Protein kinase C, interleukin-1 beta, and corticosteroids regulate shedding of the type I, 55 kDa TNF receptor from human airway epithelial cells

The Contribution of the Airway Epithelial Cell to Host Defense

In the context of cystic fibrosis, the epithelial cell has been characterized in terms of its ion transport capabilities. The ability of an epithelial cell to initiate CFTR-mediated chloride and bicarbonate transport has been recognized early as a means to regulate the thickness of the epithelial lining fluid and recently as a means to regulate the pH, thereby determining critically whether or not host defense proteins such as mucins are able to fold appropriately. This review describes how the epithelial cell senses the presence of pathogens and inflammatory conditions, which, in turn, facilitates the activation of CFTR and thus directly promotes pathogens clearance and innate immune defense on the surface of the epithelial cell. This paper summarizes functional data that describes the effect of cytokines, chemokines, infectious agents, and inflammatory conditions on the ion transport properties of the epithelial cell and relates these key properties to the molecular pathology of cystic fibrosis. Recent findings on the role of cystic fibrosis modifier genes that underscore the role of the epithelial ion transport in host defense and inflammation are discussed.

Shedding of the tumor necrosis factor (TNF) receptor from the surface of hepatocytes during sepsis limits inflammation through cGMP signaling

Proteolytic cleavage of the tumor necrosis factor (TNF) receptor (TNFR) from the cell surface contributes to anti-inflammatory responses and may be beneficial in reducing the excessive inflammation associated with multiple organ failure and mortality during sepsis. Using a clinically relevant mouse model of polymicrobial abdominal sepsis, we found that the production of inducible nitric oxide synthase (iNOS) in hepatocytes led to the cyclic guanosine monophosphate (cGMP)-dependent activation of the protease TACE (TNF-converting enzyme) and the shedding of TNFR. Furthermore, treating mice with a cGMP analog after the induction of sepsis increased TNFR shedding and decreased systemic inflammation. Similarly, increasing the abundance of cGMP with a clinically approved phosphodiesterase 5 inhibitor (sildenafil) also decreased markers of systemic inflammation, protected against organ injury, and increased circulating amounts of TNFR1 in mice with sepsis. We further confirmed that a similar iNOS-cGMP-TACE pathway was required for TNFR1 shedding by human hepatocytes in response to the bacterial product lipopolysaccharide. Our data suggest that increasing the bioavailability of cGMP might be beneficial in ameliorating the inflammation associated with sepsis.

Prenatal dexamethasone exposure in rats results in long-term epigenetic histone modifications and tumour necrosis factor-α production decrease

Glucocorticoid (GC) is often given when preterm delivery is expected. This treatment is successful in stimulating the development of the fetal lung. However, reports and related research regarding the prolonged effects of prenatal GC on the development of immunity are very limited. Some data, derived from infants whose mothers were given immunosuppressants during pregnancy for the treatment of autoimmune disorders, suggest that prenatal exposure to GC may have only a limited effect on the development of the immune system. What is unknown is whether the immune modulation effects of prenatal GC might appear at a later childhood stage and beyond. Here we evaluated the immune programming influenced by prenatal GC. Pregnant Sprague-Dawley rats received dexamethasone (DEX; 0.1 mg/kg/day) or saline at gestational days 14-20. Male offspring were killed at day 7 or day 120 after birth. Spleens were collected for immune study. Of the inflammation mediators, matrix metalloproteinase-9, tumour necrosis factor-α (TNF-α) and granulocyte-macrophage colony-stimulating factor mRNAs decreased in the prenatal DEX group at an early stage after birth. Upon concanavalin A stimulation, prenatal DEX treatment reduced TNF-α production, but not interferon-γ production, by splenocytes at day 120 after birth compared with the vehicle group. Decreased levels of active chromatin signs (acetylation of histone H3 lysines, H3K4me1/3, and H3K36me3) in TNF-α promoter were compatible with the expressions of TNF-α. Our results suggest that prenatal DEX has a profound and lasting impact on the developing immune system even to the adult stage. Epigenetic histone modifications regulate TNF-α expression following prenatal DEX in rats.

Double-stranded RNA induces shedding of the 34-kDa soluble TNFR1 from human airway epithelial cells via TLR3-TRIF-RIP1-dependent signaling: roles for dual oxidase 2- and caspase-dependent pathways

TNF, an important mediator of inflammatory and innate immune responses, can be regulated by binding to soluble TNF receptors. The 55-kDa type 1 TNFR (TNFR1), the key receptor for TNF signaling, is released to the extracellular space by two mechanisms, the inducible cleavage and shedding of 34-kDa soluble TNFR1 (sTNFR1) ectodomains and the constitutive release of full-length 55-kDa TNFR1 within exosome-like vesicles. The aim of this study was to identify and characterize TLR signaling pathways that mediate TNFR1 release to the extracellular space. To our knowledge, we demonstrate for the first time that polyinosinic-polycytidylic acid [poly (I:C)], a synthetic dsRNA analogue that signals via TLR3, induces sTNFR1 shedding from human airway epithelial (NCI-H292) cells, whereas ligands for other microbial pattern recognition receptors, including TLR4, TLR7, and nucleotide-binding oligomerization domain containing 2, do not. Furthermore, poly (I:C) selectively induces the cleavage of 34-kDa sTNFR1 ectodomains but does not enhance the release of full-length 55-kDa TNFR1 within exosome-like vesicles. RNA interference experiments demonstrated that poly (I:C)-induced sTNFR1 shedding is mediated via activation of TLR3-TRIF-RIP1 signaling, with subsequent activation of two downstream pathways. One pathway involves the dual oxidase 2-mediated generation of reactive oxygen species, and the other pathway is via the caspase-mediated activation of apoptosis. Thus, the ability of dsRNA to induce the cleavage and shedding of the 34-kDa sTNFR1 from human bronchial epithelial cells represents a novel mechanism by which innate immune responses to viral infections are modulated.

Serum Levels of Soluble TNFα Receptors (sTNFR1 and sTNFR2) During Corticosteroid Treatment in Patients with Graves' Ophthalmopathy

TNFalpha was shown to play an important role in the autoimmune inflammatory process of Graves' ophthalmopathy (GO). In our previous study we found no significant changes in serum TNFalpha levels in GO patients. The aim of the present study was to estimate an influence of corticosteroids on serum levels of TNFalpha receptors (sTNFR1 and sTNFR2) in GO patients and to assess their potential as a guideline of immunosuppressive therapy. We detected serum sTNFRI and sTNFR2 in three groups of subjects: 18 patients with clinical symptoms of ophthalmopathy [Clinical Activity Score (CAS) > or = 4, anamnesis of GO > or = 1 yr], 16 patients with Graves' disease without ophthalmopathy (Gd) and 14 healthy volunteers. Corticosteroid therapy consisted of intravenous infusions of methylprednisolone (MP) and subsequent treatment with oral prednisone (P). The serum samples were collected 24 hours before MP, 24 hours after MP, 14 days of treatment with prednisone and after the end of the corticosteroid therapy. The levels of serum sTNFR1 and sTNFR2 were determined by ELISA. Serum levels of sTNFR1 were significantly higher in GO individuals as compared to the control group (p < 0.01). We have found a significant decrease in sTNFR1 concentration in corticosteroid-respondent patients (satisfactory clinical effect, decrease of CAS > or = 1) as compared to the pretreatment values after MP treatment (p < 0.05) and after 14 days of prednisone (p < 0.01). There were significant differences in sTNFR2 level after MP treatment (p < 0.02) and after corticosteroid administration (p < 0.05) between responders and non-responders. Baseline values of sTNFRI in GO individuals were positively correlated with CAS (r = 0.6, p < 0.02).

CONCLUSIONS

TNFalpha acting through its receptors plays an important role in the pathogenesis of Graves' ophthalmopathy. Moreover, the beneficial influence of corticosteroids on the course of GO may be explained, at least in part, by an inhibition of sTNFR1 and sTNFR2. Measurement of soluble TNFalpha receptors might potentially serve as an indicator in prognostic estimation of corticosteroids' efficacy.

IL-1beta augments TNF-alpha-mediated inflammatory responses from lung epithelial cells

Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) mediate the development of numerous inflammatory lung diseases. Since IL-1beta is typically activated in situations where TNF-alpha is produced, it was hypothesized that IL-1beta alters TNF-alpha-induced proinflammatory epithelial cell function by altering TNF receptor shedding and surface abundance. In this study, the impact of IL-1beta on TNF-alpha-mediated chemokine production as well as TNF receptor surface expression and shedding were investigated from mouse pulmonary epithelial cells (MLE-15). Interleukin-1beta rapidly and persistently enhanced soluble and surface TNFR2. These effects were dependent on TNFR1 expression. TNFR2 small-interfering RNA (siRNA) shifted IL-1beta responses, significantly increasing surface and shed TNFR1 implying IL-1beta selectively modifies TNF receptors depending on cellular receptor composition. mRNA expression of both receptors was unaltered by IL-1beta up to 24 h or in combination with TNF-alpha indicating effects were post-transcriptional. Interleukin-1beta pretreatment enhanced TNF-alpha-induced macrophage inflammatory protein (MIP)-2 and KC mRNA expression as well as MIP-2 and KC protein levels at the same time point analyzed. Experiments utilizing siRNA against the TNF receptors and a TNFR1 neutralizing antibody demonstrated TNF-alpha induced MIP-2 through TNFR1, whereas both receptors may have contributed to KC production. These data suggest IL-1beta modulates TNF-alpha-mediated inflammatory lung diseases by enhancing epithelial cell TNF receptor surface expression.

Extracellular Hsp72, an endogenous DAMP, is released by virally infected airway epithelial cells and activates neutrophils via Toll-like receptor (TLR)-4

Background

Neutrophils play an important role in the pathophysiology of RSV, though RSV does not appear to directly activate neutrophils in the lower airways. Therefore locally produced cytokines or other molecules released by virally-infected airway epithelial cells are likely responsible for recruiting and activating neutrophils. Heat shock proteins (HSPs) are generally regarded as intracellular proteins acting as molecular chaperones; however, HSP72 can also be released from cells, and the implications of this release are not fully understood.

Methods

Human bronchial epithelial cells (16HBE14o-) were infected with RSV and Hsp72 levels were measured by Western blot and ELISA. Tracheal aspirates were obtained from critically ill children infected with RSV and analyzed for Hsp72 levels by ELISA. Primary human neutrophils and differentiated HL-60 cells were cultured with Hsp72 and supernatants analyzed for cytokine production. In some cases, cells were pretreated with polymyxin B prior to treatment with Hsp72. IκBα was assessed by Western blot and EMSA's were performed to determine NF-κB activation. HL-60 cells were pretreated with neutralizing antibody against TLR4 prior to Hsp72 treatment. Neutrophils were harvested from the bone marrow of wild type or TLR4-deficient mice prior to treatment with Hsp72.

Results

Infection of 16HBE14o- with RSV showed an induction of intracellular Hsp72 levels as well as extracellular release of Hsp72. Primary human neutrophils from normal donors and differentiated HL-60 cells treated with increasing concentrations of Hsp72 resulted in increased cytokine (IL-8 and TNFα) production. This effect was independent of the low levels of endotoxin in the Hsp72 preparation. Hsp72 mediated cytokine production via activation of NF-κB translocation and DNA binding. Using bone marrow-derived neutrophils from wild type and TLR4-mutant mice, we showed that Hsp72 directly activates neutrophil-derived cytokine production via the activation of TLR4.

Conclusion

Collectively these data suggest that extracellular Hsp72 is released from virally infected airway epithelial cells resulting in the recruitment and activation of neutrophils.

The brefeldin A-inhibited guanine nucleotide-exchange protein, BIG2, regulates the constitutive release of TNFR1 exosome-like vesicles

The type I, 55-kDa tumor necrosis factor receptor (TNFR1) is released from cells to the extracellular space where it can bind and modulate TNF bioactivity. Extracellular TNFR1 release occurs by two distinct pathways: the inducible proteolytic cleavage of TNFR1 ectodomains and the constitutive release of full-length TNFR1 in exosome-like vesicles. Regulation of both TNFR1 release pathways appears to involve the trafficking of cytoplasmic TNFR1 vesicles. Vesicular trafficking is controlled by ADP-ribosylation factors (ARFs), which are active in the GTP-bound state and inactive when bound to GDP. ARF activation is enhanced by guanine nucleotide-exchange factors that catalyze replacement of GDP by GTP. We investigated whether the brefeldin A (BFA)-inhibited guanine nucleotide-exchange proteins, BIG1 and/or BIG2, are required for TNFR1 release from human umbilical vein endothelial cells. Effects of specific RNA interference (RNAi) showed that BIG2, but not BIG1, regulated the release of TNFR1 exosome-like vesicles, whereas neither BIG2 nor BIG1 was required for the IL-1beta-induced proteolytic cleavage of TNFR1 ectodomains. BIG2 co-localized with TNFR1 in diffusely distributed cytoplasmic vesicles, and the association between BIG2 and TNFR1 was disrupted by BFA. Consistent with the preferential activation of class I ARFs by BIG2, ARF1 and ARF3 participated in the extracellular release of TNFR1 exosome-like vesicles in a nonredundant and additive fashion. We conclude that the association between BIG2 and TNFR1 selectively regulates the extracellular release of TNFR1 exosome-like vesicles from human vascular endothelial cells via an ARF1- and ARF3-dependent mechanism.

Effects of burn injury on myocardial signaling and cytokine secretion: Possible role of PKC

This study examined the effects of major burn injury on the cellular distribution of several PKC isoforms in adult rat hearts and examined the hypothesis that PKC plays a regulatory role in cardiomyocyte cytokine secretion. Burn trauma was given over 40% total body surface area in Sprague-Dawley rats. An in vitro model of burn injury included addition of burn serum, 10% by volume, to primary cardiomyocyte cultures (collagen perfusion). In vivo burn injury produced redistribution of PKCdelta, PKCepsilon, and PKCalpha from the cytosol (soluble) to the membrane (particulate) component of the myocardium. This activation of the PKC isoforms was evident 2 h after burn injury and progressively increased over 24 h postburn. Addition of burn serum to isolated myocytes produced similar PKC isoform redistribution from the soluble to the particulate compartment, promoted myocyte Ca2+ and Na+ loading, and promoted robust myocyte secretion of inflammatory cytokines similar to that reported after in vivo burn injury. Pretreating cardiomyocytes with either calphostin or PKCepsilon inhibitory peptide, a potent inhibitor of PKCepsilon, prevented burn serum-related redistribution of the PKCepsilon isoform and prevented burn serum-related cardiomyocyte secretion of TNF-alpha, IL-1beta, IL-6, and IL-10. These data suggest that the PKCepsilon isoform plays a pivotal role in myocardial inflammatory response to injury, altering cardiac function by modulating cardiomyocyte inflammatory cytokine response to injury.

Nucleotides induce IL-6 release from human airway epithelia via P2Y2 and p38 MAPK-dependent pathways

Extracellular nucleotides can mediate a variety of cellular functions via interactions with purinergic receptors. We previously showed that mechanical ventilation (MV) induces airway IL-6 and ATP release, modifies luminal nucleotide composition, and alters lung purinoceptor expression. Here we hypothesize that extracellular nucleotides induce secretion of IL-6 by small airway epithelial cells (SAEC). Human SAEC were stimulated with nucleotides in the presence or absence of inhibitors. Supernatants were analyzed for IL-6 and lysates for p38 MAPK activity by ELISA. RNA was analyzed by real-time RT-PCR. Rats (n=51) were randomized to groups as follows: control, small-volume MV, large-volume MV, large-volume MV-intratracheal apyrase, or small-volume MV-intratracheal adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS). After 1 h of MV, bronchoalveolar lavage fluid was analyzed for ATP and IL-6 by luminometry and ELISA. ATP and ATPgammaS increased SAEC IL-6 secretion in a time- and dose-dependent manner, an effect inhibited by apyrase. Agonists were ranked in the following order: ATPgammaS>ATP=UTP>ADP=adenosine>2-methylthio-ADP=control. SB-203580, but not U-0126 or JNK1 inhibitor, decreased nucleotide effects. Additionally, nucleotides induced p38 MAPK phosphorylation. Inhibitors of Ca2+ signaling, phospholipase C, transcription, and translation decreased IL-6 release. Furthermore, nucleotides increased IL-6 expression. In vivo, large-volume MV increased airway ATP and IL-6 concentrations. IL-6 release was decreased by apyrase and increased by ATPgammaS. Extracellular nucleotides induce P2Y2-mediated secretion of IL-6 by SAEC via Ca2+, phospholipase C, and p38 MAPK-dependent pathways. This effect is dependent on transcription and translation. Our findings were confirmed in an in vivo model, thus demonstrating a novel mechanism of nucleotide-induced IL-6 secretion by airway epithelia.

Proteasome inhibition induces TNFR1 shedding from human airway epithelial (NCI-H292) cells

The type 1 55-kDa TNF receptor (TNFR1) is an important modulator of lung inflammation. Here, we hypothesized that the proteasome might regulate TNFR1 shedding from human airway epithelial cells. Treatment of NCI-H292 human airway epithelial cells for 2 h with the specific proteasome inhibitor clasto-lactacystin beta-lactone induced the shedding of proteolytically cleaved TNFR1 ectodomains. Clasto-lactacystin beta-lactone also induced soluble TNFR1 (sTNFR1) release from the A549 pulmonary epithelial cell line, as well as from primary cultures of human small airway epithelial cells and human umbilical vein endothelial cells. Furthermore, sTNFR1 release induced by clasto-lactacystin beta-lactone was not a consequence of apoptosis or the extracellular release of TNFR1 exosome-like vesicles. The clasto-lactacystin beta-lactone-induced increase in TNFR1 shedding was associated with reductions in cell surface receptors and intracytoplasmic TNFR1 stores that were primarily localized to vesicular structures. As expected, the broad-spectrum zinc metalloprotease inhibitor TNF-alpha protease inhibitor 2 (TAPI-2) attenuated clasto-lactacystin beta-lactone-mediated TNFR1 shedding, which is consistent with its ability to inhibit the zinc metalloprotease-catalyzed cleavage of TNFR1 ectodomains. TAPI-2 also reduced TNFR1 on the cell surface and attenuated the clasto-lactacystin beta-lactone-induced reduction of intracytoplasmic TNFR1 vesicles. This suggests that TNFR1 shedding induced by clasto-lactacystin beta-lactone involves the zinc metalloprotease-dependent trafficking of intracytoplasmic TNFR1 vesicles to the cell surface. Together, these data are consistent with the conclusion that proteasomal activity negatively regulates TNFR1 shedding from human airway epithelial cells, thus identifying previously unrecognized roles for the proteasome and zinc metalloproteases in modulating the generation of sTNFRs.

The p75 neurotrophin receptor appears in plasma in diabetic rats-characterisation of a potential early test for neuropathy

AIMS/HYPOTHESIS

This study tested the premise that immunoreactivity representing the p75 neurotrophin receptor (p75(NTR)) appears in plasma of diabetic rats in association with the early stages of neuronal dysfunction or damage. We also examined whether treatment beneficial to neuropathy might reduce the p75(NTR) immunoreactivity.

METHODS

Plasma proteins were fractionated by SDS-PAGE and immunoblots exposed to p75(NTR) antibody, using receptor protein from cultured PC12 cells as an external standard. Rats were made diabetic with streptozotocin for various periods and exsanguinated. Plasma glucose, HbA(1)c and plasma proteins were determined. We also studied plasma samples from diabetic mice lacking the gene coding for p75(NTR), as well as the effect of sciatic nerve crush on healthy male Wistar rats.

RESULTS

Plasma p75(NTR) immunoreactivity began to exceed normal levels at 8 weeks after induction of diabetes, and was significantly raised at 10 (p<0.05) and 12 weeks (p<0.001). Treatment between 8 and 12 weeks with insulin, fidarestat (an aldose reductase inhibitor), nerve growth factor and neurotrophin 3 all normalised the plasma p75(NTR) immunoreactivity. Plasma from p75(NTR) (-/-) mice contained no such immunoreactivity, though it was present in plasma from wild-type mice. Following nerve crush, p75(NTR) immunoreactivity appeared in plasma of non-diabetic mice, indicating that this can be a result of nerve trauma.

CONCLUSIONS/INTERPRETATION

These observations suggest that plasma p75(NTR) immunoreactivity may serve as an early indicator of neuronal dysfunction or damage in diabetes. The time course of its appearance relates well to that of early neuropathy and its response to interventions that are neuroprotective suggests that it might mirror neurological status.

Effect of glucocorticosteroids on tumour necrosis factor-alpha-induced intercellular adhesion molecule-1 expression in cultured primary human nasal epithelial cells

OBJECTIVE

In order to confirm the direct effect of glucocorticosteroids on epithelial intercellular adhesion molecule-1 (ICAM-1) expression, we examined ICAM-1 expression on primary cultured human nasal epithelial cells (HNECs) at both protein and mRNA levels.

MATERIAL AND METHODS

HNECs were stimulated with recombinant human TNF-alpha (20 pg/mL-20 ng/mL) for specified time periods (0, 12, 24, and 48 h) and ICAM-1 mRNA and the soluble ICAM-1 (sICAM-1) concentrations were measured by quantitative RT-PCR and ELISA, respectively. We also evaluated surface expression of ICAM-1 by flow cytometry 48 h after stimulation and determined the effect of dexamethasone (DEX) on TNF-alpha-induced ICAM-1 expression.

RESULTS

Significant increases in ICAM-1 gene expression in HNECs were initially detected at 24 h, peaking at 48 h after the stimulation. The TNF-mediated-ICAM-1 mRNA and ICAM-1 surface expression at 48 h was significantly inhibited by co-incubation with human recombinant soluble TNF receptor I. Similarly, TNF-alpha-induced release sICAM-1 occurred in a time- and concentration-dependent manner. DEX 10(-6) M attenuated the TNF-alpha-induced ICAM-1 expression at mRNA and protein levels.

CONCLUSIONS

Our finding suggests a potential role for topical steroids in allergic rhinitis in suppressing inflammatory reactions in the nasal mucosa by regulating ICAM-1 expression on nasal epithelium.

Corticosteroids in sepsis: from bench to bedside?

The use of corticosteroids in patients with septic shock has been recently revisited and the use of low dose corticosteroids led to very promising results, particularly in patients with corticosteroid insufficiency. We review the different mechanisms that can account for their beneficial effects in patients. Glucocorticoids display a wide spectrum of anti-inflammatory properties that have been identified in in vitro and in vivo experimental models (e.g., inhibition of production of pro-inflammatory cytokines, free radicals, prostaglandins and inhibition of chemotaxis, and adhesion molecule expressions.) In addition, glucocorticoids have profound effects on the cardiovascular system (e.g., increasing mean blood pressure, increasing pressor sensitivity, and therefore decreasing the duration of use of catecholamines during septic shock.) Through these anti-inflammatory and cardiovascular effects, low doses of glucorticoids may improve septic shock survival.

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

Airway epithelial cells synthesize proinflammatory molecules such as IL-8, GM-CSF, RANTES, and ICAM-1, the expression of which is increased in the airways of patients with asthma. We investigated the regulation of these NF-kappa B-dependent genes by the novel protein kinase C (PKC) isoform PKC delta in 16HBE14o- human airway epithelial cells, focusing on IL-8 expression. Transient transfection with the constitutively active catalytic subunit of PKC delta (PKC delta-CAT), and treatment with bryostatin 1, an activator of PKC delta, each increased transcription from the IL-8 promoter, whereas overexpression of PKC epsilon had minor effects. Expression of a dominant negative PKC delta mutant (PKC delta-KR) or pretreatment of cells with rottlerin, a chemical PKC delta inhibitor, attenuated TNF-alpha- and phorbol ester-induced transcription from the IL-8 promoter. Bryostatin 1 treatment increased IL-8 protein abundance in primary airway epithelial cells. Selective activation of PKC delta by bryostatin also activated NF-kappa B, as evidenced by p65 RelA and p50 NF-kappa B1 binding to DNA, NF-kappa B trans-activation, and I kappa B degradation. The sufficiency of PKC delta to induce NF-kappa B nuclear translocation and binding to DNA was confirmed in a 16HBE14o- cell line inducibly expressing PKC delta-CAT under the tet-off system. Deletion of the NF-kappa B response element severely attenuated PKC delta-induced IL-8 promoter activity. Finally, PKC delta-CAT induced transcription from the GM-CSF, RANTES, and ICAM-1 promoters. Together these data suggest that PKC delta plays a key role in the regulation of airway epithelial cell NF-kappa B-dependent gene expression.

The stress- and inflammatory cytokine-induced ectodomain shedding of heparin-binding epidermal growth factor-like growth factor is mediated by p38 MAPK, distinct from the 12-O-tetradecanoylphorbol-13-acetate- and lysophosphatidic acid-induced signaling cascades

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a critical growth factor for a number of physiological and pathological processes. HB-EGF is synthesized as a membrane-anchored form (pro-HB-EGF), and pro-HB-EGF is cleaved at the cell surface to yield soluble HB-EGF by a mechanism called "ectodomain shedding." We show here that the ectodomain shedding of pro-HB-EGF in Vero cells is induced by various stress-inducing stimuli, including UV light, osmotic pressure, hyperoxidation, and translation inhibitors. The pro-inflammatory cytokine interleukin-1beta also stimulated the ectodomain shedding of pro-HB-EGF. An inhibitor of p38 MAPK (SB203580) or the expression of a dominant-negative (dn) form of p38 MAPK inhibited the stress-induced ectodomain shedding of pro-HB-EGF, whereas an inhibitor of JNK (SP600125) or the expression of dnJNK1 did not. 12-O-Tetradecanoylphorbol-13-acetate (TPA) and lysophosphatidic acid (LPA) are also potent inducers of pro-HB-EGF shedding in Vero cells. Stress-induced pro-HB-EGF shedding was not inhibited by the inhibitors of TPA- or LPA-induced pro-HB-EGF shedding or by dn forms of molecules involved in the TPA- or LPA-induced pro-HB-EGF shedding pathway. Reciprocally, SB203580 or dnp38 MAPK did not inhibit TPA- or LPA-induced pro-HB-EGF shedding. These results indicate that stress-induced pro-HB-EGF shedding is mediated by p38 MAPK and that the signaling pathway induced by stress is distinct from the TPA- or LPA-induced pro-HB-EGF shedding pathway.

Tumor necrosis factor increases MUC1 mRNA in cultured human nasal epithelial cells

OBJECTIVE

Mucins are high molecular weight glycoproteins which are normally expressed on the surface of a variety of epithelia. It is possible that shedding of such molecules from the epithelium could play a role in preventing bacterial colonization at the mucosal surface. Immunohistochemical and reverse transcriptase polymerase chain reaction(RT-PCR) analyses of human inferior turbinates have shown the existence of MUC1 mucin in nasal mucosa. However, the regulatory mechanisms of MUC1 mucin are poorly understood. In order to clarify the modulation of mucin gene expression, we developed a real-time semi-quantitative RT-PCR based on TaqMan fluorescence methodology to quantify MUC1 mRNA in primary cultured human nasal epithelial cells (HNECs).

MATERIAL AND METHODS

HNECs were stimulated with recombinant human tumor necrosis factor (TNF)-alpha (20 pg/ml to 20 ng/ml) for specified time periods (0, 12, 24 and 48 h) and MUC1 mRNA was determined by means of semi-quantitative RT-PCR.

RESULTS

Significant increases in MUC1 gene expression in HNECs were initially detected at 12 h, peaking at 24 h after stimulation. TNF-mediated MUCI mRNA expression at 24 h was significantly inhibited by co-incubation with human recombinant soluble TNF receptor.

CONCLUSIONS

TNF-mediated MUC1 gene expression may contribute to the pathogenesis of human inflammatory upper airway disorders. Also, our mucin mRNA real-time PCR provides a quantitative method for investigating the regulation of mucin gene expression in both healthy and diseased samples.

Biochemical entities that influence membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) complex expression and receptor fragment production in adherent vascular endothelium

The research aim of the present investigation was to identify leukocyte enzyme-proteases that have the capacity to biochemically recruit the passive participation of vascular endothelium in cytokine receptor 'shedding' phenomenon involving membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) complexes. Achieving this research objective involved the design of a laboratory approach that delineated to what extent enzyme-proteases released by activated macrophages directly interact with, and liberate soluble fragments of membrane-associated cytokine receptor complexes. Results from this segment of the investigation revealed that cathepsin-D, a leukocyte carboxyl/aspartate protease, altered the integrity and generated soluble fragments of TNF RII (80-kDa) and IL-1 RI (80-kDa) receptor complexes expressed by vascular endothelium. Furthermore, laboratory findings also suggested that cathepsin-D possessed the ability to variably deplete biologically functional membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) complexes. Complementary investigations isolated a carboxyl/aspartate protease from activated macrophages utilizing pepstatin-A affinity chromatography. Exposure of vascular endothelium to pepstatin-A binding proteins resulted in a detectable depletion of membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) in addition to the generation of soluble receptor fragments. Analysis of macrophage pepstatin-A binding proteins by SDS-PAGE identified a primary fraction with a molecular mass of 47-52-kDa that closely correlated with the known molecular mass of leukocyte cathepsin-D. Evaluation of macrophage pepstatin-A binding-protein fractions by non-denaturing Hb-PAGE detected a lucent proteolytic band at 47-52-kDa compatible with the known molecular mass of leukocyte cathepsin-D. Macrophage pepstatin-A binding proteins also hydrolyzed a synthetic enzyme-specific substrate that selectively recognizes cathepsin-D biochemical activity. In conclusion, the leukocyte carboxyl/aspartate protease, cathepsin-D can biochemically alter the integrity and generate soluble fragments of membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) receptor complexes expressed by vascular endothelium. The relevance of this concept is in part based on investigations that have discovered that genetic 'knock-out' mice incapable of expressing IL-1 RI (80-kDa) or TNF RI (55-kDa) receptor complexes are highly resistant to developing the pathophysiological alterations classically associated with conditions of endotoxic-shock.

CTP:phosphocholine cytidylyltransferase inhibition by ceramide via PKC-alpha, p38 MAPK, cPLA2, and 5-lipoxygenase

In a companion paper (Vivekananda J, Smith D, and King RJ. Am J Physiol Lung Cell Mol Physiol 281: L98-L107, 2001), we demonstrated that tumor necrosis factor (TNF)-alpha inhibited the activity of CTP:phosphocholine cytidylyltransferase (CT), the rate-limiting enzyme in the de novo synthesis of phosphatidylcholine (PC), and that its actions were likely exerted through a metabolite of sphingomyelin. In this paper, we explore the signaling pathway employed by TNF-alpha using C2 ceramide as a cell-penetrating sphingolipid representative of the metabolites induced by TNF-alpha. We found that in H441 cells, as reported in other cell types, cytosolic phospholipase A2 (cPLA2) is activated by TNF-alpha. We also observed that the inhibiting action of C2 ceramide on CT requires protein kinase C-alpha, p38 mitogen-activated protein kinase, and cPLA2. The actions of C2 ceramide on CT activity can be duplicated by adding 2 microM lysoPC to these cells. Furthermore, we found that the effects of C2 ceramide are dependent on 5-lipoxygenase but that cyclooxygenase II is unimportant. We hypothesize that CT activity is inhibited by the lysoPC generated as a consequence of the activation of cPLA2 by protein kinase C-alpha and p38 mitogen-activated protein kinase. The other product of the activation of cPLA2, arachidonic acid, is a substrate for the synthesis of leukotrienes, which raise intracellular Ca2+ levels and complete the activation of cPLA2.

IL-1beta enhances beta2-adrenergic receptor expression in human airway epithelial cells by activating PKC

Protein kinase C (PKC)-activated signal transduction pathways regulate cell growth and differentiation in many cell types. We have observed that interleukin (IL)-1beta upregulates beta2-adrenergic receptor (beta2-AR) density and beta2-AR mRNA in human airway epithelial cells (e.g., BEAS-2B). We therefore tested the hypothesis that PKC-activated pathways mediate IL-1beta-induced beta-AR upregulation. The role of PKC was assessed from the effects of 1) the PKC activator phorbol 12-myristate 13-acetate (PMA) on beta-AR density, 2) selective PKC inhibitors (calphostin C and Ro-31-8220) on beta-AR density, and 3) IL-1beta treatment on the cellular distribution of PKC isozymes. Recombinant human IL-1beta (0.2 nM for 18 h) increased beta-AR density to 213% of control values (P < 0.001). PMA (1 microM for 18 h) increased beta-AR density to 225% of control values (P < 0.005), whereas Ro-31-8220 and calphostin C inhibited the IL-1beta-induced upregulation of beta-AR in dose-dependent fashion. PKC isozymes detected by Western blotting included alpha, betaII, epsilon, mu, zeta, and lambda/iota. IL-1beta increased PKC-mu immunoreactivity in the membrane fraction and had no effect on the distribution of the other PKC isozymes identified. These data indicate that IL-1beta-induced beta-AR upregulation is mimicked by PKC activators and blocked by PKC inhibitors and appears to involve selective activation of the PKC-mu isozyme. We conclude that signal transduction pathways activated by PKC-mu upregulate beta2-AR expression in human airway epithelial cells.

Tumor necrosis factor alpha stimulation of human Clara cell secretory protein production by human airway epithelial cells

Clara cell secretory protein (CCSP) or uteroglobin/CC10 is a product of epithelial cells in a variety of organs including the lung. CCSP has anti-inflammatory properties and may act as an inhibitor of secretory phospholipase A2's. Tumor necrosis factor alpha (TNF-alpha) is capable of inducing the expression of gene products including a variety of cytokines and chemokines in the airway epithelium that may upregulate the airway inflammatory response. Therefore, it was of interest to determine whether this proinflammatory cytokine might also induce the production of a counterregulatory protein such as CCSP, which might modulate the inflammatory response in the airway. Normal human tracheobronchial epithelial cells in primary culture and a human bronchial epithelial cell line (BEAS-2B) were studied. CCSP mRNA levels in BEAS-2B cells were detected by ribonuclease protection assay. CCSP mRNA levels increased in response to TNF-alpha (20 ng/mL) stimulation after 8-36 h, with the peak increase at 18 h. Immunoblotting of CCSP released from BEAS-2B cells into the culture media demonstrated that TNF-alpha induced the synthesis and secretion of CCSP over 8 to 18 h. Similarly, TNF stimulated the release of CCSP from human tracheobronchial epithelial cells in primary culture at 8 and 18 h. The CCSP reporter gene including 801 bases 5' of the transcription start site did not increase transcriptional activity in response to TNF-alpha stimulation. A CCSP mRNA half-life assay indicated that TNF-alpha induced increases in CCSP mRNA at least in part at a posttranscriptional level. Therefore, TNF-alpha induces airway epithelial cell expression of human CCSP and may modulate airway inflammatory responses in this manner.

Prostaglandin E(2)-induced interleukin-6 release by a human airway epithelial cell line

Human airway epithelial cell release of interleukin (IL)-6 in response to lipid mediators was studied in an airway cell line (BEAS-2B). Prostaglandin (PG) E(2) (10(-7) M) treatment caused an increase in IL-6 release at 2, 4, 8, and 24 h. IL-6 release into the culture medium at 24 h was 3,396 +/- 306 vs. 1,051 +/- 154 pg/ml (PGE(2)-treated cells vs. control cells). PGE(2) (10(-7) to 10(-10) M) induced a dose-related increase in IL-6 release at 24 h. PGF(2 alpha) (10(-6) M) treatment caused a similar effect to that of PGE(2) (10(-7) M). PGE(2) analogs with relative selectivity for PGE(2) receptor subtypes were studied. Sulprostone, a selective agonist for the EP-3 receptor subtype had no effect on IL-6 release. 11-Deoxy-16,16-dimethyl-PGE(2), an EP-2/4 agonist, and 17-phenyl trinor PGE(2), an agonist selective for the EP-1 > EP-3 receptor subtype (10(-6) to 10(-8) M), caused dose-dependent increases in IL-6 release. 8-Bromo-cAMP treatment resulted in dose-related increases in IL-6 release. RT-PCR of BEAS-2B cell mRNA demonstrated mRNA for EP-1, EP-2, and EP-4 receptors. After PGE(2) treatment, increases in IL-6 mRNA were noted at 4 and 18 h. Therefore, PGE(2) increases airway epithelial cell IL-6 production and release.

Down-modulation through protein kinase C-alpha of lipopolysaccharide-induced expression of membrane CD14 in mouse bone marrow granulocytes

We have previously shown that stimulation of mouse bone marrow granulocytes (BMC) by lipopolysaccharide (LPS) induces the expression of CD14. We found here that phorbol 12-myristate 13-acetate (PMA) blocks this LPS effect. The aim of this study was to investigate the mechanism by which PMA can block the LPS signaling pathway in BMC. The unmodified binding of a radiolabeled LPS in PMA-treated cells indicated that the PMA effect was not the consequence of a shedding or an internalization of the LPS receptor, but was rather due to a biochemical event that follows the interaction of LPS with its receptor. The observations that a selective activator of protein kinase C (PKC)-alpha (sapintoxin D) mimics the PMA effect, whereas a selective PKC-alpha inhibitor (Ro-320432) antagonizes this effect, suggest a regulatory role of PKC-alpha in the LPS signaling pathway in mouse BMC.

Effect of nutrition on tumor necrosis factor receptors in weight-gaining and -losing rats

Previous studies showed that weight-gaining rats had greater retention and reduced turnover of 125I-labeled tumor necrosis factor (TNF)-alpha in the circulation compared with weight-losing animals. We therefore tested the hypothesis that protein-energy restriction with weight loss reduces the levels of soluble TNF-alpha receptor (sTNFR) and membrane TNFR (mTNFR) and the cellular expression of TNF-alpha mRNA. Twenty-six male rats weighing 200-220 g were fed a liquid formula diet for 10 days and divided equally into weight-gaining rats meeting all nutritional requirements (WG rats) and weight-losing rats with protein-energy restriction (WL rats). 125I-TNF-alpha binding was demonstrated in plasma and plasma membrane to proteins of molecular masses of 92 and 243 kDa, a finding identical to that seen with purified human p55. Excess unlabeled TNF-alpha displaced the binding showing its specificity. The degree of binding to plasma protein and liver plasma membrane was markedly reduced in WL rats. Northern analysis showed that the expression of p55 mRNA was increased in the lungs and reduced in kidneys of WL compared with WG rats. The expression of p75 mRNA was not influenced by the nutritional status. We conclude that levels of sTNFR and mTNFR were reduced in WL rats. Reduced sTNFR and liver mTNFR are not due to a reduction in the expression of either p55 or p75 mRNA in WL rats. Reduced mTNFR, together with reduced shedding of soluble receptors, may have a protective role in WL rats.

Hydrogen peroxide enhances shedding of type I soluble tumor necrosis factor receptor from pulmonary epithelial cells

Reactive oxygen intermediates (ROIs) are among the important mediators in the pathogenesis of lung diseases in which tumor necrosis factor (TNF) plays a pivotal role. However, the effects of ROIs on the TNF- TNF receptor system remain unclear. Effects of hydrogen peroxide on the shedding of soluble tumor necrosis factor receptor (sTNF-R) were investigated in a pulmonary epithelial cell line (A549) using enzyme-linked immunoassay. A549 cells spontaneously released type I sTNF-R (sTNF-RI) into the culture medium. Hydrogen peroxide accelerated the release of sTNF-RI from the A549 cells time- and dose- dependently. Stimulated release of sTNF-RI by hydrogen peroxide or phorbol myristate acetate (PMA) was inhibited by pretreatment with the intracellular hydroxyl radical scavengers dimethyl sulfoxide and dimethyl thiourea. A synthetic metalloproteinase inhibitor (KB-R8301) inhibited not only spontaneous release of sTNF-RI but also shedding enhanced by hydrogen peroxide and PMA. Preincubation with a protein kinase C inhibitor, calphostin C, downregulated the hydrogen peroxide- or PMA-induced shedding of sTNF-RI. Neither genistein, a tyrosine kinase inhibitor, nor H-89, a protein kinase A inhibitor, inhibited shedding of sTNF-RI by hydrogen peroxide and PMA. Although the surface expression of TNF-R assessed by 125I-TNF specific binding was decreased in the presence of hydrogen peroxide or PMA, TNF-RI mRNA transcript levels remained unchanged. These results show that hydrogen peroxide is involved in the activation of metalloproteinase and protein kinase C responsible for the shedding of sTNF-RI. Accordingly, ROIs may alter TNF action by enhanced shedding of sTNF-RI and reducing its surface receptor expression.

Induction of cytokine receptors by glucocorticoids: functional and pathological significance

Current concepts on the role of glucocorticoid hormones in the regulation of inflammatory and immune responses depict this role as being inhibitory. Over the past decade, however, a large variety of studies have shown that glucocorticoids also exert stimulatory effects on immune function, suggesting that the present concept of the role of glucocorticoids in the immune system in not sufficient and needs to be extended. Here, Jan Wiegers and Hans Reul ask how these apparently paradoxical effects fit together and what their functional and pathological significance might be.

Transforming the cell surface through proteolysis

Protein shedding, or the proteolytic cleavage of a protein from the surface of a cell, is emerging as an important mechanism in the regulation of cellular activity but it is poorly understood. Growing evidence suggesting that protein shedding and protein function are closely linked may lead to new strategies for the treatment of a wide range of diseases.

Glucocorticoids: mechanisms of action and anti-inflammatory potential in asthma

GLUCOCORTICOIDS are potent inhibitors of inflammatory processes and are widely used in the treatment of asthma. The anti-inflammatory effects are mediated either by direct binding of the glucocorticoid/glucocorticoid receptor complex to glucocorticoid responsive elements in the promoter region of genes, or by an interaction of this complex with other transcription factors, in particular activating protein-1 or nuclear factor-kappaB. Glucocorticoids inhibit many inflammation-associated molecules such as cytokines, chemokines, arachidonic acid metabolites, and adhesion molecules. In contrast, anti-inflammatory mediators often are up-regulated by glucocorticoids. In vivo studies have shown that treatment of asthmatic patients with inhaled glucocorticoids inhibits the bronchial inflammation and simultaneously improves their lung function. In this review, our current knowledge of the mechanism of action of glucocorticoids and their anti-inflammatory potential in asthma is described. Since bronchial epithelial cells may be important targets for glucocorticoid therapy in asthma, the effects of glucocorticoids on epithelial expressed inflammatory genes will be emphasized.

Stimulation of protein kinase C activity by tumor necrosis factor-alpha in bovine bronchial epithelial cells

Bronchial epithelial cell migration, attachment, and proliferation are important processes in response to airway injury. We have shown that tumor necrosis factor (TNF)-alpha stimulates the migration of bovine bronchial epithelial cells (BBEC) in vitro. We hypothesized that protein kinase C (PKC) may be one of the intracellular signaling mediators of TNF-alpha in BBEC. In this study, we have identified multiple PKC isoforms in BBEC and measured total cellular PKC activity. Polyclonal antibodies to the PKC-alpha, -beta 2, -delta, and -epsilon isoforms recognized protein bands around 80-90 kDa. BBEC primary cultures treated with either 500 U/ml TNF-alpha for 2-4 h or 100 ng/ml 12-O-tetradecanoylphorbol 13-acetate for 15 min resulted in three-to fivefold increases in PKC activity in the particulate fractions of crude cell lysates. This activity was inhibited by 1 microM calphostin C or 10 microM H-7. Similarly, TNF-alpha-stimulated BBEC migration was reduced at least twofold in the presence of H-7 or calphostin C. These studies suggest that the activation of PKC is necessary for TNF-alpha-stimulated BBEC migration.

Dexamethasone suppresses release of soluble TNF receptors by human monocytes concurrently with TNF-alpha suppression

Glucocorticoids suppress many monocyte functions, including endotoxin-stimulated release of TNF-alpha. Monocytes also release soluble receptors for TNF (sTNF-R), which can modulate TNF bioactivity. We therefore examined the effects of the glucocorticoid, dexamethasone, on the release of soluble forms of the 55 kDa and 75 kDa receptors for TNF (sTNF-R55 and sTNF-R75) by human monocytes and the human monocytic Mono Mac 6 cell line. Peripheral blood mononuclear cells (PBMC) spontaneously released 406 +/- 181 pg/10(6) cells of sTNF-R75 over 18 h in culture and Mono Mac 6 cells released 554 +/- 29 pg/10(6) cells. Lipopolysaccharide (LPS) exposure increased release of sTNF-R75 by 54 and 217%, respectively. Dexamethasone suppressed both spontaneous and LPS-stimulated release. The effect of dexamethasone was concentration dependent. At 1 mumol/L, dexamethasone suppressed the LPS-stimulated release of sTNF-R75 by 86% in PBMC and by 40% in Mono Mac 6 cells. Neither PBMC nor Mono Mac 6 cells released measurable amounts of sTNF-R55, but spontaneous release of sTNF-R55 from purified human monocytes (55 +/- 2 pg/10(6) cells over 18 h) was reduced by 45% in the presence of dexamethasone. Dexamethasone reduced bioactive TNF in PBMC cultures, as well as immunoassayable TNF-alpha, which indicates that suppression of TNF-alpha release was biologically more important than suppressed release of soluble inhibitors. Similar concurrent suppression of IL-1 beta and IL-1ra release occurred in PBMC and Mono Mac 6 cultures exposed to dexamethasone.

Regulated shedding of syndecan-1 and -4 ectodomains by thrombin and growth factor receptor activation

The syndecan family of transmembrane heparan sulfate proteoglycans is abundant on the surface of all adherent mammalian cells. Syndecans bind and modify the action of various growth factors/cytokines, proteases/antiproteases, cell adhesion molecules, and extracellular matrix components. Syndecan expression is highly regulated during wound repair, a process orchestrated by many of these effectors. Each syndecan ectodomain is shed constitutively by cultured cells, but the mechanism and significance of this shedding are not understood. Therefore, we examined (i) whether physiological agents active during wound repair influence syndecan shedding, and (ii) whether wound fluids contain shed syndecan ectodomains. Using SVEC4-10 endothelial cells we find that certain proteases and growth factors accelerate shedding of the syndecan-1 and -4 ectodomains. Protease-accelerated shedding is completely inhibited by serum-containing media. Thrombin activity is duplicated by the 14-amino acid thrombin receptor agonist peptide that directly activates the thrombin receptor and is not inhibited by serum. Epidermal growth factor family members accelerate shedding but FGF-2, platelet-derived growth factor-AB, transforming growth factor-beta, tumor necrosis factor-alpha, and vascular endothelial cell growth factor 165 do not. Shed ectodomains are soluble, stable in the conditioned medium, have the same size core proteins regardless whether shed at a basal rate, or accelerated by thrombin or epidermal growth factor-family members and are found in acute human dermal wound fluids. Thus, shedding is accelerated by activation of at least two distinct receptor classes, G protein-coupled (thrombin) and protein tyrosine kinase (epidermal growth factor). Proteases and growth factors active during wound repair can accelerate syndecan shedding from cell surfaces. Regulated shedding of syndecans suggests physiological roles for the soluble proteoglycan ectodomains.