Proteomic characterization of host response to Yersinia pestis and near neighbors

Host-pathogen interactions result in protein expression changes within both the host and the pathogen. Here, results from proteomic characterization of host response following exposure to Yersinia pestis, the causative agent of plague, and to two near neighbors, Yersinia pseudotuberculosis and Yersinia enterocolitica, are reported. Human monocyte-like cells were chosen as a model for macrophage immune response to pathogen exposure. Two-dimensional electrophoresis followed by mass spectrometry was used to identify host proteins with differential expression following exposure to these three closely related Yersinia species. This comparative proteomic characterization of host response clearly shows that host protein expression patterns are distinct for the different pathogen exposures, and contributes to further understanding of Y. pestis virulence and host defense mechanisms. This work also lays the foundation for future studies aimed at defining biomarkers for presymptomatic detection of plague.     

Plasmalemmal V-H(+)-ATPases regulate intracellular pH in human lung microvascular endothelial cells

The lung endothelium layer is exposed to continuous CO(2) transit which exposes the endothelium to a substantial acid load that could be detrimental to cell function. The Na(+)/H(+) exchanger and HCO(3)(-)-dependent H(+)-transporting mechanisms regulate intracellular pH (pH(cyt)) in most cells. Cells that cope with high acid loads might require additional primary energy-dependent mechanisms. V-H(+)-ATPases localized at the plasma membranes (pmV-ATPases) have emerged as a novel pH regulatory system. We hypothesized that human lung microvascular endothelial (HLMVE) cells use pmV-ATPases, in addition to Na(+)/H(+) exchanger and HCO(3)(-)-based H(+)-transporting mechanisms, to maintain pH(cyt) homeostasis. Immunocytochemical studies revealed V-H(+)-ATPase at the plasma membrane, in addition to the predicted distribution in vacuolar compartments. Acid-loaded HLMVE cells exhibited proton fluxes in the absence of Na(+) and HCO(3)(-) that were similar to those observed in the presence of either Na(+), or Na(+) and HCO(3)(-). The Na(+)- and HCO(3)(-)-independent pH(cyt) recovery was inhibited by bafilomycin A(1), a V-H(+)-ATPase inhibitor. These studies show a Na(+)- and HCO(3)(-)-independent pH(cyt) regulatory mechanism in HLMVE cells that is mediated by pmV-ATPases.     

Structural features of the initiator of replication protein RepB encoded by the promiscuous plasmid pMV158

The promiscuous rolling circle (RC)-replicating plasmid pMV158 encodes the 210-amino-acid initiator of replication protein, RepB. The protein relaxes supercoiled cognate DNA in a topoisomeraseI-like manner. A new vector and procedure for overproduction, scaling-up, and purification of the protein has been developed. RepB purified as a hexamer in solution, as shown by analytical ultracentrifugation assays. Circular dichroism (CD) of RepB indicated that the protein has an estimated content of around 33% alpha-helices and 20% beta-strands. Characterisation of temperature-induced transitions of the protein showed an irreversible change in the spectra when the temperature was raised above 35 degrees C, indicating that the protein undergoes a conformational change that could account for the relatively high optimal temperature of the RepB-mediated cleavage.     

Role of BMP signaling and the homeoprotein Iroquois in the specification of the cranial placodal field

Different types of placodes originate at the anterior border of the neural plate but it is still an unresolved question whether individual placodes arise as distinct ectodermal specializations in situ or whether all or a subset of the placodes originate from a common preplacodal field. We have analyzed the expression and function of the homeoprotein Iro1 in Xenopus and zebrafish embryos, and we have compared its expression with several preplacodal and placodal markers. Our results indicate that the iro1 genes are expressed in the preplacodal region, being one of the earliest markers for this area. We show that an interaction between the neural plate and the epidermis is able to induce the expression of several preplacodal markers, including Xiro1, by a similar mechanism to that previously shown for neural crest induction. In addition, we analyzed the role of BMP in the specification of the preplacodal field by studying the expression of the preplacodal markers Six1, Xiro1, and several specific placodal markers. We experimentally modified the level of BMP activity by three different methods. First, we implanted beads soaked with noggin in early neurula stage Xenopus embryos; second, we injected the mRNA that encodes a dominant negative of the BMP receptor into Xenopus and zebrafish embryos; and third, we grafted cells expressing chordin into zebrafish embryos. The results obtained using all three methods show that a reduction in the level of BMP activity leads to an expansion of the preplacodal and placodal region similar to what has been described for neural crest regions. By using conditional constructs of Xiro1, we performed gain and loss of function experiments. We show that Xiro1 play an important role in the specification of both the preplacodal field as well as individual placodes. We have also used inducible dominant negative and activator constructs of Notch signaling components to analyze the role of these factors on placodal development. Our results indicate that the a precise level of BMP activity is required to induce the neural plate border, including placodes and neural crest cells, that in this border the iro1 gene is activated, and that this activation is required for the specification of the placodes.     

High mobility group box protein 1: an endogenous signal for dendritic cell maturation and Th1 polarization

High mobility group box protein 1 (HMGB1), a DNA binding nuclear and cytosolic protein, is a proinflammatory cytokine released by monocytes and macrophages. This study addressed the hypothesis that HMGB1 is an immunostimulatory signal that induces dendritic cell (DC) maturation. We show that HMGB1, via its B box domain, induced phenotypic maturation of DCs, as evidenced by increased CD83, CD54, CD80, CD40, CD58, and MHC class II expression and decreased CD206 expression. The B box caused increased secretion of the proinflammatory cytokines IL-12, IL-6, IL-1alpha, IL-8, TNF-alpha, and RANTES. B box up-regulated CD83 expression as well as IL-6 secretion via a p38 MAPK-dependent pathway. In the MLR, B box-activated DCs acted as potent stimulators of allogeneic T cells, and the magnitude of the response was equivalent to DCs activated by exposure to LPS, nonmethylated CpG oligonucleotides, or CD40L. Furthermore, B box induced secretion of IL-12 from DCs as well as IL-2 and IFN-gamma secretion from allogeneic T cells, suggesting a Th1 bias. HMGB1 released by necrotic cells may be a signal of tissue or cellular injury that, when sensed by DCs, induces and/or enhances an immune reaction.     

Role of cross-talk between IFN-alpha-induced monocyte-derived dendritic cells and NK cells in priming CD8+ T cell responses against human tumor antigens

In the present study we evaluated the role of IFN-alpha in the generation of dendritic cells (IFN-DCs) with priming activity on CD8(+) T lymphocytes directed against human tumor Ags. A 3-day treatment of monocytes, obtained as adherent PBMCs from HLA-A*0201(+) healthy donors, with IFN-alpha and GM-CSF led to the differentiation of DCs displaying a semimature phenotype, but promptly inducing CD8(+) T cell responses after one in vitro sensitization with peptides derived from melanoma (gp100(209-217) and MART-1/Melan-A(27-35)) and adenocarcinoma (CEA(605-613)) Ags. However, these features were lost when IFN-DCs were generated from immunosorted CD14(+) monocytes. The ability of adherent PBMCs to differentiate into IFN-DCs expressing higher levels of costimulatory molecules and exerting efficient T cell priming capacity was associated with the presence of contaminating NK cells, which underwent phenotypic and functional activation upon IFN-alpha treatment. NK cell boost appeared to be mediated by both direct and indirect (i.e., mediated by IFN-DCs) mechanisms. Experiments performed to prove the role of contaminating NK cells in DC differentiation showed that IFN-DCs generated in the absence of NK were phenotypically less mature and could not efficiently prime antitumor CD8(+) lymphocytes. Reciprocally, IFN-DCs raised from immunosorted CD14(+) monocytes regained their T cell priming activity when NK cells were added to the culture before IFN-alpha and GM-CSF treatment. Together, our data suggest that the ability of IFN-DCs to efficiently prime anti-tumor CD8(+) T lymphocytes relied mostly on the positive cross-talk occurring between DCs and NK cells upon stimulation with IFN-alpha.     

Methamphetamine produces neuronal inclusions in the nigrostriatal system and in PC12 cells

Mice treated with the psychostimulant methamphetamine (MA) showed the appearance of intracellular inclusions in the nucleus of medium sized striatal neurones and cytoplasm of neurones of the substantia nigra pars compacta but not in the frontal cortex. All inclusions contained ubiquitin, the ubiquitin activating enzyme (E1), the ubiquitin protein ligase (E3-like, parkin), low and high molecular weight heat shock proteins (HSP 40 and HSP 70). Inclusions found in nigral neurones stained for alpha-synuclein, a proteic hallmark of Lewy bodies that are frequently observed in Parkinson's disease and other degenerative disorders. However, differing from classic Lewy bodies, MA-induced neuronal inclusions appeared as multilamellar bodies resembling autophagic granules. Methamphetamine reproduced this effect in cultured PC12 cells, which offered the advantage of a simple cellular model for the study of the molecular determinants of neuronal inclusions. PC12 inclusions, similar to those observed in nigral neurones, were exclusively localized in the cytoplasm and stained for alpha-synuclein. Time-dependent experiments showed that inclusions underwent a progressive fusion of the external membranes and developed an electrodense core. Inhibition of dopamine synthesis by alpha-methyl-p-tyrosine (alphaMpT), or administering the antioxidant S-apomorphine largely attenuated the formation of inclusions in PC12 cells exposed to MA. Inclusions were again observed when alphaMpT-treated cells were loaded with l-DOPA, which restored intracellular dopamine levels.     

Cardiovascular effects of methyleugenol, a natural constituent of many plant essential oils, in normotensive rats

Cardiovascular effects of intravenous (i.v.) treatment with methyleugenol (ME), a natural constituent of many plant essential oils, were investigated in normotensive rats. Additionally this study examined (I) whether the autonomic nervous system is involved in the mediation of ME-induced changes in mean aortic pressure (MAP) and heart rate (HR), and (II) whether the hypotensive effects of ME could result from its vasodilatory effects directly upon vascular smooth muscle. In both pentobarbital-anesthetized and conscious rats, i.v. bolus injections of ME (1 to 10 mg/kg) elicited similar and dose-dependent decreases in MAP. In anesthetized rats, ME decreased HR only at the highest dose (10 mg/kg), while changes of this parameter were not uniform in conscious rats. Pretreatment of anesthetized rats with bilateral vagotomy significantly reduced the bradycardia response to ME (10 mg/kg) without affecting the hypotension. In conscious rats, i.v. pretreatment with methylatropine (1 mg/kg) or hexamethonium (30 mg/kg) had no significant effect on ME-induced hypotension. In rat isolated thoracic aorta preparations, ME (0.006-1.68 mM) induced a concentration-dependent reduction of potassium (60 mM)-induced contraction. This is the first physiological evidence that i.v. treatment with ME in either anesthetized or conscious rats elicits hypotension; an effect that seems related to an active vascular relaxation rather than withdrawal of sympathetic tone.     

Expression of cholera toxin under non-AKI conditions in Vibrio cholerae El Tor induced by increasing the exposed surface of cultures

The regulatory systems controlling expression of the ctxAB genes encoding cholera toxin (CT) in the classical and El Tor biotypes of pathogenic Vibrio cholerae have been characterized and found to be almost identical. Notwithstanding this, special in vitro conditions, called AKI conditions, are required for El Tor bacteria to produce CT. The AKI conditions involve biphasic cultures. In phase 1 the organism is grown in a still tube for 4 h. In phase 2 the medium is poured into a flask to continue growth with shaking. Virtually no expression of CT occurs if this protocol is not followed. Here we demonstrated that CT expression takes place in single-phase still cultures if the volume-to-surface-area ratio is decreased, both under air and under an inert atmosphere. The expression of key genes involved in the regulation of CT production was analyzed, and we found that the expression pattern closely resembles the in vivo expression pattern.