The Antiviral Effects of Sodium Phenylbutyrate Against BoHV-1 Infection In Vitro

Introduction:

The alteration of histone acetylation is a known mechanism to regulate gene expression, and thereby affecting various cellular processes. Histone deacetylases (HDACs) are known to regulate histone acetylation by removal of the acetyl group from lysines. HDAC inhibitor such as Sodium Phenylbutyrate (PB) and Valproic Acid (VPA) have been reported to affect multiple virus infection while whether they affect BoHV-1 infection is unknown.

Objective:

The aim of the study is to investigate whether PB and VPA effects BoHV-1 infection and the virus induced inflammation related signaling including Erk1/2 and p38MAPK signaling.

Methods:

To assess the antiviral effects of PB and VPA on BoHV-1 infection, MDBK cells were treated with these inhibitors at different concentrations. Then time addition was performed to pinpoint which stages of virus infection was affected by the chemicals. In order to assess whether PB affect viral gene expression, we detected the viral IE genes such as bICP0, bICP4 and bICP22 using real-time PCR assay. The effects of PB had on the activation of inflammation related signaling including Erk1/2 and p38MAPK in response to the virus infection were also detected.

Results:

Here, for the first time we reveals that PB but not VPA affects BoHV-1 infection at late stages of infection. It affected the expression of IE genes such as bICP0, bICP4 and bICP22. Interestingly, PB enhanced the activation of both Erk1/2 and p38MAPK signaling stimulated by BoHV-1 infection.

Conclusion:

HDAC inhibitor PB significantly inhibited BoHV-1 infection partially through the interruption of certain viral IE gene expression. Though PB has been reported to have antiinflammatory effects, we found that it enhanced the activation of inflammation pertinent signaling of both Erk1/2 and p38MAPK stimulated by BoHV-1 infection.

Characterization of mutation spectrum and identification of novel mutations in ATP7B gene from a cohort of Wilson disease patients: Functional and therapeutic implications

Wilson disease (WD), a copper metabolism disorder, occurs due to the presence of mutations in the gene encoding ATP7B, a protein that primarily facilitates hepatic copper excretion. A better understanding of spectrum and functional significance of ATP7B variants is critical to formulating targeted and personalized therapies. Henceforth, we screened and sequenced 21 exons of ATP7B gene from 50 WD patients and 60 healthy subjects. We identified 28 variants comprising, seven novels in 20% alleles, while eight variations affecting 23% alleles were first time reported in Indian cohort. The c.813C>A, p.(Cys271*) (10%) was the most frequent mutation. Bioinformatics analysis revealed five of seven novel variants viz. c.1600C>A, p.(Pro534Thr); c.1616C>A, p.(Pro539His); c.1924G>T, p.(Asp642Tyr); c.2168G>C, p.(Arg723Thr); c.2174G>C, p.(Arg725Thr) resulted in protein misfolding. Sequence conservation analysis of ATP7B regions containing novel variants documented an evolutionarily conserved nature. Functional analysis of these novel variants in five different cell lines lacking inherent ATP7B expression demonstrated sensitivity to CuCl₂ -treatment, experiencing augmented cellular copper retention and decreased copper excretion as well as ceruloplasmin secretion to that of wildtype-ATP7B expressing cells. Interestingly, pharmacological chaperone 4-phenylbutyrate, a clinically approved compound, partially restored protein function of ATP7B mutants. These findings might enable novel treatment strategies in WD by clinically enhancing the protein expression of mutant ATP7B with residual copper export activity.

CFTR ameliorates high glucose-induced oxidative stress and inflammation by mediating the NF-κB and MAPK signaling pathways in endothelial cells

Diabetic cardiovascular diseases are characterized by progressive hyperglycemia, which results in excessive production of oxidative stress and pro-inflammatory cytokines. Cystic fibrosis (CF) is characterized by chronic inflammation due to mutations in CF transmembrane conductance regulator (CFTR). However, little information is available about the role of CFTR in hyperglycemia‑induced endothelial cell oxidative stress and inflammation. In the present study, a high glucose‑treatment was applied in human umbilical vein endothelial cells with CFTR overexpression or inhibition, and the oxidative and inflammatory characteristics were measured. It was shown that CFTR protein and mRNA expression were reduced by glucose in a concentration‑dependent manner. Overexpression of CFRT via adenoviral infection significantly inhibited the production of reactive oxygen species and inflammatory biomediators induced by high glucose. Conversely, pharmacological inhibition of CFTR led to the opposite effects. Mechanistically, nuclear factor‑κB (NF‑κB) and mitogen‑activated protein kinase (MAPK) signaling were activated following high glucose treatment, which were inhibited by CFTR overexpression and enhanced by CFTR inhibition. The pro‑inflammatory effect of CFTR inhibition was abolished by pharmacological inhibition of the NF‑κB or MAPK pathways. Moreover, inhibition of MAPK abrogated CFTR inhibition‑induced NF‑κB nuclear translocation, whereas NF‑κB inhibitor produced no effects on MAPK activation. Additionally, antioxidant treatment inhibited the high glucose‑induced decrease in CFTR expression and the increase in inflammatory responses. Collectively, these findings revealed that CFTR attenuates high glucose‑induced endothelial cell oxidative stress and inflammation through inactivation of NF‑κB and MAPK signaling, indicating that elevation of CFRT expression may be a novel strategy in preventing endothelial dysfunction in diabetes.

CFTR protects against vascular inflammation and atherogenesis in apolipoprotein E-deficient mice

Atherosclerosis is a chronic inflammatory disease of the vascular wall. Dysfunction of cystic fibrosis transmembrane conductance regulator (CFTR) has been shown to result in inflammatory responses in cystic fibrosis (CF) patients. However, little is known about the role of CFTR in vascular inflammation and atherogenesis. Our results showed that CFTR was dominantly expressed in macrophages of atherosclerotic plaque and reduced in aorta and aortic sinus from atherosclerotic apolipoprotein E-deficient (apoE^−/−) mice. In vivo administration of adenovirus encoding CFTR (Ad-CFTR) with apoE^−/− mice fed on high-fat diet (HFD) improved plaque stability by decreasing lipid accumulation and necrotic area and increasing smooth muscle cell content and collagen. The Ad-CFTR-treated mice also displayed reduced proinflammatory cytokines levels in aorta and peritoneal macrophages, whereas the anti-inflammatory M2 macrophage markers were increased. Confocal microscopy revealed that the infiltration of T lymphocytes, neutrophils, and macrophages in aortic sinus was markedly attenuated in Ad-CFTR-treated apoE^−/− mice. Moreover, in vitro experiments showed that overexpression of CFTR inhibited ox-LDL-induced the migration of peritoneal macrophages. Finally, it was observed that CFTR up-regulation suppressed NFκB and MAPKs activity induced by ox-LDL. Inhibition of JNK or ERK abrogated CFTR down-regulation induced NFκB activation, whereas NFκB inhibitor had no effect on JNK or ERK activation. Taken together, these results demonstrate that CFTR prevents inflammation and atherogenesis via inhibition of NFκB and MAPKs activation. Our data suggest that CFTR may present a potential therapeutic target for the treatment of vascular inflammation and development of atherosclerotic disease.

Histone Deacetylase Inhibitor Phenylbutyrate Exaggerates Heart Failure in Pressure Overloaded Mice independently of HDAC inhibition

4-Sodium phenylbutyrate (PBA) has been reported to inhibit endoplasmic reticulum stress and histone deacetylation (HDAC), both of which are novel therapeutic targets for cardiac hypertrophy and heart failure. However, it is unclear whether PBA can improve heart function. Here, we tested the effects of PBA and some other HDAC inhibitors on cardiac dysfunction induced by pressure overload. Transverse aortic constriction (TAC) was performed on male C57BL/6 mice. PBA treatment (100 mg/kg, 6 weeks) unexpectedly led to a higher mortality, exacerbated cardiac remodelling and dysfunction. Similar results were noted in TAC mice treated with butyrate sodium (BS), a PBA analogue. In contrast, other HDAC inhibitors, valproic acid (VAL) and trichostatin A (TSA), improved the survival. All four HDAC inhibitors induced histone H3 acetylation and inhibited HDAC total activity. An individual HDAC activity assay showed that rather than class II_a members (HDAC4 and 7), PBA and BS predominantly inhibited class I members (HDAC2 and 8), whereas VAL and TSA inhibited all of them. These findings indicate that PBA and BS accelerate cardiac hypertrophy and dysfunction, whereas VAL and TSA have opposing effects.

Effect of a chemical chaperone, tauroursodeoxycholic acid, on HDM-induced allergic airway disease

Endoplasmic reticulum (ER) stress-induced unfolded protein response plays a critical role in inflammatory diseases, including allergic airway disease. However, the benefits of inhibiting ER stress in the treatment of allergic airway disease are not well known. Herein, we tested the therapeutic potential of a chemical chaperone, tauroursodeoxycholic acid (TUDCA), in combating allergic asthma, using a mouse model of house dust mite (HDM)-induced allergic airway disease. TUDCA was administered during the HDM-challenge phase (preventive regimen), after the HDM-challenge phase (therapeutic regimen), or therapeutically during a subsequent HDM rechallenge (rechallenge regimen). In the preventive regimen, TUDCA significantly decreased HDM-induced inflammation, markers of ER stress, airway hyperresponsiveness (AHR), and fibrosis. Similarly, in the therapeutic regimen, TUDCA administration efficiently decreased HDM-induced airway inflammation, mucus metaplasia, ER stress markers, and AHR, but not airway remodeling. Interestingly, TUDCA administered therapeutically in the HDM rechallenge regimen markedly attenuated HDM-induced airway inflammation, mucus metaplasia, ER stress markers, methacholine-induced AHR, and airway fibrotic remodeling. These results indicate that the inhibition of ER stress in the lungs through the administration of chemical chaperones could be a valuable strategy in the treatment of allergic airway diseases.

CFTR-regulated MAPK/NF-κB signaling in pulmonary inflammation in thermal inhalation injury

The mechanism underlying pulmonary inflammation in thermal inhalation injury remains elusive. Cystic fibrosis, also hallmarked with pulmonary inflammation, is caused by mutations in CFTR, the expression of which is temperature-sensitive. We investigated whether CFTR is involved in heat-induced pulmonary inflammation. We applied heat-treatment in 16HBE14o- cells with CFTR knockdown or overexpression and heat-inhalation in rats in vivo. Heat-treatment caused significant reduction in CFTR and, reciprocally, increase in COX-2 at early stages both in vitro and in vivo. Activation of ERK/JNK, NF-κB and COX-2/PGE2 were detected in heat-treated cells, which were mimicked by knockdown, and reversed by overexpression of CFTR or VX-809, a reported CFTR mutation corrector. JNK/ERK inhibition reversed heat-/CFTR-knockdown-induced NF-κB activation, whereas NF-κB inhibitor showed no effect on JNK/ERK. IL-8 was augmented by heat-treatment or CFTR-knockdown, which was abolished by inhibition of NF-κB, JNK/ERK or COX-2. Moreover, in vitro or in vivo treatment with curcumin, a natural phenolic compound, significantly enhanced CFTR expression and reversed the heat-induced increases in COX-2/PGE2/IL-8, neutrophil infiltration and tissue damage in the airway. These results have revealed a CFTR-regulated MAPK/NF-κB pathway leading to COX-2/PGE2/IL-8 activation in thermal inhalation injury, and demonstrated therapeutic potential of curcumin for alleviating heat-induced pulmonary inflammation.

Short-chain fatty acids affect cystic fibrosis airway inflammation and bacterial growth

The hypoxic environment of cystic fibrosis airways allows the persistence of facultative anaerobic bacteria, which can produce short-chain fatty acids (SCFAs) through fermentation. However, the relevance of SCFAs in cystic fibrosis lung disease is unknown. We show that SCFAs are present in sputum samples from cystic fibrosis patients in millimolar concentrations (mean±sem1.99±0.36 mM).

SCFAs positively correlated with sputum neutrophil count and higher SCFAs were predictive for impaired nitric oxide production. We studied the effects of the SCFAs acetate, propionate and butyrate on airway inflammatory responses using epithelial cell lines and primary cell cultures. SCFAs in concentrations present in cystic fibrosis airways (0.5–2.5 mM) affected the release of granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor and interleukin (IL)-6. SCFAs also resulted in higher IL-8 release from stimulated cystic fibrosis transmembrane conductance regulator (CFTR) F508del-mutant compared to wild-type CFTR-corrected bronchial epithelial cells. At 25 mM propionate reduced IL-8 release in control but not primary cystic fibrosis epithelial cells. Low (0.5–2.5 mM) SCFA concentrations increased, while high (25–50 mM) concentrations decreased inducible nitric oxide synthase expression. In addition, SCFAs affected the growth ofPseudomonas aeruginosain a concentration- and pH-dependent manner.

Thus, our data suggest that SCFAs contribute to cystic fibrosis-specific alterations of responses to airway infection and inflammation.

Phenylbutyrate induces cathelicidin expression via the vitamin D receptor: Linkage to inflammatory and growth factor cytokines pathways

Antimicrobial peptides (AMPs) constitute an indispensable arm of innate immunity against infectious microbes in humans. Induction of endogenous AMPs may become an alternative therapy against infections. Our previous studies have demonstrated phenylbutyrate (PBA) as a novel inducer of the AMPs cathelicidin (encoded by the CAMP gene) and human beta-defensin-1 in the human bronchial epithelial cell line VA10. In this work, we have continued by studying molecular mechanisms of PBA mediated induction of LL-37 expression and associated pathways in the human bronchial epithelial cell line VA10. In this study we demonstrate vitamin D receptor (VDR) as a key transcription factor required for PBA mediated up-regulation of the CAMP gene expression. PBA also increases mRNA expression of the vitamin D3 regulated genes CYP24A1 and CD14. The siRNA knockdown of VDR reduced PBA mediated increase in CAMP, CYP24A1 and CD14 expression. Furthermore, we demonstrate that PBA enhances Toll-Like Receptor 5 ligand flagellin regulated mRNA expression of the inflammatory cytokine TNFα and chemokine CXCL8. PBA also up-regulates the expression of the genes encoding the growth factor cytokines transforming growth factor (TGF) α, TGFβ1 and TGFβ2. Our results indicate that TGFβ type I receptor and epidermal growth factor receptor are involved in PBA mediated CAMP regulation. Finally, we show that co-treatment with PBA and vitamin D3 reduces Pseudomonas aeruginosa growth in vitro.

Selective, potent blockade of the IRE1 and ATF6 pathways by 4-phenylbutyric acid analogues

BACKGROUND AND PURPOSE

4-Phenylbutyric acid (4-PBA) is a chemical chaperone that eliminates the accumulation of unfolded proteins in the endoplasmic reticulum (ER). However, its chaperoning ability is often weak and unable to attenuate the unfolded protein response (UPR) in vitro or in vivo. To develop more potent chemical chaperones, we synthesized six analogues of 4-PBA and evaluated their pharmacological actions on the UPR.

EXPERIMENTAL APPROACH

NRK-52E cells were treated with ER stress inducers (tunicamycin or thapsigargin) in the presence of each of the 4-PBA analogues; the suppressive effects of these analogues on the UPR were assessed using selective indicators for individual UPR pathways.

KEY RESULTS

2-POAA-OMe, 2-POAA-NO2 and 2-NOAA, but not others, suppressed the induction of ER stress markers GRP78 and CHOP. This suppressive effect was more potent than that of 4-PBA. Of the three major UPR branches, the IRE1 and ATF6 pathways were markedly blocked by these compounds, as indicated by suppression of XBP1 splicing, inhibition of UPRE and ERSE activation, and inhibition of JNK phosphorylation. Unexpectedly, however, these agents did not inhibit phosphorylation of PERK and eIF2α triggered by ER stress. These compounds dose-dependently inhibited the early activation of NF-κB in ER stress-exposed cells. 2-POAA-OMe and 2-POAA-NO2 also inhibited ER stress-induced phosphorylation of Akt.

CONCLUSION AND IMPLICATIONS

The 4-PBA analogues 2-POAA-OMe, 2-POAA-NO2 and 2-NOAA strongly inhibited activation of the IRE1 and ATF6 pathways and downstream pathogenic targets, including NF-κB and Akt, in ER stress-exposed cells. These compounds may be useful for therapeutic intervention in ER stress-related pathological conditions.

Abnormal trafficking of endogenously expressed BMPR2 mutant allelic products in patients with heritable pulmonary arterial hypertension

More than 200 heterozygous mutations in the type 2 BMP receptor gene, BMPR2, have been identified in patients with Heritable Pulmonary Arterial Hypertension (HPAH). More severe clinical outcomes occur in patients with BMPR2 mutations by-passing nonsense-mediated mRNA decay (NMD negative mutations). These comprise 40% of HPAH mutations and are predicted to express BMPR2 mutant products. However expression of endogenous NMD negative BMPR2 mutant products and their effect on protein trafficking and signaling function have never been described. Here, we characterize the expression and trafficking of an HPAH-associated NMD negative BMPR2 mutation that results in an in-frame deletion of BMPR2 EXON2 (BMPR2ΔEx2) in HPAH patient-derived lymphocytes and in pulmonary endothelial cells (PECs) from mice carrying the same in-frame deletion of Exon 2 (Bmpr2 (ΔEx2/+) mice). The endogenous BMPR2ΔEx2 mutant product does not reach the cell surface and is retained in the endoplasmic reticulum. Moreover, chemical chaperones 4-PBA and TUDCA partially restore cell surface expression of Bmpr2ΔEx2 in PECs, suggesting that the mutant product is mis-folded. We also show that PECs from Bmpr2 (ΔEx2/+) mice have defects in the BMP-induced Smad1/5/8 and Id1 signaling axis, and that addition of chemical chaperones restores expression of the Smad1/5/8 target Id1. These data indicate that the endogenous NMD negative BMPRΔEx2 mutant product is expressed but has a folding defect resulting in ER retention. Partial correction of this folding defect and restoration of defective BMP signaling using chemical chaperones suggests that protein-folding agents could be used therapeutically in patients with these NMD negative BMPR2 mutations.

4-Phenylbutyric acid reduces endoplasmic reticulum stress, trypsin activation, and acinar cell apoptosis while increasing secretion in rat pancreatic acini

OBJECTIVES

Endoplasmic reticulum (ER) stress leads to misfolded proteins inside the ER and initiates unfolded protein response (UPR). Unfolded protein response components are involved in pancreatic function and activated during pancreatitis. However, the exact role of ER stress in the exocrine pancreas is unclear. The present study examined the effects of 4-phenylbutyric acid (4-PBA), an ER chaperone, on acini and UPR components.

METHODS

Rat acini were stimulated with cholecystokinin (10 pmol/L to 10 nmol/L) with or without preincubation of 4-PBA. The UPR components were analyzed, including chaperone-binding protein, protein kinaselike ER kinase, X-box-binding protein 1, c-Jun NH(2)-terminal kinase, CCAAT/enhancer-binding protein homologous protein, caspase 3, and apoptosis. Effects of 4-PBA were measured on secretion, calcium, and trypsin activation.

RESULTS

4-Phenylbutyric acid led to an increase of secretion, whereas trypsin activation with supraphysiological cholecystokinin was significantly reduced. 4-Phenylbutyric acid prevented chaperone-binding protein up-regulation, diminished protein kinaselike ER kinase, and c-Jun NH2-terminal kinase phosphorylation, prohibited X-box-binding protein 1 splicing and CCAAT/enhancer-binding protein homologous protein expression, caspase 3 activation, and apoptosis caused by supraphysiological cholecystokinin.

CONCLUSION

By incubation with 4-PBA, beneficial in urea cycle deficiency, it was possible to enhance enzyme secretion to suppress trypsin activation, UPR activation, and proapoptotic pathways. The data hint new perspectives for the use of chemical chaperones in pancreatic diseases.

Cystic fibrosis: insight into CFTR pathophysiology and pharmacotherapy

Cystic fibrosis is the most common life-threatening recessively inherited disease in Caucasians. Due to early provision of care in specialized reference centers and more comprehensive care, survival has improved over time. Despite great advances in supportive care and in our understanding of its pathophysiology, there is still no cure for the disease. Therapeutic strategies aimed at rescuing the abnormal protein are either being sought after or under investigation. This review highlights salient insights into pathophysiology and candidate molecules suitable for CFTR pharmacotherapy. Clinical trials using Ataluren, VX-809 and ivacaftor have provided encouraging data. Preclinical data with inhibitors of phosphodiesterase type 5, such as sildenafil and analogs, have highlighted their potential for CFTR pharmacotherapy. Because sildenafil and analogs are in clinical use for other clinical applications, research on this class of drugs might speed up the development of new therapies for CF.

Glucocorticoids reduce inflammation in cystic fibrosis bronchial epithelial cells

Reduction of lung inflammation is one of the goals of cystic fibrosis (CF) therapy. Among anti-inflammatory molecules, glucocorticoids (GC) are one of the most prescribed. However, CF patients seem to be resistant to glucocorticoid treatment. Several molecular mechanisms that contribute to decrease anti-inflammatory effects of glucocorticoids have been identified in pulmonary diseases, but the molecular actions of glucocorticoids have never been studied in CF. In the cytoplasm, glucocorticoids bind to glucocorticoid receptor (GR) and then, control NF-κB and MAPK pathways through direct interaction with AP-1 and NF-κB in the nucleus. Conversely, MAPK can regulate glucocorticoid activation by targeting GR phosphorylation. Together these pathways regulate IL-8 release in the lung. Using bronchial epithelial cell lines derived from non CF and CF patients, we analyzed GR-based effects of glucocorticoids on NF-κB and MAPK pathways, after stimulation with TNF-α. We demonstrate that the synthetic glucocorticoid dexamethasone (Dex) significantly decreases IL-8 secretion, AP-1 and NF-κB activity in CF cells in a pro-inflammatory context. Moreover, we show that p38 MAPK controls IL-8 release by determining GR activation through specific phosphorylation on serine 211. Finally, we demonstrate a synergistic effect of dexamethasone treatment and inhibition of p38 MAPK inducing more than 90% inhibition of IL-8 production in CF cells. All together, these results demonstrate the good responsiveness to glucocorticoids of CF bronchial epithelial cells and the reciprocal link between glucocorticoids and p38 MAPK in the control of CF lung inflammation.

4-phenylbutyric Acid Regulates Collagen Synthesis and Secretion Induced by High Concentrations of Glucose in Human Gingival Fibroblasts

High glucose leads to physio/pathological alterations in diabetes patients. We investigated collagen production in human gingival cells that were cultured in high concentrations of glucose. Collagen synthesis and secretion were increased when the cells were exposed to high concentrations of glucose. We examined endoplasmic reticulum (ER) stress response because glucose metabolism is related to ER functional status. An ER stress response including the expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), inositol requiring enzyme alpha (IRE-1α) and phosphoreukaryotic initiation factor alpha (p-eIF-2α) was activated in the presence of high glucose. Activating transcription factor 4 (ATF-4), a downstream protein of p-eIF-2α as well as a transcription factor for collagen, was also phosphorylated and translocalized into the nucleus. The chemical chaperone 4-PBA inhibited the ER stress response and ATF-4 phosphorylation as well as nuclear translocation. Our results suggest that high concentrations of glucose-induced collagen are linked to ER stress and the associated phosphorylation and nuclear translocation of ATF-4.

MAPK signaling pathways regulate IL-8 mRNA stability and IL-8 protein expression in cystic fibrosis lung epithelial cell lines

Cystic fibrosis (CF) is characterized by a massive proinflammatory phenotype in the lung, caused by mutations in the CFTR gene. IL-8 and other proinflammatory mediators are elevated in the CF airway, and the immediate mechanism may depend on disease-specific stabilization of IL-8 mRNA in CF lung epithelial cells. MAPK signaling pathways impact directly on IL-8 protein expression in CF cells, and we have hypothesized that the mechanism may also involve stabilization of the IL-8 mRNA. To test this hypothesis, we have examined the effects of pharmacological and molecular inhibitors of p38, and downstream MK2, ERK1/2, and JNK, on stability of IL-8 mRNA in CF lung epithelial cells. We previously showed that tristetraprolin (TTP) was constitutively low in CF and that raising TTP destabilized the IL-8 mRNA. We therefore also tested these effects on CF lung epithelial cells stably expressing TTP. TTP binds to AU-rich elements in the 3'-UTR of the IL-8 mRNA. We find that inhibition of p38 and ERK1/2 reduces the stability of IL-8 mRNA in parental CF cells. However, neither intervention further lowers TTP-dependent destabilization of IL-8 mRNA. By contrast, inhibition of the JNK-2 pathway has no effect on IL-8 mRNA stability in parental CF cell, but rather increases the stability of the message in cells expressing high levels of TTP. However, we find that inhibition of ERK1/2 or p38 leads to suppression of the effect of JNK-2 inhibition on IL-8 mRNA stability. These data thus lend support to our hypothesis that constitutive MAPK signaling and proteasomal activity might also contribute, along with aberrantly lower TTP, to the proinflammatory phenotype in CF lung epithelial cells by increasing IL-8 mRNA stability and IL-8 protein expression.

Endoplasmic reticulum stress induced by surfactant protein C BRICHOS mutants promotes proinflammatory signaling by epithelial cells

Chronic interstitial lung disease in both adults and children is associated with mutations of the surfactant protein C (SP-C) proprotein. Among these, mutations within the distal COOH propeptide, known as the BRICHOS domain, are associated with a severe disease phenotype. We showed that prolonged expression of the BRICHOS mutants, SP-C(Δexon4) and SP-C(L188Q), destabilizes endoplasmic reticulum (ER) quality-control mechanisms (the unfolded protein response, or UPR), resulting in the induction of ER stress signaling, an inhibition of the ubiquitin/proteasome system, and the activation of apoptotic pathways. Based on recent observations that the UPR and ER stress can be linked to the induction of proinflammatory signaling, we hypothesized that the epithelial cell dysfunction mediated by SP-C BRICHOS mutants would activate proinflammatory signaling pathways. In a test of this hypothesis, A549 and human embryonic kidney epithelial (HEK293) cells, transiently transfected with either SP-C(Δexon4) or SP-C(L188Q) mutants, each promoted the upregulation of multiple UPR response genes, including homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member 1 (HERPUD1) and GRP78. Commensurate with these results, increases in IL-8 secretion occurred and were accompanied by the activation of c-Jun N-terminal kinase (JNK)/activating protein-1 signaling. The stimulation of IL-8 cytokine release was completely attenuated by treatment with the JNK-specific inhibitor, SP600125. In addition, SP-C(Δexon4), but not SP-C(L188Q), activated NFκB. The treatment of SP-C(Δexon4) transfected cells with 4-phenylbutyric acid, a small molecule chaperone known to improve protein folding, blocked the activation of NFκB, but not the release of IL-8. Taken together, the results support the role of JNK signaling in mediating SP-C BRICHOS-induced cytokine release, and provide a link between SP-C BRICHOS mutants and proinflammatory cytokine signaling.