title: Expression and assembly of a functional type IV secretion system elicit extracytoplasmic and cytoplasmic stress responses in Escherichia coli.
abstract: Conditions perturbing protein homeostasis are known to induce cellular stress responses in prokaryotes and eukaryotes. Here we show for the first time that expression and assembly of a functional type IV secretion (T4S) machinery elicit extracytoplasmic and cytoplasmic stress responses in Escherichia coli. After induction of T4S genes by a nutritional upshift and assembly of functional DNA transporters encoded by plasmid R1-16, host cells activated the CpxAR envelope stress signaling system, as revealed by induction or repression of downstream targets of the CpxR response regulator. Furthermore, we observed elevated transcript levels of cytoplasmic stress genes, such as groESL, with a concomitant increase of sigma(32) protein levels in cells expressing T4S genes. A traA null mutant of plasmid R1-16, which lacks the functional gene encoding the major pilus protein pilin, showed distinctly reduced stress responses. These results corroborated our conclusion that the activation of bacterial stress networks was dependent on the presence of functional T4S machinery. Additionally, we detected increased transcription from the rpoHp(1) promoter in the presence of an active T4S system. Stimulation of rpoHp(1) was dependent on the presence of CpxR, suggesting a hitherto undocumented link between CpxAR and sigma(32)-regulated stress networks.
authors.affiliation: Institut für Molekulare Biowissenschaften (IMB), Karl-Franzens-Universität Graz, Universitätsplatz 2, A-8010 Graz, Austria.
authors.forename: Doris
authors.initials: D
authors.lastname: Zahrl
authors.forename: Maria
authors.initials: M
authors.lastname: Wagner
authors.forename: Karin
authors.initials: K
authors.lastname: Bischof
authors.forename: Günther
authors.initials: G
authors.lastname: Koraimann
mesh_terms: D000222:Adaptation, Physiological; D001426:Bacterial Proteins; D001692:Biological Transport; D018833:Chaperonins / Q000096:biosynthesis; D003227:Conjugation, Genetic; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000502:physiology; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D008954:Models, Biological; D009154:Mutation; D018933:Pili, Sex / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011494:Protein Kinases / Q000502:physiology; D012329:RNA, Bacterial / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D018085:Regulon / Q000502:physiology; D012808:Sigma Factor / Q000096:biosynthesis / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C028715:GroE protein, E coli; D006360:Heat-Shock Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012808:Sigma Factor; C069774:heat-shock sigma factor 32; C085504:CpxR protein, Bacteria; D011494:Protein Kinases; C490475:CpxA protein, E coli; D018833:Chaperonins