ER stress signaling has an activating transcription factor 6α (ATF6)-dependent "off-switch".

In response to an accumulation of unfolded proteins in the endoplasmic reticulum (ER) lumen, three ER transmembrane signaling proteins, inositol-requiring enzyme 1 (IRE1), PRKR-like ER kinase (PERK), and activating transcription factor 6α (ATF6α), are activated. These proteins initiate a signaling and transcriptional network termed the unfolded protein response (UPR), which re-establishes cellular proteostasis. When this restoration fails, however, cells undergo apoptosis. To investigate cross-talk between these different UPR enzymes, here we developed a high-content live cell screening platform to image fluorescent UPR-reporter cell lines derived from human SH-SY5Y neuroblastoma cells in which different ER stress signaling proteins were silenced through lentivirus-delivered shRNA constructs. We observed that loss of ATF6 expression results in uncontrolled IRE1-reporter activity and increases X box-binding protein 1 (XBP1) splicing. Transient increases in both IRE1 mRNA and IRE1 protein levels were observed in response to ER stress, suggesting that IRE1 up-regulation is a general feature of ER stress signaling and was further increased in cells lacking ATF6 expression. Moreover, overexpression of the transcriptionally active N-terminal domain of ATF6 reversed the increases in IRE1 levels. Furthermore, inhibition of IRE1 kinase activity or of downstream JNK activity prevented an increase in IRE1 levels during ER stress, suggesting that IRE1 transcription is regulated through a positive feed-forward loop. Collectively, our results indicate that from the moment of activation, IRE1 signaling during ER stress has an ATF6-dependent "off-switch."

Endoplasmic reticulum stress-mediated upregulation of miR-29a enhances sensitivity to neuronal apoptosis.

Disturbance of homeostasis within the endoplasmic reticulum (ER) lumen leads to the accumulation of unfolded and misfolded proteins. This results in the activation of an evolutionary conserved stress response termed ER stress that, if unresolved, induces apoptosis. Previously the Bcl-2 homology domain 3-Only Protein Puma was identified as a mediator of ER stress-induced apoptosis in neurons. In the search of alternative contributors to ER stress-induced apoptosis, a downregulation of the anti-apoptotic Bcl-2 family protein Mcl-1 was noted during ER stress in both mouse cortical neurons and human SH-SY5Y neuroblastoma cells. Downregulation of Mcl-1 was associated with an upregulation of microRNA-29a (miR-29a) expression, and subsequent experiments showed that miR-29a targeted the 3'-untranslated region of the anti-apoptotic Bcl-2 family protein, Mcl-1. Inhibition of miR-29a expression using sequence-specific antagomirs or the overexpression of Mcl-1 decreased cell death following tunicamycin treatment, while gene silencing of Mcl-1 increased cell death. miR-29a did not alter the signalling branches of the ER stress response, rather its expression was controlled by the ER stress-induced transcription factor activating-transcription-factor-4 (ATF4). The current data demonstrate that the ATF4-mediated upregulation of miR-29a enhances the sensitivity of neurons to ER stress-induced apoptosis.

Single-cell imaging of the heat-shock response in colon cancer cells suggests that magnitude and length rather than time of onset determines resistance to apoptosis.

Targeting the proteasome is a valuable approach for cancer therapy, potentially limited by pro-survival pathways that are induced in parallel to cell death. Whether these pro-survival pathways are activated in all cells, show different activation kinetics in sensitive versus resistant cells or interact functionally with cell death pathways is unknown. We monitored activation of the heat-shock response (HSR), a key survival pathway induced by proteasome inhibition, relative to apoptosis activation in HCT116 colon cancer cells expressing enhanced green fluorescent protein (EGFP) under the control of the HSP70 promoter. Single-cell and high-content time-lapse imaging of epoxomicin treatment revealed that neither basal activity nor the time of onset of the HSR differed between resistant and sensitive populations. However, resistant cells had significantly higher and prolonged reporter activity than those that succumbed to cell death. p53 deficiency protected against cell death but failed to modulate the HSR. By contrast, inhibition of the HSR significantly increased the cytotoxicity of epoxomicin. Our data provide novel insights into the kinetics and heterogeneity of the HSR during proteasome inhibition, suggesting that the HSR modulates cell death signalling unidirectionally.

Calnexin, an ER stress-induced protein, is a prognostic marker and potential therapeutic target in colorectal cancer.

BACKGROUND: Colorectal cancer (CRC) is a leading cause of cancer mortality in the Western world and commonly treated with genotoxic chemotherapy. Stress in the endoplasmic reticulum (ER) was implicated to contribute to chemotherapeutic resistance. Hence, ER stress related protein may be of prognostic or therapeutic significance. METHODS: The expression levels of ER stress proteins calnexin, calreticulin, GRP78 and GRP94 were determined in n = 23 Stage II and III colon cancer fresh frozen tumour and matched normal tissue samples. Data were validated in a cohort of n = 11 rectal cancer patients treated with radiochemotherapy in the neoadjuvant setting. The calnexin gene was silenced using siRNA in HCT116 cells. RESULTS: There were no increased levels of ER stress proteins in tumour compared to matched normal tissue samples in Stage II or III CRC. However, increased calnexin protein levels were predictive of poor clinical outcome in the patient cohort. Data were validated in the rectal cancer cohort treated in the neoadjuvant setting. Calnexin gene-silencing significantly reduced cell survival and increased cancer cell susceptibility to 5FU chemotherapy. CONCLUSION: Increased tumour protein levels of calnexin may be of prognostic significance in CRC, and calnexin may represent a potential target for future therapies.

CHOP regulates the p53-MDM2 axis and is required for neuronal survival after seizures.

Hippocampal sclerosis is a frequent pathological finding in patients with temporal lobe epilepsy and can be caused by prolonged single or repeated brief seizures. Both DNA damage and endoplasmic reticulum stress have been implicated as underlying molecular mechanisms in seizure-induced brain injury. The CCAAT/enhancer-binding protein homologous protein (CHOP) is a transcriptional regulator induced downstream of DNA damage and endoplasmic reticulum stress, which can promote or inhibit apoptosis according to context. Recent work has proposed inhibition of CHOP as a suitable neuroprotective strategy. Here, we show that transcript and protein levels of CHOP increase in surviving subfields of the hippocampus after prolonged seizures (status epilepticus) in mouse models. CHOP was also elevated in the hippocampus from epileptic mice and patients with pharmacoresistant epilepsy. The hippocampus of CHOP-deficient mice was much more vulnerable to damage in mouse models of status epilepticus. Moreover, compared with wild-type animals, CHOP-deficient mice subject to status epilepticus developed more spontaneous seizures, displayed protracted hippocampal neurodegeneration and a deficit in a hippocampus-dependent object-place recognition task. The absence of CHOP was associated with a supra-maximal induction of p53 after status epilepticus, and inhibition of p53 abolished the cell death-promoting consequences of CHOP deficiency. The protective effect of CHOP could be partly explained by activating transcription of murine double minute 2 that targets p53 for degradation. These data demonstrate that CHOP is required for neuronal survival after seizures and caution against inhibition of CHOP as a neuroprotective strategy where excitotoxicity is an underlying pathomechanism.

Motoneurons secrete angiogenin to induce RNA cleavage in astroglia.

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disorder affecting motoneurons. Mutations in angiogenin, encoding a member of the pancreatic RNase A superfamily, segregate with ALS. We previously demonstrated that angiogenin administration shows promise as a neuroprotective therapeutic in studies using transgenic ALS mice and primary motoneuron cultures. Its mechanism of action and target cells in the spinal cord, however, are largely unknown. Using mixed motoneuron cultures, motoneuron-like NSC34 cells, and primary astroglia cultures as model systems, we here demonstrate that angiogenin is a neuronally secreted factor that is endocytosed by astroglia and mediates neuroprotection in paracrine. We show that wild-type angiogenin acts unidirectionally to induce RNA cleavage in astroglia, while the ALS-associated K40I mutant is also secreted and endocytosed, but fails to induce RNA cleavage. Angiogenin uptake into astroglia requires heparan sulfate proteoglycans, and engages clathrin-mediated endocytosis. We show that this uptake mechanism exists for mouse and human angiogenin, and delivers a functional RNase output. Moreover, we identify syndecan 4 as the angiogenin receptor mediating the selective uptake of angiogenin into astroglia. Our data provide new insights into the paracrine activities of angiogenin in the nervous system, and further highlight the critical role of non-neuronal cells in the pathogenesis of ALS.

'Mild mitochondrial uncoupling' induced protection against neuronal excitotoxicity requires AMPK activity.

The preconditioning response conferred by a mild uncoupling of the mitochondrial membrane potential (Δψ(m)) has been attributed to altered reactive oxygen species (ROS) production and mitochondrial Ca(2+) uptake within the cells. Here we have explored if altered cellular energetics in response to a mild mitochondrial uncoupling stimulus may also contribute to the protection. The addition of 100 nM FCCP for 30 min to cerebellar granule neurons (CGNs) induced a transient depolarization of the Δψ(m), that was sufficient to significantly reduce CGN vulnerability to the excitotoxic stimulus, glutamate. On investigation, the mild mitochondrial 'uncoupling' stimulus resulted in a significant increase in the plasma membrane levels of the glucose transporter isoform 3, with a hyperpolarisation of Δψ(m) and increased cellular ATP levels also evident following the washout of FCCP. Furthermore, the phosphorylation state of AMP-activated protein kinase (AMPK) (Thr 172) was increased within 5 min of the uncoupling stimulus and elevated up to 1h after washout. Significantly, the physiological changes and protection evident after the mild uncoupling stimulus were lost in CGNs when AMPK activity was inhibited. This study identifies an additional mechanism through which protection is mediated upon mild mitochondrial uncoupling: it implicates increased AMPK signalling and an adaptive shift in energy metabolism as mediators of the preconditioning response associated with FCCP-induced mild mitochondrial uncoupling.

AMP-activated protein kinase (AMPK)-induced preconditioning in primary cortical neurons involves activation of MCL-1.

Neuronal preconditioning is a phenomenon where a previous exposure to a sub-lethal stress stimulus increases the resistance of neurons towards a second, normally lethal stress stimulus. Activation of the energy stress sensor, AMP-activated protein kinase (AMPK) has been shown to contribute to the protective effects of ischaemic and mitochondrial uncoupling-induced preconditioning in neurons, however, the molecular basis of AMPK-mediated preconditioning has been less well characterized. We investigated the effect of AMPK preconditioning using 5-aminoimidazole-4-carboxamide riboside (AICAR) in a model of NMDA-mediated excitotoxic injury in primary mouse cortical neurons. Activation of AMPK with low concentrations of AICAR (0.1 mM for 2 h) induced a transient increase in AMPK phosphorylation, protecting neurons against NMDA-induced excitotoxicity. Analysing potential targets of AMPK activation, demonstrated a marked increase in mRNA expression and protein levels of the anti-apoptotic BCL-2 family protein myeloid cell leukaemia sequence 1 (MCL-1) in AICAR-preconditioned neurons. Interestingly, over-expression of MCL-1 protected neurons against NMDA-induced excitotoxicity while MCL-1 gene silencing abolished the effect of AICAR preconditioning. Monitored intracellular Ca²âº levels during NMDA excitation revealed that MCL-1 over-expressing neurons exhibited improved bioenergetics and markedly reduced Ca²âº elevations, suggesting a potential mechanism through which MCL-1 confers neuroprotection. This study identifies MCL-1 as a key effector of AMPK-induced preconditioning in neurons.

Clinical application of a systems model of apoptosis execution for the prediction of colorectal cancer therapy responses and personalisation of therapy.

OBJECTIVE: Key to the clinical management of colorectal cancer is identifying tools which aid in assessing patient prognosis and determining more effective and personalised treatment strategies. We evaluated whether an experimental systems biology strategy which analyses the susceptibility of cancer cells to undergo caspase activation can be exploited to predict patient responses to 5-fluorouracil-based chemotherapy and to case-specifically identify potential alternative targeted treatments to reactivate apoptosis. DESIGN: We quantified five essential apoptosis-regulating proteins (Pro-Caspases 3 and 9, APAF-1, SMAC and XIAP) in samples of Stage II (n = 13) and III (n=17) tumour and normal colonic (n = 8) tissue using absolute quantitative immunoblotting and employed systems simulations of apoptosis signalling to predict the susceptibility of tumour cells to execute apoptosis. Additional systems analyses assessed the efficacy of novel apoptosis-inducing therapeutics such as XIAP antagonists, proteasome inhibitors and Pro-Caspase-3-activating compounds in restoring apoptosis execution in apoptosis-incompetent tumours. RESULTS: Comparisons of caspase activity profiles demonstrated that the likelihood of colorectal tumours to undergo apoptosis decreases with advancing disease stage. Systems-level analysis correctly predicted positive or negative outcome in 85% (p=0.004) of colorectal cancer patients receiving 5-fluorouracil based chemotherapy and significantly outperformed common uni- and multi-variate statistical approaches. Modelling of individual patient responses to novel apoptosis-inducing therapeutics revealed markedly different inter-individual responses. CONCLUSIONS: Our study represents the first proof-of-concept example demonstrating the significant clinical potential of systems biology-based approaches for predicting patient outcome and responsiveness to novel targeted treatment paradigms.

Bone morphogenetic protein 3 controls insulin gene expression and is down-regulated in INS-1 cells inducibly expressing a hepatocyte nuclear factor 1A-maturity-onset diabetes of the young mutation.

Inactivating mutations in the transcription factor hepatocyte nuclear factor (HNF) 1A cause HNF1A-maturity-onset diabetes of the young (HNF1A-MODY), the most common monogenic form of diabetes. To examine HNF1A-MODY-induced defects in gene expression, we performed a microarray analysis of the transcriptome of rat INS-1 cells inducibly expressing the common hot spot HNF1A frameshift mutation, Pro291fsinsC-HNF1A. Real-time quantitative PCR (qPCR), Western blotting, immunohistochemistry, reporter assays, and chromatin immunoprecipitation (ChIP) were used to validate alterations in gene expression and to explore biological activities of target genes. Twenty-four hours after induction of the mutant HNF1A protein, we identified a prominent down-regulation of the bone morphogenetic protein 3 gene (Bmp-3) mRNA expression. Reporter assays, qPCR, and Western blot analysis validated these results. In contrast, inducible expression of wild-type HNF1A led to a time-dependent increase in Bmp-3 mRNA and protein levels. Moreover, reduced protein levels of BMP-3 and insulin were detected in islets of transgenic HNF1A-MODY mice. Interestingly, treatment of naïve INS-1 cells or murine organotypic islet cultures with recombinant human BMP-3 potently increased their insulin levels and restored the decrease in SMAD2 phosphorylation and insulin gene expression induced by the HNF1A frameshift mutation. Our study suggests a critical link between HNF1A-MODY-induced alterations in Bmp-3 expression and insulin gene levels in INS-1 cells and indicates that the reduced expression of growth factors involved in tissue differentiation may play an important role in the pathophysiology of HNF1A-MODY.

Analyzing proteasomal subunit expression reveals Rpt4 as a prognostic marker in stage II colorectal cancer.

Colorectal cancer is a leading cause of cancer-related deaths worldwide. Early diagnosis and treatment of colorectal cancer is the key to improving survival rates and as such a need exists to identify patients who may benefit from adjuvant chemotherapy. The dysregulation of the ubiquitin-proteasome system (UPS) has been implicated in oncogenesis and cancer cell survival, and proteasome inhibitors are in clinical use for a number of malignancies including multiple myeloma. In our study, we examined the protein expression of several key components of the UPS in colorectal cancer using immunohistochemistry to determine expression levels of ubiquitinylated proteins and the proteasomal subunits, 20S core and Rpt4 in a cohort of 228 patients with colon cancer. Multivariate Cox analysis revealed that neither the intensity of either ubiquitinylated proteins or the 20S core was predictive in either Stage II or III colon cancer for disease free survival or overall survival. In contrast, in Stage II patients increased Rpt4 staining was significantly associated with disease free survival (Cox proportional hazard ratio 0.605; p = 0.0217). Our data suggest that Rpt4 is an independent prognostic variable for Stage II colorectal cancer and may aid in the decision of which patients undergo adjuvant chemotherapy.

Activity of protein kinase CK2 uncouples Bid cleavage from caspase-8 activation.

In the present study, we quantitatively analysed the interface between apoptosis initiation and execution by determining caspase-8 activation, Bid cleavage and mitochondrial engagement (onset of mitochondrial depolarisation) in individual HeLa cervical cancer cells following exposure to tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL). Employing resonance-energy-transfer probes containing either the caspase-8 recognition site IETD or full-length Bid, we observed a significant delay between the times of caspase-8 activation and Bid cleavage, suggesting the existence of control steps separating these two processes. Subsequent analyses suggested that the divergence of caspase-8 activation and Bid cleavage are critically controlled by kinase signalling: inhibiting protein kinase CK2 by using 5,6-dichloro-l-(beta-D-ribofuranosyl-1)-benzimidazole (DRB) or by overexpression of a dominant-negative CK2alpha catalytic subunit largely eliminated the lag time between caspase-8 activation and Bid cleavage. We conclude that caspase-8 activation and Bid cleavage are temporally uncoupled events, providing transient tolerance to caspase-8 activities.

AMP-activated protein kinase mediates apoptosis in response to bioenergetic stress through activation of the pro-apoptotic Bcl-2 homology domain-3-only protein BMF.

Heterozygous loss-of-function mutations in the hepatocyte nuclear factor 1A (HNF1A) gene result in the pathogenesis of maturity-onset diabetes-of-the-young type 3, (HNF1A-MODY). This disorder is characterized by a primary defect in metabolism-secretion coupling and decreased beta cell mass, attributed to excessive beta cell apoptosis. Here, we investigated the link between energy stress and apoptosis activation following HNF1A inactivation. This study employed single cell fluorescent microscopy, flow cytometry, gene expression analysis, and gene silencing to study the effects of overexpression of dominant-negative (DN)-HNF1A expression on cellular bioenergetics and apoptosis in INS-1 cells. Induction of DN-HNF1A expression led to reduced ATP levels and diminished the bioenergetic response to glucose. This was coupled with activation of the bioenergetic stress sensor AMP-activated protein kinase (AMPK), which preceded the onset of apoptosis. Pharmacological activation of AMPK using aminoimidazole carboxamide ribonucleotide (AICAR) was sufficient to induce apoptosis in naive cells. Conversely, inhibition of AMPK with compound C or AMPKα gene silencing protected against DN-HNF1A-induced apoptosis. Interestingly, AMPK mediated the induction of the pro-apoptotic Bcl-2 homology domain-3-only protein Bmf (Bcl-2-modifying factor). Bmf expression was also elevated in islets of DN-HNF1A transgenic mice. Furthermore, knockdown of Bmf expression in INS-1 cells using siRNA was sufficient to protect against DN-HNF1A-induced apoptosis. Our study suggests that overexpression of DN-HNF1A induces bioenergetic stress and activation of AMPK. This in turn mediates the transcriptional activation of the pro-apoptotic Bcl-2-homology protein BMF, coupling prolonged energy stress to apoptosis activation.

Bcl-2 homology domain 3-only proteins Puma and Bim mediate the vulnerability of CA1 hippocampal neurons to proteasome inhibition in vivo.

Bcl-2 homology domain 3 (BH3)-only proteins are pro-apoptotic Bcl-2 family members that play important roles in upstream cell death signalling during apoptosis. Proteasomal stress has been shown to contribute to the pathology of cerebral ischaemia and many neurodegenerative disorders. Here we explored the contribution of BH3-only proteins in mediating proteasome-inhibition-induced apoptosis in the murine brain in vivo. Stereotactic intrahippocampal microinjection of the selective proteasome inhibitor epoxomicin (2.5 nmol) induced a delayed apoptosis within only the CA1 hippocampal neurons and not neurons within the CA3 or dentate gyrus regions, a selective vulnerability similar to that seen during ischaemia. This injury developed over a time-course of 3 days and was characterized by positive terminal deoxynucleotidyl transferase dUTP nick end labelling staining and nuclear condensation. Previous work from our laboratory has identified the BH3-only protein p53-upregulated mediator of apoptosis (Puma) as mediating proteasome-inhibition-induced apoptosis in cultured neural cells. Genetic deletion of puma reduced the number of terminal deoxynucleotidyl transferase dUTP nick end labelling-positive cells within the CA1 following epoxomicin microinjection but it did not provide a complete protection. Subsequent studies identified the BH3-only protein Bim as also being upregulated during proteasome inhibition in organotypic hippocampal slice cultures and after epoxomicin treatment in vivo. Interestingly, the genetic deletion of bim also afforded significant neuroprotection, although this protection was less pronounced. In summary, we demonstrate that the BH3-only proteins Puma and Bim mediate the delayed apoptosis of CA1 hippocampal neurons induced by proteasome inhibition in vivo, and that either BH3-only protein can only partly compensate for the deficiency of the other.

Reduced hippocampal damage and epileptic seizures after status epilepticus in mice lacking proapoptotic Puma.

The functional significance of neuronal death for pathogenesis of epilepsy and the underlying molecular mechanisms thereof remain incompletely understood. The p53 transcription factor has been implicated in seizure damage, but its target genes and the influence of cell death under its control on epilepsy development are unknown. In the present study, we report that status epilepticus (SE) triggered by intra-amygdala kainic acid in mice causes rapid p53 accumulation and subsequent hippocampal damage. Expression of p53-up-regulated mediator of apoptosis (Puma), a proapoptotic Bcl-2 homology domain 3-only protein under p53 control, was increased within a few hours of SE. Induction of Puma was blocked by pharmacologic inhibition of p53, and hippocampal damage was also reduced. Puma induction was also blocked in p53-deficient mice subject to SE. Compared to Puma-expressing mice, Puma-deficient mice had significantly smaller hippocampal lesions after SE. Long-term, continuous telemetric EEG monitoring revealed a approximately 60% reduction in the frequency of epileptic seizures in the Puma-deficient mice compared to Puma-expressing mice. These are the first data showing genetic deletion of a proapoptotic protein acting acutely to influence neuronal death subsequently alters the phenotype of epilepsy in the long-term, supporting the concept that apoptotic pathway activation is a trigger of epileptogenesis.-Engel, T., Murphy, B. M., Hatazaki, S., Jimenez-Mateos, E. M., Concannon, C. G., Woods, I., Prehn, J. H. M., Henshall, D. C. Reduced hippocampal damage and epileptic seizures after status epilepticus in mice lacking proapoptotic Puma.

Regulation of glucose transporter 3 surface expression by the AMP-activated protein kinase mediates tolerance to glutamate excitation in neurons.

Ischemic and excitotoxic events within the brain result in rapid and often unfavorable depletions in neuronal energy levels. Here, we investigated the signaling pathways activated in response to the energetic stress created by transient glutamate excitation in cerebellar granule neurons. We characterized a glucose dependent hyperpolarization of the mitochondrial membrane potential (Delta psi(m)) in the majority of neurons after transient glutamate excitation. Expression levels of the primary neuronal glucose transporters (GLUTs) isoforms 1, 3, 4, and 8 were found to be unaltered within a 24 h period after excitation. However, a significant increase only in GLUT3 surface expression was identified 30 min after excitation, with this high surface expression remaining significantly above control levels in many neurons for up to 4 h. Glutamate excitation induced a rapid alteration in the AMP:ATP ratio that was associated with the activation of the AMP-activated protein kinase (AMPK). Interestingly, pharmacological activation of AMPK with AICAR (5-aminoimidazole-4-carboxamide riboside) alone also increased GLUT3 surface expression, with a hyperpolarization of Delta psi(m) evident in many neurons. Notably, inhibition of the CaMKK (calmodulin-dependent protein kinase kinase) had little affect on GLUT translocation, whereas the inhibition or knockdown of AMPK (compound C, siRNA) activity prevented GLUT3 translocation to the cell surface after glutamate excitation. Furthermore, gene silencing of GLUT3 eradicated the increase in Delta psi(m) associated with transient glutamate excitation and potently sensitized neurons to excitotoxicity. In summary, our data suggest that the activation of AMPK and its regulation of cell surface GLUT3 expression is critical in mediating neuronal tolerance to excitotoxicity.

Differential expression patterns of Puma and Hsp70 following proteasomal stress in the hippocampus are key determinants of neuronal vulnerability.

Proteasomal stress is believed to contribute to the pathology of ischemic brain injury and several neurodegenerative disorders, but can activate both cytoprotective and cell death-inducing pathways. Here we have utilized the complex environment of organotypic hippocampal slice cultures (OHSCs) to investigate the stress responses activated in different neuronal populations following proteasome inhibition. Incubation of OHSCs with the specific proteasome inhibitors, epoxomicin or bortezomib led to a selective injury of the CA1 pyramidal neurons although similarly increased levels of poly-ubiquitinylated proteins were detected throughout all regions of the hippocampus. Micro-dissection, quantitative PCR and immunohistochemical analyses of epoxomicin-treated OHSCs identified a selective activation of cytoprotective genes in non-vulnerable regions, and a selective activation of p53 target genes within the CA1. Genetic deletion of the pro-apoptotic p53 target gene, p53-upregulated modulator of apoptosis (puma), significantly reduced injury within the CA1 following proteasomal inhibition. Activation of cytoprotective genes by treatment with inducers of heat shock protein 70 inhibited the selective activation of p53 signaling within the CA1 and protected CA1 neurons from epoxomicin-induced cell death. In summary, we demonstrate that the reciprocal activation of p53/p53-upregulated modulator of apoptosis and heat shock protein 70 signalling determines the selective vulnerability of neurons to proteasome inhibition.

The amyloid precursor protein intracellular domain(AICD) disrupts actin dynamics and mitochondrial bioenergetics.

The amyloid precursor protein (APP) is critically involved in the pathogenesis of Alzheimer's disease, and is strongly up-regulated in response to traumatic, metabolic, or toxic insults to the nervous system. The processing of APP by gamma/epsilon-secretase activity results in the generation of the APP intracellular domain (AICD). Previously, we have shown that AICD induces the expression of genes (transgelin, alpha2-actin) with functional roles in actin organization and dynamics and demonstrated that the induction of AICD and its co-activator Fe65 (AICD/Fe65) resulted in a loss of organized filamentous actin structures within the cell. As mitochondrial function is thought to be reliant on ordered actin dynamics, we examined mitochondrial function in human SHEP neuroblastoma cells inducibly expressing AICD/Fe65. Confocal analysis of the mitochondrial membrane potential (DeltaPsim) identified a significant decrease in the DeltaPsim in the AICD50/Fe65 over-expressing cells. This was paralleled by significantly reduced ATP levels and decreased basal superoxide production. Overexpression of the proposed AICD target gene transgelin in SHEP-SF parental cells and primary neurons was sufficient to destabilize actin filaments, depolarize DeltaPsim, and significantly alter mitochondrial distribution and morphology. Our data demonstrate that the induction of AICD/Fe65 or transgelin significantly alters actin dynamics and mitochondrial function in neuronal cells.

Modulation of gene expression and cytoskeletal dynamics by the amyloid precursor protein intracellular domain (AICD).

Amyloidogenic processing of the amyloid precursor protein (APP) results in the generation of beta-amyloid, the main constituent of Alzheimer plaques, and the APP intracellular domain (AICD). Recently, it has been demonstrated that AICD has transactivation potential; however, the targets of AICD-dependent gene regulation and hence the physiological role of AICD remain largely unknown. We analyzed transcriptome changes during AICD-dependent gene regulation by using a human neural cell culture system inducible for expression of AICD, its coactivator FE65, or the combination of both. Induction of AICD was associated with increased expression of genes with known function in the organization and dynamics of the actin cytoskeleton, including alpha2-Actin and Transgelin (SM22). AICD target genes were also found to be differentially regulated in the frontal cortex of Alzheimer's disease patients compared with controls as well as in AICD/FE65 transiently transfected murine cortical neurons. Confocal image analysis of neural cells and cortical neurons expressing both AICD and FE65 confirmed pronounced changes in the organization of the actin cytoskeleton, including the destabilization of actin fibers and clumping of actin at the sites of cellular outgrowth. Our data point to a role of AICD in developmental and injury-related cytoskeletal dynamics in the nervous system.