NLRP6 Plays an Important Role in Early Hepatic Immunopathology Caused by Schistosoma mansoni Infection.

Schistosomiasis is a debilitating parasitic disease that affects more than 200 million people worldwide and causes approximately 280,000 deaths per year. Inside the definitive host, eggs released by Schistosoma mansoni lodge in the intestine and especially in the liver where they induce a granulomatous inflammatory process, which can lead to fibrosis. The molecular mechanisms initiating or promoting hepatic granuloma formation remain poorly understood. Inflammasome activation has been described as an important pathway to induce pathology mediated by NLRP3 receptor. Recently, other components of the inflammasome pathway, such as NLRP6, have been related to liver diseases and fibrotic processes. Nevertheless, the contribution of these components in schistosomiasis-associated pathology is still unknown. In the present study, using dendritic cells, we demonstrated that NLRP6 sensor is important for IL-1ß production and caspase-1 activation in response to soluble egg antigens (SEA). Furthermore, the lack of NLRP6 has been shown to significantly reduce periovular inflammation, collagen deposition in hepatic granulomas and mRNA levels of α-SMA and IL-13. Livers of Nlrp6-/- mice showed reduced levels of CXCL1/KC, CCL2, CCL3, IL-5, and IL-10 as well as Myeloperoxidase (MPO) and Eosinophilic Peroxidase (EPO) enzymatic activity. Consistently, the frequency of macrophage and neutrophil populations were lower in the liver of NLRP6 knockout mice, after 6 weeks of infection. Finally, it was further demonstrated that the onset of hepatic granuloma and collagen deposition were also compromised in Caspase-1-/- , IL-1R-/- and Gsdmd-/- mice. Our findings suggest that the NLRP6 inflammasome is an important component for schistosomiasis-associated pathology.

Structural features of PhoX, one of the phosphate-binding proteins from Pho regulon of Xanthomonas citri.

In Escherichia coli, the ATP-Binding Cassette transporter for phosphate is encoded by the pstSCAB operon. PstS is the periplasmic component responsible for affinity and specificity of the system and has also been related to a regulatory role and chemotaxis during depletion of phosphate. Xanthomonas citri has two phosphate-binding proteins: PstS and PhoX, which are differentially expressed under phosphate limitation. In this work, we focused on PhoX characterization and comparison with PstS. The PhoX three-dimensional structure was solved in a closed conformation with a phosphate engulfed in the binding site pocket between two domains. Comparison between PhoX and PstS revealed that they originated from gene duplication, but despite their similarities they show significant differences in the region that interacts with the permeases.

Transcriptional and post-transcriptional regulation of pst2 operon expression in Vibrio cholerae O1.

One of the most abundant proteins in V. cholerae O1 cells grown under inorganic phosphate (Pi) limitation is PstS, the periplasmic Pi-binding component of the high-affinity Pi transport system Pst2 (PstSCAB), encoded in pst2 operon (pstS-pstC2-pstA2-pstB2). Besides its role in Pi uptake, Pst2 has been also associated with V. cholerae virulence. However, the mechanisms regulating pst2 expression and the non-stoichiometric production of the Pst2 components under Pi-limitation are unknown. A computational-experimental approach was used to elucidate the regulatory mechanisms behind pst2 expression in V. cholerae O1. Bioinformatics analysis of pst2 operon nucleotide sequence revealed start codons for pstS and pstC genes distinct from those originally annotated, a regulatory region upstream pstS containing potential PhoB-binding sites and a pstS-pstC intergenic region longer than predicted. Analysis of nucleotide sequence between pstS-pstC revealed inverted repeats able to form stem-loop structures followed by a potential RNAse E-cleavage site. Another putative RNase E recognition site was identified within the pstA-pstB intergenic sequence. In silico predictions of pst2 operon expression regulation were subsequently tested using cells grown under Pi limitation by promoter-lacZ fusion, gel electrophoresis mobility shift assay and quantitative RT-PCR. The experimental and in silico results matched very well and led us to propose a pst2 promoter sequence upstream of pstS gene distinct from the previously annotated. Furthermore, V. cholerae O1 pst2 operon transcription is PhoB-dependent and generates a polycistronic mRNA molecule that is rapidly processed into minor transcripts of distinct stabilities. The most stable was the pstS-encoding mRNA, which correlates with PstS higher levels relative to other Pst2 components in Pi-starved cells. The relatively higher stability of pstS and pstB transcripts seems to rely on the secondary structures at their 3' untranslated regions that are known to block 3'-5' exonucleolytic attacks.

Phosphate regulated proteins of Xanthomonas citri subsp. citri: a proteomic approach.

Xanthomonas citri subsp. citri (X. citri) is the causative agent of the citrus canker, a disease that affects several citrus plants in Brazil and across the world. Although many studies have demonstrated the importance of genes for infection and pathogenesis in this bacterium, there are no data related to phosphate uptake and assimilation pathways. To identify the proteins that are involved in the phosphate response, we performed a proteomic analysis of X. citri extracts after growth in three culture media with different phosphate concentrations. Using mass spectrometry and bioinformatics analysis, we showed that X. citri conserved orthologous genes from Pho regulon in Escherichia coli, including the two-component system PhoR/PhoB, ATP binding cassette (ABC transporter) Pst for phosphate uptake, and the alkaline phosphatase PhoA. Analysis performed under phosphate starvation provided evidence of the relevance of the Pst system for phosphate uptake, as well as both periplasmic binding proteins, PhoX and PstS, which were formed in high abundance. The results from this study are the first evidence of the Pho regulon activation in X. citri and bring new insights for studies related to the bacterial metabolism and physiology. Biological significance Using proteomics and bioinformatics analysis we showed for the first time that the phytopathogenic bacterium X. citri conserves a set of proteins that belong to the Pho regulon, which are induced during phosphate starvation. The most relevant in terms of conservation and up-regulation were the periplasmic-binding proteins PstS and PhoX from the ABC transporter PstSBAC for phosphate, the two-component system composed by PhoR/PhoB and the alkaline phosphatase PhoA.

Stability of the pstS transcript of Escherichia coli.

The pst operon of Escherichia coli is composed of five genes that encode a high-affinity phosphate transport system. As a member of the PHO regulon, pst transcription is activated under phosphate shortage conditions. Under phosphate-replete conditions, the pst operon also functions as a negative regulator of the PHO genes. Transcription of pst is initiated at the promoter located upstream to the first gene, pstS. Immediately after its synthesis, the primary transcript of pst is cleaved into shorter mRNA molecules. The transcription unit corresponding to pstS is significantly more abundant than the transcripts of the other pst genes due to stabilisation of pstS mRNA by a repetitive extragenic palindrome (REP) structure downstream to the pstS locus. The presence of the REP sequence also results in an increased level of PstS proteins. However, the surplus level of PstS proteins produced in the presence of REP does not contribute to the repressive role of Pst in PHO expression.