Inhibition of the p38 pathway upregulates macrophage JNK and ERK activities, and the ERK, JNK, and p38 MAP kinase pathways are reprogrammed during differentiation of the murine myeloid M1 cell line

Melatonin alleviates high-fat-diet-induced dry eye by regulating macrophage polarization via IFT27 and lowering ERK/JNK phosphorylation

Dry eye disease is the most common ocular surface disease globally, requiring a more effective treatment. We observed that a high-fat diet induced macrophage polarization to M1 and further induced inflammation in the meibomian and lacrimal glands. A four-week treatment with melatonin (MLT) eye drops can regulate macrophage polarization and alleviate dry eye signs. To investigate the therapeutic effects and mechanisms of action of MLT on high-fat-diet-induced dry eye disease in mice, RAW 264.7 cells pretreated with LPS and/or MLT underwent digital RNA with the perturbation of genes sequencing (DRUG-seq). Results showed that IFT27 was up-regulated, and MAPK pathways were suppressed after MLT pre-treatment. ERK/JNK phosphorylation was reduced in meibomian glands of MLT-treated dry eye mice and increased in IFT27 knockdown RAW 264.7 cells. In summary, MLT regulated macrophage polarization via IFT27 and reduced ERK/JNK phosphorylation. These results support that MLT is a promising medication for dry eye disease.

Tristetraprolin promotes survival of mammary progenitor cells by restraining TNFα levels

Tristetraprolin (TTP) is an RNA binding protein that destabilizes mRNAs of factors involved in proliferation, invasiveness, and inflammation. Disruption of the gene that codes for TTP (Zfp36) led to severe arthritis, autoimmunity, cachexia and dermatitis in mice. It has been shown that these phenotypes were mostly due to excessive TNFα levels in the affected tissues. We have previously reported that TTP expression is required for lactation maintenance. Our results indicated that conditional MG TTP-KO female mice displayed early involution due to the untimely induction of pro-inflammatory pathways led mostly by TNFα overexpression. Here we show that reducing TTP levels not only affects the fully differentiated mammary gland, but also harms morphogenesis of this tissue by impairing the progenitor cell population. We found that Zfp36 expression is linked to mammary stemness in human and mice. In addition, diminishing TTP expression and activity induced apoptosis of stem-like mouse mammary cells, reduced its ability to form mammospheres in culture and to develop into complete glands when implanted into cleared mammary fat pads in vivo. Our results show that survival of the stem-like cells is compromised by increased levels of inflammatory cytokines and stimulation of signaling cascades involving NFκB, STAT3 and MAPK-p38 activation. Moreover, TNFα overexpression and the consequent p38 phosphorylation would be the leading cause of progenitor cell death upon TTP expression restriction. Taken together, our results reveal the relevance of TTP for the maintenance of the mammary progenitor cell compartment by maintaining local TNFα levels at bay.

Pseudomonas aeruginosa induces p38MAP kinase-dependent IL-6 and CXCL8 release from bronchial epithelial cells via a Syk kinase pathway

Pseudomonas aeruginosa (Pa) infection is a major cause of airway inflammation in immunocompromised and cystic fibrosis (CF) patients. Mitogen-activated protein (MAP) and tyrosine kinases are integral to inflammatory responses and are therefore potential targets for novel anti-inflammatory therapies. We have determined the involvement of specific kinases in Pa-induced inflammation. The effects of kinase inhibitors against p38MAPK, MEK 1/2, JNK 1/2, Syk or c-Src, a combination of a p38MAPK with Syk inhibitor, or a novel narrow spectrum kinase inhibitor (NSKI), were evaluated against the release of the proinflammatory cytokine/chemokine, IL-6 and CXCL8 from BEAS-2B and CFBE41o- epithelial cells by Pa. Effects of a Syk inhibitor against phosphorylation of the MAPKs were also evaluated. IL-6 and CXCL8 release by Pa were significantly inhibited by p38MAPK and Syk inhibitors (p<0.05). Phosphorylation of HSP27, but not ERK or JNK, was significantly inhibited by Syk kinase inhibition. A combination of p38MAPK and Syk inhibitors showed synergy against IL-6 and CXCL8 induction and an NSKI completely inhibited IL-6 and CXCL8 at low concentrations. Pa-induced inflammation is dependent on p38MAPK primarily, and Syk partially, which is upstream of p38MAPK. The NSKI suggests that inhibiting specific combinations of kinases is a potent potential therapy for Pa-induced inflammation.

Parthenolide ameliorates Concanavalin A-induced acute hepatitis in mice and modulates the macrophages to an anti-inflammatory state

Parthenolide, the principal sesquiterpene lactone present in medicinal plants such as feverfew, has anti-microbial, anti-inflammatory and anticancer activities. In the present study, we investigated the protective role of parthenolide against acute hepatitis in mice. Mice acute hepatitis were induced by Concanavalin A and treated by parthenolide in vivo. Results shown that parthenolide remarkably reduced the congestion and necroinflammation of the mice livers with Concanavalin A-induced acute hepatitis. Meanwhile, parthenolide treatment recover the liver function which indicated by decreased the serum alanine transaminase and alkaline phosphatase activities and promoted the expression of Ki67 in the livers of these mice. In addition, parthenolide administration suppressed the Concanavalin A-induced immune reaction, as indicated by the number of F4/80, CD49b and CD4 cells present in the liver. Furthermore, parthenolide also significantly reduced the expression of pro-inflammatory cytokines such as IFN-γ, TNF-α, IL-17A, IL-1β and IL-6 in lipopolysaccharide (LPS)-stimulated RAW264.7 cells in vitro. Moreover, parthenolide exposure decreased the phosphorylation of STAT3 and p38, and promoted the phosphorylation of p53 in RAW264.7 cells in vitro. In conclusion, parthenolide represents a drug candidate to protect the liver against Concanavalin A-induced acute hepatitis. The possible molecular mechanism involves the anti-inflammatory effects of parthenolide may by suppressing the STAT3/p38 signals and enhanced the p53 signals.

IL-17 intensifies IFN-γ-induced NOS2 upregulation in RAW 264.7 cells by further activating STAT1 and NF-κB

Interleukin-17 (IL-17) is a signature cytokine of Th17 cells. Previous research has indicated that IL-17 plays a proinflammatory role by exacerbating interferon-γ (IFN-γ)-induced inflammation. However, prior to this study, it was not known whether inducible nitric oxide synthase (iNOS or NOS2), a signature molecule of inflammation, could be intensified by IL-17 when combined with IFN-γ. Thus, we explored the roles and underlying mechanisms of IL-17 and IFN-γ in the regulation of NOS2 expression in RAW 264.7 cells using qPCR, western blot analysis, colorimetric analysis, ChIP assay and statistical analysis. Although IL-17 alone did not induce NOS2 expression or nitric oxide (NO) production, as shown by western blot analysis and colorimetric analysis, it intensified IFN-γ-induced NOS2 upregulation and NO production in RAW 264.7 cells. The alteration of relevant transcription factors demonstrated that a combination of IFN-γ and IL-17 enhanced Tyr701-phosphorylated signal transducer and activator of transcription 1 [p-STAT1(Y701)] and nuclear factor-κB (NF-κB) activation, nuclear translocations and their binding to the NOS2 promoter, compared with IFN-γ alone, as illustrated by the results of the western blot analysis and ChIP assay. Also, using the corresponding inhibitors of STAT1 and NF-κB, we noted downregulation of the expression of NOS2 induced by IFN-γ alone or in combination with IL-17, respectively. In addition, IFN-γ increased phosphorylated (p-)p38 mitogen-activated protein kinase (MAPK), and accelerated the activation of the NF-κB pathway and the expression of NOS2, but phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) was reduced by treatment with IFN-γ and IL-17. IL-17 intensified the activation of the NF-κB pathway and NOS2 upregulation induced by IFN-γ by increasing the phosphorylation of p38 MAPK and limiting the phosphorylation of ERK1/2. Taken together, these results suggest that IL-17 intensified IFN-γ-induced NOS2 upregulation and NO production by increasing the transcription activity of p-STAT1(Y701) and NF-κB in RAW 264.7 cells. Further activation of the NF-κB pathway induced by IL-17 relied on enhanced phosphorylation of p38 MAPK and decreased phosphorylation of ERK1/2. The mechanism suggested in this study provides novel information which may be used for anti-inflammatory therapy with IL-17.

Bacterial fucose-rich polysaccharide stabilizes MAPK-mediated Nrf2/Keap1 signaling by directly scavenging reactive oxygen species during hydrogen peroxide-induced apoptosis of human lung fibroblast cells

Continuous free radical assault upsets cellular homeostasis and dysregulates associated signaling pathways to promote stress-induced cell death. In spite of the continuous development and implementation of effective therapeutic strategies, limitations in treatments for stress-induced toxicities remain. The purpose of the present study was to determine the potential therapeutic efficacy of bacterial fucose polysaccharides against hydrogen peroxide (H2O2)-induced stress in human lung fibroblast (WI38) cells and to understand the associated molecular mechanisms. In two different fermentation processes, Bacillus megaterium RB-05 biosynthesized two non-identical fucose polysaccharides; of these, the polysaccharide having a high-fucose content (∼ 42%) conferred the maximum free radical scavenging efficiency in vitro. Structural characterizations of the purified polysaccharides were performed using HPLC, GC-MS, and (1)H/(13)C/2D-COSY NMR. H2O2 (300 µM) insult to WI38 cells showed anti-proliferative effects by inducing intracellular reactive oxygen species (ROS) and by disrupting mitochondrial membrane permeability, followed by apoptosis. The polysaccharide (250 µg/mL) attenuated the cell death process by directly scavenging intracellular ROS rather than activating endogenous antioxidant enzymes. This process encompasses inhibition of caspase-9/3/7, a decrease in the ratio of Bax/Bcl2, relocalization of translocated Bax and cytochrome c, upregulation of anti-apoptotic members of the Bcl2 family and a decrease in the phosphorylation of MAPKs (mitogen activated protein kinases). Furthermore, cellular homeostasis was re-established via stabilization of MAPK-mediated Nrf2/Keap1 signaling and transcription of downstream cytoprotective genes. This molecular study uniquely introduces a fucose-rich bacterial polysaccharide as a potential inhibitor of H2O2-induced stress and toxicities.

Disruption of prostate epithelial differentiation pathways and prostate cancer development

One of the foremost problems in the prostate cancer (PCa) field is the inability to distinguish aggressive from indolent disease, which leads to difficult prognoses and thousands of unnecessary surgeries. This limitation stems from the fact that the mechanisms of tumorigenesis in the prostate are poorly understood. Some genetic alterations are commonly reported in prostate tumors, including upregulation of Myc, fusion of Ets genes to androgen-regulated promoters, and loss of Pten. However, the specific roles of these aberrations in tumor initiation and progression are poorly understood. Likewise, the cell of origin for PCa remains controversial and may be linked to the aggressive potential of the tumor. One important clue is that prostate tumors co-express basal and luminal protein markers that are restricted to their distinct cell types in normal tissue. Prostate epithelium contains layer-specific stem cells as well as rare bipotent cells, which can differentiate into basal or luminal cells. We hypothesize that the primary oncogenic cell of origin is a transient-differentiating bipotent cell. Such a cell must maintain tight temporal and spatial control of differentiation pathways, thus increasing its susceptibility for oncogenic disruption. In support of this hypothesis, many of the pathways known to be involved in prostate differentiation can be linked to genes commonly altered in PCa. In this article, we review what is known about important differentiation pathways (Myc, p38MAPK, Notch, PI3K/Pten) in the prostate and how their misregulation could lead to oncogenesis. Better understanding of normal differentiation will offer new insights into tumor initiation and may help explain the functional significance of common genetic alterations seen in PCa. Additionally, this understanding could lead to new methods for classifying prostate tumors based on their differentiation status and may aid in identifying more aggressive tumors.

A Speculative Role for Stromal Gastrin Signaling in Development and Dissemination of Pancreatic Ductal Adenocarcinoma

The peptide growth factor gastrin and its receptor, the G-protein coupled cholecystokinin receptor type B (CCK_BR), play an integral role in the growth and progression of pancreatic ductal adenocarcinoma (PDAC). Gastrin immunoreactivity is found in the fetal pancreas but its expression is not detected in normal pancreas after birth, except when it is re-expressed in malignant lesions.

Diverse patterns of cyclooxygenase-independent metalloproteinase gene regulation in human monocytes

BACKGROUND AND PURPOSE Matrix metalloproteinase (MMP) production from monocyte/macrophages is implicated in matrix remodelling and modulation of inflammation. However, knowledge of the patterns and mechanisms of gene regulation of MMPs and their endogenous tissue inhibitors (TIMPs) is fragmentary. MMP up-regulation may be a target for cyclooxygenase (COX) and prostaglandin (PG) receptor inhibition, but the extent and mechanisms of COX-independent MMP up-regulation are unclear. EXPERIMENTAL APPROACH We studied MMP mRNA expression and selected protein levels in human peripheral blood monocytes before and after adhesion, upon stimulation with bacterial lipopolysaccharide (LPS), PGE(2) or forskolin and after culturing with monocyte colony-stimulating factor on plastic or human fibronectin for up to 7 days. KEY RESULTS Monocyte adherence for 2 h transiently up-regulated COX-2, MMP-1, MMP-7 and MMP-10 mRNAs, and persistently up-regulated MMP-2, MMP-9, MMP-14 and MMP-19 mRNAs. LPS, PGE(2) or forskolin selectively increased MMP-1, MMP-9, MMP-10, MMP-12 and MMP-14 mRNAs. LPS increased PGE(2) production through COX but up-regulated MMP levels independently of COX. Differential dependence on inhibition of p42/44 and p38 mitogen-activated protein kinases, c-jun N-terminal kinase and inhibitor of κB kinase2 paralleled the diverse patterns of MMP stimulation by LPS. Differentiation on plastic increased mRNA levels of MMP-7, MMP-9, MMP-12 and MMP-14 and TIMP-2 and TIMP-3 independently of COX; fibronectin accelerated MMP but not TIMP up-regulation. CONCLUSIONS AND IMPLICATIONS Adhesion, LPS stimulation and maturation of human monocytes lead to selective, COX-independent MMP and TIMP gene regulation, which is a potential target for selective inhibition by signalling kinase inhibitors.

Blocking epidermal growth factor receptor activation by 3,3'-diindolylmethane suppresses ovarian tumor growth in vitro and in vivo

Genetic alterations, including the overexpression of epidermal growth factor receptor (EGFR) (in approximately 70% of ovarian tumors), play a crucial role in the signal transduction pathways that regulate key cellular functions, such as cell survival and proliferation, and are responsible for compromising traditional chemotherapy. 3,3'-Diindolylmethane (DIM) is an indole compound present in Brassica vegetables. In our previous studies, we demonstrated that BR-DIM, a formulated version of DIM, suppressed the growth of ovarian cancer cells by causing cell cycle arrest and apoptosis. In the present study, we delineated the mechanism by which DIM suppressed the growth of SKOV-3, OVCAR-3, and TOV-21G human ovarian cancer cells. DIM treatment caused significant down-regulation of the constitutive EGFR protein level as well as phosphorylation of EGFR at Tyr1068, Tyr992, Tyr845, and Tyr1173 in various ovarian cancer cells. To determine whether DIM suppressed the activation of EGFR by activating phosphorylation, cells were treated with epidermal growth factor. Epidermal growth factor treatment significantly blocked the DIM-mediated inhibition of EGFR activation and apoptosis in both SKOV-3 and OVCAR-3 cells. In addition, DIM treatment drastically reduced the phosphorylation of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK), which are downstream to EGFR, without affecting their protein levels. DIM treatment also inhibited the kinase activity of ERK, as observed by the down-regulation of phospho-E twenty-six like transcription factor 1 (p-ELK1) in all three ovarian cancer cell lines. DIM significantly suppressed the growth of ovarian tumors in vivo. Tumor growth suppressive effects of DIM in SKOV-3 tumor xenografts were associated with reduced phosphorylation of EGFR, MEK, and ERK. These results indicate that DIM induces apoptosis in ovarian cancer cells by inhibiting the EGFR-ERK pathway in vitro and in vivo.

Distinct regulation of mitogen-activated protein kinase activities is coupled with enhanced cardiac differentiation of human embryonic stem cells

Improving cardiac differentiation of human pluripotent stem cells is mandatory to provide functional heart muscle cells for novel therapies. Here, we have investigated the enhancing effect of the small molecule SB203580, a p38 MAPK inhibitor, on cardiomyogenesis in hESC by monitoring the phosphorylation patterns of the major MAPK pathway components p38, JNK and ERK by western immunoblotting. A remarkable drop in phosphorylation levels of all three MAPK pathways was induced after overnight embryoid body (EB) formation. Upon further differentiation, phosphorylation dynamics in EBs were specifically altered by distinct inhibitor concentrations. At 5μM of SB203580, cardiomyogenesis was most efficient and associated with the expected p38 pathway inhibition. In parallel, JNK activation was observed suggesting a regulatory interlink between these pathways in hESC ultimately supporting cardiac differentiation. In contrast, moderately elevated SB203580 concentrations (15-30μM) resulted in complete disruption of cardiomyogenesis which was associated with prominent inhibition of ERK and further elevated JNK activity. We propose that a tightly-balanced pattern in MAPK phosphorylation is important for early mesoderm and subsequent cardiomyocyte formation. Our data provide novel insights into molecular consequences of small molecule supplementation in hESC differentiation, emphasizing the role of MAPK-signaling.

MLK3 is critical for breast cancer cell migration and promotes a malignant phenotype in mammary epithelial cells

The malignant phenotype in breast cancer is driven by aberrant signal transduction pathways. Mixed-lineage kinase-3 (MLK3) is a mammalian mitogen-activated protein kinase kinase kinase (MAP3K) that activates multiple MAPK pathways. Depending on the cellular context, MLK3 has been implicated in apoptosis, proliferation, migration and differentiation. Here we investigated the effect of MLK3 and its signaling to MAPKs in the acquisition of malignancy in breast cancer. We show that MLK3 is highly expressed in breast cancer cells. We provide evidence that MLK3's catalytic activity and signaling to c-jun N-terminal kinase (JNK) is required for migration of highly invasive breast cancer cells and for MLK3-induced migration of mammary epithelial cells. Expression of active MLK3 is sufficient to induce the invasion of mammary epithelial cells, which requires AP-1 activity and is accompanied by the expression of several proteins corresponding to AP-1-regulated invasion genes. To assess MLK3's contribution to the breast cancer malignant phenotype in a more physiological setting, we implemented a strategy to inducibly express active MLK3 in the preformed acini of MCF10A cells grown in 3D Matrigel. Induction of MLK3 expression dramatically increases acinar size and modestly perturbs apicobasal polarity. Remarkably, MLK3 expression induces luminal repopulation and suppresses the expression of the pro-apoptotic protein BimEL, as has been observed in Her2/Neu-expressing acini. Taken together, our data show that MLK3-JNK-AP-1 signaling is critical for breast cancer cell migration and invasion. Our current study uncovers both a proliferative and novel antiapoptotic role for MLK3 in the acquisition of a malignant phenotype in mammary epithelial cells. Thus, MLK3 may be an important therapeutic target for the treatment of invasive breast cancer.

Mice lacking Tbk1 activity exhibit immune cell infiltrates in multiple tissues and increased susceptibility to LPS-induced lethality

TBK1 is critical for immunity against microbial pathogens that activate TLR4- and TLR3-dependent signaling pathways. To address the role of TBK1 in inflammation, mice were generated that harbor two copies of a mutant Tbk1 allele. This Tbk1(Δ) allele encodes a truncated Tbk1(Δ) protein that is catalytically inactive and expressed at very low levels. Upon LPS stimulation, macrophages from Tbk1(Δ/Δ) mice produce normal levels of proinflammatory cytokines (e.g., TNF-α), but IFN-β and RANTES expression and IRF3 DNA-binding activity are ablated. Three-month-old Tbk1(Δ/Δ) mice exhibit mononuclear and granulomatous cell infiltrates in multiple organs and inflammatory cell infiltrates in their skin, and they harbor a 2-fold greater amount of circulating monocytes than their Tbk1(+/+) and Tbk1(+/Δ) littermates. Skin from 2-week-old Tbk1(Δ/Δ) mice is characterized by reactive changes, including hyperkeratosis, hyperplasia, necrosis, inflammatory cell infiltrates, and edema. In response to LPS challenge, 3-month-old Tbk1(Δ/Δ) mice die more quickly and in greater numbers than their Tbk1(+/+) and Tbk1(+/Δ) counterparts. This lethality is accompanied by an overproduction of several proinflammatory cytokines in the serum of Tbk1(Δ/Δ) mice, including TNF-α, GM-CSF, IL-6, and KC. This overproduction of serum cytokines in Tbk1(Δ/Δ) mice following LPS challenge and their increased susceptibility to LPS-induced lethality may result from the reactions of their larger circulating monocyte compartment and their greater numbers of extravasated immune cells.

c-Jun N-terminal kinase binding domain-dependent phosphorylation of mitogen-activated protein kinase kinase 4 and mitogen-activated protein kinase kinase 7 and balancing cross-talk between c-Jun N-terminal kinase and extracellular signal-regulated kinase pathways in cortical neurons

The c-Jun N-terminal kinase (JNK) is a mitogen-activated protein kinase (MAPK) activated by stress-signals and involved in many different diseases. Previous results proved the powerful effect of the cell permeable peptide inhibitor d-JNKI1 (d-retro-inverso form of c-Jun N-terminal kinase-inhibitor) against neuronal death in CNS diseases, but the precise features of this neuroprotection remain unclear. We here performed cell-free and in vitro experiments for a deeper characterization of d-JNKI1 features in physiological conditions. This peptide works by preventing JNK interaction with its c-Jun N-terminal kinase-binding domain (JBD) dependent targets. We here focused on the two JNK upstream MAPKKs, mitogen-activated protein kinase kinase 4 (MKK4) and mitogen-activated protein kinase kinase 7 (MKK7), because they contain a JBD homology domain. We proved that d-JNKI1 prevents MKK4 and MKK7 activity in cell-free and in vitro experiments: these MAPKK could be considered not only activators but also substrates of JNK. This means that d-JNKI1 can interrupt downstream but also upstream events along the JNK cascade, highlighting a new remarkable feature of this peptide. We also showed the lack of any direct effect of the peptide on p38, MEK1, and extracellular signal-regulated kinase (ERK) in cell free, while in rat primary cortical neurons JNK inhibition activates the MEK1-ERK-Ets1/c-Fos cascade. JNK inhibition induces a compensatory effect and leads to ERK activation via MEK1, resulting in an activation of the survival pathway-(MEK1/ERK) as a consequence of the death pathway-(JNK) inhibition. This study should hold as an important step to clarify the strong neuroprotective effect of d-JNKI1.

Cytokine-induced epithelial permeability changes are regulated by the activation of the p38 mitogen-activated protein kinase pathway in cultured Caco-2 cells

Increased intestinal/epithelial permeability in sepsis and endotoxemia has been noted to be induced by proinflammatory cytokines such as interferon-gamma, TNF-alpha, and IL-1beta. The p38 mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in regulating the inflammatory response induced by these cytokines. We tested the hypothesis that epithelial permeability changes are regulated through the p38 MAPK signaling pathway. Caco-2 cells were cultured for 21 days and then stimulated with a cytokine mixture (CytoMix: TNF-alpha, interferon-gamma, and IL-1beta). Epithelial barrier function was evaluated by measuring permeability in an Ussing chamber. CytoMix-induced changes of MAPKs (p38, c-Jun amino-terminal kinase, and extracellular-regulated kinase), NO production, and inflammatory responses (IL-6 and IL-8 levels) were also assessed. The signaling pathways were further studied by pretreating cells with SB203580, a specific p38 MAPK inhibitor. CytoMix increased permeability at 24 and 48 h but not at 4 h. This was associated with increased IL-6 and IL-8 production, as well as increases in phosphorylation of all three MAPKs. Treatment with SB203580 completely blocked p38 activity with transient inhibition of p38 phosphorylation. SB203580 also prevented the CytoMix-induced permeability increase and reduced NO, IL-6, and IL-8 levels. The results suggest that p38 MAPK plays an important role in regulating epithelial barrier function during inflammation.

Transforming growth factor-beta-activated protein kinase 1-binding protein (TAB)-1alpha, but not TAB1beta, mediates cytokine-induced p38 mitogen-activated protein kinase phosphorylation and cell death in insulin-producing cells

Previous studies have indicated that the p38 MAPK participates in signaling events that lead to the death of the insulin-producing beta-cell. The aim of the present study was to elucidate the role of the TGF-beta-activated protein kinase 1-binding protein 1 (TAB1) in the cytokine-induced activation of p38. Levels of TAB1 mRNA and protein were analyzed by real-time PCR and immunoblotting, and TAB1 expression in mouse and human islet cells was down-regulated using lipofection of diced-small interfering RNA. TAB1 overexpression in beta-TC6 cells was achieved by transient transfections followed by fluorescence activated cell sorting. Phosphorylation of p38, c-Jun N-terminal kinase, and ERK was assessed by immunoblotting, and viability was determined using vital staining with bisbenzimide and propidium iodide. We observed that TAB1 is expressed in insulin-producing cells. Cytokine (IL-1beta + interferon-gamma)-stimulated p38 phosphorylation was significantly increased by TAB1alpha overexpression, but not TAB1beta overexpression, in beta-TC6 cells. The TAB1alpha-augmented p38 phosphorylation was paralleled by an increased cell death rate. Treatment of islet cells with diced-small interfering RNA specific for TAB1, but not for TGF-beta-activated kinase 1, resulted in lowered cytokine-induced p38 phosphorylation and protection against cell death. The cytokine-induced phosphorylation of c-Jun N-terminal kinase and ERK was not affected by changes in TAB1 levels. Finally, TAB1 phosphorylation was decreased by the p38 inhibitor SB203580. We conclude that TAB1alpha, but not TAB1beta, plays an important role in the activation of p38 in insulin-producing cells and therefore also in cytokine-induced beta-cell death.

LPS induces IL-10 production by human alveolar macrophages via MAPKinases- and Sp1-dependent mechanisms

BACKGROUND

IL-10 is a cytokine mainly produced by macrophages that plays key roles in tolerance to inhaled antigens and in lung homeostasis. Its regulation in alveolar macrophages (HAM), the resident lung phagocytes, remains however unknown.

METHODS

The present study investigated the role of intracellular signalling and transcription factors controlling the production of IL-10 in LPS-activated HAM from normal nonsmoking volunteers.

RESULTS

LPS (1-1000 pg/ml) induced in vitro IL-10 production by HAM, both at mRNA and protein levels. LPS also activated the phosphorylation of ERK, p38 and JNK MAPkinases (immunoblots) and Sp-1 nuclear activity (EMSA). Selective inhibitors of MAPKinases (respectively PD98059, SB203580 and SP600125) and of Sp-1 signaling (mithramycin) decreased IL-10 expression in HAM. In addition, whilst not affecting IL-10 mRNA degradation, the three MAPKinase inhibitors completely abolished Sp-1 activation by LPS in HAM.

CONCLUSION

These results demonstrate for the first time that expression of IL-10 in lung macrophages stimulated by LPS depends on the concomitant activation of ERK, p38 and JNK MAPKinases, which control downstream signalling to Sp-1 transcription factor. This study further points to Sp-1 as a key signalling pathway for IL-10 expression in the lung.

Dynamic positive feedback phosphorylation of mixed lineage kinase 3 by JNK reversibly regulates its distribution to Triton-soluble domains

MLK3 (mixed lineage kinase 3) is a widely expressed, mammalian serine/threonine protein kinase that activates multiple MAPK pathways. Previously our laboratory used in vivo labeling/mass spectrometry to identify phosphorylation sites of activated MLK3. Seven of 11 identified sites correspond to the consensus motif for phosphorylation by proline-directed kinases. Based on these results, we hypothesized that JNK, or another proline-directed kinase, phosphorylates MLK3 as part of a feedback loop. Herein we provide evidence that MLK3 can be phosphorylated by JNK in vitro and in vivo. Blockade of JNK results in dephosphorylation of MLK3. The hypophosphorylated form of MLK3 is inactive and redistributes to a Triton-insoluble fraction. Recovery from JNK inhibition restores MLK3 solubility and activity, indicating that the redistribution process is reversible. This work describes a novel mode of regulation of MLK3, by which JNK-mediated feedback phosphorylation of MLK3 regulates its activation and deactivation states by cycling between Triton-soluble and Triton-insoluble forms.

Cell type-dependent control of NF-Y activity by TGF-beta

Transforming growth factor beta (TGF-beta) is a pluripotent cytokine that regulates cell growth and differentiation in a cell type-dependent fashion. TGF-beta exerts its effects through the activation of several signaling pathways. One involves membrane proximal events that lead to nuclear translocation of members of the Smad family of transcriptional regulators. TGF-beta can also activate MAPK cascades. Here, we show that TGF-beta induces nuclear translocation of the NF-YA subunit of the transcription factor NF-Y by a process that requires activation of the ERK cascade. This results in increased binding of endogenous NF-Y to chromatin and TGF-beta-dependent transcriptional regulation of the NF-Y target gene cyclin A2. Interestingly, the kinetics of NF-YA relocalization differs between epithelial cells and fibroblasts. NIH3T3 fibroblasts show an elevated basal level of phosphorylated p38 and delayed nuclear accumulation of NF-YA after TGF-beta treatment. In contrast, MDCK cells show low basal p38 activation, higher basal ERK phosphorylation and more rapid localization of NF-YA after induction. Thus, NF-Y activation by TGF-beta1 involves ERK1/2 and potentially an interplay between MAPK pathways, thereby opening the possibility for finely tuned transcriptional regulation.

Role of MLK3 in the regulation of mitogen-activated protein kinase signaling cascades

Mixed-lineage protein kinase 3 (MLK3) is a member of the mitogen-activated protein (MAP) kinase kinase kinase group that has been implicated in multiple signaling cascades, including the NF-kappaB pathway and the extracellular signal-regulated kinase, c-Jun NH(2)-terminal kinase (JNK), and p38 MAP kinase pathways. Here, we examined the effect of targeted disruption of the murine Mlk3 gene. Mlk3(-/-) mice were found to be viable and healthy. Primary embryonic fibroblasts prepared from these mice exhibited no major signaling defects. However, we did find that MLK3 deficiency caused a selective reduction in tumor necrosis factor (TNF)-stimulated JNK activation. Together, these data demonstrate that MLK3 contributes to the TNF signaling pathway that activates JNK.

B-Raf-dependent expression of vascular endothelial growth factor-A in Kaposi sarcoma-associated herpesvirus-infected human B cells

Kaposi sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV/HHV-8) is etiologically linked to Kaposi sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease. Vascular endothelial growth factor-A (VEGF-A) is one of the essential factors required in KSHV pathogenesis, mainly due to its ability to mediate angiogenesis. In this report we analyzed the relationship between Raf and VEGF-A expression in KSHV-infected hematopoietic cells. All of the KSHV-infected cell lines (derived from PEL) expressed higher levels of B-Raf and VEGF-A when compared with uninfected cells. Inhibition of Raf to mitogen-induced extracellular kinase (MEK) to extracellular signal-related kinase (ERK) signaling, either by the use of MEK inhibitor (PD98059) or by siRNA specific to B-Raf, significantly lowered VEGF-A expression. In addition, B-Raf-induced VEGF-A expression was demonstrated to be sufficient to enhance tubule formation in endothelial cells. Interestingly, we did not observe mutation in the B-Raf gene of the KSHV-infected PEL cell lines. Taken together, we report for the first time the ability of Raf-associated signaling to play a role in the expression of VEGF-A in KSHV-infected hematopoietic cells.

Defective up-regulation of CD49d in final maturation of NOD mouse macrophages

Macrophages are potent regulators of both innate and adaptive immunity. They play a central role in the development of autoimmune diabetes and are among the first cells to appear in peri-islet infiltrates of NOD mice that spontaneously develop diabetes. Since efficient adhesion and migration are crucial for proper macrophage trafficking, we examined the migration and fibronectin (FN) adhesion capacity of NOD macrophages, as well as the regulation and expression of the FN receptors alpha4beta1 and alpha5beta1. When compared to macrophages from control strains, resident NOD macrophages showed a reduced ability to adhere to and migrate on FN, a delayed clearance following peritoneal inflammation, and substantially lower expression levels of the alpha4beta1 integrin alpha chain, CD49d. NOD bone marrow-derived macrophages were specifically defective in the LPS-induced increase in CD49d expression. Moreover, the mitogen-activated protein kinase extracellular signal-regulated kinase-1/2 negatively regulated macrophage CD49d expression and strongly suppressed its expression in NOD macrophages. The data presented herein indicate that the LPS-activated signaling cascade plays a critical role in CD49d expression of macrophages. Mature NOD macrophages are characterized by decreased CD49d expression and show defective CD49d-mediated adhesion to FN.

Inhibition of p38 mitogen-activated protein kinase augments progression of remnant kidney model by activating the ERK pathway

p38, a mitogen-activated protein kinase, is a major intracellular signaling molecule involved in inflammation. To test the hypothesis that p38 mediates renal disease progression, we administered a novel p38 alpha inhibitor, NPC31169, to rats with remnant kidneys (RKs). RK rats showed increased p38 activation at 9 weeks (by p38 kinase assay), which was blocked by the inhibitor. In contrast to our expectation, treatment with the NPC31169 resulted in worse renal function, more proteinuria, and more severe glomerulosclerosis and tubulointerstitial injury. p38 inhibition resulted in marked cell proliferation in RK rats, with more proliferating tubular cells, myofibroblasts, and macrophages. In contrast, p38 suppression resulted in less tubular cell apoptosis. Interestingly, Western blot demonstrated increased ERK1/2 phosphorylation in p38-treated rats. No histological changes were observed in p38 inhibited sham-operated rats. Our findings indicate that, whereas blocking p38 usually shows benefit in inflammatory disease, in this model p38 inhibition resulted in accelerated renal progression. We conclude that blocking p38-dependent inflammation may have resulted in enhanced proliferation and increased ERK1/2 activation, and thereby explains the worse renal lesions observed.

MAP kinases differentially regulate the expression of macrophage hyperactivity after thermal injury

Thermal injury increases the capacity of macrophages (Mphi) to produce various inflammatory mediators, (i.e., Mphi hyperactivity), which is believed to be involved in the development of subsequent immunosuppression, sepsis, and multiple organ failure. The signal transduction pathways involved in the expression of Mphi hyperactivity post-burn, however, remain to be clearly elucidated. To study this C57BL/6 female mice were subjected to a 25% TBSA burn and splenic Mphis were isolated 7 days later. LPS-stimulated inflammatory mediator production and MAPK expression (P38 ERK 1/2 and JNK) were determined. Burn injury increased LPS-induced P38 MAPK, suppressed JNK activation and ERK 1/2 activation was unaltered. These changes in MAPK activation were paralleled by the increased production of PGE(2), TNF-alpha, IL-1beta, IL-6, and IL-10. Differential sensitivity to the inhibition of the MAPK pathways was observed with regard to the mediator evaluated and the presence or absence of burn injury. In general cytokine production in the burn group was in part resistant to the inhibition of a single MAPK pathway as compared with shams. Thus, burn injury increases cross-talk between the MAPKs pathways, suggesting that alterations MAPK activation and signal transduction contribute to the development Mphi hyperactivity post-injury.

Feedback control of the protein kinase TAK1 by SAPK2a/p38alpha

TAB1, a subunit of the kinase TAK1, was phosphorylated by SAPK2a/p38alpha at Ser423, Thr431 and Ser438 in vitro. TAB1 became phosphorylated at all three sites when cells were exposed to cellular stresses, or stimulated with tumour necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) or lipopolysaccharide (LPS). The phosphorylation of Ser423 and Thr431 was prevented if cells were pre-incubated with SB 203580, while the phosphorylation of Ser438 was partially inhibited by PD 184352. Ser423 is the first residue phosphorylated by SAPK2a/p38alpha that is not followed by proline. The activation of TAK1 was enhanced by SB 203580 in LPS-stimulated macrophages, and by proinflammatory cytokines or osmotic shock in epithelial KB cells or embryonic fibroblasts. The activation of TAK1 by TNF-alpha, IL-1 or osmotic shock was also enhanced in embryonic fibroblasts from SAPK2a/p38alpha-deficient mice, while incubation of these cells with SB 203580 had no effect. Our results suggest that TAB1 participates in a SAPK2a/p38alpha-mediated feedback control of TAK1, which not only limits the activation of SAPK2a/p38alpha but synchronizes its activity with other signalling pathways that lie downstream of TAK1 (JNK and IKK).

Association of sustained ERK activity with integrin beta3 induction during receptor activator of nuclear factor kappaB ligand (RANKL)-directed osteoclast differentiation

Osteoclast differentiation is a multi-step process that involves cell proliferation, commitment, and fusion. Some adhesion molecules, including integrin alphavbeta3, have been shown to have roles in osteoclast fusion. In the course of studying with pharmacologic agents known to inhibit protein tyrosine kinases of the Src family, we found that radicicol increased cell fusion during receptor activator of nuclear factor kappaB ligand (RANKL)-driven differentiation of osteoclasts at concentrations far below the ones shown to inhibit its targets in previous studies. Treatments of low doses of radicicol to RAW 264.7 cells that undergo osteoclastic differentiation in the presence of RANKL enhanced the RANKL-induced gene expression of integrin beta3 without any effect on the expression of integrin alphav, which was constitutively high. The cell surface level of integrin alphavbeta3 complexes was consequently augmented by radicicol. In addition, sustained ERK and MEK activation was observed in cells treated with both radicicol and RANKL. More importantly, modulation of ERK activity by the MEK inhibitor U0126 or the gene transduction of a constitutively active form of MEK resulted in a suppression and increment, respectively, of integrin beta3 induction by RANKL. Our data indicate that sustained ERK activity is associated with integrin beta3 induction and subsequent cell surface expression of the alphavbeta3 integrin complex, which may contribute to cell fusion during RANKL-directed osteoclastogenesis.

Sex-specific p38 MAP kinase activation following trauma-hemorrhage: involvement of testosterone and estradiol

Although immune functions are markedly depressed in males and not in proestrous females following trauma-hemorrhage (T-H), the mechanisms responsible for the divergent responses remain unknown. Because sex steroids modulate the activation of p38, our aim was to determine whether differences in the activation of p38 by phosphorylation (p38-P) might contribute to the sex-dimorphic immune response following T-H. The effects of testosterone and estradiol on the activation of p38 were also examined. Intact male mice (C3H/HeN), castrated males treated with vehicle, 5alpha-dihydrotestosterone (DHT), or 17beta-estradiol, and proestrous females were subjected to trauma (i.e., midline laparotomy) and hemorrhagic shock (35 +/- 5 mmHg for 90 min and resuscitation) or sham operation. At 2 h thereafter, splenic (SMphi) and peritoneal macrophages (PMphi) were harvested and cultured (with 10 microg/ml LPS), and Western blot analysis was carried out for quantification of p38 and p38-P. Sex, testosterone and estradiol plasma levels, and T-H did not alter the constitutive expression of p38 in SMphi and PMphi. In contrast, the activated form of p38 (p38-P) was markedly increased in SMphi and PMphi from female shams compared with male shams. Moreover, the phosphorylation of p38-P increased in males after T-H, whereas it decreased in females under those conditions. Castration before T-H prevented the increase in p38-P in males. Castrated animals treated with DHT displayed increased p38-P following T-H, whereas 17beta-estradiol had no effect on p38-P in castrated mice. Thus 1) sex influences the activation of p38 MAP kinase, 2) DHT is responsible for the increased activation of p38 in male mice, and 3) this sex-specific activation of p38 might be responsible for the sexually dimorphic immune response following T-H.

Activation of p38 MAPK induces cell cycle arrest via inhibition of Raf/ERK pathway during muscle differentiation

Cell cycle arrest is essential for initiation of muscle differentiation in myoblasts. Given the previously described essential role for p38 MAPK in myogenesis, we undertook the present study to investigate the role of p38 MAPK in the cell cycle arrest that initiates muscle differentiation. p38 MAPK activity increased during, and was required for, muscle differentiation. Inhibition of p38 MAPK stimulated Raf and ERK activities, and induced cell proliferation in differentiation medium. The concomitant inhibition of p38 MAPK and ERK, however, failed to induce differentiation or proliferation. In conclusion, inhibition of the Raf/ERK pathway and the consequent cell cycle arrest is one of the major functions of p38 MAPK during muscle differentiation.