in cultured hippocampal neurons cultured in hyperexcitable conditions. In addition, Golgi fragmentation was found in cultured neurons with hyperactivity due to prolonged blockade of GABA(A)-mediated inhibition or withdrawal of NMDA receptor antagonism. The interplay between neuronal hyperactivity and Golgi structure established in this study thus reveals a previously uncharacterized impact of neuronal activity on organelle structure. This finding may have important roles in protein processing and trafficking in the Golgi as well as effects on neuronal signaling.

T-cell death following immune activation is mediated by mitochondria-localized SARM

Following acute-phase infection, activated T cells are terminated to achieve immune homeostasis, failure of which results in lymphoproliferative and autoimmune diseases. We report that sterile α- and heat armadillo-motif-containing protein (SARM), the most conserved Toll-like receptors adaptor, is proapoptotic during T-cell immune response. SARM expression is significantly reduced in natural killer (NK)/T lymphoma patients compared with healthy individuals, suggesting that decreased SARM supports NK/T-cell proliferation. T cells knocked down of SARM survived and proliferated more significantly compared with wild-type T cells following influenza infection in vivo. During activation of cytotoxic T cells, the SARM level fell before rising, correlating inversely with cell proliferation and subsequent T-cell clearance. SARM knockdown rescued T cells from both activation- and neglect-induced cell deaths. The mitochondria-localized SARM triggers intrinsic apoptosis by generating reactive oxygen species and depolarizing the mitochondrial potential. The proapoptotic function is attributable to the C-terminal sterile alpha motif and Toll/interleukin-1 receptor domains. Mechanistically, SARM mediates intrinsic apoptosis via B cell lymphoma-2 (Bcl-2) family members. SARM suppresses B cell lymphoma-extra large (Bcl-xL) and downregulates extracellular signal-regulated kinase phosphorylation, which are cell survival effectors. Overexpression of Bcl-xL and double knockout of Bcl-2 associated X protein and Bcl-2 homologous antagonist killer substantially reduced SARM-induced apoptosis. Collectively, we have shown how T-cell death following infection is mediated by SARM-induced intrinsic apoptosis, which is crucial for T-cell homeostasis.

Radiofrequency currents exert cytotoxic effects in NB69 human neuroblastoma cells but not in peripheral blood mononuclear cells

Recently, a number of electric and electrothermal therapies have been applied to the treatment of specific cancer types. However, the cellular and molecular mechanisms involved in the response to such therapies have not been well characterized yet. Capacitive-resistive electric transfer (CRET) therapy uses electric currents at frequencies within the 0.45–0.6 MHz range to induce hyperthermia in target tissues. Preliminary trials in cancer patients have shown consistent signs that CRET could slow down growth of tumor tissues in brain gliomas, without inducing detectable damage in the surrounding healthy tissue. Previous studies by our group have shown that subthermal treatment with 0.57-MHz electric currents can induce a cytostatic, not cytotoxic response in HepG2 human hepatocarcinoma cells; such effect being mediated by cell cycle alterations. In contrast, the study of the response of NB69 human neuroblastoma cells to the same electric treatment revealed consistent indications of cytotoxic effects. The present study extends the knowledge on the response of NB69 cells to the subthermal stimulus, comparing it to that of primary cultures of human peripheral blood mononuclear cells (PBMC) exposed to the same treatment. The results showed no sensitivity of PBMC to the 0.57 MHz subthermal currents and confirmed that the treatment exerts a cytotoxic action in NB69 cells. The data also revealed a previously undetected cytostatic response of the neuroblastoma cell line. CRET currents affected NB69 cell proliferation by significantly reducing the fraction of cells in the phase G₂/M of the cell cycle at 12 h of exposure. These data provide new information on the mechanisms of response to CRET therapy, and are consistent with a cytotoxic and/or cytostatic action of the electric treatment, which would affect human cells of tumor origin but not normal cells with a low proliferation rate.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein-induced lysosomal translocation of proapoptotic effectors is mediated by phosphofurin acidic cluster sorting protein-2 (PACS-2)

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of liver cancer cell lines requires death receptor-5 (DR5)-dependent permeabilization of lysosomal membranes. Ligated DR5 triggers recruitment of the proapoptotic proteins Bim and Bax to lysosomes, releasing cathepsin B into the cytosol where it mediates mitochondria membrane permeabilization and activation of executioner caspases. Despite the requirement for lysosome membrane permeabilization during TRAIL-induced apoptosis, little is known about the mechanism that controls recruitment of Bim and Bax to lysosomal membranes. Here we report that TRAIL induces recruitment of the multifunctional sorting protein phosphofurin acidic cluster sorting protein-2 (PACS-2) to DR5-positive endosomes in Huh-7 cells where it forms an immunoprecipitatable complex with Bim and Bax on lysosomal membranes. shRNA-targeted knockdown of PACS-2 prevents recruitment of Bim or Bax to lysosomes, blunting the TRAIL-induced lysosome membrane permeabilization. Consistent with the reduced lysosome membrane permeabilization, shRNA knockdown of PACS-2 in Huh-7 cells reduced TRAIL-induced apoptosis and increased clonogenic cell survival. The determination that recombinant PACS-2 bound Bim but not Bax in vitro and that shRNA knockdown of Bim blocked Bax recruitment to lysosomes suggests that TRAIL/DR5 triggers endosomal PACS-2 to recruit Bim and Bax to lysosomes to release cathepsin B and induce apoptosis. Together, these findings provide insight into the lysosomal pathway of apoptosis.

Loss of soluble N-ethylmaleimide-sensitive factor attachment protein α (αSNAP) induces epithelial cell apoptosis via down-regulation of Bcl-2 expression and disruption of the Golgi

Intracellular trafficking represents a key mechanism that regulates cell fate by participating in either prodeath or prosurvival signaling. Soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein α (αSNAP) is a well known component of vesicle trafficking machinery that mediates intermembrane fusion. αSNAP increases cell resistance to cytotoxic stimuli, although mechanisms of its prosurvival function are poorly understood. In this study, we found that either siRNA-mediated knockdown of αSNAP or expression of its dominant negative mutant induced epithelial cell apoptosis. Apoptosis was not caused by activation of the major prodeath regulators Bax and p53 and was independent of a key αSNAP binding partner, NSF. Instead, death of αSNAP-depleted cells was accompanied by down-regulation of the antiapoptotic Bcl-2 protein; it was mimicked by inhibition and attenuated by overexpression of Bcl-2. Knockdown of αSNAP resulted in impairment of Golgi to endoplasmic reticulum (ER) trafficking and fragmentation of the Golgi. Moreover, pharmacological disruption of ER-Golgi transport by brefeldin A and eeyarestatin 1 or siRNA-mediated depletion of an ER/Golgi-associated p97 ATPase recapitulated the effects of αSNAP inhibition by decreasing Bcl-2 level and triggering apoptosis. These results reveal a novel role for αSNAP in promoting epithelial cell survival by unique mechanisms involving regulation of Bcl-2 expression and Golgi biogenesis.

Role of 17β-estradiol and testosterone in apoptosis

17β-Estradiol (E2) and Testosterone (T) exert actions in most animal tissues, in addition to the reproductive system. Thus, both sex steroid hormones affect growth and different cell functions in several organs. Accordingly, the nuclear estrogen (ER) and androgen (AR) receptors are ubiquitously expressed. Moreover, ER and AR may have non-classical intracellular localizations, e.g. plasma membrane, mitochondria and endoplasmic reticulum, raising additional complexity to the functional roles of E2 and T. In addition to the modulation of gene transcription by direct interaction with their cognate nuclear receptors, the steroids can rapidly activate signaling pathways by a non-genomic mechanism mediated by receptors identical to or different from known steroid receptors. Among various functions, E2 and T can regulate apoptosis through those pathways. In mitochondria, the presence of ER and AR and actions of estrogen and androgen have been shown, in keeping with the organelle being a control point of apoptosis. The most recurrent action for each steroid hormone is the protection of mitochondria against different insults, resulting in antiapoptosis. This review summarizes the molecular basis of the modulation of programmed cell death by E2 and T in several tissues.

Paclitaxel induces apoptosis through activation of nuclear protein kinase C-δ and subsequent activation of Golgi associated Cdk1 in human hormone refractory prostate cancer

PURPOSE

Emerging evidence shows that the translocation of apoptosis related factors on cellular organelles, such as mitochondria, endoplasmic reticulum, Golgi apparatus and nucleus, has a crucial role in the apoptotic process. We characterized the effect of paclitaxel (Sigma®) on Golgi involved apoptosis in human hormone refractory prostate cancer.

MATERIALS AND METHODS

FACScan™ flow cytometric analysis was used to determine cell cycle distribution and the subG1 (apoptosis) population. Protein expression and localization were detected by Western blot, confocal microscopic examination and the sucrose gradient separation technique.

RESULTS

Paclitaxel induced Golgi apparatus disassembly and interaction between Golgi complexes and mitochondria. Discontinuous sucrose gradient fractionation was used to determine and collect Golgi containing fractions. Data revealed that paclitaxel induced an increase of Cdk1 activity and DR5 expression on the Golgi complex that was associated with increased cleavage of caspase-8, a DR5 downstream factor, and caspase-3 into catalytically active fragments. Data were validated by confocal immunofluorescence microscopy. Golgi associated effects were inhibited by the Cdk1 inhibitor roscovitine (Sigma), suggesting a critical role for Golgi-Cdk1. Also, paclitaxel caused an increase of nuclear but not of Golgi associated PKC-δ activity. The selective PKC-δ inhibitor rottlerin (Sigma) completely inhibited the increase of Golgi-Cdk1 activity, suggesting that nuclear PKC-δ served as an upstream regulator of Golgi-Cdk1.

CONCLUSIONS

Data suggest that paclitaxel induces nuclear translocation and activation of PKC-δ, which in turn causes Golgi-Cdk1 activation, leading to Golgi associated DR5 up-regulation, and caspase-8 and 3 activation. Golgi mediated signaling cascades facilitate mitochondria involved apoptotic pathways and at least partly explain the anticancer activity of paclitaxel action.

Redox state-dependent aggregation of mitochondria induced by cytochrome c

Cytochrome c is known to play central role in apoptosis. Here, it is shown that ferricytochrome c, but not ferrocytochrome c is able to directly induce the aggregation of rat liver mitochondria, similar to the effect caused by magnesium ions at high concentrations. The aggregation was revealed by a decrease in light dispersion of mitochondrial suspension and it was confirmed by the optical microscopy. In the medium containing NADH and cytochrome c, mitochondrial aggregation was initiated only after exhaustion of NADH leading to oxidation of cytochrome c. The aggregation induced by 30 μM ferricytochrome c, but not by 5 mM MgCl(2), was completely inhibited by 30-100 μM ferricyanide, thus indicating that ferricyanide-cytochrome c specific interaction prevents mitochondrial aggregation. After completion of the aggregation caused by ferricytochrome c, this effect cannot be readily reversed by subsequent reduction of cytochrome c. The aggregation induced by ferricytochrome c and/or magnesium ions explains masking of the external NADH-oxidase activity of mitochondria in vitro reported in the literature. This new cytochrome c redox state-dependent phenomenon might also be involved in more complex mechanisms controlling aggregation (clustering) of mitochondria in vivo under the influence of pro-apoptotic factors and requires further study.

TIG3 tumor suppressor-dependent organelle redistribution and apoptosis in skin cancer cells

TIG3 is a tumor suppressor protein that limits keratinocyte survival during normal differentiation. It is also important in cancer, as TIG3 level is reduced in tumors and in skin cancer cell lines, suggesting that loss of expression may be required for cancer cell survival. An important goal is identifying how TIG3 limits cell survival. In the present study we show that TIG3 expression in epidermal squamous cell carcinoma SCC-13 cells reduces cell proliferation and promotes morphological and biochemical apoptosis. To identify the mechanism that drives these changes, we demonstrate that TIG3 localizes near the centrosome and that pericentrosomal accumulation of TIG3 alters microtubule and microfilament organization and organelle distribution. Organelle accumulation at the centrosome is a hallmark of apoptosis and we demonstrate that TIG3 promotes pericentrosomal organelle accumulation. These changes are associated with reduced cyclin D1, cyclin E and cyclin A, and increased p21 level. In addition, Bax level is increased and Bcl-XL level is reduced, and cleavage of procaspase 3, procaspase 9 and PARP is enhanced. We propose that pericentrosomal localization of TIG3 is a key event that results in microtubule and microfilament redistribution and pericentrosomal organelle clustering and that leads to cancer cell apoptosis.

Involvement of BCL2 family members in the regulation of human oocyte and early embryo survival and death: gene expression and beyond

In women, up to 99.9% of the oocyte stockpile formed during fetal life is decimated by apoptosis. Apoptotic features are also detected in human preimplantation embryos both in vivo and in vitro. Despite the important consequences of cell death processes to oocyte competence and early embryonic development, little is known about its genetic and molecular control. B cell lymphoma-2 (BCL2) family proteins are major regulators of cell death and survival. Here, we present a literature review on BCL2 family expression and protein distribution in human and animal oocytes and early embryos. Most of the studies focused on the expression of two antagonistic members: the founding and survival family member BCL2 and its proapoptotic homolog BAX. However, recent transcriptomic analyses have identified novel candidate genes related to oocyte and/or early embryonic viability (such as BCL2L10) or commitment to apoptosis (e.g. BIK). Interestingly, some BCL2 proteins appear to be differentially distributed at the subcellular level during oocyte maturation and early embryonic development, a process probably linked to the functional compartmentalization of the ooplasm and blastomere. Assessment of BCL2 family involvement in regulating the survival of human oocytes and embryos may be of particular value for diagnosis and assisted reproductive technology. We suggest that implications of not only aberrant gene expression but also abnormal subcellular protein redistribution should be established in pathological conditions resulting in infertility.

Promotion of experimental thrombus formation by the procoagulant activity of breast cancer cells

The routine observation of tumor emboli in the peripheral blood of patients with carcinomas raises questions about the clinical relevance of these circulating tumor cells. Thrombosis is a common clinical manifestation of cancer, and circulating tumor cells may play a pathogenetic role in this process. The presence of coagulation-associated molecules on cancer cells has been described, but the mechanisms by which circulating tumor cells augment or alter coagulation remains unclear. In this study we utilized suspensions of a metastatic adenocarcinoma cell line, MDA-MB-231, and a non-metastatic breast epithelial cell line, MCF-10A, as models of circulating tumor cells to determine the thrombogenic activity of these blood-foreign cells. In human plasma, both metastatic MDA-MB-231 cells and non-metastatic MCF-10A cells significantly enhanced clotting kinetics. The effect of MDA-MB-231 and MCF-10A cells on clotting times was cell number-dependent and inhibited by a neutralizing antibody to tissue factor (TF) as well as inhibitors of activated factor X and thrombin. Using fluorescence microscopy, we found that both MDA-MB-231 and MCF-10A cells supported the binding of fluorescently labeled thrombin. Furthermore, in a model of thrombus formation under pressure-driven flow, MDA-MB-231 and MCF-10A cells significantly decreased the time to occlusion. Our findings indicate that the presence of breast epithelial cells in blood can stimulate coagulation in a TF-dependent manner, suggesting that tumor cells that enter the circulation may promote the formation of occlusive thrombi under shear flow conditions.

Post-translational myristoylation: Fat matters in cellular life and death

Myristoylation corresponds to the irreversible covalent linkage of the 14-carbon saturated fatty acid, myristic acid, to the N-terminal glycine of many eukaryotic and viral proteins. It is catalyzed by N-myristoyltransferase. Typically, the myristate moiety participates in protein subcellular localization by facilitating protein-membrane interactions as well as protein-protein interactions. Myristoylated proteins are crucial components of a wide variety of functions, which include many signalling pathways, oncogenesis or viral replication. Initially, myristoylation was described as a co-translational reaction that occurs after the removal of the initiator methionine residue. However, it is now well established that myristoylation can also occur post-translationally in apoptotic cells. Indeed, during apoptosis hundreds of proteins are cleaved by caspases and in many cases this cleavage exposes an N-terminal glycine within a cryptic myristoylation consensus sequence, which can be myristoylated. The principal objective of this review is to provide an overview on the implication of myristoylation in health and disease with a special emphasis on post-translational myristoylation. In addition, new advancements in the detection and identification of myristoylated proteins are also briefly reviewed.

The enhanced value of combining conventional and "omics" analyses in early assessment of drug-induced hepatobiliary injury

The InnoMed PredTox consortium was formed to evaluate whether conventional preclinical safety assessment can be significantly enhanced by incorporation of molecular profiling ("omics") technologies. In short-term toxicological studies in rats, transcriptomics, proteomics and metabolomics data were collected and analyzed in relation to routine clinical chemistry and histopathology. Four of the sixteen hepato- and/or nephrotoxicants given to rats for 1, 3, or 14days at two dose levels induced similar histopathological effects. These were characterized by bile duct necrosis and hyperplasia and/or increased bilirubin and cholestasis, in addition to hepatocyte necrosis and regeneration, hepatocyte hypertrophy, and hepatic inflammation. Combined analysis of liver transcriptomics data from these studies revealed common gene expression changes which allowed the development of a potential sequence of events on a mechanistic level in accordance with classical endpoint observations. This included genes implicated in early stress responses, regenerative processes, inflammation with inflammatory cell immigration, fibrotic processes, and cholestasis encompassing deregulation of certain membrane transporters. Furthermore, a preliminary classification analysis using transcriptomics data suggested that prediction of cholestasis may be possible based on gene expression changes seen at earlier time-points. Targeted bile acid analysis, based on LC-MS metabonomics data demonstrating increased levels of conjugated or unconjugated bile acids in response to individual compounds, did not provide earlier detection of toxicity as compared to conventional parameters, but may allow distinction of different types of hepatobiliary toxicity. Overall, liver transcriptomics data delivered mechanistic and molecular details in addition to the classical endpoint observations which were further enhanced by targeted bile acid analysis using LC/MS metabonomics.

Endosome-mitochondria juxtaposition during apoptosis induced by H. pylori VacA

The vacuolating cytotoxin (VacA) is an important virulence factor of Helicobacter pylori with pleiotropic effects on mammalian cells, including the ability to trigger mitochondria-dependent apoptosis. However, the mechanism by which VacA exerts its apoptotic function is unclear. Using a genetic approach, in this study we show that killing by VacA requires the proapoptotic Bcl-2 family members BAX and BAK at the mitochondrial level, but not adequate endoplasmic reticulum Ca²(+) levels, similarly controlled by BAX and BAK. A combination of subcellular fractionation and imaging shows that wild-type VacA, but not mutants in its channel-forming region, induces the accumulation of BAX on endosomes and endosome-mitochondria juxtaposition that precedes the retrieval of active BAX on mitochondria. It is noteworthy that in Bax- and Bak-deficient cells, VacA is unable to cause endosome-mitochondria juxtaposition and is not retrieved in mitochondria. Thus, VacA causes BAX/BAK-dependent juxtaposition of endosomes and mitochondria early in the process of cell death, revealing a new function for these proapoptotic proteins in the regulation of relative position of organelles.

Src-family kinase signaling, actin-mediated membrane trafficking and organellar dynamics in the control of cell fate: lessons to be learned from the adenovirus E4orf4 death factor

Evidence has accumulated that there are different modes of regulated cell death, which share overlapping signaling pathways. Cytoskeletal-dependent inter-organellar communication as a result of protein and lipid trafficking in and out of organelles has emerged as a common, key issue in the regulation of cell death modalities. The movement of proteins and lipids between cell compartments is believed to relay death signals in part through modifications of organelles dynamics. Little is known, however, regarding how trafficking is integrated within stress signaling pathways directing organelle-specific remodeling events. In this review, we discuss emerging evidence supporting a role for regulated changes in actin dynamics and intracellular membrane flow. Based on recent findings using the adenovirus E4orf4 death factor as a probing tool to tackle the mechanistic underpinnings that control alternative modes of cell death, we propose the existence of multifunctional platforms at the endosome-Golgi interface regulated by SFK-signaling. These endosomal platforms could be mobilized during cell activation processes to reorganize cellular membranes and promote inter-organelle signaling.

Akt and 14-3-3 control a PACS-2 homeostatic switch that integrates membrane traffic with TRAIL-induced apoptosis

TRAIL selectively kills diseased cells in vivo, spurring interest in this death ligand as a potential therapeutic. However, many cancer cells are resistant to TRAIL, suggesting the mechanism mediating TRAIL-induced apoptosis is complex. Here we identify PACS-2 as an essential TRAIL effector, required for killing tumor cells in vitro and virally infected hepatocytes in vivo. PACS-2 is phosphorylated at Ser437 in vivo, and pharmacologic and genetic studies demonstrate Akt is an in vivo Ser437 kinase. Akt cooperates with 14-3-3 to regulate the homeostatic and apoptotic properties of PACS-2 that mediate TRAIL action. Phosphorylated Ser437 binds 14-3-3 with high affinity, which represses PACS-2 apoptotic activity and is required for PACS-2 to mediate trafficking of membrane cargo. TRAIL triggers dephosphorylation of Ser437, reprogramming PACS-2 to promote apoptosis. Together, these studies identify the phosphorylation state of PACS-2 Ser437 as a molecular switch that integrates cellular homeostasis with TRAIL-induced apoptosis.

At the crossroads of homoeostasis and disease: roles of the PACS proteins in membrane traffic and apoptosis

The endomembrane system in mammalian cells has evolved over the past two billion years from a simple endocytic pathway in a single-celled primordial ancestor to complex networks supporting multicellular structures that form metazoan tissue and organ systems. The increased organellar complexity of metazoan cells requires additional trafficking machinery absent in yeast or other unicellular organisms to maintain organ homoeostasis and to process the signals that control proliferation, differentiation or the execution of cell death programmes. The PACS (phosphofurin acidic cluster sorting) proteins are one such family of multifunctional membrane traffic regulators that mediate organ homoeostasis and have important roles in diverse pathologies and disease states. This review summarizes our current knowledge of the PACS proteins, including their structure and regulation in cargo binding, their genetics, their roles in secretory and endocytic pathway traffic, interorganellar communication and how cell-death signals reprogramme the PACS proteins to regulate apoptosis. We also summarize our current understanding of how PACS genes are dysregulated in cancer and how viral pathogens ranging from HIV-1 to herpesviruses have evolved to usurp the PACS sorting machinery to promote virus assembly, viral spread and immunoevasion.