ERK and p38 MAP kinase are involved in downregulation of cell surface TNF receptor 1 induced by acetoxycycloheximide

Extending in silico mechanism-of-action analysis by annotating targets with pathways: application to cellular cytotoxicity readouts

Background: An in silico mechanism-of-action analysis protocol was developed, comprising molecule bioactivity profiling, annotation of predicted targets with pathways and calculation of enrichment factors to highlight targets and pathways more likely to be implicated in the studied phenotype. Results: The method was applied to a cytotoxicity phenotypic endpoint, with enriched targets/pathways found to be statistically significant when compared with 100 random datasets. Application on a smaller apoptotic set (10 molecules) did not allowed to obtain statistically relevant results, suggesting that the protocol requires modification such as analysis of the most frequently predicted targets/annotated pathways. Conclusion: Pathway annotations improved the mechanism-of-action information gained by target prediction alone, allowing a better interpretation of the predictions and providing better mapping of targets onto pathways.

Deoxynivalenol induces ectodomain shedding of TNF receptor 1 and thereby inhibits the TNF-α-induced NF-κB signaling pathway

Trichothecene mycotoxins are known to inhibit eukaryotic translation and to trigger the ribotoxic stress response, which regulates gene expression via the activation of the mitogen-activated protein (MAP) kinase superfamily. In this study, we found that deoxynivalenol induced the ectodomain shedding of tumor necrosis factor (TNF) receptor 1 (TNFRSF1A) and thereby inhibited the TNF-α-induced signaling pathway. In human lung carcinoma A549 cells, deoxynivalenol and 3-acetyldeoxynivalenol inhibited the expression of intercellular adhesion molecule-1 (ICAM-1) induced by TNF-α more strongly than that induced by interleukin 1α (IL-1α), whereas T-2 toxin and verrucarin A exerted nonselective inhibitory effects. Deoxynivalenol and 3-acetyldeoxynivalenol also inhibited the nuclear factor κB (NF-κB) signaling pathway induced by TNF-α, but not that induced by IL-1α. Consistent with these findings, deoxynivalenol and 3-acetyldeoxynivalenol induced the ectodomain shedding of TNF receptor 1 by TNF-α-converting enzyme (TACE), also known as a disintegrin and metalloproteinase 17 (ADAM17). In addition to the TACE inhibitor TAPI-2, the MAP kinase or extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor U0126 and the p38 MAP kinase inhibitor SB203580, but not the c-Jun N-terminal kinase (JNK) inhibitor SP600125, suppressed the ectodomain shedding of TNF receptor 1 induced by deoxynivalenol and reversed its selective inhibition of TNF-α-induced ICAM-1 expression. Our results demonstrate that deoxynivalenol induces the TACE-dependent ectodomain shedding of TNF receptor 1 via the activation of ERK and p38 MAP kinase, and thereby inhibits the TNF-α-induced NF-κB signaling pathway.

Translation inhibitors and their unique biological properties

In eukaryotes, many translation inhibitors have been widely used as bioprobes to evaluate the contribution of translation to signaling pathways and cellular functions. Several types of translation inhibitors are also known to trigger the activation of the mitogen-activated protein kinase superfamily in an intracellular mechanism called ribotoxic stress response. This perspective focuses on the biological properties of recently identified translation inhibitors that trigger ribotoxic stress response, particularly glutarimides as well as triene-ansamycins.

Cytotrienin A, a translation inhibitor that induces ectodomain shedding of TNF receptor 1 via activation of ERK and p38 MAP kinase

Cytotrienin A, a member of the triene-ansamycin family, was initially identified to be an inducer of apoptosis and recently shown to be an inhibitor of translation that interferes with eukaryotic elongation factor 1A function. In human lung carcinoma A549 cells, cytotrienin A was found to inhibit more strongly the cell-surface expression of intercellular adhesion molecule-1 (ICAM-1) induced by tumor necrosis factor (TNF)-α than the expression induced by interleukin (IL)-1α. Cytotrienin A induced the ectodomain shedding of TNF receptor 1 by TNF-α-converting enzyme (TACE). The TACE inhibitor TAPI-2 antagonized the selective inhibitory effect of cytotrienin A on inhibitor of nuclear factor-κB-α (IκBα) degradation as well as ICAM-1 expression in TNF-α-stimulated cells. The MEK inhibitor U0126 and the p38 MAP kinase inhibitor SB203580, but not the JNK inhibitor SP600125, prevented the ectodomain shedding of TNF receptor 1 induced by cytotrienin A and reversed the inhibitory effects of cytotrienin A on the TNF-α-induced IκBα degradation. In the presence of both U0126 and SB203580, cytotrienin A inhibited TNF-α- and IL-1α-induced ICAM-1 expression at almost equivalent concentrations. Thus, our present results demonstrate that cytotrienin A is a translation inhibitor that triggers ribotoxic stress response and selectively inhibits the TNF-α-induced ICAM-1 expression by inducing the ectodomain shedding of TNF receptor 1 via the activation of ERK and p38 MAP kinase.

p38 mitogen-activated protein kinase and PI3-kinase are involved in up-regulation of mu opioid receptor transcription induced by cycloheximide

Despite several decades of efforts to develop safer, efficacious, and non-addictive opioids for pain treatment, morphine remains the most valuable painkiller in contemporary medicine. Morphine and endogenous mu opioid peptides exert their pharmacological actions mainly through the mu opioid receptor (MOR). Analgesic effects of opioids in animals are dependent on the MOR expression levels, as demonstrated by studies of MOR-knockout mice (homo/heterozygotes) and MOR-less expressing mice. Surprisingly, in the course of our investigation to understand the mechanisms involved in the regulation of MOR gene expression, cycloheximide (CHX), a known protein synthesis inhibitor, markedly induced accumulation of MOR mRNAs in both MOR-negative and -positive cells. This induction was blocked by inhibitors of phosphoinositide 3-kinase (PI3-K) and p38 MAPK, but not by a p42/44 MAPK inhibitor. In vitro, CHX was found to activate the MOR promoter and this activation was suppressed by inhibition of PI3-K. The transcriptional activator Sox18 was recruited to the MOR promoter in CHX-treated cells and this recruitment was also inhibited by the PI3-K and p38 MAPK inhibitors, Ly294002 and SB203580, respectively. Consistently, acetylation of histone H3 and induction of H3-K4 methylation were detected while reductions of histone deacetylase 2 binding and H3-K9 methylation were observed on the promoter. Furthermore, the MOR mRNA accumulation was almost completely inhibited in the presence of actinomycin-D, indicating that this effect occurs mainly through activation of the transcriptional machinery. These observations suggest that CHX directly induces MOR gene transcription by recruiting the active transcription factor Sox18 to the MOR promoter through PI3- and/or p38 MAPK pathways.

Phosphodiesterase 6 subunits are expressed and altered in idiopathic pulmonary fibrosis

Background

Idiopathic Pulmonary Fibrosis (IPF) is an unresolved clinical issue. Phosphodiesterases (PDEs) are known therapeutic targets for various proliferative lung diseases. Lung PDE6 expression and function has received little or no attention. The present study aimed to characterize (i) PDE6 subunits expression in human lung, (ii) PDE6 subunits expression and alteration in IPF and (iii) functionality of the specific PDE6D subunit in alveolar epithelial cells (AECs).

Methodology/Principal Findings

PDE6 subunits expression in transplant donor (n = 6) and IPF (n = 6) lungs was demonstrated by real-time quantitative (q)RT-PCR and immunoblotting analysis. PDE6D mRNA and protein levels and PDE6G/H protein levels were significantly down-regulated in the IPF lungs. Immunohistochemical analysis showed alveolar epithelial localization of the PDE6 subunits. This was confirmed by qRT-PCR from human primary alveolar type (AT)II cells, demonstrating the down-regulation pattern of PDE6D in IPF-derived ATII cells. In vitro, PDE6D protein depletion was provoked by transforming growth factor (TGF)-β1 in A549 AECs. PDE6D siRNA-mediated knockdown and an ectopic expression of PDE6D modified the proliferation rate of A549 AECs. These effects were mediated by increased intracellular cGMP levels and decreased ERK phosphorylation.

Conclusions/Significance

Collectively, we report previously unrecognized PDE6 expression in human lungs, significant alterations of the PDE6D and PDE6G/H subunits in IPF lungs and characterize the functional role of PDE6D in AEC proliferation.

Structure-activity relationships and the cytotoxic effects of novel diterpenoid alkaloid derivatives against A549 human lung carcinoma cells

The cytotoxicity of three alkaloids from the roots of Aconitum yesoense var. macroyesoense as well as 36 semi-synthetic C(20)-diterpenoid atisine-type alkaloid derivatives against A549 human lung carcinoma cells was examined. Ten acylated alkaloid derivatives, pseudokobusine 11-veratroate (9), 11-anisoate (12), 6,11-dianisoate (14), 11-p-nitrobenzoate (18), 11,15-di-p-nitrobenzoate (22), 11-cinnamate (25) and 11-m-trifluoromethylbenzoate (27), and kobusine 11-p-trifluoromethylbenzoate (35), 11-m-trifluoromethylbenzoate (36) and 11,15-di-p-nitrobenzoate (39), exhibited cytotoxic activity, and 11,15-dianisoylpseudokobusine (16) was found to be the most potent cytotoxic agent. Their IC(50) values against A549 cells ranged from 1.72 to 5.44 μM. In the occurrence of cytotoxic effects of atisine-type alkaloids, replacement by an acyl group at both C-11 and C-15 resulted in the enhancement of activity of the parent alkaloids compared to that from having hydroxy groups at this position, and the presence of a hydroxy group at the C-6 position was required for the cytotoxic effects. These acylated alkaloid derivatives inhibit cell growth through G1 arrest.

Suppressive effects of liquid crystal compounds on the growth of the A549 human lung cancer cell line

The aim of this study was to evaluate the biological activity and pharmacological activity of several amphiphilic liquid-crystalline compounds (LCs), i.e. phenylpyrimidine derivatives possessing D-glucamine and cyanobiphenyl derivatives with a terminal hydroxyl unit, to explore novel anti-cancer functions of the LCs. The anti-cancer properties of the LCs were investigated in A549 human lung cancer cells by assessing cell growth, cell cycle distribution, and cell signaling pathways using a flow cytometer and a Western blot analysis. In addition, the effect of LCs on the growth of WI-38 normal fibroblasts was examined. Consequently, the phenylpyrimidine derivatives and cyanobiphenyl derivatives showed cytostatic effects, causing the suppression of cell growth through G1 phase arrest in A549 cells. Further analyses using phenylpyrimidine derivatives and precursors of a cyanobiphenyl compound demonstrated the structure-activity relationships. One of the phenylpyrimidine derivatives inhibited A549 growth without any toxicity to normal fibroblasts. As a result, a novel pharmacological function was hypothesized to be inherent in the structure of the LCs themselves, and the dependence of the tumor-specific activity on the hydrophobic group of phenylpyrimidine derivatives therefore remains an interesting issue. Our results suggest the possibility that the LCs themselves may act as a novel type of chemotherapeutic agent.

CD14 signaling restrains chronic inflammation through induction of p38-MAPK/SOCS-dependent tolerance

Current thinking emphasizes the primacy of CD14 in facilitating recognition of microbes by certain TLRs to initiate pro-inflammatory signaling events and the importance of p38-MAPK in augmenting such responses. Herein, this paradigm is challenged by demonstrating that recognition of live Borrelia burgdorferi not only triggers an inflammatory response in the absence of CD14, but one that is, in part, a consequence of altered PI3K/AKT/p38-MAPK signaling and impaired negative regulation of TLR2. CD14 deficiency results in increased localization of PI3K to lipid rafts, hyperphosphorylation of AKT, and reduced activation of p38. Such aberrant signaling leads to decreased negative regulation by SOCS1, SOCS3, and CIS, thereby compromising the induction of tolerance in macrophages and engendering more severe and persistent inflammatory responses to B. burgdorferi. Importantly, these altered signaling events and the higher cytokine production observed can be mimicked through shRNA and pharmacological inhibition of p38 activity in CD14-expressing macrophages. Perturbation of this CD14/p38-MAPK-dependent immune regulation may underlie development of infectious chronic inflammatory syndromes.

Macrophages express CD14 which partners with Toll-like receptor 2/1 to recognize bacterial lipoproteins such as those of Borrelia burgdorferi, the causative agent of Lyme disease. In vitro evidence demonstrates that blocking CD14 recognition of bacterial components ablates innate host cell inflammatory responses. Similarly, blocking downstream p38 kinase activity dampens the cellular response to these same microbial stimuli. This body of work underpins two well-established paradigms which cite the primacy of CD14 in facilitating TLR recognition of microbes to initiate proinflammatory signaling events and the importance of p38 in augmenting such responses. However, contrary to these paradigms, our prior study using a mouse model of Lyme disease demonstrated an association between CD14 deficiency, increased bacterial burden, and more severe and persistent disease. Herein, we provide a mechanistic explanation for this unanticipated host immune response implicating impaired negative regulation of inflammatory signaling pathways as an underlying cause. Consequent to impaired negative regulation the host becomes “intolerant” of continued exposure to bacteria and thus mounts a perpetual inflammatory response to their presence. An intriguing question raised by these findings is whether individual differences in the severity and clinical course of infection might reflect the susceptibility of the patient's innate immune system to tolerization.

Odoroside A and ouabain inhibit Na+/K+-ATPase and prevent NF-kappaB-inducible protein expression by blocking Na+-dependent amino acid transport

Inflammatory cytokines, such as tumor necrosis factor (TNF)-alpha and interleukin-1 (IL-1), trigger the activation of transcription factor NF-kappaB that induces the expression of a variety of genes, including intercellular adhesion molecule (ICAM)-1. Odoroside A [3beta-O-(beta-D-diginosyl)-14-hydroxy-5beta,14beta-card-20(22)-enolide] was found to inhibit the cell-surface expression of ICAM-1 induced by TNF-alpha and IL-1 at comparable concentrations in human lung carcinoma A549 cells. In this study, the molecular mechanism underlying the inhibition of TNF-alpha-induced cell-surface ICAM-1 expression by odoroside A together with the specific Na(+)/K(+)-ATPase inhibitor ouabain was further investigated. Odoroside A and ouabain neither prevented IkappaBalpha degradation nor NF-kappaB translocation to the nucleus upon TNF-alpha stimulation. While odoroside A and ouabain had no inhibitory effect on the induction of ICAM-1 mRNA, they inhibited the TNF-alpha-induced ICAM-1 expression at the protein level. Consistent with these results, odoroside A and ouabain potently reduced de novo protein synthesis, largely due to its ability to block Na(+)-dependent transport of amino acids across the plasma membrane, but not to interfering with the translation machinery. As a direct molecular target, odoroside A was found to inhibit the ATP-hydrolyzing activity of Na(+)/K(+)-ATPase as potently as ouabain. These results clearly demonstrate that odoroside A and ouabain prevent NF-kappaB-inducible protein expression by blocking the Na(+)-dependent amino acid transport.