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Pathogenesis of Mycoplasma pneumoniae infection is considered to be in part attributed to excessive immune responses. Mycoplasma pneumoniae shows strong cytoadherence to host cells and this cytoadherence is thought to be involved in the progression of pneumonia. However, the interaction between the cytoadherence and the immune responses is not known in detail. In this study, we demonstrated that the induction of pro-inflammatory cytokines in the human monocyte cell line THP-1 is dependent on the property of cytoadherence of M. pneumoniae. A wild-type strain of M. pneumoniae with cytoadherence ability induced pro-inflammatory cytokines such as tumour necrosis factor-α and interleukin-1β (IL-1β). Whereas, heat-killed M. pneumoniae and cytoadherence-deficient mutants of M. pneumoniae caused significantly less production of pro-inflammatory cytokines than the wild-type strain. The wild-type strain induced pro-inflammatory cytokines in an endocytosis-independent manners, but the induction by heat-killed M. pneumoniae and cytoadherence-deficient mutants was dependent on endocytosis. Moreover, the wild-type strain induced caspase-1 production and ATP efflux, promoting the maturation of IL-1β and release of the pro-IL-1β precursor, whereas heat-killed M. pneumoniae and the cytoadherence-deficient mutants failed to induce them. These data suggest that the cytoadherence ability of M. pneumoniae activates immune responses and is involved in the pathogenesis of M. pneumoniae infection. [ABSTRACT FROM AUTHOR]

Pathogenesis of Mycoplasma pneumoniae infection is considered to be in part attributed to excessive immune responses. Recently, a mycoplasma lipoprotein has been shown to induce nuclear factor κB (NF-κB) activation through toll-like receptor 1 (TLR1), TLR2 and TLR6. In this study, we examined the ability of lipoproteins from M. pneumoniae to activate NF-κB through TLR1- and TLR2-dependent, but TLR6-independent, pathways, and the active components responsible for the NF-κB activation through the TLR6-independent pathway were identified. The active lipoproteins were found to be MPN611 and MPN162 of M. pneumoniae (designated N-ALP1 and N-ALP2, respectively). Purified N-ALP1 and N-ALP2 from M. pneumoniae and triacylated partial synthetic lipopeptides of N-ALP1 and N-ALP2 augmented the levels of NF-κB induction through TLR1- and TLR2-dependent pathways, whereas diacylated partial synthetic lipopeptides of N-ALP1 and N-ALP2 activated NF-κB through TLR1-, TLR2- and TLR6-dependent pathways. These data suggest that N-ALP1 and N-ALP2 would be triacylated lipoproteins. The activity of N-ALP1 and N-ALP2 was decreased with a pretreatment of lipoprotein lipase, and partially decreased by protease treatment, indicating that the lipid moiety of N-ALP1 and N-ALP2 is critical for the NF-κB activation. Thus, triacylated lipoproteins derived from M. pneumoniae might activate NF-κB through TLR1 and TLR2, but not TLR6. [ABSTRACT FROM AUTHOR]

The antimicrobial protein granulysin is considered to play an important role in the defence mechanism against bacterial infection. We previously reported thatAcholeplasma laidlawii-induced transactivation of the granulysin promoter in a human monocytic cell line, THP-1, is regulated by activator protein-1 and CCAAT/enhancer binding protein-β (C/EBPβ), but not by nuclear factor-κB. Moreover, liver-enriched transcriptional inhibitory protein (LIP), a C/EBPβ isoform, was strongly induced inA. laidlawii-stimulated THP-1 cells. However, the level of liver-enriched transcriptional activator protein (LAP), another C/EBPβ isoform, was essentially constant. Accordingly, we speculated that LIP would down-regulateA. laidlawii-induced granulysin gene expression in THP-1 cells. In the present study, we examined whether LAP augmentsA. laidlawii-induced granulysin gene expression using conditional LAP-expressing THP-1 cells in a tetracycline-controlled expression system. Our results indicated that conditional expression of LAP augmentedA. laidlawii-induced expression of granulysin mRNA. In addition, the granulysin protein was observed inA. laidlawii-stimulated, LAP-expressing THP-1 cells. Our results suggest that the expression of LAP plays a critical role in the expression of the granulysin gene in macrophages. [ABSTRACT FROM AUTHOR]

Mycoplasmas are known to enhance human immunodeficiency virus (HIV) replication, and mycoplasma-derived lipid extracts have been reported to activate nuclear factor-κB (NF-κB) through Toll-like receptors (TLRs). In this study, we examined the involvement of TLRs in the activation of HIV long-terminal repeats (LTR) by mycoplasma and their active components responsible for the TLR activation. Lipid-associated membrane proteins (LAMPs) from two species of mycoplasma ( Mycoplasma fermentans and M. penetrans) that are associated with acquired immune-deficiency syndrome (AIDS), were found to activate HIV LTRs in a human monocytic cell line, THP-1. NF-κB deletion from the LTR resulted in inhibition of the activation. The LTR activation by M. fermentans LAMPs was inhibited by a dominant negative (DN) construct of TLR1 and TLR6, whereas HIV LTR activation by M. penetrans LAMPs was inhibited by DN TLR1, but not by DN TLR6. These results indicate that the activation of HIV LTRs by M. fermentans and M. penetrans LAMPs is dependent on NF-κB, and that the activation of HIV LTR by M. fermentans LAMPs is mediated through TLR1, TLR2 and TLR6. In contrast, the LTR activation by M. penetrans LAMPs is carried out through TLR1 and TLR2, but not TLR6. Subsequently, the active component of M. penetrans and M. fermentans LAMPs was purified by reverse-phase high-performance liquid chromatography (HPLC). Interestingly, the purified lipoprotein of M. penetrans LAMPs (LPMp) was able to activate NF-κB through TLR1 and TLR2. On the other hand, the activation of NF-κB by purified lipoprotein of M. fermentans LAMPs (LPMf) was mediated through TLR2 and TLR6, but not TLR1. [ABSTRACT FROM AUTHOR]

We previously reported that inducible granulysin gene expression in a human monocytic cell line, THP-1 is dominantly dependent on transcription factor activator protein-1 (AP-1). Here, we further examined the precise regulatory mechanisms underlying granulysin gene expression using THP-1 cells treated with Acholeplasma laidlawii. Transfection of reporter gene constructs into THP-1 cells indicated that the presence of a positive regulatory element(s) is located from -329 to -85 base pairs, containing two distinct AP-1 binding sites and one nuclear factor-κB (NF-κB) binding site. Deletion or mutation of the NF-κB binding site failed to affect inducible promoter activity, whereas deletion or mutation of both the AP-1 binding sites abrogated the promoter activity. Interestingly, deletion of the putative CCAAT/enhancer binding protein β (C/EBPβ) binding site upstream of the positive regulatory element induced the augmentation of granulysin promoter activity. Electrophoretic mobility shift assays demonstrated that nuclear extract prepared from A. laidlawii-treated THP-1 cells generated a specific binding to oligonucleotides, including AP-1, C/EBPβ, and NF-κB element. Furthermore, over-expression of liver-enriched transcriptional activator protein, a subunit of C/EBPβ, augmented A. laidlawii-induced granulysin promoter activity, whereas over-expression of liver-enriched transcriptional inhibitory protein inhibited the promoter activity. NF-κB p50 homodimer had no transactivation property, although it bound to the NF-κB site. These results indicate that AP-1 and C/EBPβ, but not NF-κB participate in the regulation of inducible granulysin gene expression in THP-1 cells. Moreover, the Toll-like receptor 2-dependent signalling pathway may be involved in A. laidlawii-induced transactivation of the granulysin promoter. Thus, these results suggest that the gene expression of granulysin in macrophages would be... [ABSTRACT FROM AUTHOR]

SummaryAn antimicrobial protein granulysin is constitutively expressed in cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. However, little is known about the precise regulatory mechanisms underlying granulysin gene expression. In this study, we examined the regulatory mechanisms underlying granulysin gene expression using a human monocytic cell line, THP-1, treated with Acholeplasma laidlawii. The level of granulysin mRNA expression in THP-1 cells was significantly augmented in response to stimulation with A. laidlawii. The transfection of reporter gene constructs into THP-1 cells indicated that DNA sequences between residues -329 and -239, relative to the transcriptional start site of the granulysin gene, are responsible for mediating gene induction. In addition, mutagenesis of a putative activator protein-1 (AP-1)-binding site between residues -277 and -271 in the granulysin promoter resulted in the reduction of granulysin promoter activity. Electrophoretic mobility shift assays (EMSA) demonstrated that nuclear extract prepared from A. laidlawii-treated THP-1 cells can generate specific binding to DNA oligonucleotides encompassing the AP-1-binding site, whereas unstimulated nuclear extract from the cells failed to do so. Furthermore, competition and supershift assays confirmed that A. laidlawii can induce the activation of AP-1. These results indicate that AP-1 dominantly participates in the regulation of inducible granulysin gene expression in THP-1 cells. Therefore, the finding of inducible granulysin gene expression by A. laidlawii suggests that inducible granulysin in macrophages may function as a protective weapon when microbial invasion occurs. [ABSTRACT FROM AUTHOR]