Differential expression of Listeria monocytogenes virulence genes in mammalian host cells

Abstract

We have used RT-PCR and GFP-mediated uorescence to analyse the regulation of PrfA-dependent virulence genes of Listeria monocytogenes during proliferation in mammalian host cells. Our data show that most of the PrfA-regulated virulence genes are more eciently expressed, as measured by transcript levels, when L. monocytogenes is grown in macrophages and macrophage-like cells rather than in epithelial cells, hepatocytes or endothelial cells. The promoters for hly and plcA are predominantly activated within the phagosomal compartment, while those for actA and inlC are predominantly activated in the host cell cytosol. Expression of actA and plcB precedes that of inlC after infection of epithelial cells and macrophages. Little transcription of inlA or inlB is observed in epithelial cells and there is only slightly more in macrophages. In both cell types the level of transcription of the inlAB operon is lower than is seen under extracellular growth conditions in rich media, which is compatible with the assumption that InlA and InlB are not required during intracellular growth of the bacteria. Activation of the PrfA-independent iap promoter is also low during intracellular growth, although the gene product (p60) is required for cell viability. The levels of the PrfA-dependent virulence gene transcripts do not correlate with the amount of prfA transcript present, which is low under all intracellular conditions analysed, suggesting that the prfA transcript is either highly unstable in bacteria that are growing intracellularly, or that the small amount of PrfA produced is highly activated by additional component(s).

The Listeria monocytogenes InlC protein interferes with innate immune responses by targeting the IκB kinase subunit IKKα

“…As shown in Fig. 1B, in contrast to LLO, which is already expressed at the onset of infection, InlC expression gradually increased inside the cells over time, in perfect agreement with the previously reported transcriptional analysis of the inlC gene (12,13). Moreover, as shown by immunofluorescence analysis, the InlC protein was detected in both the cytosol and the nucleus of infected cells (Fig.…”

“…The expression of inlC has been shown to be highly induced intracellularly at rather late stages of infection (12)(13)(14). A recent analysis of the entire Listeria transcriptome in various in vitro, ex vivo, and in vivo conditions of growth confirmed stronger inlC expression in the intestine and blood than in rich broth media (15).…”

Two Listeria monocytogenes Vaccine Vectors That Express Different Molecular Forms of Human Papilloma Virus-16 (HPV-16) E7 Induce Qualitatively Different T Cell Immunity That Correlates with Their Ability to Induce Regression of Established Tumors Immortalized by HPV-16

“…Peptides generated by phagocytosis and degradation in the phagosomal-lysosomal compartment can be efficiently presented by MHC class II molecules to CD4 ϩ T cells. The hly gene (that encodes for the LLO hemolysin) is up-regulated in the phagosome (38). Since they use the same promoter, the LLO-E7 fusion protein and E7 are also probably up-regulated, while Lm-LLO-E7 and Lm-E7 are in the phagosome.…”

Regulation of expression of type I signal peptidases in Listeria monocytogenes

“…During infection, L. monocytogenes modulates its production of virulence factors according to its needs (Bubert et al, 1999). For example, expression of LLO and phosphatidylinositol-specific phospholipase C (PI-PLC) is upregulated in the phagosomal compartment, where these proteins are essential for phagosomal escape; while ActA expression is strongly induced when bacteria have reached the cytosolic compartment of the infected host cell, where the protein is required for actin polymerization and bacterial motility.…”