In silico identification and characterization of the MAPK family members of unicellular model eukaryote Tetrahymena thermophila

An atypical MAPK regulates translocation of a GATA transcription factor in response to chemoattractant stimulation

The Dictyostelium atypical mitogen-activated protein kinase (MAPK) Erk2 is required for chemotactic responses to cAMP as amoeba undergo multicellular development. In this study, Erk2 was found to be essential for the cAMP-stimulated translocation of the GATA transcription factor GtaC as indicated by the distribution of a GFP-GtaC reporter. Erk2 was also found to be essential for the translocation of GtaC in response to external folate, a foraging signal that directs the chemotaxis of amoeba to bacteria. Erk1, the only other Dictyostelium MAPK, was not required for the GtaC translocation to either chemoattractant, indicating that GFP-GtaC is a kinase translocation reporter specific for atypical MAPKs. The translocation of GFP-GtaC in response to folate was absent in mutants lacking the folate receptor Far1 or the coupled G-protein subunit Gα4. Loss of GtaC function resulted in enhanced chemotactic movement to folate, suggesting that GtaC suppresses responses to folate. The alteration of four Erk2-preferred phosphorylation sites in GtaC impacted the translocation of GFP-GtaC in response to folate and the GFP-GtaC-mediated rescue of aggregation and development of gtaC- cells. The ability of different chemoattractants to stimulate Erk2-regulated GtaC translocation suggests that atypical MAPK-mediated regulation of transcription factors can contribute to different cell fates.

Alarmins from conjunctival fibroblasts up-regulate matrix metalloproteinases in corneal fibroblasts

AIM

To explore the effects of alarmins produced by necrotic human conjunctival fibroblasts on the release of matrix metalloproteinases (MMPs) by human corneal fibroblasts (HCFs).

METHODS

A necrotic cell supernatant (NHCS) was prepared by subjecting human conjunctival fibroblasts to three cycles of freezing and thawing. The amounts of interleukin (IL)-1β and tumor necrosis factor (TNF)-α in NHCS were determined by enzyme-linked immunosorbent assays. HCFs exposed to NHCS or other agents in culture were assayed for the release of MMPs as well as for intracellular signaling by immunoblot analysis. The abundance of MMP mRNAs in HCFs was examined by reverse transcription and real-time polymerase chain reaction analysis.

RESULTS

NHCS increased the release of MMP-1 and MMP-3 by HCFs as well as the amounts of the corresponding mRNAs in the cells. NHCS also induced activation of mitogen-activated protein kinase (MAPK) signaling pathways mediated by extracellular signal-regulated kinase (ERK), p38, and c-Jun NH₂-terminal kinase (JNK) as well as elicited that of the nuclear factor (NF)-κB signaling pathway by promoting phosphorylation of the endogenous NF-κB inhibitor IκB-α. Inhibitors of MAPK and NF-κB signaling as well as IL-1 and TNF-α receptor antagonists attenuated the NHCS-induced release of MMP-1 and MMP-3 by HCFs. Furthermore, IL-1β and TNF-α were both detected in NHCS, and treatment of HCFs with these cytokines induced the release of MMP-1 and MMP-3 in a concentration-dependent manner.

CONCLUSION

Alarmins, including IL-1β and TNF-α, produced by necrotic human conjunctival fibroblasts triggered MMP release in HCFs through activation of MAPK and NF-κB signaling. IL-1β and TNF-α are therefore potential therapeutic targets for the amelioration of corneal stromal degradation in severe ocular burns.

Antiphospholipid antibody-activated NETs exacerbate trophoblast and endothelial cell injury in obstetric antiphospholipid syndrome

Despite the widespread use of antiplatelets and anticoagulants, women with antiphospholipid syndrome (APS) may face pregnancy complications associated with placental dysplasia. Neutrophil extracellular traps (NETs) are involved in the pathogenesis of many autoimmune diseases, including vascular APS; however, their role in obstetric APS is unclear. Herein, we investigated the role of NETs by quantifying cell‐free DNA and NET marker levels. Live‐cell imaging was used to visualize NET formation, and MAPK signalling pathway proteins were analysed. Cell migration, invasion and tube formation assays were performed to observe the effects of NETs on trophoblasts and human umbilical vein endothelial cells (HUVECs). The concentrations of cell‐free DNA and NETs in sera of pregnant patients with APS were elevated compared with that of healthy controls (HCs) matched to gestational week. APS neutrophils were predisposed to spontaneous NET release and IgG purified from the patients (APS‐IgG) induced neutrophils from HCs to release NETs. Additionally, APS‐IgG NET induction was abolished with inhibitors of reactive oxygen species, AKT, p38 MAPK and ERK1/2. Moreover, NETs were detrimental to trophoblasts and HUVECs. In summary, APS‐IgG‐induced NET formation deserves further investigation as a potential novel therapeutic target in obstetrical APS.

Streptococcus Suis Serotype 2 Stimulates Neutrophil Extracellular Traps Formation via Activation of p38 MAPK and ERK1/2

Streptococcus suis serotype 2 is a major pathogen of swine streptococcicosis, which result in serious economic loss worldwide. SS2 is an important zoonosis causing meningitis and even death in humans. Neutrophil extracellular traps (NETs) constitute a significant bactericidal strategy of innate immune. The battle between SS2 and NETs may account for the pathogenicity of SS2. However, the molecular mechanism underlying release of SS2-induced NETs remains unclear. In this study, SS2 was found to induce NETs within 2–4 h, and was dependent on reactive oxygen species (ROS) from NADPH oxidase. Moreover, SS2 could activate neutrophil p38 MAPK and ERK1/2. Blockage of p38 MAPK or ERK1/2 activation decreased SS2-induced NETs formation by 65 and 85%, respectively. In addition, NADPH oxidase derived ROS inhibition negatively affected phosphorylation of p38 MAPK and ERK1/2 in SS2 induced neutrophils. Both TLR2 and TLR4 were significantly up-regulated by SS2 infection in blood cells in vivo and neutrophils in vitro, which indicates these two receptors are involved in SS2 recognition. Blocking TLR4 signaling could further inhibit the activation of ERK1/2, but not p38 MAPK; however, TLR4 signaling inhibition reduced NETs formation induced by SS2. In conclusion, SS2 could be recognized by TLR2 and/or TLR4, initiating NETs formation signaling pathways in a NADPH oxidase derived ROS dependent manner. ROS will activate p38 MAPK and ERK1/2, which ultimately induces NETs formation.

Toxic proteins from Croton tiglium L. exert a proinflammatory effect by inducing release of proinflammatory cytokines and activating the p38-MAPK signaling pathway

The aim of the present study was to determine the toxic targets of proteins from Croton tiglium L. and to investigate the potential mechanism of their toxicity. The toxic targets were determined by oral medication and intraperitoneal injection. The median lethal dose of oral medication in mice was calculated using Bliss software (2,752.8–3,407.5 mg/kg), and that of intraperitoneal injection was 195.8–272.69 mg/kg. The results of histopathological examination demonstrated that the kidney was primarily impaired by intraperitoneal injection, with slight degeneration of renal tubular epithelial cells. As to oral medication, the digestive tract was primarily injured, which manifested as congestion, bleeding, serious edema and other symptoms. Oral administration of the proteins caused gastrointestinal edema by increasing the intestinal permeability. Severe edema was associated with the inflammatory response, therefore the association between the toxicity of the proteins and inflammation was investigated. The proinflammatory effects of the crude proteins on the release of inflammatory mediator prostaglandin E2 (PGE2) were evaluated through intraperitoneal injection and the production of proinflammatory cytokines in RAW264.7 macrophages. Maximum PGE2 was released in the mice in vivo following intraperitoneal injection with 400 mg crude protein/kg body weight. Proinflammatory cytokines in macrophages, including tumor necrosis factor-α and interleukin-1β, were produced in dose- and time-dependent manners in vitro. furthermore, the expressions of cell signaling molecules were detected by western blotting. The inflammatory response induced by crude protein in macrophages was associated with the mitogen-activated protein kinase (MAPK) signaling pathway mainly including p38-MAPK, extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinase 1/2/3 and the activated p38-MAPK signaling pathway. However, extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinases 1–3 exhibited no significant response.

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

In ciliates, unicellular representatives of the bikont branch of evolution, inter- and intracellular signalling pathways have been analysed mainly in Paramecium tetraurelia, Paramecium multimicronucleatum and Tetrahymena thermophila and in part also in Euplotes raikovi. Electrophysiology of ciliary activity in Paramecium spp. is a most successful example. Established signalling mechanisms include plasmalemmal ion channels, recently established intracellular Ca²⁺ -release channels, as well as signalling by cyclic nucleotides and Ca²⁺ . Ca²⁺ -binding proteins (calmodulin, centrin) and Ca²⁺ -activated enzymes (kinases, phosphatases) are involved. Many organelles are endowed with specific molecules cooperating in signalling for intracellular transport and targeted delivery. Among them are recently specified soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), monomeric GTPases, H⁺ -ATPase/pump, actin, etc. Little specification is available for some key signal transducers including mechanosensitive Ca²⁺ -channels, exocyst complexes and Ca²⁺ -sensor proteins for vesicle-vesicle/membrane interactions. The existence of heterotrimeric G-proteins and of G-protein-coupled receptors is still under considerable debate. Serine/threonine kinases dominate by far over tyrosine kinases (some predicted by phosphoproteomic analyses). Besides short-range signalling, long-range signalling also exists, e.g. as firmly installed microtubular transport rails within epigenetically determined patterns, thus facilitating targeted vesicle delivery. By envisaging widely different phenomena of signalling and subcellular dynamics, it will be shown (i) that important pathways of signalling and cellular dynamics are established already in ciliates, (ii) that some mechanisms diverge from higher eukaryotes and (iii) that considerable uncertainties still exist about some essential aspects of signalling.