Characterization of stm3030 and stm3031 genes of Salmonella enterica serovar Typhimurium in relation to cephalosporin resistance.

BACKGROUND/PURPOSE: The outer membrane protein STM3031 had been shown to confer Salmonella enterica serovar Typhimurium resistance to ceftriaxone. In this study, the STM3030 was increased in strain R200 and decreased in strain R200(Δstm3031). How stm3030 and stm3031 contributing to antibiotic resistance was investigated. METHODS: The level of STM3030 protein in R200(Δstm3031) were compared between 01-4, R200, and R200(Δstm3031) by 2-DE analysis. The stm3030 gene deleted strain, R200(Δstm3030), was generated by the one-step inactivation chromosome gene method. The various antibiotic susceptibility of strains 01-4, R200, R200(Δstm3031) and R200(Δstm3030) were determined by agar dilutions assays and E-test. The co-transcription of stm3031 and stm3030 were determined by RT-PCR. The promoter activities of these two genes fused with LacZ were determined. The binding of the regulatory protein BaeR on the promoter of both genes was detected by EMSA. The interaction between STM3030 and STM3031 proteins was determined by GST pull-down assay. RESULTS: Strain R200(Δstm3030) displayed a 32- to 64-fold reduction in resistance to cephalosporin drugs. Transcription analyses revealed that stm3030 and stm3031 are independent genes and that the promoter of stm3030 is stronger than that of stm3031. The regulator BaeR binds to the promoter region of stm3031 but not that of stm3030. The STM3031 decreased in R200(Δstm3030) compared to R200 by western blot analysis. The pull-down assay revealed that STM3030 and STM3031 bind to each other. CONCLUSION: Our data indicate that STM3030 has a chaperone-like activity and may modulate or stabilize STM3031, leading to resistance of S. enterica serovar Typhimurium to cephalosporin drugs.

Complexity of the Mycoplasma fermentans M64 genome and metabolic essentiality and diversity among mycoplasmas.

Recently, the genomes of two Mycoplasma fermentans strains, namely M64 and JER, have been completely sequenced. Gross comparison indicated that the genome of M64 is significantly bigger than the other strain and the difference is mainly contributed by the repetitive sequences including seven families of simple and complex transposable elements ranging from 973 to 23,778 bps. Analysis of these repeats resulted in the identification of a new distinct family of Integrative Conjugal Elements of M. fermentans, designated as ICEF-III. Using the concept of "reaction connectivity", the metabolic capabilities in M. fermentans manifested by the complete and partial connected biomodules were revealed. A comparison of the reported M. pulmonis, M. arthritidis, M. genitalium, B. subtilis, and E. coli essential genes and the genes predicted from the M64 genome indicated that more than 73% of the Mycoplasmas essential genes are preserved in M. fermentans. Further examination of the highly and partly connected reactions by a novel combinatorial phylogenetic tree, metabolic network, and essential gene analysis indicated that some of the pathways (e.g. purine and pyrimidine metabolisms) with partial connected reactions may be important for the conversions of intermediate metabolites. Taken together, in light of systems and network analyses, the diversity among the Mycoplasma species was manifested on the variations of their limited metabolic abilities during evolution.

Proteomics characterization of cytoplasmic and lipid-associated membrane proteins of human pathogen Mycoplasma fermentans M64.

Mycoplasma fermentans is a potent human pathogen which has been implicated in several diseases. Notably, its lipid-associated membrane proteins (LAMPs) play a role in immunomodulation and development of infection-associated inflammatory diseases. However, the systematic protein identification of pathogenic M. fermentans has not been reported. From our recent sequencing results of M. fermentans M64 isolated from human respiratory tract, its genome is around 1.1 Mb and encodes 1050 predicted protein-coding genes. In the present study, soluble proteome of M. fermentans was resolved and analyzed using two-dimensional gel electrophoresis. In addition, Triton X-114 extraction was carried out to enrich amphiphilic proteins including putative lipoproteins and membrane proteins. Subsequent mass spectrometric analyses of these proteins had identified a total of 181 M. fermentans ORFs. Further bioinformatics analysis of these ORFs encoding proteins with known or so far unknown orthologues among bacteria revealed that a total of 131 proteins are homologous to known proteins, 11 proteins are conserved hypothetical proteins, and the remaining 39 proteins are likely M. fermentans-specific proteins. Moreover, Triton X-114-enriched fraction was shown to activate NF-kB activity of raw264.7 macrophage and a total of 21 lipoproteins with predicted signal peptide were identified therefrom. Together, our work provides the first proteome reference map of M. fermentans as well as several putative virulence-associated proteins as diagnostic markers or vaccine candidates for further functional study of this human pathogen.

The expression levels of outer membrane proteins STM1530 and OmpD, which are influenced by the CpxAR and BaeSR two-component systems, play important roles in the ceftriaxone resistance of Salmonella enterica serovar Typhimurium.

Significant increases in STM3031, STM1530, and AcrD protein levels and significant decreases in OmpC and OmpD protein levels are present when the ceftriaxone-resistant Salmonella enterica serovar Typhimurium R200 strain is compared with the ceftriaxone-susceptible strain 01-4. AcrD is known to be involved in drug export, and STM3031 seems to play a key role in ceftriaxone resistance. Here, we examine the roles of STM1530, OmpC, and OmpD in ceftriaxone resistance. An ompD gene deletion mutant showed 4-fold higher ceftriaxone resistance than 01-4. An ompC gene deletion mutant showed 4-fold higher cephalothin and erythromycin resistance than 01-4, but there was no effect on ceftriaxone resistance. However, a stm1530 deletion mutant did show >64-fold lower ceftriaxone resistance than R200. Moreover, the STM3031 protein was significantly decreased in R200(Δstm1530) compared to R200. STM3031 expression has been shown to be influenced by the two-component system regulator gene baeR. CpxR seems to modulate BaeR. A cpxA-cpxR gene deletion mutant showed >2,048-fold lower ceftriaxone resistance than R200. The outer membrane protein profile of R200(ΔcpxAR) showed significant decreases in STM3031 and STM1530 compared to R200, while OmpD had returned to the level found in 01-4. Furthermore, the stm3031, stm1530, and ompD mRNA levels were correlated with their protein expression levels in these strains, while decreases in the mRNA levels of the efflux pump acrB, acrD, and acrF genes were found in R200(ΔcpxAR). Findings similar to those for R200(ΔcpxAR) were found for R200(ΔbaeSR). These results, together with those for STM3031 and the fact that STM1530 is an outer membrane protein, suggest that STM1530 and OmpD are influenced by the CpxAR and BaeSR two-component systems and that this contributes to S. enterica serovar Typhimurium ceftriaxone resistance.

Genome sequence of the repetitive-sequence-rich Mycoplasma fermentans strain M64.

Mycoplasma fermentans is a microorganism commonly found in the genitourinary and respiratory tracts of healthy individuals and AIDS patients. The complete genome of the repetitive-sequence-rich M. fermentans strain M64 is reported here. Comparative genomics analysis revealed dramatic differences in genome size between this strain and the recently completely sequenced JER strain.

Repression of btuB gene transcription in Escherichia coli by the GadX protein.

BACKGROUND: BtuB (B twelve uptake) is an outer membrane protein of Escherichia coli. It serves as a receptor for cobalamines uptake or bactericidal toxin entry. A decrease in the production of the BtuB protein would cause E. coli to become resistant to colicins. The production of BtuB has been shown to be regulated at the post-transcriptional level. The secondary structure of 5' untranslated region of btuB mRNA and the intracellular concentration of adenosylcobalamin (Ado-Cbl) would affect the translational efficiency and RNA stability of btuB gene. The transcriptional regulation of btuB expression is still unclear. RESULTS: To determine whether the btuB gene is also transcriptionally controlled by trans-acting factors, a genomic library was screened for clones that enable E. coli to grow in the presence of colicin E7, and a plasmid carrying gadX and gadY genes was isolated. The lacZ reporter gene assay revealed that these two genes decreased the btuB promoter activity by approximately 50%, and the production of the BtuB protein was reduced by approximately 90% in the presence of a plasmid carrying both gadX and gadY genes in E. coli as determined by Western blotting. Results of electrophoretic mobility assay and DNase I footprinting indicated that the GadX protein binds to the 5' untranslated region of the btuB gene. Since gadX and gadY genes are more highly expressed under acidic conditions, the transcriptional level of btuB in cells cultured in pH 7.4 or pH 5.5 medium was examined by quantitative real-time PCR to investigate the effect of GadX. The results showed the transcription of gadX with 1.4-fold increase but the level of btuB was reduced to 57%. CONCLUSIONS: Through biological and biochemical analysis, we have demonstrated the GadX can directly interact with btuB promoter and affect the expression of btuB. In conclusion, this study provides the first evidence that the expression of btuB gene is transcriptionally repressed by the acid responsive genes gadX and gadY.

A putative lytic transglycosylase tightly regulated and critical for the EHEC type three secretion.

Open reading frame l0045 in the pathogenic island of enterohemorrhagic Escherichia coli O157:H7 has been predicted to encode a lytic transglycosylase that is homologous to two different gene products encoded by the same bacteria at loci away from the island. To deduce the necessity of the presence in the island, we created an l0045-deleted strain of EHEC and observed that both the level of cytosolic EspA and that of the other type III secreted proteins in the media were affected. In a complementation assay, a low level-expressing L0045 appeared to recover efficiently the type III secretion (TTS). On the other hand, when l0045 was driven to express robustly, the intracellular levels of representative TTS proteins were severely suppressed. This suppression is apparently caused by the protein of L0045 per se since introducing an early translational termination codon abolished the suppression. Intriguingly, the authentic L0045 was hardly detected in all lysates of EHEC differently prepared while the same construct was expectedly expressed in the K-12 strain. A unique network must exist in EHEC to tightly regulate the presence of L0045, and we found that a LEE regulator (GrlA) is critically involved in this regulation.

Blockade of JAK2 activity suppressed accumulation of ß-catenin in leukemic cells.

The Wnt/ß-catenin pathway has been implicated in leukemogenesis. We found ß-catenin abnormally accumulated in both human acute T cell leukemia Jurkat cells and human erythroleukemia HEL cells. ß-Catenin can be significantly down-regulated by the Janus kinase 2 specific inhibitor AG490 in these two cells. AG490 also reduces the luciferase activity of a reporter plasmid driven by LEF/ß-catenin promoter. Similar results were observed in HEL cells infected with lentivirus containing shRNA against JAK2 gene. After treatment with 50 µM AG490 or shRNA, the mRNA expression levels of ß-catenin, APC, Axin, ß-Trcp, GSK3α, and GSK3ß were up-regulated within 12-16 h. However, only the protein levels of GSK3ß and ß-Trcp were found to have increased relative to untreated cells. Knockdown experiments revealed that the AG490-induced inhibition of ß-catenin can be attenuated by shRNA targeting ß-TrCP. Taken together; these results suggest that ß-Trcp plays a key role in the cross-talk between JAK/STAT and Wnt/ß-catenin signaling in leukemia cells.

Outer membrane protein STM3031 (Ail/OmpX-like protein) plays a key role in the ceftriaxone resistance of Salmonella enterica serovar Typhimurium.

Previously, the putative outer membrane protein STM3031 has been correlated with ceftriaxone resistance in Salmonella enterica serovar Typhimurium. In this study, this protein was almost undetectable in the ceftriaxone-susceptible strain 01-4, but its levels were increased in 01-4 isogenic strains for which MICs were higher. The stm3031 gene deletion mutant, R200(Deltastm3031), was generated and showed >64-fold lower ceftriaxone resistance than R200, supporting a key role for STM3031 in ceftriaxone resistance. To investigate which outer membrane protein(s) was associated with resistance, the outer membrane protein profiles of 01-4, R200, and R200(Deltastm3031) were compared proteomically. Nine proteins were identified as altered. The expression levels of AcrA, TolC, STM3031, STM1530, VacJ, and Psd in R200 were increased; those of OmpC, OmpD, and OmpW were decreased. The expression levels of OmpD, OmpW, STM1530, VacJ, and Psd, but not those of OmpC, AcrA, and TolC, in R200(Deltastm3031) were returned to the levels in strain 01-4. Furthermore, the genes' mRNA levels correlated with their protein levels when the three strains were compared. The detection of higher AcrB levels, linked to higher acrB, acrD, and acrF mRNA levels, in strain R200 than in strains 01-4 and R200(Deltastm3031) suggests that AcrB, AcrD, and AcrF participate in ceftriaxone resistance. Taken together with the location of STM3031 in the outer membrane, these results suggest that STM3031 plays a key role in ceftriaxone resistance, probably by reducing permeability via a decreased porin OmpD level and enhancing export via increased AcrD efflux pump activity.

An OXA-66/OXA-51-like carbapenemase and possibly an efflux pump are associated with resistance to imipenem in Acinetobacter baumannii.

We investigated the mechanisms involved in imipenem resistance in 23 clinical strains of Acinetobacter baumannii. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed the presence of a 30-kDa protein in imipenem-intermediate A. baumannii (IIAB) and imipenem-resistant A. baumannii (IRAB) strains; this protein was almost undetectable in imipenem-susceptible A. baumannii (ISAB) strains. The 30-kDa protein was identified as an OXA-51-like carbapenemase using two-dimensional gel electrophoresis and mass spectrometry. Similar to other recent findings, bla(OXA-51-like) genes were found to exist in all 23 clinical strains; however, the transcript levels of bla(OXA-51-like) in the IIAB and IRAB were higher than in the ISAB strains using reverse transcriptase PCR (RT-PCR) and real-time RT-PCR assays. This change was due to the presence of an insertion sequence, ISAba1, upstream of bla(OXA-51-like) in the IIAB and IRAB strains that was not present in the ISAB strains. The introduction of bla(OXA-66) (a bla(OXA-51)(-like) gene), identified in ISAB ab1254 and IRAB ab1266, into Escherichia coli TOP10 cells resulted in 3.95-fold and 7.90-fold elevations in resistance to imipenem, respectively. Furthermore, when ISAB ab8 and ISAB ab1254 and their in vitro-selected imipenem-resistant mutants ISAB ab8(r) and ISAB ab1254(r) were compared, the results showed no change in the bla(OXA-66)/bla(OXA-51-like) gene sequences, in expression of the gene, and in the outer membrane protein profiles. However, there was a four- to eightfold reduction in imipenem resistance upon adding carbonyl cyanide m-chlorophenylhydrazone. Taken together, these results suggest that the OXA-66/OXA-51-like carbapenemase contributes to intrinsic resistance to imipenem; however, drug export by an efflux pump may be more important and/or occur more frequently in imipenem-resistant A. baumannii. Furthermore, this is the first report of a Taiwanese strain of an OXA-66/OXA-51-like carbapenemase that confers imipenem resistance in A. baumannii.

A proteomic approach to study Salmonella enterica serovar Typhimurium putative transporter YjeH associated with ceftriaxone resistance.

Mutant 6B7 of Salmonella enterica serovar Typhimurium has a transposon inserted in the putative transporter gene yjeH and shows a more-than-fourfold reduction in resistance to ceftriaxone. In this report we have used proteomic analysis to compare outer membrane protein profiles between this mutant and its parental strain R200. Five identified proteins were found to be altered. Of these proteins, the level of expression of the porin OmpD was increased and those of the putative outer membrane proteins STM1530 and STM3031, a subunit of the proton-pumping oxidoreductase NuoB and the heat shock protein MopA were decreased in 6B7 strain. Although the function of the yjeH gene remains unknown, a complementation assay suggested that the OmpD, STM1530, STM3031, NuoB, and MopA proteins are associated with ceftriaxone resistance and the expression of these proteins is influenced by the putative transporter gene yjeH in S. enterica serovar Typhimurium.

Correlation between ceftriaxone resistance of Salmonella enterica serovar Typhimurium and expression of outer membrane proteins OmpW and Ail/OmpX-like protein, which are regulated by BaeR of a two-component system.

Mutant 7F2 of Salmonella enterica serovar Typhimurium has a transposon inserted in the regulator gene baeR of a two-component system and showed a more-than-fourfold reduction in resistance to ceftriaxone. Complementation analysis suggested an association among the outer membrane proteins OmpW and STM3031, ceftriaxone resistance, and baeR.

Expression of cytoplasmic-domain substituted epidermal growth factor receptor inhibits tumorigenicity of EGFR-overexpressed human glioblastoma multiforme.

The accumulated results of recent clinical studies have indicated that aberrant epidermal growth factor receptor (EGFR) activation due to gene amplification and/or rearrangement contributes to increased malignancy and poor prognosis in many human cancers, especially in human glioblastoma multiforme (GBM). The elevated EGFR signaling in GBM has been correlated with shorter interval to relapse and lower survival rates, even in patients treated with surgery, radiation therapy, and/or chemotherapy. Therefore, the blockade of EGFR signaling in GBM may provide an ideal alternative therapeutic strategy. In this study, two EGFR-overexpressing human GBM cell lines (i.e., DBTRG and GBM 8901) were used as a model system. We demonstrated that expression of a human EGFR (EGFRt-EGFP) chimera protein in which the cytoplasmic domain is substituted by EGFP significantly reduced the EGF-induced endogenous EGFR autophosphorylation, EGF-induced downstream extra-cellular signal-regulated kinase (ERK) and Akt signaling, and the proportion of internalized receptors in EGF stimulated cells. Furthermore, these cells' anchorage-independent growth in vitro was decreased and their tumorigenicity in vivo abrogated or strongly suppressed. Our data suggest that EGFRt-EGFP abrogates tumor growth by disrupting receptor activation via competing for EGF-like ligands, forming non-activated heterodimers with endogenous EGFR, and inhibiting the EGFR endosomal signaling by substantially diminishing receptor internalization. This treatment modality (termed 'dominant-negative EGFR therapy') and its efficacy for gliomas or other tumors are under scrutiny.