Journal Watch
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RNA editing: potential for prion strains?
Elk has 129 leu/leu; other cervids are met/met
6% of mule deer bucks in Colorado had CWD in 1996
Prion allotypes deposited in Val 21O lle and met 129 val
CJD after an embolization of intercostal arteries with cadaveric dura mater
Alzheimer tau protein high in CJD cerebrospinal fluid
Differential diagnosis of Alzheimer's disease
Autocatalysis and cooperative mechanisms with rogue prion
All-D amyloid -- it's still toxic
Upcoming articles --JBC
Tyrosine kinase also in calveolae
Glutamine repeat diseases: also toxic beta-sheets?
Anthracyclines show promise as drug class
Finding normal function for prion protein
RNA editing: applicable to prion mRNA?

Regulation of serotonin-2C receptor G-protein coupling by RNA editing

(Long Letter to Nature)  Nature 387, 303 (1997)
 C M Burns, H Chu, S M Rueter, L K Hutchinson, H Canton,  E Sanders-Bush & R B Emeson 
New studies have shown that RNA transcripts encoding the serotonin (5-hydroxytryptamine, 5-HT) receptor subtype, 5-HT2C, undergo RNA editing. Genomically encoded adenosine residues in the pre-messenger RNA are converted to inosines, resulting in three amino-acid changes. These changes are confined to the region of the receptor that is involved in signal transduction, an intra-cellular loop involved in G protein binding, so the editing may have an effect on appetite and mood, and cause epileptic seizures.

The changes occur as an imperfect inverted repeat in the intron following exon 3 forms double-stranded RNA. Bulges are deaminated, causing four A to I transitions translated as G in three amino aid substitutions. These deaminations vary by tissue as to extent, giving rise to over a dozen final polypeptide chains. The variations have regulatory significance -- note that it is the deaminases that are regulated rather than isozyme substitution or allosteric control of the actual receptor.
RNA editing is found in in apolipoprotein B (one C to U conversion), in glutamate-gated calcium channels such as AMPA and kainate, again with functional significance to gating and calcium permeability.

Regulation of serotonin-2C receptor G-protein coupling by RNA editing: The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) elicits a wide array of physiological effects by binding to several receptor subtypes. The 5-HT2 family of receptors belongs to a large group of seven-transmembrane-spanning G-protein-coupled receptors and includes three receptor subtypes (5-HT2A, 5-HT2B and 5-HT2C) which are linked to phospholipase C, promoting the hydrolysis of membrane phospholipids and a subsequent increase in the intracellular levels of inositol phosphates and diacylglycerol.

The authors show that transcripts encoding the 2C subtype of serotonin receptor (5-HT2CR) undergo RNA editing events in which genomically encoded adenosine residues are converted to inosines by the action of double- stranded RNA adenosine deaminase(s). Sequence analysis of complementary DNA isolates from dissected brain regions have indicated the tissue-specific expression of seven major 5- HT2C receptor isoforms encoded by eleven distinct RNA species.

Editing of 5- HT2CR messenger RNAs alters the amino-acid coding potential of the predicted second intracellular loop of the receptor and can lead to a 10 to 15-fold reduction in the efficacy of the interaction between receptors and their G proteins. These observations indicate that RNA editing is a new mechanism for regulating serotonergic signal transduction and suggest that this post-transcriptional modification may be critical for modulating the different cellular functions that are mediated by other members of the G-protein-coupled receptor superfamily.

Prions do not have introns within their coding region. However, they do have an inverted complementary repeat that is reported to form hairpin stems in the repeat region. Also, in hamster, the prion mRNA is reported to be variably processed, sometimes with exon 2 excised. Should prions experience mRNA editing, it could explain tissue specific strain effects because the effect of editing is to create a pseudo-allele.

Is codon 129 of prion protein polymorphic in human beings but not in animals?

Lancet 349 #9065 31 May 1997
Hermann M Sch”tzl, Franziska Wopfner, Sabine Gilch, Albrecht von Brunn, Gundula J”ger 
 Genecenter, Max von Pettenkofer-Institut f¸r Virology, 
University of Munich, D-81377 Munich, Germany (H M Sch”tzl) 
In human beings, there is a polymorphism at aminoacid position 129 of the prion protein which influences susceptibility to prion infection. In European populations, the usual distribution pattern is about 50% heterozygosity for methionine/valine (Met/Val), 40% homozygosity for methionine (Met/Met), and 10% for valine (Val/Val). Methionine homozygosity predisposes to sporadic Creutzfeldt Jakob disease (CJD) as well as acquired CJD.1

In patients with new variant CJD (nvCJD) Met/Met has been invariably found.2 Structural models ascribe importance to position 129 in stabilising the conformation of PrP by interaction with other aminoacid residues. Conformational change from alpha-helical to beta-sheet structure is thought to be a primary event in prion diseases. The figure shows the location of the alpha-helical regions revealed by computer-assisted structure prediction and of structural regions determined by a nuclear magnetic resonance-based model of murine PrP(121-231).3

We investigated whether codon 129 had a similar allelic distribution in other mammals. Our sequence analysis of about 150 samples representing more than 50 mammalian species has shown a remarkable uniformity of homozygosity for methionine at this position.4 This finding applies also for non-human mammalian PrPs analysed by other groups. Why the aminoacid 129 is polymorphic in humans but not in animals is unclear. Amino acid polymorphisms at other positions in murine and sheep PrP have been shown to affect susceptibility to prion disease.

                90       100       110       120      129        140         150        160
                .         .         .         .        .          .           .          .       .
Wapiti deer	GQGG-THSQWNKPSKPKTNMKHVAGAAAAGAVVGGLGGYLLGSAMSRPLIHFGNDYEDRYYRENMYRYPNQVYYRPVDQYN
Dybowski deer       -                                  M     

Predicted aminoacid sequences of Wapiti and Dybowski deer were compared to PrPs of sheep, cattle, mouse, and human beings. Dots indicate identical aminoacids. Location of postulated -helical and determined -helical/þ-sheet regions is indicated. Aminoacid sequence alignment (90‚170)

Here we report the first mammalian PrP with an aminoacid other than methionine at the position 129. The PrP gene of the Wapiti deer (Cervus elaphus canadensis) encodes leucine at both alleles (figure). DNA extracted from peripheral lymphocytes of three independent samples (kindly provided by Dr Gaukler, Zoological Gardens at N¸rnberg, Germany) were PCR-amplified with degenerate primers and the PCR fragments were sequenced directly.

Analysis of another deer species (Cervus nippon dybowskii, Dybowski deer) found methionine at this position. Interestingly, a prion disorder named chronic wasting disease has been found in elks and deers in Montana, USA.5 Whether this disorder is acquired by infection or has a sporadic or genetic origin is unknown.

In view of the current epidemic of bovine spongiform encephalopathy (BSE) further sequence analysis of cattle and other ungulates would be advisable as genotype variability of the PrP gene might influence susceptibility to infection with BSE-derived prions.

References

1 Palmer MS, Dryden AJ, Hughes JT, et al. Homozygous prion protein genotype predisposes to sporadic Creutzfeldt-Jacob disease. Nature 1991; 352: 340‚42.

2 Will RG, Ironside JW, Zeidler M, et al. A new variant of Creutzfeldt-Jakob disease in the UK. Lancet 1996; 347: 921‚25.

3 Riek R, Hornemann S, Wider G, Billeter M, Glockshuber R, W¸thrich K. NMR structure of the mouse protein domain PrP (121‚231). Nature 1996; 382: 180‚82.

4 Sch”tzl HM, Da Costa M, Taylor L, Cohen FE, Prusiner SB. Prion protein gene variation among primates. J Mol Biol 1995; 245: 362‚74.

5 Williams ES, Young S. Chronic wasting disease of captive mule deer: a spongiform encephalopathy. J Wildl Dis 1980; 16: 89‚98.

Chronic wasting disease, deer and elk - USA (Colorado)

23 Apr 97
Tim Harris
European Secretary
Animal Transportation Association
PO Box 251 Redhill Surrey England RH1 5FU
The Colorado Division of Wildlife issued a news release on Chronic Wasting Disease (CWI). A survey in the fall of 1996 of brain tissue of hunter harvested mule deer revealed that 6% of the bucks were affected. There were also less than 1% of elk affected.

"Deer and elk affected by CWI show progressive loss of body condition, behavioral changes, excessive salivation, increased drinking and urination, depression and eventual death. Once signs develop, infected animals probably live only a few weeks or months, but the length of incubation and the infectious period are unknown. There is no evidence of humans coming in contact with CWD will be affected. However, the Division reminds people that as a precaution they should not eat the meat of animals showing signs of the disease, etc. State and federal officials have found no increase in Creutzfeldt-Jacob disease anywhere in North America."

This advice is completely irresponsible and ignorant. The hunter has no way of telling whether or not an animal is infectious. Meat will be contaminated from peripheral innervation. If 6% of the anilmals are clinically ill, then as many as 95% could be infectious. -- webmaster

Prion protein allotypes in sporadic and familial CJD

Nat Med 3 (5): 521-525 (May 1997) 
Silvestrini MC, Cardone F, Maras B, Pucci P, Barra D, Brunori M, Pocchiari M
A characteristic feature of CJD is the accumulation in the brain of the amyloid protease-resistant protein PrPres. PrPres derives from a host-encoded, protease-sensitive isoform, PrPsen. Mutations of this protein are linked to familial variants of the disease, and the presence of a methionine or valine residue at the polymorphic position 129 may be critical in sporadic CJD cases. We found that in the brain of patients heterozygous for the mutation in which isoleucine is substituted for valine at codon 210 (Val21Olle), the PrPres is formed by both the wild-type and mutant PrPsen. We also found that in a sporadic CJD patient, who was heterozygous (Met/Val) at position 129, PrPres is also formed by both allotypes. These data associate transmissible spongiform encephalopathies with other amyloidosis, although the nature of the transmissible agent remains unsettled.

Human TSE disease -- viral or protein only?

 Nat Med 3 (5): 521-525 (May 1997)
Bruce Chesebro commentary on above article
Rocky Mountain Laboratories, Hamilton, MT 59840, USA 

Elevated levels of tau-protein in cerebrospinal fluid of patients with CJD

Neurosci Lett 225 (3): 210-212 (Apr 11 1997) 
Otto M, Wiltfang J, Tumani H, Zerr I, Lantsch M, Kornhuber J, Weber T, Kretzschmar HA, Poser S
Creutzfeldt-Jakob disease (CJD) is a rare, fatal, neurodegenerative disease caused by a transmissible agent designated as proteinaceous infectious agent (prion). Searching for biochemical markers of CJD, we analysed cerebrospinal fluid (CSF) samples of 53 patients for tau-protein using an enzyme linked immunoassay (ELISA).

In a group of 21 patients with definite CJD seen in the German case control study for CJD, tau-protein concentrations in CSF were significantly higher than in two control-groups of patients with other diseases (median 13,153 pg/ml, range 1,533-27,648 pg/ml; P = 0.0001). One group comprised 19 patients who were seen in the same study and were diagnosed as having other dementing diseases (tau concentration: median 558 pg/ml, range 233-1,769 pg/ml). The second control group comprised 13 patients from our hospital with no dementing disease (tau concentration: median 296 pg/ml, range 109-640 pg/ml). We conclude that determination of tau protein levels in CSF is a useful marker for laboratory diagnosis of CJD.

Autocatalytic processes in cooperative mechanisms of prion diseases

FEBS Lett 407 (1): 1-6 (Apr 21 1997) 
Laurent M
According to the leading theory, the agent responsible for prion diseases would be the conformational isomer PrP(Sc) of a cellular protein PrP(C), the pathogenic form PrP(Sc) multiplying by converting the normal protein into a likeness of itself. The pathogenic isoform could catalyze the conformational transition so that the process, taken as a whole, is autocatalytic. However, in this simple but atypic model, unrealistic values of rate parameters are needed in order to account for the kinetics of the propagation of prion diseases. In this paper, I show that these limits can be overcome by assuming that catalysis proceeds through a multimeric assembly of the pathogenic isoform of the prion protein. Such a structure would indeed be able to provide cooperativity both at the assembly and conformational change levels, strongly reinforcing the autocatalytic character of the activated process. Moreover, such a property is a prerequisite to endow the metabolic system with dynamic bistability. Together with a good agreement regarding experimental data, this analysis is closely akin to Griffith's original idea concerning the thermodynamic conditions required for autocatalyzed modifications of any protein.

All-D-Enantiomers of -Amyloid Exhibit Similar Biological Properties to All-L--Amyloids

Commentary by Webmaster:

Here's a clever and informative experiment fronom Alzheimer amyloid that could be quickly implemented for prion hydrophobic core as well. Synthetic amyloid fragment made of D-amino acids should have the same physical and chemical properties in mirror image as the normal L version [modulo secondary issues with isooleucine and threonine]. This means it could form amyloid fibers, beta-sheets, or membrane channels as before but not bind former ligands properly, be they large or small, if stereochemistry is present.

In other words, it allows dissecting out those properties involving stereospecific interaction with other molecules from those that just depend on self-interactions (beta sheets still ok) or bulk chemical properties. They found that D and L had the expected similar physical properties and induced similar levels of toxicity in cultured hippocampal neurons, which sharply limits the role of stereospecific interactions. Other proteins could still be involved but not through direct contact.

It will be interesting to see if prion core fragment has the same property -- I would guess that it will have the same toxicity but not be infectious nor have the ability to recruit normal prion conformer.

 
JBC Volume 272, Number 11, Issue of March 14, 1997 pp. 7431-7436
David H. Cribbs  , Christian J. Pike , Shari L. Weinstein , Peter Velazquez and Carl W. Cotman 
The amyloidogenic peptide -amyloid has previously been shown to bind to neurons in the form of fibrillar clusters on the cell surface, which induces neurodegeneration and activates a program of cell death characteristic of apoptosis. To further investigate the mechanism of A neurotoxicity, we synthesized the all-D- and all-L-stereoisomers of the neurotoxic truncated form of A (A25-35) and the full-length peptide (A1-42) and compared their physical and biological properties. We report that the purified peptides exhibit nearly identical structural and assembly characteristics as assessed by high performance liquid chromatography, electron microscopy, circular dichroism, and sedimentation analysis.

In addition, both enantiomers induce similar levels of toxicity in cultured hippocampal neurons. These data suggest that the neurotoxic actions of A result not from stereoisomer-specific ligand-receptor interactions but rather from A cellular interactions in which fibril features of the amyloidogenic peptide are a critical feature. The promiscuous nature of these -sheet-containing fibrils suggests that the accumulation of amyloidogenic peptides in vivo as extracellular deposits represents a site of bioactive peptides with the ability to provide inappropriate signals to cells leading to cellular degeneration and disease.

JBC: articles of possible interest

June 6, 97
Henrike Hartmann, Jorge Busciglio, Karl-Heinz Baumann, Matthias Staufenbiel, Bruce A. Yankner 
            Developmental regulation of presenilin-1 processing in the
            brain suggests a role in neuronal differentiation 
            1997 272: J. Biol. Chem. 1997 June 6 272(23). 14505. 

Oscar B. Goodman, Jr., Jason G. Krupnick, Vsevolod V. Gurevich, Jeffrey L. Benovic, James H. Keen 
            Arrestin/clathrin interaction. Localization of the arrestin
            binding locus to the clathrin terminal domain. 
            1997 272: J. Biol. Chem. 1997 June 6 272(23). 15017. 

Jason G. Krupnick, Oscar B. Goodman, Jr., James H. Keen, Jeffrey L. Benovic 
            Arrestin/clathrin interaction. Localization of the clathrin
            binding domain of nonvisual arrestins to the carboxyl terminus. 
            1997 272: J. Biol. Chem. 1997 June 6 272(23). 15011. 

Perry E. Bickel, Philipp E. Scherer, Jan E. Schnitzer, Phil Oh, Michael P. Lisanti, Harvey F.Lodish 
            Flotillin and epidermal surface antigen define a new family of
           caveolae-associated integral membrane proteins 
            1997 272: J. Biol. Chem. 1997 May 23 272(21). 13793. 

Kurt J. Doege, Silvija N. Coulter, Lauren M. Meek, Kirstin Maslen, Jill G. Wood 
            A human-specific polymorphism in the coding region of the
            aggrecan gene. Variable number of tandem repeats produce a
            range of core protein sizes in the general population. 
            1997 272: J. Biol. Chem. 1997 May 23 272(21). 13974. . 

Brendan A. Kluszynski, Chinpal Kim, W. Page Faulk 
            Zinc as a cofactor for heparin neutralization by histidine-rich glycoprotein 
            1997 272: J. Biol. Chem. 1997 May 23 272(21). 13541.

Abigail S. Hackam, Tian-Li Wang, William B. Guggino, Garry R. Cutting 
            The N-terminal domain of human GABA receptor {rho}1 subunits
            contains signals for homooligomeric and heterooligomeric  interaction 
            1997 272: J. Biol. Chem. 1997 May 23 272(21). 13750. . 

Yi-Te Hsu, Richard J. Youle 
            Nonionic detergents induce dimerization among members of the Bcl-2 family 
            1997 272: J. Biol. Chem. 1997 May 23 272(21). 13829. . 
 
May 30, 1997 JBC
Christine von Poser, Konstantin Ichtchenko, Xuguang Shao, Josep Rizo, Thomas C. Sudhof 
            The evolutionary pressure to inactivate. A subclass of  synaptotagmins with an
            amino acid substitution that abolishes  Ca2+ binding. 
            1997 272: J. Biol. Chem. 1997 May 30 272(22). 14314. 




Nature 386 (6622): 232-234 (Mar 1997)[LETTER] Typing prion isoforms
Parchi P, Capellari S, Chen SG, Petersen RB, Gambetti P, Kopp N, Brown P, Kitamoto T, Tateishi J, Giese A, Kretzschmar H

Nature 386 (6625): 564 (Apr 1997) Biochemical typing of scrapie strains
Somerville RA, Chong A, Mulqueen OU, Birkett CR, Wood SC, Hope J

 

Tyrosine Kinase Receptors Concentrated in Caveolae-like Domains from Neuronal Plasma Membrane

JBC Volume 272, Number 6, Issue of February 7, 1997 pp. 3554-3559 Chengbiao Wu, Stefan Butz, Yun-shu Ying and Richard Anderson

Recent evidence suggests that tyrosine kinases are highly organized in caveolae of tissue culture cells. We now report the isolation of a membrane domain from neuronal plasma membranes that has the biochemical characteristics of caveolae. A low density membrane (LDM) fraction with the same density as caveolae was highly enriched in tyrosine kinases such as insulin receptors, neurotrophin receptors, Eph family receptors, and Fyn. Grb2, Ras, heterotrimeric GTP-binding proteins, and Erk2 were also concentrated in the LDM. Incubation of the LDM fraction at 37݃C stimulated the phosphorylation on tyrosine of multiple, resident proteins, whereas the bulk membrane fraction was devoid of tyrosine kinase activity. The LDM, which makes up ~5-10% of the plasma membrane protein, appears to be organized for signal transduction.

Glutamine repeats and inherited neurodegenerative diseases: molecular aspects.

Curr Opin Struct Biol 6 (6): 848-858 (Dec 1996) 
Perutz MF
Several dominantly inherited, late onset, neurodegenerative diseases are due to expansion of CAG repeats, leading to expansion of glutamine repeats in the affected proteins. These proteins are of very different sizes and, with one exception, show no sequence homology to known proteins or to each other; their functions are unknown. In some, the glutamine repeat starts near the N-terminus, in another near the middle and in another near the C-terminus, but regardless of these differences, no disease has been observed in individuals with fewer than 37 repeats, and absence of disease has never been found in those with more than 41 repeats.

Protein constructs with more than 41 repeats are toxic to E. coli and to CHO cells in culture, and they elicit ataxia in transgenic mice. These observations argue in favour of a distinct change of structure associated with elongation beyond 37-41 glutamine repeats. The review describes experiments designed to find out what these structures might be and how they could influence the properties of the proteins of which they form part. Poly-L-glutamines form pleated sheets of beta-strands held together by hydrogen bonds between their amides. Incorporation of glutamine repeats into a small protein of known structure made it associate irreversibly into oligomers. That association took place during the folding of the protein molecules and led to their becoming firmly interlocked by either strand- or domain-swapping. Thermodynamic considerations suggest that elongation of glutamine repeats beyond a certain length may lead to a phase change from random coils to hydrogen-bonded hairpins. Possible mechanisms of expansion of CAG repeats are discussed in the light of looped DNA model structures.

Effectiveness of Anthracycline Against Experimental Prion Disease in Syrian Hamsters

16 May 97 Science 276 #5315 1119-1121 1997
Tagliavini Fi, ... P. Cassutti, M. A. Cervini, J.  Lansen, M. Salmona, C. Post
Prion diseases are transmissible neurodegenerative conditions characterized by the accumulation of protease-resistant forms of the prion protein (PrP), termed PrPres, in the brain. Insoluble PrPres tends to aggregate into amyloid fibrils. The anthracycline 4-iodo-4-deoxy-doxorubicin (IDX) binds to amyloid fibrils and induces amyloid resorption in patients with systemic amyloidosis. To test IDX in an experimental model of prion disease, Syrian hamsters were inoculated intracerebrally either with scrapie-infected brain homogenate or with infected homogenate coincubated with IDX. In IDX-treated hamsters, clinical signs of disease were delayed and survival time was prolonged. Neuropathological examination showed a parallel delay in the appearance of brain changes and in the accumulation of PrPres and PrP amyloid.

Prion diseases, such as scrapie of sheep, spongiform encephalopathy of cattle, and Creutzfeldt-Jakob disease of humans, are transmissible neurodegenerative conditions characterized by the accumulation of protease-resistant forms of the prion protein (PrP), termed PrPres, in the brain (1). Unlike the normal PrP, PrPres has a large amount of -sheet secondary structure and a strong tendency to aggregate into amyloid fibrils (2). Deposition of PrPres and PrP amyloid is accompanied by nerve cell degeneration and glial cell proliferation, leading to the clinical signs of disease (3). In scrapie-infected hamsters, survival time is prolonged by the amyloid-binding dye Congo red (4). Congo red inhibits the accumulation of PrPres in scrapie-infected neuroblastoma cells without affecting the metabolism of normal PrP (5).

The anthracycline 4-iodo-4-deoxy-doxorubicin (IDX) (Fig. 1A) is a recently developed derivative of doxorubicin, a drug of proven efficacy in a large number of malignancies (6). The administration of IDX to eight patients with plasma cell dyscrasias complicated by immunoglobulin light-chain amyloidosis resulted in the partial resorption of amyloid deposits in three cases. In addition, four of the eight patients exhibited discernible clinical improvement, two patients showed reduced symptoms of the disease, and the other two patients were rendered stable (7). This unexpected activity of the compound was confirmed by further studies showing that IDX binds strongly to amyloid fibrils of different chemical composition, inhibits in vitro assembly of insulin into amyloid fibrils, and reduces amyloid deposits in a murine model of reactive amyloidosis (8). Thus, IDX can be regarded as a prototype of a class of drugs that are able to inhibit amyloidogenesis, reverse tissue deposition of amyloid fibrils, or both.

A wide variety of compounds has been tested in the treatment of prion diseases (14). A few of these compounds, particularly amphotericin B and sulfated polyanions, were effective in retarding the appearance of clinical symptoms and prolonging the survival of animals experimentally infected with scrapie (15). These compounds are structurally dissimilar and have diverse activity. Amphotericin B, for example, is an antifungal agent, whereas heteropolyanions such as HPA-23 are antivirals. Although these molecules are known to be active at the cell membrane, their mechanism of action in experimental scrapie is still unknown. Other antiviral compounds such as amantadine, vidarabine, and acyclovir have been used in patients with Creutzfeldt-Jakob disease with inconclusive results (14).

According to the prion hypothesis, the major component of the agent responsible for transmission of prion disease is PrPres, and prion propagation results from the conformational conversion of normal PrP into an altered form, catalyzed by PrPres (1). IDX was administered intracerebrally at the same time as the scrapie agent. This experimental design was dictated by IDX's intrinsic cytotoxicity and pharmacokinetic properties, as well as by its limited ability to pass the blood-brain barrier (16). It is conceivable that the delay in PrPres accumulation and the neuropathological and behavioral changes seen may have been a consequence of IDX's binding to abnormal PrP, inhibiting the availability of this protein to act as a template for the conversion of the normal protein. It is unlikely that the anti-scrapie effects of IDX could be due to its cytotoxic properties, because PrP mRNA levels and tubulin concentrations remained unchanged by the treatment. Nevertheless, the possibility that changes in PrP expression could have occurred in IDX-treated animals during the early phase of infection cannot be ruled out.

The results of this study indicate that IDX, although inappropriate for actual treatment of prion diseases because of its cytotoxicity and pharmacokinetic properties, is a prototype of a class of compounds having anti-prion effects. Furthermore, the ability of IDX to bind to different types of amyloid protein (8) suggests the possibility that these compounds could also be active in other amyloid-related neurodegenerative diseases.

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Roland Heynkes comments

F. Tagliavini et al. found, that an anthracycline similar to amphotericin B and heparin extends the incubation time of hamster scrapy. But they mixed it with the infectious brain homogenate one hour before the intracerebral inoculation. Therefore we can not exclude an in vitro artefact which would not be reproduced when the infectious agent and the anthracycline are given separately. I hope that there are similar studies going on with antisense oligonucleotides, which should be much more specific and perhaps can reduce the expression of the prion protein.

Finding normal function for prion protein

5.18.97 Webmaster commentary

A normal function for prion protein at the molecular level has still not been identified. While a little surprising, given the research effort, a lot of other neurological disorders are in the same boat. In the last two Nature's, progress has been made on normal role. It is instructive to see how that progress was made and whether the techniques are potentially applicable to prion protein.

1. The first case has to do with Alzheimers, which is about 10% genetic so far , like CJD. Though Alzheimers has some serious parallels to CJD as a disease, there is no overlap in genes whose defects are sufficient to cause the respective diseases. In the case of presenilin 1 and 2, they were found homologous to a nematode protein of known function, a protein important in neurogenesis.. A homologous CNS developmental gene was also found in fruit fly, at the level of 53% sequence identity, with highly conserved residues in the region where mutations can cause familial Alzheimer in humans.

The advantage here is that a lot is known about these organisms and genetic work is rapid. No homologue of prion protein has been found by hybridization in nematode or fruitfly; however, these entire genomes are being rapidly sequenced which would allow searches for weaker homologues.

2. The other is a gene involved in obesity, leptin [Nature 387 206-09 1997 ] which isn't transported to the CNS in problem conditions. The protein had total lack of sequence resemblance to any known protein except leptins from other mammals [sound familiar] but in this case the 3D structure was practically super-imposable on the structures for ciliary neurotrophic factor, granulocyte colony-stimulating factor, leukemia inhibitory factor, and human growth hormone. Sort of odd bed-fellows at first sight, these paralogues, but the similarity also extended to the respective receptors. So the leptin people got their foot in the door this way, now can tap into what is known about these other proteins.

So far, searching the 3D structural databases has not turned up anything like the NMR structure for prion protein -- I assume someone somewhere is checking in once a month or so on the new structures. Of course, the NMR structure might not be fully native or it is the [unknown] beta sheet that we should be looking for!

The best that can be done for now, quickly and cheaply, along these lines is to sequence the prion gene in a wider range of animals, starting in and around salmon and amphibians, and proceeding back.

Presenilin 1 is required for Notch1 and DII1 expression in the paraxial mesoderm

Nature 387, 288 (1997) (Letter )
P C Wong, H Zheng, ..., Van der Ploeg & S S Sisodia
Approximately 10% of cases of Alzheimers disease are familial and associated with autosomal dominant inheritance of mutations in genes encoding the amyloid precursor protein, presenilin 1 (PS1) and presenilin 2 (PS2). Mutations in PS1 are linked to about 25% of cases of early-onset familial Alzheimers disease. PS1, which is endoproteolytically processed in vivo, is a multipass transmembrane protein and is a functional homologue of SEL-12, a Caenorhabditis elegans protein that facilitates signalling mediated by the Notch/LIN-12 family of receptors. To examine potential roles for PS1 in facilitating Notch-mediated signalling during mammalian embryogenesis, the authors generated mice with targeted disruptions of PS1 alleles (PS1-1-mice). PS1-1- embryos exhibited abnormal patterning of the axial skeleton and spinal ganglia, phenotypes traced to defects in somite segmentation and differentiation. Moreover, expression of mRNA encoding Notch1 and Dll1 (delta-like gene 1), a vertebrate Notch ligand, is markedly reduced in the presomitic mesoderm of PS1-1- embryos compared to controls. Hence, PS1 is required for the spatiotemporal expression of Notch1 and Dll1, which are essential for somite segmentation and maintenance of somite borders.

RNA editing: applicable to prion mRNA?

Regulation of serotonin-2C receptor G-protein coupling by RNA editing                
C M Burns, H Chu, ... & R B Emeson 
Nature 387, 303 (1997)  (Letter to Nature)
New studies have shown that RNA transcripts encoding the serotonin (5-hydroxytryptamine, 5-HT) receptor subtype, 5-HT2C, undergo RNA editing. Genomically encoded adenosine residues in the pre-messenger RNA are converted to inosines, resulting in three amino-acid changes. These changes are confined to the region of the receptor that is involved in signal transduction, so the editing may have an effect on appetite and mood, and cause epileptic seizures.

Regulation of serotonin-2C receptor G-protein coupling by RNA editing The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) elicits a wide array of physiological effects by binding to several receptor subtypes. The 5-HT2 family of receptors belongs to a large group of seven-transmembrane-spanning G-protein-coupled receptors and includes three receptor subtypes (5-HT2A, 5-HT2B and 5-HT2C) which are linked to phospholipase C, promoting the hydrolysis of membrane phospholipids and a subsequent increase in the intracellular levels of inositol phosphates and diacylglycerol. Here we show that transcripts encoding the 2C subtype of serotonin receptor (5-HT2CR) undergo RNA editing events in which genomically encoded adenosine residues are converted to inosines by the action of double- stranded RNA adenosine deaminase(s).

Sequence analysis of complementary DNA isolates from dissected brain regions have indicated the tissue-specific expression of seven major 5- HT2C receptor isoforms encoded by eleven distinct RNA species. Editing of 5- HT2CR messenger RNAs alters the amino-acid coding potential of the predicted second intracellular loop of the receptor and can lead to a 10--15-fold reduction in the efficacy of the interaction between receptors and their G proteins. These observations indicate that RNA editing is a new mechanism for regulating serotonergic signal transduction and suggest that this post-transcriptional modification may be critical for modulating the different cellular functions that are mediated by other members of the G-protein-coupled receptor superfamily.

If this is a general phenomenon, it would vastly complicate understanding the regulation of cells of this type. In prion protein, one could speculate that sporadic CJD might arise from such a mechanism. Mouse prion codon 55 has been reported not to be represented in mouse prion protein [ JMB 245 362-374 1995] -- webmaster.

Differential diagnosis of Alzheimer's disease

Neurology 48 (5 Suppl 6): S2-S9 (May 1997) 
Geldmacher DS, Whitehouse PJ Jr
Accurate diagnosis of dementia is essential to provide appropriate treatment as well as patient and family counseling. It may be difficult to differentiate dementia from delirium. In addition, several features distinguish dementia from depression, but the two can coexist and the distinction may be uncertain. Dementias can be grouped into two categories: dementia that presents without prominent motor signs and dementia that presents with prominent motor signs.

Dementias without prominent motor signs include Alzheimer's disease, frontotemporal dementia, and Creutzfeld-Jakob and other prion diseases. Dementias characterized at onset by prominent motor signs include dementias with Lewy bodies, idiopathic Parkinson's disease, progressive supranuclear palsy, cortico-basal ganglionic degeneration, hydrocephalus, Huntington's disease, and vascular dementia. Routine diagnostic steps include a careful history, mental status screening, laboratory and imaging studies, and neuropsychologic testing. Genetic testing is available, but its use is controversial and raises complex ethical questions.

CJD after an embolization of intercostal arteries with cadaveric dura mater suggesting systemic transmission

Defebvre L, Destee A, Caron J, Ruchoux MM, Wurtz A, Remy J
Neurology 48 (5): 1470-1471 (May 1997) No abstract available online
Department of Neurology A, Hospital R. Salengro, Lille, France. 

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