A Combined Cell-Worm Approach to Search for Compounds Counteracting the Toxicity of Tau Oligomers In Vivo

A clear relationship between the tau assemblies and toxicity has still to be established. To correlate the tau conformation with its proteotoxic effect in vivo, we developed an innovative cell-worm-based approach. HEK293 cells expressing tau P301L under a tetracycline-inducible system (HEK T-Rex) were employed to produce different tau assemblies whose proteotoxic potential was evaluated using C. elegans. Lysates from cells induced for five days significantly reduced the worm's locomotor activity. This toxic effect was not related to the total amount of tau produced by cells or to its phosphorylation state but was related to the formation of multimeric tau assemblies, particularly tetrameric ones. We investigated the applicability of this approach for testing compounds acting against oligomeric tau toxicity, using doxycycline (Doxy) as a prototype drug. Doxy affected tau solubility and promoted the disassembly of already formed toxic aggregates in lysates of cells induced for five days. These effects translated into a dose-dependent protective action in C. elegans. These findings confirm the validity of the combined HEK T-Rex cells and the C. elegans-based approach as a platform for pharmacological screening.

C. elegans detects toxicity of traumatic brain injury generated tau

Traumatic brain injury (TBI) is associated with widespread tau pathology in about 30% of patients surviving late after injury. We previously found that TBI in mice induces the formation of an abnormal form of tau (tau^TBI) which progressively spreads from the site of injury to remote brain regions. Intracerebral inoculation of TBI brain homogenates into naïve mice induced progressive tau pathology, synaptic loss and late cognitive decline, suggesting a pivotal role of tau^TBI in post-TBI neurodegeneration. However, the possibility that tau^TBI was a marker of TBI-associated neurodegeneration rather than a toxic driver of functional decline could not be excluded.

Here we employed the nematode C. elegans as a biosensor to test the pathogenic role of TBI generated tau. The motility of this nematode depends on efficient neuromuscular transmission and is exceptionally sensitive to the toxicity of amyloidogenic proteins, providing a tractable model for our tests. We found that worms exposed to brain homogenates from chronic but not acute TBI mice, or from mice in which tau^TBI had been transmitted by intracerebral inoculation, had impaired motility and neuromuscular synaptic transmission. Results were similar when worms were given brain homogenates from transgenic mice overexpressing tau P301L, a tauopathy mouse model, suggesting that TBI-induced and mutant tau have similar toxic properties. P301L brain homogenate toxicity was similar in wild-type and ptl-1 knock-out worms, indicating that the nematode tau homolog protein PTL-1 was not required to mediate the toxic effect. Harsh protease digestion to eliminate the protein component of the homogenates, pre-incubation with anti-tau antibodies or tau depletion by immunoprecipitation, abolished the toxicity. Homogenates of chronic TBI brains from tau knock-out mice were not toxic to C. elegans, whereas oligomeric recombinant tau was sufficient to impair their motility.

This study indicates that tau^TBI impairs motor activity and synaptic transmission in C. elegans and supports a pathogenic role of tau^TBI in the long-term consequences of TBI. It also sets the groundwork for the development of a C. elegans-based platform for screening anti-tau compounds.

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Traumatic brain injury (TBI) in mice induces a progressive tau pathology.

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Brain-injured tissue from chronic but not acute TBI mice impairs C. elegans motility.

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TBI tissue immunodepleted of tau or from tau knock-out mice has no toxic effect.

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Brain-injured tissue from TBI mice impairs neuromuscular transmission in worms.

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C. elegans is a tractable model for investigating tau toxicity generated by TBI.

Liquid-Liquid Phase Separation in Physiology and Pathophysiology of the Nervous System

Molecules within cells are segregated into functional domains to form various organelles. While some of those organelles are delimited by lipid membranes demarcating their constituents, others lack a membrane enclosure. Recently, liquid-liquid phase separation (LLPS) revolutionized our view of how segregation of macromolecules can produce membraneless organelles. While the concept of LLPS has been well studied in the areas of soft matter physics and polymer chemistry, its significance has only recently been recognized in the field of biology. It occurs typically between macromolecules that have multivalent interactions. Interestingly, these features are present in many molecules that exert key functions within neurons. In this review, we cover recent topics of LLPS in different contexts of neuronal physiology and pathology.

Coiled-Coil Motifs of RNA-Binding Proteins: Dynamicity in RNA Regulation

Neuronal granules are biomolecular condensates that concentrate high quantities of RNAs and RNA-related proteins within neurons. These dense packets of information are trafficked from the soma to distal sites rich in polysomes, where local protein synthesis can occur. Movement of neuronal granules to distal sites, and local protein synthesis, play a critical role in synaptic plasticity. The formation of neuronal granules is intriguing; these granules lack a membrane and instead phase separate due to protein and RNA interactions. Low complexity motifs and RNA binding domains are highly prevalent in these proteins. Here, we introduce the role that coiled-coil motifs play in neuronal granule proteins, and investigate the structure-function relationship of coiled-coil proteins in RNA regulation. Interestingly, low complexity domains and coiled-coil motifs are highly dynamic, allowing for increased functional response to environmental influences. Finally, biomolecular condensates have been suggested to drive the formation of toxic, neurodegenerative proteins such as TDP-43 and tau. Here, we review the conversion of coiled-coil motifs to amyloid structures, and speculate a role that neuronal granules play in coiled-coil to amyloid conversions of neurodegenerative proteins.

Super-Resolution Imaging to Study Co-Localization of Proteins and Synaptic Markers in Primary Neurons

Synapses are the functional elements of neurons and their defects or losses are at the basis of several neurodegenerative and neurological disorders. Imaging studies are widely used to investigate their function and plasticity in physiological and pathological conditions. Because of their size and structure, localization studies of proteins require high-resolution imaging techniques. In this protocol, we describe a procedure to study in primary neurons the co-localization of target proteins with synaptic markers at a super-resolution level using structured illumination microscopy (SIM). SIM is a patterned-light illumination technique that doubles the spatial resolution of wide-field microscopy, reaching a detail of around 100 nm. The protocol indicates the required controls and settings for robust co-localization studies and an overview of the statistical methods to analyze the imaging data properly.

Cytoplasmic Polyadenylation Element Binding Proteins CPEB1 and CPEB3 Regulate the Translation of FosB and Are Required for Maintaining Addiction-Like Behaviors Induced by Cocaine

A recurrent and devastating feature of addiction to a drug of abuse is its persistence, which is mediated by maladaptive long-term memories of the highly pleasurable experience initially associated with the consumption of the drug. We have recently found that members of the CPEB family of proteins (Cytoplasmic Polyadenylation Element-Binding Proteins) are involved in the maintenance of spatial memory. However, their possible role in the maintenance of memories that sustain addictive behavior has yet to be explored. Little is known about any of the mechanisms for maintaining memories for addictive behavior. To address the mechanisms whereby addictive behavior is maintained over time, we utilized a conditional transgenic mouse model expressing a dominant-negative version of CPEB1 that abolishes the activity in the forebrain of two of the four CPEB isoforms (CPEB1 and CPEB3). We found that, following cocaine administration, these dominant-negative (DN) CPEB mice showed a significant decrease, when compared to wild type (WT) mice, in both locomotor sensitizations and conditioned place preference (CPP), two indices of addictive behavior. Supporting these behavioral results, we also found a difference between WT and DN-CPEB1-3 mice in the cocaine-induced synaptic depression in the core of the Nucleus Accumbens (NAc). Finally, we found that (1) CPEB is reduced in transgenic mice following cocaine injections and that (2) FosB, known for its contribution to establishing the addictive phenotype, when its expression in the striatum is increased by drug administration, is a novel target of CPEBs molecules. Thus, our study highlights how CPEB1 and CPEB3 act on target mRNAs to build the neuroadaptative implicit memory responses that lead to the development of the cocaine addictive phenotypes in mammals.

Super Resolution Microscopy of SUMO Proteins in Neurons

The ubiquitously expressed SUMO proteins regulate a plethora of cellular pathways and processes. While they have a predominantly nuclear localization, extranuclear roles of SUMO isoforms at the synapse have also been described, making SUMOylation one of the major post-translational regulators of nerve functions. These findings have however recently been challenged, at least for SUMO1, by the analysis of knock-in mice expressing His₆-HA-SUMO1, where the authors failed to detect the protein at the synapse. In the ongoing dispute, the subcellular distribution in neurons of SUMO2/3 and of the E2 SUMO ligase Ubc9 has not been examined. To investigate whether SUMO proteins do or do not localize at the synapse, we studied their localization in hippocampal primary neurons by super resolution microscopy. We found that SUMO1, SUMO2/3, and Ubc9 are primarily nuclear proteins, which also colocalize partially with pre- and post-synaptic markers such as synaptophysin and PSD95.

The Persistence of Hippocampal-Based Memory Requires Protein Synthesis Mediated by the Prion-like Protein CPEB3

Consolidation of long-term memories depends on de novo protein synthesis. Several translational regulators have been identified, and their contribution to the formation of memory has been assessed in the mouse hippocampus. None of them, however, has been implicated in the persistence of memory. Although persistence is a key feature of long-term memory, how this occurs, despite the rapid turnover of its molecular substrates, is poorly understood. Here we find that both memory storage and its underlying synaptic plasticity are mediated by the increase in level and in the aggregation of the prion-like translational regulator CPEB3 (cytoplasmic polyadenylation element-binding protein). Genetic ablation of CPEB3 impairs the maintenance of both hippocampal long-term potentiation and hippocampus-dependent spatial memory. We propose a model whereby persistence of long-term memory results from the assembly of CPEB3 into aggregates. These aggregates serve as functional prions and regulate local protein synthesis necessary for the maintenance of long-term memory.

SUMOylation Is an Inhibitory Constraint that Regulates the Prion-like Aggregation and Activity of CPEB3

Protein synthesis is crucial for the maintenance of long-term-memory-related synaptic plasticity. The prion-like cytoplasmic polyadenylation element-binding protein 3 (CPEB3) regulates the translation of several mRNAs important for long-term synaptic plasticity in the hippocampus. Here, we provide evidence that the prion-like aggregation and activity of CPEB3 is controlled by SUMOylation. In the basal state, CPEB3 is a repressor and is soluble. Under these circumstances, CPEB3 is SUMOylated in hippocampal neurons both in vitro and in vivo. Following neuronal stimulation, CPEB3 is converted into an active form that promotes the translation of target mRNAs, and this is associated with a decrease of SUMOylation and an increase of aggregation. A chimeric CPEB3 protein fused to SUMO cannot form aggregates and cannot activate the translation of target mRNAs. These findings suggest a model whereby SUMO regulates translation of mRNAs and structural synaptic plasticity by modulating the aggregation of the prion-like protein CPEB3.

Neuralized1 activates CPEB3: a function for nonproteolytic ubiquitin in synaptic plasticity and memory storage

The cytoplasmic polyadenylation element-binding protein 3 (CPEB3), a regulator of local protein synthesis, is the mouse homolog of ApCPEB, a functional prion protein in Aplysia. Here, we provide evidence that CPEB3 is activated by Neuralized1, an E3 ubiquitin ligase. In hippocampal cultures, CPEB3 activated by Neuralized1-mediated ubiquitination leads both to the growth of new dendritic spines and to an increase of the GluA1 and GluA2 subunits of AMPA receptors, two CPEB3 targets essential for synaptic plasticity. Conditional overexpression of Neuralized1 similarly increases GluA1 and GluA2 and the number of spines and functional synapses in the hippocampus and is reflected in enhanced hippocampal-dependent memory and synaptic plasticity. By contrast, inhibition of Neuralized1 reduces GluA1 and GluA2 levels and impairs hippocampal-dependent memory and synaptic plasticity. These results suggest a model whereby Neuralized1-dependent ubiquitination facilitates hippocampal plasticity and hippocampal-dependent memory storage by modulating the activity of CPEB3 and CPEB3-dependent protein synthesis and synapse formation.

Juvenile papillomatosis of the breast in young male: a case report

Juvenile papillomatosis of the breast ("Swiss cheese disease'') is a benign localized proliferative condition of the breast which occurs almost exclusively in young adult women. Patients with this lesion often have a family history of breast carcinoma, but rarely carcinoma may coexist with the lesion at the time of diagnosis. We present a case of a young male with juvenile papillomatosis of the breast. The pathology and clinical management of this rare lesion is discussed.

Essential role of coiled coils for aggregation and activity of Q/N-rich prions and PolyQ proteins

The functional switch of glutamine/asparagine (Q/N)-rich prions and the neurotoxicity of polyQ-expanded proteins involve complex aggregation-prone structural transitions, commonly presumed to be forming β sheets. By analyzing sequences of interaction partners of these proteins, we discovered a recurrent presence of coiled-coil domains both in the partners and in segments that flank or overlap Q/N-rich and polyQ domains. Since coiled coils can mediate protein interactions and multimerization, we studied their possible involvement in Q/N-rich and polyQ aggregations. Using circular dichroism and chemical crosslinking, we found that Q/N-rich and polyQ peptides form α-helical coiled coils in vitro and assemble into multimers. Using structure-guided mutagenesis, we found that coiled-coil domains modulate in vivo properties of two Q/N-rich prions and polyQ-expanded huntingtin. Mutations that disrupt coiled coils impair aggregation and activity, whereas mutations that enhance coiled-coil propensity promote aggregation. These findings support a coiled-coil model for the functional switch of Q/N-rich prions and for the pathogenesis of polyQ-expansion diseases.

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.

Invasive ductal carcinoma arising in ectopic breast tissue of the axilla. Case report and review of the literature

Mammary carcinoma arising in ectopic breast tissue is an uncommon occurrence. Most reported cases have involved ductal carcinoma, but other types, such as medullary, papillary, and lobular carcinomas, have been described. For pathologists, the diagnosis of mammary carcinoma arising in ectopic breast tissue can be difficult, especially in the axilla, where carcinoma of adnexal origin must be excluded. We describe a 51-year-old woman who developed invasive secretory ductal carcinoma in ectopic left axillary breast tissue and micrometastatic carcinoma in an ipsilateral axillary lymph node. The carcinoma arose in a left axillary mass that had been present for several years, from which she had secreted fluid during prior menstrual periods.

Mutant prion protein expression is associated with an alteration of the Rab GDP dissociation inhibitor alpha (GDI)/Rab11 pathway

The prion protein (PrP) is a glycosylphosphatidylinositol-anchored membrane glycoprotein that plays a vital role in prion diseases, a class of fatal neurodegenerative disorders of humans and animals. Approximately 20% of human prion diseases display autosomal dominant inheritance and are linked to mutations in the PrP gene on chromosome 20. PrP mutations are thought to favor the conformational conversion of PrP into a misfolded isoform that causes disease by an unknown mechanism. The PrP mutation D178N/Met-129 is linked to fatal familial insomnia, which causes severe sleep abnormalities and autonomic dysfunction. We showed by immunoelectron microscopy that this mutant PrP accumulates abnormally in the endoplasmic reticulum and Golgi of transfected neuroblastoma N2a cells. To investigate the impact of intracellular PrP accumulation on cellular homeostasis, we did a two-dimensional gel-based differential proteomics analysis. We used wide range immobilized pH gradient strips, pH 4-7 and 6-11, to analyze a large number of proteins. We found changes in proteins involved in energy metabolism, redox regulation, and vesicular transport. Rab GDP dissociation inhibitor alpha (GDI) was one of the proteins that changed most. GDI regulates vesicular protein trafficking by acting on the activity of several Rab proteins. We found a specific reduction in the level of functional Rab11 in mutant PrP-expressing cells associated with impaired post-Golgi trafficking. Our data are consistent with a model by which mutant PrP induces overexpression of GDI, activating a cytotoxic feedback loop that leads to protein accumulation in the secretory pathway.

Neurotoxic and gliotrophic activity of a synthetic peptide homologous to Gerstmann-Sträussler-Scheinker disease amyloid protein

Amyloid fibrils in Gerstmann-Sträussler-Scheinker (GSS) disease are composed of a fragment of the prion protein (PrP), the N and C termini of which correspond to ragged residues 81-90 and 144-153. A synthetic peptide spanning the sequence 82-146 (PrP 82-146) polymerizes into protease-resistant fibrils with the tinctorial properties of amyloid. We investigated the biological activity of PrP 82-146 and of two nonamyloidogenic variants of PrP 82-146 with scrambled amino acid sequence 106-126 or 127-146. Cortical neurons prepared from rat and mouse embryos were chronically exposed to the PrP 82-146 peptides (10-50 microM). PrP 82-146 and the partially scrambled peptides induced neuronal death with a similar dose-response pattern, indicating that neurotoxicity was independent of amyloid fibril formation. Neurotoxicity was significantly reduced by coadministration of an anti-oligomer antibody, suggesting that PrP 82-146 oligomers are primarily responsible for triggering cell death. Neurons from PrP knock-out (Prnp0/0) mice were significantly less sensitive to PrP 82-146 toxicity than neurons expressing PrP. The gliotrophic effect of PrP 82-146 was determined by [methyl-3H]-thymidine incorporation in cultured astrocytes. Treatment with PrP 82-146 stimulated [methyl-3H]-thymidine uptake 3.5-fold. This activity was significantly less when the 106-126 or 127-146 regions were disrupted, indicating that PrP 82-146 amyloid activates the gliotrophic response. Prnp0/0 astrocytes were insensitive to the proliferative stimulus of PrP 82-146. These results underline the role of cerebral accumulation of abnormally folded PrP fragments and indicate that cellular PrP governs the pathogenic process.

Analysis of the cerebellar proteome in a transgenic mouse model of inherited prion disease reveals preclinical alteration of calcineurin activity

Inherited prion diseases are linked to insertional and point mutations in the prion protein (PrP) gene, which favor conversion of PrP into a conformationally altered, pathogenic isoform. The cellular mechanism by which this process causes neurological dysfunction is unknown. Transgenic (Tg) (PG14) mice express a mouse PrP homolog of a nine-octapeptide insertion associated with an inherited prion disorder. These mice develop a progressive neurological syndrome characterized by ataxia and cerebellar atrophy due to synaptic degeneration in the molecular layer and massive apoptosis of granule neurons. To investigate the molecular events that may contribute to neurological dysfunction, we carried out a differential proteomic analysis of cerebella from Tg(PG14) mice at the preclinical, onset, and symptomatic phases of their neurological illness. 2-D maps of cerebellar proteins from Tg(PG14) mice were compared to those obtained from age-matched Tg(WT) mice that express wild-type PrP and remain healthy. Proteins whose levels were significantly modified in at least one stage of the Tg(PG14) disease were identified by PMF. Analysis detected a preclinical decrease of the calcium/calmodulin-dependent phosphatase calcineurin (CaN) in granule neurons, suggesting that dysregulation of CaN activity induced by mutant PrP may be responsible for the cerebellar dysfunction in Tg(PG14) mice.

Conditions of endoplasmic reticulum stress favor the accumulation of cytosolic prion protein

After signal sequence-dependent targeting to the endoplasmic reticulum (ER), prion protein (PrP) undergoes several post-translational modifications, including glycosylation, disulfide bond formation, and the addition of a glycosylphosphatidylinositol anchor. As a result, multiple isoforms are generated. Because of the intrinsic weakness of the PrP signal sequence, a fraction of newly synthesized molecules fails to translocate and localizes to the cytosol. The physiopathologic role of this cytosolic isoform is still being debated. Here we have shown that, in both cultured cell lines and primary neurons, ER stress conditions weaken PrP co-translational translocation, favoring accumulation of aggregation-prone cytosolic species, which retain the signal sequence but lack N-glycans and disulfides. Inhibition of proteasomes further increases the levels of cytosolic PrP. Overexpression of spliced XBP1 facilitates ER translocation, suggesting that downstream elements of the Ire1-XBP1 pathway are involved in PrP targeting. These studies reveal a link between ER stress and the formation of cytosolic PrP isoforms potentially endowed with novel signaling or cytotoxic functions.

Cytosolic prion protein (PrP) is not toxic in N2a cells and primary neurons expressing pathogenic PrP mutations

Inherited prion diseases are linked to mutations in the prion protein (PrP) gene, which favor conversion of PrP into a conformationally altered, pathogenic isoform. The cellular mechanism by which this process causes neurological dysfunction is unknown. It has been proposed that neuronal death can be triggered by accumulation of PrP in the cytosol because of impairment of proteasomal degradation of misfolded PrP molecules retrotranslocated from the endoplasmic reticulum (Ma, J., Wollmann, R., and Lindquist, S. (2002) Science 298, 1781-1785). To test whether this neurotoxic mechanism is operative in inherited prion diseases, we evaluated the effect of proteasome inhibitors on the viability of transfected N2a cells and primary neurons expressing mouse PrP homologues of the D178N and nine octapeptide mutations. We found that the inhibitors caused accumulation of an unglycosylated, aggregated form of PrP exclusively in transfected N2a expressing PrP from the cytomegalovirus promoter. This form contained an uncleaved signal peptide, indicating that it represented polypeptide chains that had failed to translocate into the ER lumen during synthesis, rather than retrogradely translocated PrP. Quantification of N2a viability in the presence of proteasome inhibitors demonstrated that accumulation of this form was not toxic. No evidence of cytosolic PrP was found in cerebellar granule neurons from transgenic mice expressing wild-type or mutant PrPs from the endogenous promoter, nor were these neurons more susceptible to proteasome inhibitor toxicity than neurons from PrP knock-out mice. Our analysis fails to confirm the previous observation that mislocation of PrP in the cytosol is neurotoxic, and argues against the hypothesis that perturbation of PrP metabolism through the proteasomal pathway plays a pathogenic role in prion diseases.

The neurotoxicity of prion protein (PrP) peptide 106–126 is independent of the expression level of PrP and is not mediated by abnormal PrP species

A synthetic peptide homologous to region 106-126 of the prion protein (PrP) is toxic to cells expressing PrP, but not to PrP knockout neurons, arguing for a specific role of PrP in mediating the peptide's activity. Whether this is related to a gain of toxicity or a loss of function of PrP is not clear. We explored the possibility that PrP106-126 triggered formation of PrP(Sc) or other neurotoxic PrP species. We found that PrP106-126 did not induce detergent-insoluble and protease-resistant PrP, nor did it alter its membrane topology or cellular distribution. We also found that neurons expressing endogenous or higher level of either wild-type PrP or a nine-octapeptide insertional mutant were equally susceptible to PrP106-126, and that sub-physiological PrP expression was sufficient to restore vulnerability to the peptide. These results indicate that PrP106-126 interferes with a PrP function that requires only low protein levels, and is not impaired by a pathogenic insertion in the octapeptide region.

Proteasome inhibition and aggregation in Parkinson's disease: a comparative study in untransfected and transfected cells

Dysfunction of the ubiquitin-proteasome system (UPS) has been implicated in Parkinson's disease (PD) and other neurodegenerative disorders. We have investigated the effect of UPS inhibition on the metabolism of alpha-synuclein (SYN) and parkin, two proteins genetically and histopathologically associated to PD. Pharmacological inhibition of proteasome induced accumulation of both parkin and SYN in transfected PC12 cells. We found that this effect was caused by increased protein synthesis rather than impairment of protein degradation, suggesting that inhibition of the UPS might lead to non-specific up-regulation of cytomegalovirus (CMV)-driven transcription. To investigate whether endogenous parkin and SYN can be substrate of the UPS, untransfected PC12 cells and primary mesencephalic neurones were exposed to proteasome inhibitors, and parkin and SYN expression was evaluated at both protein and mRNA level. Under these conditions, we found that proteasome inhibitors did not affect the level of endogenous parkin and SYN. However, we confirmed that dopaminergic neurones were selectively vulnerable to the toxicity of proteasome inhibitors. Our results indicate that studies involving the use of proteasome inhibitors, particularly those in which proteins are expressed from a heterologous promoter, are subjected to potential artefacts that need to be considered for the interpretation of the role of UPS in PD pathogenesis.

Mutant PrP is delayed in its exit from the endoplasmic reticulum, but neither wild-type nor mutant PrP undergoes retrotranslocation prior to proteasomal degradation

The cellular mechanisms by which prions cause neurological dysfunction are poorly understood. To address this issue, we have been using cultured cells to analyze the localization, biosynthesis, and metabolism of PrP molecules carrying mutations associated with familial prion diseases. We report here that mutant PrP molecules are delayed in their maturation to an endoglycosidase H-resistant form after biosynthetic labeling, suggesting that they are impaired in their exit from the endoplasmic reticulum (ER). However, we find that proteasome inhibitors have no effect on the maturation or turnover of either mutant or wild-type PrP molecules. Thus, in contrast to recent studies from other laboratories, our work indicates that PrP is not subject to retrotranslocation from the ER into the cytoplasm prior to degradation by the proteasome. We find that in transfected cells, but not in cultured neurons, proteasome inhibitors cause accumulation of an unglycosylated, signal peptide-bearing form of PrP on the cytoplasmic face of the ER membrane. Thus, under conditions of elevated expression, a small fraction of PrP chains is not translocated into the ER lumen during synthesis, and is rapidly degraded in the cytoplasm by the proteasome. Finally, we report a previously unappreciated artifact caused by treatment of cells with proteasome inhibitors: an increase in PrP mRNA level and synthetic rate when the protein is expressed from a vector containing a viral promoter. We suggest that this phenomenon may explain some of the dramatic effects of proteasome inhibitors observed in other studies. Our results clarify the role of the proteasome in the cell biology of PrP, and suggest reasonable hypotheses for the molecular pathology of inherited prion diseases.

Dose intensification of mitoxantrone in combination with paclitaxel in advanced breast cancer: a phase II study

BACKGROUND

Paclitaxel and mitoxantrone are highly active agents in the treatment of advanced breast cancer (ABC). This study evaluated the combination of paclitaxel and mitoxantrone in patients with advanced breast cancer to determine activity and toxicity.

PATIENTS AND METHOD

42 patients with ABC were treated with paclitaxel at a fixed dose of 175 mg/m2 intravenous (IV) by a 3-hour infusion on day 1, while mitoxantrone was given by 2 mg/m2 increments, starting from 10 mg/m2 by bolus IV injection on day 1 after paclitaxel. Cycles were repeated every 3 weeks. Mitoxantrone doses were increased if the maximum tolerated dose (MTD) had not been reached.

RESULT

The overall response rate (CR + PR) was 69% (CI 95%: 55-83). Six (14%) patients obtained CR and 23 (55%) PR with a median duration of response of 8 months (range 2-16). There were no differences in response rates (RR) between the three levels of mitoxantrone. Median time to failure and survival were 7 months (range 1-26) and 12 months (range 2-29), respectively. After 12 months 14 (33%) patients had died and 8 (19%) patients were alive after 18 months. MTD was reached at 14 mg/m2 level of mitoxantrone. Leukopenia was evident in 39 (93%) of total patients and was severe in 28 (67%) patients. All non-hematological toxicity observed was mild.

CONCLUSION

This trial shows the activity of paclitaxel and mitoxantrone in ABC and finds that a dose of 14 mg/m2 of mitoxantrone is the MTD in combination with a fixed dose of 175 mg/m2 of paclitaxel without granulocyte colony stimulating factor (G-CSF).