Transmissible and genetic prion diseases share a common pathway of neurodegeneration

Prion diseases can be infectious, sporadic and genetic. The infectious forms of these diseases, including bovine spongiform encephalopathy and Creutzfeldt-Jakob disease, are usually characterized by the accumulation in the brain of the transmissible pathogen, an abnormally folded isoform of the prion protein (PrP) termed PrPSc. However, certain inherited PrP mutations appear to cause neurodegeneration in the absence of PrPSc, working instead by favoured synthesis of CtmPrP, a transmembrane form of PrP. The relationship between the neurodegeneration seen in transmissible prion diseases involving PrPSc and that associated with ctmPrP has remained unclear. Here we find that the effectiveness of accumulated PrPSc in causing neurodegenerative disease depends upon the predilection of host-encoded PrP to be made in the ctmPrP form. Furthermore, the time course of PrPSc accumulation in transmissible prion disease is followed closely by increased generation of CtmPrP. Thus, the accumulation of PrPSc appears to modulate in trans the events involved in generating or metabolising CtmPrP. Together, these data suggest that the events of CtmPrP-mediated neurodegeneration may represent a common step in the pathogenesis of genetic and infectious prion diseases.     

Are elicitins cryptograms in plant-Oomycete communications?

Stimulation of plant natural defenses is an important challenge in phytoprotection prospects. In that context, elicitins, which are small proteins secreted by Phytophthora and Pythium species, have been shown to induce a hypersensitive-like reaction in tobacco plants. Moreover, these plants become resistant to their pathogens, and thus this interaction constitutes an excellent model to investigate the signaling pathways leading to plant resistance. However, most plants are not reactive to elicitins, although they possess the functional signaling pathways involved in tobacco responses to elicitin. The understanding of factors involved in this reactivity is needed to develop agronomic applications. In this review, it is proposed that elicitins could interact with regulating cell wall proteins before they reach the plasma membrane. Consequently, the plant reactivity or nonreactivity status could result from the equilibrium reached during this interaction. The possibility of overexpressing the elicitins directly from genomic DNA in Pichia pastoris allows site-directed mutagenesis experiments and structure/function studies. The recent discovery of the sterol carrier activity of elicitins brings a new insight on their molecular activity. This constitutes a crucial property, since the formation of a sterol-elicitin complex is required to trigger the biological responses of tobacco cells and plants. Only the elicitins loaded with a sterol are able to bind to their plasmalemma receptor, which is assumed to be an allosteric calcium channel. Moreover, Phytophthora and Pythium do not synthesize the sterols required for their growth and their fructification, and elicitins may act as shuttles trapping the sterols from the host plants. Sequence analysis of elicitin genes from several Phytophthora species sheds unexpected light on the phylogenetic relationships among the genus, and suggests that the expression of elicitins is under tight regulatory control. Finally, general involvement of these lipid transfer proteins in the biology of Pythiaceae, and in plant defense responses, is discussed. A possible scheme for the coevolution between Phytophthora and tobacco plants is approached.     

Mutations in ATP2A2, encoding a Ca2+ pump, cause Darier disease

Darier disease (DD) is an autosomal-dominant skin disorder characterized by loss of adhesion between epidermal cells (acantholysis) and abnormal keratinization. Recently we constructed a 2.4-Mb, P1-derived artificial chromosome contig spanning the DD candidate region on chromosome 12q23-24.1. After screening several genes that mapped to this region, we identified mutations in the ATP2A2 gene, which encodes the sarco/endoplasmic reticulum Ca2(+)-ATPase type 2 isoform (SERCA2) and is highly expressed in keratinocytes. Thirteen mutations were identified, including frameshift deletions, in-frame deletions or insertions, splice-site mutations and non-conservative missense mutations in functional domains. Our results demonstrate that mutations in ATP2A2 cause DD and disclose a role for this pump in a Ca(2+)-signalling pathway regulating cell-to-cell adhesion and differentiation of the epidermis.     

The Pendred syndrome gene encodes a chloride-iodide transport protein

Pendred syndrome is the most common form of syndromic deafness and characterized by congenital sensorineural hearing loss and goitre. This disorder was mapped to chromosome 7 and the gene causing Pendred syndrome (PDS) was subsequently identified by positional cloning. PDS encodes a putative transmembrane protein designated pendrin. Pendrin is closely related to a family of sulfate transport proteins that includes the rat sulfate-anion transporter (encoded by Sat-1; 29% amino acid sequence identity), the human diastrophic dysplasia sulfate transporter (encoded by DTD; 32%) and the human sulfate transporter 'downregulated in adenoma' (encoded by DRA; 45%). On the basis of this homology and the presence of a slightly modified sulfate-transporter signature sequence comprising its putative second transmembrane domain, pendrin has been proposed to function as a sulfate transporter. We were unable to detect evidence of sulfate transport following the expression of pendrin in Xenopus laevis oocytes by microinjection of PDS cRNA or in Sf9 cells following infection with PDS-recombinant baculovirus. The rates of transport for iodide and chloride were significantly increased following the expression of pendrin in both cell systems. Our results demonstrate that pendrin functions as a transporter of chloride and iodide, but not sulfate, and may provide insight into thyroid physiology and the pathophysiology of Pendred syndrome.     

Genomic instability in Gadd45a-deficient mice.

Gadd45a-null mice generated by gene targeting exhibited several of the phenotypes characteristic of p53-deficient mice, including genomic instability, increased radiation carcinogenesis and a low frequency of exencephaly. Genomic instability was exemplified by aneuploidy, chromosome aberrations, gene amplification and centrosome amplification, and was accompanied by abnormalities in mitosis, cytokinesis and growth control. Unequal segregation of chromosomes due to multiple spindle poles during mitosis occurred in several Gadd45a -/- cell lineages and may contribute to the aneuploidy. Our results indicate that Gadd45a is one component of the p53 pathway that contributes to the maintenance of genomic stability.     

CACP, encoding a secreted proteoglycan, is mutated in camptodactyly-arthropathy-coxa vara-pericarditis syndrome.

Altered growth and function of synoviocytes, the intimal cells which line joint cavities and tendon sheaths, occur in a number of skeletal diseases. Hyperplasia of synoviocytes is found in both rheumatoid arthritis and osteoarthritis, despite differences in the underlying aetiologies of the two disorders. We have studied the autosomal recessive disorder camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP; MIM 208250) to identify biological pathways that lead to synoviocyte hyperplasia, the principal pathological feature of this syndrome. Using a positional-candidate approach, we identified mutations in a gene (CACP) encoding a secreted proteoglycan as the cause of CACP. The CACP protein, which has previously been identified as both 'megakaryocyte stimulating factor precursor' and 'superficial zone protein', contains domains that have homology to somatomedin B, heparin-binding proteins, mucins and haemopexins. In addition to expression in joint synovium and cartilage, CACP is expressed in non-skeletal tissues including liver and pericardium. The similarity of CACP sequence to that of other protein families and the expression of CACP in non-skeletal tissues suggest it may have diverse biological activities.     

Spastin, a new AAA protein, is altered in the most frequent form of autosomal dominant spastic paraplegia

Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a genetically heterogeneous neurodegenerative disorder characterized by progressive spasticity of the lower limbs. Among the four loci causing AD-HSP identified so far, the SPG4 locus at chromosome 2p2-1p22 has been shown to account for 40-50% of all AD-HSP families. Using a positional cloning strategy based on obtaining sequence of the entire SPG4 interval, we identified a candidate gene encoding a new member of the AAA protein family, which we named spastin. Sequence analysis of this gene in seven SPG4-linked pedigrees revealed several DNA modifications, including missense, nonsense and splice-site mutations. Both SPG4 and its mouse orthologue were shown to be expressed early and ubiquitously in fetal and adult tissues. The sequence homologies and putative subcellular localization of spastin suggest that this ATPase is involved in the assembly or function of nuclear protein complexes.     

Structural basis for self-association and receptor recognition of human TRAF2

Tumour necrosis factor (TNF)-receptor-associated factors (TRAFs) form a family of cytoplasmic adapter proteins that mediate signal transduction from many members of the TNF-receptor superfamily and the interleukin-1 receptor. They are important in the regulation of cell survival and cell death. The carboxy-terminal region of TRAFs (the TRAF domain) is required for self-association and interaction with receptors. The domain contains a predicted coiled-coil region that is followed by a highly conserved TRAF-C domain. Here we report the crystal structure of the TRAF domain of human TRAF2, both alone and in complex with a peptide from TNF receptor-2 (TNF-R2). The structures reveal a trimeric self-association of the TRAF domain, which we confirm by studies in solution. The TRAF-C domain forms a new, eight-stranded antiparallel beta-sandwich structure. The TNF-R2 peptide binds to a conserved shallow surface depression on one TRAF-C domain and does not contact the other protomers of the trimer. The nature of the interaction indicates that an SXXE motif may be a TRAF2-binding consensus sequence. The trimeric structure of the TRAF domain provides an avidity-based explanation for the dependence of TRAF recruitment on the oligomerization of the receptors by their trimeric extracellular ligands.     

1-(substituted)benzyl-5-aminoimidazole-4-carboxamides are potent orally active inhibitors of Trypanosoma cruzi in mice

1-(Substituted)benzyl-5-aminoimidazole-4-carboxamides are potent orally active inhibitors of Trypanosoma cruzi infections in mice. The most active compounds are the 1-(4-chlorobenzyl)- and 1-(3,4-dichlorobenzyl)-analogs (L-153,094 [2] and L-153,153 [4], resp.) which are approximately 7-fold more potent upon oral administration than nifurtimox (Lampit) in suppressing parasite levels in the blood of mice with acute Trypanosoma cruzi infections.