Modulation of secretory leukoprotease inhibitor gene expression in human bronchial epithelial cells by phorbol ester

The secretory leukocyte protease inhibitor (SLPI) in pathophysiology of non-communicable diseases: Evidence from experimental studies to clinical applications

Non-communicable diseases (NCDs) are a worldwide health issue because of their prevalence, negative impacts on human welfare, and economic costs. Protease enzymes play important roles in viral and NCD diseases. Slowing disease progression by inhibiting proteases using small-molecule inhibitors or endogenous inhibitory peptides appears to be crucial. Secretory leukocyte protease inhibitor (SLPI), an inflammatory serine protease inhibitor, maintains protease/antiprotease balance. SLPI is produced by host defense effector cells during inflammation to prevent proteolytic enzyme-induced tissue damage. The etiology of noncommunicable illnesses is linked to SLPI's immunomodulatory and tissue regeneration roles. Disease phases are associated with SLPI levels and activity changes in regional tissue and circulation. SLPI has been extensively evaluated in inflammation, but rarely in NCDs. Unfortunately, the thorough evaluation of SLPI's pathophysiological functions in NCDs in multiple research models has not been published elsewhere. In this review, data from PubMed from 2014 to 2023 was collected, analysed, and categorized into in vitro, in vivo, and clinical studies. According to the review, serine protease inhibitor (SLPI) activity control is linked to non-communicable diseases (NCDs) and other illnesses. Overexpression of the SLPI gene and protein may be a viable diagnostic and therapeutic target for non-communicable diseases (NCDs). SLPI is also cytoprotective, making it a unique treatment. These findings suggest that future research should focus on these pathways using advanced methods, reliable biomarkers, and therapy approaches to assess susceptibility and illness progression. Implications from this review will help pave the way for a new therapeutic target and diagnosis marker for non-communicable diseases.

Secretory leukocyte protease inhibitor (SLPI) in cancer pathophysiology: Mechanisms of action and clinical implications

Cancer is a multifaceted disorder frequently linked to the dysregulation of several biological processes. The SLPI is a multifunctional protein involved in the modulation of immunological response and the inhibition of protease activities. SLPI acts as an inhibitor of proteases, exerts antibacterial properties, and suppresses the transcription of proinflammatory genes through the nuclear factor-kappa B (NF-κB) pathway. The role of this protein as a regulatory agent has been implicated in various types of cancer. Recent research has revealed that SLPI upregulation in cancer cells enhances the metastatic capacity of epithelial malignancies, indicating the deleterious effects of this protein. Furthermore, SLPI interacts intricately with other cancer-promoting factors, including matrix metalloproteinase-2 (MMP-2), MMP-9, the NF-κB and Akt pathways, and the p53-upregulated modulator of apoptosis (PUMA). This review provides an overview of the role of SLPI in cancer pathophysiology, emphasizing its expression in cancer cells and tissues, its potential as a prognostic biomarker, and its therapeutic promise as a target in cancer treatment. The mechanisms of SLPI action in cancer, including its anti-inflammatory effects, regulation of cell proliferation and angiogenesis, and modulation of the tumor microenvironment, have been investigated. The clinical implications of SLPI in cancer have been discussed, including its potential as a diagnostic and prognostic biomarker, its role in chemoresistance, and its therapeutic potential in several types of cancer, such as hepatocellular carcinoma (HCC), colorectal cancer (CRC), pancreatic cancer, head and neck squamous cell carcinoma (HNSCC), ovarian cancer (OvCa), prostate cancer (PC), gastric cancer (GC), breast cancer, and other cancers. In addition, we emphasized the significance of SLPI in cancer, which offers fresh perspectives on potential targets for cancer therapy.

Endogenous secretory leukocyte protease inhibitor inhibits microbial-induced monocyte activation

In the intestine, epithelial factors condition incoming immune cells including monocytes to adapt their threshold of activation and prevent undesired inflammation. Colonic epithelial cells express Secretory Leukocyte Protease Inhibitor (SLPI), an inhibitor of NF kappa light chain enhancer of activated B cells (NF-κB) that mediates epithelial hyporesponsiveness to microbial stimuli. Uptake of extracellular SLPI by monocytes has been proposed to inhibit monocyte activation. We questioned whether monocytes can produce SLPI and whether endogenous SLPI can inhibit monocyte activation. We demonstrate that human THP-1 monocytic cells produce SLPI and that CD68⁺ SLPI-producing cells can be detected in human intestinal lamina propria. Knockdown of SLPI in human THP-1 cells significantly increased NF-κB activation and subsequent C-X-C motif chemokine ligand 8 (CXCL8) and TNF-α production in response to microbial stimulation. Reconstitution of SLPI-deficient cells with either full-length SLPI or SLPI lacking its signal peptide rescued inhibition of NF-κB activation and cytokine production, demonstrating that endogenous SLPI inhibits monocytic cell activation. Unexpectedly, exogenous SLPI did not inhibit CXCL8 or TNF-α production, despite efficient uptake. Our data argue that endogenous SLPI can regulate the threshold of activation in monocytes, thereby preventing activation by commensal bacteria in mucosal tissues.

High expression of secretory leukocyte protease inhibitor (SLPI) in stage III micro-satellite stable colorectal cancer is associated with reduced disease recurrence

Secretory leukocyte protease inhibitor (SLPI) is a pleiotropic protein produced by healthy intestinal epithelial cells. SLPI regulates NF-κB activation, inhibits neutrophil proteases and has broad antimicrobial activity. Recently, increased SLPI expression was found in various types of carcinomas and was suggested to increase their metastatic potential. Indeed, we demonstrated that SLPI protein expression in colorectal cancer (CRC) liver metastases and matched primary tumors is associated with worse outcome, suggesting that SLPI promotes metastasis in human CRC. However, whether SLPI plays a role in CRC before distant metastases have formed is unclear. Therefore, we examined whether SLPI expression is associated with prognosis in CRC patients with localized disease. Using a cohort of 226 stage II and 160 stage III CRC patients we demonstrate that high SLPI protein expression is associated with reduced disease recurrence in patients with stage III micro-satellite stable tumors treated with adjuvant chemotherapy, independently of established clinical risk factors (hazard rate ratio 0.54, P-value 0.03). SLPI protein expression was not associated with disease-free survival in stage II CRC patients. Our data suggest that the role of SLPI in CRC may be different depending on the stage of disease. In stage III CRC, SLPI expression may be unfavorable for tumors, whereas SLPI expression may be beneficial for tumors once distant metastases have established.

Identifying Biomarkers from Transcriptomic Signatures in Renal Allograft Biopsies Using Deceased and Living Donors

The survival of transplant kidneys using deceased donors (DD) is inferior to living donors (LD). In this study, we conducted a whole-transcriptome expression analysis of 24 human kidney biopsies paired at 30 minutes and 3 months post-transplantation using DD and LD. The transcriptome profile was found significantly different between two time points regardless of donor types. There were 446 differentially expressed genes (DEGs) between DD and LD at 30 minutes and 146 DEGs at 3 months, with 25 genes common to both time points. These DEGs reflected donor injury and acute immune responses associated with inflammation and cell death as early as at 30 minutes, which could be a precious window of potential intervention. DEGs at 3 months mainly represented the changes of adaptive immunity, immunosuppressive treatment, remodeling or fibrosis via different networks and signaling pathways. The expression levels of 20 highly DEGs involved in kidney diseases and 10 genes dysregulated at 30 minutes were found correlated with renal function and histology at 12 months, suggesting they could be potential biomarkers. These genes were further validated by quantitative polymerase chain reaction (qPCR) in 24 samples analysed by microarray, as well as in a validation cohort of 33 time point unpaired allograft biopsies. This analysis revealed that SERPINA3, SLPI and CBF were up-regulated at 30 minutes in DD compared to LD, while FTCD and TASPN7 were up-regulated at both time points. At 3 months, SERPINA3 was up-regulated in LD, but down-regulated in DD, with increased VCAN and TIMP1, and decreased FOS, in both donors. Taken together, divergent transcriptomic signatures between DD and LD, and changed by the time post-transplantation, might contribute to different allograft survival of two type kidney donors. Some DEGs including FTCD and TASPN7 could be novel biomarkers not only for timely diagnosis, but also for early precise genetic intervention at donor preservation, implantation and post-transplantation, in particular to effectively improve the quality and survival of DD.

Secretory Leukocyte Protease Inhibitor (SLPI) in mucosal tissues: Protects against inflammation, but promotes cancer

The immune system is continuously challenged with large quantities of exogenous antigens at the barriers between the external environment and internal human tissues. Antimicrobial activity is essential at these sites, though the immune responses must be tightly regulated to prevent tissue destruction by inflammation. Secretory Leukocyte Protease Inhibitor (SLPI) is an evolutionarily conserved, pleiotropic protein expressed at mucosal surfaces, mainly by epithelial cells. SLPI inhibits proteases, exerts antimicrobial activity and inhibits nuclear factor-kappa B (NF-κB)-mediated inflammatory gene transcription. SLPI maintains homeostasis at barrier tissues by preventing tissue destruction and regulating the threshold of inflammatory immune responses, while protecting the host from infection. However, excessive expression of SLPI in cancer cells may have detrimental consequences, as recent studies demonstrate that overexpression of SLPI increases the metastatic potential of epithelial tumors. Here, we review the varied functions of SLPI in the respiratory tract, skin, gastrointestinal tract and genitourinary tract, and then discuss the mechanisms by which SLPI may contribute to cancer.

Secretory leukocyte protease inhibitor and progranulin as possible regulators of cervical remodeling in pregnancy

Secretory leukocyte protease inhibitor (SLPI) and progranulin (PGRN) are secretory proteins with an anti-inflammatory property. Their involvement in cervical remodeling in pregnant uterus is not yet elucidated. Thus, this study aimed to explore the significance of SLPI and PGRN in the maintenance of pregnancy by investigating the factors associated with their expression levels at the cervix. Concentrations of SLPI and PGRN proteins were measured in cervical mucus samples collected from asymptomatic pregnant women at 24-26 weeks of gestation (n = 166). The concentrations of those molecules were analyzed with clinical parameters related to risk for preterm delivery (PD). In pregnant mice, we evaluated the effect of lipopolysaccharide-induced inflammation and progesterone effect modulation on cervical mRNA expression of SLPI and PGRN. The cervical PGRN level was significantly lower in women with short cervix (<35 mm) and with a history of threatened PD. In women with short cervix, cervical SLPI concentrations were positively correlated with inflammatory cytokines, interleukin-6 (R² = 0.75) and interleukin-8 (R² = 0.71). In pregnant mice, cervical mRNA expressions of PGRN and SLPI were increased in response to progesterone supplementation and were suppressed by a progesterone antagonist, mifepristone. Lipopolysaccharide-induced inflammation caused remarkable upregulation in cervical SLPI mRNA level but not in PGRN. Progesterone and local inflammation are the factors controlling expression levels of PGRN and SLPI at the cervix. The observed relationship of PGRN and SLPI levels in the cervical mucus with PD-related clinical parameters supports that those anti-inflammatory molecules possibly play a significant role in appropriate regulation of cervical remodeling.

Expression of the immune modulator secretory leukocyte protease inhibitor (SLPI) in colorectal cancer liver metastases and matched primary tumors is associated with a poorer prognosis

Secretory leukocyte protease inhibitor (SLPI), a pleiotropic protein expressed by healthy intestinal epithelial cells, functions as an inhibitor of NF-κB and neutrophil proteases and exerts antimicrobial activity. We previously showed SLPI suppresses intestinal epithelial chemokine production in response to microbial contact. Increased SLPI expression was recently detected in various types of carcinoma. In addition, accumulating evidence indicates SLPI expression is favorable for tumor cells. In view of these findings and the abundance of SLPI in the colonic epithelium, we hypothesized SLPI promotes colorectal cancer (CRC) growth and metastasis. Here, we aimed to establish whether SLPI expression in CRC is related to clinical outcome. Using a cohort of 507 patients with CRC who underwent resection of liver metastases, we show that high SLPI protein expression in both liver metastases and primary CRC is associated with significantly shorter overall survival after resection of liver metastases. The prognostic value of SLPI in CRC patients with liver metastases implies a role for SLPI in the formation of metastasis of human CRC. Based on the immune regulatory functions of SLPI, we anticipate that expression of SLPI provides tumors with a mechanism to evade infiltration by immune cells.

Elevated concentration of secretory leukocyte protease inhibitor in the cervical mucus before delivery

BACKGROUND

Cervical remodeling during parturition progresses under exquisite regulation by immunologic mediators and proteases. Secretory leukocyte protease inhibitor is a secretory protein that can function as an antimicrobial peptide, an antiinflammatory molecule, and a protease inhibitor. The involvement of secretory leukocyte protease inhibitor in cervical remodeling before and during parturition is understood poorly.

OBJECTIVE

We aimed to reveal the role of secretory leukocyte protease inhibitor in the cervical remodeling process before normal term delivery and to evaluate its utility as a predictive biomarker for timing of delivery.

STUDY DESIGN

Cervical mucus samples were collected prospectively at weekly prenatal visits from a cohort of pregnant women at term. The secretory leukocyte protease inhibitor concentrations in 95 mucus samples that were obtained from 49 women with uncomplicated pregnancy who subsequently underwent normal vaginal delivery were assessed. Alterations in secretory leukocyte protease inhibitor concentrations at term and the association of secretory leukocyte protease inhibitor levels with the time to delivery were analyzed.

RESULTS

A moderate positive correlation with significance was detected between cervical mucus secretory leukocyte protease inhibitor concentrations and days to delivery (r = 0.38; P = .0001). The secretory leukocyte protease inhibitor concentration was significantly higher in samples that were collected within 7 days of delivery when compared with samples that were collected >7 days before delivery (P = .001). Secretory leukocyte protease inhibitor concentrations were also significantly higher in samples from women with premature rupture of membranes when compared with those without premature rupture of membranes (P = .01), all of whom delivered within 7 days. A logistic regression analysis revealed that the cervical secretory leukocyte protease inhibitor level was a significant parameter for the prediction of the onset of delivery. (P = .017; unit odds ratio, 1.28; 95% confidence interval, 1.07-1.61). A cut-off value of cervical secretory leukocyte protease inhibitor/total protein to predict delivery within 7 days was determined to be 1.62 μg/mg (sensitivity, 0.69; specificity, 0.72) using receiver operating characteristic curve-analysis.

CONCLUSION

Secretory leukocyte protease inhibitor concentrations in the cervical mucus elevate progressively before delivery in uncomplicated term pregnancies. Our findings suggest that cervical secretory leukocyte protease inhibitor is a candidate biomarker for delivery prediction.

SLPI and inflammatory lung disease in females

During the course of certain inflammatory lung diseases, SLPI (secretory leucoprotease inhibitor) plays a number of important roles. As a serine antiprotease it functions to protect the airways from proteolytic damage due to neutrophil and other immune cell-derived serine proteases. With respect to infection it has known antimicrobial and anti-viral properties that are likely to contribute to host defence. Another of its properties is the ability to control inflammation within the lung where it can interfere with the transcriptional induction of pro-inflammatory gene expression induced by NF-κB (nuclear factor κB). Thus, factors that regulate the expression of SLPI in the airways can impact on disease severity and outcome. Gender represents once such idiosyncratic factor. In females with CF (cystic fibrosis), it is now thought that circulating oestrogen contributes, in part, to the observed gender gap whereby females have worse disease and poorer prognosis than males. Conversely, in asthma, sufferers who are females have more frequent exacerbations at times of low-circulating oestrogen. In the present paper, we discuss how SLPI participates in these events and speculate on whether regulatory mechanisms such as post-transcriptional modulation by miRNAs (microRNAs) are important in the control of SLPI expression in inflammatory lung disease.

Antimicrobial peptides and pregnancy

Antimicrobial peptides (AMPs) are small proteins produced by epithelial surfaces and inflammatory cells, which have broad-spectrum antimicrobial and immunomodulatory activities. They are known to be important in a number of infectious and inflammatory conditions and have been shown to be present in a number of sites throughout the female reproductive tract. Inflammation and infection are associated with a number of complications of pregnancy including preterm labor, and AMPs may play a key role in maintaining and protecting pregnancy. The aim of this review is to describe the expression and function of AMPs in the pregnant female reproductive tract and their relation to preterm labor.

Secretory leukocyte protease inhibitor and elafin/trappin-2: versatile mucosal antimicrobials and regulators of immunity

Elafin and secretory leukocyte protease inhibitor (SLPI) are pleiotropic molecules chiefly synthesized at the mucosal surface that have a fundamental role in the surveillance against microbial infections. Their initial discovery as anti-proteases present in the inflammatory milieu in chronic pathologies such as those of the lung suggested that they may play a role in keeping in check extracellular proteases released during the excessive activation of innate immune cells such as neutrophils. This soon proved to be a simplistic explanation, as other functions were also soon ascribed to these molecules (antimicrobial, modulation of innate and adaptive immunity, regulation of tissue repair). Data emanating from patients with chronic pathologies (in the lung and elsewhere) have shown that SLPI and elafin are often inactivated in inflammatory secretions, either through the action of host or microbial products, justifying attempts at antiprotease supplementation in clinical protocols. Although these have been sparse, proof of principle has been demonstrated, and future challenges will undoubtedly rest with improvements in methods of delivery in the context of tissue inflammation and in careful selection of patients more likely to benefit from SLPI/elafin augmentation.

Serum and bronchial lavage fluid concentrations of IL-8, SLPI, sCD14 and sICAM-1 in patients with COPD and asthma

BACKGROUND

Airway inflammation is associated with an increased expression and release of inflammatory reactants that regulate processes of cell migration, activation and degranulation. The purpose of this study was to quantify bronchial lavage (BAL) fluid and serum levels of chemokine (IL-8), secretory leukocyte protease inhibitor (SLPI), soluble intracellular adhesion molecules-1 (sICAM-1) and sCD14, as surrogate markers of inflammatory and immune response in asthma and chronic obstructive pulmonary disease (COPD) patients with similar disease duration time.

METHODS

Biomarkers in serum and BAL fluid from asthma (n=13) and COPD (n=25) patients were measured using commercially available ELISA kits.

RESULTS

We found that in asthma and COPD groups the concentrations of IL-8 and SLPI are significantly higher in BAL fluid than in serum, while levels of sICAM-1 and sCD14 in BAL fluid are significantly lower than in serum. Of these 4 measured biomarkers, only the BAL IL-8 was higher in COPD patients when compared to asthma (P<0.05). In both groups, BAL IL-8 correlated with SLPI (r=0.577, P<0.01 and r=0.589, P<0.05, respectively). In patients with COPD the BAL sICAM-1 correlated with sCD14 (r=0.576, P<0.01), while in asthma patients BAL sICAM-1 correlated with FEV(1)/FVC (r=0.418, P<0.01). Moreover, in asthma patients the serum SLPI correlated with sCD14 (r=0.688, P<0.01) and serum sICAM-1 negatively correlated with FEV(1)/FVC (r=-0.582, P<0.05).

CONCLUSION

Our findings point to the importance of selecting a correct biological fluid when analyzing specific biomarkers, and also show that of 4 measured biomarkers, only the BAL IL-8 was higher in COPD patients when compared to asthma.

Secretory leukocyte protease inhibitor and its potential interactions with elastase and cathepsin B in gingival crevicular fluid and saliva from patients with chronic periodontitis

BACKGROUND AND OBJECTIVE

Elastase is carried into the oral cavity by gingival crevicular fluid (GCF) from periodontal lesions. Our study investigated the regulation of elastase activity by secretory leukocyte protease inhibitor (SLPI) and the possible action of another GCF protease on this protective salivary component.

MATERIAL AND METHODS

Whole-mouth saliva (WMS), parotid saliva (PS) and GCF were obtained from 19 patients with periodontitis. The concentrations of active elastase and cathepsin B were determined using peptide substrates. SLPI and alpha1-proteinase inhibitor (alpha1PI) concentrations were determined using enzyme-linked immunosorbent assays (ELISAs). The molecular forms of SLPI were examined by immunoblotting.

RESULTS

The molar concentrations of elastase, cathepsin B and alpha1PI were higher in GCF than in WMS and especially PS (p < 0.0002). The GCF SLPI concentrations were also higher than the WMS SLPI concentrations (p < 0.05). All WMS components increased with GCF content, significantly for elastase and SLPI (p < 0.002). In GCF, the concentration of alpha1PI was higher than the concentration of SLPI (p < 0.0002), while there was no significant difference for WMS. SLPI and elastase levels in GCF and WMS were inversely related (p < 0.005). In SLPI immunoblots, PS contained only the intact 14-kDa molecule of SLPI, while WMS also contained an 8-kDa fragment. For WMS there was a positive correlation between SLPI degradation and cathepsin B (p < 0.002). Incubation of WMS alone or of PS with GCF in the presence of cysteine proteinase activators caused SLPI immunoreactivity to shift to 8 kDa.

CONCLUSION

For GCF, serum-derived alpha1PI is the major elastase inhibitor, but in WMS SLPI probably reduces activity. The inflamed gingivae can be an additional source of SLPI in the oral cavity, but here the molecule is apparently cleaved by GCF cysteine proteinases, such as cathepsin B.

SLPI and elafin: one glove, many fingers

Elafin and SLPI (secretory leucocyte protease inhibitor) have multiple important roles both in normal homoeostasis and at sites of inflammation. These include antiprotease and antimicrobial activity as well as modulation of the response to LPS (lipopolysaccharide) stimulation. Elafin and SLPI are members of larger families of proteins secreted predominantly at mucosal sites, and have been shown to be modulated in multiple pathological conditions. We believe that elafin and SLPI are important molecules in the controlled functioning of the innate immune system, and may have further importance in the integration of this system with the adaptive immune response. Recent interest has focused on the influence of inflamed tissues on the recruitment and phenotypic modulation of cells of the adaptive immune system and, indeed, the local production of elafin and SLPI indicate that they are ideally placed in this regard. Functionally related proteins, such as the defensins and cathelicidins, have been shown to have direct effects upon dendritic cells with potential alteration of their phenotype towards type I or II immune responses. This review addresses the multiple functions of elafin and SLPI in the inflammatory response and discusses further their roles in the development of the adaptive immune response.

Human immunodeficiency virus type 1 stimulates the expression and production of secretory leukocyte protease inhibitor (SLPI) in oral epithelial cells: a role for SLPI in innate mucosal immunity

The innate immune response is a key barrier against pathogenic microorganisms such as human immunodeficiency virus type 1 (HIV-1). Because HIV-1 is rarely transmitted orally, we hypothesized that oral epithelial cells participate in the innate immune defense against this virus. We further hypothesized that secretory leukocyte protease inhibitor (SLPI), a 12-kDa mucosal antiviral protein, is a component of the host immune response to this virus. Here we demonstrated constitutive expression and production of SLPI in immortalized human oral keratinocytes. Brief exposure of cells to HIV-1 BaL and HXB2 significantly increased SLPI mRNA and protein production compared to that in mock-exposed cells (P < 0.01), as evaluated by real-time quantitative reverse transcription-PCR and enzyme-linked immunosorbent assay. HIV-1-mediated stimulation of SLPI occurred at the transcriptional level, was dose and time dependent, was elicited by heat-inactivated and infectious viruses, and did not depend on cellular infection. Experiments with purified retroviral proteins showed that the stimulatory effect was induced specifically by external envelope glycoproteins from HIV-1 and simian immunodeficiency virus. SLPI responsiveness to HIV-1 was also observed in an unrelated oral epithelial cell line and in normal (nonimmortalized) human oral epithelial cells isolated from healthy uninfected gingival tissues. In this first report of SLPI regulation by HIV-1, we show that the expression and production of the antimicrobial and anti-inflammatory protein can be stimulated in oral epithelial cells by the virus through interactions with gp120 in the absence of direct infection. These findings indicate that SLPI is a component of the oral mucosal response to HIV-1.

Syk tyrosine kinase participates in beta1-integrin signaling and inflammatory responses in airway epithelial cells

The protein tyrosine kinase Syk is critically involved in immunoreceptor signaling in hematopoietic cells. Recent studies demonstrate Syk expression in nonhematopoietic cells, including fibroblasts, endothelial cells, hepatocytes, and breast epithelium. However, the role of Syk in these cells is uncertain. We hypothesized that Syk is expressed in respiratory epithelial cells (EC) and that it functions as a signaling molecule involved in inflammatory responses in the epithelium. With the use of immunohistochemistry, Western blot, PCR, and laser scanning confocal microscopy, Syk was detected in human, rat, and mouse bronchial epithelium in situ and in cultured human bronchial EC in primary cells and the cell lines HS-24 and BEAS-2B. Syk-dependent signaling pathways in EC were initiated by engagement of beta1-integrin receptors. Stimulation of beta1-integrin receptors by fibronectin or antibody cross-linking caused redistribution of Syk from a cytoplasmic to plasma membrane localization. In stimulated cells, Syk and beta1-integrin colocalized. In addition, following beta1-integrin receptor engagement, tyrosine phosphorylation of Syk was observed. Expression of the intercellular adhesion molecule-1 (ICAM-1) and production of IL-6, both important molecules in lung inflammation, was downregulated in EC treated with Syk small interfering RNA or Syk inhibitor piceatannol. We propose that Syk is involved in signaling pathways induced by integrin engagement in airway EC. Syk-mediated signaling regulates IL-6 and ICAM-1 expression and may be important in the pathophysiology of lung inflammation.

Sputum sol neutrophil elastase activity in bronchiectasis: differential modulation by syndecan-1

The persistently dominant activity of neutrophil elastase in bronchial secretions replete with antielastases is crucial to the pathogenesis of bronchiectasis. We hypothesize that components in the bronchial secretions bind neutrophil elastase and compromise the inhibitory efficiency of prevailing antielastases. Zymographic analysis of sputum sols from patients with bronchiectasis found elastase activity in a polydisperse, alcian blue-stained zone of high molecular mass. This suggested that neutrophil elastase was complexed with polyanionic partners. Western blot analysis found not only the polyanionic partner, heparan sulfate/syndecan-1, but also the physiological antielastases, secretory leukoproteinase inhibitor and alpha1-antitrypsin, in the complex. Both dissociative density gradient ultracentrifugation and heparin displacement revealed that elastase dissociated from heparan sulfate/syndecan-1 was fully inhibited by the endogenous antielastases. This contrasts with the effects of exogenous antielastases on sputum neutrophil elastase activity-that of alpha1-antitrypsin was limited, but that of secretory leukoproteinase inhibitor was facilitated. Similarly, complexed elastase on blots of sputum sol zymographs was bound and inhibited by exogenous secretory leukoproteinase inhibitor but not by exogenous alpha1-antitrypsin. Taken together, the results bring a new focus to heparan sulfate/syndecan-1 complexed with neutrophil elastase in inflamed bronchial secretions as a target for modulating elastase susceptibility to physiological antielastases.

Profile of gene expression induced by the tumour promotor TPA in murine epithelial cells

Malignant transformation of mouse skin by chemical carcinogens and tumour promoters, such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), is a multistage process that leads to squamous cell carcinoma (SCC) formation. In an effort to identify tumour-associated genes, we studied the influence of short-term TPA-treatment on the gene expression profile of murine skin. A comprehensive microarray with some 5,000 murine gene specific cDNA fragments was established and hybridised with pooled RNA derived from control and TPA-treated dorsal skin samples. Of these genes, 54 were up- and 35 were down-regulated upon TPA application. Additionally, we performed suppression subtractive hybridisation (SSH) with respective RNA pools to generate and analyse a cDNA library enriched for TPA-inducible genes. Expression data of selected genes were confirmed by quantitative real-time PCR and Northern blot analysis. Comparison of microarray and SSH data revealed that 26% of up-regulated genes identified by expression profiling matched with those present in the SSH library. Besides numerous known genes, we identified a large set of unknown cDNAs that represent previously unrecognised TPA-regulated genes in murine skin with potential function in tumour promotion. Additionally, some TPA-induced genes, such as Sprr1A, Saa3, JunB, Il4ralpha, Gp38, RalGDS and Slpi exhibit high basal level in advanced stages of skin carcinogenesis, suggesting that at least a subgroup of the identified TPA-regulated genes may contribute to tumour progression and metastasis.

Increased expression of the secretory leukocyte proteinase inhibitor in Wegener's granulomatosis

The secretory leucocyte proteinase inhibitor (SLPI) is a low molecular weight, tissue-specific inhibitor of proteases, such as elastase and cathepsin G. It is the major local protease inhibitor in the upper airways. Proteinase 3, the main autoantigen in Wegener's granulomatosis (WG), can degrade SLPI proteolytically. In addition, SLPI is sensitive to oxidative inactivation by myeloperoxidase-generated free oxygen radicals. SLPI also has an antimicrobial capacity that can be of interest, as infection is considered to play a role in the pathogenesis of WG. This study focuses on SLPI expression in patients suffering from WG, something that to our knowledge has not been explored hitherto. Serum samples and nasal biopsies were obtained from 12 Swedish WG patients, while buffy coats were obtained from 33 American WG patients. SLPI levels in serum were measured by means of ELISA and the protein was detected by means of immunohistochemistry in nasal biopsies. mRNA expression was studied by means of in situ hybridization on nasal biopsies and RT-PCR on leucocytes. IL-6 or ESR were measured as markers of inflammatory activity. Cystatin C or creatinine was measured as a marker of renal filtration. White blood cell counts were registered. In serum, we found close to normal SLPI levels, without any correlation to IL-6. Two patients had greatly elevated values, both of them suffering from severe renal engagement. Strong SLPI mRNA expression was found in nasal biopsies. RT-PCR on leucocyte mRNA showed normal or greatly elevated expression of SLPI mRNA, correlating with disease activity. Leukocyte SLPI expression seems to be up-regulated in active WG. Serum levels were measured in a small number of patients and were found to be close to normal. Lack of correlation to the acute phase response indicates a specific regulation. This might be linked to an altered protease/antiprotease balance. These findings could indicate that SLPI locally participates in the anti-inflammatory and perhaps antimicrobial response in WG.

Novel distribution of the secretory leucocyte proteinase inhibitor in kidney

The secretory leucocyte proteinase inhibitor (SLPI) is a low molecular weight, tissue-specific inhibitor of, for example, elastase and cathepsin G, which also have antimicrobial capacity. SLPI has been localised to the respiratory, gastrointestinal and genital tracts, but so far not to the kidney. The presence of SLPI in renal tubuli cells was demonstrated using immunohistochemistry and, by means of in situ hybridisation on human renal biopsies, we were able to demonstrate SLPI production. In various inflammatory conditions in the kidneys, the protease-antiprotease balance is disturbed. For this reason, as well as the possible role in the defence against ascending urinary tract infections, it is interesting to establish a source of SLPI in renal tubuli cells.

Cytokine-mediated induction of the human elafin gene in pulmonary epithelial cells is regulated by nuclear factor-kappaB

Elafin, a low molecular-weight proteinase inhibitor, is a member of the recently described trappin gene family. These proteins are thought to play important roles in the regulation of inflammation and are expressed in multiple epithelia. Elafin is found within the lung, and its expression can be induced by inflammatory mediators. The molecular mechanisms that mediate its induction are not understood. In this study we investigated the transcriptional regulation of the elafin gene in pulmonary epithelial cell lines. Transfection of elafin promoter constructs into the elafin-expressing pulmonary epithelial cell line A549 identified a number of positive-acting elements. Cytokine-mediated inducibility of the elafin gene promoter was shown to occur through a nuclear factor (NF)-kappaB site present within the minimal promoter. This site was shown to bind to NF-kappaB proteins within nuclear extracts from cytokine stimulated cell lines as well as to in vitro-translated RelA. Cotransfection with both RelA and NF-kappaB-inducing kinase induced reporter gene activation via this site, and mutagenesis experiments confirmed that it was crucial for induction of elafin gene activity. These results clearly identify a role for elafin in the inflammatory response of the airway epithelium to pathogenic insult and show that this response is mediated by an NF-kappaB site within the proximal promoter.

Secretion and gene expression of secretory leukocyte protease inhibitor by human airway submucosal glands

Submucosal glands were isolated within 4 h of death from tracheae and bronchi obtained from autopsied lungs, and the secretory response of secretory leukocyte protease inhibitor (SLPI) was examined with ELISA and a secretory index. Although human neutrophil elastase (HNE) at low concentrations increased SLPI secretion above the control level (i.e., 149% of control level at 10(-11) M), HNE at high concentrations significantly decreased it below the control level (i.e., 16% of control level at 10(-7) M). The decrease in SLPI concentration was shown to result from the degradation of SLPI by excessive HNE. Methacholine induced significant secretion (i.e., 363% of control level at 10(-5) M) that was abolished by both M(1) and M(3) receptor antagonists. A semiquantitative analysis of SLPI mRNA by RT-PCR and Southern blot showed that compared with the superficial epithelium, submucosal glands had a 30-fold or higher level of SLPI mRNA. Both HNE and methacholine significantly increased the level of SLPI mRNA in submucosal glands in a dose-dependent manner (i.e., 357% of control level at 10(-7) M and 175% of control level at 10(-5) M, respectively). These findings indicate that human airway submucosal glands can transcribe 30-fold or more SLPI mRNA than the superficial epithelium and that SLPI mRNA transcription and secretion are regulated by both HNE and muscarinic receptors.

Constitutive and regulated secretion of secretory leukocyte proteinase inhibitor by human intestinal epithelial cells

BACKGROUND & AIMS

Epithelial cells participate in immune regulation and mucosal integrity by generating a range of biologically active mediators. In the intestine, little is known about the potential endogenous anti-inflammatory molecules. Secretory leukocyte proteinase inhibitor (SLPI) is a major serine proteinase inhibitor, a potent antibiotic, and thus a potential anti-inflammatory molecule, although it is not known if it is secreted by intestinal epithelial cells.

METHODS

We show, by reverse-transcription polymerase chain reaction, the presence of SLPI messenger RNA in human model intestinal epithelial cell lines (Caco2-BBE, T84, and HT29-Cl.19A) and human jejunum and colon biopsy specimens. The polymerase chain reaction product was cloned and sequenced and is identical to that of SLPI isolated previously from the human parotid gland.

RESULTS

As analyzed by enzyme-linked immunosorbent assay, the constitutive secretion of SLPI occurs in a markedly polarized manner toward the apical surface and is enhanced by inflammatory mediators including tumor necrosis factor alpha and interleukin 1beta (approximately 3.5-fold increase over control value). SLPI release is also stimulated by activation of protein kinase C isoenzymes, but not by activation of adenosine 3',5'-cyclic monophosphate- or Ca(2+)-regulated signaling molecules. SLPI protein is detectable in intestinal lavage fluids collected from normal adult humans. Recombinant SLPI attenuates digestive enzyme (trypsin)- or leukocyte proteinase (elastase)-induced permeability alteration of a model epithelia in a dose-dependent manner. Moreover, SLPI exhibits an antibacterial activity against at least one major intestinal pathogen, Salmonella typhimurium. In contrast, SLPI does not influence epithelial barrier integrity as assessed by transepithelial conductance measurements or electrogenic ion transport.

CONCLUSIONS

These results establish that human intestinal epithelium expresses and apically secretes SLPI, a molecule that may significantly contribute to the protection against attack from inflammatory cells and digestive enzymes, as well as against microbial infection.

Trout ovulatory proteins: site of synthesis, regulation, and possible biological function

The mRNA transcripts for trout ovulatory proteins (TOPs) are dramatically up-regulated at the time of ovulation. Previous studies indicated that TOPs were produced by the ovaries and were also present in the coelomic fluid that bathes ovulated eggs. In the present study, Western analysis indicated that TOPs were not present in the coelomic fluid prior to ovulation and therefore must be secreted into the coelomic fluid in large quantities during and after ovulation. Using in situ hybridization and immunocytochemistry, TOP mRNA and proteins were localized to the granulosa cell layer of the postovulatory follicle. A whole-follicle in vitro incubation system was used to look at the effects of various mediators on TOP mRNA and protein levels. Results of several different secondary messenger agonists suggest that TOPs are regulated through a G protein-mediated pathway that does not involve cAMP but may involve the activation of protein kinase C. Other agonists that had significant effects on TOP RNA and/or protein included transforming growth factor alpha (TGF-alpha), serine proteases, corticosteroids, bacterial lipopolysaccharide, and the nitric oxide generator SNAP ([+/-]-S-nitroso-N-acetylpenicillamine). Overall, while several compounds caused significant effects, none were able to reproduce the increase in TOP RNA and protein that occurs in vivo, suggesting that the natural mediator of TOPs may still be untested, or that a combination of mediators may be involved. Finally, coelomic fluid inhibited the growth of the Gram negative bacterium, P. aeruginosa, and this inhibition was lost following immunoprecipitation of TOPs. This suggests that one function of TOPs may be to protect ovulated eggs from bacterial infection.

Regulation of SLPI and elafin release from bronchial epithelial cells by neutrophil defensins

Secretory leukocyte proteinase inhibitor (SLPI) is a serine proteinase inhibitor that is produced locally in the lung by cells of the submucosal bronchial glands and by nonciliated epithelial cells. Its main function appears to be the inhibition of neutrophil elastase (NE). Recently, NE was found to enhance SLPI mRNA levels while decreasing SLPI protein release in airway epithelial cells. Furthermore, glucocorticoids were shown to increase both constitutive and NE-induced SLPI mRNA levels. In addition to NE, stimulated neutrophils also release alpha-defensins. Defensins are small, antimicrobial polypeptides that are found in high concentrations in purulent secretions of patients with chronic airway inflammation. Like NE, defensins induce interleukin-8 production in airway epithelial cells. This induction is sensitive to inhibition by the glucocorticoid dexamethasone and is prevented in the presence of alpha(1)-proteinase inhibitor. The aim of the present study was to investigate the effect of defensins on the production of SLPI and the related NE inhibitor elafin/SKALP in primary bronchial epithelial cells (PBECs). Defensins significantly increase SLPI protein release by PBECs in a time- and dose-dependent fashion without affecting SLPI mRNA synthesis. In the presence of alpha(1)-proteinase inhibitor, the defensin-induced SLPI protein release is further enhanced, but no effect was observed on SLPI mRNA levels. Dexamethasone did not affect SLPI protein release from control or defensin-treated PBECs. In addition, we observed a constitutive release of elafin/SKALP by PBECs, but this was not affected by defensins. The present results suggest a role for defensins in the dynamic regulation of the antiproteinase screen in the lung at sites of inflammation.

Identification of the secretory leukocyte protease inhibitor (SLPI) as a target of IRF-1 regulation

Interferon Regulatory Factor (IRF)-1 is a multifunctional transcription factor, involved in cell growth regulation, pathogen response and immune activation. To identify novel gene targets that may contribute to IRF-1 mediated activities, RNA fingerprinting was performed using NIH3T3 cells that inducibly express a hybrid form of IRF-1 under tetracycline regulated control. Secretory leukocyte protease inhibitor (SLPI) - a regulator of inflammation and an inhibitor of the LPS response - was identified as a gene repressed after doxycycline induced IRF-1 expression. Preliminary analysis of the human SLPI promoter identified an ISRE-like site located within the -221 to -200 region to which IRF-1 binds and a second, putative IRF-1 binding site upstream of the TATA box. Furthermore, co-transfection studies demonstrated that SLPI expression was inhibited by IRF-1 co-expression. The identification of SLPI as a target of IRF-1 regulation reveals a unique involvement of IRF-1 in repression of gene transcription and assigns a novel role for IRF-1 in inflammation.

Reactive oxygen intermediates stimulate interleukin-6 production in human bronchial epithelial cells

Reactive oxygen intermediates (ROIs) play an important role in the initiation and progression of lung diseases. In this study, we investigated whether ROIs were involved in the induction of interleukin (IL)-6 in human bronchial epithelial cells. We exposed normal human bronchial epithelial cells as well as a human bronchial epithelial cell line, HS-24, to ROIs. We measured the amount of IL-6 in the culture supernatants using ELISA and the IL-6 mRNA levels using RT-PCR. Superoxide anions (O-2), but not hydrogen peroxide (H2O2), increased IL-6 production. To examine whether it is a cell type-specific mechanism of airway epithelial cells, the experiments were also performed in human lung fibroblasts, WI-38-40. In WI-38-40 cells, neither O-2 nor H2O2 increased IL-6 production. In contrast, tumor necrosis factor (TNF)-alpha (200 U/ml) induced IL-6 at the protein and mRNA levels in both airway epithelial cells and lung fibroblasts. This cytokine-induced IL-6 production was significantly suppressed by several antioxidants, including dimethyl sulfoxide (DMSO), in airway epithelial cells. In WI-38-40 cells, DMSO was not able to suppress IL-6 production induced by TNF-alpha. Pretreatment with DMSO recovered the TNF-alpha-induced depletion of intracellular reduced glutathione in HS-24 cells. These findings indicate that oxidant stress specifically induces IL-6 production in human bronchial epithelial cells and that in these cells ROIs may be involved in IL-6 production after stimulation with cytokines such as TNF-alpha. Presumably, ROIs participate in the local immune response in lung diseases via IL-6 release from bronchial epithelial cells.

Structure of the murine secretory leukoprotease inhibitor (Slpi) gene and chromosomal localization of the human and murine SLPI genes

Secretory leukoprotease inhibitor (SLPI) is a serine protease inhibitor involved in antineutrophil elastase protection at inflammatory sites. To elucidate both the function and regulation of SLPI in vivo, we isolated and characterized the mouse Slpi gene. An entire 3-kb mouse Slpi gene fragment was sequenced, including an 0. 8-kb 5'-flanking region, the 2.2-kb Slpi gene, and a 0.1-kb 3'-flanking region. The mouse Slpi gene spans 2,222 base pairs containing four exons and three introns. All splicing borders between exons and introns are conserved as predicted by GT-AG rules. Using primer extension analysis, the transcription start site was located 20 nucleotides upstream from the methionine (ATG) initiation codon. At the defined transcription start site, the sequence TCA+1GAGC is present. These results indicate that both mouse and human genomic structure are highly conserved. Using fluorescence in situ hybridization, we confirmed that, consistent with the genomic similarity, the human SLPI gene is localized on chromosome 20q12-13. 2 and the mouse homologue on chromosome 2H, which are syntenic with each other.

Induction of SLPI (ALP/HUSI-I) in epidermal keratinocytes

Secretory leukocyte protease inhibitor (SLPI) is a small, cationic protein that is known to be constitutively expressed by several glandular epithelia. SLPI inhibits leukocyte-derived proteinases, has anti-HIV-1, antibacterial, and anti-fungal properties, and interferes with the induction of synthesis of proinflammatory mediators in monocytes and macrophages. We now report that at both the mRNA and the protein level, SLPI shows inducible expression in a nonglandular epithelium. A weak expression of SLPI was found in the stratum granulosum of adult normal human epidermis; however, in lesional psoriatic epidermis and in migrating keratinocytes of healing wounds, a strong cytoplasmic staining was seen in the suprabasal keratinocytes. Remarkably, in the dermis adjacent to SLPI-expressing keratinocytes, SLPI was found extracellularly associated with elastin fibers, whereas the dermis in normal skin was negative. In cell culture, SLPI was hardly expressed in monolayers of proliferating keratinocytes. Differentiating cultures with a phenotype of normal skin expressed low levels of SLPI, whereas cultures with a regenerative/psoriatic phenotype expressed high levels. Functional studies with recombinant SLPI indicated that its antibacterial spectrum and potency are distinct from other anti-microbial peptides such as lysozyme and defensins. In view of the multiple functions of SLPI and the inducibility, we propose that it acts as an important first line defence mechanism in cutaneous injury.

Lipopolysaccharide-related stimuli induce expression of the secretory leukocyte protease inhibitor, a macrophage-derived lipopolysaccharide inhibitor

Mouse secretory leukocyte protease inhibitor (SLPI) was recently characterized as a lipopolysaccharide (LPS)-induced product of macrophages that antagonizes their LPS-induced activation of NF-kappaB and production of NO and tumor necrosis factor (TNF) (F. Y. Jin, C. Nathan, D. Radzioch, and A. Ding, Cell 88:417-426, 1997). To better understand the role of SLPI in innate immune and inflammatory responses, we examined the kinetics of SLPI expression in response to LPS, LPS-induced cytokines, and LPS-mimetic compounds. SLPI mRNA was detectable in macrophages by Northern blot analysis within 30 min of exposure to LPS but levels peaked only at 24 to 36 h and remained elevated at 72 h. Despite the slowly mounting and prolonged response, early expression of SLPI mRNA was cycloheximide resistant. Two LPS-induced proteins-interleukin-10 (IL-10) and IL-6-also induced SLPI, while TNF and IL-1beta did not. The slow attainment of maximal induction of SLPI by LPS in vitro was mimicked by infection with Pseudomonas aeruginosa in vivo, where SLPI expression in the lung peaked at 3 days. Two LPS-mimetic molecules-taxol from yew bark and lipoteichoic acid (LTA) from gram-positive bacterial cell walls-also induced SLPI. Transfection of macrophages with SLPI inhibited their LTA-induced NO production. An anti-inflammatory role for macrophage-derived SLPI seems likely based on SLPI's slowly mounting production in response to constituents of gram-negative and gram-positive bacteria, its induction both as a direct response to LPS and as a response to anti-inflammatory cytokines induced by LPS, and its ability to suppress the production of proinflammatory products by macrophages stimulated with constituents of both gram-positive and gram-negative bacteria.

The elastase-induced expression of secretory leukocyte protease inhibitor is decreased in remodelled airway epithelium

During airway inflammation, proteinases such as human leukocyte elastase are actively secreted. Secretory leukocyte protease inhibitor is a major serine proteinase inhibitor, secreted by bronchial, bronchiolar and lung epithelial cells. We recently identified secretory leukocyte protease inhibitor in human nasal epithelium, exclusively in remodelled areas of the surface epithelium. We now investigated the influence of remodelling and inflammation of the nasal tissue on the in vitro capacity of these cells to respond to human leukocyte elastase. Primary cultures of surface epithelial cells were established from various nasal polyp samples. At confluency, cell cultures were exposed to different human leukocyte elastase concentrations. The secretory leukocyte protease inhibitor immunocytolocalisation, expression and secretion were then investigated. Immunocytochemistry, showed a human leukocyte elastase dose-dependent increase of secretory leukocyte protease inhibitor containing cells and a basal extracellular localization of secretory leukocyte protease inhibitor after incubation with 100 microg/ml human leukocyte elastase. The relative amount of secretory leukocyte protease inhibitor mRNA transcripts increased with respect to the human leukocyte elastase concentration. Nevertheless, the potential stimulation of secretory leukocyte protease inhibitor secretion by human leukocyte elastase was lower in the more remodelled and inflamed tissue. Our results suggest that the contribution of the surface epithelial cells of poorly remodelled tissues to the protection against the deleterious effect of neutrophil proteinases is severely decreased in highly remodelled and inflamed tissues.

Bacterial pneumonia causes augmented expression of the secretory leukoprotease inhibitor gene in the murine lung

The cDNA of murine secretory leukoprotease inhibitor (SLPI) was cloned from a mouse lung cDNA library. The amino acid sequence deduced from the cDNA showed 58 and 51% homology with those of human and porcine SLPI, respectively. A two-domain structure with similar amino acid sequences, four intradomain disulfide bonds, and high proline content, which are characteristics common to human and porcine SLPI, was also found in the mouse protein. The amino acid residues for the signal sequence and active site are also conserved in mouse SLPI. RNase protection assay showed the expression of the SLPI gene in liver, intestine, spleen, and epididymis, suggesting the distribution of SLPI in tissues other than lung and seminal vesicles. In the lung infected with Streptococcus pneumoniae strain FP1284, 10 h after inoculation of bacteria the number of SLPI mRNA transcripts was three times higher than baseline. The increased level of expression remained constant for at least 48 h. This result clearly contrasts to that obtained for spleen, in which the SLPI mRNA transcript level was mostly unchanged during the course of pneumonia. These facts suggested the local regulation of the SLPI gene expression in vivo in response to inflammatory stimuli at the site of inflammation.

Cis-acting region associated with lung cell-specific expression of the secretory leukoprotease inhibitor gene

Secretory leukoprotease inhibitor (SLPI) is a serine protease inhibitor, produced locally in respiratory and genital glands, but not in the liver. In the present study the promoter region of this gene was analyzed to better understand the molecular mechanisms involved in transcriptional regulation. DNase-I hypersensitive sites were detected within 1 kbp upstream of exon I in chromatin structures of type II pneumocyte cell line A549 and utero-cervical cell line HeLa, both of which express SLPI mRNA transcripts. The function of the SLPI promoter encompassing these DNase-I hypersensitive sites has been studied by deletion analysis with the luciferase gene as a transient expression vector. In this analysis, we found three transcription control regions that function in A549 cells but not in nonlung cell lines, such as HeLa and hepatoma Hep G2. Among three cis-regulatory regions, a proximal 41-bp region (-132 to -92 bp relative to the transcription start site) is responsible for the most striking magnitude of transcriptional activity. This region corresponds to the transcriptional activating sequence detected in another lung cell line, HS-24, indicating that this 41-bp sequence is required for lung cell-specific expression. An electrophoretic mobility shift assay demonstrated that this 41-bp promoter region contains an 11-bp recognition sequence for two nuclear binding proteins, one of which is abundant in lung cell lines, and the other in nonlung cell lines. These results suggest that the ratio of these two nuclear binding proteins confers the cell type specificity on the expression pattern of the SLPI gene.

Secretory leukocyte protease inhibitor (SLPI) in mucosal fluids inhibits HIV-I

Despite the presence of HIV-1 in the oral cavity, transmission of the virus through saliva has not been proven. Consistent with these observations, we recently identified an endogenous 12 kD protein, secretory leukocyte protease inhibitor (SLPI), in saliva which blocks HIV-1 infection in vitro. Whereas other salivary proteins tested were inactive, purified native or recombinant SLPI inhibited HIV-1 infection of human monocytes at 100 ng ml-1. Levels of SLPI quantitated by ELISA in saliva from control and HIV-1 infected individuals exceeded this level, consistent with in vivo antiviral activity. As in saliva, levels of SLPI mRNA determined by Northern hybridization, and protein as assessed by immunohistochemistry in the salivary glands of control and infected populations were comparable. In contrast to adults, oral transmission occurs in infants, possibly due to their lack of fully developed salivary glands. To determine whether the inadequate antiviral protection might be compensated for by maternal sources, we evaluated breast milk samples obtained 6 months postpartum. Levels of SLPI were significantly lower than in saliva and not sufficient to provide antiviral protection in contrast to colostrum samples in which SLPI levels were equivalent to those in saliva and able to inhibit HIV-1 infection when tested in vitro. These data suggest that breast milk may provide transient antiviral activity in the newborn, but that this maternal source of SLPI is of insufficient duration to maintain protection against mucosal transmission of the virus over time. The high functional levels of SLPI in saliva and the low levels in mature breast milk correlate with negligible rates of HIV-1 transmission by saliva and higher rates by breast feeding.

The cloning and characterization of a murine secretory leukocyte protease inhibitor cDNA

Human secretory leukocyte protease inhibitor (hSLPI) is produced by epithelial cells at mucosal surfaces, where it regulates both the neutrophil-mediated inflammation that characterizes inflammatory diseases, and pathogens themselves via both antiprotease and "defensin-like" activities. Additionally, hSLPI may regulate other processes such as cutaneous desquamation and placental invasiveness. To better understand the primary physiologic roles of SLPI, it will be important to establish a genetically tractable animal model, the most attractive candidate being the mouse. In this report, the cloning and characterization of murine (m) SLPI is described. mSLPI is encoded by a single copy gene, and appears structurally highly similar to hSLPI. At the same time, significant differences between mSLPI and hSLPI are presented, notably a difference in expression pattern, and a structural difference in the protease binding site that correlates with a difference in the spectrum of protease inhibiton. Such species-specific evolution of this protease inhibitor is notable given that species-specific structure-function differences have previously been reported for the alpha-1 antitrypsin family.

Secretory leukocyte protease inhibitor: a macrophage product induced by and antagonistic to bacterial lipopolysaccharide

To explore regulation of potentially lethal responses to bacterial lipopolysaccharide (LPS), we used differential display under LPS-free conditions to compare macrophage cell lines from two strains of mice congenic for a locus affecting LPS sensitivity. LPS-hyporesponsive cells, primary macrophages, and polymorphonuclear leukocytes transcribed secretory leukocyte protease inhibitor (SLPI), a known epithelial cell-derived inhibitor of leukocyte serine proteases. Transfection of macrophages with SLPI suppressed LPS-induced activation of NF-kappa B and production of nitric oxide and TNF alpha. The ability of interferon-gamma (IFN gamma) to restore LPS responsiveness is a hallmark of the LPS-hyporesponsive phenotype. IFN gamma suppressed expression of SLPI and restored LPS responsiveness to SLPI-producing cells. Thus, SLPI is an LPS-induced IFN gamma-suppressible phagocyte product that serves to inhibit LPS responses.

Transcriptional activation of RACTK1 K+ channel gene by apical alkalization in renal cortical collecting duct cells

We have previously demonstrated that RACTK1 cDNA encodes a pH sensitive K+ channel expressed in the apical side of renal collecting tubule cells. To determine whether extracellular pH induces the RACTK1 gene expression in the renal cortical collecting duct (CCD) cells, we measured mRNA of the RACTK1 using cultured rabbit CCD cells. Alkalization of incubation medium activated the transcription of the RACKTK1 gene in a time- and dose-dependent manner after 1 h, and reached a maximal level after 12 h. To examine whether the stimulation of mRNA by alkalization of body fluid occurs also in vivo, mRNA levels were measured in mice loaded with acid or alkali. The RACTK1 mRNA was increased in association with the rise in urinary pH. To examine side face of the effect of pH on stimulation of mRNA, we observed the effect of pH in the apical or the basolateral side in the preparation where CCD cells were cultured on filter membrane supports. Alkalization of the apical side but not of the basolateral side, was shown to be a determinant in inducting the RACTK1 mRNA. These findings suggest that, in addition to rapid direct regulation of RACTK1 K+ channel conductance by intracellular pH, this channel is also regulated by the changes in luminal pH through synthesis of channel protein by transcriptional activation.

Structural diversity in the 5'-untranslated region of cytokine-stimulated human inducible nitric oxide synthase mRNA

Inducible nitric oxide synthase, the critical enzyme responsible for the enhanced synthesis of nitric oxide in inflammatory states, is widely expressed in mammalian cells. To evaluate potential regulatory roles of the 5'-untranslated region (UTR) in the human inducible nitric oxide synthase gene, the transcription initiation sites and structure of the 5'-UTR of human inducible nitric oxide synthase were examined. Freshly isolated human alveolar macrophages, bronchial epithelial cells, and several types of cultured cells were evaluated following stimulation with cytokines (i.e. interferon-gamma, interleukin-1 beta, tumor necrosis factor-alpha, and interleukin-6). The mRNA was analyzed by reverse transcription-polymerase chain reaction. Northern analysis, and 5'-rapid amplification of cDNA ends. Despite the presence of a TATA box in the promoter region, multiple transcription initiation sites were observed, some extending several hundred base pairs upstream from the main TATA-directed initiation site. Alternative splicing in the 5'-UTR of human inducible nitric oxide synthase mRNA resulted in further diversity. The TATA-independent inducible nitric oxide synthase mRNA transcripts were up-regulated by cytokines. The long and complex 5'-UTRs contain eight partially overlapping open reading frames upstream of the putative inducible nitric oxide synthase ATG, which may have an important role in translational regulation of human inducible nitric oxide synthase mRNA.