14-3-3 proteins: regulation of endoplasmic reticulum localization and surface expression of membrane proteins

The density and composition of cell surface proteins are major determinants for cellular functions. Regulation of cell surface molecules occurs at several levels, including the efficiency of surface transport, and is therefore of great interest. As the major phosphoprotein-binding modules, 14-3-3 proteins are known for their crucial roles in a wide range of cellular activities, including the subcellular localization of target proteins. Accumulating evidence suggests a role for 14-3-3 in surface transport of membrane proteins, in which 14-3-3 binding reduces endoplasmic reticulum (ER) localization, thereby promoting surface expression of membrane proteins. Here, we focus on recent evidence of 14-3-3-mediated surface transport and discuss the possible molecular mechanisms.     

Attenuated CagA oncoprotein in Helicobacter pylori from Amerindians in Peruvian Amazon

Population genetic analyses of bacterial genes whose products interact with host tissues can give new understanding of infection and disease processes. Here we show that strains of the genetically diverse gastric pathogen Helicobacter pylori from Amerindians from the remote Peruvian Amazon contain novel alleles of cagA, a major virulence gene, and reveal distinctive properties of their encoded CagA proteins. CagA is injected into the gastric epithelium where it hijacks pleiotropic signaling pathways, helps Hp exploit its special gastric mucosal niche, and affects the risk that infection will result in overt gastroduodenal diseases including gastric cancer. The Amerindian CagA proteins contain unusual but functional tyrosine phosphorylation motifs and attenuated CRPIA motifs, which affect gastric epithelial proliferation, inflammation, and bacterial pathogenesis. Amerindian CagA proteins induced less production of IL-8 and cancer-associated Mucin 2 than did those of prototype Western or East Asian strains and behaved as dominant negative inhibitors of action of prototype CagA during mixed infection of Mongolian gerbils. We suggest that Amerindian cagA is of relatively low virulence, that this may have been selected in ancestral strains during infection of the people who migrated from Asia into the Americas many thousands of years ago, and that such attenuated CagA proteins could be useful therapeutically.     

Synapse Elimination Triggered by BMP4 Exocytosis and Presynaptic BMP Receptor Activation

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Roles of Ca2+ in hyphal and yeast-form growth inCandida albicans. Growth regulation by altered extracellular and intracellular free Ca2+ concentrations

The dimorphic fungusCandida albicans has both a yeast form and a hyphal form. When yeast-form cells were starved and then transferred to aN-acetylglucosamine medium, the formation of true hyphae from the unbudded yeast-form cells was induced. Removal of Ca²⁺ from the medium with EGTA inhibited hyphal formation by 50%, resulting in only thin and short hyphae. Externally applied excess Ca²⁺ (>10⁻²M) also affected the hyphal formation, resulting in formation of pseudohyphae. This effect required a high concentration of Ca²⁺ but was Ca²⁺-specific. Deprivation of Ca²⁺ also inhibited yeast-form growth. Interestingly, such cells had abnormally wide bud necks and became defective in cell separation. To measure cytosolic free Ca²⁺, fura-2 was introduced into hyphal cells by electroporation. Its normal value was estimated to be about 100 nM. The electroporation caused transient elevation of cytosolic free Ca²⁺ concentration and transient cessation of hyphal growth. There was a close correlation between the timing of recovery of Ca²⁺ concentration and that of the resumption of hyphal growth. Our results demonstrate the importance of extracellular and intracellular free Ca²⁺ for the growth ofC. albicans.     

Effects of cold stress on glutathione and related enzymes in rat erythrocytes

Effects of acute and chronic cold stress on glutathione and related enzymes in rat erythrocytes were investigated. Blood from both cold-acclimated (CA) and cold-adapted (CG) rats had significantly lower concentrations of glutathione than blood from control animals. Superoxide dismutase activity was increased significantly in CA rats and tended to rise in CG rats. Activity of glutathione peroxidase in erythrocytes was inconsistent in that it tended to increase in CA rats but decreased significantly in CG rats. The results may imply that CG rats suffered deleterious effects of hydrogen peroxide. On the other hand, there were marked decreases in glutathione peroxidase and glutathione reductase activities in acutely cold-exposed rats in conjunction with unchanged levels of glutathione. In all treatments the state of riboflavin metabolism was estimated to be adequate, since no increases were observed in the erythrocyte glutathione reductase activity coefficient.     

Role of C-terminal Membrane-proximal Basic Residues in Cell Surface Trafficking of HIV Coreceptor GPR15 Protein

Cell surface density of G protein-coupled receptors (GPCRs) is controlled by dynamic molecular interactions that often involve recognition of the distinct sequence signals on the cargo receptors. We reported previously that the RXR-type dibasic motif in the distal C-terminal tail of an HIV coreceptor GPR15 negatively regulates the cell surface expression by mediating the coatomer protein I complex-dependent retrograde transport to the endoplasmic reticulum (ER). Here we demonstrate that another pair of basic residues (Arg³¹⁰-Arg³¹¹) in the membrane-proximal region of the C-terminal tail plays a pivotal role in mediating the anterograde trafficking of GPR15. The Ala mutation of the C-terminal membrane-proximal basic residues (MPBRs) (R310/311A) abolished the O-glycosylation and cell surface expression of GPR15. The subcellular fractionation and immunocytochemistry assays indicated that the R310/311A mutant was more localized in the ER but much less in the trans-Golgi when compared with the wild-type GPR15, suggesting the positive role of Arg³¹⁰-Arg³¹¹ in the ER-to-Golgi transport of GPR15. Sequence analysis on human GPCRs showed that the basic residues are frequent in the membrane-proximal region of the C-terminal tail. Similar to GPR15, mutation of the C-terminal MPBRs resulted in a marked reduction of the cell surface expression in multiple different GPCRs. Our results suggest that the C-terminal MPBRs are critically involved in mediating the anterograde trafficking of a broad range of membrane proteins, including GPCRs.     

Analysis of factors controlling responses of an aquatic microcosm to organic loading

The changes in the numbers of individuals of the constituent species and ammonia concentrations in 6 subsystems (Bacteria, bacteria-Cyclidium, bacteria-Aeolosoma, bacteria-Chlorella, bacteria-Cyclidium-Chlorella, bacteria-Aeolosoma-Chlorella) of an aquatic microcosm were examined after the addition of organic substance (peptone) at both the young and mature stages of succession. Organic loading led to decreases in the numbers of bacteria and Aeolosoma after temporary increases in their numbers and an oscillation in the numbers of Cyclidium but the densities of these populations were maintained at constant values in the presence of Chlorella. When organic substance was added at a young stage where the photosynthetic activities of algae were high, invertebrates, especially Aeolosoma, were damaged by unionized ammonia which was formed as the pH value increased. In contrast, organic loading at the mature stage enhanced the population densities and biomasses of all constituent species.     

A phylogenomic perspective on diversity,hybridization and evolutionary affinities in the stickleback genus Pungitius

Hybridization and convergent evolution are phenomena of broad interest in evolutionary biology, but their occurrence poses challenges for reconstructing evolutionary affinities among affected taxa. Sticklebacks in the genus Pungitius are a case in point: evolutionary relationships and taxonomic validity of different species and populations in this circumpolarly distributed species complex remain contentious due to convergent evolution of traits regarded as diagnostic in their taxonomy, and possibly also due to frequent hybridization among taxa. To clarify the evolutionary relationships among different Pungitius species and populations globally, as well as to study the prevalence and extent of introgression among recognized species, genomic data sets of both reference genome‐anchored single nucleotide polymorphisms and de novo assembled RAD‐tag loci were constructed with RAD‐seq data. Both data sets yielded topologically identical and well‐supported species trees. Incongruence between nuclear and mitochondrial DNA‐based trees was found and suggested possibly frequent hybridization and mitogenome capture during the evolution of Pungitius sticklebacks. Further analyses revealed evidence for frequent nuclear genetic introgression among Pungitius species, although the estimated proportions of autosomal introgression were low. Apart from providing evidence for frequent hybridization, the results challenge earlier mitochondrial and morphology‐based hypotheses regarding the number of species and their affinities in this genus: at least seven extant species can be recognized on the basis of genetic data. The results also shed new light on the biogeographical history of the Pungitius‐complex, including suggestion of several trans‐Arctic invasions of Europe from the Northern Pacific. The well‐resolved phylogeny should facilitate the utility of this genus as a model system for future comparative evolutionary studies.