Sphingosine kinase, phosphatidylinositol 3-kinase, Akt, NF-κB, and p300 are required for CCL5 production in Mycobacterium bovis Bacillus Calmette–Guérin (BCG)-infected epithelial cells

Biglycan- and Sphingosine Kinase-1 Signaling Crosstalk Regulates the Synthesis of Macrophage Chemoattractants

In its soluble form, the extracellular matrix proteoglycan biglycan triggers the synthesis of the macrophage chemoattractants, chemokine (C-C motif) ligand CCL2 and CCL5 through selective utilization of Toll-like receptors (TLRs) and their adaptor molecules. However, the respective downstream signaling events resulting in biglycan-induced CCL2 and CCL5 production have not yet been defined. Here, we show that biglycan stimulates the production and activation of sphingosine kinase 1 (SphK1) in a TLR4- and Toll/interleukin (IL)-1R domain-containing adaptor inducing interferon (IFN)-β (TRIF)-dependent manner in murine primary macrophages. We provide genetic and pharmacological proof that SphK1 is a crucial downstream mediator of biglycan-triggered CCL2 and CCL5 mRNA and protein expression. This is selectively driven by biglycan/SphK1-dependent phosphorylation of the nuclear factor NF-κB p65 subunit, extracellular signal-regulated kinase (Erk)1/2 and p38 mitogen-activated protein kinases. Importantly, in vivo overexpression of soluble biglycan causes Sphk1-dependent enhancement of renal CCL2 and CCL5 and macrophage recruitment into the kidney. Our findings describe the crosstalk between biglycan- and SphK1-driven extracellular matrix- and lipid-signaling. Thus, SphK1 may represent a new target for therapeutic intervention in biglycan-evoked inflammatory conditions.

Sphingosine-1-phosphate signaling: unraveling its role as a drug target against infectious diseases

Sphingosine-1-phosphate (S1P) signaling is reported in variety of cell types, including immune, endothelial and cancerous cells. It is emerging as a crucial regulator of cellular processes, such as apoptosis, cell proliferation, migration, differentiation and so on. This signaling pathway is initiated by the intracellular production and secretion of S1P through a cascade of enzymatic reactions. Binding of S1P to different S1P receptors (S1PRs) activates different downstream signaling pathways that regulate the cellular functions differentially depending upon the cell type. An accumulating body of evidence suggests that S1P metabolism and signaling is often impaired during infectious diseases; thus, its manipulation might be helpful in the treatment of such diseases. In this review, we summarize recent advances in our understanding of the S1P signaling pathway and its candidature as a novel drug target against infectious diseases.

Melatonin-mediated Bim up-regulation and cyclooxygenase-2 (COX-2) down-regulation enhances tunicamycin-induced apoptosis in MDA-MB-231 cells

Melatonin is involved in many physiological functions, and it has differential effects on apoptosis in normal and cancer cells. However, the mechanism of its antitumor roles is not well understood. In this study, we show that melatonin enhances tunicamycin-induced apoptosis in human breast carcinoma MDA-MB-231 cells. Melatonin up-regulates pro-apoptotic protein Bim expression at the transcriptional levels in the presence of tunicamycin. Melatonin inhibits tunicamycin-induced COX-2 expression in MDA-MB-231 cells. Furthermore, inhibition of COX-2 activity using the COX-2 inhibitor, NS398, increases tunicamycin-induced apoptosis. Interestingly, these effects were not associated with melatonin receptor signal pathways. Pertussis toxin (a general Gi protein inhibitor) or luzindole (a nonspecific melatonin receptor antagonist) did not reverse the effect of melatonin. In addition, melatonin blocked tunicamycin-induced NF-κB transcriptional activity, p65 nuclear translocation, and p38 MAPK activation. Melatonin-mediated p38 MAPK inhibition contributed to decreased COX-2 mRNA stability. Taken together, our results suggest that melatonin enhances antitumor function through up-regulation of Bim expression and down-regulation of COX-2 expression in tunicamycin-treated MDA-MB-231 cells.

Inhibitory effects of melatonin on the lipopolysaccharide-induced CC chemokine expression in BV2 murine microglial cells are mediated by suppression of Akt-induced NF-κB and STAT/GAS activity

Melatonin influences sleep and circadian rhythm, and it has anti-inflammatory functions. However, the mechanism of its anti-inflammatory roles is not well understood. In our studies, we show that melatonin blocked lipopolysaccharide (LPS)-induced CCL2 (monocyte chemotactic protein-1; MCP-1), CCL5 (Regulated upon Activation, Normal T-cell Expressed, and Secreted), and CCL9 (macrophage inflammatory protein-1γ) chemokine mRNA expression in BV2 murine microglial cells. Melatonin markedly inhibited LPS-induced Akt phosphorylation and NF-κB activation. Furthermore, melatonin inhibited LPS-induced STAT1/3 phosphorylation and interferon-gamma activated sequence (GAS)-driven transcriptional activity. Interestingly, these effects were not associated with reactive oxygen species scavenging effects of melatonin or melatonin receptor signal pathways. Taken together, our results suggested that melatonin has anti-inflammatory functions through down-regulation of chemokine expression by inhibition of NF-κB and STAT/GAS activation in LPS-stimulated BV2 murine microglial cell line.

Regulation of CC ligand 5/RANTES by acid sphingomyelinase and acid ceramidase

Acid sphingomyelinase (aSMase) generates the bioactive lipid ceramide (Cer) from hydrolysis of sphingomyelin (SM). However, its precise roles in regulating specific sphingolipid-mediated biological processes remain ill defined. Interestingly, the aSMase gene gives rise to two distinct enzymes, lysosomal sphingomyelinase (L-SMase) and secretory sphingomyelinase (S-SMase) via alternative trafficking of a shared protein precursor. Previously, our laboratory identified Ser(508) as a crucial residue for the constitutive and regulated secretion of S-SMase in response to inflammatory cytokines, and demonstrated a role for S-SMase in formation of select cellular Cer species (Jenkins, R. W., Canals, D., Idkowiak-Baldys, J., Simbari, F., Roddy, P., Perry, D. M., Kitatani, K., Luberto, C., and Hannun, Y. A. (2010) J. Biol. Chem. 285, 35706-35718). In the present study using a chemokine/cytokine screen, we identified the chemokine CCL5 (formerly known as RANTES) as a candidate-specific downstream target for aSMase. Regulation of CCL5 by aSMase was subsequently validated using both loss-of-function and gain-of-function models indicating that aSMase is both necessary and sufficient for CCL5 production. Interestingly, cells deficient in acid ceramidase (aCDase) also exhibited defects in CCL5 induction, whereas cells deficient in sphingosine kinase-1 and -2 exhibited higher levels of CCL5, suggesting that sphingosine and not sphingosine 1-phosphate (S1P) is responsible for the positive signal to CCL5. Consistent with this, co-expression of aSMase and aCDase was sufficient to strongly induce CCL5. Taken together, these data identify a novel role for aSMase (particularly S-SMase) in chemokine elaboration by pro-inflammatory cytokines and highlight a novel and shared function for aSMase and aCDase.

Involvement of phosphoinositide 3-kinase gamma in the neuro-inflammatory response and cognitive impairments induced by beta-amyloid 1-40 peptide in mice

Alzheimer disease (AD) is the most common form of dementia in the elderly, and the neuro-pathological hallmarks of AD include neurofibrillary tangles (NFT), and deposition of beta-amyloid (Abeta) in extracellular plaques. In addition, chronic inflammation due to recruitment of activated glial cells to amyloid plaques are an invariant component in AD, and several studies have reported that the use of non-steroidal anti-inflammatory drugs (NSAIDs) may provide a measure of protection against AD. In this report we have investigated whether phosphoinositide 3-kinase gamma (PI3Kgamma), which is important in inflammatory cell migration, plays a critical role in the neuro-inflammation, synaptic dysfunction, and cognitive deficits induced by intracerebroventricular injection of Abeta(1-40) in mice. We found that the selective inhibitor of PI3Kgamma, AS605240, was able to attenuate the Abeta(1-40)-induced accumulation of activated astrocytes and microglia in the hippocampus, and decrease immuno-staining for p-Akt and cyclooxygenase-2 (COX-2). Interestingly, Abeta(1-40) activated macrophages treated with AS605240 or another PI3Kgamma inhibitor, AS252424, displayed impaired chemotaxis in vitro, but their expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) was unaffected. Finally, AS605240 prevented Abeta(1-40)-induced cognitive deficits and synaptic dysfunction, but failed to modify scopolamine-induced amnesia. Our data suggests that inhibition of PI3Kgamma may represent a novel therapeutic target for treating AD patients.

Mycobacterium bovis Bacillus Calmette-Guérin (BCG)-induced activation of PI3K/Akt and NF-kB signaling pathways regulates expression of CXCL10 in epithelial cells

CXCL10 production is a critical step in limiting mycobacterial infection. Although induction of this chemokine by mycobacteria in epithelial cells has been reported, it is still unclear how CXCL10 is regulated in Mycobacterium bovis BCG-infected epithelial cells. In this study, we demonstrate that phosphatidylinoditol 3-kinase (PI3K)/Akt and the nuclear factor kB (NF-kB) signaling pathways play an important role in CXCL10 expression at the protein and mRNA level in A549 cells. We demonstrate that treatment of A549 cells with LY294002 and wortmannin, two PI3K inhibitors, inhibited M. bovis BCG-induced CXCL10 expression. In addition, treatment of A549 cells with an Akt inhibitor significantly blocked M. bovis BCG-induced CXCL10 production. Moreover, our data show that treatment of epithelial cells with CAPE, BAY 11-7082, and PDTC three selective inhibitors of NF-kB, significantly reduced the effect of M. bovis BCG on induced CXCL10 mRNA expression (74%, 69% and 83% inhibition by 8microM CAPE, 10microM BAY 11-7082 and 3microM PDTC as assessed by real-time PCR, respectively). In accordance with the gene induction, the production of CXCL10 was also significantly reduced by these inhibitors. Finally, the inhibition of PI3K affect NF-kB activation in M. bovis BCG-infected cells, indicating that PI3K activity is required for the M. bovis BCG-induced activation of NF-kB. The functional association between PI3K/Akt and NF-kB demonstrates another mechanism in the regulation of M. bovis BCG-induced CXCL10 in A549 cells.

Expression and regulation of chemokines in mycobacterial infection

Chemokines are the key molecules that recruit immune cells by chemotaxis and act in leukocyte activation during mycobacterial diseases. Currently, tuberculosis is a leading infectious disease affecting millions of people worldwide. The purpose of this review is to describe a series of recent scientific evidence concerning to the protective role of some members of the CC- and the CXC chemokine subfamilies for the control of mycobacterial infection. The discussion will (1) highlight the effectiveness of some chemokines as potent immunoprophylactic tool for controlling the mycobacterial establishment within the host, (2) describe recent work on the relevance of cellular signaling pathways by which mycobacterial antigens mediate chemokine induction, and (3) summarize current progress in the understanding of the potential use of chemokines as potent adjuvants in antimycobacterial immune responses.

Regulation of human beta-defensin-2 by Mycobacterium bovis bacillus Calmette-Guérin (BCG): involvement of PKC, JNK, and PI3K in human lung epithelial cell line (A549)

Human beta-defensin (HBD)-2 is an inducible antimicrobial peptide that plays an important role in innate immunity. Induction of this peptide by mycobacteria in epithelial cells has been reported. However, the mechanism(s) by which Mycobacterium bovis bacillus Calmette-Guérin (BCG) triggers gene transcription of HBD-2 remains poorly understood. In the present work we found that treatment of human epithelial cells with Ro32-0432 or Gö6976, two selective inhibitors of protein kinase C (PKC), significantly reduced the effect of M. bovis BCG on induced HBD-2 mRNA expression (65 and 80% inhibition by 10microM Ro32-0432, and 1microM Gö6976 as assessed by real-time PCR, respectively). Moreover, there was increased activation of c-Jun N-terminal kinase (JNK) and phosphatidylinositol-3-kinase (PI3K)/Akt in A549 cells infected with M. bovis BCG, and this JNK and PI3K activation was mediated through PKC. Finally, we found that M. bovis BCG-induced HBD-2 mRNA gene expression in A549 cells was dependent on JNK, and PI3K determined by real-time PCR analysis, which was attenuated by inhibitors of JNK (SP600125 and AG126), and PI3K (wortmannin and Ly294002). These studies are the first to show that M. bovis BCG-induced HBD-2 mRNA expression in A549 cells is regulated at least in part through activation of signaling proteins of PKC, JNK and PI3K.