Human genome search in celiac disease: mutated gliadin T-cell-like epitope in two human proteins promotes T-cell activation

Discovery of a number of novel and known human genes whose protein products bear striking similarity to two or more wheat gliadin domains raised the possibility that human intestinal non-HLA peptides homologous to celiac T-cell epitopes could play a role in non-HLA gene specification in celiac disease. Database searching of the entire human genome identified only 11 gut-expressed proteins with high T-cell epitope homology, particularly to the DQ2-gamma-I-gliadin epitope (i.e. TFIIA, FOXJ2 and IgD; mean BestFit quality score=40 versus random value of 24). Others were similar to DQ2-alpha-I-gliadin (i.e. PAX9; BestFit quality 46 versus 20 for random), or DQ2-alpha-II-gliadin (PHLDA1, known in mice as the T-cell death-associated gene; BestFit quality 43 versus 30 for random) epitopes. Among proteins previously screened for gliadin homology, noteworthy was achaete scute homologous protein (DQ2-alpha-I-gliadin; BestFit quality 41 versus 22 for random). With the exception of IgD, all are nuclear factors. Paying particular attention to the position of potential major histocompatibility complex (MHC) anchor residues, several were selected for testing in a DQ2-gamma-I-gliadin-restricted T-cell system. All native 10-mer peptides were inactive, even when deamidated, but V96F substitution of deamidated TFIIA amino acid residues 91-100 stimulated IL-2 release at levels exceeding the wheat gliadin positive control. Also active, but only slightly, was L1009F substitution of AIB3 amino acid residues 1004-1013. PlotSimilarity alignment of TFIIAs from eight species revealed subthreshold similarity score in the peptide region, in contrast to the highly conserved amino and carboxy termini. Molecular modeling of TFIIA[V96F] peptide points to an important juxtaposition of an upwardly projecting phenylalanine residue at peptide position 6 that likely contacts a receptor complementarity-determining region, and a downwardly projecting glutamic acid residue that fits into the shallow MHC P7 pocket. These observations tentatively point to a new multi-gene hypothesis for the initiation of celiac disease in which deamidated free human peptides with T-cell epitope homology (particularly those made more homologous by mutation) escape negative selection, as per deamidation of the HEL(48-62) peptide in the hen egg lysozyme model of autoimmunity. Deamidation following peptide release due to injury triggers inflammation, thereafter repeatedly provoked by dietary gliadin immunodominant peptides concentrated in the proximal small intestine.     

Altered DNA mutation spectrum in aflatoxin b1-treated transgenic mice that express the hepatitis B virus x protein

Humans chronically infected with hepatitis B virus (HBV) are at further risk of liver cancer upon exposure to dietary aflatoxin B1 (AFB1), a carcinogenic product of the mold Aspergillus flavus. For the present study, we utilized double-transgenic mice (ATX mice) that express the HBV X protein (HBx) and possess a bacteriophage lambda transgene to evaluate the in vivo effect of HBx expression on AFB1-induced DNA mutations. The expression of HBx correlated with a 24% increase in mutation frequency overall and an approximately twofold increase in the incidence of G/C-to-T/A transversion mutations following AFB1 exposure. These results are consistent with a model in which expression of HBx during chronic HBV infection may contribute to the development of hepatocellular carcinoma following exposure to environmental carcinogens.     

Avian disease at the Salton Sea

A review of existing records and the scientific literature was conducted for occurrences of avian diseases affecting free-ranging avifauna within the Salton Sea ecosystem. The period for evaluation was 1907 through 1999. Records of the U.S. Department of Agriculture, Bureau of Biological Survey and the scientific literature were the data sources for the period of 1907–1939. The narrative reports of the U.S. Fish and Wildlife Service's Sonny Bono National Wildlife Refuge Complex and the epizootic database of the U.S. Geological Survey's National Wildlife Health Center were the primary data sources for the remainder of the evaluation. The pattern of avian disease at the Salton Sea has changed greatly over time. Relative to past decades, there was a greater frequency of major outbreaks of avian disease at the Salton Sea during the 1990s than in previous decades, a greater variety of disease agents causing epizootics, and apparent chronic increases in the attrition of birds from disease. Avian mortality was high for about a decade beginning during the mid-1920s, diminished substantially by the 1940s and was at low to moderate levels until the 1990s when it reached the highest levels reported. Avian botulism (Clostridium botulinum type C) was the only major cause of avian disease until 1979 when the first major epizootic of avian cholera (Pasteurella multocidia) was documented. Waterfowl and shorebirds were the primary species affected by avian botulism. A broader spectrum of species have been killed by avian cholera but waterfowl have suffered the greatest losses. Avian cholera reappeared in 1983 and has joined avian botulism as a recurring cause of avian mortality. In 1989, avian salmonellosis (Salmonella typhimurium) was first diagnosed as a major cause of avian disease within the Salton Sea ecosystem and has since reappeared several times, primarily among cattle egrets (Bubulcus ibis). The largest loss from a single epizootic occurred in 1992, when an estimated 155000 birds, primarily eared grebes (Podiceps nigricollis), died from an undiagnosed cause. Reoccurrences of that unknown malady have continued to kill substantial numbers of eared grebes throughout the 1990s. The first major epizootic of type C avian botulism in fish-eating birds occurred in 1996 and killed large numbers of pelicans (Pelecanus occidentalis & P. erythrorhynchos). Avian botulism has remained as a major annual cause of disease in pelicans. In contrast, the chronic on-Sea occurrence of avian botulism in waterfowl and shorebirds of previous decades was seldom seen during the 1990s. Newcastle disease became the first viral disease to cause major bird losses at the Salton Sea when it appeared in the Mullet Island cormorant (Phalacrocorax auritus) breeding colony during 1997 and again during 1998.     

Export of L-isoleucine from Corynebacterium glutamicum: a two-gene-encoded member of a new translocator family

Bacteria possess amino acid export systems, and Corynebacterium glutamicum excretes L-isoleucine in a process dependent on the proton motive force. In order to identify the system responsible for L-isoleucine export, we have used transposon mutagenesis to isolate mutants of C. glutamicum sensitive to the peptide isoleucyl-isoleucine. In one such mutant, strong peptide sensitivity resulted from insertion into a gene designated brnF encoding a hydrophobic protein predicted to possess seven transmembrane spanning helices. brnE is located downstream of brnF and encodes a second hydrophobic protein with four putative membrane-spanning helices. A mutant deleted of both genes no longer exports L-isoleucine, whereas an overexpressing strain exports this amino acid at an increased rate. BrnF and BrnE together are also required for the export of L-leucine and L-valine. BrnFE is thus a two-component export permease specific for aliphatic hydrophobic amino acids. Upstream of brnFE and transcribed divergently is an Lrp-like regulatory gene required for active export. Searches for homologues of BrnFE show that this type of exporter is widespread in prokaryotes but lacking in eukaryotes and that both gene products which together comprise the members of a novel family, the LIV-E family, generally map together within a single operon. Comparisons of the BrnF and BrnE phylogenetic trees show that gene duplication events in the early bacterial lineage gave rise to multiple paralogues that have been retained in alpha-proteobacteria but not in other prokaryotes analyzed.     

Mechanism of aerobic transformation of carbon tetrachloride by poplar cells

The biochemical mechanism of carbon tetrachloride transformation by poplarcells was investigated using an axenic poplar cell culture.After one-day incubations of poplar cells under aerobic conditions, about 1.5% of dosedcarbon tetrachloride was transformed to carbon dioxide, about 0.001% to chloroform andabout 3% of the carbon was bound to insoluble poplar cellular materials. The productionof carbon dioxide increased under aerobic conditions while the formation of chloroformand cell binding of carbon tetrachloride-carbon was enhanced under anaerobic conditions.Both carbon dioxide production and cell binding were significantly inhibitedby a general inhibitor of cytochrome P-450 activity (carbon monoxide) and by specific P-450 2E1 inhibitors(chlorzoxazone, isoniazid, 4-methylpyrazole and 1-phenylimidazole). However, no inhibitory effects were observed when the cells were incubated in thepresence of lignin peroxidase inhibitors (NaVO₃ and 3-amino-1,2,4-triazole). These resultssuggest that an enzyme similar to mammalian cytochrome P450-2E1 is involved inthe metabolism of carbon tetrachloride by poplar cells. This study demonstratesan environmental biodegradative process for carbon tetrachloridethat operates under aerobic conditions.     

David Sabatini--a lifelong fascination with organelles

As a pioneer molecular cell biologist, highly skilled in both morphological and biochemical approaches, David Sabatini was a key figure in laying the foundation for the field of intracellular protein trafficking with his seminal studies on cotranslational translocation of nascent polypeptides in the endoplasmic reticulum and the intracellular sorting of plasma membrane proteins in polarized epithelial cells.     

Effects of diazepam and stress on lung inflammatory response in OVA-sensitized rats

The influence of stress and diazepam treatment on airway inflammation was investigated in ovalbumin (OVA)-sensitized rats. Animals were injected with OVA plus aluminum hydroxide intraperitoneally (day 0) and boosted with OVA subcutaneously (day 7). From the first to 13th day after sensitization, rats were treated with diazepam, and 1 h later they were placed in a shuttle box where they received 50 mild escapable foot shocks/day preceded by a sound signal (S). Response during the warning (S) canceled shock delivery and terminated the S. On day 14, rats were submitted to a single session of 50 inescapable foot shocks preceded by S and then were challenged with OVA. High levels of stress were detected in shocked animals, manifested as ultrasonic vocalizations. Morphometric analysis of stressed animals revealed a significant increase in both edema and lymphomononucleated cells in airways compared with controls. Diazepam treatment reduced edema in stressed and nonstressed rats. No differences were found in polymorphonucleated cell infiltration. Diazepam treatment reduced lymphomononucleated cell infiltration in stressed animals. These data suggest that stress and diazepam treatment play relevant roles in edema and lymphomononucleated airway inflammation in OVA-sensitized rats.     

GLUT4 retention in adipocytes requires two intracellular insulin-regulated transport steps

Insulin regulates glucose uptake into fat and muscle by modulating the distribution of the GLUT4 glucose transporter between the surface and interior of cells. The GLUT4 trafficking pathway overlaps with the general endocytic recycling pathway, but the degree and functional significance of the overlap are not known. In this study of intact adipocytes, we demonstrate, by using a compartment-specific fluorescence-quenching assay, that GLUT4 is equally distributed between two intracellular pools: the transferrin receptor-containing endosomes and a specialized compartment that excludes the transferrin receptor. These pools of GLUT4 are in dynamic communication with one another and with the cell surface. Insulin-induced redistribution of GLUT4 to the surface requires mobilization of both pools. These data establish a role for the general endosomal system in the specialized, insulin-regulated trafficking of GLUT4. Trafficking through the general endosomal system is regulated by rab11. Herein, we show that rab11 is required for the transport of GLUT4 from endosomes to the specialized compartment and for the insulin-induced translocation to the cell surface, emphasizing the importance of the general endosomal pathway in the specialized trafficking of GLUT4. Based on these findings we propose a two-step model for GLUT4 trafficking in which the general endosomal recycling compartment plays a specialized role in the insulin-regulated traffic of GLUT4. This compartment-based model provides the framework for understanding insulin-regulated trafficking at a molecular level.