Cyclic AMP inhibits p38 activation via CREB-induced dynein light chain

Myokine musclin alleviates lipid accumulation in 3T3-L1 adipocytes through PKA/p38-mediated upregulation of lipolysis and suppression of lipogenesis

Musclin (MUS), an exercise-responsive myokine, has been documented to attenuate inflammation and enhance physical endurance. However, the effects of MUS on differentiation and related molecular mechanisms in adipocytes have not yet been studied. In this study, we found that treatment with MUS attenuated lipid accumulation in fully differentiated 3T3-L1 cells. Furthermore, MUS treatment enhanced lipolysis assessed by glycerol release, and caused apoptosis, whereas it reduced the expression of lipogenic proteins, such as PPARγ and processed SREBP1. Treatment with MUS augmented phosphorylated PKA expression, whereas suppressed p38 phosphorylation in 3T3-L1 adipocytes. H89, a selective PKA inhibitor reduced the effects of MUS on lipogenic lipid accumulation as well as lipolysis except for apoptosis. These results suggest that MUS promotes lipolysis and suppresses lipogenesis through a PKA/p38-dependent pathway, thereby ameliorating lipid deposition in cultured adipocytes. The current study offers the potential of MUS as a therapeutic approach for treating obesity with few side effects.

Plants as Modulators of Melanogenesis: Role of Extracts, Pure Compounds and Patented Compositions in Therapy of Pigmentation Disorders

The kingdom of plants as a "green biofabric" of valuable bioactive molecules has long been used in many ailments. Currently, extracts and pure compounds of plant origin are used to aid in pigmentation skin problems by influencing the process of melanogenesis. Melanin is a very important pigment that protects human skin against ultraviolet radiation and oxidative stress. It is produced by a complex process called melanogenesis. However, disturbances in the melanogenesis mechanism may increase or decrease the level of melanin and generate essential skin problems, such as hyperpigmentation and hypopigmentation. Accordingly, inhibitors or activators of pigment formation are desirable for medical and cosmetic industry. Such properties may be exhibited by molecules of plant origin. Therefore, that literature review presents reports on plant extracts, pure compounds and compositions that may modulate melanin production in living organisms. The potential of plants in the therapy of pigmentation disorders has been highlighted.

Clinical, Genetic and Functional Characterization of a Novel AVPR2 Missense Mutation in a Woman with X-Linked Recessive Nephrogenic Diabetes Insipidus

Nephrogenic diabetes insipidus (NDI) is a rare disorder characterized by renal unresponsiveness to the hormone vasopressin, leading to excretion of large volumes of diluted urine. Mutations in the arginine vasopressin receptor-2 (AVPR2) gene cause congenital NDI and have an X-linked recessive inheritance. The disorder affects almost exclusively male family members, but female carriers occasionally present partial phenotypes due to skewed inactivation of the X-chromosome. Here, we report a rare case of a woman affected with X-linked recessive NDI, presenting an average urinary output of 12 L/day. Clinical and biochemical studies showed incomplete responses to water deprivation and vasopressin stimulation tests. Genetic analyses revealed a novel heterozygous missense mutation (c.493G > C, p.Ala165Pro) in the AVPR2 gene. Using a combination of in-silico protein modeling with human cellular models and molecular phenotyping, we provide functional evidence for phenotypic effects. The mutation destabilizes the helical structure of the AVPR2 transmembrane domains and disrupts its plasma membrane localization and downstream intracellular signaling pathways upon activation with its agonist vasopressin. These defects lead to deficient aquaporin 2 (AQP2) membrane translocation, explaining the inability to concentrate urine in this patient.

Fluoroquinolones Suppress TGF-β and PMA-Induced MMP-9 Production in Cancer Cells: Implications in Repurposing Quinolone Antibiotics for Cancer Treatment

BACKGROUND

Fluoroquinolones (FQs) are potent antimicrobials with multiple effects on host cells and tissues. Although FQs can attenuate cancer invasion and metastasis, the underlying molecular mechanisms remain unclear. Matrix metalloproteinase-9 (MMP-9) has functional roles in tumor angiogenesis, invasion, and metastasis, and is associated with cancer progression and poor prognosis, suggesting that inhibitors of MMP-9 activity and transcription are prime candidates for cancer therapy. Despite numerous preclinical data supporting the use of MMP-9 inhibitors as anticancer drugs, the few available examples are not therapeutically useful due to low specificity and off-target effects. We examined the effects of FQs on MMP-9 production in cancer cells following transforming growth factor beta (TGF-β) and phorbol 12-myristate 13-acetate (PMA) stimulation.

EXPERIMENTAL APPROACHES

Using confluent cultures of HepG2 and A549 cells, the effects of FQs (ciprofloxacin, levofloxacin, clinafloxacin, gatifloxacin, and enrofloxacin) on TGF-β and PMA-induced MMP-9 mRNA expression and production were studied in RNA extracts and culture supernatants, respectively. FQs specifically abrogated TGF-β and PMA-induced MMP-9 levels and activity in a concentration and time-dependent manner, without affecting other MMPs or proteins involved in epithelial-mesenchymal transition. Additionally, FQs inhibited TGF-β and PMA-induced cell migration via p38 and cyclic AMP signaling pathways.

CONCLUSIONS AND IMPLICATIONS

Overall, we demonstrated that FQs inhibit cancer cell migration and invasion by downregulating MMP-9 expression and revealed the cellular mechanisms underlying their potential value in cancer treatment.

Effect of L-thyroxine administration on long-term potentiation and accompanying mitogen-activated protein kinases in rats

The present study investigated the differences in the activation of c-Jun NH2-terminal kinases (JNK), p38 mitogen-activated protein kinases (p38^MAPK ), and extracellular signal-regulated kinases 1/2 (Erk1/2) 1 hr after the induction of long-term potentiation (LTP) between rats with hyperthyroidism that was produced at two different stages of development. Hyperthyroidism was produced in rats by daily injections of L-thyroxine (T4, ip., 0.2 mg/kg) to their dams for lactation period or to the rats itself during the young adult period. LTP was induced by application of high-frequency stimulation protocol. Five-min averages of the excitatory postsynaptic potential (EPSP) slopes and population spike (PS) amplitudes at the end of recording were averaged to measure the magnitude of LTP. Total and phosphorylated levels of Erk1/2, JNK, and P38-MAPK were assessed via western blotting in these hippocampi. LTP was found to be impaired in both groups of hyperthyroidisms, but this impairment observed together with increased expression and phosphorylation of ERK1/2, and increased phosphorylation of JNK in rats treated maternally with T4 compared to those treated adultly. These results suggest that excessiveness of thyroid hormone has longstanding effects on hippocampal function and may account for failed LTP in both early and relatively late stage of development depending on various molecular pathways, such as ERK1/2 and JNK.

The RasGEF FgCdc25 regulates fungal development and virulence in Fusarium graminearum via cAMP and MAPK signalling pathways

Ras GTPases act as molecular switches to control various cellular processes by coupling integrated signals in eukaryotes. Activities of Ras GTPases are triggered by Ras GTPase guanine nucleotide exchange factors (RasGEFs) in general, whereas the role of RasGEF in plant pathogenic fungi is largely unknown. In this study, we characterized the only RasGEF protein in Fusarium graminearum, FgCdc25, by combining genetic, cytological and phenotypic strategies. FgCdc25 directly interacted with RasGTPase FgRas2, but not FgRas1, to regulate growth and sexual reproduction. Mutation of the FgCDC25 gene resulted in decreased toxisome formation and deoxynivalenol (DON) production, which was largely depended on cAMP signalling. In addition, FgCdc25 indirectly interacted with FgSte11 in FgSte11-Ste7-Gpmk1 cascade, and the ΔFgcdc25 strain totally abolished the formation of infection structures and was nonpathogenic in planta, which was partially recovered by addition of exogenous cAMP. In contrast, FgCdc25 directly interplayed with FgBck1 in FgBck1-MKK1-Mgv1 cascade to negatively control cell wall integrity. Collectively, these results suggest that FgCdc25 modulates cAMP and MAPK signalling pathways and further regulates fungal development, DON production and plant infection in F. graminearum.

Epac1 Restores Normal Insulin Signaling through a Reduction in Inflammatory Cytokines

We have previously reported that Epac1 reduced inflammatory cytokines, which is protective to the diabetic retina. We have also published that impaired insulin signaling occurs in the diabetic retina. A reduction in interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNFα) by Epac1 could potentially restore normal insulin signal transduction. Confocal microscopy was performed to localize the insulin receptor in the retina of Epac1 floxed and endothelial cell-specific Epac1 knockout mice. Whole retinal lysates from Epac1 floxed and endothelial cell-specific Epac1 knockout mice were used to investigate proteins involved in the insulin signaling cascade. Primary human REC were cultured in normal and high glucose followed by Epac1 agonist treatment or transfection with IL-1β or TNFα siRNA for protein analyses of insulin signaling proteins. Decreased expression of the insulin receptor was observed in the Epac1 knockout mouse retinal vasculature compared to floxed littermates. Work in mice showed that loss of Epac1 decreased insulin signaling proteins. Treatment with an Epac1 agonist decreased p38 and JNK signaling and increased insulin signaling, as did inhibition of IL-1β or TNFα using siRNA when added to REC grown in high glucose. Taken together, Epac1 can restore normal insulin signaling in the retinal vasculature through reductions in inflammatory cytokines.

Mitogen-activated protein kinase pathways in sepsis treatment

Sepsis is a characteristic set of systemic reactions to overwhelming infection that remains a major cause of death in critically ill patients. Endotoxins or lipopolysaccharides from gram-negative bacteria play a major role in the pathogenesis by inducing an over-production of inflammatory cytokines, which usually triggers beneficial inflammatory responses but causes tissue injury and lethal multiple organ failure in excessive amounts. The production of inflammatory cytokines depends on the activation of many intracellular signaling pathways, including nuclear factor-κB (NF-κB) pathway and three mitogen-activated protein kinase (MAPK) pathways. This review of important MAPK pathways underscores the essential role of MKP-1 in the negative control of sepsis. Herein is a summary of the roles of MAPK pathways in the production of inflammatory cytokines and the possibility of targeting these pathways for the treatment of sepsis.

Molecular context of Schistosoma mansoni transmission in the molluscan environments: A mini-review

Schistosoma mansoni, being transmitted by some freshwater Biomphalaria snails, is a major causative agent of human schistosomiasis. In the absence of effective vaccine and alternative drug designs to fight against the disease, and with the limitations of molluscicide application, developing more efficient strategies to interrupt the snail-mediated parasite transmission is being emphasized as potentially instrumental in the efforts toward schistosomiasis elimination, hence, necessitating thorough and comprehensive understanding of the fundamental mechanisms involved in the transmission process. Based on the current advances, this paper presents a concise exposition of the cellular, biochemical, genetic and immunological dynamics of the complex and statge-by-stage interactions between the parasite and its vector in their aquatic environment. It also highlights the possible crosstalk between the parasite's intracellular cyclic adenosine monophosphate (cAMP) and p38 mitogen-activated protein kinase (p38 MAPK) during the intramolluscan stage. Undoubtedly, decades of intensive investigation have untangled many S. mansoni-B. glabrata complexities, yet many aspects of the parasite-vector cycle which can help define potential control clues await further elucidation.

Detrimental effects of melanocortin-1 receptor (MC1R) variants on the clinical outcomes of BRAF V600 metastatic melanoma patients treated with BRAF inhibitors

Melanocortin-1 receptor (MC1R) plays a key role in skin pigmentation, and its variants are linked with a higher melanoma risk. The influence of MC1R variants on the outcomes of patients with metastatic melanoma (MM) treated with BRAF inhibitors (BRAFi) is unknown. We studied the MC1R status in a cohort of 53 consecutive BRAF-mutated patients with MM treated with BRAFi. We also evaluated the effect of vemurafenib in four ^V600 BRAF melanoma cell lines with/without MC1R variants. We found a significant correlation between the presence of MC1R variants and worse outcomes in terms of both overall response rate (ORR; 59% versus 95%, P = 0.011 univariate, P = 0.028 multivariate analysis) and progression-free survival (PFS) shorter than 6 months (72% versus 33%, P = 0.012 univariate, P = 0.027 multivariate analysis). No difference in overall survival (OS) was reported, probably due to subsequent treatments. Data in vitro showed a significant different phosphorylation of Erk1/2 and p38 MAPK during treatment, associated with a greater increase in vemurafenib IC50 in MC1R variant cell lines.

PKA and cAMP/CNG Channels Independently Regulate the Cholinergic Ca(2+)-Response of Drosophila Mushroom Body Neurons

The mushroom bodies (MBs) are the most prominent structures in adult Drosophila brain. They have been involved in several crucial functions, such as learning and memory, sleep, locomotor activity, and decision making.

The mushroom bodies (MBs), one of the main structures in the adult insect brain, play a critical role in olfactory learning and memory. Though historical genes such as dunce and rutabaga, which regulate the level of cAMP, were identified more than 30 years ago, their in vivo effects on cellular and physiological mechanisms and particularly on the Ca²⁺-responses still remain largely unknown. In this work, performed in Drosophila, we took advantage of in vivo bioluminescence imaging, which allowed real-time monitoring of the entire MBs (both the calyx/cell-bodies and the lobes) simultaneously. We imaged neuronal Ca²⁺-activity continuously, over a long time period, and characterized the nicotine-evoked Ca²⁺-response. Using both genetics and pharmacological approaches to interfere with different components of the cAMP signaling pathway, we first show that the Ca²⁺-response is proportional to the levels of cAMP. Second, we reveal that an acute change in cAMP levels is sufficient to trigger a Ca²⁺-response. Third, genetic manipulation of protein kinase A (PKA), a direct effector of cAMP, suggests that cAMP also has PKA-independent effects through the cyclic nucleotide-gated Ca²⁺-channel (CNG). Finally, the disruption of calmodulin, one of the main regulators of the rutabaga adenylate cyclase (AC), yields different effects in the calyx/cell-bodies and in the lobes, suggesting a differential and regionalized regulation of AC. Our results provide insights into the complex Ca²⁺-response in the MBs, leading to the conclusion that cAMP modulates the Ca²⁺-responses through both PKA-dependent and -independent mechanisms, the latter through CNG-channels.

Overexpression of CREB protein protects from tunicamycin-induced apoptosis in various rat cell types

Endoplasmic reticulum (ER) stress plays an essential role in unfolded protein response induced apoptosis contributing to several pathological conditions. Glycogen synthase kinase-3β (GSK-3β) plays a central role in several apoptotic signaling, including ER stress, as the active form of GSK-3β induces apoptosis. The phosphorylation of cAMP responsive element (CRE) binding protein (CREB) Ser-133 (S133) residue is the end-point of various signaling pathways, like growth factor signaling, while the Ser-129 (S129) residue is phosphorylated by GSK-3β. The significance of the ubiquitously expressed transcription factor CREB is demonstrated in prolonged, tunicamycin (TM)-induced ER stress in this study. In the experiments wild-type (wt) CREB, S129Ala, S133Ala or S129Ala-S133Ala mutant CREB expressing PC12 rat pheochromocytoma cell lines showed increased survival under TM-evoked prolonged ER stress compared to wtPC12 cells. After TM treatment ER stress was activated in all PC12 cell types. Lithium and SB-216763, the selective, well-known inhibitors of GSK-3β, decreased TM-induced apoptosis and promoted cell survival. The proapoptotic BH3-only Bcl-2 family member Bcl-2-interacting mediator of cell death (Bim) level was decreased in the different CREB overexpressing PC12 cells as a result of TM treatment. CREB overexpression also inhibited the sequestration of Bim protein from tubulin molecules, as it was demonstrated in wtPC12 cells. Transient expression of wtCREB diminished TM-induced apoptosis in wtPC12, Rat-1 and primary rat vascular smooth muscle cells. These findings demonstrate a novel role of CREB in different cell types as a potent protector against ER stress.

Prostaglandin E2 inhibits α-smooth muscle actin transcription during myofibroblast differentiation via distinct mechanisms of modulation of serum response factor and myocardin-related transcription factor-A

Differentiation of lung fibroblasts into contractile protein-expressing myofibroblasts by transforming growth factor-β1 (TGF-β1) is a critical event in the pathogenesis of pulmonary fibrosis. Transcription of the contractile protein α-smooth muscle actin (α-SMA) is mediated by the transcription factor serum-response factor (SRF) along with its co-activator, myocardin-related transcription factor-A (MRTF-A). The endogenous lipid mediator prostaglandin E2 (PGE2) exerts anti-fibrotic effects, including the inhibition of myofibroblast differentiation. However, the mechanism by which PGE2 inhibits α-SMA expression is incompletely understood. Here, we show in normal lung fibroblasts that PGE2 reduced the nuclear accumulation of MRTF-A·SRF complexes and consequently inhibited α-SMA promoter activation. It did so both by independently inhibiting SRF gene expression and nuclear import of MRTF-A. We identified that p38 MAPK is critical for TGF-β1-induced SRF gene expression and that PGE2 inhibition of SRF expression is associated with its ability to inhibit p38 activation. Its inhibition of MRTF-A import occurs via activation of cofilin 1 and inactivation of vasodilator-stimulated phosphoprotein. Similar effects of PGE2 on SRF gene expression were observed in fibroblasts from the lungs of patients with idiopathic pulmonary fibrosis. Thus, PGE2 is the first substance described to prevent myofibroblast differentiation by disrupting, via distinct mechanisms, the actions of both SRF and MRTF-A.

Calcitonin gene-related peptide regulates type IV hypersensitivity through dendritic cell functions

Dendritic cells (DCs) play essential roles in both innate and adaptive immune responses. In addition, mutual regulation of the nervous system and immune system is well studied. One of neuropeptides, calcitonin gene-related peptide (CGRP), is a potent regulator in immune responses; in particular, it has anti-inflammatory effects in innate immunity. For instance, a deficiency of the CGRP receptor component RAMP 1 (receptor activity-modifying protein 1) results in higher cytokine production in response to LPS (lipopolysaccharide). On the other hand, how CGRP affects DCs in adaptive immunity is largely unknown. In this study, we show that CGRP suppressed Th1 cell differentiation via inhibition of IL-12 production in DCs using an in vitro co-culture system and an in vivo ovalbumin-induced delayed-type hypersensitivity (DTH) model. CGRP also down-regulated the expressions of chemokine receptor CCR2 and its ligands CCL2 and CCL12 in DCs. Intriguingly, the frequency of migrating CCR2⁺ DCs in draining lymph nodes of RAMP1-deficient mice was higher after DTH immunization. Moreover, these CCR2⁺ DCs highly expressed IL-12 and CD80, resulting in more effective induction of Th1 differentiation compared with CCR2⁻ DCs. These results indicate that CGRP regulates Th1 type reactions by regulating expression of cytokines, chemokines, and chemokine receptors in DCs.

Signaling pathways involved in isoprostane-mediated fibrogenic effects in rat hepatic stellate cells

Despite evidence supporting a potential role for F2-isoprostanes (F2-IsoP's) in liver fibrosis, their signaling mechanisms are poorly understood. We have previously provided evidence that F2-IsoP's stimulate hepatic stellate cell (HSC) proliferation and collagen hyperproduction by activation of a modified form of isoprostane receptor homologous to the classic thromboxane receptor (TP). In this paper, we examined which signal transduction pathways are set into motion by F2-IsoP's to exert their fibrogenic effects. HSCs were isolated from rat liver, cultured to their activated myofibroblast-like phenotype, and then treated with the isoprostane 15-F2t-isoprostane (15-F2t-IsoP). Inositol trisphosphate (IP3) and adenosine 3',5'-cyclic monophosphate (cAMP) levels were determined using commercial kits. Mitogen-activated protein kinase (MAPK) and cyclin D1 expression was assessed by Western blotting. Cell proliferation and collagen synthesis were determined by measuring [(3)H]thymidine and [(3)H]proline incorporation, respectively. 15-F2t-IsoP elicited an activation of extracellular-signal-regulated kinase (ERK), p38 MAPK, and c-Jun NH2-terminal kinase (JNK), which are known to be also regulated by G-protein-coupled receptors. Preincubation with specific ERK (PD98059), p38 (SB203580), or JNK (SP600125) inhibitors prevented 15-F2t-IsoP-induced cell proliferation and collagen synthesis. 15-F2t-IsoP decreased cAMP levels within 30 min, suggesting binding to the TPβ isoform and activation of Giα protein. Also, 15-F2t-IsoP increased IP3 levels within a few minutes, suggesting that the Gq protein pathway is also involved. In conclusion, the fibrogenic effects of F2-IsoP's in HSCs are mediated by downstream activation of MAPKs, through TP binding that couples via both Gqα and Giα proteins. Targeting TP receptor, or its downstream pathways, may contribute to preventing oxidative damage in liver fibrosis.

Hypoxia inducible factor-1α mediates iron uptake which induces inflammatory response in amoeboid microglial cells in developing periventricular white matter through MAP kinase pathway

Iron accumulation occurs in tissues such as periventricular white matter (PWM) in response to hypoxic injuries, and microglial cells sequester excess iron following hypoxic exposure. As hypoxia has a role in altering the expression of proteins involved in iron regulation, this study was aimed at examining the interaction between hypoxia inducible factor (HIF)-1α and proteins involved in iron transport in microglial cells, and evaluating the mechanistic action of deferoxamine and KC7F2 (an inhibitor of HIF-1α) in iron mediated hypoxic injury. Treating the microglial cultures with KC7F2, led to decreased expression of transferrin receptor and divalent metal transporter-1. Administration of deferoxamine or KC7F2 to hypoxic microglial cells enhanced extracellular signal-regulated kinase (ERK) phosphorylation (p-ERK), but decreased the phosphorylation of p38 (p-p38). The increased p-ERK further phosphorylated the cAMP response element-binding protein (p-CREB) which in turn may have resulted in the increased mitogen activated protein kinase (MAPK) phosphatase 1 (MKP1), known to dephosphorylate MAPKs. Consistent with the decrease in p-p38, the production of pro-inflammatory cytokines TNF-α and IL-1β was reduced in hypoxic microglia treated with deferoxamine and SB 202190, an inhibitor for p38. This suggests that the anti-inflammatory effect exhibited by deferoxamine is by inhibition of p-p38 induced inflammation through the pERK-pCREB-MKP1 pathway, whereas that of KC7F2 requires further investigation. The present results suggest that HIF-1α may mediate iron accumulation in hypoxic microglia and KC7F2, similar to deferoxamine, might provide limited protection against iron induced PWMD.

Chronic psychological stress induces the accumulation of myeloid-derived suppressor cells in mice

Chronic psychological stress has been shown to adversely impact immune system functions and compromise host defenses against various infections. However, the underlying mechanisms remain elusive. Recent studies have demonstrated that myeloid-derived suppressor cells (MDSCs) play an important role in regulating immunity. It is of interest to explore whether or not chronic psychological stress plays immunosuppressive functions partially by inducing MDSCs accumulation. In this work, we report that chronic psychological stress led to the accumulation of CD11b+Gr1+ cells in the bone marrow of BALB/c mice. Repeated β-agonist infusion showed no such effect. However, β-adrenergic blockade, but not glucocorticoids blockade, partially reversed the accumulation of CD11b+Gr1+ cells under the condition of chronic psychological stress, suggesting catecholamines collaborate with other factors to induce the accumulation. Further exploration indicates that cyclooxygenase 2 (COX-2)-prostaglandin E2 (PGE2) loop might act downstream to induce the accumulation. A majority of the accumulated CD11b+Gr1+ cells were Ly6G+Ly6C(low) immature neutrophils, which inhibited cytokine release of macrophages as well as T cell responsiveness. Moreover, the accumulated CD11b+Gr1+ cells under the condition of chronic psychological stress expressed multiple inhibitory molecules. Taken together, our data demonstrate for the first time that chronic psychological stress induces MDSCs accumulation in mice, which can contribute to immunosuppression.

Cyclic AMP suppresses TGF-β-mediated adaptive Tregs differentiation through inhibiting the activation of ERK and JNK

The second messenger cAMP is involved in the regulation of many cellular activities partially through modulating the MAPK pathways. The role of cAMP in TGF-β-mediated adaptive Tregs differentiation remains elusive. In this work, we show that cAMP inhibits antigen-nonspecific proliferation of murine CD4+ T cells without significant promotion of apoptosis. Moreover, cAMP suppresses TGF-β-induced expression of forkhead transcription factor Foxp3. 6-MB-cAMP, a site-selective activator of PKA, mimics the role of cAMP in TGF-β-induced Foxp3 expression. Further exploration reveals that TGF-β activates ERK and JNK, but not p38. cAMP and 6-MB-cAMP block TGF-β-induced activation of ERK and JNK through transcription-independent manner and transcription-dependent manner, respectively. Since direct inhibition of ERK or JNK activity mimics the effects of cAMP during this process, our work suggests that cAMP suppresses TGF-β-mediated adaptive Tregs differentiation through, at least partially, inhibiting the activation of ERK and JNK.

Protective effect of survivin in Doxorubicin-induced cell death in h9c2 cardiac myocytes

BACKGROUND AND OBJECTIVES

Apoptosis has been known to be an important mechanism of doxorubicin-induced cardiotoxicity. Survivin, which belongs to the inhibitor of apoptosis protein family, is associated with apoptosis and alteration of the cardiac myocyte molecular pathways. Therefore, we investigated the anti-apoptotic effect and cellular mechanisms of survivin using a protein delivery system in a doxorubicin-induced cardiac myocyte injury model.

MATERIALS AND METHODS

We constructed a recombinant survivin which was fused to the protein transduction domain derived from HIV-TAT protein. In cultured H9c2 cardiac myocytes, TAT-survivin (1 µM) was added for 1 hour prior to doxorubicin (1 µM) treatment for 24 hours. Cell viability and apoptosis were evaluated by 2-(4,5-dimethyltriazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, caspase-3 activity, and terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling assay. We measured the expression levels of several apoptosis-related signal proteins.

RESULTS

The survivin level was significantly reduced in a dose dependent manner up to 1 µM of doxorubicin in concentration. Purified recombinant TAT-survivin protein was efficiently delivered to H9c2 cardiac myocytes, and its transduction showed an anti-apoptotic effect, demonstrated by reduced caspase-3 activity and the apoptotic index, concomitantly with increased cell viability against doxorubicin injury. The phosphorylation of p38 mitogen-activated protein (MAP) kinase and the release of Smac from mitochondria were suppressed and the expression levels of Bcl-2 and cAMP response element-binding protein (CREB), the transcription factor of Bcl-2, were recovered following TAT-survivin transduction, indicating that survivin had an anti-apoptotic effect against doxorubicin injury.

CONCLUSION

Our results suggest that survivin has a potentially cytoprotective effect against doxorubicin-induced cardiac myocyte apoptosis through mechanisms that involve a decrease in the phosphorylation of p38 MAP kinase, mitochondrial Smac release, and increased expression of Bcl-2 and CREB.

Prostaglandin E2 inhibits IL-23 and IL-12 production by human monocytes through down-regulation of their common p40 subunit

The heterodimeric cytokine IL-23 is important for the maintenance of Th17 cells, which are pivotal mediators of autoimmune diseases like rheumatoid arthritis, colitis, and multiple sclerosis. Prostaglandin E2 (PGE2) is a soluble regulator of inflammation that has both pro- and anti-inflammatory properties. PGE2 has been shown to elevate the IL-23 production by dendritic cells (DC). Monocytes are also producers of IL-23 but the effect of PGE2 on IL-23 production by human monocytes has hardly been investigated. We show here that PGE2 blocks the production of IL-23 by LPS-stimulated monocytes in an IL-10 and IL-1β independent manner. This effect was due to the down-regulation of the p40 subunit of IL-23 on mRNA and protein level. The p40 subunit is shared by IL-12 and, consistently, PGE2 also lowered the IL-12 production by monocytes. These effects of PGE2 were cAMP-dependent since the cAMP enhancer forskolin strongly reduced IL-23 and IL-12 production by monocytes. Taken together, PGE2 acts in an anti-inflammatory manner by lowering IL-23 production by monocytes while it has the opposite effect in DC. Our data may help to reconcile controversial point of views on the pro- and anti-inflammatory nature of PGE2 by making a strong case for a cell type-dependent function.

Isomenthone protects human dermal fibroblasts from TNF-α-induced death possibly by preventing activation of JNK and p38 MAPK

Cell death evoked by tumor necrosis factor-α (TNF-α) is regulated by the TNF-α receptor-associated death domain containing protein, which interacts with and activates apoptotic proteases triggering cell death. c-Jun N-terminal kinase (JNK) and p38 MAPK, induce the apoptotic program and are indispensible early elements in stress-induced apoptosis that control the release of cytochrome c. Isomenthone is a constituent of the essential oil of Mentha arvensis L. and is used as a fragrance and flavor in the cosmetic, drug, and food industries. In this study, we investigated the protective effects of isomenthone against TNF-α-induced cell death and its mechanism in human dermal fibroblasts. To understand the cytoprotective role of isomenthone, MTT and terminal deoxynucleotidyl transferase dUTP nick end labeling assays for cell viability and enzyme-linked immunosorbent assay analysis for the mechanistic study were performed. We found that isomenthone inhibited the TNF-α-mediated reduction in cell viability and inhibited the increase in apoptosis under a serum-free condition. Isomenthone also blocked the JNK and p38 MAPK pathways and downstream apoptotic events. These results indicate that isomenthone has the potential to protect fibroblasts against TNF-α-induced cell death under a serum-deprived condition by blocking activation of the JNK and p38 MAPK pathways and downstream apoptotic events.

Unconventional functions of microtubule motors

With the functional characterization of proteins advancing at fast pace, the notion that one protein performs different functions - often with no relation to each other - emerges as a novel principle of how cells work. Molecular motors are no exception to this new development. Here, we provide an account on recent findings revealing that microtubule motors are multifunctional proteins that regulate many cellular processes, in addition to their main function in transport. Some of these functions rely on their motor activity, but others are independent of it. Of the first category, we focus on the role of microtubule motors in organelle biogenesis, and in the remodeling of the cytoskeleton, especially through the regulation of microtubule dynamics. Of the second category, we discuss the function of microtubule motors as static anchors of the cargo at the destination, and their participation in regulating signaling cascades by modulating interactions between signaling proteins, including transcription factors. We also review atypical forms of transport, such as the cytoplasmic streaming in the oocyte, and the movement of cargo by microtubule fluctuations. Our goal is to provide an overview of these unexpected functions of microtubule motors, and to incite future research in this expanding field.

Lethality in a murine model of pulmonary anthrax is reduced by combining nuclear transport modifier with antimicrobial therapy

BACKGROUND

In the last ten years, bioterrorism has become a serious threat and challenge to public health worldwide. Pulmonary anthrax caused by airborne Bacillus anthracis spores is a life-threatening disease often refractory to antimicrobial therapy. Inhaled spores germinate into vegetative forms that elaborate an anti-phagocytic capsule along with potent exotoxins which disrupt the signaling pathways governing the innate and adaptive immune responses and cause endothelial cell dysfunction leading to vascular injury in the lung, hypoxia, hemorrhage, and death.

METHODS/PRINCIPAL FINDINGS

Using a murine model of pulmonary anthrax disease, we showed that a nuclear transport modifier restored markers of the innate immune response in spore-infected animals. An 8-day protocol of single-dose ciprofloxacin had no significant effect on mortality (4% survival) of A/J mice lethally infected with B. anthracis Sterne. Strikingly, mice were much more likely to survive infection (52% survival) when treated with ciprofloxacin and a cell-penetrating peptide modifier of host nuclear transport, termed cSN50. In B. anthracis-infected animals treated with antibiotic alone, we detected a muted innate immune response manifested by cytokines, tumor necrosis factor alpha (TNFα), interleukin (IL)-6, and chemokine monocyte chemoattractant protein-1 (MCP-1), while the hypoxia biomarker, erythropoietin (EPO), was greatly elevated. In contrast, cSN50-treated mice receiving ciprofloxacin demonstrated a restored innate immune responsiveness and reduced EPO level. Consistent with this improvement of innate immunity response and suppression of hypoxia biomarker, surviving mice in the combination treatment group displayed minimal histopathologic signs of vascular injury and a marked reduction of anthrax bacilli in the lungs.

CONCLUSIONS

We demonstrate, for the first time, that regulating nuclear transport with a cell-penetrating modifier provides a cytoprotective effect, which enables the host's immune system to reduce its susceptibility to lethal B. anthracis infection. Thus, by combining a nuclear transport modifier with antimicrobial therapy we offer a novel adjunctive measure to control florid pulmonary anthrax disease.

Early intensive insulin therapy attenuates the p38 pathway in the renal cortex and indices of nephropathy in diabetic rats

In this rodent study, we compared the effects of early versus late intensive insulin therapy on diabetic nephropathy and potential causal mechanisms. Diabetes was induced in rats by high-fat diet and low-dose streptozotocin. Intensive insulin therapy was initiated in the early intensive insulin therapy groups as soon as diabetes was confirmed and lasted for 8 (8wEI group) and 16 weeks (16wEI group). In the late insulin therapy group (LI group), intensive insulin treatment was initiated 8 weeks later and lasted for 8 weeks. Age-matched diabetic rats (8wDM group and 16wDM group) and non-diabetic rats (8wNC group and 16wNC group) served as controls. Histological analysis, real-time PCR, and western blot were performed in renal cortex specimens. Glomerular hypertrophy and mesangial matrix expansion were prominent in the 16wDM and LI groups while the EI groups remained normal and similar to the 16wNC group. Western blots revealed that p38 MAPK activities in the EI groups decreased significantly, whereas the level in the LI group was markedly higher than the 16wEI group, and not different from the DM groups. Activities of MKK3/6, CREB and MKP-1 proteins as well as CREB and MKP-1 mRNA showed a similar pattern. Therefore, we concluded that early intensive insulin treatment and attainment of good glycemic control counteracted some renal molecular pathways associated with epigenetic metabolic memory to minimize risk of diabetic nephropathy. However, late insulin therapy did not abrogate the increased renal cortical p38 MAPK pathway activation in diabetic rats and led to glomerular hypertrophy and extracellular matrix expansion.

Cyclic AMP: a selective modulator of NF-κB action

It has been known for several decades that cyclic AMP (cAMP), a prototypical second messenger, transducing the action of a variety of G-protein-coupled receptor ligands, has potent immunosuppressive and anti-inflammatory actions. These actions have been attributed in part to the ability of cAMP-induced signals to interfere with the function of the proinflammatory transcription factor Nuclear Factor-kappaB (NF-κB). NF-κB plays a crucial role in switching on the gene expression of a plethora of inflammatory and immune mediators, and as such is one of the master regulators of the immune response and a key target for anti-inflammatory drug design. A number of fundamental molecular mechanisms, contributing to the overall inhibitory actions of cAMP on NF-κB function, are well established. Paradoxically, recent reports indicate that cAMP, via its main effector, the protein kinase A (PKA), also promotes NF-κB activity. Indeed, cAMP actions appear to be highly cell type- and context-dependent. Importantly, several novel players in the cAMP/NF-κB connection, which selectively direct cAMP action, have been recently identified. These findings not only open up exciting new research avenues but also reveal novel opportunities for the design of more selective, NF-κB-targeting, anti-inflammatory drugs.

Regulation of Sertoli cell activin A and inhibin B by tumour necrosis factor α and interleukin 1α: interaction with follicle-stimulating hormone/adenosine 3',5'-cyclic phosphate signalling

Regulation of crucial events during spermatogenesis involves dynamic changes in cytokine production and interactions across the cycle of the seminiferous epithelium. Regulation of activin A and inhibin B production by the inflammatory cytokines, tumour necrosis factor α (TNFα) and interleukin 1α (IL1α), alone and in conjunction with FSH or a cAMP analogue (dibutyryl cAMP), was examined in cultures of Sertoli cells from 20-day old rats. Both TNFα and IL1α stimulated activin A secretion and expression of its subunit (β(A)) mRNA, and suppressed inhibin B secretion and expression of its subunit (α and β(B)) mRNAs. The actions of TNFα and IL1α were opposed by FSH and dibutyryl cAMP. Both cytokines inhibited FSH/dibutyryl cAMP-stimulated inhibin B secretion and mRNA expression as well as stem cell factor mRNA expression. Both cytokines also inhibited FSH-induced cAMP production, and reduced baseline FSH receptor mRNA expression. These data highlight the reciprocal relationship that exists between FSH/cAMP signalling and inflammatory cytokine signalling pathways in the control of Sertoli cell function, and production of activin A/inhibin B in particular. It is anticipated that these interactions play important roles in the fine control of events during the cycle of the seminiferous epithelium and in the inhibition of spermatogenesis during inflammation.

Toll-like receptors and signalling in spermatogenesis and testicular responses to inflammation--a perspective

It is self-evident that infection and inflammation in the reproductive tract can inhibit male fertility, but the observation that fertility may also be compromised by systemic inflammation and disease is more difficult to explain. Recent studies implicating microbial pattern-recognition receptors, such as the Toll-like receptors (TLRs), as well as inflammatory cytokines and their signalling pathways, in testicular function have cast new light on this mysterious link between infection/inflammation and testicular dysfunction. It is increasingly evident that signalling pathways normally involved in controlling inflammation play fundamental roles in regulating Sertoli cell activity and responses to reproductive hormones, in addition to promoting immune responses within the testis. Many of the negative effects of inflammation on spermatogenesis may be attributed to elevated production of inflammation-related gene products within the circulation and the testis, which subsequently exert disruptive effects on spermatogenic cell development and survival, as well as the ability of the Sertoli cells to provide support for spermatogenesis. These interactions have important implications for testicular dysfunction and disease, and may eventually provide new opportunities for therapeutic interventions.

Activation of p38 mitogen-activated protein kinase by norepinephrine in T-lineage cells

The catecholamine norepinephrine (NE) stimulates T lymphocytes through a beta-adrenergic receptor (βAR)/adenylyl cyclase (AC)/cyclic AMP (cAMP)/protein kinase A (PKA) pathway, leading to altered cell responsiveness and apoptosis. p38 Mitogen-activated protein kinase (MAPK), a major intracellular signalling mediator for cellular and environmental stressors, is involved in the production of immune modulators and in the regulation of T-cell development, survival and death. In these studies we investigated the relationship among NE signalling, p38 MAPK activity and T-cell death. We showed that NE stimulation of BALB/c mouse thymocytes and S49 thymoma cells selectively increases the dual phosphorylation and activity of p38α MAPK. p38 MAPK activation involves the βAR, Gs protein, AC, cAMP and PKA, as determined through the use of a βAR antagonist, activators of AC and cAMP, and S49 clonal mutants deficient in Gs and PKA. Dual phosphorylation of p38 MAPK is also dependent on its own catalytic activity. Inhibition of p38 MAPK activity revealed its involvement in cAMP-mediated activating transcription factor-2 (ATF-2) phosphorylation, Fas ligand messenger RNA (mRNA) up-regulation, and cell death. These results identify a mechanism through which NE stimulation of the βAR/Gs/PKA pathway activates p38 MAPK, which can be potentiated by autophosphorylation, and leads to changes in T-cell dynamics, in part through the regulation of Fas ligand mRNA expression.

Elevated cAMP opposes (TNF-alpha)-induced loss in the barrier integrity of corneal endothelium

PURPOSE

Elevated cyclic adenosine monophosphate (cAMP) enhances the barrier integrity of the corneal endothelium and thereby facilitates stromal hydration control, which is necessary for corneal transparency. This study investigates whether elevated cAMP is effective against the tumor necrosis factor-alpha (TNF-alpha)-induced loss of barrier integrity in monolayers of bovine corneal endothelial cells (BCEC).

METHODS

BCEC in primary culture were used for the study. Trans-endothelial electrical resistance (TER), a measure of barrier integrity, was determined by electrical cell-substrate impedance sensing. The changes were also ascertained by measuring paracellular permeability to fluorescein isothiocyanate (FITC)-dextran (10 kDa) across cells grown on porous culture inserts, and by immunofluorescence imaging of the apical junctional complex (AJC). The activation of p38 MAP kinase was assessed using western blotting.

RESULTS

Co-treatment with forskolin, which activates adenylate cyclase, and rolipram, which inhibits cAMP-dependent phosphodiesterase PDE4, reduced the TNF-alpha-induced increase in the flux of FITC-dextran. Similar co-treatment also prevented the TNF-alpha-induced disorganization of zona occludens-1 (ZO-1) and cadherins at the AJC. Co-treatment, as well pre-treatment, with forskolin plus rolipram prevented the TNF-alpha-induced decrease in TER. The influence of the agents was significant after 12 h of exposure to the cytokine. This effect was also mimicked by A2B agonists, adenosine and 5'-N-ethylcarboxamidoadenosine (NECA), which are known to mobilize cAMP in BCEC. Elevated cAMP also inhibited the cytokine-induced activation of p38 MAP kinase, and further blocked the disassembly of microtubules as well as the disruption of the PAMR (peri-junctional actomyosin ring) at the AJC.

CONCLUSIONS

These results suggest that elevated cAMP opposes the TNF-alpha-induced loss in barrier integrity of the corneal endothelium. This effect follows inhibition of the cytokine-induced activation of p38 MAP kinase and its downstream signaling involved in the disruption of AJC and PAMR, as well as the disassembly of microtubules.

Reciprocal regulation of aquaporin-2 abundance and degradation by protein kinase A and p38-MAP kinase

Arginine-vasopressin (AVP) modulates the water channel aquaporin-2 (AQP2) in the renal collecting duct to maintain homeostasis of body water. AVP binds to vasopressin V2 receptors (V2R), increasing cAMP, which promotes the redistribution of AQP2 from intracellular vesicles into the plasma membrane. cAMP also increases AQP2 transcription, but whether altered degradation also modulates AQP2 protein levels is not well understood. Here, elevation of cAMP increased AQP2 protein levels within 30 minutes in primary inner medullary collecting duct (IMCD) cells, in human embryonic kidney (HEK) 293 cells ectopically expressing AQP2, and in mouse kidneys. Accelerated transcription or translation did not explain this increase in AQP2 abundance. In IMCD cells, cAMP inhibited p38-mitogen-activated protein kinase (p38-MAPK) via activation of protein kinase A (PKA). Inhibition of p38-MAPK associated with decreased phosphorylation (serine 261) and polyubiquitination of AQP2, preventing proteasomal degradation. Our results demonstrate that AVP enhances AQP2 protein abundance by altering its proteasomal degradation through a PKA- and p38-MAPK-dependent pathway.

Differential roles of PKA and Epac on the production of cytokines in the endotoxin-stimulated primary cultured microglia

To further understand the anti-inflammatory effect of adenosine cyclic 3',5'-monophosphate (cAMP), we examined the effect of protein kinase A (PKA) and cAMP-responsive guanine nucleotide exchange factor (Epac) on the transcription and production of cytokines and on the activity of mitogen-activated protein kinases (MAPK) p38 and glycogen synthase kinase-3β (GSK-3β) in endotoxin-treated rat primary cultured microglia. The PKA specific agonist N6-benzoyladenosine-3,5-cAMP (6-Bnz-cAMP) not only inhibited the transcription and production of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) but also enhanced the transcription and expression of IL-10, while the Epac selective analog 8-(4-chlorophenylthio)-2-O-methyladenosine-3,5-cAMP (8-pCPT-2'-O-Me-cAMP) merely repressed the TNF-α expression. Western blots assays indicated that 6-Bnz-cAMP significantly inhibited lipopolysaccharide-induced activation of both p38 and GSK-3β in a dose-dependent manner; in contrast, 8-pCPT-2'-O-Me-cAMP only slightly repressed GSK-3β activity at large doses. Pretreatment with H-89, a specific PKA antagonist, could completely reverse the effect of 6-Bnz-cAMP on cytokines expressions and kinases activities but had no effect on the performance of 8-pCPT-2'-O-Me-cAMP. Our findings indicate that PKA and Epac exert differential effect on the expression of inflammatory cytokines such as TNF-α, IL-1β, and IL-10, possibly owing to the different effects on the downstream effectors, MAPK p38, and GSK-3β.

Adenosine receptor A2A deficiency in leukocytes increases arterial neointima formation in apolipoprotein E-deficient mice

OBJECTIVE

To use the mice deficient in both adenosine receptor A(2A)(A(2A)R(-/-)) and apolipoprotein E (apoE(-/-)) to investigate the role of A(2A)R in mediating the interactions of leukocytes with injured arterial walls and the formation of arterial neointima induced by a guide wire.

METHODS AND RESULTS

In apoE(-/-) mice, A(2A)R deficiency increased the size of the arterial neointima in injured carotid arteries by 83%. Arterial neointima formation was also enhanced in chimeric mice that underwent bone marrow transplantation (these mice lacked A(2A)R in their bone marrow-derived cells). Epifluorescence intravital microscopy showed that neutrophil rolling and adherence to the injured arterial area were enhanced by 80% and 110% in A(2A)R(-/-)/apoE(-/-) mice, respectively. This phenomenon occurred even though the protein levels of homing molecules on A(2A)R-deficient neutrophils were unchanged from those of wild-type neutrophils. A(2A)R-deficient neutrophils exhibited an increase in the phosphorylation of p38 mitogen-activated protein kinase, P-selectin glycoprotein ligand-1 (PSGL-1) clustering, and the affinity of b(2) integrins. The inhibition of p38 phosphorylation abrogated the increased PSGL-1 clustering and beta(2) integrin affinity, thus reversing the increased homing ability of A(2A)R-deficient leukocytes.

CONCLUSION

A(2A)R plays a complex role in inflammation and tissue injury. The deficiency of A(2A)R enhances the homing ability of leukocytes and increases the formation of the arterial neointima after injury. A(2A)R antagonists are being tested for the treatment of neurodegenerative and other chronic diseases. An evaluation of the effect of A(2A)R antagonists on arterial restenosis after arterial angioplasty should be conducted.

Farnesol induces hydrogen peroxide resistance in Candida albicans yeast by inhibiting the Ras-cyclic AMP signaling pathway

Farnesol, a Candida albicans cell-cell signaling molecule that participates in the control of morphology, has an additional role in protection of the fungus against oxidative stress. In this report, we show that although farnesol induces the accumulation of intracellular reactive oxygen species (ROS), ROS generation is not necessary for the induction of catalase (Cat1)-mediated oxidative-stress resistance. Two antioxidants, alpha-tocopherol and, to a lesser extent, ascorbic acid effectively reduced intracellular ROS generation by farnesol but did not alter farnesol-induced oxidative-stress resistance. Farnesol inhibits the Ras1-adenylate cyclase (Cyr1) signaling pathway to achieve its effects on morphology under hypha-inducing conditions, and we demonstrate that farnesol induces oxidative-stress resistance by a similar mechanism. Strains lacking either Ras1 or Cyr1 no longer exhibited increased protection against hydrogen peroxide upon preincubation with farnesol. While we also observed the previously reported increase in the phosphorylation level of Hog1, a known regulator of oxidative-stress resistance, in the presence of farnesol, the hog1/hog1 mutant did not differ from wild-type strains in terms of farnesol-induced oxidative-stress resistance. Analysis of Hog1 levels and its phosphorylation states in different mutant backgrounds indicated that mutation of the components of the Ras1-adenylate cyclase pathway was sufficient to cause an increase of Hog1 phosphorylation even in the absence of farnesol or other exogenous sources of oxidative stress. This finding indicates the presence of unknown links between these signaling pathways. Our results suggest that farnesol effects on the Ras-adenylate cyclase cascade are responsible for many of the observed activities of this fungal signaling molecule.

Nicotine enhances murine airway contractile responses to kinin receptor agonists via activation of JNK- and PDE4-related intracellular pathways

Background

Nicotine plays an important role in cigarette-smoke-associated airway disease. The present study was designed to examine if nicotine could induce airway hyperresponsiveness through kinin receptors, and if so, explore the underlying mechanisms involved.

Methods

Murine tracheal segments were cultured for 1, 2 or 4 days in serum-free DMEM medium in presence of nicotine (1 and 10 μM) or vehicle (DMSO). Contractile responses induced by kinin B₁ receptor agonist, des-Arg⁹-bradykinin, and B₂ receptor agonist, bradykinin, were monitored with myographs. The B₁ and B₂ receptor mRNA expressions were semi-quantified using real-time PCR and their corresponding protein expressions assessed with confocal-microscopy-based immunohistochemistry. Various pharmacological inhibitors were used for studying intracellular signaling pathways.

Results

Four days of organ culture with nicotine concentration-dependently increased kinin B₁ and B₂ receptor-mediated airway contractions, without altering the kinin receptor-mediated relaxations. No such increase was seen at day 1 or day 2. The airway contractile responses to 5-HT, acetylcholine and endothelin receptor agonists remained unaffected by nicotine. Two different neuronal nicotinic receptor antagonists MG624 and hexamethonium blocked the nicotine-induced effects. The enhanced contractile responses were accompanied by increased mRNA and protein expression for both kinin receptors, suggesting the involvement of transcriptional mechanisms. Confocal-microscopy-based immunohistochemistry showed that 4 days of nicotine treatment induced activation (phosphorylation) of c-Jun N-terminal kinase (JNK), but not extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38. Inhibition of JNK with its specific inhibitor SP600125 abolished the nicotine-induced effects on kinin receptor-mediated contractions and reverted the enhanced receptor mRNA expression. Administration of phosphodiesterase inhibitors (YM976 and theophylline), glucocorticoid (dexamethasone) or adenylcyclase activator (forskolin) suppressed the nicotine-enhanced airway contractile response to des-Arg⁹-bradykinin and bradykinin.

Conclusions

Nicotine induces airway hyperresponsiveness via transcriptional up-regulation of airway kinin B₁ and B₂ receptors, an effect mediated via neuronal nicotinic receptors. The underlying molecular mechanisms involve activation of JNK- and PDE4-mediated intracellular inflammatory signal pathways. Our results might be relevant to active and passive smokers suffering from airway hyperresponsiveness, and suggest new therapeutic targets for the treatment of smoke-associated airway disease.

Selective unresponsiveness to the inhibition of p38 MAPK activation by cAMP helps L929 fibroblastoma cells escape TNF-alpha-induced cell death

Background

The cyclic AMP (cAMP) signaling pathway has been reported to either promote or suppress cell death, in a cell context-dependent manner. Our previous study has shown that the induction of dynein light chain (DLC) by cAMP response element-binding protein (CREB) is required for cAMP-mediated inhibition of mitogen-activated protein kinase (MAPK) p38 activation in fibroblasts, which leads to suppression of NF-κB activity and promotion of tumor necrosis factor-α (TNF-α)-induced cell death. However, it remains unknown whether this regulation is also applicable to fibroblastoma cells.

Methods

Intracellular cAMP was determined in L929 fibroblastoma cells after treatment of the cells with various cAMP elevation agents. Effects of cAMP in the presence or absence of the RNA synthesis inhibitor actinomycin D or small interfering RNAs (siRNAs) against CREB on TNF-α-induced cell death in L929 cells were measured by propidium iodide (PI) staining and subsequent flow cytomety. The activation of p38 and c-Jun N-terminal protein kinase (JNK), another member of MAPK superfamily, was analyzed by immunoblotting. JNK selective inhibitor D-JNKi1 and p38 selective inhibitor SB203580 were included to examine the roles of JNK and p38 in this process. The expression of DLC or other mediators of cAMP was analyzed by immunoblotting. After ectopic expression of DLC with a transfection marker GFP, effects of cAMP on TNF-α-induced cell death in GFP+ cells were measured by PI staining and subsequent flow cytomety.

Results

Elevation of cAMP suppressed TNF-α-induced necrotic cell death in L929 fibroblastoma cells via CREB-mediated transcription. The pro-survival role of cAMP was associated with selective unresponsiveness of L929 cells to the inhibition of p38 activation by cAMP, even though cAMP significantly inhibited the activation of JNK under the same conditions. Further exploration revealed that the induction of DLC, the major mediator of p38 inhibition by cAMP, was impaired in L929 cells. Enforced inhibition of p38 activation by using p38 specific inhibitor or ectopic expression of DLC reversed the protection of L929 cells by cAMP from TNF-α-induced cell death.

Conclusion

These data suggest that the lack of a pro-apoptotic pathway in tumor cells leads to a net survival effect of cAMP.

Inactivation of the adenosine A2A receptor protects apolipoprotein E-deficient mice from atherosclerosis

BACKGROUND

Atherosclerosis is a chronic inflammatory disease of the arterial vessel wall. The A(2A) receptor (A(2A)R) plays a central role in many antiinflammatory effects of adenosine. However, the role of A(2A)R in atherosclerosis is not clear.

METHODS AND RESULTS

The knockout of A(2A)R in apolipoprotein E-deficient (Apoe(-/-)/A(2A)R(-/-)) mice led to an increase in body weight and levels of blood cholesterol and proinflammatory cytokines, as well as the inflammation status of atherosclerotic lesions. Unexpectedly, Apoe(-/-)/A(2A)R(-/-) mice developed smaller lesions, as did chimeric Apoe(-/-) mice lacking A(2A)R in bone marrow-derived cells (BMDCs). The lesions of those mice exhibited a low density of foam cells and the homing ability of A(2A)R-deficient monocytes did not change. Increased foam cell apoptosis was detected in atherosclerotic lesions of Apoe(-/-)/A(2A)R(-/-) mice. In the absence of A(2A)R, macrophages incubated with oxidized LDL or in vivo-formed foam cells also exhibited increased apoptosis. A(2A)R deficiency in foam cells resulted in an increase in p38 mitogen-activated protein kinase (MAPK) activity. Inhibition of p38 phosphorylation abrogated the increased apoptosis of A(2A)R-deficient foam cells.

CONCLUSIONS

Inactivation of A(2A)R, especially in BMDCs, inhibits the formation of atherosclerotic leisons, suggesting that A(2A)R inactivation may be useful for the treatment of atherosclerosis.

Ligusticum chuanxiong as a potential neuroprotectant for preventing serum deprivation-induced apoptosis in rat pheochromocytoma cells: functional roles of mitogen-activated protein kinases

ETHNOPHARMACOLOGICAL RELEVANCE

Ligusticum chuanxiong (LC) as a common component in many traditional Chinese medicinal formulas and decoctions has been used to treat different central nervous diseases, suggesting a neuroprotective function.

AIM OF THE STUDY

To investigate the functional roles of mitogen-activated protein kinases (MAPKs) in mediating the neuroprotection of LC.

MATERIALS AND METHODS

Different extractions of LC were applied with or without MAPK inhibitor to test their protection against serum deprivation-induced apoptosis in rat neuronal-like pheochromocytoma (PC12) cells as revealed by an MTT assay or Hoechst staining. Western blot was used to identify the activations of MAPKs.

RESULTS

The most effective butanol extraction (LC-BuOH) was used in the following experiments. LC-BuOH reversed serum deprivation-induced decreased phosphorylation of extracellular signal-regulated kinase (ERK) and increased phosphorylation of c-Jun NH(2)-terminal kinase (JNK) and p38, the family of MAPKs. A PKA inhibitor, blocked the protection of LC-BuOH and partially blocked LC-BuOH-induced alterations in MAPKs, suggesting that the LC-BuOH regulates MAPKs through both PKA-dependent and -independent pathways. Although PD 98059, an inhibitor of MEK which activates ERK, blocked LC-BuOH-induced ERK phosphorylation, it did not block the protection of LC-BuOH.

CONCLUSIONS

LC-BuOH mediates protection by suppressing JNK/p38 instead of activating ERK activity.

The adenylyl cyclase-cAMP system suppresses TARC/CCL17 and MDC/CCL22 production through p38 MAPK and NF-kappaB in HaCaT keratinocytes

Patients with atopic dermatitis (AD) have significantly reduced plasma cAMP levels, and the cAMP level is correlated with the immunopathogenesis of AD. The production of thymus and activation-regulated chemokine (TARC/CCL17) and macrophage-derived chemokine (MDC/CCL22) in keratinocytes is significantly enhanced in patients with AD. In the present study, we investigated the in vitro effects of the adenylyl cyclase-cAMP system on IFN-gamma and TNF-alpha-stimulated production of TARC and MDC in human HaCaT keratinocytes. Both forskolin (a direct activator of adenylyl cyclase) and dibutyryl-cAMP (DBcAMP, a permeable analog of cAMP) suppressed production of TARC and MDC in parallel with the activation of NF-kappaB in IFN-gamma and TNF-alpha-stimulated HaCaT cells. Moreover, inhibition of NF-kappaB suppressed TARC and MDC production induced by IFN-gamma plus TNF-alpha. However, dideoxyforskolin, a forskolin derivative that does not activate cAMP, failed to suppress the secretion of these chemokines. An inhibitor of p38 MAPK suppressed the production of TARC and MDC in parallel to the activation of NF-kappaB in HaCaT cells. Of note, the IFN-gamma plus TNF-alpha-stimulated activation of p38 MAPK was suppressed following incubation with forskolin or DBcAMP alone. These results indicate that the adenylyl cyclase-cAMP system has an inhibitory role in IFN-gamma plus TNF-alpha-stimulated production of TARC and MDC in HaCaT keratinocytes by inhibiting NF-kappaB activation through p38 MAPK pathway, implying that the adenylyl cyclase-cAMP system could be a candidate therapeutic target of Th2-skewed skin inflammation such as AD.

Noradrenaline reduces the ATP-stimulated phosphorylation of p38 MAP kinase via beta-adrenergic receptors-cAMP-protein kinase A-dependent mechanism in cultured rat spinal microglia

To elucidate the involvement of the noradrenergic system in the regulation of spinal microglial activity, we examined the effects of noradrenaline (NA) on the phosphorylation of three MAP kinases (extracellular signal-regulated kinase (ERK), p38, or c-Jun N-terminal kinase (JNK)) stimulated by ATP in rat cultured spinal microglia using Western blotting. ATP (100 microM) quickly induced the phosphorylation of three MAP kinases and MKK3/6, which are upstream kinases of p38. Under these conditions, NA inhibited only the ATP-stimulated phosphorylation of p38 in a time (30-60 min)- and dose (10-100 microM)-dependent manner, but did not affect those of ERK, JNK, or MKK3/6. The inhibitory action of NA was completely reversed by pretreatment with propranolol, an antagonist for beta-adrenoceptors, or both atenolol and ICI118551, selective antagonists for beta1 and beta2, respectively. Treatment with dibutyryl cAMP or the selective activator of PKA mimicked the inhibitory effect of NA. Furthermore, treatment with KT5720, an inhibitor of protein kinase A, completely blocked the action of NA. These data suggest that NA could control the activation of p38 through the beta1/2-adrenergic pathways, which include the production of cAMP and the activation of PKA. Simultaneously, we found that NA also markedly inhibited the ATP-induced increase in the expression of tumor necrosis factor (TNF)-alpha mRNA through beta-adrenergic pathways. Furthermore, preincubation with either actinomycin D or cyclohexamide, general inhibitors of transcription or protein synthesis, respectively, almost completely blocked the inhibitory action of NA on the ATP-stimulated phosphorylation of p38. These results suggest that de novo synthesis of certain factors by NA through beta-adrenoceptors would participate in the modulation of p38 activity. Thus, the inhibitory system via beta1/2-adrenergic pathways in spinal microglia appears to have an important role in the modulation of microglial functions through the downregulation of p38 activity.

p38 MAPK contributes to CD54 expression and the enhancement of phagocytic activity during macrophage development

p38 is a subfamily of the mitogen-activated protein kinase (MAPK) superfamily with four isoforms. It has been well established that p38 plays a central role in the production of inflammatory molecules and is therefore required for the activation of macrophages in response to inflammatory stimuli. However, little is known about the roles of p38 in macrophage development. The difficulty to get mice deficient in multiple p38 isoforms complicates the study of p38 in macrophage development. With the model of bone marrow-derived murine macrophages and highly selective p38alpha/beta inhibitors SB203580 and SB239063, here we report that macrophage colony-stimulating factor (M-CSF) induces p38 activation during macrophage development. Inhibition of p38 activity showed minor effects on macrophage proliferation or survival, and did not block CD14, F4/80 expression. However, p38 inhibitors resulted in a significant reduction in CD54 expression and impaired phagocytic activity. Taken together, our data suggest that p38 contributes to macrophage development.

Cyclic AMP inhibits JNK activation by CREB-mediated induction of c-FLIP(L) and MKP-1, thereby antagonizing UV-induced apoptosis

The cyclic AMP (cAMP) signaling pathway has been reported to either promote or suppress apoptosis, in a cell context-dependent manner. Our previous study has shown that cAMP, by protein kinase A (PKA)-cAMP response element-binding protein (CREB)-dynein light chain (DLC) pathway, negatively regulates mitogen-activated protein kinase p38 activation, thereby contributing to tumor necrosis factor (TNF)-alpha-induced apoptosis in certain types of cells. However, it remains largely unknown how cAMP suppresses apoptosis. Here we report that cAMP antagonized UV-induced apoptosis in Rat-1 and NIH 3T3 cells. Despite that cAMP significantly suppressed UV-induced p38 activation, inhibition of p38 activity showed no significant effect on UV-induced cell death in both cell lines. Further studies revealed that cAMP antagonized UV-induced apoptosis by inhibition of c-Jun N-terminal protein kinase (JNK) activation. The induction of the long form of cellular FLICE-inhibitory protein (c-FLIP(L)) and mitogen-activated protein kinase phosphatase-1 (MKP-1), but not DLC and p21(WAF1) by CREB was required for cAMP-mediated inhibition of JNK activation. The suppression by cAMP of UV-induced apoptosis was reversed by c-FLIP(L) small-interfering RNA (siRNA) or MKP-1 siRNA, which released the inhibition of JNK activation by cAMP. Thus, our results provide a molecular mechanism by which cAMP suppresses JNK activation and antagonizes apoptosis.

Structure and Dynamics of LC8 Complexes with KXTQT-Motif Peptides: Swallow and Dynein Intermediate Chain Compete for a Common Site

The dynein light chain LC8 is an integral subunit of the cytoplasmic dynein motor complex that binds directly to and promotes assembly of the dynein intermediate chain (IC). LC8 interacts also with a variety of putative dynein cargo molecules such as Bim, a proapoptotic Bcl2 family protein, which have the KXTQT recognition sequence and neuronal nitric oxide synthase (nNOS), which has the GIQVD fingerprint but shares the same binding grooves at the LC8 dimer interface. The work reported here investigates the interaction of LC8 with IC and a putative cargo, Swallow, which share the KXTQT recognition sequence, and addresses the apparent paradox of how LC8, as part of dynein, mediates binding to cargo. The structures of Drosophila LC8 bound to peptides from IC and Swallow solved by X-ray diffraction show that the IC and Swallow peptides bind in the same grooves at the dimer interface. Differences in flexibility between bound and free LC8 were evaluated from hydrogen isotope exchange experiments using heteronuclear NMR spectroscopy. Peptide binding causes an increase in protection from exchange primarily in residues that interact directly with the peptide, such as the beta-strand intertwined at the interface and the N-terminal end of helix alpha2. There is considerably more protection upon Swallow binding, consistent with tighter binding relative to IC. Comparison with the LC8/nNOS complex shows how both the GIQVD and KXTQT fingerprints are recognized in the same groove. The similar structures of LC8/IC and LC8/Swa and the tighter binding of Swallow call into question the role for LC8 as a cargo adaptor protein, and suggest that binding of LC8 to Swallow serves another function, possibly that of a dimerization engine, which is independent of its role in dynein.

Innate immunity of the newborn: basic mechanisms and clinical correlates

The fetus and newborn face a complex set of immunological demands, including protection against infection, avoidance of harmful inflammatory immune responses that can lead to pre-term delivery, and balancing the transition from a sterile intra-uterine environment to a world that is rich in foreign antigens. These demands shape a distinct neonatal innate immune system that is biased against the production of pro-inflammatory cytokines. This bias renders newborns at risk of infection and impairs responses to many vaccines. This Review describes innate immunity in newborns and discusses how this knowledge might be used to prevent and treat infection in this vulnerable population.