Induction of type III secretion in Shigella flexneri is associated with differential control of transcription of genes encoding secreted proteins

Abstract

Shigella, the etiological agent of human bacillary dysentery, invades the colonic epithelium where it induces an intense inflammatory response. Entry of Shigella into epithelial cells involves a type III secretion machinery, encoded by the mxi and spa operons, and the IpaA-D secreted proteins. In this study, we have identified secreted proteins of 46 and 60 kDa as the products of virA and ipaH9.8, respectively, the latter being a member of the ipaH multigene family. Inactivation of virA did not affect entry into epithelial cells. Using lacZ transcriptional fusions, we found that transcription of virA and four ipaH genes, but not that of the ipaBCDA and mxi operons, was markedly increased during growth in the presence of Congo red and in an ipaD mutant, two conditions in which secretion through the Mxi-Spa machinery is enhanced. Transcription of the virA and ipaH genes was also transiently activated upon entry into epithelial cells. These results suggest that transcription of the virA and ipaH genes is regulated by the type III secretion machinery and that a regulatory cascade differentially controls transcription of genes encoding secreted proteins, some of which, like virA, are not required for entry.

Analysis of virulence plasmid gene expression defines three classes of effectors in the type III secretion system of Shigella flexneri

“…The increased expression of ospF, ipaH4, ipaH7, ospC1, virA and ipaH9 detected in the present analysis is consistent with previous results obtained using lacZ transcriptional fusions (Demers et al, 1998;Mavris et al, 2002b) and with the presence, in the 59 region of these genes, of a putative MxiE box exhibiting at least 14 matches out of 16 positions with the MxiE box consensus sequence (Fig. 3).…”

“…>1 ; 3> >3 ; 5> >5 ; 7> >7 ; 9> >9 ; 11> >11 ; 13> <1 ≥13 had been activated upon entry of bacteria into epithelial cells, as shown previously for ipaH1, ipaH4, ipaH7, ipaH9 and virA genes (Demers et al, 1998), and that this activation was dependent on the presence of MxiE. No MxiEdependent expression of ospG was observed from the reporter plasmid (Kane et al, 2002), which is consistent with the hypothesis presented above that ospG is expressed from the ipaH9 promoter.…”

“…Previous analyses indicated that transcription of a number of genes encoding substrates of the TTS apparatus is induced when the TTS apparatus is deregulated in ipaB and ipaD mutants constructed either by insertion of a non-polar cassette in ipaB or ipaD or by integration of a suicide plasmid in ipaB (Demers et al, 1998;Mavris et al, 2002a, b). To determine the repertoire of genes whose expression is increased when the activity of secretion is deregulated, the transcription profile of a strain carrying the ipaB4 allele (corresponding to the inactivation of ipaB by integration of a suicide plasmid) was compared with that of the wild-type strain.…”

“…constitutively active in bacteria growing in broth, by inactivation of ipaB or ipaD (Menard et al, 1994a). Conditions of active or deregulated secretion lead to increased transcription of members of the ipaH family, ospF, virA and ospC1, but not genes of the entry region (Demers et al, 1998;Mavris et al, 2002a). Transcription of genes regulated by the TTS apparatus activity involves both MxiE, a transcriptional activator of the AraC family encoded by the entry region, and IpgC, the chaperone for the IpaB and IpaC translocators, acting as a co-activator of MxiE (Mavris et al, 2002a).…”

Delivery of Biologically Active Anti-Inflammatory Cytokines IL-10 and IL-1ra In Vivo by the Shigella Type III Secretion Apparatus

“…The efficiency of a potential secretion signal that may be contained within amino-terminal of the Shigella effector IpaH9.8 (30) was investigated by using the first 30 and 60 residues of IpaH9.8 to construct IpaH 30 -IL-10, IpaH 30 -IL-1ra, IpaH 60 -IL-10, and IpaH 60 -IL-1ra. We also used the previously defined secretion domain contained within amino residues derived from Yersinia enterocolitica effector YopE (31) to construct YopE 50 -IL-10.…”