Cytosolic prion protein induces apoptosis in human neuronal cell SH-SY5Y via mitochondrial disruption pathway

Prion protein-dependent regulation of p53-MDM2 crosstalk during endoplasmic reticulum stress and doxorubicin treatments might be essential for cell fate in human breast cancer cell line, MCF-7

In this study, we investigated the effect of doxorubicin and tunicamycin treatment alone or in combination on MDM-, Cul9-and prion protein (PrP)-mediated subcellular regulation of p53 in the context of apoptosis and autophagy. MTT analysis was performed to determine the cytotoxic effect of the agents. Apoptosis was monitorized by ELISA, flow cytometry and JC-1 assay. Monodansylcadaverine assay was performed for autophagy. Western blotting and immunofluorescence were performed to determine p53, MDM2, CUL9 and PrP levels. Doxorubicin increased p53, MDM2 and CUL9 levels in a dose-dependent manner. Expression of p53 and MDM2 was higher at the 0.25 μM concentration of tunicamycin compared to the control, but it decreased at 0.5 μM and 1 μM concentrations. CUL9 expression was significantly decreased only after treatment of tunicamycin at 0.25 μM. According to its glycosylation status, the upper band of PrP increased only in combination treatment. In combination treatment, p53 expression was higher than control, whereas MDM2 and CUL9 expressions were decreased. Combination treatments may make MCF-7 cells more susceptible to apoptosis rather than autophagy. In conclusion, PrP may be important in determining the fate of cell death through crosstalk between proteins such as p53 and MDM2 under endoplasmic reticulum (ER) stress conditions. Further studies are needed to obtain in-depth information on these potential molecular networks.

Extensive Disturbances of Intracellular Components and Dysfunctions of Biological Pathways in the Brain Tissues During Prion Infection - China's Studies

The study describes some of the major findings of changes in intracellular components and biological pathways in the brain during prion infection and hypothesizes some important physiological and pathological approaches mainly based on our studies. Omics techniques analysis of messenger RNA (mRNA) and proteins were carried out in the study. Meanwhile, Western blot, immunohistochemistry, and immunofluorescence were used for protein analysis in different signaling pathways. Statistical analyses were used to describe the protein differences in signaling pathways of infected and normal samples. This report reviewed and summarized our studies on the aberrant changes in intracellular components and biological functions in the brains of prion disease (PrD). Omics analyses proposed extensive abnormal alterations of brain mRNAs transcriptions, protein expressions, and post-translational modifications. The molecular disturbances for microtubule instability and depolymerization, the dysregulations of different signals related with neuron loss and synaptic plasticity, the abnormalities of mitochondrial and endoplasmic reticulum stress, and disturbance of intracellular reactive oxygen species homeostasis during prion infection were precisely analyzed and reviewed. Aberrant disturbances of numerous biological molecules and signals in brain tissues were found during prion infection.

Prion Protein Protects Cancer Cells against Endoplasmic Reticulum Stress Induced Apoptosis

Unfolded protein response (UPR) is an adaptive reaction for cells to reduce endoplasmic reticulum (ER) stress. In many types of cancers, such as lung cancer and pancreatic cancer, cancer cells may harness ER stress to facilitate their survival and growth. Prion protein (PrP) is a glycosylated cell surface protein that has been shown to be up-regulated in many cancer cells. Since PrP is a protein prone to misfolding, ER stress can result in under-glycosylated PrP, which in turn may activate ER stress. To assess whether ER stress leads to the production of under-glycosylated PrP and whether under-glycosylated PrP may contribute to ER stress thus leading to cancer cell apoptosis, we treated different cancer cells with brefeldin A (BFA), thapsigargin (Thps), and tunicamycin (TM). We found that although BFA, Thps, and TM treatment activated UPR, only ATF4 was consistently activated by these reagents, but not other branches of ER stress. However, the canonical PERK-eIF2α-ATF4 did not account for the observed activation of ATF4 in lung cancer cells. In addition, BFA, but neither Thps nor TM, significantly stimulated the expression of cytosolic PrP. Finally, we found that the levels of PrP contributed to anti-apoptosis activity of BFA-induced cancer cell death. Thus, the pathway of BFA-induced persistent ER stress may be targeted for lung and pancreatic cancer treatment.

Exercise protects against diabetic cardiomyopathy by the inhibition of the endoplasmic reticulum stress pathway in rats

To explore the protective effect of exercise training on the injury of myocardium tissues induced by streptozotocin (STZ) in diabetic rats and the relationship with endoplasmic reticulum stress (ERS), the male sprague‐dawley (SD) rats were fed with high‐fat and high‐sugar diet for 4 weeks, followed by intraperitoneal injection of STZ, 40 mg/kg, to establish a diabetes model, and then 10 rats were randomly selected as diabetes mellitus (DM) controls and 20 eligible diabetic rats were randomized into two groups: low‐intensity exercise training (n = 10) and high‐intensity exercise training (n = 10). After 12 weeks of exercise training, rats were killed and serum samples were used to determine cardiac troponin‐I (cTn‐I). Myocardial tissues were sampled for morphological analysis to detect myocardial cell apoptosis, and to analyze protein expression of glucose‐regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), and caspase‐12. Different intensities (low and high) significantly reduced serum cTn‐I levels compared with the DCM group (p < 0.01), and significantly reduced the percentage of apoptotic myocardial cells and improved the parameters of cardiac function. Hematoxylin and eosin and Masson staining indicated that exercise training could attenuate myocardial apoptosis. Additionally, exercise training significantly reduced GRP78, CHOP, and cleaved caspase‐12 protein expression in an intensity‐dependent manner. These findings suggest that exercise appeared to ameliorate diabetic cardiomyopathy by inhibiting endoplasmic reticulum stress‐induced apoptosis in diabetic rats.

Do prion protein gene polymorphisms induce apoptosis in non-mammals?

Genetic variations such as single nucleotide polymorphisms (SNPs) in prion protein coding gene, Prnp, greatly affect susceptibility to prion diseases in mammals. Here, the coding region of Prnp was screened for polymorphisms in redeared turtle, Trachemys scripta. Four polymorphisms, L203V, N205I, V225A and M237V, were common in 15 out of 30 turtles; in one sample, three SNPs, L203V, N205I and M237V, and in the remaining 14 samples, only L203V and N205I polymorphisms, were investigated. Besides, C658T, C664T, C670A and C823A SNPs were silent mutations. To elucidate the relationship between the SNPs and apoptosis, TUNEL assays and active caspase-3 immunodetection techniques in brain sections of the polymorphic samples were performed. The results revealed that TUNEL-positive cells and active caspase-3-positive cells in the turtles with four polymorphisms were significantly increased compared with those of the turtles with two polymorphisms (P less than 0.01 and P less than 0.05, respectively). In conclusion, this study provides preliminary information about the possible relationship between SNPs within the Prnp locus and apoptosis in a non-mammalian species, Trachemys scripta, in which prion disease has never been reported.

Downregulation of Pygopus 2 inhibits vascular mimicry in glioma U251 cells by suppressing the canonical Wnt signaling pathway

Gliomas are the most common type of malignant primary brain tumor, and the Wnt signaling pathway is associated with glioma malignancy. Pygopus protein plays an important role in developmental brain patterning, and has been identified to be a component of the Wnt signaling pathway. In the present study, the Pygopus 2 (Pygo2) protein was examined in 80 glioma tissue samples. Short hairpin (sh)RNA-Pygo2 was transfected into glioma U251 cells, and the cell proliferation, colony formation and bromodeoxyuridine (BrdU) incorporation were analyzed. Western blot analysis and reverse transcription-polymerase chain reaction were used to detect the expression of Pygo2. A vascular mimicry assay was performed to examine the vascular mimicry of U251 cells. A luciferase reporter assay was used to detect the β-catenin/Wnt system. The cyclin D1 protein was also detected using western blot analysis. The results demonstrated that inhibition of the expression of Pygo2 significantly triggered the decrease of cell proliferation, colony formation and BrdU incorporation compared with the cells treated with scramble control shRNA (shRNA-Scr). shRNA-Pygo2 transfection was found to inhibit vascular-mimicry and block the Wnt signaling pathway compared to the cells transfected with shRNA-Scr. The transfection of shRNA-Pygo2 also decreased the expression of the Wnt target gene cyclin D1. In conclusion, shRNA-Pygo2 suppressed glioma cell proliferation effectively and inhibited vascular mimicry by inhibiting the expression of cyclin D1 in the canonical Wnt/β-catenin pathway in brain glioma cells.

Antioxidant peroxiredoxin 6 protein rescues toxicity due to oxidative stress and cellular hypoxia in vitro, and attenuates prion-related pathology in vivo

Protein misfolding, mitochondrial dysfunction and oxidative stress are common pathomechanisms that underlie neurodegenerative diseases. In prion disease, central to these processes is the post-translational transformation of cellular prion protein (PrP(c)) to the aberrant conformationally altered isoform; PrP(Sc). This can trigger oxidative reactions and impair mitochondrial function by increasing levels of peroxynitrite, causing damage through formation of hydroxyl radicals or via nitration of tyrosine residues on proteins. The 6 member Peroxiredoxin (Prdx) family of redox proteins are thought to be critical protectors against oxidative stress via reduction of H2O2, hydroperoxides and peroxynitrite. In our in vitro studies cellular metabolism of SK-N-SH human neuroblastoma cells was significantly decreased in the presence of H2O2 (oxidative stressor) or CoCl2 (cellular hypoxia), but was rescued by treatment with exogenous Prdx6, suggesting that its protective action is in part mediated through a direct action. We also show that CoCl2-induced apoptosis was significantly decreased by treatment with exogenous Prdx6. We proposed a redox regulator role for Prdx6 in regulating and maintaining cellular homeostasis via its ability to control ROS levels that could otherwise accelerate the emergence of prion-related neuropathology. To confirm this, we established prion disease in mice with and without astrocyte-specific antioxidant protein Prdx6, and demonstrated that expression of Prdx6 protein in Prdx6 Tg ME7-animals reduced severity of the behavioural deficit, decreased neuropathology and increased survival time compared to Prdx6 KO ME7-animals. We conclude that antioxidant Prdx6 attenuates prion-related neuropathology, and propose that augmentation of endogenous Prdx6 protein represents an attractive adjunct therapeutic approach for neurodegenerative diseases.

Cytosolically expressed PrP GPI-signal peptide interacts with mitochondria

We previously reported that PrP GPI-anchor signal peptide (GPI-SP) is specifically degraded by the proteasome. Additionally, we showed that the point mutation P238S, responsible for a genetic form of prion diseases, while not affecting the GPI-anchoring process, results in the accumulation of PrP GPI-SP, suggesting the possibility that PrP GPI-anchor signal peptide could play a role in neurodegenerative prion diseases. We now show that PrP GPI-SP, when expressed as a cytosolic peptide, is able to localize to the mitochondria and to induce mitochondrial fragmentation and vacuolarization, followed by loss in mitochondrial membrane potential, ultimately resulting in apoptosis. Our results identify the GPI-SP of PrP as a novel candidate responsible for the impairment in mitochondrial function involved in the synaptic pathology observed in prion diseases, establishing a link between PrP GPI-SP accumulation and neuronal death.

Human leptin triggers proliferation of A549 cells via blocking endoplasmic reticulum stress-related apoptosis

Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. Leptin is a pleiotropic hormone with antiapoptotic and proliferative roles involved in several systems. However, there is no known antiapoptotic mechanism of leptin in non-small cell lung cancer (NSCLC). So, we investigated the antiapoptotic mechanism of leptin in NSCLC. Proliferation, apoptosis, and the specific mechanism of leptin-transfected cells were analyzed in this study. Leptin, p-Perk, IRE1, cleaved ATF6, spliced XBP1, eIF2-α, TRAF2, CHOP, and caspase 12 proteins were detected by Western blot, and endoplasmic reticulum (ER) stress-related mRNA was detected by semi-quantitative reverse transcription PCR (RT-PCR). Leptin in A549 and transfected cells inhibited cisplatin-activated ER stress-associated mRNA transcription and activation of proteins. ER stress unfolded protein response (UPR) proteins, PERK and ATF6, were involved in leptin-triggered apoptosis. XBP1 and TRAF2 were increased significantly when treated with cisplatin in A549-siLPT and non-transfected cells. CHOP expression was blocked in A549 and transfected cells (LPT-PeP and LPT-EX cells). In conclusion, leptin can promote the proliferation of A549 cells through blocking ER stress-mediated apoptosis. This blocking is mediated by the p-Perk and ATF6 pathway through blocking activation of CHOP.

Human gastrin-releasing peptide triggers growth of HepG2 cells through blocking endoplasmic reticulum stress-mediated apoptosis

Gastrin-releasing peptide (GRP) is a kind of neural peptide that plays an important role in the growth of various human cancer cells. However, very little is known about the relationship between GRP and apoptosis in human hepatocellular carcinoma cells. This study investigated the influences of GRP on apoptosis, as well as the mechanism that triggers HepG2 growth. The effects of GRP on cell proliferation were examined by analysis of lactate dehydrogenase. The GRP, caspase 12, and CHOP protein were detected in HepG2 and HL-7702 cells by Western blot, and endoplasmic reticulum (ER) stress-related mRNA transcription was detected by reverse transcription polymerase chain reaction. To explore the specific pathway by which GRP induces the cell growth, we investigated the apoptosis-related pathway. The expression of GRP in HL-7702 cells inhibited tunicamycin triggered ER stress-associated XBP1, ATF4, and TRAF2 mRNA transcription. Three main ER stress-unfolded protein response pathway proteins, including spliced XBP1, cleaved ATF6, IRE1-α, PERK, and eIF2-α, were increased significantly. Furthermore, the cleaved caspase 12 activation was blocked and CHOP expression was inhibited when GRP was expressed either in HepG2 or HL-7702 cells. In conclusion, GRP triggers the growth of HepG2 cells through blocking the ER stress-mediated pathway.

Protective effect of proanthocyanidins on anoxia-reoxygenation injury of myocardial cells mediated by the PI3K/Akt/GSK-3β pathway and mitochondrial ATP-sensitive potassium channel

The aim of the present study was to examine the protective effect of proanthocyanidins anoxia-reoxygenation injury of myocardial cells and its association with phosphatidylinositol-3-kinase/Akt and glycogen synthase kinase (PI3K/Akt/GSK)-3β and ATP-sensitive potassium channels. Neonatal rat myocardial cells were cultured and an anoxia-reoxygenation model was established following pretreatment with various drugs. The experiment was divided into five groups according to an experimental scheme. An MTT assay was used to examine the cell survival, and reactive oxygen species (ROS) levels and apoptosis were detected by flow cytometry. Myocardial apoptosis was also examined by terminal deoxynucleotidyl transferase dUTP nick end labeling staining and western blot analysis was employed to detect the expression levels of caspase-3, p-Akt and p-glycogen synthase kinase (GSK)-3β. The results revealed that myocardial cells in the anoxia-reoxygenation group (A/R) exhibited reduced survival rates, increased ROS levels and enhanced caspase-3 expression, as compared with the control group (CN; P<0.05). However, the increase in p-Akt and p-GSK-3β expression was not significantly different. In the proanthocyanidin pretreatment group (PC) the myocardial cell survival rate was increased, ROS levels were reduced, caspase-3 expression was decreased and p-Akt and p-GSK-3β expression levels were significantly increased as compared with the A/R group (P<0.05). Blockade of the PIK3/Akt channel by LY294002 eliminated the protective effects of proanthocyanidins and induced a significant decrease in p-Akt protein and p-GSK-3β expression levels as compared with the PC group. The inhibitor of mitochondrial ATP-sensitive potassium (mitoKATP) channels, 5-HD, also significantly suppressed the protective effects of proanthocyanidins, but had no evident impact on p-Akt and p-GSK-3β expression as compared with the PC group. In conclusion, pretreatment with proanthocyanidins had a protective effect on rat myocardial cell anoxia/reoxygenation injury. This effect is associated with the activation of the PI3K/Akt/GSK-3β signaling pathway and the opening of mitoKATP channels, which may have important roles downstream of PI3K.

Liraglutide alleviates diabetic cardiomyopathy by blocking CHOP-triggered apoptosis via the inhibition of the IRE-α pathway

Clinically, diabetes mellitus is closely associated with and induces certain cardiovascular diseases. The aim of this study was to investigate endoplasmic reticulum (ER) stress-associated apoptosis of diabetic cardiomyopathy (DCM), and explore the protective mechanism of liraglutide. The DCM model was established with a high-fat diet and streptozotocin (STZ). Cardiac function was detected by echocardiogram examination and hematoxylin-eosin staining. ER stress unfolded protein response (UPR) hallmarks [inositol-requiring enzyme-α (IRE-α), p-Perk and ATF6] and transcription factors were detected with western blotting. Apoptosis inducers CHOP, c-Jun amino terminal kinase (JNK) and casapse-12 were also examined with western blotting. The results indicated that liraglutide is capable of improving cardiac function in DCM rats (P<0.05). IRE-α expression was significantly increased in the DCM group compared with the control group (P<0.05), and liraglutide is capable of decreasing IRE-α expression. X-box transcription factor-1 (XBP-1) was significantly spliced in the model group, and downregulated in the liraglutide-treated group. CHOP protein was upregulated in the DCM group, but inactivated by liraglutide treatment. In conclusion, liraglutide is capable of protecting DCM and blocking CHOP-mediated ER stress by inhibiting the IRE-α UPR pathway.

Melittin protein inhibits the proliferation of MG63 cells by activating inositol-requiring protein-1α and X-box binding protein 1-mediated apoptosis

The aim of the present study was to explore the pro-apoptotic effect and specific mechanism of action of melittin (MEL) in humans. The effects of MEL on apoptosis in osteosarcoma and fetal osteoblast cells were investigated, and the mechanism that induced MG63 cell growth was also explored. The effects of MEL on cell proliferation were detected by a 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide analysis. Apoptosis was detected by flow cytometric analysis. MEL protein, inositol-requiring protein-1 (IRE-α), phosphorylated-protein kinase R-like endoplasmic reticulum (ER) kinase, spliced X-box-1 (XBP1), eukaryotic translation initiation factor-2α, cleaved activating transcription factor-6, caspase-12 and C/EBP homology protein (CHOP) were detected in three groups and two cell lines by western blot analysis. The results indicated that the expression or incubation of MEL in the MG63 cells triggered apoptosis and the inhibition of proliferation. One protein from the ER stress unfolded protein response pathway, IRE-α, was involved in the MEL-induced apoptosis in MG63 cells. Furthermore, spliced XBP1 protein was significantly increased in the MEL peptide incubated and MEL expressing groups of MG63 cells. Furthermore, CHOP protein expression was activated in MG63 cells following being incubated with or expressing MEL. In conclusion, MEL serves as an effective factor that inhibits the proliferation of MG63 cells via activating the ER stress-mediated apoptosis pathway. This activation is triggered by the IRE-α pathway mediated by inducing CHOP protein expression.

Human leptin protein induces proliferation of A549 cells via inhibition of PKR-like ER kinase and activating transcription factor-6 mediated apoptosis

PURPOSE

To investigate the anti-apoptotic mechanism of leptin in non-small cell lung cancer.

MATERIALS AND METHODS

The influences of leptin on apoptosis were investigated, analyzing the mechanism that triggers growth of A549 cells. The effects of leptin on cell proliferation were examined by XTT analysis. Leptin, C/EBP homologous protein (CHOP), phosphorylated-PKR-like ER kinase (p-Perk), inositol requiring proteins-1, spliced X-box transcription factor-1 (XBP1), cleaved activating transcription factor-6 (ATF6), eukaryotic translation initiation factor-2α, caspase-12 and CHOP protein were detected in four groups by western blot, and endoplasmic reticulum (ER) stress related mRNA were detected by reverse transcription PCR.

RESULTS

The expression of leptin in A549 and leptin transfected cells inhibited cisplatin activated ER stress-associated mRNA transcription and protein activation. Two ER stress unfolded protein response pathways, PERK and ATF6, were involved, and XBP1 and tumor necrosis factor receptor-associated factor 2 (TRAF2) were increased significantly when treated with cisplatin in A549-siRNA against leptin cells. Furthermore, CHOP expression was inhibited upon leptin expression in A549, LPT-PeP and LPT-EX cells.

CONCLUSION

Leptin serves as an important factor that promotes the growth of A549 cells through blocking ER stress-mediated pathways. This blocking is triggered by p-Perk and ATF6 via inhibition of CHOP expression.

N-terminally truncated forms of human cathepsin F accumulate in aggresome-like inclusions

The contribution of individual cysteine cathepsins as positive mediators of programmed cell death is dependent on several factors, such as the type of stimuli, intensity and duration of the stimulus, and cell type involved. Of the eleven human cysteine cathepsins, cathepsin F is the only cathepsin that exhibits an extended N-terminal proregion, which contains a cystatin-like domain. We predicted that the wild-type human cathepsin F contains three natively disordered regions within the enzyme's propeptide and various amino acid stretches with high fibrillation propensity. Wild-type human cathepsin F and its N-terminally truncated forms, Ala(20)-Asp(484) (Δ(19)CatF), Pro(126)-Asp(484) (Δ(125)CatF), and Met(147)-Asp(484) (Δ(146)CatF) were cloned into the pcDNA3 vector and overexpressed in HEK 293T cells. Wild-type human cathepsin F displayed a clear vesicular labeling and colocalized with the LAMP2 protein, a lysosomal marker. However, all three N-terminally truncated forms of human cathepsin F were recovered as insoluble proteins, suggesting that the deletion of at least the signal peptides (Δ(19)CatF), results in protein aggregation. Noteworthy, they concentrated large perinuclear-juxtanuclear aggregates that accumulated within aggresome-like inclusions. These inclusions showed p62-positive immunoreactivity and were colocalized with the autophagy marker LC3B, but not with the LAMP2 protein. In addition, an approximately 2-3 fold increase in DEVDase activity was not sufficient to induce apoptotic cell death. These results suggested the clearance of the N-terminally truncated forms of human cathepsin F via the autophagy pathway, underlying its protective and prosurvival mechanisms.

Glucagon-Like Peptide-1 Analog Liraglutide Protects against Diabetic Cardiomyopathy by the Inhibition of the Endoplasmic Reticulum Stress Pathway

Aim. This study aimed to investigate whether the glucagon-like peptide-1 analog liraglutide (LIRA) can protect against diabetic cardiomyopathy and explore the related mechanism. Methods. Rats were divided into 6 groups: a nondiabetic group, diabetic cardiomyopathy rats without LIRA treatment, diabetic cardiomyopathy rats with LIRA treatment (with high-, medium-, and low-dose, resp.), and diabetic cardiomyopathy rats treated with insulin. Cardiac function was examined by echocardiography before and after treatment. The histopathology of the heart was examined with H&E staining. The mRNA levels of XBP1, ATF4, and TRAF2 were analyzed by RT-PCR, and the expression of glucose-regulated protein 78 (Grp78), enhancer-binding protein homologous protein (CHOP), caspase-3, and caspase-12 was detected by western blot. Results. LIRA strongly improved cardiac function from both echocardiographic and histopathologic analyses, but insulin only partly increased cardiac function by improving FS and LVPW values. LIRA treatment can significantly decrease the expression of XBP1, ATF4, and TRAF2 (P < 0.01). LIRA also significantly downregulates the expression of Grp78, caspase-3 (P < 0.01), CHOP, and caspase-12 (P < 0.05). Conclusions. LIRA can protect against diabetic cardiomyopathy by inactivating the ER stress pathway. The improvement in cardiac function by LIRA is independent of glucose control.

Activation of the macroautophagic system in scrapie-infected experimental animals and human genetic prion diseases

Macroautophagy is an important process for removing misfolded and aggregated protein in cells, the dysfunction of which has been directly linked to an increasing number of neurodegenerative disorders. However, the details of macroautophagy in prion diseases remain obscure. Here we demonstrated that in the terminal stages of scrapie strain 263K-infected hamsters and human genetic prion diseases, the microtubule-associated protein 1 light chain 3 (LC3) was converted from the cytosolic form to the autophagosome-bound membrane form. Macroautophagy substrate sequestosome 1 (SQSTM1) and polyubiquitinated proteins were downregulated in the brains of sick individuals, indicating enhanced macroautophagic protein degradation. The levels of mechanistic target of rapamycin (MTOR) and phosphorylated MTOR (p-MTOR) were significantly decreased, which implies that this enhancement of the macroautophagic response is likely through the MTOR pathway which is a negative regulator for the initiation of macroautophagy. Dynamic assays of the autophagic system in the brains of scrapie experimental hamsters after inoculation showed that alterations of the autophagic system appeared along with the deposits of PrP(Sc) in the infected brains. Immunofluorescent assays revealed specific staining of autophagosomes in neurons that were not colocalized with deposits of PrP(Sc) in the brains of scrapie infected hamsters, however, autophagosome did colocalize with PrP(Sc) in a prion-infected cell line after treatment with bafilomycin A(1). These results suggest that activation of macroautophagy in brains is a disease-correlative phenomenon in prion diseases.

Molecular interaction of TPPP with PrP antagonized the CytoPrP-induced disruption of microtubule structures and cytotoxicity

Background

Tubulin polymerization promoting protein/p25 (TPPP/p25), known as a microtubule-associated protein (MAP), is a brain-specific unstructured protein with a physiological function of stabilizing cellular microtubular ultrastructures. Whether TPPP involves in the normal functions of PrP or the pathogenesis of prion disease remains unknown. Here, we proposed the data that TPPP formed molecular complex with PrP. We also investigated its influence on the aggregation of PrP and fibrillization of PrP106–126 in vitro, its antagonization against the disruption of microtubule structures and cytotoxicity of cytosolic PrP in cells, and its alternation in the brains of scrapie-infected experimental hamsters.

Methodology/Principal Findings

Using pull-down and immunoprecipitation assays, distinct molecular interaction between TPPP and PrP were identified and the segment of TPPP spanning residues 100–219 and the segment of PrP spanning residues 106–126 were mapped as the regions responsible for protein interaction. Sedimentation experiments found that TPPP increased the aggregation of full-length recombinant PrP (PrP23–231) in vitro. Transmission electron microscopy and Thioflavin T (ThT) assays showed that TPPP enhanced fibril formation of synthetic peptide PrP106–126 in vitro. Expression of TPPP in the cultured cells did not obviously change the microtubule networks observed by a tubulin-specific immunofluorescent assay and cell growth features measured by CCK8 tests, but significantly antagonized the disruption of microtubule structures and rescued the cytotoxicity caused by the accumulation of cytosolic PrP (CytoPrP). Furthermore, Western blots identified that the levels of the endogenous TPPP in the brains of scrapie-infected experimental hamsters were significantly reduced.

Conclusion/Significance

Those data highlight TPPP may work as a protective factor for cells against the damage effects of the accumulation of abnormal forms of PrPs, besides its function as an agent for dynamic stabilization of microtubular ultrastructures.

Cell type-specific neuroprotective activity of untranslocated prion protein

Background

A key pathogenic role in prion diseases was proposed for a cytosolic form of the prion protein (PrP). However, it is not clear how cytosolic PrP localization influences neuronal viability, with either cytotoxic or anti-apoptotic effects reported in different studies. The cellular mechanism by which PrP is delivered to the cytosol of neurons is also debated, and either retrograde transport from the endoplasmic reticulum or inefficient translocation during biosynthesis has been proposed. We investigated cytosolic PrP biogenesis and effect on cell viability in primary neuronal cultures from different mouse brain regions.

Principal Findings

Mild proteasome inhibition induced accumulation of an untranslocated form of cytosolic PrP in cortical and hippocampal cells, but not in cerebellar granules. A cyclopeptolide that interferes with the correct insertion of the PrP signal sequence into the translocon increased the amount of untranslocated PrP in cortical and hippocampal cells, and induced its synthesis in cerebellar neurons. Untranslocated PrP boosted the resistance of cortical and hippocampal neurons to apoptotic insults but had no effect on cerebellar cells.

Significance

These results indicate cell type-dependent differences in the efficiency of PrP translocation, and argue that cytosolic PrP targeting might serve a physiological neuroprotective function.