Evidence for protein X binding to a discontinuous epitope on the cellular prion protein during scrapie prion propagation

Studies on the transmission of human (Hu) prions to transgenic (Tg) mice suggested that another molecule provisionally designated protein X participates in the formation of nascent scrapie isoform of prion protein (PrPSc). We report the identification of the site at which protein X binds to the cellular isoform of PrP (PrPC) using scrapie-infected mouse (Mo) neuroblastoma cells transfected with chimeric Hu/MoPrP genes even though protein X has not yet been isolated. Substitution of a Hu residue at position 214 or 218 prevented PrPSc formation. The side chains of these residues protrude from the same surface of the C-terminal alpha-helix and form a discontinuous epitope with residues 167 and 171 in an adjacent loop. Substitution of a basic residue at positions 167, 171, or 218 also prevented PrPSc formation: at a mechanistic level, these mutant PrPs appear to act as "dominant negatives" by binding protein X and rendering it unavailable for prion propagation. Our findings seem to explain the protective effects of basic polymorphic residues in PrP of humans and sheep and suggest therapeutic and prophylactic approaches to prion diseases.

Antibodies inhibit prion propagation and clear cell cultures of prion infectivity

Prions are the transmissible pathogenic agents responsible for diseases such as scrapie and bovine spongiform encephalopathy. In the favoured model of prion replication, direct interaction between the pathogenic prion protein (PrPSc) template and endogenous cellular prion protein (PrPC) is proposed to drive the formation of nascent infectious prions. Reagents specifically binding either prion-protein conformer may interrupt prion production by inhibiting this interaction. We examined the ability of several recombinant antibody antigen-binding fragments (Fabs) to inhibit prion propagation in cultured mouse neuroblastoma cells (ScN2a) infected with PrPSc. Here we show that antibodies binding cell-surface PrPC inhibit PrPSc formation in a dose-dependent manner. In cells treated with the most potent antibody, Fab D18, prion replication is abolished and pre-existing PrPSc is rapidly cleared, suggesting that this antibody may cure established infection. The potent activity of Fab D18 is associated with its ability to better recognize the total population of PrPC molecules on the cell surface, and with the location of its epitope on PrPC. Our observations support the use of antibodies in the prevention and treatment of prion diseases and identify a region of PrPC for drug targeting.

Solution structure of a 142-residue recombinant prion protein corresponding to the infectious fragment of the scrapie isoform

The scrapie prion protein (PrPSc) is the major, and possibly the only, component of the infectious prion; it is generated from the cellular isoform (PrPC) by a conformational change. N-terminal truncation of PrPSc by limited proteolysis produces a protein of approximately 142 residues designated PrP 27-30, which retains infectivity. A recombinant protein (rPrP) corresponding to Syrian hamster PrP 27-30 was expressed in Escherichia coli and purified. After refolding rPrP into an alpha-helical form resembling PrPC, the structure was solved by multidimensional heteronuclear NMR, revealing many structural features of rPrP that were not found in two shorter PrP fragments studied previously. Extensive side-chain interactions for residues 113-125 characterize a hydrophobic cluster, which packs against an irregular beta-sheet, whereas residues 90-112 exhibit little defined structure. Although identifiable secondary structure is largely lacking in the N terminus of rPrP, paradoxically this N terminus increases the amount of secondary structure in the remainder of rPrP. The surface of a long helix (residues 200-227) and a structured loop (residues 165-171) form a discontinuous epitope for binding of a protein that facilitates PrPSc formation. Polymorphic residues within this epitope seem to modulate susceptibility of sheep and humans to prion disease. Conformational heterogeneity of rPrP at the N terminus may be key to the transformation of PrPC into PrPSc, whereas the discontinuous epitope near the C terminus controls this transition.

Definitive chemoradiotherapy for T4 and/or M1 lymph node squamous cell carcinoma of the esophagus

PURPOSE

To investigate the efficacy and feasibility of concurrent chemoradiotherapy for locally advanced carcinoma of the esophagus.

PATIENTS AND METHODS

Fifty-four patients with clinically T4 and/or M1 lymph node (LYM) squamous cell carcinoma of the esophagus were enrolled. Patients received protracted infusion of fluorouracil 400 mg/m(2)/24 hours on days 1 to 5 and 8 to 12, 2-hour infusion of cisplatin 40 mg/m(2) on days 1 and 8, and concurrent radiation therapy at a dose of 30 Gy in 15 fractions over 3 weeks. Filgrastim was prophylactically administered to 35 patients. This schedule was repeated twice every 5 weeks, for a total radiation dose of 60 Gy, followed by two courses of fluorouracil (800 mg/m(2)/24 hours for 5 days) and cisplatin (80 mg/m(2) on day 1).

RESULTS

There were 21 patients with T4M0 disease, one with T2M1 LYM, 17 with T3M1 LYM, and 15 withT4M1 LYM. Forty-nine patients (91%) completed at least the chemoradiotherapy segment. The 18 patients (33%) who achieved a complete response included nine (25%) of the 36 with T4 disease and nine (50%) of the 18 with non-T4 disease. Major toxicities were leukocytopenia and esophagitis; there were four (7%) treatment-related deaths. Prophylactic filgrastim reduced the incidence of grade 3 or worse leukopenia without improving dose-intensity or response. With a median follow-up duration of 43 months, median survival time was 9 months. The 3-year survival rate was 23%.

CONCLUSION

Despite its significant toxicity, this combined modality seemed to have curative potential even in cases of locally advanced carcinoma of the esophagus.

Expression of survivin is correlated with cancer cell apoptosis and is involved in the development of human pancreatic duct cell tumors

BACKGROUND

Survivin is a new member of the inhibitor of apoptosis family of antiapoptotic proteins. This protein was expressed selectively in all the most common human carcinomas but not in normal adult tissues. To our knowledge, the relation between survivin expression and apoptosis or tumorigenesis has not yet been studied in pancreatic neoplasms.

METHODS

The authors investigated the expression of survivin in 4 pancreatic carcinoma cell lines and 56 human pancreatic tissues (5 cases of normal, 12 cases of chronic pancreatitis [CP], 26 cases of pancreatic duct cell adenocarcinoma [PDC], 16 lesions of 13 intraductal papillary-mucinous tumor [IPMT] by immunohistochemistry, immunoblotting, and reverse transcription-polymerase chain reaction (RT-PCR) to examine the association of its expression with tumor apoptosis and/or tumorigenesis.

RESULTS

Survivin expression was found in the tumor cells but not in the nonneoplastic pancreatic tissues (normal and CP tissues). Survivin expression was observed in 20 of 26 cases of PDC (76.9%) and in 9 of 16 IPMT lesions that ranged from adenoma to invasive (56.3%) by immunohistochemistry. Survivin was more frequently expressed in malignant tumors than in benign tumors (P = 0.0089). In PDC, high levels of survivin expression were associated significantly with a reduction in the apoptotic index of the tumor cells (0.445% +/- 0.150% vs. 0.961% +/- 0.378%; P < 0.0001).

CONCLUSIONS

These data suggest that the expression of survivin may be upregulated during an early step of tumorigenesis and during the development of cancer by reducing the cancer cell apoptosis.

COOH-terminal sequence of the cellular prion protein directs subcellular trafficking and controls conversion into the scrapie isoform

Efficient formation of scrapie isoform of prion protein (PrP(Sc)) requires targeting PrP(Sc) by glycophosphatidyl inositol (GPI) anchors to caveolae-like domains (CLDs). Redirecting the cellular isoform of prion protein (PrP(C)) to clathrin-coated pits by creating chimeric PrP molecules with four different COOH-terminal transmembrane domains prevented the formation of PrP(Sc). To determine if these COOH-terminal transmembrane segments prevented PrP(C) from refolding into PrP(Sc) by altering the structure of the polypeptide, we fused the 28-aa COOH termini from the Qa protein. Two COOH-terminal Qa segments differing by a single residue direct the transmembrane protein to clathrin-coated pits or the GPI form to CLDs; PrP(Sc) was formed from GPI-anchored PrP(C) but not from transmembrane PrP(C). Our findings argue that PrP(Sc) formation is restricted to a specific subcellular compartment and as such, it is likely to involve auxiliary macromolecules found within CLDs.

Detection and chemical identification of natural bio-antimutagens. A case of the green tea factor

A bio-antimutagen, isolated from Japanese green tea (leaves of Camellia sinensis), reduced high spontaneous mutations due to altered DNA-polymerase III in a mutator strain of Bacillus subtilis. Chemical studies showed that the factor was epigallo-catechin-gallate (EGCg).

Lymph-node metastases: efficacy for detection with helical CT in patients with gastric cancer

PURPOSE

To determine the efficacy of helical computed tomography (CT) in the detection of lymphadenopathy in patients with gastric cancer.

MATERIALS AND METHODS

Helical CT (5-mm section thickness, 5-mm/sec table incrementation) was performed in 58 patients (39 men, 19 women; mean age, 63.8 years) with gastric cancer; 1,082 lymph nodes (138 positive, 944 negative for metastasis) were resected at surgery. Findings at CT and resection were compared. Sensitivity for detecting lymph nodes was evaluated according to nodal size and presence of metastasis.

RESULTS

Seven (1.1%) of 649 lymph nodes 1-4 mm, 160 (45.1%) of 355 nodes 5-9 mm, and 56 (72%) of 78 nodes larger than 9 mm were detected at CT. For nodes of at least 5 mm, sensitivity for detecting metastasis-positive nodes (79 [75.2%] of 105 nodes) was higher than that for detecting metastasis-negative nodes (137 [41.8%] of 328; P < .01). Differences between positive and negative nodes in CT attenuation (110 HU +/- 25 vs 66 HU +/- 32) and short-to-long axis ratios (0.81 +/- 0.15 vs 0.57 +/- 0.15; P < .001) were significant.

CONCLUSION

Helical CT is effective for detection of metastatic lymphadenopathy from gastric cancer. CT attenuation and lymph-node configuration aid in diagnosis of malignant adenopathy.

Conformational transitions in peptides containing two putative alpha-helices of the prion protein

Prions are composed largely, if not entirely, of the scrapie isoform of the prion protein (PrPSc). Conversion of the cellular isoform (PrPC) to PrPSc is accompanied by a diminution in the alpha-helical content and an increase in the beta-sheet structure. To investigate the structural basis of this transition, peptide fragments corresponding to Syrian hamster PrP residues 90 to 145 and 109 to 141, which contain the most conserved residues of the prion protein and the first two putative alpha-helical regions in a PrPC model, were studied using infrared spectroscopy and circular dichroism. The peptides could be induced to form alpha-helical structures in aqueous solutions in the presence of organic solvents, such as trifluoroethanol and hexafluoroisopropanol, or detergents, such as sodium dodecyl sulfate and dodecyl phosphocholine. NaCl at physiological concentration or acetonitrile induced the peptides to acquire substantial beta-sheet. The intermolecular nature of the beta-sheet was evident in the formation of rod-shaped polymers as detected by electron microscopy. Resistance to hydrolysis by proteinase K and epitope mapping argue that the beta-sheet structures were formed by the interaction of residues lying between 109 and 141. A similar range of residues was shown by nuclear magnetic resonance spectroscopy to be capable of forming alpha-helices. The alpha-helical structures seem to require a hydrophobic support from either intermolecular interactions or the hydrophobic environment provided by micelles, in agreement with the predicted hydrophobic nature of the packing surface among the four putative helices of PrPC and the outer surfaces of the first two helices. Our results suggest that perturbation of the packing environment of the highly conserved residues is a possible mechanism for triggering the conversion of PrPC to PrPSc where alpha-helices appear to be converted into beta-sheets.

Mimicking dominant negative inhibition of prion replication through structure-based drug design

Recent progress determining the structure of the host-encoded prion protein (PrP(C)) and the role of auxiliary molecules in prion replication permits a more rational approach in the development of therapeutic interventions. Our objective is to identify a new class of lead compounds that mimic the dominant negative PrP(C) mutants, which inhibit an abnormal isoform (PrP(Sc)) formation. A computational search was conducted on the Available Chemicals Directory for molecules that mimic both the spatial orientation and basic polymorphism of PrP residues 168, 172, 215, and 219, which confer dominant negative inhibition. The search revealed 1,000 potential candidates that were visually analyzed with respect to the structure of this four-residue epitope on PrP(C). Sixty-three compounds were tested for inhibition of PrP(Sc) formation in scrapie-infected mouse neuroblastoma cells (ScN2a). Two compounds, Cp-60 (2-amino-6-[(2-aminophenyl)thio]-4-(2-furyl)pyridine-3, 5-dicarbonitrile) and Cp-62 (N'1-(¿5-[(4, 5-dichloro-1H-imidazol-1-yl)methyl]-2-furyl¿carbonyl)-4 methoxybenzene-1-sulfonohydrazide), inhibited PrP(Sc) formation in a dose-dependent manner and demonstrated low levels of toxicity. A substructure search of the Available Chemicals Directory based on Cp-60 identified five related molecules, three of which exhibited activities comparable to Cp-60. Mimicking dominant negative inhibition in the design of drugs that inhibit prion replication may provide a more general approach to developing therapeutics for deleterious protein-protein interactions.

Adrenal sensitivity to adrenocorticotropin varies diurnally

To further characterize diurnal changes in the rhythm in adrenal responsiveness to ACTH, we have measured ACTH distribution volume, MCR, and t 1/2. These do not change between morning and evening in groups of untreated, dexamethasone-pretreated, or hypophysectomized female rats. To characterize the nature of the change in adrenal responsiveness to ACTH, dexamethasone-pretreated rats were infused for 2 h with a variety of doses of ACTH in the morning and evening. The adrenal response to an infusion rate of ACTH that maximally stimulated the adrenals (200 pg/100 g BW.min) was the same in the morning and evening, showing that adrenal capacity does not change. However, infusion of ACTH at lower rates (50-100 pg/100 g BW.min) revealed that the slope of the steroid response curve increased between morning and evening, demonstrating a diurnal change in adrenal sensitivity to ACTH. These results together with previous data showing that the magnitude and time course of the adrenal cAMP response to ACTH changes diurnally strongly suggest that ACTH receptor affinity or coupling with adenylate cyclase changes diurnally. In other experiments, plasma ACTH and corticosterone levels were determined in groups of young and adult male and adult female untreated rats killed at 4-h intervals around the clock. Peak sensitivity to ACTH was found at lights-out, and trough sensitivity was found at lights-on, suggesting that the experimentally demonstrated rhythm occurs normally.

Determination of an iron suspension in water by laser-induced breakdown spectroscopy with two sequential laser pulses

We have applied laser-induced breakdown spectroscopy to quantitative analysis of colloidal and particulate iron in water. A coaxial sample flow apparatus developed in our previous work, which allowed us to control the atmosphere of laser-induced plasma, was used. Using sequential laser pulses from two Q-switched Nd:YAG lasers as excitation sources, the FeO(OH) concentration in the tens of ppb range was determined with an optimum interval between two laser pulses and an optimum delay time of a detector gate from the second pulse. The detection limit of Fe decreased substantially using two sequential laser pulse excitations:  the 0.6 ppm limit of single pulse excitation to 16 ppb with sequential pulse excitation. The effects of the second laser pulse on the plasma emission were studied. The concentration of iron in fine particles in boiler water sampled from a commercially operated thermal power plant has been determined successfully by this method. The results show the capability of laser-induced breakdown spectroscopy in determining suspended colloidal and particulate impurities in a simple and quick way.

Postnatal development of a GABA deficit and disturbance of neural functions in mice lacking GAD65

The 65-kDa isoform of glutamic acid decarboxylase (GAD65) is believed to play an essential role for GABA synthesis in the central nervous system. Using mice with targeted disruption of the GAD65 gene (GAD65(-/-) mice) we investigated the contribution of GAD65 to GABA synthesis in different brain areas during postnatal development and in adulthood. In the amygdala, hypothalamus and parietal cortex of GAD65(+/+) mice an increase of GABA levels was observed during postnatal development, most prominently between the first and second month after birth. This increase appeared to be dependent on GAD65, as it was delayed by 2 months in GAD65(+/-) mice and was not observed in GAD65(-/-) mice. Likely as a consequence of their GABA deficit, adult GAD65(-/-) mice showed a largely abnormal neural activity with frequent paroxysmal discharges and spontaneous seizures. They furthermore displayed increased anxiety-like behaviour in a light/dark avoidance test and reduced intermale aggression, as well as a reduced forced-swimming-induced immobility indicative of an antidepressant-like behavioural change. Adult GAD65(+/-) mice did not show behavioural disturbances except for a reduced aggressive behaviour that was comparable to that in GAD65(-/-) mice. We conclude that GAD65-mediated GABA synthesis may be crucially involved in control of emotional behaviour and indispensable for a tonic inhibition that prevents the development of hyperexcitability in the maturating central nervous system. Aggressive, and possibly other social behaviour may be especially prone to regulation through GAD65-mediated GABA synthesis.

Arcadlin is a neural activity-regulated cadherin involved in long term potentiation

Neural activity results in long term changes that underlie synaptic plasticity. To examine the molecular basis of activity-dependent plasticity, we have used differential cloning techniques to identify genes that are rapidly induced in brain neurons by synaptic activity. Here, we identify a novel cadherin molecule Arcadlin (activity-regulated cadherin-like protein). arcadlin mRNA is rapidly and transiently induced in hippocampal granule cells by seizures and by N-methyl-D-aspartate-dependent synaptic activity in long term potentiation. The extracellular domain of Arcadlin is most homologous to protocadherin-8; however, the cytoplasmic region is distinct from that of any cadherin family member. Arcadlin protein is expressed at the synapses and shows a homophilic binding activity in a Ca2+-dependent manner. Furthermore, application of Arcadlin antibody reduces excitatory postsynaptic potential amplitude and blocks long term potentiation in hippocampal slices. Its close homology with cadherins, its rapid inducibility by neural activity, and its involvement in synaptic transmission suggest that Arcadlin may play an important role in activity-induced synaptic reorganization underlying long term memory.

A synthetic peptide initiates Gerstmann-Sträussler-Scheinker (GSS) disease in transgenic mice

The molecular basis of the infectious, inherited and sporadic forms of prion diseases is best explained by a conformationally dimorphic protein that can exist in distinct normal and disease-causing isoforms. We identified a 55-residue peptide of a mutant prion protein that can be refolded into at least two distinct conformations. When inoculated intracerebrally into the appropriate transgenic mouse host, 20 of 20 mice receiving the beta-form of this peptide developed signs of central nervous system dysfunction at approximately 360 days, with neurohistologic changes that are pathognomonic of Gerstmann-Sträussler-Scheinker disease. By contrast, eight of eight mice receiving a non-beta-form of the peptide failed to develop any neuropathologic changes more than 600 days after the peptide injections. We conclude that a chemically synthesized peptide refolded into the appropriate conformation can accelerate or possibly initiate prion disease.