Introductory Paragraph Several pathogenic bacteria, including Listeria monocytogenes, use an F-actin motility process to spread between mammalian cells1. Actin ‘comet tails’ propel Listeria through the cytoplasm, resulting in bacteria-containing membrane protrusions that are internalized by neighboring cells. The mechanism by which Listeria overcomes cortical tension to generate protrusions is unknown. Here, we identify bacterial and host proteins that directly regulate protrusions. We show that efficient spreading between polarized epithelial cells requires the secreted Listeria virulence protein InlC. We next identify the mammalian adaptor protein Tuba as a ligand of InlC. InlC binds to a C-terminal SH3 domain in Tuba, which normally engages the human actin regulatory protein N-WASP2. InlC promotes protrusion formation by inhibiting Tuba and N-WASP, most likely by impairing binding of N-WASP to the Tuba SH3 domain. Tuba and N-WASP are known to control the structure of apical junctions in epithelial cells3. We demonstrate that, by inhibiting Tuba and N-WASP, InlC makes taut apical junctions become slack. Experiments with myosin II inhibitors indicate that InlC-mediated perturbation of junctions accounts for the role of this bacterial protein in protrusion formation. Collectively, our results suggest that InlC promotes bacterial dissemination by relieving cortical tension, thereby enhancing the ability of motile bacteria to deform the plasma membrane into protrusions.

Analysis of Listeria monocytogenes ptsH, hprK, and ccpA mutants defective in carbon catabolite repression (CCR) control revealed significant alterations in the expression of PrfA-dependent genes. The hprK mutant showed high up-regulation of PrfA-dependent virulence genes upon growth in glucose-containing medium whereas expression of these genes was even slightly down-regulated in the ccpA mutant compared to the wild-type strain. The ptsH mutant could only grow in a rich culture medium, and here the PrfA-dependent genes were up-regulated as in the hprK mutant. As expected, HPr-Ser-P was not produced in the hprK and ptsH mutants and synthesized at a similar level in the ccpA mutant as in the wild-type strain. However, no direct correlation was found between the level of HPr-Ser-P or HPr-His-P and PrfA activity when L. monocytogenes was grown in minimal medium with different phosphotransferase system (PTS) carbohydrates. Comparison of the transcript profiles of the hprK and ccpA mutants with that of the wild-type strain indicates that the up-regulation of the PrfA-dependent virulence genes in the hprK mutant correlates with the down-regulation of genes known to be controlled by the efficiency of PTS-mediated glucose transport. Furthermore, growth in the presence of the non-PTS substrate glycerol results in high PrfA activity. These data suggest that it is not the component(s) of the CCR or the common PTS pathway but, rather, the component(s) of subsequent steps that seem to be involved in the modulation of PrfA activity.Listeria monocytogenes, a gram-positive, facultative intracellular human pathogen, escapes from the primary phagosome, replicates efficiently in the host cell's cytosol, and spreads from cell to cell. These processes, which are of major importance for pathogenesis of an L. monocytogenes infection, require several, well-characterized virulence factors (for recent reviews, see references 17, 32 and 63), like internalins (InlA, InlB, and

Listeria monocytogenes is able to efficiently utilize glycerol as a carbon source. In a defined minimal medium, the growth rate (during balanced growth) in the presence of glycerol is similar to that in the presence of glucose or cellobiose. Comparative transcriptome analyses of L. monocytogenes showed high-level transcriptional upregulation of the genes known to be involved in glycerol uptake and metabolism (glpFK and glpD) in the presence of glycerol (compared to that in the presence of glucose and/or cellobiose). Levels of expression of the genes encoding a second putative glycerol uptake facilitator (GlpF 2 ) and a second putative glycerol kinase (GlpK 2 ) were less enhanced under these conditions. GlpK 1 but not GlpK 2 was essential for glycerol catabolism in L. monocytogenes under extracellular conditions, while the loss of GlpK 1 affected replication in Caco-2 cells less than did the loss of GlpK 2 and GlpD. Additional genes whose transcription levels were higher in the presence of glycerol than in the presence of glucose and cellobiose included those for two dihydroxyacetone (Dha) kinases and many genes that are under carbon catabolite repression control. Transcriptional downregulation in the presence of glycerol (compared to those in the presence glucose and cellobiose) was observed for several genes and operons that are positively regulated by glucose, including genes involved in glycolysis, N metabolism, and the biosynthesis of branched-chain amino acids. The highest level of transcriptional upregulation was observed for all PrfA-dependent genes during early and late logarithmic growth in glycerol. Under these conditions, a low level of HPr-Ser-P and a high level of HPr-His-P were present in the cells, suggesting that all enzyme IIA (EIIA) (or EIIB) components of the phosphotransferase system (PTS) permeases expressed will be phosphorylated. These and other data suggest that the phosphorylation state of PTS permeases correlates with PrfA activity.Listeria monocytogenes is known as a facultative intracellular pathogen that can cause severe systemic infections in humans (for recent reviews, see references 15 and 47). This bacterial pathogen has therefore been extensively studied in the last decades preferentially with respect to its virulence genes and the encoded virulence factors. The virulence factors identified were shown to be involved mainly in the intracellular (cytosolic) growth cycle, and their genes were highly expressed under intracellular growth conditions (26). Most of the virulence genes are under the control of the transcription activator PrfA, whose expression is regulated at the transcriptional and the posttranscriptional levels (for recent reviews, see references 21 and 27). In addition, the activity of the PrfA protein is modulated by an as-yet-unknown factor(s) whose production appears to be linked to the metabolism of L. monocytogenes.

Listeria monocytogenes strains expressing high levels of the virulence regulator PrfA (mutant PrfA* or wild-type PrfA) show strong growth inhibition in minimal media when they are supplemented with glucose but not when they are supplemented with glucose-6-phosphate compared to the growth of isogenic strains expressing low levels of PrfA. A significantly reduced rate of glucose uptake was observed in a PrfA*-overexpressing strain growing in LB supplemented with glucose. Comparative transcriptome analyses were performed with RNA isolated from a prfA mutant and an isogenic strain carrying multiple copies of prfA or prfA* on a plasmid. These analyses revealed that in addition to high transcriptional up-regulation of the known PrfA-regulated virulence genes (group I), there was less pronounced up-regulation of the expression of several phage and metabolic genes (group II) and there was strong down-regulation of several genes involved mainly in carbon and nitrogen metabolism in the PrfA*-overexpressing strain (group III). Among the latter genes are the nrgAB, gltAB, and glnRA operons (involved in nitrogen metabolism), the ilvB operon (involved in biosynthesis of the branched-chain amino acids), and genes for some ABC transporters. Most of the down-regulated genes have been shown previously to belong to a class of genes in Bacillus subtilis whose expression is negatively affected by impaired glucose uptake. Our results lead to the conclusion that excess PrfA (or PrfA*) interferes with a component(s) essential for phosphotransferase system-mediated glucose transport.

Recent studies have identified several new genes inIn vitro transcription performed with promoters of some class III genes showed strict SigB-dependent but PrfAindependent transcription initiation. Transcription starting at the prfA promoter PprfA2 was also optimal with SigB-loaded RNA polymerase, suggesting a direct link between SigB-and PrfA-dependent gene expression.