Alphavirus Restriction by IFITM Proteins

Interferon inducible transmembrane proteins (IFITMs) are broad‐spectrum antiviral factors. In cell culture the entry of many enveloped viruses, including orthomyxo‐, flavi‐, and filoviruses, is inhibited by IFITMs, though the mechanism(s) involved remain unclear and may vary between viruses. We demonstrate that Sindbis and Semliki Forest virus (SFV), which both use endocytosis and acid‐induced membrane fusion in early endosomes to infect cells, are restricted by the early endosomal IFITM3. The late endosomal IFITM2 is less restrictive and the plasma membrane IFITM1 does not inhibit normal infection by either virus. IFITM3 inhibits release of the SFV capsid into the cytosol, without inhibiting binding, internalization, trafficking to endosomes or low pH‐induced conformational changes in the envelope glycoprotein. Infection by SFV fusion at the cell surface was inhibited by IFITM1, but was equally inhibited by IFITM3. Furthermore, an IFITM3 mutant (Y20A) that is localized to the plasma membrane inhibited infection by cell surface fusion more potently than IFITM1. Together, these results indicate that IFITMs, in particular IFITM3, can restrict alphavirus infection by inhibiting viral fusion with cellular membranes. That IFITM3 can restrict SFV infection by fusion at the cell surface equivalently to IFITM1 suggests that IFITM3 has greater antiviral potency against SFV.      

Identification of two proteins that interact with the Erp virulence factor from Mycobacterium tuberculosis by using the bacterial two-hybrid system

Background  

The exported repetitive protein (erp) gene encodes a secreted 36-kDa protein with a central domain containing several proline-glycine-leucine-threonine-serine (PGLTS) repeats. It has been demonstrated that erp is a virulence-associated factor since the disruption of this gene impairs the growth of Mycobacterium bovis and Mycobacterium tuberculosis in mice.     

HP1alpha recruitment to DNA damage by p150CAF-1 promotes homologous recombination repair

Heterochromatin protein 1 (HP1), a major component of constitutive heterochromatin, is recruited to DNA damage sites. However, the mechanism involved in this recruitment and its functional importance during DNA repair remain major unresolved issues. Here, by characterizing HP1α dynamics at laser-induced damage sites in mammalian cells, we show that the de novo accumulation of HP1α occurs within both euchromatin and heterochromatin as a rapid and transient event after DNA damage. This recruitment is strictly dependent on p150CAF-1, the largest subunit of chromatin assembly factor 1 (CAF-1), and its ability to interact with HP1α. We find that HP1α depletion severely compromises the recruitment of the DNA damage response (DDR) proteins 53BP1 and RAD51. Moreover, HP1α depletion leads to defects in homologous recombination-mediated repair and reduces cell survival after DNA damage. Collectively, our data reveal that HP1α recruitment at early stages of the DDR involves p150CAF-1 and is critical for proper DNA damage signaling and repair.     

Elaboración de una herramienta para la estimación del riesgo de mortalidad a corto y medio plazo tras el alta de una Unidad de Hospitalización de Agudos de Geriatría

Objectives

To identify predictive factors for 6 and 12-months mortality after discharge from a geriatric acute care unit, and from these, derive a mortality-risk index.

Methods and analysis

Prospective cohort study will be conducted on patients over 70 years-old admitted to a geriatric acute care unit and survived to hospital discharge. The main outcome measure will be mortality at 6 months and 12 months after discharge. Independent variables include sociodemographics, functional status, comorbidities, and clinical and laboratory characteristics. Risk factors associated with mortality will be constructed using multivariate logistic regression models. To build the mortality index, points will be assigned to each risk factor by dividing each beta coefficient in the logistic model by the lowest beta coefficient. A score will be assigned to each subject by adding up the points for each risk factor present in the model. The predictive accuracy of the model will be determined by comparing the predicted versus observed mortality in the study population and calculating the area under the ROC curves in both populations.

Conclusions

The risk-mortality index developed would allow an easy estimate to be made of individual risk of death at 6 months and 12 months after discharge from a geriatric acute care unit, with the purpose of establishing care plans and individualising treatment, according to real objectives.     

The adaptive acid response in Mesorhizobium sp.

Mesorhizobium huakuii strain LL56 and Mesorhizobium sp. strain LL22, which nodulate Lotus glaber, developed an adaptive acid response during exponential growth upon exposure to sublethal acid conditions. The adaptive acid response was found to be dependent on the sublethal pH and the strain intrinsic acid tolerance: the lowest adaptation pH was 4.0 for strain LL56 and 5.7 for strain LL22, and the lowest pH values tolerated after adaptation were 3.0 and 4.0, respectively. Both complex and minimal medium allowed the development of the adaptive acid response, although in complex medium this response was more effective. Three low molecular weight polypeptides (LMWPs) showed increased expression in strain LL56 during the adaptation to pH 4.0. However, the adaptive acid tolerance was only partially dependent on de novo protein synthesis, and constitutive systems may play a significant role on the acid tolerance of Mesorhizobium huakuii strain LL56.     

Endocytosis of a chimera between human pro-urokinase and the plant toxin saporin: an unusual internalization mechanism.

A fluorescent derivative of a chimeric toxin between human pro-urokinase and the plant ribosome-inactivating protein saporin (p-uPA-Sap(TRITC)), has been prepared in order to study the endocytosis of this potentially antimetastatic conjugate in the murine model cell line LB6 clone19 (Cl19) transfected with the human urokinase receptor gene. The physiological internalization of urokinase-inhibitor complexes is triggered by the interaction of plasminogen inhibitors (PAIs) with receptors belonging to the low density lipoprotein-related receptor protein (LRP) family, and involves a macro-quaternary structure including uPAR, LRP, and PAIs. However, in contrast to this mechanism, we observed a two-step process: first, the urokinase receptor (uPAR) acts as the anchoring factor on the plasma membrane; subsequently, LRP acts as the endocytic trigger. Once the chimera is bound to the plasma membrane by interaction with uPAR, we suggest that a possible exchange may occur to transfer the toxin to LRP via the saporin moiety and begin the internalization. So an unusual endocytic process is described, where the toxin enters the cell via a receptor different from that used to bind the plasma membrane.     

Different expression levels of the TAP peptide transporter lead to recognition of different antigenic peptides by tumor-specific CTL

Decreased antigenicity of cancer cells is a major problem in tumor immunology. This is often acquired by an expression defect in the TAP. However, it has been reported that certain murine Ags appear on the target cell surface upon impairment of TAP expression. In this study, we identified a human CTL epitope belonging to this Ag category. This epitope is derived from preprocalcitonin (ppCT) signal peptide and is generated within the endoplasmic reticulum by signal peptidase and signal peptide peptidase. Lung cancer cells bearing this antigenic peptide displayed low levels of TAP, but restoration of their expression by IFN-γ treatment or TAP1 and TAP2 gene transfer abrogated ppCT Ag presentation. In contrast, TAP upregulation in the same tumor cells increased their recognition by proteasome/TAP-dependent peptide-specific CTLs. Thus, to our knowledge, ppCT(16-25) is the first human tumor epitope whose surface expression requires loss or downregulation of TAP. Lung tumors frequently display low levels of TAP molecules and might thus be ignored by the immune system. Our results suggest that emerging signal peptidase-generated peptides represent alternative T cell targets, which permit CTLs to destroy TAP-impaired tumors and thus overcome tumor escape from CD8(+) T cell immunity.