Delineation of upstream signaling events in the salmonella pathogenicity island 2 transcriptional activation pathway.
Survival and replication in the intracellular environment are critical components of the ability of Salmonella enterica serovar Typhimurium to establish systemic infection in the murine host. Intracellular survival is mediated by a number of genetic loci, including Salmonella pathogenicity island 2 (SPI2). SPI2 is a 40-kb locus encoding a type III secretion system that secretes effector molecules, which permits bacterial survival and replication in the intracellular environment of host cells. A two-component regulatory system, ssrAB, is also encoded in SPI2 and controls expression of the secretion system and effectors. While the environmental signals to which SPI2 responds in vivo are not known, activation of expression is dependent on OmpR and can be stimulated in vitro by chelation of cations or by a shift from rich to acidic minimal medium. In this work, we demonstrated that SPI2 activation is associated with OmpR in the phosphorylated form (OmpR-P). Mutations in envZ and ackA-pta, which disrupted two distinct sources of OmpR phosphorylation, indicated that SPI2 activation by chelators or a shift from rich to acidic minimal medium is largely dependent on functional EnvZ. In contrast, the PhoPQ pathway is not required for SPI2 activation in the presence of OmpR-P. As in the case of in vitro stimulation, SPI2 expression in macrophages correlates with the presence of OmpR-P. Additionally, EnvZ, but not acetyl phosphate, is required for maximal expression of SPI2 in the intracellular environment, suggesting that the in vitro SPI2 activation pathway is the same as that used in vivo.
Kim
Charles C
CC
Microbiology and Immunology, 299 Campus Drive, Stanford University Medical Center, Stanford, CA 94305, USA. cckim@stanford.edu
Falkow
Stanley
S
D000084:Acetate Kinase / Q000235:genetics / Q000502:physiology; D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D002614:Chelating Agents / Q000378:metabolism; D029968:Escherichia coli Proteins; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D008264:Macrophages / Q000382:microbiology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D009097:Multienzyme Complexes / Q000235:genetics / Q000502:physiology; D016254:Mutagenesis, Insertional; D010709:Phosphate Acetyltransferase / Q000235:genetics / Q000502:physiology; D010766:Phosphorylation; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002614:Chelating Agents; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D009097:Multienzyme Complexes; C079792:PhoQ protein, Bacteria; D012329:RNA, Bacterial; C440638:SPI-2 protein, Salmonella; C119761:SsrB protein, Salmonella typhimurium; D015534:Trans-Activators; D014157:Transcription Factors; C112177:osmolarity response regulator proteins; C096222:tmRNA; C061064:PhoP protein, Bacteria; D010709:Phosphate Acetyltransferase; D000084:Acetate Kinase; C057843:envZ protein, E coli