Loss-of-function mutations at the rim of the funnel of mechanosensitive channel MscL

MscL is a bacterial mechanosensitive channel that is activated directly by membrane stretch. Although the gene has been cloned and the crystal structure of the closed channel has been defined, how membrane tension causes conformational changes in MscL remains largely unknown. To identify the site where MscL senses membrane tension, we examined the function of the mutants generated by random and scanning mutagenesis. In vitro (patch-clamp) and in vivo (hypoosmotic-shock) experiments showed that when a hydrophilic amino acid replaces one of the hydrophobic residues that are thought to make contact with the membrane lipid near the periplasmic end of the M1 or M2 transmembrane domain, MscL loses the ability to open in response to membrane tension. Hydrophilic (asparagine) substitution of the other residues in the lipid-protein interface did not impair the channel's mechanosensitivity. These observations suggest that the disturbance of the hydrophobic interaction between the membrane lipid and the periplasmic rim of the channel's funnel impairs the function of MscL.     

Fetal cells in mother rats contribute to the remodeling of liver and kidney after injury

Fetal microchimerism indicates a mixture of cells of maternal and fetal origin seen in maternal tissues during and after pregnancy. Controversy exists about whether persistent fetal microchimerism is related with some autoimmune disorders occurring during and after pregnancy. In the current experiment, an animal model in which EGFP positive cells were taken as fetal-origin cells was designed to detect the fetal microchimerism in various maternal organs. Ethanol drinking and gentamicin injection were adopted to induce liver and kidney injury simultaneously. EGFP positive cells were engrafted not only in the maternal circulation and bone marrow, but also in the liver and kidney as hepatocytes and tubular cells, respectively. These results indicate that fetal cells are engrafted to maternal hematopoietic system without apparent injury and they also contribute to the repairing process of maternal liver and kidney.     

Type III protein secretion mechanism in mammalian and plant pathogens

The type III protein secretion system (TTSS) is a complex organelle in the envelope of many Gram-negative bacteria; it delivers potentially hundreds of structurally diverse bacterial virulence proteins into plant and animal cells to modulate host cellular functions. Recent studies have revealed several basic features of this secretion system, including assembly of needle/pilus-like secretion structures, formation of putative translocation pores in the host membrane, recognition of N-terminal/5' mRNA-based secretion signals, and requirement of small chaperone proteins for optimal delivery and/or expression of effector proteins. Although most of our knowledge about the TTSS is derived from studies of mammalian pathogenic bacteria, similar and unique features are learned from studies of plant pathogenic bacteria. Here, we summarize the most salient aspects of the TTSS, with special emphasis on recent findings.     

NF-kappa B-inducing kinase establishes self-tolerance in a thymic stroma-dependent manner

Physical contact between thymocytes and the thymic stroma is essential for T cell maturation and shapes the T cell repertoire in the periphery. Stromal elements that control these processes still remain elusive. We used a mouse strain with mutant NF-kappaB-inducing kinase (NIK) to examine the mechanisms underlying the breakdown of self-tolerance. This NIK-mutant strain manifests autoimmunity and disorganized thymic structure with abnormal expression of Rel proteins in the stroma. Production of immunoregulatory T cells that control autoreactive T cells was impaired in NIK-mutant mice. The autoimmune disease seen in NIK-mutant mice was reproduced in athymic nude mice by grafting embryonic thymus from NIK-mutant mice, and this was rescued by supply of exogenous immunoregulatory T cells. Impaired production of immunoregulatory T cells by thymic stroma without normal NIK was associated with altered expression of peripheral tissue-restricted Ags, suggesting an essential role of NIK in the thymic microenvironment in the establishment of central tolerance.     

Treatment with alpha-galactosylceramide attenuates the development of bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is an end-stage disorder for which efficacious therapeutic options are not readily available. Although its pathogenesis is poorly understood, pulmonary fibrosis occurs as a result of various inflammations. NKT cells modulate inflammation because of their ability to produce large amounts of cytokines by stimulation with their glycolipid ligand. In the present study, we investigated the effects of alpha-galactosylceramide (alpha-GalCer), a selective NKT cell ligand, on the development of bleomycin-induced pulmonary fibrosis. Treatment of mice with alpha-GalCer prolonged their survival under bleomycin administration by attenuating the development of pulmonary fibrosis. The protective effects of alpha-GalCer were associated with an increase in the pulmonary level of IFN-gamma and a decrease in the pulmonary level of fibrogenic cytokines such as TGF-beta and connective tissue growth factor. The initial pulmonary inflammation caused by bleomycin was also attenuated by alpha-GalCer with the reduction of the macrophage inflammatory protein-2 level. The protective effects of alpha-GalCer were markedly reduced in mice lacking NKT cells or as a result of treatment with anti-IFN-gamma Ab. These results suggest that alpha-GalCer suppresses bleomycin-induced acute pulmonary inflammation and thus attenuates the development of pulmonary fibrosis possibly by regulating several cytokine levels.     

Human coronavirus 229E binds to CD13 in rafts and enters the cell through caveolae

CD13, a receptor for human coronavirus 229E (HCoV-229E), was identified as a major component of the Triton X-100-resistant membrane microdomain in human fibroblasts. The incubation of living fibroblasts with an anti-CD13 antibody on ice gave punctate labeling that was evenly distributed on the cell surface, but raising the temperature to 37 degrees C before fixation caused aggregation of the labeling. The aggregated labeling of CD13 colocalized with caveolin-1 in most cells. The HCoV-229E virus particle showed a binding and redistribution pattern that was similar to that caused by the anti-CD13 antibody: the virus bound to the cell evenly when incubated on ice but became colocalized with caveolin-1 at 37 degrees C; importantly, the virus also caused sequestration of CD13 to the caveolin-1-positive area. Electron microscopy confirmed that HCoV-229E was localized near or at the orifice of caveolae after incubation at 37 degrees C. The depletion of plasmalemmal cholesterol with methyl beta-cyclodextrin significantly reduced the HCoV-229E redistribution and subsequent infection. A caveolin-1 knockdown by RNA interference also reduced the HCoV-229E infection considerably. The results indicate that HCoV-229E first binds to CD13 in the Triton X-100-resistant microdomain, then clusters CD13 by cross-linking, and thereby reaches the caveolar region before entering cells.     

Ubiquilin interacts with ubiquitylated proteins and proteasome through its ubiquitin-associated and ubiquitin-like domains

Mammalian cells acquire tolerance against multiple stressors through the high-level expression of stress-responsible genes. We have previously demonstrated that protein-disulfide isomerase (PDI) together with ubiquilin are up-regulated in response to hypoxia/brain ischemia, and play critical roles in resistance to these damages. We show here that ubiquilin interacts preferentially with poly-ubiquitin chains and 19S proteasome subunits. Taken together, these results suggest that ubiquitin could serve as an adaptor protein that both interacts with PDI and mediates the delivery of poly-ubiquitylated proteins to the proteasome in the cytosol in the vicinity of the endoplasmic reticulum membrane.