Regulation of airway epithelial cell NF-kappa B-dependent gene expression by protein kinase C delta

Unraveling the link between PTBP1 and severe asthma through machine learning and association rule mining method

Severe asthma is a chronic inflammatory airway disease with great therapeutic challenges. Understanding the genetic and molecular mechanisms of severe asthma may help identify therapeutic strategies for this complex condition. RNA expression data were analyzed using a combination of artificial intelligence methods to identify novel genes related to severe asthma. Through the ANOVA feature selection approach, 100 candidate genes were selected among 54,715 mRNAs in blood samples of patients with severe asthmatic and healthy groups. A deep learning model was used to validate the significance of the candidate genes. The accuracy, F1-score, AUC-ROC, and precision of the 100 genes were 83%, 0.86, 0.89, and 0.9, respectively. To discover hidden associations among selected genes, association rule mining was applied. The top 20 genes including the PTBP1, RAB11FIP3, APH1A, and MYD88 were recognized as the most frequent items among severe asthma association rules. The PTBP1 was found to be the most frequent gene associated with severe asthma among those 20 genes. PTBP1 was the gene most frequently associated with severe asthma among candidate genes. Identification of master genes involved in the initiation and development of asthma can offer novel targets for its diagnosis, prognosis, and targeted-signaling therapy.

A genome-wide CRISPR screen in human prostate cancer cells reveals drivers of macrophage-mediated cell killing and positions AR as a tumor-intrinsic immunomodulator

The crosstalk between prostate cancer (PCa) cells and the tumor microenvironment plays a pivotal role in disease progression and metastasis and could provide novel opportunities for patient treatment. Macrophages are the most abundant immune cells in the prostate tumor microenvironment (TME) and are capable of killing tumor cells. To identify genes in the tumor cells that are critical for macrophage-mediated killing, we performed a genome-wide co-culture CRISPR screen and identified AR, PRKCD, and multiple components of the NF-κB pathway as hits, whose expression in the tumor cell are essential for being targeted and killed by macrophages. These data position AR signaling as an immunomodulator, and confirmed by androgen-deprivation experiments, that rendered hormone-deprived tumor cells resistant to macrophage-mediated killing. Proteomic analyses showed a downregulation of oxidative phosphorylation in the PRKCD- and IKBKG-KO cells compared to the control, suggesting impaired mitochondrial function, which was confirmed by electron microscopy analyses. Furthermore, phosphoproteomic analyses revealed that all hits impaired ferroptosis signaling, which was validated transcriptionally using samples from a neoadjuvant clinical trial with the AR-inhibitor enzalutamide. Collectively, our data demonstrate that AR functions together with the PRKCD and the NF-κB pathway to evade macrophage-mediated killing. As hormonal intervention represents the mainstay therapy for treatment of prostate cancer patients, our findings may have direct implications and provide a plausible explanation for the clinically observed persistence of tumor cells despite androgen deprivation therapy.

12-O-tetradecanoylphorbol-13-acetate Reduces Activation of Hepatic Stellate Cells by Inhibiting the Hippo Pathway Transcriptional Coactivator YAP

Although protein kinase C (PKC) regulates various biological activities, including cell proliferation, differentiation, migration, tissue remodeling, gene expression, and cell death, the antifibrotic effect of PKC in myofibroblasts is not fully understood. We investigated whether 12-O-tetradecanoylphorbol-13-acetate (TPA), a PKC activator, reduced the activation of hepatic stellate cells (HSCs) and explored the involvement of the Hippo pathway transcriptional coactivator YAP. We analyzed the effect of TPA on the proliferation and expression of α-smooth muscle actin (SMA) in the LX-2 HSC line. We also analyzed the phosphorylation of the Hippo pathway molecules YAP and LATS1 and investigated YAP nuclear translocation. We examined whether Gö 6983, a pan-PKC inhibitor, restored the TPA-inhibited activities of HSCs. Administration of TPA decreased the growth rate of LX-2 cells and inhibited the expression of α-SMA and collagen type I alpha 1 (COL1A1). In addition, TPA induced phosphorylation of PKCδ, LATS1, and YAP and inhibited the nuclear translocation of YAP compared with the control. These TPA-induced phenomena were mostly ameliorated by Gö 6983. Our results indicate that PKCδ exerts an antifibrotic effect by inhibiting the Hippo pathway in HSCs. Therefore, PKCδ and YAP can be used as therapeutic targets for the treatment of fibrotic diseases.

A Combined Transcriptomic and Proteomic Approach to Reveal the Effect of Mogroside V on OVA-Induced Pulmonary Inflammation in Mice

Mogroside V is a bioactive ingredient extracted from the natural food Siraitia grosvenorii which possesses functions that stimulate lung humidification and cough relief activities, but its underlying mechanisms were rarely studied. To estimate its potential protective effect on ovalbumin (OVA)-induced pulmonary inflammation and understand its system-wide mechanism, integrated omics was applied in this study. Mogroside V effectively reduced the levels of IgE, TNF-α, and IL-5 in OVA-induced mice. The results of RNA-seq and data-independent acquisition proteomics approach revealed that 944 genes and 341 proteins were differentially expressed in the normal control group (NC) and ovalbumin-induced control group (OC) and 449 genes and 259 proteins were differentially expressed between the OC and the group treated with 50 mg/kg mogroside V (MV). After a combined analysis of the transcriptome and the proteome, 93 major pathways were screened, and we discovered that mogroside V exerts an anti-inflammation effect in the lung via NF-κB and JAK-STAT, both of which are among the signaling pathways mentioned above. In addition, we found that the key regulatory molecules (Igha, Ighg1, NF-κB, Jak1, and Stat1) in the two pathways were activated in inflammation and inhibited by mogroside V. Thus, mogroside V may be the main bioactivity component in S. grosvenorii that exerts lung humidification and cough relief effects.

Allergen inhalation generates pro-inflammatory oxidised phosphatidylcholine associated with airway dysfunction

Oxidised phosphatidylcholines (OxPCs) are produced under conditions of elevated oxidative stress and can contribute to human disease pathobiology. However, their role in allergic asthma is unexplored. The aim of this study was to characterise the OxPC profile in the airways after allergen challenge of people with airway hyperresponsiveness (AHR) or mild asthma. The capacity of OxPCs to contribute to pathobiology associated with asthma was also to be determined.Using bronchoalveolar lavage fluid from two human cohorts, OxPC species were quantified using ultra-high performance liquid chromatography-tandem mass spectrometry. Murine thin-cut lung slices were used to measure airway narrowing caused by OxPCs. Human airway smooth muscle (HASM) cells were exposed to OxPCs to assess concentration-associated changes in inflammatory phenotype and activation of signalling networks.OxPC profiles in the airways were different between people with and without AHR and correlated with methacholine responsiveness. Exposing patients with mild asthma to allergens produced unique OxPC signatures that associated with the severity of the late asthma response. OxPCs dose-dependently induced 15% airway narrowing in murine thin-cut lung slices. In HASM cells, OxPCs dose-dependently increased the biosynthesis of cyclooxygenase-2, interleukin (IL)-6, IL-8, granulocyte-macrophage colony-stimulating factor and the production of oxylipins via protein kinase C-dependent pathways.Data from human cohorts and primary HASM cell culture show that OxPCs are present in the airways, increase after allergen challenge and correlate with metrics of airway dysfunction. Furthermore, OxPCs may contribute to asthma pathobiology by promoting airway narrowing and inducing a pro-inflammatory phenotype and contraction of airway smooth muscle. OxPCs represent a potential novel target for treating oxidative stress-associated pathobiology in asthma.

Bronchoconstriction: a potential missing link in airway remodelling

In asthma, progressive structural changes of the airway wall are collectively termed airway remodelling. Despite its deleterious effect on lung function, airway remodelling is incompletely understood. As one of the important causes leading to airway remodelling, here we discuss the significance of mechanical forces that are produced in the narrowed airway during asthma exacerbation, as a driving force of airway remodelling. We cover in vitro, ex vivo and in vivo work in this field, and discuss up-to-date literature supporting the idea that bronchoconstriction may be the missing link in a comprehensive understanding of airway remodelling in asthma.

Protein Kinase C-Delta (PKCδ) Tyrosine Phosphorylation is a Critical Regulator of Neutrophil-Endothelial Cell Interaction in Inflammation

BACKGROUND

Neutrophil dysfunction plays an important role in inflammation-induced tissue injury. Previously, we identified protein kinase C-δ (PKCδ) as a critical controller of neutrophil activation and trafficking but how PKCδ is regulated in inflammation has not been delineated. PKCδ activity is regulated by tyrosine phosphorylation on multiple sites. Tyrosine155 is a key regulator of apoptosis and gene expression, but its role in proinflammatory signaling is not known.

METHODS

In-vitro studies - superoxide anion (O2) and neutrophil extracellular traps (NETs) were measured in bone marrow neutrophils (BMN) isolated from wild type (WT) and PKCδY155F knock-in mice (PKCδ tyrosine 155 → phenylalanine). Our novel 3D biomimetic microfluidic assay (bMFA) was used to delineate PKCδ-mediated regulation of individual steps in neutrophil adhesion and migration using WT and PKCδY155F BMN and mouse lung microvascular endothelial cells (MLMVEC). In-vivo studies - WT and PKCδY155F knock-in mice underwent sham or cecal ligation and puncture surgery and the lungs harvested 24 h post-surgery.

RESULTS

In vitro - PKCδY155F BMN had significantly reduced O2 and NETs release compared with WT. WT BMN, but not PKCδY155F BMN, demonstrated significant adhesion and migration across tumor necrosis factor-activated MLMVEC in bMFA. PKCδ inhibition significantly reduced WT BMN adhesion and migration under low shear and near bifurcations, but had no effect on PKCδY155F BMN. In vivo - mutation of PKCδ tyrosine 155 significantly decreased neutrophil migration into the lungs of septic mice.

CONCLUSIONS

PKCδ tyrosine 155 is a key phosphorylation site controlling proinflammatory signaling and neutrophil-endothelial cell interactions. These studies provide mechanistic insights into PKCδ regulation during inflammation.

Protein kinase C-delta inhibition is organ-protective, enhances pathogen clearance, and improves survival in sepsis

Sepsis is a leading cause of morbidity and mortality in intensive care units. Previously, we identified Protein Kinase C-delta (PKCδ) as an important regulator of the inflammatory response in sepsis. An important issue in development of anti-inflammatory therapeutics is the risk of immunosuppression and inability to effectively clear pathogens. In this study, we investigated whether PKCδ inhibition prevented organ dysfunction and improved survival without compromising pathogen clearance. Sprague Dawley rats underwent sham surgery or cecal ligation and puncture (CLP) to induce sepsis. Post-surgery, PBS or a PKCδ inhibitor (200µg/kg) was administered intra-tracheally (IT). At 24 hours post-CLP, there was evidence of lung and kidney dysfunction. PKCδ inhibition decreased leukocyte influx in these organs, decreased endothelial permeability, improved gas exchange, and reduced blood urea nitrogen/creatinine ratios indicating organ protection. PKCδ inhibition significantly decreased bacterial levels in the peritoneal cavity, spleen and blood but did not exhibit direct bactericidal properties. Peritoneal chemokine levels, neutrophil numbers, or macrophage phenotypes were not altered by PKCδ inhibition. Peritoneal macrophages isolated from PKCδ inhibitor-treated septic rats demonstrated increased bacterial phagocytosis. Importantly, PKCδ inhibition increased survival. Thus, PKCδ inhibition improved survival and improved survival was associated with increased phagocytic activity, enhanced pathogen clearance, and decreased organ injury.

Quercetin Directly Targets JAK2 and PKCδ and Prevents UV-Induced Photoaging in Human Skin

Quercetin is a naturally occurring polyphenol present in various fruits and vegetables. The bioactive properties of quercetin include anti-oxidative, anti-cancer, anti-inflammatory, and anti-diabetic effects. However, the effect of quercetin on skin aging and the direct molecular targets responsible have remained largely unknown. Herein, we investigated the protective effect of quercetin against UV-mediated skin aging and the molecular mechanisms responsible. Treatment with quercetin suppressed UV-induced matrix metalloproteinase-1 (MMP-1) and cyclooxygenase-2 (COX-2) expression and prevented UV-mediated collagen degradation in human skin tissues. Quercetin exerted potent inhibitory effects towards UV-induced activator protein-1 (AP-1) and nuclear factor-kappa B (NF-κB) activity. Further examination of the upstream signaling pathways revealed that quercetin can attenuate UV-mediated phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N terminal kinases (JNK), protein kinase B (Akt), and signal transducer and activator of transcription 3 (STAT3). Kinase assays using purified protein demonstrated that quercetin can directly inhibit protein kinase C delta (PKCδ) and Janus kinase 2 (JAK2) kinase activity. Quercetin was observed to bind to PKCδ and JAK2 in pull-down assays. These findings suggest that quercetin can directly target PKCδ and JAK2 in the skin to elicit protective effects against UV-mediated skin aging and inflammation. Our results highlight the potential use of quercetin as a natural agent for anti-skin aging applications.

The Role of Tyrosine Phosphorylation of Protein Kinase C Delta in Infection and Inflammation

Protein Kinase C (PKC) is a family composed of phospholipid-dependent serine/threonine kinases that are master regulators of inflammatory signaling. The activity of different PKCs is context-sensitive and these kinases can be positive or negative regulators of signaling pathways. The delta isoform (PKCδ) is a critical regulator of the inflammatory response in cancer, diabetes, ischemic heart disease, and neurodegenerative diseases. Recent studies implicate PKCδ as an important regulator of the inflammatory response in sepsis. PKCδ, unlike other members of the PKC family, is unique in its regulation by tyrosine phosphorylation, activation mechanisms, and multiple subcellular targets. Inhibition of PKCδ may offer a unique therapeutic approach in sepsis by targeting neutrophil-endothelial cell interactions. In this review, we will describe the overall structure and function of PKCs, with a focus on the specific phosphorylation sites of PKCδ that determine its critical role in cell signaling in inflammatory diseases such as sepsis. Current genetic and pharmacological tools, as well as in vivo models, that are used to examine the role of PKCδ in inflammation and sepsis are presented and the current state of emerging tools such as microfluidic assays in these studies is described.

Inhibitory mechanism of ginsenoside Rh3 on granulocyte-macrophage colony-stimulating factor expression in UV-B-irradiated murine SP-1 keratinocytes

Background

Ultraviolet (UV) goes through the epidermis and promotes release of inflammatory cytokines in keratinocytes. Granulocyte–macrophage colony-stimulating factor (GM-CSF), one of the keratinocyte-derived cytokines, regulates proliferation and differentiation of melanocytes. Extracellular signal–regulated kinase (ERK1/2) and protein kinase C (PKC) signaling pathways regulate expression of GM-CSF. Based on these results, we found that ginsenoside Rh3 prevented GM-CSF production and release in UV-B–exposed SP-1 keratinocytes and that this inhibitory effect resulted from the reduction of PKCδ and ERK phosphorylation.

Methods

We investigated the mechanism by which ginsenoside Rh3 from Panax ginseng inhibited GM-CSF release from UV-B–irradiated keratinocytes.

Results

Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) or UV-B induced release of GM-CSF in the SP-1 keratinocytes. To elucidate whether the change in GM-CSF expression could be related to PKC signaling, the cells were pretreated with H7, an inhibitor of PKC, and irradiated with UV-B. GM-CSF was decreased by H7 in a dose-dependent manner. When we analyzed which ginsenosides repressed GM-CSF expression among 15 ginsenosides, ginsenoside Rh3 showed the largest decline to 40% of GM-CSF expression in enzyme-linked immunosorbent assay. Western blot analysis showed that TPA enhanced the phosphorylation of PKCδ and ERK in the keratinocytes. When we examined the effect of ginsenoside Rh3, we identified that ginsenoside Rh3 inhibited the TPA-induced phosphorylation levels of PKCδ and ERK.

Conclusion

In summary, we found that ginsenoside Rh3 impeded UV-B–induced GM-CSF production through repression of PKCδ and ERK phosphorylation in SP-1 keratinocytes.

PKCδ inhibition as a novel medical countermeasure for radiation-induced vascular damage

In the event of a radiologic catastrophe, endothelial cell and neutrophil dysfunction play important roles in tissue injury. Clinically available therapeutics for radiation-induced vascular injury are largely supportive. PKCδ was identified as a critical regulator of the inflammatory response, and its inhibition was shown to protect critical organs during sepsis. We used a novel biomimetic microfluidic assay (bMFA) to interrogate the role of PKCδ in radiation-induced neutrophil-endothelial cell interaction and endothelial cell function. HUVECs formed a complete lumen in bMFA and were treated with 0.5, 2, or 5 Gy ionizing radiation (IR). At 24 h post-IR, the cells were treated with a PKCδ inhibitor for an additional 24 h. Under physiologic shear flow, the role of PKCδ on endothelium function and neutrophil adherence/migration was determined. PKCδ inhibition dramatically attenuated IR-induced endothelium permeability increase and significantly decreased neutrophil migration across IR-treated endothelial cells. Moreover, neutrophil adhesion to irradiated endothelial cells was significantly decreased after PKCδ inhibition in a flow-dependent manner. PKCδ inhibition downregulated IR-induced P-selectin, intercellular adhesion molecule 1, and VCAM-1 but not E-selectin overexpression. PKCδ is an important regulator of neutrophil-endothelial cell interaction post-IR, and its inhibition can serve as a potential radiation medical countermeasure.-Soroush, F., Tang, Y., Zaidi, H. M., Sheffield, J. B., Kilpatrick, L. E., Kiani, M. F. PKCδ inhibition as a novel medical countermeasure for radiation-induced vascular damage.

PKD signaling and pancreatitis

BACKGROUND

Acute pancreatitis is a serious medical disorder with no current therapies directed to the molecular pathogenesis of the disorder. Inflammation, inappropriate intracellular activation of digestive enzymes, and parenchymal acinar cell death by necrosis are the critical pathophysiologic processes of acute pancreatitis. Thus, it is necessary to elucidate the key molecular signals that mediate these pathobiologic processes and develop new therapeutic strategies to attenuate the appropriate signaling pathways in order to improve outcomes for this disease. A novel serine/threonine protein kinase D (PKD) family has emerged as key participants in signal transduction, and this family is increasingly being implicated in the regulation of multiple cellular functions and diseases.

METHODS

This review summarizes recent findings of our group and others regarding the signaling pathway and the biological roles of the PKD family in pancreatic acinar cells. In particular, we highlight our studies of the functions of PKD in several key pathobiologic processes associated with acute pancreatitis in experimental models.

RESULTS

Our findings reveal that PKD signaling is required for NF-κB activation/inflammation, intracellular zymogen activation, and acinar cell necrosis in rodent experimental pancreatitis. Novel small-molecule PKD inhibitors attenuate the severity of pancreatitis in both in vitro and in vivo experimental models. Further, this review emphasizes our latest advances in the therapeutic application of PKD inhibitors to experimental pancreatitis after the initiation of pancreatitis.

CONCLUSIONS

These novel findings suggest that PKD signaling is a necessary modulator in key initiating pathobiologic processes of pancreatitis, and that it constitutes a novel therapeutic target for treatments of this disorder.

In Vitro Neutrophil Migration Requires Protein Kinase C-Delta (δ-PKC)-Mediated Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) Phosphorylation

Dysregulated release of neutrophil reactive oxygen species and proteolytic enzymes contributes to both acute and chronic inflammatory diseases. Therefore, molecular regulators of these processes are potential targets for new anti-inflammatory therapies. We have shown previously that myristoylated alanine-rich C-kinase substrate (MARCKS), a well-known actin binding protein and protein kinase C (PKC) substrate, is a key regulator of neutrophil functions. In the current study, we investigate the role of PKC-mediated MARCKS phosphorylation in neutrophil migration and adhesion in vitro. We report that treatment of human neutrophils with the δ-PKC inhibitor rottlerin significantly attenuates f-Met-Leu-Phe (fMLF)-induced MARCKS phosphorylation (IC50=5.709 μM), adhesion (IC50=8.4 μM), and migration (IC50=6.7 μM), while α-, β-, and ζ-PKC inhibitors had no significant effect. We conclude that δ-PKC-mediated MARCKS phosphorylation is essential for human neutrophil migration and adhesion in vitro. These results implicate δ-PKC-mediated MARCKS phosphorylation as a key step in the inflammatory response of neutrophils.

Aldose reductase participates in the downregulation of T cell functions due to suppressor macrophages

The cell-to-cell contact of T lymphocytes with immunosuppressive macrophages causes marked changes in the tyrosine phosphorylation of some cytosolic proteins of T cells. By phosphoproteome analysis, we identified a 36-kDa protein as aldose reductase (AR). The AR expression in T cells was not changed by TCR stimulation or due to cell-to-cell transmission of suppressor signals from immunosuppressive macrophages. Therefore, AR phosphorylation/dephosphorylation is essential for the transduction of TCR-mediated T-cell stimulatory signals, and moreover plays important roles for the cross-talk of immunosuppressive macrophage-derived suppressor signals with the signaling pathways for T-cell activation. Moreover, AR played important roles in the upregulation of ERK1/2-mediated signaling pathways in T lymphocytes. Notably, the enzymatic activity of AR was not required for its signaling action. Taken together, it is concluded that AR mediates intracellular transmission of the suppressor signal of immunosuppressive macrophages toward downstream ERK1/2 pathways, possibly through its direct interaction with acceptor proteins.

Effective delivery of a rationally designed intracellular peptide drug with gold nanoparticle-peptide hybrids

A novel gold nanoparticle-peptide hybrid strategy was developed to intracellularly deliver a potent PKCδ inhibitor peptide for the treatment of acute lung injury. The gold nanoparticle-peptide hybrids showed good stability with high uptake, and demonstrated in vitro and in vivo efficacy. Our formulation strategy shows great promise in intracellular delivery of peptides.

Biodistribution and Efficacy of Targeted Pulmonary Delivery of a Protein Kinase C-δ Inhibitory Peptide: Impact on Indirect Lung Injury

Sepsis and sepsis-induced lung injury remain a leading cause of death in intensive care units. We identified protein kinase C-δ (PKCδ) as a critical regulator of the acute inflammatory response and demonstrated that PKCδ inhibition was lung-protective in a rodent sepsis model, suggesting that targeting PKCδ is a potential strategy for preserving pulmonary function in the setting of indirect lung injury. In this study, whole-body organ biodistribution and pulmonary cellular distribution of a transactivator of transcription (TAT)-conjugated PKCδ inhibitory peptide (PKCδ-TAT) was determined following intratracheal (IT) delivery in control and septic [cecal ligation and puncture (CLP)] rats to ascertain the impact of disease pathology on biodistribution and efficacy. There was negligible lung uptake of radiolabeled peptide upon intravenous delivery [<1% initial dose (ID)], whereas IT administration resulted in lung retention of >65% ID with minimal uptake in liver or kidney (<2% ID). IT delivery of a fluorescent-tagged (tetramethylrhodamine-PKCδ-TAT) peptide demonstrated uniform spatial distribution and cellular uptake throughout the peripheral lung. IT delivery of PKCδ-TAT at the time of CLP surgery significantly reduced PKCδ activation (tyrosine phosphorylation, nuclear translocation and cleavage) and acute lung inflammation, resulting in improved lung function and gas exchange. Importantly, peptide efficacy was similar when delivered at 4 hours post-CLP, demonstrating therapeutic relevance. Conversely, spatial lung distribution and efficacy were significantly impaired at 8 hours post-CLP, which corresponded to marked histopathological progression of lung injury. These studies establish a functional connection between peptide spatial distribution, inflammatory histopathology in the lung, and efficacy of this anti-inflammatory peptide.

Activation of PKC-δ in HTLV-1-infected T cells

Protein kinase C (PKC)-δ is a member of the PKC family. It has been implicated in tumor suppression as well as survival of various cancers. The aggressive malignancy of T lymphocytes known as adult T-cell leukemia (ATL) is associated with human T-cell leukemia virus type 1 (HTLV-1) infection. In this study, we show that HTLV-1-infected T cells are characterized by phosphorylation and nuclear translocation of PKC-δ. Expression of HTLV-1 regulatory protein Tax increased PKC-δ phosphorylation. Blockade of PKC-δ by rottlerin suppressed PKC-δ phosphorylation and inhibited cell viability in HTLV-1-infected T-cell lines and primary ATL cells. Rottlerin induced cell cycle arrest at the G1 phase and caspase-mediated apoptosis of HTLV-1-infected T cells. Rottlerin downregulated the expression of proteins involved in G1/S cell cycle transition, cyclin D2, CDK4 and 6, and c-Myc, resulting in dephosphorylation of retinoblastoma protein (pRb). Furthermore, rottlerin reduced the expression of important anti-apoptotic proteins (e.g., survivin, XIAP, Bcl-xL and c-FLIP) and Bcl-2 phosphorylation, and activated the pro-apoptotic protein Bax. Our results showed that permanent activation of nuclear factor-κB (NF-κB) by HTLV-1 Tax allows infected cells to escape cell cycle arrest and apoptosis and that PKC-δ mediates Tax-induced activation of NF-κB. Based on these findings, new therapies designed to target PKC-δ could be potentially useful in the treatment of ATL.

M3 mAChR-mediated IL-8 expression through PKC/NF-κB signaling pathways

OBJECTIVE

M3 muscarinic acetylcholine receptor (mAChR) plays an important role in the regulation of cytokine production in inflammatory diseases. In this study, we explored the precise role of M3 mAChR under stimulation with agonist in IL-8 expression and of the signaling pathway involved in this process.

MATERIALS AND METHODS

Recombinant U2OS cells stably expressing M3 mAChR as a model system were stimulated by carbachol to evaluate the role of M3 mAChR in the expression of IL-8.

RESULTS

Activation of M3 mAChR with carbachol increased both IL-8 mRNA and protein expression in a concentration-dependent manner. Elevated IL-8 expression was completely antagonized by atropine, 4-DAMP and tiotropium. M3 mAChR-mediated IL-8 expression was almost completely inhibited by the NF-κB inhibitor BAY11-7082 and, to a lesser extent, by U0126, SB203580, and SP600125, which are inhibitors for ERK1/2, p38, and JNK, respectively. Furthermore, M3 mAChR-mediated NF-κB activation and IL-8 expression were simultaneously attenuated by the PKC inhibitor calphostin C, whereas PMA, a PKC activator, mimicked the effects of carbachol, inducing IL-8 expression.

CONCLUSIONS

Our findings offer insights into the specific and critical role of M3 mAChR in regulating inflammatory response and indicate M3 mAChR/PKC/NF-κB signaling axis driven by endogenous acetylcholine as a potential therapeutic targets for inflammatory diseases.

Protein kinase C and acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a major public health problem and a leading source of morbidity in intensive care units. Lung tissue in patients with ARDS is characterized by inflammation, with exuberant neutrophil infiltration, activation, and degranulation that is thought to initiate tissue injury through the release of proteases and oxygen radicals. Treatment of ARDS is supportive primarily because the underlying pathophysiology is poorly understood. This gap in knowledge must be addressed to identify urgently needed therapies. Recent research efforts in anti-inflammatory drug development have focused on identifying common control points in multiple signaling pathways. The protein kinase C (PKC) serine-threonine kinases are master regulators of proinflammatory signaling hubs, making them attractive therapeutic targets. Pharmacological inhibition of broad-spectrum PKC activity and, more importantly, of specific PKC isoforms (as well as deletion of PKCs in mice) exerts protective effects in various experimental models of lung injury. Furthermore, PKC isoforms have been implicated in inflammatory processes that may be involved in the pathophysiologic changes that result in ARDS, including activation of innate immune and endothelial cells, neutrophil trafficking to the lung, regulation of alveolar epithelial barrier functions, and control of neutrophil proinflammatory and prosurvival signaling. This review focuses on the mechanistic involvement of PKC isoforms in the pathogenesis of ARDS and highlights the potential of developing new therapeutic paradigms based on the selective inhibition (or activation) of specific PKC isoforms.

Inhibition of protein kinase C delta attenuates allergic airway inflammation through suppression of PI3K/Akt/mTOR/HIF-1 alpha/VEGF pathway

Vascular endothelial growth factor (VEGF) is supposed to contribute to the pathogenesis of allergic airway disease. VEGF expression is regulated by a variety of stimuli such as nitric oxide, growth factors, and hypoxia-inducible factor-1 alpha (HIF-1α). Recently, inhibition of the mammalian target of rapamycin (mTOR) has been shown to alleviate cardinal asthmatic features, including airway hyperresponsiveness, eosinophilic inflammation, and increased vascular permeability in asthma models. Based on these observations, we have investigated whether mTOR is associated with HIF-1α-mediated VEGF expression in allergic asthma. In studies with the mTOR inhibitor rapamycin, we have elucidated the stimulatory role of a mTOR-HIF-1α-VEGF axis in allergic response. Next, the mechanisms by which mTOR is activated to modulate this response have been evaluated. mTOR is known to be regulated by phosphoinositide 3-kinase (PI3K)/Akt or protein kinase C-delta (PKC δ) in various cell types. Consistent with these, our results have revealed that suppression of PKC δ by rottlerin leads to the inhibition of PI3K/Akt activity and the subsequent blockade of a mTOR-HIF-1α-VEGF module, thereby attenuating typical asthmatic attack in a murine model. Thus, the present data indicate that PKC δ is necessary for the modulation of the PI3K/Akt/mTOR signaling cascade, resulting in a tight regulation of HIF-1α activity and VEGF expression. In conclusion, PKC δ may represent a valuable target for innovative therapeutic treatment of allergic airway disease.

Pulmonary endothelial protein kinase C-delta (PKCδ) regulates neutrophil migration in acute lung inflammation

Excessive neutrophil migration across the pulmonary endothelium into the lung and release of oxidants and proteases are key elements in pathogenesis of acute lung injury. Previously, we identified protein kinase C-delta (PKCδ) as an important regulator of proinflammatory signaling in human neutrophils and demonstrated that intratracheal instillation of a TAT-conjugated PKCδ inhibitory peptide (PKCδ-TAT) is lung protective in a rat model of sepsis-induced indirect pulmonary injury (cecal ligation and puncture). In the present study, intratracheal instillation of this PKCδ inhibitor resulted in peptide distribution throughout the lung parenchyma and pulmonary endothelium and decreased neutrophil influx, with concomitant attenuation of sepsis-induced endothelial ICAM-1 and VCAM-1 expression in this model. To further delineate the role of PKCδ in regulating neutrophil migration, we used an in vitro transmigration model with human pulmonary microvascular endothelial cells (PMVECs). Consistent with in vivo findings, inhibition of PMVEC PKCδ decreased IL-1β-mediated neutrophil transmigration. PKCδ regulation was stimulus-dependent; PKCδ was required for transmigration mediated by IL-1β and fMLP (integrin-dependent), but not IL-8 (integrin-independent). PKCδ was essential for IL-1β-mediated neutrophil adherence and NF-κB-dependent expression of ICAM-1 and VCAM-1. In PMVECs, IL-1β-mediated production of ROS and activation of redox-sensitive NF-κB were PKCδ dependent, suggesting an upstream signaling role. Thus, PKCδ has an important role in regulating neutrophil-endothelial cell interactions and recruitment to the inflamed lung.

Inflammatory signalings involved in airway and pulmonary diseases

In respiratory diseases, there is an increased expression of multiple inflammatory proteins in the respiratory tract, including cytokines, chemokines, and adhesion molecules. Chemokines have been shown to regulate inflammation and immune cell differentiation. Moreover, many of the known inflammatory target proteins, such as matrix metalloproteinase-9 (MMP-9), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), cyclooxygenase-2 (COX-2), and cytosolic phospholipase A₂ (cPLA₂), are associated with airway and lung inflammation in response to various stimuli. Injuriously environmental stimuli can access the lung through either the airways or the pulmonary and systemic circulations. The time course and intensity of responses by resident and circulating cells may be regulated by various inflammatory signalings, including Src family kinases (SFKs), protein kinase C (PKC), growth factor tyrosine kinase receptors, nicotinamide adenine dinucleotide phosphate (NADPH)/reactive oxygen species (ROS), PI3K/Akt, MAPKs, nuclear factor-kappa B (NF-κB), activator protein-1 (AP-1), and other signaling molecules. These signaling molecules regulate both key inflammatory signaling transduction pathways and target proteins involved in airway and lung inflammation. Here, we discuss the mechanisms involved in the expression of inflammatory target proteins associated with the respiratory diseases. Knowledge of the mechanisms of inflammation regulation could lead to the pharmacological manipulation of anti-inflammatory drugs in the respiratory diseases.

PKCδ as a regulator for TGFβ1-induced α-SMA production in a murine nonalcoholic steatohepatitis model

The precise mechanism of TGFβ1 signaling in the progression of non-alcoholic steatohepatitis (NASH) has remained unclear. In particular, a potential regulatory mechanism by which PKCδ affects profibrogenic gene expression had never been explored. In this study, therefore, the role of PKCδ in TGFβ1 mediated α-SMA expression was investigated using NASH model mice. In preparation of the NASH model, male C57BL6/J mice were fed a methionine-choline-deficient (MCD) diet for 3 weeks, after which time they were intraperitoneally injected with lipopolysaccharide (LPS). In addition, Tlr4(Lps-d) (CH3/HeJ) mice were used to demonstrate the TGFβ1 signaling's dependency on TLR4 induction. Liver histology and hepatic hepatitis markers were investigated, and hepatic gene expression levels were determined by real-time PCR. Acute liver injury by LPS injection specifically elevated not only α-SMA expression but also phospho-PKCδ in this model. In contrast, Tlr4(Lps-d) (CH3/HeJ) and blockade of TGFβ1 receptor by SB431542 resulted in a significant reduction of PKCδ activation and α-SMA expression. Moreover, the TGFβ1-induced α-SMA production was significantly reduced by a specific PKCδ inhibitor. These findings suggested that PKCδ plays a critical role in TGFβ1-induced α-SMA production in a NASH model. Thus, this was the first demonstration of the involvement of PKCδ in the regulation of α-SMA expression in NASH liver tissues, and the impaired induction of PKCδ phosphorylation by LPS in a steatohepatitis condition. Interestingly, treatment by PKCδ inhibitor caused dramatic reduction of myofibroblast activation, indicating that PKCδ represents a promising target for treating NASH.

Porcine reproductive and respiratory syndrome virus induces interleukin-15 through the NF-κB signaling pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) mainly infects macrophages/dendritic cells and modulates cytokine expression in these cells. Interleukin-15 (IL-15) is a pleiotropic cytokine involved in wide range of biological activities. It has been shown to be essential for the generation, activation, and proliferation of NK and NKT cells and for the survival and activation of CD8(+) effector and memory T cells. In this study, we discovered that PRRSV infection upregulated IL-15 production at both the mRNA and protein levels in porcine alveolar macrophages (PAMs), blood monocyte-derived macrophages (BMo), and monocyte-derived dendritic cells (DCs). We subsequently demonstrated that the NF-κB signaling pathway was essential for PRRSV infection-induced IL-15 production. First, addition of an NF-κB inhibitor drastically reduced PRRSV infection-induced IL-15 production. We then found that NF-κB was indeed activated upon PRRSV infection, as evidenced by IκB phosphorylation and degradation. Moreover, we revealed an NF-κB binding motif in the cloned porcine IL-15 (pIL-15) promoter, deletion of which abrogated the pIL-15 promoter activity in PRRSV-infected alveolar macrophages. In addition, we demonstrated that PRRSV nucleocapsid (N) protein had the ability to induce IL-15 production in porcine alveolar macrophage cell line CRL2843 by transient transfection, which was mediated by its multiple motifs, and it also activated NF-κB. These data indicated that PRRSV infection-induced IL-15 production was likely through PRRSV N protein-mediated NF-κB activation. Our findings provide new insights into the molecular mechanisms underling the IL-15 production induced by PRRSV infection.

Infection of human alveolar macrophages by human coronavirus strain 229E

Human coronavirus strain 229E (HCoV-229E) commonly causes upper respiratory tract infections. However, lower respiratory tract infections can occur in some individuals, indicating that cells in the distal lung are susceptible to HCoV-229E. This study determined the virus susceptibility of primary cultures of human alveolar epithelial cells and alveolar macrophages (AMs). Fluorescent antibody staining indicated that HCoV-229E could readily infect AMs, but no evidence was found for infection in differentiated alveolar epithelial type II cells and only a very low level of infection in type II cells transitioning to the type I-like cell phenotype. However, a human bronchial epithelial cell line (16HBE) was readily infected. The innate immune response of AMs to HCoV-229E infection was evaluated for cytokine production and interferon (IFN) gene expression. AMs secreted significant amounts of tumour necrosis factor alpha (TNF-α), regulated on activation normal T-cell expressed and secreted (RANTES/CCL5) and macrophage inflammatory protein 1β (MIP-1β/CCL4) in response to HCoV-229E infection, but these cells exhibited no detectable increase in IFN-β or interleukin-29 in mRNA levels. AMs from smokers had reduced secretion of TNF-α compared with non-smokers in response to HCoV-229E infection. Surfactant protein A (SP-A) and SP-D are part of the innate immune system in the distal lung. Both surfactant proteins bound to HCoV-229E, and pre-treatment of HCoV-229E with SP-A or SP-D inhibited infection of 16HBE cells. In contrast, there was a modest reduction in infection in AMs by SP-A, but not by SP-D. In summary, AMs are an important target for HCoV-229E, and they can mount a pro-inflammatory innate immune response to infection.

Effect of protein kinase C delta (PKC-δ) inhibition on the transcriptome of normal and systemic sclerosis human dermal fibroblasts in vitro

Previous studies demonstrated that protein kinase C- δ (PKC-δ) inhibition with the selective inhibitor, rottlerin, resulted in potent downregulation of type I collagen expression and production in normal human dermal fibroblasts and abrogated the exaggerated type I collagen production and expression in fibroblasts cultured from affected skin from patients with the fibrosing disorder systemic sclerosis (SSc). To elucidate the mechanisms involved in the ability of PKC-δ to regulate collagen production in fibroblasts, we examined the effects of PKC-δ inhibition on the transcriptome of normal and SSc human dermal fibroblasts. Normal and SSc human dermal fibroblasts were incubated with rottlerin (5 µM), and their gene expression was analyzed by microarrays. Pathway analysis and gene ontology analysis of differentially expressed genes in each comparison were performed. Identification of significantly overrepresented transcriptional regulatory elements (TREs) was performed using the Promoter Analysis and Interaction Network Toolset (PAINT) program. PKC-δ activity was also inhibited using RNA interference (siRNA) and by treating fibroblasts with a specific PKC-δ inhibitory cell permeable peptide. Differential gene expression of 20 genes was confirmed using real time PCR. PKC-δ inhibition caused a profound change in the transcriptome of normal and SSc human dermal fibroblasts in vitro. Pathway and gene ontology analysis identified multiple cellular and organismal pathways affected by PKC-δ inhibition. Furthermore, both pathway and PAINT analyses indicated that the transcription factor NFκB played an important role in the transcriptome changes induced by PKC-δ inhibition. Multiple genes involved in the degradation of the extracellular matrix components were significantly reduced in SSc fibroblasts and their expression was increased by PKC-δ inhibition. These results indicate that isoform-specific inhibition of PKC-δ profibrotic effects may represent a novel therapeutic approach for SSc and other fibrotic diseases.

Rottlerin exhibits antiangiogenic effects in vitro

Rottlerin, a natural product purified from Mallotus philippinensis, has a number of target molecules and biological effects. We recently found that Rottlerin caused growth arrest in MCF-7 breast cancer cells and human immortalized keratinocytes, through inhibition of NFκB and downregulation of cyclin D-1. To evaluate whether this effect could be generalized to primary cells, human microvascular endothelial cells were treated with Rottlerin. In this study, we demonstrated that Rottlerin prevents basal and TNFα-stimulated NFκB nuclear migration and DNA binding also in human microvascular endothelial cell, where NFκB inhibition was accompanied by the downregulation of NFκB target gene products, such as cyclin D-1 and endothelin-1, which are essential molecules for endothelial cell proliferation and survival. Rottlerin, indeed, inhibited human microvascular endothelial cells proliferation and tube formation on Matrigel. Rottlerin also increases cytoplasmic free calcium and nitric oxide levels and downregulates endothelin converting enzyme-1 expression, thus contributing to the drop in endothelin-1 and growth arrest. These results suggest that Rottlerin may prove useful in the development of therapeutic agents against angiogenesis.

Butyrophilin-like 1 encodes an enterocyte protein that selectively regulates functional interactions with T lymphocytes

Although local regulation of T-cell responses by epithelial cells is increasingly viewed as important, few molecules mediating such regulation have been identified. Skint1, a recently identified member of the Ig-supergene family expressed by thymic epithelial cells and keratinocytes, specifies the murine epidermal intraepithelial lymphocyte (IEL) repertoire. Investigating whether Skint1-related molecules might regulate IEL in other compartments, this study focuses on buytrophilin-like 1 (Btnl1), which is conspicuously similar to Skint1 and primarily restricted to small intestinal epithelium. Btnl1 protein is mostly cytoplasmic, but surface expression can be induced, and in vivo Btnl1 can be detected adjacent to the IEL. In a newly developed culture system, enforced epithelial cell expression of Btnl1 attenuated the cells' response to activated IEL, as evidenced by suppression of IL-6 and other inflammatory mediators. These findings offer a unique perspective on emerging genetic data that Btnl genes may comprise novel and important local regulators of gut inflammation.

Silencing of thrombospondin-1 is critical for myc-induced metastatic phenotypes in medulloblastoma

Mechanisms by which c-Myc (Myc) amplification confers aggressive medulloblastoma phenotypes are poorly defined. Here, we show using orthotopic models that high Myc expression promotes cell migration/invasion and induces metastatic tumors, which recapitulate aggressive histologic features of Myc-amplified primary human medulloblastoma. Using ChIP-chip analysis, we identified cell migration and adhesion genes, including Tsp-1/THBS1, ING4, PVRL3, and PPAP2B, as Myc-bound loci in medulloblastoma cells. Expression of Tsp-1 was most consistently and robustly diminished in medulloblastoma cell lines and primary human tumors with high Myc expression (n = 101, P = 0.032). Strikingly, stable Tsp-1 expression significantly attenuated in vitro transformation and invasive/migratory properties of high Myc-expressing medulloblastoma cells without altering cell proliferation, whereas RNA interference-mediated Myc knockdown was consistently accompanied by increased Tsp-1 levels and reduced cell migration and invasion in medulloblastoma cells. Chromatin immunoprecipitation (ChIP) assays revealed colocalization of Myc and obligate partner Max and correlated diminished RNA polymerase II occupancy (∼3-fold decrease, P < 0.01) with increased Myc binding at a core Tsp-1 promoter. Reporter gene and/or gel shift assays confirmed direct repression of Tsp-1 transcription by Myc and also identified JPO2, a Myc interactor associated with metastatic medulloblastoma, as a cofactor in Myc-mediated Tsp-1 repression. These findings indicate the Myc-regulatory network targets Tsp-1 via multiple mechanisms in medulloblastoma transformation, and highlight a novel critical role for Tsp-1 in Myc-mediated aggressive medulloblastoma phenotypes.

Phorbol ester-induced human cytomegalovirus major immediate-early (MIE) enhancer activation through PKC-delta, CREB, and NF-kappaB desilences MIE gene expression in quiescently infected human pluripotent NTera2 cells

The ways in which human cytomegalovirus (HCMV) major immediate-early (MIE) gene expression breaks silence from latency to initiate the viral replicative cycle are poorly understood. A delineation of the signaling cascades that desilence the HCMV MIE genes during viral quiescence in the human pluripotent N-Tera2 (NT2) cell model provides insight into the molecular mechanisms underlying HCMV reactivation. In this model, we show that phorbol 12-myristate 13-acetate (PMA) immediately activates the expression of HCMV MIE RNA and protein and greatly increases the MIE-positive (MIE(+)) NT2 cell population density; levels of Oct4 (pluripotent cell marker) and HCMV genome penetration are unchanged. Decreasing PKC-delta activity (pharmacological, dominant-negative, or RNA interference [RNAi] method) attenuates PMA-activated MIE gene expression. MIE gene activation coincides with PKC-delta Thr505 phosphorylation. Mutations in MIE enhancer binding sites for either CREB (cyclic AMP [cAMP] response element [CRE]) or NF-kappaB (kappaB) partially block PMA-activated MIE gene expression; the ETS binding site is negligibly involved, and kappaB does not confer MIE gene activation by vasoactive intestinal peptide (VIP). The PMA response is also partially attenuated by the RNAi-mediated depletion of the CREB or NF-kappaB subunit RelA or p50; it is not diminished by TORC2 knockdown or accompanied by TORC2 dephosphorylation. Mutations in both CRE and kappaB fully abolish PMA-activated MIE gene expression. Thus, PMA stimulates a PKC-delta-dependent, TORC2-independent signaling cascade that acts through cellular CREB and NF-kappaB, as well as their cognate binding sites in the MIE enhancer, to immediately desilence HCMV MIE genes. This signaling cascade is distinctly different from that elicited by VIP.

Protection against sepsis-induced lung injury by selective inhibition of protein kinase C-δ (δ-PKC)

Inflammation and proinflammatory mediators are activators of δ-PKC. In vitro, δ-PKC regulates proinflammatory signaling in neutrophils and endothelial and epithelial cells, cells that can contribute to lung tissue damage associated with inflammation. In this study, a specific δ-PKC TAT peptide inhibitor was used to test the hypothesis that inhibition of δ-PKC would attenuate lung injury in an animal model of ARDS. Experimental ARDS was induced in rats via 2CLP, a model of polymicrobial sepsis. Following 2CLP surgery, the δ-PKC TAT inhibitory peptide (2CLP+δ-PKC TAT in PBS) or PBS (2CLP+PBS) was administered intratracheally. Controls consisted of SO, where animals underwent a laparotomy without 2CLP. Twenty-four hours after SO or 2CLP, blood, BALF, and lung tissue were collected. 2CLP induced δ-PKC phosphorylation in the lung within 24 h. Treatment with the δ-PKC TAT inhibitory peptide significantly decreased pulmonary δ-PKC phosphorylation, indicating effective inhibition of δ-PKC activation. Plasma and BALF levels of the chemokines CINC-1 and MIP-2 were elevated in 2CLP + PBS rats as compared with SO rats. Treatment with δ-PKC TAT reduced 2CLP-induced elevations in chemokine levels in BALF and plasma, suggesting that δ-PKC modulated chemokine expression. Most importantly, intratracheal administration of δ-PKC TAT peptide significantly attenuated inflammatory cell infiltration, disruption of lung architecture, and pulmonary edema associated with 2CLP. Thus, δ-PKC is an important regulator of proinflammatory events in the lung. Targeted inhibition of δ-PKC exerted a lung-protective effect 24 h after 2CLP.

Prostaglandin E2/EP1 signaling pathway enhances intercellular adhesion molecule 1 (ICAM-1) expression and cell motility in oral cancer cells

Oral squamous cell carcinoma has a striking tendency to migrate and metastasize. Cyclooxygenase (COX)-2, the inducible isoform of prostaglandin (PG) synthase, has been implicated in tumor metastasis. However, the effects of COX-2 on human oral cancer cells are largely unknown. We found that overexpression of COX-2 or exogenous PGE(2) increased migration and intercellular adhesion molecule 1 (ICAM)-1 expression in human oral cancer cells. Using pharmacological inhibitors, activators, and genetic inhibition of EP receptors, we discovered that the EP1 receptor, but not other PGE receptors, is involved in PGE(2)-mediated cell migration and ICAM-1 expression. PGE(2)-mediated migration and ICAM-1 up-regulation were attenuated by inhibitors of protein kinase C (PKC)δ, and c-Src. Activation of the PKCδ, c-Src, and AP-1 signaling pathway occurred after PGE(2) treatment. PGE(2)-induced expression of ICAM-1 and migration activity were inhibited by a specific inhibitor, siRNA, and mutants of PKCδ, c-Src, and AP-1. In addition, migration-prone sublines demonstrated that cells with increased migration ability had higher expression of COX-2 and ICAM-1. Taken together, these results indicate that the PGE(2) and EP1 interaction enhanced migration of oral cancer cells through an increase in ICAM-1 production.

Lipoteichoic acid enhances IL-6 production in human synovial fibroblasts via TLR2 receptor, PKCdelta and c-Src dependent pathways

Patients with rheumatoid arthritis (RA) are at increased risk of developing infections and appear to be particularly susceptible to septic arthritis. Lipoteichoic acid (LTA), a cell wall component of Gram-positive bacteria is an amphiphilic, negatively charged glycolipid. However, the effects of LTA on human synovial fibroblasts are largely unknown. We investigated the signaling pathway involved in IL-6 production stimulated by LTA in rheumatoid arthritis synovial fibroblasts (RASF). LTA caused concentration- and time-dependent increases in IL-6 production. LTA-mediated IL-6 production was attenuated by Toll-like receptor 2 (TLR2) monoclonal antibody or siRNA. Pretreatment with PKCdelta inhibitor (rottlerin), c-Src inhibitor (PP2), AP-1 inhibitor (tanshinone IIA) and NF-kappaB inhibitor (PDTC and TPCK) also inhibited the potentiating action of LTA. However, focal adhesion kinase (FAK) mutant and siRNA did not affect LTA-mediated IL-6 production. Stimulation of cells with LTA increased the PKCdelta and c-Src phosphorylation and kinase activity. LTA increased the accumulation of p-c-Jun and p-p65 in the nucleus, as well as AP-1 and NF-kappaB luciferase activity. LTA-mediated increase of AP-1 and NF-kappaB luciferase activity was inhibited by rottlerin and PP2 or TLR2 and PKCdelta siRNA or c-Src mutant. Our results suggest that LTA-increased IL-6 production in human synovial fibroblasts via the TLR2 receptor, PKCdelta, c-Src, AP-1 and NF-kappaB signaling pathways.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Aldose reductase inhibition suppresses the expression of Th2 cytokines and airway inflammation in ovalbumin-induced asthma in mice

Airway inflammation induced by reactive oxygen species-mediated activation of redox-sensitive transcription factors is the hallmark of asthma, a prevalent chronic respiratory disease. In various cellular and animal models, we have recently demonstrated that, in response to multiple stimuli, aldose reductase (AR) regulates the inflammatory signals mediated by NF-kappaB. Because NF-kappaB-mediated inflammation is a major characteristic of asthma pathogenesis, we have investigated the effect of AR inhibition on NF-kappaB and various inflammatory markers in cellular and animal models of asthma using primary human small airway epithelial cells and OVA-sensitized/challenged C57BL/6 mice, respectively. We observed that pharmacological inhibition or genetic ablation of AR by small interfering RNA prevented TNF-alpha- as well as LPS-induced apoptosis; reactive oxygen species generation; synthesis of inflammatory markers IL-6, IL-8, and PGE(2); and activation of NF-kappaB and AP-1 in small airway epithelial cells. In OVA-challenged mice, we observed that administration of an AR inhibitor markedly reduced airway hyperresponsiveness, IgE levels, eisonophils infiltration, and release of Th2 type cytokines in the airway. Our results indicate that AR inhibitors may offer a novel therapeutic approach to treat inflammatory airway diseases such as asthma.

Protein kinase Cdelta stimulates proteasome-dependent degradation of C/EBPalpha during apoptosis induction of leukemic cells

Background

The precise regulation and maintenance of balance between cell proliferation, differentiation and death in metazoan are critical for tissue homeostasis. CCAAT/enhancer-binding protein alpha (C/EBPα) has been implicated as a key regulator of differentiation and proliferation in various cell types. Here we investigated the potential dynamic change and role of C/EBPα protein during apoptosis induction.

Methodology/Principal Findings

Upon onset of apoptosis induced by various kinds of inducers such as NSC606985, etoposide and others, C/EBPα expression presented a profound down-regulation in leukemic cell lines and primary cells via induction of protein degradation and inhibition of transcription, as assessed respectively by cycloheximide inhibition test, real-time quantitative RT-PCR and luciferase reporter assay. Applying chemical inhibition, forced expression of dominant negative mutant and catalytic fragment (CF) of protein kinase Cdelta (PKCδ), which was proteolytically activated during apoptosis induction tested, we showed that the active PKCδ protein contributed to the increased degradation of C/EBPα protein. Three specific proteasome inhibitors antagonized C/EBPα degradation during apoptosis induction. More importantly, ectopic expression of PKCδ-CF stimulated the ubiquitination of C/EBPα protein, while the chemical inhibition of PKCδ action significantly inhibited the enhanced ubiquitination of C/EBPα protein under NSC606985 treatment. Additionally, silencing of C/EBPα expression by small interfering RNAs enhanced, while inducible expression of C/EBPα inhibited NSC606985/etoposide-induced apoptosis in leukemic cells.

Conclusions/Significance

These observations indicate that the activation of PKCδ upon apoptosis results in the increased proteasome-dependent degradation of C/EBPα, which partially contributes to PKCδ-mediated apoptosis.

Sequential activation of protein kinase C isoforms by organic dust is mediated by tumor necrosis factor

Dust samples collected from Nebraska swine confinement facilities (hog dust extract [HDE]) are known to elicit proinflammatory cytokine release from human bronchial epithelial (HBE) cells in vitro. This response involves the activation of two protein kinase C (PKC) isoforms: PKCalpha and PKCepsilon. Experiments were designed to investigate the relationship between the two isoenzymes and the degree to which each is responsible for cytokine release in HBE. Experiments also examined the contribution of TNF-alpha to IL-6 and IL-8 release. PKCalpha and PKCepsilon activities were inhibited using isoform-specific pharmacologic inhibitors and genetically modified dominant-negative (DN) expressing cell lines. Release of the proinflammatory cytokines IL-6, IL-8, and TNF-alpha was measured and PKC isoform activities assessed. We found that HDE stimulates PKCalpha activity by 1 hour, and within 6 hours the activity returns to baseline. PKCalpha-specific inhibitor or PKCalphaDN cells abolish this HDE-mediated effect. Both IL-6 and IL-8 release are likewise diminished under these conditions compared with normal HBE, and treatment with TNF-alpha-neutralizing antibody does not further inhibit cytokine release. In contrast, PKCepsilon activity was enhanced by 6 hours after HDE treatment. TNF-alpha blockade abrogated this effect. HDE-stimulated IL-6, but not IL-8 release in PKCepsilonDN cells. The concentration of TNF-alpha released by HDE-stimulated HBE is sufficient to have a potent cytokine-eliciting effect. A time course of TNF-alpha release suggests that TNF-alpha is produced after PKCalpha activation, but before PKCepsilon. These results suggest a temporal ordering of events responsible for the release of cytokines, which initiate and exacerbate inflammatory events in the airways of people exposed to agricultural dust.

Oxidized low-density lipoprotein-induced matrix metalloproteinase-9 expression via PKC-delta/p42/p44 MAPK/Elk-1 cascade in brain astrocytes

After ischemic injury to brain, disruption of the blood-brain barrier (BBB) raises the possibility of exposing the central nervous system (CNS) to oxidized low-density lipoprotein (oxLDL), a risk factor implicated in neurodegenerative diseases. Matrix metalloproteinases (MMPs), especially MMP-9, contribute to extracellular matrix (ECM) remodeling during the CNS diseases. However, the molecular mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes remained unclear. Here, we reported that oxLDL induced MMP-9 expression via a PKC-delta/p42/p44 MAPK-dependent Elk-1 activation in rat brain astrocyte (RBA)-1 cells, revealed by gelatin zymography, RT-PCR, and Western blotting analyses. These responses were attenuated by pretreatment with pharmacological inhibitors and transfection with dominant negative mutants. Moreover, Elk-1-mediated MMP-9 gene transcription was confirmed by transfection with an Elk-1 binding site-mutated MMP-9 promoter construct (mt-Ets-MMP9), which blocked oxLDL-stimulated MMP-9 luciferase activity. Understanding the regulatory mechanisms by which oxLDL induced MMP-9 expression in astrocytes might provide a new therapeutic strategy of brain diseases.

Effect of curcumin on acidic pH-induced expression of IL-6 and IL-8 in human esophageal epithelial cells (HET-1A): role of PKC, MAPKs, and NF-kappaB

Human esophageal epithelial cells play a key role in esophageal inflammation in response to acidic pH during gastroesophageal reflux disease (GERD), increasing secretion of IL-6 and IL-8. The mechanisms underlying IL-6 and IL-8 expression and secretion in esophageal epithelial cells after acid stimulation are not well characterized. We investigated the role of PKC, MAPK, and NF-kappaB signaling pathways and transcriptional regulation of IL-6 and IL-8 expression in HET-1A cells exposed to acid. Exposure of HET-1A cells to pH 4.5 induced NF-kappaB activity and enhanced IL-6 and IL-8 secretion and mRNA and protein expression. Acid stimulation of HET-1A cells also resulted in activation of MAPKs and PKC (alpha and epsilon). Curcumin, as well as inhibitors of NF-kappaB (SN-50), PKC (chelerythrine), and p44/42 MAPK (PD-098059) abolished the acid-induced expression of IL-6 and IL-8. The JNK inhibitor SP-600125 blocked expression/secretion of IL-6 but only partially attenuated IL-8 expression. The p38 MAPK inhibitor SB-203580 did not inhibit IL-6 expression but exerted a stronger inhibitory effect on IL-8 expression. Together, these data demonstrate that 1) acid is a potent inducer of IL-6 and IL-8 production in HET-1A cells; 2) MAPK and PKC signaling play a key regulatory role in acid-mediated IL-6 and IL-8 expression via NF-kappaB activation; and 3) the anti-inflammatory plant compound curcumin inhibits esophageal activation in response to acid. Thus IL-6 and IL-8 expression by acid may contribute to the pathobiology of mucosal injury in GERD, and inhibition of the NF-kappaB/proinflammatory cytokine pathways may emerge as important therapeutic targets for treatment of esophageal inflammation.

Protein kinase D1 mediates NF-kappaB activation induced by cholecystokinin and cholinergic signaling in pancreatic acinar cells

The transcription factor NF-kappaB plays a critical role in inflammatory and cell death responses during acute pancreatitis. Previous studies in our laboratory demonstrated that protein kinase C (PKC) isoforms PKCdelta and epsilon are key regulators of NF-kappaB activation induced by cholecystokinin-8 (CCK-8), tumor necrosis factor-alpha, and ethanol. However, the downstream participants in regulating NF-kappaB activation in exocrine pancreas remain poorly understood. Here, we demonstrate that protein kinase D1 (PKD1) is a key downstream target of PKCdelta and PKCepsilon in pancreatic acinar cells stimulated by two major secretagogues, CCK-8 and the cholinergic agonist carbachol (CCh), and that PKD1 is necessary for NF-kappaB activation induced by CCK-8 and CCh. Both CCK-8 and CCh dose dependently induced a rapid and striking activation of PKD1 in rat pancreatic acinar cells, as measured by in vitro kinase assay and by phosphorylation at PKD1 activation loop (Ser744/748) or autophosphorylation site (Ser916). The phosphorylation and activation of PKD1 correlated with NF-kappaB activity stimulated by CCK-8 or CCh, as measured by NF-kappaB DNA binding. Either inhibition of PKCdelta or epsilon by isoform-specific inhibitory peptides, genetic deletion of PKCdelta and epsilon in pancreatic acinar cells, or knockdown of PKD1 by using small interfering RNAs in AR42J cells resulted in a marked decrease in PKD1 and NF-kappaB activation stimulated by CCK-8 or CCh. Conversely, overexpression of PKD1 resulted in augmentation of CCK-8- and CCh-stimulated NF-kappaB activation. Finally, the kinetics of PKD1 and NF-kappaB activation during cerulein-induced rat pancreatitis showed that both PKD1 and NF-kappaB activation were early events during acute pancreatitis and that their time courses of response were similar. Our results identify PKD1 as a novel early convergent point for PKCdelta and epsilon in the signaling pathways mediating NF-kappaB activation in pancreatitis.

Differences in the length of the carboxyl terminus mediate functional properties of neurokinin-1 receptor

The neurokinin-1 receptor (NK1R) has two naturally occurring forms that differ in the length of the carboxyl terminus: a full-length receptor consisting of 407 aa and a truncated receptor consisting of 311 aa. We examined whether there are differential signaling properties attributable to the carboxyl terminus of this receptor by using stably transfected human embryonic kidney (HEK293) cell lines that express either full-length or truncated NK1R. Substance P (SP) specifically triggered intracellular calcium increase in HEK293 cells expressing full-length NK1R but had no effect in the cells expressing the truncated NK1R. In addition, in cells expressing full-length NK1R, SP activated NF-kappaB and IL-8 mRNA expression, but in cells expressing the truncated NK1R, SP did not activate NF-kappaB, and it decreased IL-8 mRNA expression. In cells expressing full-length NK1R, SP stimulated phosphorylation of PKCdelta but inhibited phosphorylation of PKCdelta in cells expressing truncated NK1R. There are also differences in the timing of SP-induced ERK activation in cells expressing the two different forms of the receptor. Full-length NK1R activation of ERK was rapid (peak within 1-2 min), whereas truncated NK1R-mediated activation was slower (peak at 20-30 min). Thus, the carboxyl terminus of NK1R is the structural basis for differences in the functional properties of the full-length and truncated NK1R. These differences may provide important information toward the design of new NK1R receptor antagonists.

Regulation of neutral sphingomyelinase-2 (nSMase2) by tumor necrosis factor-alpha involves protein kinase C-delta in lung epithelial cells

Neutral sphingomyelinases (N-SMases) are major candidates for stress-induced ceramide production, but there is still limited knowledge of the regulatory mechanisms of the cloned N-SMase enzyme-nSMase2. We have reported that p38 mitogen-activated protein kinase (MAPK) was upstream of nSMase2 in tumor necrosis-alpha (TNF-alpha)-stimulated A549 cells ( J Biol Chem 282: 1384-1396, 2007 ). Here, we report a role for protein kinase C (PKC) in mediating TNF-induced translocation of nSMase2 from the Golgi to the plasma membrane (PM). Pharmacological inhibition of PKCs prevented TNF-stimulated nSMase2 translocation to the PM in A549 cells. Using phorbol 12-myristate 13-acetate (PMA) as a tool to dissect PKC responses, we found that PMA induced nSMase2 translocation to the PM in a time- and dose-dependent manner. Pharmacological inhibitors and specific siRNA implicated the novel PKCs, specifically PKC-delta, in both TNF and PMA-stimulated nSMase2 translocation. However, PMA did not increase in vitro N-SMase activity and PKC-delta did not regulate TNF-induced N-SMase activity. Furthermore, PKC-delta and nSMase2 did not coimmunoprecipitate, suggesting that other signaling proteins may be involved. PMA-stimulated nSMase2 translocation was independent of p38 MAPK, and neither PKC inhibitors nor small interfering RNA had significant effects on TNF-stimulated p38 MAPK activation, indicating that PKC-delta does not act through p38 MAPK in regulating nSMase2. Finally, down-regulation of PKC-delta inhibited induction of vascular cell and intercellular adhesion molecules, previously identified as downstream of nSMase2 in A549 cells. Taken together, these data implicate PKC-delta as a regulator of nSMase2 and, for the first time, identify nSMase2 as a point of cross-talk between the PKC and sphingolipid pathways.

Upregulation of protein kinase cdelta in vascular smooth muscle cells promotes inflammation in abdominal aortic aneurysm

BACKGROUND

The development of abdominal aortic aneurysms (AAAs) involves a complex interplay of extracellular matrix degradation, inflammation, and apoptosis. We have previously shown that protein kinase Cdelta (PKCdelta) plays a critical role in vascular smooth muscle cell (vSMC) apoptosis in the setting of oxidative stresses. Here, we show that PKCdelta is also involved in the signaling that draws inflammatory cells to aneurismal tissue.

MATERIALS AND METHODS

Immunostaining for monocyte chemotactic factor (MCP)-1 and PKCdelta was performed on paraffin-fixed arterial sections. Enzyme-linked immunosorbent assay to detect MCP-1 produced by vSMCs was performed on media from cultured rat A10 cells after cytokine induction with or without the PKCdelta-specific inhibitor rottlerin. Migration of isolated lymphocytes was evaluated in response to media from activated A10 cells.

RESULTS

Human AAAs show widespread and elevated expression of PKCdelta that is not seen in normal aortic tissues. Cytokine stimulation of cultured vSMCs induced vigorous production of the key chemotactant MCP-1, the expression of which was PKCdelta dependent. Stimulated vSMCs were capable of inducing the migration of leukocytes, and this effect was also dependent on PKCdelta activity. Staining of human AAA tissue for MCP-1 showed an expression pattern that was identical to that of PKCdelta and smooth muscle specific alpha-actin.

CONCLUSIONS

PKCdelta is widely expressed in human AAA vessel walls and mediates MCP-1 expression by vSMCs, which could contribute to the inflammatory process. These findings, coupled with earlier studies of PKCdelta, suggest that PKCdelta plays a central role in the pathogenesis of AAAs and may be a potential target for future therapies.

Activation of Syk by protein kinase C-delta regulates thrombin-induced intercellular adhesion molecule-1 expression in endothelial cells via tyrosine phosphorylation of RelA/p65

Protein kinase C-delta (PKC-delta) plays a pivotal role in mediating thrombin-induced NF-kappaB activation and ICAM-1 expression in endothelial cells. However, the downstream mechanisms mediating its function are unclear. In this study, we show that PKC-delta-mediated activation of protein-tyrosine kinase Syk plays an important role in thrombin signaling of NF-kappaB activation and intercellular adhesion molecule-1 (ICAM-1) expression in endothelial cells. Stimulation of human vascular endothelial cells with thrombin resulted in a time-dependent phosphorylation of Syk on tyrosine 525 and 526, an indication of Syk activation. Inhibition of PKC-delta by pharmacological and genetic approaches prevented Syk activation by thrombin. These results place Syk downstream of PKC-delta in transmitting thrombin-activated signaling in endothelial cells. Consistent with this, thrombin-induced NF-kappaB activity and ICAM-1 expression were prevented by the expression of a kinase-defective mutant or RNA interference knockdown of Syk. Similarly, inhibiting Syk also impaired NF-kappaB activity and ICAM-1 expression induced by a constitutively active mutant of PKC-delta. Analysis of the NF-kappaB pathway showed that Syk contributes to thrombin-induced NF-kappaB activation by controlling its transactivation potential and that this response is associated with tyrosine phosphorylation of RelA/p65. Thus, these data unveil a novel pathway in which Syk signals downstream of PKC-delta to mediate thrombin induced ICAM-1 expression in endothelial cells by increasing transcriptional capacity of NF-kappaB via a mechanism that relies on tyrosine phosphorylation of RelA/p65.

Phorbol ester-stimulated NF-kappaB-dependent transcription: roles for isoforms of novel protein kinase C

Since protein kinase C (PKC) isoforms are variously implicated in the activation of NF-kappaB, we have investigated the role of PKC in the activation of NF-kappaB-dependent transcription by the diacyl glycerol (DAG) mimetic, phorbol 12-myristate 13-acetate (PMA), and by tumour necrosis factor (TNF) alpha in pulmonary A549 cells. The PKC selective inhibitors, Ro31-8220, Gö6976, GF109203X and Gö6983, revealed no effect on TNFalpha-induced NF-kappaB DNA binding and a similar lack of effect on serine 32/36 phosphorylated IkappaBalpha and the loss of total IkappaBalpha indicates that activation of the core IKK-IkappaBalpha-NF-kappaB cascade by TNFalpha does not involve PKC. In contrast, differential sensitivity of an NF-kappaB-dependent reporter to Ro31-8220, Gö6976, GF109203X and Gö6983 (EC(50)s 0.46 microM, 0.34 microM, >10 microM and >10 microM respectively) suggests a role for protein kinase D in transcriptional activation by TNFalpha. Compared with TNFalpha, PMA weakly induces NF-kappaB DNA binding and this effect was not associated with serine 32/36 phosphorylation of IkappaBalpha. However, PMA-stimulated NF-kappaB DNA binding was inhibited by Ro31-8220 (10 microM), GF109203X (10 microM) and Gö6983 (10 microM), but not by Gö6976 (10 microM), suggesting a role for novel PKC isoforms. Furthermore, a lack of positive effect of calcium mobilising agents on both NF-kappaB DNA binding and on transcriptional activation argues against major roles for classical PKCs. This, combined with the ability of both GF109203X and Gö6983 to prevent enhancement of TNFalpha-induced NF-kappaB-dependent transcription by PMA, further indicates a role for novel PKCs in NF-kappaB transactivation. Finally, siRNA-mediated knockdown of PKCdelta and epsilon expression did not affect TNFalpha-induced NF-kappaB-dependent transcription. However, knockdown of PKCdelta expression significantly inhibited PMA-stimulated luciferase activity, whereas knockdown of PKCepsilon was without effect. Furthermore, combined knockdown of PKCdelta and epsilon revealed an increased inhibitory effect on PMA-stimulated NF-kappaB-dependent transcription suggesting that PMA-induced NF-kappaB-dependent transcription is driven by novel PKC isoforms, particularly PKCdelta and epsilon.