The role of P-glycoprotein/cellular prion protein interaction in multidrug-resistant breast cancer cells treated with paclitaxel

We previously reported that treatment with P-glycoprotein (P-gp) substrates promotes in vitro invasion in multidrug-resistant (MDR) breast cancer cells. This effect is initiated by the P-gp pump function and mediated by interaction of P-gp with some unknown component(s). However, the underlying mechanism(s) remains poorly understood. Here we confirm a novel physical interaction between P-gp and cellular prion protein (PrP(c)). Blocking P-gp activity or depletion of PrP(c) inhibited paclitaxel (P-gp substrate)- induced invasion. Paclitaxel further facilitated the formation of P-gp/PrP(c) clusters residing in caveolar domains and promoted the association of P-gp with caveolin-1. Both caveolin-1 and the integrity of caveolae were required for the drug-induced invasion. In addition, the P-gp/PrP(c) complex also played an important role in anti-apoptotic activity of MCF7/Adr cells.These data provide new insights into the mode by which MDR breast cancers evade cytotoxic attacks from P-gp substrates and also suggest a role for P-gp/ PrP(c) interaction in this process.

Prion protein protects against zinc-mediated cytotoxicity by modifying intracellular exchangeable zinc and inducing metallothionein expression

PrPC contains several octapeptide repeats sequences toward the N-terminus which have binding affinity for divalent metals such as copper, zinc, nickel and manganese. However, the link between PrPC expression and zinc metabolism remains elusive. Here we studied the relationship between PrPC and zinc ions intracellular homeostasis using a cell line expressing a doxycycline-inducible PrPC gene. No significant difference in 65Zn2+ uptake was observed in cells expressing PrPC when compared with control cells. However, PrPC-expressing cells were more resistant to zinc-induced toxicity, suggesting an adaptative mechanism induced by PrPC. Using zinquin-ethyl-ester, a specific fluorophore for vesicular free zinc, we observed a significant re-localization of intracellular exchangeable zinc in vesicles after PrPC expression. Finally, we demonstrated that PrPC expression induces metallothionein (MT) expression, a zinc-upregulated zinc-binding protein. Taken together, these results suggest that PrPC modifies the intracellular localization of zinc rather than the cellular content and induces MT upregulation. These findings are of major importance since zinc deregulation is implicated in several neurodegenerative disorders. It is postulated that in prion diseases the conversion of PrPC to PrPSc may deregulate zinc homeostasis mediated by metallothionein.

Increased PrPC expression correlates with endoglin (CD105) positive microvessels in advanced carotid lesions

Normal cellular prion protein (PrP(C)) has multiple functions but its role in the development of atherosclerosis has not been studied. Our pilot microarray data showed increased expression of PrP(C) in tissue samples of complicated carotid lesions. Therefore in this study, we aimed to investigate its localisation within atherosclerotic arteries and its concentration in patient plasma. PrP(C) expression was examined using an enzyme immunometric assay (EIA) in plasma from patients undergoing endarterectomy. Carotid specimens and control vascular transplants were studied for PrP(C) and CD105 (endoglin, a marker of active vessels) expression by immunohistochemistry and real-time PCR. Patients with carotid disease had higher levels of plasma PrP(C) than the control group [4.35 ng/ml (n = 22; 3.1-5.3) vs. 1.95 ng/ml (n = 21; 1.1-2.5), P < 0.001]. Furthermore, CD105-positive plaques had higher PrP(C) expression which colocalized with CD105 in neovessels. There was a significant correlation between mRNA expression of PrP(C) and CD105 in tested plaques (P < 0.001; r = 0.7) supporting our immunohistochemical findings. We conclude that PrP(C) is expressed in carotid specimens and may be associated with neovessel growth or survival in these plaques. Our results suggest a role for PrP(C) in modulating neovessel formation in complicated plaques.

Pathologic prion protein infects cells by lipid-raft dependent macropinocytosis

Transmissible spongiform encephalopathies, including variant-Creutzfeldt-Jakob disease (vCJD) in humans and bovine spongiform encephalopathies in cattle, are fatal neurodegenerative disorders characterized by protein misfolding of the host cellular prion protein (PrP(C)) to the infectious scrapie form (PrP(Sc)). However, the mechanism that exogenous PrP(Sc) infects cells and where pathologic conversion of PrP(C) to the PrP(Sc) form occurs remains uncertain. Here we report that similar to the mechanism of HIV-1 TAT-mediated peptide transduction, processed mature, full length PrP contains a conserved N-terminal cationic domain that stimulates cellular uptake by lipid raft-dependent, macropinocytosis. Inhibition of macropinocytosis by three independent means prevented cellular uptake of recombinant PrP; however, it did not affect recombinant PrP cell surface association. In addition, fusion of the cationic N-terminal PrP domain to a Cre recombinase reporter protein was sufficient to promote both cellular uptake and escape from the macropinosomes into the cytoplasm. Inhibition of macropinocytosis was sufficient to prevent conversion of PrP(C) to the pathologic PrP(Sc) form in N2a cells exposed to strain RML PrP(Sc) infected brain homogenates, suggesting that a critical determinant of PrP(C) conversion occurs following macropinocytotic internalization and not through mere membrane association. Taken together, these observations provide a cellular mechanism that exogenous pathological PrP(Sc) infects cells by lipid raft dependent, macropinocytosis.

The cellular prion protein PrP(c) is involved in the proliferation of epithelial cells and in the distribution of junction-associated proteins

Background

The physiological function of the ubiquitous cellular prion protein, PrP^c, is still under debate. It was essentially studied in nervous system, but poorly investigated in epithelial cells. We previously reported that PrP^c is targeted to cell–cell junctions of polarized epithelial cells, where it interacts with c-Src.

Methodology/Findings

We show here that, in cultured human enterocytes and in intestine in vivo, the mature PrP^c is differentially targeted either to the nucleus in dividing cells or to cell–cell contacts in polarized/differentiated cells. By proteomic analysis, we demonstrate that the junctional PrP^c interacts with cytoskeleton-associated proteins, such as gamma- and beta-actin, alpha-spectrin, annexin A2, and with the desmosome-associated proteins desmoglein, plakoglobin and desmoplakin. In addition, co-immunoprecipitation experiments revealed complexes associating PrP^c, desmoglein and c-Src in raft domains. Through siRNA strategy, we show that PrP^c is necessary to complete the process of epithelial cell proliferation and for the sub-cellular distribution of proteins involved in cell architecture and junctions. Moreover, analysis of the architecture of the intestinal epithelium of PrP^c knock-out mice revealed a net decrease in the size of desmosomal junctions and, without change in the amount of BrdU incorporation, a shortening of the length of intestinal villi.

Conclusions/Significance

From these results, PrP^c could be considered as a new partner involved in the balance between proliferation and polarization/differentiation in epithelial cells.

Expression of alpha-hemoglobin stabilizing protein and cellular prion protein in a subclone of murine erythroleukemia cell line MEL

Alpha-Hemoglobin stabilizing protein (AHSP) functions as the erythroid-specific molecular chaperon for alpha-globin. AHSP gene expression has been reported to be downregulated in hematopoietic tissues of animals suffering from prion diseases though the mechanism remains to be clarified. Herein, we demonstrate that MELhipod8 cells, a subclone of murine erythroleukemia (MEL) cells, have prion protein (PrPc) on the cell surface and have highly inducible expression of the AHSP and alpha- and beta-globin genes, resembling the expression pattern of the PrP and AHSP genes in bipotential erythroid- and megakaryocyte-lineage cells followed by erythroid differentiation in normal erythropoiesis. Moreover, MELhipod8 cells exhibit greater effective erythroid differentiation with a population of hemoglobinized normoblast-like cells than that observed for the parental MEL cells. These findings suggest that MELhipod8 cells could provide a mechanism for downregulation of the AHSP gene in prion diseases.

Overexpression of cellular prion protein alters postischemic Erk1/2 phosphorylation but not Akt phosphorylation and protects against focal cerebral ischemia

PURPOSE

The physiological function of the cellular prion protein (PrPC) is still unclear. A growing body of evidence suggests that PrPC has neuroprotective properties and that its deletion increases susceptibility to focal cerebral ischemia. The purpose of this study was to elucidate the role of PrPC overexpression in ischemic brain injury in vivo.

METHODS

PrPC overexpressing (TG35) and wild type (WT) mice were subjected to a 90-minute transient focal cerebral ischemia followed by infarct volume analysis 24 hours after lesion. To identify effects of PrPC overexpression on signalling pathways important for the regulation of ischemic cell death, we studied postischemic activation and expression of Akt and Erk1/2 using quantitative Western Blot analysis.

RESULTS

TG35 mice displayed significantly smaller infarct volumes and showed reduced early postischemic Erk1/2 phosphorylation, a pathway known to exacerbate neuronal injury following transient cerebral ischemia. In contrast, PrPC overexpression did not change postischemic Akt phosphorylation, which acts anti-apoptotic and is reduced in PrPC knockout animals.

CONCLUSIONS

These results demonstrate that PrPC overexpression reduces deleterious Erk1/2 activation but does not affect Akt activation after transient cerebral ischemia, suggesting a role for distinct cytosolic signalling pathways in PrPC mediated neuroprotection.

Characterization of prion susceptibility in Neuro2a mouse neuroblastoma cell subclones

In this study, we established Neuro2a (N2a) neuroblastoma subclones and characterized their susceptibility to prion infection. The N2a cells were treated with brain homogenates from mice infected with mouse prion strain Chandler. Of 31 N2a subclones, 19 were susceptible to prion as those cells became positive for abnormal isoform of prion protein (PrP(Sc)) for up to 9 serial passages, and the remaining 12 subclones were classified as unsusceptible. The susceptible N2a subclones expressed cellular prion protein (PrP(C)) at levels similar to the parental N2a cells. In contrast, there was a variation in PrP(C) expression in unsusceptible N2a subclones. For example, subclone N2a-1 expressed PrP(C) at the same level as the parental N2a cells and prion-susceptible subclones, whereas subclone N2a-24 expressed much lower levels of PrP mRNA and PrP(C) than the parental N2a cells. There was no difference in the binding of PrP(Sc) to prion-susceptible and unsusceptible N2a subclones regardless of their PrP(C) expression level, suggesting that the binding of PrP(Sc) to cells is not a major determinant for prion susceptibility. Stable expression of PrP(C) did not confer susceptibility to prion in unsusceptible subclones. Furthermore, the existence of prion-unsusceptible N2a subclones that expressed PrP(C) at levels similar to prion-susceptible subclones, indicated that a host factor(s) other than PrP(C) and/or specific cellular microenvironments are required for the propagation of prion in N2a cells. The prion-susceptible and -unsusceptible N2a subclones established in this study should be useful for identifying the host factor(s) involved in the prion propagation.

Prion strain- and species-dependent effects of antiprion molecules in primary neuronal cultures

Transmissible spongiform encephalopathies (TSE) arise as a consequence of infection of the central nervous system by prions and are incurable. To date, most antiprion compounds identified by in vitro screening failed to exhibit therapeutic activity in animals, thus calling for new assays that could more accurately predict their in vivo potency. Primary nerve cell cultures are routinely used to assess neurotoxicity of chemical compounds. Here, we report that prion strains from different species can propagate in primary neuronal cultures derived from transgenic mouse lines overexpressing ovine, murine, hamster, or human prion protein. Using this newly developed cell system, the activity of three generic compounds known to cure prion-infected cell lines was evaluated. We show that the antiprion activity observed in neuronal cultures is species or strain dependent and recapitulates to some extent the activity reported in vivo in rodent models. Therefore, infected primary neuronal cultures may be a relevant system in which to investigate the efficacy and mode of action of antiprion drugs, including toward human transmissible spongiform encephalopathy agents.

Cellular prion protein regulates the motor behaviour performance and anxiety-induced responses in genetically modified mice

The cellular prion protein (PrP(C)) is a sialoglycoprotein involved in neuroplasticity processes and synaptic transmission. This study investigated behavioural responses (balance in the rota-rod test at 24 rpm, motility in the open-field test, anxiety in the elevated plus-maze test) in Zurich developed wild-type adult mice (WT, controls of normal PrP(C) expression), in knockout (KO) mice (Prnp(0/0), with no PrP(C) expression), and in PrP(C) overexpressing Tg-20 mice. After 8 min in the rota-rod test, Tg-20 animals presented significantly fewer falls (1.08+/-1.56 falls) than both WT (7.27+/-4.36) and KO (7.6+/-6.15) mice (p<0.01). In the open field test, Tg-20 animals showed significantly increased motility [rearing=23.4+/-7.85, crossing=97.30+/-32.11) when compared with KO mice (rearing=5.45+/-3.69 and crossing=59.73+/-15.43) or WT mice (rearing=6.5+/-20.23 and crossing=45.18+/-20.33) (p<0.01). In the elevated plus-maze test, Tg-20 mice showed less anxiety (head projections=7.3+/-1.62) when compared with WT animals (3.38+/-0.67) (p<0.05). Moreover, KO mice spent more time in the centre of the plus maze (37.80+/-5.57 s) than did WT mice (22.57+/-3.82) (p<0.05). PrP(C) overexpressing mice evoked increased motility, less anxiety, and increased equilibrium when compared with WT control animals in the behavioural protocols used. KO animals also tended to evoke fewer anxiety-related responses in the elevated plus-maze test. These findings indicate that the levels of PrP(C) in adult life are associated with possible changes in motility, anxiety, and equilibrium.

Cellular prion protein protects against reactive-oxygen-species-induced DNA damage

Although the cellular form of the prion protein (PrPC) is critical for the development of prion disease through its conformational conversion into the infectious form (PrPSc), the physiological role of PrPC is less clear. Using alkaline single-cell gel electrophoresis (the Comet assay), we show that expression of PrPC protects human neuroblastoma SH-SY5Y cells against DNA damage under basal conditions and following exposure to reactive oxygen species, either hydroxyl radicals following exposure to Cu2+ or Fe2+ or singlet oxygen following exposure to the photosensitizer methylene blue and white light. Cells expressing either PrPDeltaoct which lacks the octapeptide repeats or the prion-disease-associated mutants A116V or PG14 had increased levels of DNA damage compared to cells expressing PrPC. In PrPSc-infected mouse ScN2a cells there was a significant increase in DNA damage over noninfected N2a cells (median tail DNA 2.87 and 7.33%, respectively). Together, these data indicate that PrPC has a critical role to play in protecting cells against reactive-oxygen-species-mediated DNA damage; a function which requires the octapeptide repeats in the protein, is lost in disease-associated mutants of the protein or upon conversion to PrPSc, and thus provide further support for the neuroprotective role for PrPC.

Efficacy of adjuvant chemotherapy according to Prion protein expression in patients with estrogen receptor-negative breast cancer

BACKGROUND

Prion protein (PrPc) has been previously reported to be associated with resistance to proapoptotic stimuli. We evaluated whether the expression of PrPc was associated with the resistance to adjuvant chemotherapy in patients with estrogen receptor (ER) -negative breast cancer.

PATIENTS AND METHODS

The expression of PrPc by primary tumors was assessed by immunohistochemistry in a series of 756 patients included in two randomized trials that compared anthracycline-based chemotherapy to no chemotherapy. The PrPc expression was correlated with ER expression and the benefit of adjuvant chemotherapy was assessed according to PrPc expression in patients with ER-negative tumors.

RESULTS

Immunostaining analysis showed that PrPc was mainly expressed by myoepithelial cells in normal breast tissue. Tissue microarray analysis from 756 breast tumors showed that PrPc was associated with ER-negative breast cancer subsets (P < 0.001). Adjuvant chemotherapy was not associated with a significant risk reduction for death in patients with ER-negative/PrPc-positive disease [adjusted hazard ratio (HR) for death = 0.98, 95% confidence interval (CI) 0.45-2.1, P = 0.95], while it decreased the risk for death (HR = 0.39, 95% CI 0.2-0.74, P = 0.004) in patients with ER-negative/PrPc-negative tumors.

CONCLUSION

These data indicate that ER-negative/PrPc-negative phenotype is associated with a high sensitivity to adjuvant chemotherapy.

Cellular prion protein expression in astrocytes modulates neuronal survival and differentiation

The functions of cellular prion protein (PrP(C)) are under intense debate and PrP(C) loss of function has been implicated in the pathology of prion diseases. Neuronal PrP(C) engagement with stress-inducible protein-1 and laminin (LN) plays a key role in cell survival and differentiation. The present study evaluated whether PrP(C) expression in astrocytes modulates neuron-glia cross-talk that underlies neuronal survival and differentiation. Astrocytes from wild-type mice promoted a higher level neuritogenesis than astrocytes obtained from PrP(C)-null animals. Remarkably, neuritogenesis was greatly diminished in co-cultures combining PrP(C)-null astrocytes and neurons. LN secreted and deposited at the extracellular matrix by wild-type astrocytes presented a fibrillary pattern and was permissive for neuritogenesis. Conversely, LN coming from PrP(C)-null astrocytes displayed a punctate distribution, and did not support neuronal differentiation. Additionally, secreted soluble factors from PrP(C)-null astrocytes promoted lower levels of neuronal survival than those secreted by wild-type astrocytes. PrP(C) and stress-inducible protein-1 were characterized as soluble molecules secreted by astrocytes which participate in neuronal survival. Taken together, these data indicate that PrP(C) expression in astrocytes is critical for sustaining cell-to-cell interactions, the organization of the extracellular matrix, and the secretion of soluble factors, all of which are essential events for neuronal differentiation and survival.

Differential expression of calcium-related genes in gastric cancer cells transfected with cellular prion protein

The prion protein (PrPC) has a primary role in the pathogenesis of transmissible spongiform encephalopathies, which causes prion disorders partially due to Ca2+ dysregulation. In our previous work, we found that overexpressed PrPC in gastric cancer was involved in apoptosis, cell proliferation, and metastasis of gastric cancer. To better understand how PrPC acts in gastric cancer, a human microarray was performed to select differentially regulated genes that correlate with the biological function of PrPC. The microarray data were analyzed and revealed 3798 genes whose expression increased at least 2-fold in gastric cancer cells transfected with PrPC. These genes encode proteins involved in several aspects of cell biology, among which, we specially detected molecules related to calcium, especially the S100 calcium-binding proteins, and found that PrPC upregulates S100A1, S100A6, S100B, and S100P but downregulates CacyBP in gastric cancer cells. We also found that intracellular Ca2+ levels in cells transfected with PrPC increased, whereas these levels decreased in knockdowns of these cells. Taken together, PrPC might increase intracellular Ca2+, partially through calcium-binding proteins, or PrPC might upregulate the expression of S100 proteins, partially through stimulating the intracellular calcium level in gastric cancer. Though the underlying mechanisms need further exploration, this study provides a new insight into the role of PrPC in gastric cancer and enriches our knowledge of prion protein.

Prion proteins: a biological role beyond prion diseases

The biological role of the scrapie isoform of prion protein (PrP(Sc)) as an infectious agent in numerous human and non-human disorders of the central nervous system is well established. In contrast, and despite decades of intensive research, the physiological function of the endogenous cellular form of the prion protein (PrP(C)) remains elusive. In mammals, the ubiquitous expression of PrP(C) suggests biological functions other than its pathological role in propagating the accumulation of its misfolded isotype. Other functions that have been attributed to PrP(C) include signal transduction, synaptic transmission and protection against cell death through the apoptotic pathway. More recently, immunoregulatory properties of PrP(C) have been reported. We review accumulating in vitro and in vivo evidence regarding physiological functions of PrP(C).

Increased PrP mRNA expression in lymphoid follicles of the ileal Peyer's patch of sheep experimentally exposed to the scrapie agent

To understand the functional role of cellular prion protein (PrP(C)) in the initiation and maintenance of prion disease within the host, it is important to obtain a more detailed understanding of PrP(C) transcription in tissues during the development of disease. Using an experimental model with oral infection, we examined the effect of scrapie and the accumulation of the scrapie related form of the prion protein (PrP(Sc)) on the expression level of PrP mRNA in the ileal Peyer's patch of sheep. In the early phase of infection, prior to PrP(Sc) accumulation, no effect on the PrP expression was detected. However, it was found that lambs with PrP genotypes associated with high susceptibility for scrapie generally had higher PrP mRNA levels than lambs with less susceptible genotypes. Further, in highly susceptible VRQ/VRQ sheep at a stage of disease with high accumulation of PrP(Sc), real-time RT-PCR and microdissection were used to investigate levels of PrP mRNA in four different tissue compartments. An increased level of PrP mRNA was found in lymphoid follicles of infected sheep compared with controls, indicating upregulation of PrP expression in the follicles to compensate for the loss of PrP(C) converted to PrP(Sc), or that PrP(Sc) accumulation directly or indirectly influences the PrP expression. Still, the PrP expression level in the follicles was low compared with the other compartments investigated, suggesting that although increased PrP expression could contribute to PrP(Sc) accumulation, other factors are also important in the processes leading to accumulation of PrP(Sc) in the follicles.

Prion protein facilitates hormone-induced differentiation of mammary gland epithelial cells

Expression of prion protein has been reported for a variety of cell types including neuronal cells, haematopoietic stem cells, lymphocytes, fibroblasts, and epithelial cells. However, the characterization of the physiological roles exhibited by this protein is still in progress and multiple biological functions have been described to date. In this study we have characterized the contribution of prion protein during hormone-induced differentiation of mouse mammary gland epithelial cells. We present evidence that prion expression enhances the differentiation-capabilities of these cells indicating novel physiological roles during mammary gland development. In addition we were able to demonstrate the presence of prion molecules resistant to mild proteinase digestion in differentiated mammary gland epithelial cells. This represents the first report of proteinase-resistant prion proteins in a physiological, non-pathogenic context.

Phosphorothioate oligonucleotides reduce PrP levels and prion infectivity in cultured cells

Prions are composed solely of the disease-causing prion protein (PrPSc) that is formed from the cellular isoform PrPC by a posttranslational process. Here we report that short phosphorothioate DNA (PS-DNA) oligonucleotides diminished the levels of both PrPC and PrPSc in prion-infected neuroblastoma (ScN2a) cells. The effect of PS-DNA on PrP levels was independent of the nucleotide sequence. The effective concentration (EC50) of PS-DNA required to achieve half-maximal diminution of PrPSc was approximately 70 nM, whereas the EC50 of PS-DNA for PrPC was more than 50-fold greater. This finding indicated that diminished levels of PrPSc after exposure to PS-DNA are unlikely to be due to decreased PrPC levels. Bioassays in transgenic mice demonstrated a substantial diminution in the prion infectivity after ScN2a cells were exposed to PS-DNAs. Whether PS-DNA will be useful in the treatment of prion disease in people or livestock remains to be established.

Cellular prion protein is increased in the plasma and peri-infarcted brain tissue after acute stroke

The physiologic properties of the normal cellular prion protein (PrP(C)) have not been established fully, although recent evidence showed its upregulation in cerebral ischaemia. Using patients, animal models, and in vitro studies we aimed to identify in detail the expression and localization of PrP(C) in ischemic stroke. Patients in acute phase of ischaemic stroke had increased plasma levels of circulating PrP(C) as compared to healthy age- and gender-matched controls (3.1 +/- 1.4 vs. 1.9 +/- 0.7 ng/ml, P = 0.002). Immunohistochemistry showed increased expression of PrP(C) in the soma of peri-infarcted neurones as well as in the endothelial cells (EC) of micro-vessels and inflammatory cells in peri-infarcted brain tissue from patients who survived for 2-34 days after an initial stroke. The same pattern was repeated 1-48 hr after MCAO. RT-PCR showed increased gene expression of PrP(C) by human foetal neurons (HFN) after 12 hr of oxygen glucose deprivation (OGD), which remained increased after 24 hr reperfusion. Western blotting confirmed that protein expression was similarly upregulated, and fluorescent labeling showed a notable increase in peri-nuclear and axonal PrP(C) staining intensity. Increased plasma PrP(C) seems to reflect endogenous expression in acute stroke-affected brain tissue. Increased cellular expression in peri-infarcted regions may influence hypoxia-induced cell damage, although the effects on EC survival and angiogenesis remain to be elucidated.

Bcl‐2 overexpression delays caspase‐3 activation and rescues cerebellar degeneration in prion‐deficient mice that overexpress amino‐terminally truncated prion

Prnp knockout mice that overexpress an amino-truncated form of PrPc (deltaPrP) are ataxic and display cerebellar cell loss and premature death. Studies on the molecular and intracellular events that trigger cell death in these mutants may contribute to elucidate the functions of PrPc and to the design of treatments for prion disease. Here we examined the effects of Bcl-2 overexpression in neurons on the development of the neurological syndrome and cerebellar pathology of deltaPrP. We show that deltaPrP overexpression activates the stress-associated kinases ERK1-2 in reactive astroglia, p38 and the phosphorylation of p53, which leads to the death of cerebellar neurons in mutant mice. We found that the expression of deltaPrP in cell lines expressing very low levels of PrPc strongly induces the activation of apoptotic pathways, thereby leading to caspase-3 activation and cell death, which can be prevented by coexpressing Bcl-2. Finally, we corroborate in vivo that neuronal-directed Bcl-2 overexpression in deltaPrP mice (deltaPrP Bcl-2) markedly reduces caspase-3 activation, glial activation, and neuronal cell death in cerebellum by improving locomotor deficits and life expectancy.

Normal cellular prion protein protects against manganese-induced oxidative stress and apoptotic cell death

The normal prion protein is abundantly expressed in the central nervous system, but its biological function remains unclear. The prion protein has octapeptide repeat regions that bind to several divalent metals, suggesting that the prion proteins may alter the toxic effect of environmental neurotoxic metals. In the present study, we systematically examined whether prion protein modifies the neurotoxicity of manganese (Mn) by comparing the effect of Mn on mouse neural cells expressing prion protein (PrP(C)-cells) and prion-knockout (PrP(KO)-cells). Exposure to Mn (10microM-10mM) for 24 h produced a dose-dependent cytotoxic response in both PrP(C)-cells and PrP(KO)-cells. Interestingly, PrP(C)-cells (EC(50) 117.6microM) were more resistant to Mn-induced cytotoxicity, as compared to PrP(KO)-cells (EC(50) 59.9microM), suggesting a protective role for PrP(C) against Mn neurotoxicity. Analysis of intracellular Mn levels showed less Mn accumulation in PrP(C)-cells as compared to PrP(KO)-cells, but no significant changes in the expression of the metal transporter proteins transferrin and DMT-1. Furthermore, Mn-induced mitochondrial depolarization and reactive oxygen species (ROS) generation were significantly attenuated in PrP(C)-cells as compared to PrP(KO)-cells. Measurement of antioxidant status revealed similar basal levels of glutathione (GSH) in PrP(C)-cells and PrP(KO)-cells; however, Mn treatment caused greater depletion of GSH in PrP(KO)-cells. Mn-induced mitochondrial depolarization and ROS production were followed by time- and dose-dependent activation of the apoptotic cell death cascade involving caspase-9 and -3. Notably, DNA fragmentation induced by both Mn treatment and the oxidative stress inducer hydrogen peroxide (100microM) was significantly suppressed in PrP(C)-cells as compared to PrP(KO)-cells. Together, these results demonstrate that prion protein interferes with divalent metal Mn uptake and protects against Mn-induced oxidative stress and apoptotic cell death.