Functional involvement of TMF/ARA160 in Rab6-dependent retrograde membrane traffic

The small GTPase Rab6 regulates retrograde membrane traffic from endosomes to the Golgi apparatus and from the Golgi to the endoplasmic reticulum (ER). We examined the role of a Rab6-binding protein, TMF/ARA160 (TATA element modulatory factor/androgen receptor-coactivator of 160 kDa), in this process. High-resolution immunofluorescence imaging revealed that TMF signal surrounded Rab6-positive Golgi structures and immunoelectron microscopy revealed that TMF is concentrated at the budding structures localized at the tips of cisternae. The knockdown of either TMF or Rab6 by RNA interference blocked retrograde transport of endocytosed Shiga toxin from early/recycling endosomes to the trans-Golgi network, causing missorting of the toxin to late endosomes/lysosomes. However, the TMF knockdown caused Rab6-dependent displacement of N-acetylgalactosaminyltransferase-2 (GalNAc-T2), but not beta1,4-galactosyltransferase (GalT), from the Golgi. Analyses using chimeric proteins, in which the cytoplasmic regions of GalNAc-T2 and GalT were exchanged, revealed that the cytoplasmic region of GalNAc-T2 plays a crucial role in its TMF-dependent Golgi retention. These observations suggest critical roles for TMF in two Rab6-dependent retrograde transport processes: one from endosomes to the Golgi and the other from the Golgi to the ER.     

Impairment in a negative regulatory system for TCR signaling in CD4+ T cells from old mice

To examine the involvement of lipid rafts in an age-associated decline in T cell function, we analyzed the effect of aging on the constituents of lipid rafts in resting mouse CD4(+) T cells. We found a pronounced, age-dependent reduction in PAG/Cbp, which is involved in the regulation of Src family kinases (SFKs) by recruiting Csk (a negative regulator of SFKs) to lipid rafts. This reduction is specific for T cells and is attributed, at least in part, to the reduction in its mRNA level. The reduction of PAG accompanies marked impairment in recruiting Csk to lipid rafts and a concomitant decrease in the inactive forms of SFKs. These findings indicate that old mouse CD4(+) T cells have a defect in a negative SFK regulatory system.     

Legumain/asparaginyl endopeptidase controls extracellular matrix remodeling through the degradation of fibronectin in mouse renal proximal tubular cells

Legumain/asparaginyl endopeptidase (EC 3.4.22.34) is a novel cysteine protease that is abundantly expressed in the late endosomes and lysosomes of renal proximal tubular cells. Recently, emerging evidence has indicated that legumain might play an important role in control of extracellular matrix turnover in various pathological conditions such as tumor growth/metastasis and progression of atherosclerosis. We initially found that purified legumain can directly degrade fibronectin, one of the main components of the extracellular matrix, in vitro. Therefore, we examined the effect of legumain on fibronectin degradation in cultured mouse renal proximal tubular cells. Fibronectin processing can be inhibited by chloroquine, an inhibitor of lysosomal degradation, and can be enhanced by the overexpression of legumain, indicating that fibronectin degradation occurs in the presence of legumain in lysosomes from renal proximal tubular cells. Furthermore, in legumain-deficient mice, unilateral ureteral obstruction (UUO)-induced renal interstitial protein accumulation of fibronectin and renal interstitial fibrosis were markedly enhanced. These findings indicate that legumain might have an important role in extracellular matrix remodeling via the degradation of fibronectin in renal proximal tubular cells.     

A neural-specific F-box protein Fbs1 functions as a chaperone suppressing glycoprotein aggregation

Fbs1 is an F-box protein present abundantly in the nervous system. Similar to the ubiquitously expressed Fbs2, Fbs1 recognizes N-glycans at the innermost position as a signal for unfolded glycoproteins, probably in the endoplasmic reticulum-associated degradation pathway. Here, we show that the in vivo majority of Fbs1 is present as Fbs1-Skp1 heterodimers or Fbs1 monomers but not SCF(Fbs1) complex. The inefficient SCF complex formation of Fbs1 and the restricted presence of SCF(Fbs1) bound on the endoplasmic reticulum membrane were due to the short linker sequence between the F-box domain and the sugar-binding domain. In vitro, Fbs1 prevented the aggregation of the glycoprotein through the N-terminal unique sequence of Fbs1. Our results suggest that Fbs1 assists clearance of aberrant glycoproteins in neuronal cells by suppressing aggregates formation, independent of ubiquitin ligase activity, and thus functions as a unique chaperone for those proteins.     

CD1d degradation in Chlamydia trachomatis-infected epithelial cells is the result of both cellular and chlamydial proteasomal activity

Chlamydia trachomatis is an obligate intracellular pathogen that can persist in the urogenital tract. Mechanisms by which C. trachomatis evades clearance by host innate immune responses are poorly described. CD1d is MHC-like, is expressed by epithelial cells, and can signal innate immune responses by NK and NKT cells. Here we demonstrate that C. trachomatis infection down-regulates surface-expressed CD1d in human penile urethral epithelial cells through proteasomal degradation. A chlamydial proteasome-like activity factor (CPAF) interacts with the CD1d heavy chain, and CPAF-associated CD1d heavy chain is then ubiquitinated and directed along two distinct proteolytic pathways. The degradation of immature glycosylated CD1d was blocked by the proteasome inhibitor lactacystin but not by MG132, indicating that degradation was not via the conventional proteasome. In contrast, the degradation of non-glycosylated CD1d was blocked by lactacystin and MG132, consistent with conventional cellular cytosolic degradation of N-linked glycoproteins. Immunofluorescent microscopy confirmed the interruption of CD1d trafficking to the cell surface, and the dislocation of CD1d heavy chains into both the cellular cytosol and the chlamydial inclusion along with cytosolic CPAF. C. trachomatis targeted CD1d toward two distinct proteolytic pathways. Decreased CD1d surface expression may help C. trachomatis evade detection by innate immune cells and may promote C. trachomatis persistence.     

Microdose clinical trial: quantitative determination of fexofenadine in human plasma using liquid chromatography/electrospray ionization tandem mass spectrometry

A sample treatment procedure and high-sensitive liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for quantitative determination of fexofenadine in human plasma was developed for a microdose clinical trial with a cold drug, i.e., a non-radioisotope-labeled drug. Fexofenadine and terfenadine, as internal standard, were extracted from plasma samples using a 96-well solid-phase extraction plate (Oasis HLB). Quantitation was performed on an ACQUITY UPLC system and an API 5000 mass spectrometer by multiple reaction monitoring. Chromatographic separation was achieved on an XBridge C18 column (100 mm x 2.1 mm i.d., particle size 3.5 microm) using acetonitrile/2 mM ammonium acetate (91:9, v/v) as the mobile phase at a flow rate of 0.6 ml/min. The analytical method was validated in accordance with the FDA guideline for validation of bioanalytical methods. The calibration curve was linear in the range of 10-1000 pg/ml using 200 microl of plasma. Analytical method validation for the clinical dose, for which the calibration curve was linear in the range of 1-500 ng/ml using 20 microl of plasma, was also conducted. Each method was successfully applied for making determinations in plasma using LC/ESI-MS/MS after administration of a microdose (100 microg solution) and a clinical dose (60 mg dose) in eight healthy volunteers.     

Hsp105α suppresses Adriamycin-induced cell death via nuclear localization signal-dependent nuclear accumulation

Heat shock protein 105 (Hsp105) is a molecular chaperone, and the isoforms Hsp105α and Hsp105β exhibit distinct functions with different subcellular localizations. Hsp105β localizes in the nucleus and induces the expression of the major heat shock protein Hsp70, whereas cytoplasmic Hsp105α is less effective in inducing Hsp70 expression. Hsp105 shuttles between the cytoplasm and the nucleus; the subcellular localization is governed by the relative activities of the nuclear localization signal (NLS) and nuclear export signal (NES). Here, we show that nuclear accumulation of Hsp105α but not Hsp105β is involved in Adriamycin (ADR) sensitivity. Knockdown of Hsp105α induces cell death at low ADR concentration, at which ADR is less effective in inducing cell death in the presence of Hsp105α. Of note, Hsp105 is localized in the nucleus under these conditions, even though Hsp105β is not expressed, indicating that Hsp105α accumulates in the nucleus in response to ADR treatment. The exogenously expressed Hsp105α but not its NLS mutant localizes in the nucleus of ADR-treated cells. In addition, the expression level of the nuclear export protein chromosomal maintenance 1 (CRM1) was decreased by ADR treatment of cells, and CRM1 knockdown caused nuclear accumulation of Hsp105α both in the presence and absence of ADR. These results indicating that Hsp105α accumulates in the nucleus in a manner dependent on the NLS activity via the suppression of nuclear export. Our findings suggest a role of nuclear Hsp105α in the sensitivity against DNA-damaging agents in tumor cells.     

Conserved metabolic enzymes as vaccine antigens for giardiasis

Giardia lamblia is a leading protozoal cause of diarrheal disease worldwide. Infection is associated with abdominal pain, malabsorption and weight loss, and protracted post-infectious syndromes. A human vaccine is not available against G. lamblia. Prior studies with human and murine immune sera have identified several parasite antigens, including surface proteins and metabolic enzymes with intracellular functions. While surface proteins have demonstrated vaccine potential, they can exhibit significant variation between G. lamblia strains. By comparison, metabolic enzymes show greater conservation but their vaccine potential has not been established. To determine whether such proteins can serve as vaccine candidates, we focused on two enzymes, α-enolase (ENO) and ornithine carbamoyl transferase (OCT), which are involved in glycolysis and arginine metabolism, respectively. We show in a cohort of patients with confirmed giardiasis that both enzymes are immunogenic. Intranasal immunization with either enzyme antigen in mice induced strong systemic IgG1 and IgG2b responses and modest mucosal IgA responses, and a marked 100- to 1,000-fold reduction in peak trophozoite load upon oral G. lamblia challenge. ENO immunization also reduced the extent and duration of cyst excretion. Examination of 44 cytokines showed only minimal intestinal changes in immunized mice, although a modest increase of CCL22 was observed in ENO-immunized mice. Spectral flow cytometry revealed increased numbers and activation state of CD4 T cells in the small intestine and an increase in α4β7-expressing CD4 T cells in mesenteric lymph nodes of ENO-immunized mice. Consistent with a key role of CD4 T cells, immunization of CD4-deficient and Rag-2 deficient mice failed to induce protection, whereas mice lacking IgA were fully protected by immunization, indicating that immunity was CD4 T cell-dependent but IgA-independent. These results demonstrate that conserved metabolic enzymes can be effective vaccine antigens for protection against G. lamblia infection, thereby expanding the repertoire of candidate antigens beyond primary surface proteins.     

A novel chordin-like protein inhibitor for bone morphogenetic proteins expressed preferentially in mesenchymal cell lineages

Chordin is a bone morphogenetic protein (BMP) inhibitor that has been identified as a factor dorsalizing the Xenopus embryo. A novel secreted protein, CHL (for chordin-like), with significant homology to chordin, was isolated from mouse bone marrow stromal cells. Injection of CHL RNA into Xenopus embryos induced a secondary axis. Recombinant CHL protein inhibited the BMP4-dependent differentiation of embryonic stem cells in vitro and interacted directly with BMPs, similar to chordin. However, CHL also weakly bound to TGFbetas. In situ hybridization revealed that the mouse CHL gene, located on the X chromosome, was expressed predominantly in mesenchyme-derived cell types: (1) the dermatome and limb bud mesenchyme and, later, the subdermal mesenchyme and the chondrocytes of the developing skeleton during embryogenesis and (2) a layer of fibroblasts/connective tissue cells in the gastrointestinal tract, the thick straight segments of kidney tubules, and the marrow stromal cells in adults. An exception was expression in the neural cells of the olfactory bulb and cerebellum. Interestingly, the spatiotemporal expression patterns of CHL were distinct from those of chordin in many areas examined. Thus, CHL may serve as an important BMP regulator for differentiating mesenchymal cells, especially during skeletogenesis, and for developing specific neurons.