Substitutions of PrP N-terminal histidine residues modulate scrapie disease pathogenesis and incubation time in transgenic mice

Prion diseases have been linked to impaired copper homeostasis and copper induced-oxidative damage to the brain. Divalent metal ions, such as Cu2+ and Zn2+, bind to cellular prion protein (PrPC) at octapeptide repeat (OR) and non-OR sites within the N-terminal half of the protein but information on the impact of such binding on conversion to the misfolded isoform often derives from studies using either OR and non-OR peptides or bacterially-expressed recombinant PrP. Here we created new transgenic mouse lines expressing PrP with disrupted copper binding sites within all four histidine-containing OR's (sites 1-4, H60G, H68G, H76G, H84G, "TetraH>G" allele) or at site 5 (composed of residues His-95 and His-110; "H95G" allele) and monitored the formation of misfolded PrP in vivo. Novel transgenic mice expressing PrP(TetraH>G) at levels comparable to wild-type (wt) controls were susceptible to mouse-adapted scrapie strain RML but showed significantly prolonged incubation times. In contrast, amino acid replacement at residue 95 accelerated disease progression in corresponding PrP(H95G) mice. Neuropathological lesions in terminally ill transgenic mice were similar to scrapie-infected wt controls, but less severe. The pattern of PrPSc deposition, however, was not synaptic as seen in wt animals, but instead dense globular plaque-like accumulations of PrPSc in TgPrP(TetraH>G) mice and diffuse PrPSc deposition in (TgPrP(H95G) mice), were observed throughout all brain sections. We conclude that OR and site 5 histidine substitutions have divergent phenotypic impacts and that cis interactions between the OR region and the site 5 region modulate pathogenic outcomes by affecting the PrP globular domain.

Bortezomib before and after high-dose therapy in myeloma: long-term results from the phase III HOVON-65/GMMG-HD4 trial

The Dutch-Belgian Cooperative Trial Group for Hematology Oncology Group-65/German-speaking Myeloma Multicenter Group-HD4 (HOVON-65/GMMG-HD4) phase III trial compared bortezomib (BTZ) before and after high-dose melphalan and autologous stem cell transplantation (HDM, PAD arm) compared with classical cytotoxic agents prior and thalidomide after HDM (VAD arm) in multiple myeloma (MM) patients aged 18-65 years. Here, the long-term follow-up and data on second primary malignancies (SPM) are presented. After a median follow-up of 96 months, progression-free survival (censored at allogeneic transplantation, PFS) remained significantly prolonged in the PAD versus VAD arm (hazard ratio (HR)=0.76, 95% confidence interval (95% CI) of 0.65-0.89, P=0.001). Overall survival (OS) was similar in the PAD versus VAD arm (HR=0.89, 95% CI: 0.74-1.08, P=0.24). The incidence of SPM were similar between the two arms (7% each, P=0.73). The negative prognostic effects of the cytogenetic aberration deletion 17p13 (clone size ⩾10%) and renal impairment at baseline (serum creatinine >2 mg dl^-1) on PFS and OS remained abrogated in the PAD but not VAD arm. OS from first relapse/progression was similar between the study arms (HR=1.02, P=0.85). In conclusion, the survival benefit with BTZ induction/maintenance compared with classical cytotoxic agents and thalidomide maintenance is maintained without an increased risk of SPM.

Role of caspases in CD95-induced biphasic activation of acid sphingomyelinase

Acid sphingomyelinase (A-SMase) plays an important role in the initiation of CD95 signaling by forming ceramide-enriched membrane domains that enable clustering and activation of the death receptors. In TNF-R1 and TRAIL-R1/R2 signaling, A-SMase also contributes to the lysosomal apoptosis pathway triggered by receptor internalization. Here, we investigated the molecular mechanism of CD95-mediated A-SMase activation, demonstrating that A-SMase is located in internalized CD95-receptosomes and is activated by the CD95/CD95L complex in a biphasic manner.Since several caspases have been described to be involved in the activation of A-SMase, we evaluated expression levels of caspase-8, caspase-7 and caspase-3 in CD95-receptosomes. The occurrence of cleaved caspase-8 correlated with the first peak of A-SMase activity and translocation of the A-SMase to the cell surface which could be blocked by the caspase-8 inhibitor IETD.Inhibition of CD95-internalization selectively reduced the second phase of A-SMase activity, suggesting a fusion between internalized CD95-receptosomes and an intracellular vesicular pool of A-SMase. Further analysis demonstrated that caspase-7 activity correlates with the second phase of the A-SMase activity, whereas active caspase-3 is present at early and late internalization time points. Blocking caspases-7/ -3 by DEVD reduced the second phase of A-SMase activation in CD95-receptosomes suggesting the potential role of caspase-7 or -3 for late A-SMase activation.In summary, we describe a biphasic A-SMase activation in CD95-receptosomes indicating (I.) a caspase-8 dependent translocation of A-SMase to plasma membrane and (II.) a caspase-7 and/or -3 dependent fusion of internalized CD95-receptosomes with intracellular A-SMase-containing vesicles.

Genetic factors influencing the risk of multiple myeloma bone disease

A major complication of multiple myeloma (MM) is the development of osteolytic lesions, fractures and bone pain. To identify genetic variants influencing the development of MM bone disease (MBD), we analyzed MM patients of European ancestry (totaling 3774), which had been radiologically surveyed for MBD. Each patient had been genotyped for ~6 00 000 single-nucleotide polymorphisms with genotypes for six million common variants imputed using 1000 Genomes Project and UK10K as reference. We identified a locus at 8q24.12 for MBD (rs4407910, OPG/TNFRSF11B, odds ratio=1.38, P=4.09 × 10(-9)) and a promising association at 19q13.43 (rs74676832, odds ratio=1.97, P=9.33 × 10(-7)). Our findings demonstrate that germline variation influences MBD and highlights the importance of RANK/RANKL/OPG pathway in MBD development. These findings will contribute to the development of future strategies for prevention of MBD in the early precancerous phases of MM.

Abstract 2955: Trail-R2: A death receptor turns malignant upon nuclear localization

High intracellular expression of death receptor TRAIL-R2 correlates with poor prognosis for different tumor entities and thus suggests tumor-promoting activity of intracellular TRAIL-R2. We demonstrate that TRAIL-R2 interacts with the core Microprocessor components Drosha and DGCR8 and the associated regulatory proteins p68, hnRNPA1, NF45 and NF90 in the nucleus. Knockdown of TRAIL-R2 enhances Drosha-mediated processing of pri-let-7 resulting in increased levels of mature let-7, reduced expression of let-7-targets Lin28B and HMGA2 and inhibition of cell proliferation. In contrast, high abundance of nuclear TRAIL-R2, often detected in pancreatic cancer, correlates with enhanced expression of HMGA2 and dictates worse prognosis. Importantly, knockdown of TRAIL-R2 inhibits pancreatic tumor growth in an orthotopic xenotransplantation mouse model and reduced nuclear levels of TRAIL-R2 accompany differentiation of pancreatic epithelial cells in vitro. In conclusion, we define a novel function of nuclear TRAIL death receptor contributing to malignancy by inhibition of let-7-maturation (Haselmann et al., Gastroenterology epub ahead of print).

In extension to our work on pancreatic cancer we further show nuclear TRAIL-R2 functions to be of relevance in breast cancer bone metastasis. Stably shRNA- transfected clones of MDAMB231 cells revealed metastatic lesions in only 2/12 mice upon TRAIL-R2 knock-down, whereas TRAIL-R1 and control knock-down clones exhibited multiple metastases throughout the groups of 12 mice each. Under in vitro conditions some decreased apoptosis rate was observed in both TRAIL-R knock-down clonal populations compared to the controls upon TRAIL treatment. Preliminary results suggest Mesenchymal-Epithelial-Transition (as indicated by increased E-Cadherin expression in TRAIL-R2 knock-down cells) as a mechanism for reduced metastasis.

In summary, we show nuclear death receptor TRAIL-R2 to significantly contribute to malignant progression in two different pre-clinical tumor models. Thus, targeted intervention to prevent nuclear localization may serve as a novel therapeutic strategy.

Supported by DFG (TR 1063/2-1 and TR 1063/3-1 - SKELMET FOR 1586).

Citation Format: Holger Kalthoff, Verena Haselmann, Alexandra Kurz, Uwe Bertsch, Sebastian Huebner, Hendrik Fritsche, Charlotte Hauser, Christian Schem, Rob Tower, Thorsten Heilmann, Sanjay Tiwari, Claus C. Glüer, Anna Trauzold. Trail-R2: A death receptor turns malignant upon nuclear localization. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2955. doi:10.1158/1538-7445.AM2014-2955

Compartmentalization of TNF-related apoptosis-inducing ligand (TRAIL) death receptor functions: emerging role of nuclear TRAIL-R2

Localized in the plasma membrane, death domain-containing TNF-related apoptosis-inducing ligand (TRAIL) receptors, TRAIL-R1 and TRAIL-R2, induce apoptosis and non-apoptotic signaling when crosslinked by the ligand TRAIL or by agonistic receptor-specific antibodies. Recently, an increasing body of evidence has accumulated that TRAIL receptors are additionally found in noncanonical intracellular locations in a wide range of cell types, preferentially cancer cells. Thus, besides their canonical locations in the plasma membrane and in intracellular membranes of the secretory pathway as well as endosomes and lysosomes, TRAIL receptors may also exist in autophagosomes, in nonmembraneous cytosolic compartment as well as in the nucleus. Such intracellular locations have been mainly regarded as hide-outs for these receptors representing a strategy for cancer cells to resist TRAIL-mediated apoptosis. Recently, a novel function of intracellular TRAIL-R2 has been revealed. When present in the nuclei of tumor cells, TRAIL-R2 inhibits the processing of the primary let-7 miRNA (pri-let-7) via interaction with accessory proteins of the Microprocessor complex. The nuclear TRAIL-R2-driven decrease in mature let-7 enhances the malignancy of cancer cells. This finding represents a new example of nuclear activity of typically plasma membrane-located cytokine and growth factor receptors. Furthermore, this extends the list of nucleic acid targets of the cell surface receptors by pri-miRNA in addition to DNA and mRNA. Here we review the diverse functions of TRAIL-R2 depending on its intracellular localization and we particularly discuss the nuclear TRAIL-R2 (nTRAIL-R2) function in the context of known nuclear activities of other normally plasma membrane-localized receptors.

Nuclear death receptor TRAIL-R2 inhibits maturation of let-7 and promotes proliferation of pancreatic and other tumor cells

BACKGROUND & AIMS

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL-R1) (TNFRSF10A) and TRAIL-R2 (TNFRSF10B) on the plasma membrane bind ligands that activate apoptotic and other signaling pathways. Cancer cells also might have TRAIL-R2 in the cytoplasm or nucleus, although little is known about its activities in these locations. We investigated the functions of nuclear TRAIL-R2 in cancer cell lines.

METHODS

Proteins that interact with TRAIL-R2 initially were identified in pancreatic cancer cells by immunoprecipitation, mass spectrometry, and immunofluorescence analyses. Findings were validated in colon, renal, lung, and breast cancer cells. Functions of TRAIL-R2 were determined from small interfering RNA knockdown, real-time polymerase chain reaction, Drosha-activity, microRNA array, proliferation, differentiation, and immunoblot experiments. We assessed the effects of TRAIL-R2 overexpression or knockdown in human pancreatic ductal adenocarcinoma (PDAC) cells and their ability to form tumors in mice. We also analyzed levels of TRAIL-R2 in sections of PDACs and non-neoplastic peritumoral ducts from patients.

RESULTS

TRAIL-R2 was found to interact with the core microprocessor components Drosha and DGCR8 and the associated regulatory proteins p68, hnRNPA1, NF45, and NF90 in nuclei of PDAC and other tumor cells. Knockdown of TRAIL-R2 increased Drosha-mediated processing of the let-7 microRNA precursor primary let-7 (resulting in increased levels of mature let-7), reduced levels of the let-7 targets (LIN28B and HMGA2), and inhibited cell proliferation. PDAC tissues from patients had higher levels of nuclear TRAIL-R2 than non-neoplastic pancreatic tissue, which correlated with increased nuclear levels of HMGA2 and poor outcomes. Knockdown of TRAIL-R2 in PDAC cells slowed their growth as orthotopic tumors in mice. Reduced nuclear levels of TRAIL-R2 in cultured pancreatic epithelial cells promoted their differentiation.

CONCLUSIONS

Nuclear TRAIL-R2 inhibits maturation of the microRNA let-7 in pancreatic cancer cell lines and increases their proliferation. Pancreatic tumor samples have increased levels of nuclear TRAIL-R2, which correlate with poor outcome of patients. These findings indicate that in the nucleus, death receptors can function as tumor promoters and might be therapeutic targets.

Anle138b: a novel oligomer modulator for disease-modifying therapy of neurodegenerative diseases such as prion and Parkinson's disease

In neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD) and prion diseases, deposits of aggregated disease-specific proteins are found. Oligomeric aggregates are presumed to be the key neurotoxic agent. Here we describe the novel oligomer modulator anle138b [3-(1,3-benzodioxol-5-yl)-5-(3-bromophenyl)-1H-pyrazole], an aggregation inhibitor we developed based on a systematic high-throughput screening campaign combined with medicinal chemistry optimization. In vitro, anle138b blocked the formation of pathological aggregates of prion protein (PrP^Sc) and of α-synuclein (α-syn), which is deposited in PD and other synucleinopathies such as dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Notably, anle138b strongly inhibited all prion strains tested including BSE-derived and human prions. Anle138b showed structure-dependent binding to pathological aggregates and strongly inhibited formation of pathological oligomers in vitro and in vivo both for prion protein and α-synuclein. Both in mouse models of prion disease and in three different PD mouse models, anle138b strongly inhibited oligomer accumulation, neuronal degeneration, and disease progression in vivo. Anle138b had no detectable toxicity at therapeutic doses and an excellent oral bioavailability and blood–brain-barrier penetration. Our findings indicate that oligomer modulators provide a new approach for disease-modifying therapy in these diseases, for which only symptomatic treatment is available so far. Moreover, our findings suggest that pathological oligomers in neurodegenerative diseases share structural features, although the main protein component is disease-specific, indicating that compounds such as anle138b that modulate oligomer formation by targeting structure-dependent epitopes can have a broad spectrum of activity in the treatment of different protein aggregation diseases.

From high-throughput cell culture screening to mouse model: identification of new inhibitor classes against prion disease

Transmissible spongiform encephalopathies (TSE) or prion diseases belong to a category of fatal and so far untreatable neurodegenerative conditions. All prion diseases are characterized by both degeneration in the central nervous system (CNS) in humans and animals and the deposition and accumulation of Proteinase K-resistant prion protein (PrP(res)). Until now, no pharmaceutical product has been available to cure these diseases or to alleviate their associated symptoms. Here, a cell-culture screening system is described that allows for the large-scale analysis of the PrP(res) inhibitory potential of a library of compounds and the identification of structural motifs leading potent compounds able to cause PrP(res) clearance at the cellular level. Based on different scrapie-infected cell lines, 10,000 substances were tested, out of which 530 potential inhibitors were identified. After re-screening and validation using a series of dilutions, 14 compounds were identified as the most effective. These 14 compounds were then used for therapeutic studies in a mouse bioassay to test and verify their in vivo potency. Two compounds exhibited therapeutic potential in the mouse model by significantly extending the survival time of intracerebrally infected mice, when treated 90 days after infection with scrapie.

Modulation of CD4+ T-cell activation by CD95 co-stimulation

CD95 is a dual-function receptor that exerts pro- or antiapoptotic effects depending on the cellular context, the state of activation, the signal threshold and the mode of ligation. In this study, we report that CD95 engagement modulates TCR/CD3-driven signaling pathways in resting T lymphocytes in a dose-dependent manner. While high doses of immobilized CD95 agonists silence T cells, lower concentrations augment activation and proliferation. We analyzed the co-stimulatory capacity of CD95 in detail in resting human CD4(+) T cells, and demonstrate that low-dose ligand-induced co-internalization of CD95 and TCR/CD3 complexes enables non-apoptotic caspase activation, the prolonged activation of MAP kinases, the upregulation of antiapoptotic proteins associated with apoptosis resistance, and the activation of transcription factors and cell-cycle regulators for the induction of proliferation and cytokine production. We propose that the levels of CD95L on antigen-presenting cells (APCs), neighboring T cells or epithelial cells regulate inhibitory or co-stimulatory CD95 signaling, which in turn is crucial for fine-tuning of primary T-cell activation.

Psychosocial outcome following genetic risk counselling for familial colorectal cancer. A comparison of affected patients and family members

Few studies have reported prospective data on psychosocial outcomes after genetic counselling in families with suspected hereditary non-polyposis colorectal cancer (HNPCC). This prospective study examines the impact of multidisciplinary risk counselling on the psychosocial outcome of 139 affected cancer patients and 233 family members without cancer at risk for HNPCC. Participants completed questionnaires specific to HNPCC before and 8 weeks after attending the familial cancer clinic. Affected patients' levels of distress were closely related to their health status and exceeded that of unaffected individuals, as did worry regarding their relatives' risk. A significant reduction in general anxiety (Hospital Anxiety and Depression Scale), distress specific to familial CRC (Impact of Events Scale) and general cancer worry (Distress Hereditary Disorder) was demonstrated after counselling in both affected patients and unaffected individuals. Reduction in distress was more pronounced in affected patients given a high risk of HNPCC compared with those at intermediate risk. Among unaffected individuals, distress declined regardless of what clinical risk they were assigned. Their perceptions of risk and cancer-related threat declined, while confidence in effective surveillance increased. These results suggest the beneficial effects of multidisciplinary counselling even when high-risk information is conveyed. A patient's previous cancer experience is likely to contribute to clinically relevant distress (15% of those patients), indicating the need for appropriate counselling.

Different structural stability and toxicity of PrP(ARR) and PrP(ARQ) sheep prion protein variants

The polymorphisms at amino acid residues 136, 154, and 171 in ovine prion protein (PrP) have been associated with different susceptibility to scrapie: animals expressing PrP(ARQ) [PrP(Ala136/Arg154/Gln171)] show vulnerability, whereas those that express PrP(ARR) [PrP(Ala136/Arg154/Arg171)] are resistant to scrapie. The aim of this study was to evaluate the in vitro toxic effects of PrP(ARR) and PrP(ARQ) variants in relation with their structural characteristics. We show that both peptides cause cell death inducing apoptosis but, unexpectedly, the scrapie resistant PrP(ARR) form was more toxic than the scrapie susceptible PrP(ARQ) variant. Moreover, the alpha-helical conformation of PrP(ARR) was less stable than that of PrP(ARQ) and the structural determinants responsible of these different conformational stabilities were characterized by spectroscopic analysis. We observed that PrP toxicity was inversely related to protein structural stability, being the unfolded conformation more toxic than the native one. However, the PrP(ARQ) variant displays a higher propensity to form large aggregates than PrP(ARR). Interestingly, in the presence of small amounts of PrP(ARR), PrP(ARQ) aggregability was reduced to levels similar to that of PrP(ARR). Thus, in contrast to PrP(ARR) toxicity, scrapie transmissibility seems to reside in the more stable conformation of PrP(ARQ) that allows the formation of large amyloid fibrils.

The configuration of the Cu2+ binding region in full-length human prion protein compared with the isolated octapeptide

The cellular prion protein (PrP(C)) is a copper binding protein. The molecular features of the Cu(2+) binding sites have been investigated and characterized by spectroscopic experiments on PrP(C)-derived peptides and the correctly folded human full-length PrP(C) (hPrP-[23-231]). These experiments allowed us to distinguish two different configurations of copper binding. The different copper complexes depend on sequence context, buffer conditions and stoichiometry of copper. The combined information of spectroscopic data from our EXAFS, EPR and ENDOR experiments was used to create models for these two copper complexes. A large number of conformations of these models were calculated using molecular mechanics computations, and the simulated spectra of these structures were compared with our experimental data. Common features and differences of the copper binding motifs are discussed in this paper and it remains for future investigations to study whether different configurations are associated with different functional states of PrP(C).

Lentivector-mediated RNAi efficiently suppresses prion protein and prolongs survival of scrapie-infected mice

Prion diseases are fatal neurodegenerative diseases characterized by the accumulation of PrP(Sc), the infectious and protease-resistant form of the cellular prion protein (PrP(C)). We generated lentivectors expressing PrP(C)-specific short hairpin RNAs (shRNAs) that efficiently silenced expression of the prion protein gene (Prnp) in primary neuronal cells. Treatment of scrapie-infected neuronal cells with these lentivectors resulted in an efficient and stable suppression of PrP(Sc) accumulation. After intracranial injection, lentiviral shRNA reduced PrP(C) expression in transgenic mice carrying multiple copies of Prnp. To test the therapeutic potential of lentiviral shRNA, we used what we believe to be a novel approach in which the clinical situation was mimicked. We generated chimeric mice derived from lentivector-transduced embryonic stem cells. Depending on the degree of chimerism, these animals carried the lentiviral shRNAs in a certain percentage of brain cells and expressed reduced levels of PrP(C). Importantly, in highly chimeric mice, survival after scrapie infection was significantly extended. Taken together, these data suggest that lentivector-mediated RNA interference could be an approach for the treatment of prion disease.

The configuration of the Cu2+ binding region in full-length human prion protein

The cellular prion protein (PrP(C)) is a Cu(2+) binding protein connected to the outer cell membrane. The molecular features of the Cu(2+) binding sites have been investigated and characterized by spectroscopic experiments on PrP(C)-derived peptides and the recombinant human full-length PrP(C )(hPrP-[23-231]). The hPrP-[23-231] was loaded with (63)Cu under slightly acidic (pH 6.0) or neutral conditions. The PrP(C)/Cu(2+)-complexes were investigated by extended X-ray absorption fine structure (EXAFS), electron paramagnetic resonance (EPR), and electron nuclear double resonance (ENDOR). For comparison, peptides from the copper-binding octarepeat domain were investigated in different environments. Molecular mechanics computations were used to select sterically possible peptide/Cu(2+) structures. The simulated EPR, ENDOR, and EXAFS spectra of these structures were compared with our experimental data. For a stoichiometry of two octarepeats per copper the resulting model has a square planar four nitrogen Cu(2+) coordination. Two nitrogens belong to imidazole rings of histidine residues. Further ligands are two deprotonated backbone amide nitrogens of the adjacent glycine residues and an axial oxygen of a water molecule. Our complex model differs significantly from those previously obtained for shorter peptides. Sequence context, buffer conditions and stoichiometry of copper show marked influence on the configuration of copper binding to PrP(C).

Unaltered prion protein cleavage in plasminogen-deficient mice

In normal brains and cultured cells, cellular prion protein (PrP) is partially found as N-terminally truncated fragments, designated C1 and C2. The cleavage of recombinant PrP to a fragment corresponding to C1 can be mediated by the protease plasmin (Pln) in vitro, suggesting that plasmin might be responsible for the generation of the C1 fragment in vivo as well. The cleavage pattern of PrP found in both brain lysates and other tissues of plasminogen knock-out mice, however, is unaltered. The presence of C1 fragment in homogenates from plasminogen-deficient mice in a comparable ratio with full-length PrP as can be found in wild-type animals indicates that other proteases in addition to plasmin are responsible for PrP cleavage in vivo.

Conversion efficiency of bank vole prion protein in vitro is determined by residues 155 and 170, but does not correlate with the high susceptibility of bank voles to sheep scrapie in vivo

The misfolded infectious isoform of the prion protein (PrP(Sc)) is thought to replicate in an autocatalytic manner by converting the cellular form (PrP(C)) into its pathogenic folding variant. The similarity in the amino acid sequence of PrP(C) and PrP(Sc) influences the conversion efficiency and is considered as the major determinant for the species barrier. We performed in vitro conversion reactions on wild-type and mutated PrP(C) to determine the role of the primary sequence for the high susceptibility of bank voles to scrapie. Different conversion efficiencies obtained with bank vole and mouse PrP(C) in reactions with several prion strains were due to differences at amino acid residues 155 and 170. However, the conversion efficiencies obtained with mouse and vole PrP(C) in reactions with sheep scrapie did not correlate with the susceptibility of the respective species to this prion strain. This discrepancy between in vitro and in vivo data may indicate that at least in the case of scrapie transmission to bank voles additional host factors can strongly modulate the species barrier. Furthermore, in vitro conversion reactions with different prion strains revealed that the degree of alteration of the conversion efficiency induced by amino acid exchanges was varying according to the prion strain. These results support the assumption that the repertoire of conformations adopted by a certain PrP(C) primary sequence is decisive for its convertibility to the strain-specific PrP(Sc) conformation.

Systematic identification of antiprion drugs by high-throughput screening based on scanning for intensely fluorescent targets

Conformational changes and aggregation of specific proteins are hallmarks of a number of diseases, like Alzheimer's disease, Parkinson's disease, and prion diseases. In the case of prion diseases, the prion protein (PrP), a neuronal glycoprotein, undergoes a conformational change from the normal, mainly alpha-helical conformation to a disease-associated, mainly beta-sheeted scrapie isoform (PrP(Sc)), which forms amyloid aggregates. This conversion, which is crucial for disease progression, depends on direct PrP(C)/PrP(Sc) interaction. We developed a high-throughput assay based on scanning for intensely fluorescent targets (SIFT) for the identification of drugs which interfere with this interaction at the molecular level. Screening of a library of 10,000 drug-like compounds yielded 256 primary hits, 80 of which were confirmed by dose response curves with half-maximal inhibitory effects ranging from 0.3 to 60 microM. Among these, six compounds displayed an inhibitory effect on PrP(Sc) propagation in scrapie-infected N2a cells. Four of these candidate drugs share an N'-benzylidene-benzohydrazide core structure. Thus, the combination of high-throughput in vitro assay with the established cell culture system provides a rapid and efficient method to identify new antiprion drugs, which corroborates that interaction of PrP(C) and PrP(Sc) is a crucial molecular step in the propagation of prions. Moreover, SIFT-based screening may facilitate the search for drugs against other diseases linked to protein aggregation.

Automated PrPres amplification using indirect sonication

Prions, which mainly consist of the scrapie isoform of the prion protein (PrP(Sc)), induce the misfolding of the physiological prion protein (PrP(C)). The Protein Misfolding Cyclic Amplification (PMCA), a process consisting of sonication and incubation, is one of the few methods thought to model autocatalytic prion replication and generation of proteinase K (PK)-resistant PrP (PrPres) in vitro. Here we show for the first time that the amplification may be achieved through direct as well as indirect sonication (water bath sonication using sealed sample containers), allowing the PMCA method to be automated. The automated method may serve as a valuable tool in high throughput screening for the diagnosis or compound identification for treatment of prion disease. The in vitro amplification process is weakly facilitated by divalent cations such as Mn, Zn and Ni, but not Cu, however, the presence of metal ions decreases the stability of PrPres against proteinase K digestion.

Single particle analysis of manganese-induced prion protein aggregates

Prion diseases are characterized by the conversion of the cellular prion protein (PrP(C)) to a disease-specific aggregated isoform (PrP(Sc)). We have shown that Mn(2+) ions amplify aggregation, whereas Cu(2+) has an inhibitory effect. To characterize Mn(2+)-induced aggregates, we used cross-correlation analysis as well as scanning for intensely fluorescent targets in an SDS-dependent aggregation assay with fluorescently labeled PrP. We found that the effect of Mn(2+) was mainly due to the association of preformed PrP oligomers to larger aggregates, rapidly reversible by EDTA, and independent of the histidine-dependent copper-binding sites of PrP, suggesting that Mn(2+) induces reversible intermolecular binding. In contrast, the inhibitory effect of Cu(2+) required binding to histidine-containing binding sites, indicating that binding of copper affects the structure of PrP(C) which in turn modifies the susceptibility to manganese and the ability to aggregate. These findings suggest that copper and manganese may also affect prion propagation in vivo.

Novel G335V mutation in the tau gene associated with early onset familial frontotemporal dementia

Mutations in the tau gene cause familial frontotemporal dementia and parkinsonism linked to chromosome 17. Here we describe a novel missense mutation in exon 12 of the tau gene, G335V, in a German family with frontotemporal dementia of early age at onset, in the third decade of life. Functional analysis of recombinant tau protein with the G335V mutation showed a dramatically reduced ability to promote microtubule assembly and a more rapid and accelerated tau filament formation, suggesting that the primary effect of the mutation might be the provision of a pool of unbound tau making it available for aberrant tau aggregation.

A new method to determine the structure of the metal environment in metalloproteins: investigation of the prion protein octapeptide repeat Cu2+ complex

Since high-intensity synchrotron radiation is available, "extended X-ray absorption fine structure" spectroscopy (EXAFS) is used for detailed structural analysis of metal ion environments in proteins. However, the information acquired is often insufficient to obtain an unambiguous picture. ENDOR spectroscopy allows the determination of hydrogen positions around a metal ion. However, again the structural information is limited. In the present study, a method is proposed which combines computations with spectroscopic data from EXAFS, EPR, electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM). From EXAFS a first picture of the nearest coordination shell is derived which has to be compatible with EPR data. Computations are used to select sterically possible structures, from which in turn structures with correct H and N positions are selected by ENDOR and ESEEM measurements. Finally, EXAFS spectra are re-calculated and compared with the experimental data. This procedure was successfully applied for structure determination of the Cu(2+) complex of the octapeptide repeat of the human prion protein. The structure of this octarepeat complex is rather similar to a pentapeptide complex which was determined by X-ray structure analysis. However, the tryptophan residue has a different orientation: the axial water is on the other side of the Cu.

Effect of metal ions on de novo aggregation of full-length prion protein

It is well established that the prion protein (PrP) contains metal ion binding sites with specificity for copper. Changes in copper levels have been suggested to influence incubation time in experimental prion disease. Therefore, we studied the effect of heavy metal ions (Cu(2+), Mn(2+), Ni(2+), Co(2+), and Zn(2+)) in vitro in a model system that utilizes changes in the concentration of SDS to induce structural conversion and aggregation of recombinant PrP. To quantify and characterize PrP aggregates, we used fluorescently labelled PrP and cross-correlation analysis as well as scanning for intensely fluorescent targets in a confocal single molecule detection system. We found a specific strong pro-aggregatory effect of Mn(2+) at low micromolar concentrations that could be blocked by nanomolar concentration of Cu(2+). These findings suggest that metal ions such as copper and manganese may also affect PrP conversion in vivo.

Identification of the actin-binding domain of Ins(1,4,5)P3 3-kinase isoform B (IP3K-B)

Dewaste et al. [Dewaste, Moreau, De Smedt, Bex, De Smedt, Wuytaack, Missiaen and Erneux (2003) Biochem. J. 374, 41-49] showed that over-expressed EGFP (enhanced green fluorescent protein) fused to Ins(1,4,5)P3 3-kinase B (IP3K-B) co-localizes with the cytoskeleton, as well as with the endoplasmic reticulum and the plasma membrane. The domains responsible for these subcellular localizations are not yet identified. For the endogenous enzyme, we confirmed both actin and endoplasmic reticulum localization by employing a high affinity antibody against IP3K-B. F-actin targeting is exclusively dependent on the non-catalytic N-terminal region of IP3K-B. By expressing fragments of this N-terminal domain as EGFP-fusion proteins and inspecting transfected cells by confocal microscopy, we characterized a distinct 63-amino-acid domain comprising amino acids 108-170 of the enzyme which is responsible for F-actin targeting. A truncation of this fragment from both sides revealed that the full size of this segment is essential for this function. Deletion of this segment in a full-length over-expressed IP3K-B-EGFP-fusion protein completely abolished F-actin interaction. Direct interaction of this actin-binding segment with only F-actin, but not with G-actin, was observed in vitro using a bacterially expressed, affinity-purified GST (glutathione S-transferase)-Rattus norvegicus IP3K (aa 108-170) fusion protein. Helix-breaking mutations within this isolated segment abolished the F-actin binding properties both in vitro and when over-expressed in cells, indicating that an intact secondary structure is essential for actin targeting. The segment shows sequence similarities to the actin-binding region in IP3K-A, but no similarity to other actin-binding domains.

Rat inositol 1,4,5-trisphosphate 3-kinase C is enzymatically specialized for basal cellular inositol trisphosphate phosphorylation and shuttles actively between nucleus and cytoplasm

The calcium-liberating second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) is converted to inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) by Ins(1,4,5)P3 3-kinases (IP3Ks) that add a fourth phosphate group to the 3-position of the inositol ring. Two isoforms of IP3Ks (named A and B) from different vertebrate species have been well studied. Recently the cloning and examination of a human full-length cDNA encoding a novel isoform, termed human IP3K-C (HsIP3K-C), has been reported. In the present study we report the cloning of a full-length cDNA encoding a rat homologue of HsIP3K-C with a unique mRNA expression pattern, which differs remarkably from the tissue distribution of HsIP3K-C. Of the rat tissues examined, rat IP3K-C (RnIP3K-C) is mainly present in heart, brain, and testis and shows the strongest expression in an epidermal tissue, namely tongue epithelium. RnIP3K-C has a calculated molecular mass of approximately 74.5 kDa and shows an overall identity of approximately 75% with HsIP3K-C. A bacterially expressed, enzymatically active and Ca2+-calmodulin-regulated fragment of this isoform displays remarkable enzymatic properties like a very low Km for Ins(1,4,5)P3 ( approximately 0.2 microm), substrate inhibition by high concentrations of Ins(1,4,5)P3, allosteric product activation by Ins(1,3,4,5)P4 in absence of Ca2+-calmodulin (Ka(app) 0.52 microm), and the ability to efficiently phosphorylate a second InsP3 substrate, inositol 2,4,5-trisphosphate, to inositol 2,4,5,6-tetrakisphosphate in the presence of Ins(1,3,4,5)P4. Furthermore, the RnIP3K-C fused with a fluorescent protein tag is actively transported into and out of the nucleus when transiently expressed in mammalian cells. A leucine-rich nuclear export signal and an uncharacterized nuclear import activity are localized in the N-terminal domain of the protein and determine its nucleocytoplasmic shuttling. These findings point to a particular role of RnIP3K-C in nuclear inositol trisphosphate phosphorylation and cellular growth.

The second messenger binding site of inositol 1,4,5-trisphosphate 3-kinase is centered in the catalytic domain and related to the inositol trisphosphate receptor site

A segment of inositol 1,4,5-trisphosphate 3-kinase responsible for inositol 1,4,5-trisphosphate (InsP(3)) binding was characterized and confirmed by three different approaches employing the fully active expressed catalytic domain of the enzyme. Part of this moiety was protected from limited tryptic proteolysis by InsP(3). Sequencing of two fragments of 16 and 21 kDa, generated in the absence or presence of InsP(3), respectively, identified segment Glu-271 to Arg-305 as being protected. 15 monoclonal antibodies, all binding to epitopes within this region, inhibited enzyme activity and interfered with inositol phosphate binding. Detailed enzyme kinetic parameters of 32 site-directed mutants revealed residues Arg-276 and Lys-303 in this segment and Arg-322, located nearby, as directly involved in and five other closely neighbored residues, all located within a segment of 73 amino acids, as also influencing InsP(3) binding. Part of this region is similar in sequence to an InsP(3) binding segment in InsP(3) receptors. Combined with the finding that mutants influencing only ATP binding all lie outside this region, these data indicate that an InsP(3) binding core domain is inserted between two segments acting together in ATP binding and phosphate transfer.

A novel A-isoform-like inositol 1,4,5-trisphosphate 3-kinase from chicken erythrocytes exhibits alternative splicing and conservation of intron positions between vertebrates and invertebrates

Based on the partial peptide sequence of inositol 1,4, 5-trisphosphate 3-kinase purified with 135 000-fold enrichment from chicken erythrocytes, cDNA-fragments were cloned by RT-PCR using degenerate oligonucleotides. Subsequent hybridization screening of an embryonic chicken cDNA library and 5'-RACE yielded a cDNA-contig of 2418 bp, encoding a 452 amino acid protein. The amino acid sequence shows the highest degree of homology with A-isoforms of inositol 1,4,5-trisphosphate 3-kinase (65% identities), whereas homology towards B and C isoforms was lower (57% and 52% amino acid identities respectively). These findings reveal a new tissue-specific pattern of A-isoform expression, a form which so far has only been found in brain and testes. Two overlapping lambda-genomic clones for chicken inositol 1,4,5-trisphosphate 3-kinase, isolated by hybridization screening, covered 18 499 bp of genomic sequence. This contig included four exons: three of them were present in all cDNA clones, whereas one was only represented in a single cDNA clone. In addition, the sequence of the latter differed from the other cDNAs by an in-frame deletion of 72 bp within the coding region for the catalytic domain of the enzyme. This divergent cDNA suggests the existence of alternative splice products, at least in embryonic tissue.A comparison of the position of introns, with the respective introns known from the corresponding gene from Caenorhabditis elegans, revealed a high degree of conservation of intron positions between vertebrates and invertebrates. Functional data for the enzyme suggests that the conserved exons represent defined functional protein modules.

Functional analysis of isolated cpn10 domains and conserved amino acid residues in spinach chloroplast co-chaperonin by site-directed mutagenesis

The possibilities of independent function of the two chaperonin 10 (cpn10) domains of the cpn10 homologue from spinach chloroplasts and the role of five conserved amino acid residues in the N-terminal cpn10 unit were investigated. Recombinant single domain proteins and complete chloroplast cpn10 proteins carrying amino acid exchanges of conserved residues in their N-terminal cpn10 domain were expressed in Escherichia coli and partially purified. The function of the recombinant proteins was tested using GroEL as chaperonin 60 (cpn60) partner for in vitro refolding of denatured ribulose-1,5-bisphosphate carboxylase (Rubisco). Interaction with cpn60 was also monitored by the ability to inhibit GroEL ATPase activity. In vitro both isolated cpn10 domains were found to be incapable of co-chaperonin function. All mutants were also severely impaired in cpn10 function. The results are interpreted in terms of an essential role of the exchanged amino acid residues for the interaction between co-chaperonin and cpn60 partner and in terms of a functional coupling of both cpn10 domains. To test the function of mutant chloroplast cpn10 proteins in vivo the cpn10 deficiency of E. coli strain CG712 resulting in an inability to assemble lambda-phage was exploited in a complementation assay. Transformation with plasmids directing the expression of mutant chloroplas cpn10 proteins in two cases restored lambda-phage assembly in this bacterial strain to the same extent as did transformation with a plasmid encoding wild-type cpn10 protein. In contrast a plasmid encoded third mutant and truncated forms of chloroplast cpn10 showed significantly reduced complementation efficiencies.

Spinach chloroplast cpn21 co-chaperonin possesses two functional domains fused together in a toroidal structure and exhibits nucleotide-dependent binding to plastid chaperonin 60

Chloroplasts contain a 21-kDa co-chaperonin polypeptide (cpn21) formed by two GroES-like domains fused together in tandem. Expression of a double-domain spinach cpn21 in Escherichia coli groES mutant strains supports growth of bacteriophages lambda and T5, and will also suppress a temperature-sensitive growth phenotype of a groES619 strain. Each domain of cpn21 expressed separately can function independently to support bacteriophage lambda growth, and the N-terminal domain will additionally suppress the temperature-sensitive growth phenotype. These results indicate that chloroplast cpn21 has two functional domains, either of which can interact with GroEL in vivo to facilitate bacteriophage morphogenesis. Purified spinach cpn21 has a ring-like toroidal structure and forms a stable complex with E. coli GroEL in the presence of ADP and is functionally interchangeable with bacterial GroES in the chaperonin-facilitated refolding of denatured ribulose-1,5-bisphosphate carboxylase. Cpn21 also inhibits the ATPase activity of GroEL. Cpn21 binds with similar efficiency to both the alpha and beta subunits of spinach cpn60 in the presence of adenine nucleotides, with ATP being more effective than ADP. The tandemly fused domains of cpn21 evolved early and are present in a wide range of photosynthetic eukaryotes examined, indicating a high degree of conservation of this structure in chloroplasts.

Identification, characterization, and DNA sequence of a functional "double" groES-like chaperonin from chloroplasts of higher plants

Chloroplasts of higher plants contain a nuclear-encoded protein that is a functional homolog of the Escherichia coli chaperonin 10 (cpn10; also known as groES). In pea (Pisum sativum), chloroplast cpn10 was identified by its ability to (i) assist bacterial chaperonin 60 (cpn60; also known as groEL) in the ATP-dependent refolding of chemically denatured ribulose-1,5-bisphosphate carboxylase and (ii) form a stable complex with bacterial cpn60 in the presence of Mg.ATP. The subunit size of the pea protein is approximately 24 kDa--about twice the size of bacterial cpn10. A cDNA encoding a spinach (Spinacea oleracea) chloroplast cpn10 was isolated, sequenced, and expressed in vitro. The spinach protein is synthesized as a higher molecular mass precursor and has a typical chloroplast transit peptide. Surprisingly, however, attached to the transit peptide is a single protein, comprised of two distinct cpn10 molecules in tandem. Moreover, both halves of this "double" cpn10 are highly conserved at a number of residues that are present in all cpn10s that have been examined. Upon import into chloroplasts the spinach cpn10 precursor is processed to its mature form of approximately 24 kDa. N-terminal amino acid sequence analysis reveals that the mature pea and spinach cpn10 are identical at 13 of 21 residues.

A plant homologue to mammalian brain 14-3-3 protein and protein kinase C inhibitor

We have isolated cDNA clones of Spinacea oleracea L. and Oenothera hookeri of 930 and 1017 base pairs, respectively. The open reading frame deduced from the Oenothera sequence codes for a protein of a calculated molecular mass of 29,200. The primary amino acid sequence exhibits a very high degree (88%) of homology to the 14-3-3 protein from bovine brain, and protein kinase C inhibitor from sheep brain. Subsequently the plant protein was partially purified from leaf extract. The partially purified plant protein inhibited protein kinase C from sheep brain in a heterologous assay system. The active fraction consisted of 5-6 different polypeptides of similar molecular size. One of these proteins crossreacted with a peptide-specific antibody against protein kinase C inhibitor protein from sheep brain.