Disease relevance of hly

• We found that the placenta was highly susceptible to bacteria, including avirulent bacteria, such as an L. monocytogenes mutant with an hly deletion (DeltaLLO) and a nonpathogenic species, Listeria innocua, suggesting that permissive trophoblastic cells, trapping bacteria, provide a protective niche for bacterial survival [1].
• A unique nonsynonymous mutation was found in the hly gene of L. monocytogenes isolates that were associated with the 1985 California outbreak and were the epidemic phage type [2].
• Methods for curing endogenous prophages from the comK attachment site in 10403S-derived strains were developed. pPL1 was used to introduce the hly and actA genes at comK-attBB' in deletion strains derived from 10403S and SLCC-5764 [3].
• Bacillus subtilis strains expressing listeriolysin O (LLO) and simultaneously LLO and p60 protein were constructed [4].
• The hly and actA genes were transcriptionally fused to Escherichia coli lacZ and Bacillus pumilus cat-86 (cat), and the fusions were integrated in single copies into the L. monocytogenes chromosome [5].

High impact information on hly

• A PEST-like sequence in listeriolysin O essential for Listeria monocytogenes pathogenicity [6].
• LLO lacking the PEST-like sequence accumulated in the host-cell cytosol, suggesting that this sequence targets LLO for degradation [6].
• Anti-LLO mAb did not opsonize Listeria but, rather, acted within macrophages to neutralize LLO [7].
• Previous work showed that activated lymphocytes were highly sensitive to LLO-induced apoptosis, whereas resting lymphocytes were less susceptible [8].
• Furthermore, treatment of resting splenic lymphocytes with recombinant IFN-alphaA enhanced their susceptibility to LLO-induced apoptosis [8].

Chemical compound and disease context of hly

• The beta-glucoside cellobiose has been reported to specifically repress the PrfA-dependent virulence genes hly and plcA in Listeria monocytogenes NCTC 7973 [9].
• By swapping dissimilar residues from a pH-insensitive orthologue, perfringolysin O (PFO), we identified leucine 461 as unique to pathogenic Listeria and responsible for the acidic pH optimum of LLO [10].
• Listeriolysin O (LLO) is a cholesterol-dependent cytolysin that is an essential virulence factor of Listeria monocytogenes [11].
• We demonstrate conclusively that the bacterial exotoxin listeriolysin O (LLO) is a target Ag for eliciting CD4+ T cell responses following infection with Listeria monocytogenes [12].
• Listeriolysin O (LLO), a major virulence factor of the intracellular bacterium Listeria monocytogenes, shares with other known 'thiol-activated toxins' a conserved undecapeptide, ECTGLAWEWWR, located in the C-terminal region of the protein and containing the unique cysteine of the molecule [13].

Biological context of hly

• It is shown that PrfA protein is able to bind, independently of additional factors, to a 109bp DNA fragment including the entire hly promoter sequence with the anticipated PrfA binding site ('PrfA-box') [14].
• The addition of a Paf-containing extract does not lead to significant protein binding to these two hly target sequences in the absence of PrfA but converts the complex (CIII) consisting of PrfA and the 109 bp hly DNA fragment to a slower migrating PrfA-Paf-DNA complex (CI) [14].
• DNase I footprint experiments show that purified PrfA protects sequences of dyad symmetry previously proposed as PrfA binding sites in the hly and in the inlA promoter regions [14].
• A total of 133 Listeria monocytogenes isolates were characterized by ribotyping and allelic analysis of the virulence genes hly, actA, and inlA to uncover linkages between independent phylogenetic and specific virulence markers [15].
• The r-BCG strains pAT261:Hly or pMV306:Hly expressed plasmid multicopies or chromosomal single copies of the hly gene, respectively [16].

Anatomical context of hly

• Several bacterial proteins contributing to these events have been identified, including the invasion proteins internalin A (InlA) and B (InlB), the secreted pore-forming toxin listeriolysin O (LLO) which promotes the escape from the phagocytic vacuole, and the surface protein ActA which is required for actin polymerization and bacterial movement [17].
• The hemolytic activity of LLO in the presence of p60 protein decreased which indicates that p60 promoted adhesion and subsequent invasion of professional phagocytes [4].
• E. coli diamenopimelate (dap) auxotroph, harboring plasmid pGB2Omegainv-hly, express the inv gene from Yersinia pseudotubercolosis that confers the ability to invade nonprofessional phagocytic cells and the hly gene from Listeria monocytogenes that allows expression of lystreriolysin O, a perforin cytolysin able to perfore phagosomal membranes [18].
• In contrast, both fusions were active in the cytosol of J774 cells, and the activity of the actA fusion was approximately 3-fold higher than that of the hly fusion under these conditions [5].
• When 3T6 fibroblasts were transfected with the hly gene without the 5' signal sequence, inhibition of growth, lack of cell layer confluency, and altered (spherical) cell morphology were observed [19].

Associations of hly with chemical compounds

• Moreover, concentrations of cellobiose and other sugars required for repression of hly expression (> 1 mM) were found to significantly enhance growth of L. monocytogenes cultures, suggesting that the repression phenomenon probably results from a metabolic effect of sugar utilization rather than a signal-sensing response [20].
• By using the hly-based system as an in vivo expression technology tool, nine in vivo-induced loci of L. monocytogenes were identified, including genes encoding (i) the previously known in vivo-inducible phosphatidylinositol phospholipase C and (ii) a putative N-acetylglucosamine epimerase, possibly involved in teichoic acid biosynthesis [21].
• Surprisingly, hly expression was still repressed by glucose, as observed for the parental strain [22].
• An exotoxin from a Gram-positive organism, listeriolysin-o, and the lipopolysaccharide (LPS) endotoxin from a Gram-negative organism were also effective. gamma/delta T cell responses to LPS were under lps gene control [23].
• Here we describe the pH-dependence of vacuolar perforation by LLO, using the membrane-impermeant fluorophore 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) to monitor the pH and integrity of vacuoles in mouse bone marrow-derived macrophages [24].

Regulatory relationships of hly

• Finally, in comparison to induction in broth cultures, actA was highly induced (226-fold) and hly was moderately induced (20-fold) in J774 cells [5].
• In order to test whether the catabolite co-repressor P-Ser-HPr might be involved in PrfA regulation, we used a Bacillus subtilis strain (BUG1199) containing L. monocytogenes prfA under control of pspac and the lacZ reporter gene fused to the PrfA-activated hly promoter [25].
• A plasmid in which the iap gene is placed under the control of the PrfA-dependent hly promoter was constructed and introduced into B. subtilis [26].
• IFN-beta pretreatment enhanced LLO-mediated signaling through this pathway, consistent with its ability to increase membrane damage. p38MAPK activation in response to LLO was independent of TLR4, a putative LLO receptor, and inhibition of p38MAPK neither enhanced nor prevented LLO-induced death [27].

Other interactions of hly

• How InlA, InlB, LLO or ActA interact with the mammalian cells is beginning to be deciphered [17].
• Specific binding of PrfA-containing extracts from strain EGD to the hly and actA promoter sequences was strongly inhibited by iron, whereas that of extracts from strain NCTC 7973 was only slightly reduced [28].
• The most discriminatory 600-bp fragments identified in the housekeeping and stress response genes differentiated the isolates into 8 to 10 subtypes; intergenic region sequences yielded 8 and 12 allelic types based on 335- and 242-bp sequences for hly-mpl and plcA-hly, respectively [29].
• The ability to induce cellular apoptosis was retained by all mutants tested, except the prfA and delta hly mutants, both of which are unable to produce listeriolysin [30].
• Genes iap, hly, plcB, InlA and InlB of L. monocytogenes 10403S had higher homology to those of strain EGD (>98%) than isolate H4 [31].

Analytical, diagnostic and therapeutic context of hly

• Recombinant listeriolysin O and internalin A were used as antigens in an enzyme-linked immunosorbent assay (ELISA) for the specific detection of anti-Listeria monocytogenes antibodies in cattle [32].
• Use of listeriolysin O and internalin A in a seroepidemiological study of listeriosis in Swiss dairy cows [32].
• We previously described an unknown proteinaceous component from crude bacterial cell extracts, which, together with PrfA, formed a specific complex (CI) in electrophoretic mobility shift assays (EMSA) with an hly promoter probe [33].
• Using the highly sensitive polymerase chain reaction method, hly mRNA was detectable in BMM phi infected with L. monocytogenes EGD or SLCC53, but totally absent in M3-infected BMM phi [34].
• Twenty-five-milliliter samples of reconstituted nonfat dry milk (NFDM) were seeded with L. monocytogenes and processed to concentrate the bacteria by centrifugation, and this was followed by nucleic acid extraction and amplification with hly-specific primers [35].

References