Biomedical subjects

J R Echenique

Publications and source records attributed to J R Echenique.

5 recordsLinked to original sources

PubMed2001

Competence repression under oxygen limitation through the two-component MicAB signal-transducing system in Streptococcus pneumoniae and involvement of the PAS domain of MicB.

In Streptococcus pneumoniae, a fermentative aerotolerant and catalase-deficient human pathogen, oxidases with molecular oxygen as substrate are important for virulence and for competence. The signal-transducing two-component systems CiaRH and ComDE mediate the response to oxygen, culminating in competence. In this work we show that the two-component MicAB system, whose MicB kinase carries a PAS domain, is also involved in competence repression under oxygen limitation. Autophosphorylation of recombinant MicB and phosphotransfer to recombinant MicA have been demonstrated. Mutational analysis and in vitro assays showed that the C-terminal part of the protein and residue L100 in the N-terminal cap of its PAS domain are both crucial for autokinase activity in vitro. Although no insertion mutation in micA was obtained, expression of the mutated allele micA59DA did not change bacterial growth and overcame competence repression under microaerobiosis. This was related to a strong instability of MicA59DA-PO(4) in vitro. Thus, mutations which either reduced the stability of MicA-PO(4) or abolished kinase activity in MicB were related to competence derepression under microaerobiosis, suggesting that MicA-PO(4) is involved in competence repression when oxygen becomes limiting. The micAB genes are flanked by mutY and orfC. MutY is an adenine glycosylase involved in the repair of oxidized pyrimidines. OrfC shows the features of a metal binding protein. We did not obtain insertion mutation in orfC, suggesting its requirement for growth. It is proposed that MicAB, with its PAS motif, may belong to a set of functions important in the protection of the cell against oxidative stress, including the control of competence.

Amino Acid Sequence↗

PubMed2001

Competence modulation by the NADH oxidase of Streptococcus pneumoniae involves signal transduction.

Oxygen controls competence development in Streptococcus pneumoniae. Oxygen signaling involves the two-component signal transduction systems CiaRH and ComDE and the competence-stimulating peptide encoded by comC and processed by ComAB. We found that NADH oxidase (Nox) was required for optimal competence. Transcriptional analysis and genetic dissection showed that Nox was involved in post-transcriptional activation of the response regulator ComE and in the transcriptional control of ciaRH and comCDE. Thus, in S. pneumoniae, Nox, with O(2) as its secondary substrate, is part of the O(2)-signaling pathway.

Bacterial Proteins↗

PubMed2000

Competence regulation by oxygen in Streptococcus pneumoniae: involvement of ciaRH and comCDE.

Anaerobic aerotolerant Streptococcus pneumoniae modulates its genetic transformability and its virulence in response to the oxygen concentration. The activity of a single protein encoded by nox and showing NADH oxidase activity is involved in these adaptive responses to O2. Northern blot analysis of wild-type cultures grown under aerobic and microaerobic conditions indicated transcriptional control of comCDE by O2. An O2-independent mutant strain carrying the gain-of-function mutation comE38KE was isolated and its analysis showed that ComE is a key point in competence stimulation by O2. Plasmid insertion mutations in ciaRH revealed that this two component signal-transducing system negatively regulates comCDE transcription. The level of comCDE transcripts appears as a major control point in competence regulation by O2 and also by growth phase and cell density.

Anaerobiosis↗

PubMed1992

Characterization of a high-affinity iron transport system in Acinetobacter baumannii.

Analysis of a clinical isolate of Acinetobacter baumannii showed that this bacterium was able to grow under iron-limiting conditions, using chemically defined growth media containing different iron chelators such as human transferrin, ethylenediaminedi-(o-hydroxyphenyl)acetic acid, nitrilotriacetic acid, and 2,2'-bipyridyl. This iron uptake-proficient phenotype was due to the synthesis and secretion of a catechol-type siderophore compound. Utilization bioassays using the Salmonella typhimurium iron uptake mutants enb-1 and enb-7 proved that this siderophore is different from enterobactin. This catechol siderophore was partially purified from culture supernatants by adsorption chromatography using an XAD-7 resin. The purified component exhibited a chromatographic behavior and a UV-visible light absorption spectrum different from those of 2,3-dihydroxybenzoic acid and other bacterial catechol siderophores. Furthermore, the siderophore activity of this extracellular catechol was confirmed by its ability to stimulate energy-dependent uptake of 55Fe(III) as well as to promote the growth of A. baumannii bacterial cells under iron-deficient conditions imposed by 60 microM human transferrin. Polyacrylamide gel electrophoresis analysis showed the presence of iron-regulated proteins in both inner and outer membranes of this clinical isolate of A. baumannii. Some of these membrane proteins may be involved in the recognition and internalization of the iron-siderophore complexes.

Acinetobacter calcoaceticus↗

PubMedDate not supplied

Experimental retinopathy of prematurity: angiostatic inhibition by nimodipine, ginkgo-biloba, and dipyridamole, and response to different growth factors.

PURPOSE: To investigate whether commonly used vasodilating drugs ameliorate angiogenesis in experimental retinopathy of prematurity (ROP), and to study the response of these drugs to different growth factors. METHODS: We used a rat and mouse model of oxygen-induced ischemic retinopathy. Animals were treated with nimodipine, gingko-biloba and dipyridamole intraperitoneally starting the day before exposure to room air (day 1). Controls were injected with vehicle solution only. Eyes were processed histopathologically with serial sections and neovascularization was measured by counting the nuclei within the retinal internal limiting membrane, by a masked observer. Retinal and vitreous tissues were assayed by ELISA for VEGF, PDGF and TGFbeta2. RESULTS: Nimodipine significantly inhibited the growth of new vessels in rats. The number of nuclei was 310 +/- 69 in the control group (n:14) and 121 +/- 53 in the treated ones (n:14), (p<0.0005). Similar results were found with ginkgo-biloba extracts: 344 +/- 53 (n:15) in controls, and 136 +/- 29 (n:11) in treated ones (p<0.0005), and with dipyridamole: 303 +/- 69 (n:13) in controls, and 131 +/- 48.5 in treated rats (p<0.0005). Results were similar in mice. 186 +/- 45 (n:7) nuclei counted in controls against 90 +/- 25 (n:6) for dipyridamole treated (p<0.0005); and 81 +/- 21 for ginkgo-biloba treated animals (p<0.0005). A gradual, very significant increase in VEGF values in response to relative hypoxia (room air) contrasted with the significant inhibition noted both with ginkgo-biloba extracts and dipyridamole. TGFbeta2 and PDGF both showed a gradual increase in relative hypoxia at days 2 and 4 of room air (p<0.0005). Treated animals showed marked inhibition of the three growth factors. CONCLUSIONS: All three drugs markedly inhibited angiogenesis in experimental ROP. Growth factors were elevated in hypoxic conditions. Treated animals showed significant decreases of PDGF, VEGF, and TGFbeta2 in retinal and vitreous tissues.

Animals↗