Absence of the Birt-Hogg-Dubé gene product is associated with increased hypoxia-inducible factor transcriptional activity and a loss of metabolic flexibility.

Under conditions of reduced tissue oxygenation, hypoxia-inducible factor (HIF) controls many processes, including angiogenesis and cellular metabolism, and also influences cell proliferation and survival decisions. HIF is centrally involved in tumour growth in inherited diseases that give rise to renal cell carcinoma (RCC), such as Von Hippel-Lindau syndrome and tuberous sclerosis complex. In this study, we examined whether HIF is involved in tumour formation of RCC in Birt-Hogg-Dubé syndrome. For this, we analysed a Birt-Hogg-Dubé patient-derived renal tumour cell line (UOK257) that is devoid of the Birt-Hogg-Dubé protein (BHD) and observed high levels of HIF activity. Knockdown of BHD expression also caused a threefold activation of HIF, which was not as a consequence of more HIF1α or HIF2α protein. Transcription of HIF target genes VEGF, BNIP3 and CCND1 was also increased. We found nuclear localization of HIF1α and increased expression of VEGF, BNIP3 and GLUT1 in a chromophobe carcinoma from a Birt-Hogg-Dubé patient. Our data also reveal that UOK257 cells have high lactate dehydrogenase, pyruvate kinase and 3-hydroxyacyl-CoA dehydrogenase activity. We observed increased expression of pyruvate dehydrogenase kinase 1 (a HIF gene target), which in turn leads to increased phosphorylation and inhibition of pyruvate dehydrogenase. Together with increased protein levels of GLUT1, our data reveal that UOK257 cells favour glycolytic rather than lipid metabolism (a cancer phenomenon termed the 'Warburg effect'). UOK257 cells also possessed a higher expression level of the L-lactate influx monocarboxylate transporter 1 and consequently utilized L-lactate as a metabolic fuel. As a result of their higher dependency on glycolysis, we were able to selectively inhibit the growth of these UOK257 cells by treatment with 2-deoxyglucose. This work suggests that targeting glycolytic metabolism may be used therapeutically to treat Birt-Hogg-Dubé-associated renal lesions.

Control of HIF-1{alpha} and vascular signaling in fetal lung involves cross talk between mTORC1 and the FGF-10/FGFR2b/Spry2 airway branching periodicity clock.

Lung development requires coordinated signaling between airway and vascular growth, but the link between these processes remains unclear. Mammalian target of rapamycin complex-1 (mTORC1) can amplify hypoxia-inducible factor-1α (HIF-1α) vasculogenic activity through an NH(2)-terminal mTOR binding (TOS) motif. We hypothesized that this mechanism coordinates vasculogenesis with the fibroblast growth factor (FGF)-10/FGF-receptor2b/Spry2 regulator of airway branching. First, we tested if the HIF-1α TOS motif participated in epithelial-mesenchymal vascular signaling. mTORC1 activation by insulin significantly amplified HIF-1α activity at fetal Po(2) (23 mmHg) in human bronchial epithelium (16HBE14o-) and induced vascular traits (Flk1, sprouting) in cocultured human embryonic lung mesenchyme (HEL-12469). This enhanced activation of HIF-1α by mTORC1 was abolished on expression of a HIF-1α (F99A) TOS-mutant and also suppressed vascular differentiation of HEL-12469 cocultures. Next, we determined if vasculogenesis in fetal lung involved regulation of mTORC1 by the FGF-10/FGFR2b/Spry2 pathway. Fetal airway epithelium displayed distinct mTORC1 activity in situ, and its hyperactivation by TSC1(-/-) knockout induced widespread VEGF expression and disaggregation of Tie2-positive vascular bundles. FGF-10-coated beads grafted into fetal lung explants from Tie2-LacZ transgenic mice induced localized vascular differentiation in the peripheral mesenchyme. In rat fetal distal lung epithelial (FDLE) cells cultured at fetal Po(2), FGF-10 induced mTORC1 and amplified HIF-1α activity and VEGF secretion without induction of ERK1/2. This was accompanied by the formation of a complex between Spry2, the cCBL ubiquitin ligase, and the mTOR repressor, TSC2, which abolished GTPase activity directed against Rheb, the G protein inducer of mTORC1. Thus, mTORC1 links HIF-1α-driven vasculogenesis with the FGF-10/FGFR2b/Spry2 airway branching periodicity regulator.

Endotoxin-induced nitric oxide production rescues airway growth and maturation in atrophic fetal rat lung explants.

Inflammation induces premature maturation of the fetal lung but the signals causing this effect remain unclear. We determined if nitric oxide (NO) synthesis, evoked by Escherichia coli lipopolysaccharide (LPS, 2 microg ml-1), participated in this process. Fetal rat lung airway surface complexity rose 2.5-fold over 96h in response to LPS and was associated with increased iNOS protein expression and activity. iNOS inhibition by N6-(1-iminoethyl)-L-lysine-2HCl (L-NIL) abolished this and induced airway atrophy similar to untreated explants. Surfactant protein-C (SP-C) expression was also induced by LPS and abolished by L-NIL. As TGFbeta suppresses iNOS activity, we determined if feedback regulation modulated NO-dependent maturation. LPS induced TGFbeta1 release and SMAD4 nuclear translocation 96 h after treatment. Treatment of explants with a blocking antibody against TGFbeta1 sustained NO production and airway morphogenesis whereas recombinant TGFbeta1 antagonized these effects. Feedback regulation of NO synthesis by TGFbeta may, thus, modulate airway branching and maturation of the fetal lung.

iNOS initiates and sustains metabolic arrest in hypoxic lung adenocarcinoma cells: mechanism of cell survival in solid tumor core.

Nitric oxide (NO) modulates cellular metabolism by competitively inhibiting the reduction of O2 at respiratory complex IV. The aim of this study was to determine whether this effect could enhance cell survival in the hypoxic solid tumor core by inducing a state of metabolic arrest in cancer cells. Mitochondria from human alveolar type II-like adenocarcinoma (A549) cells showed a fourfold increase in NO-sensitive 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM) fluorescence and sixfold increase in Ca2+-insensitive NO synthase (NOS) activity during equilibration from Po2s of 100-->23 mmHg, which was abolished by N(omega)-nitro-L-arginine methyl ester-HCl (L-NAME) and the inducible NOS (iNOS) inhibitor, N6-(1-iminoethyl)-L-lysine dihydrochloride (L-NIL). Similarly, cytosolic and compartmented DAF-FM fluorescence increased in intact cells during a transition between ambient Po2 and 23 mmHg and was abolished by transfection with iNOS antisense oligonucleotides (AS-ODN). In parallel, mitochondrial membrane potential (deltapsi(m)), measured using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolo-carbocyanine iodide (JC-1), decreased to a lower steady state in hypoxia without change in glycolytic rate, adenylate energy charge, or cell viability. However, L-NAME or iNOS AS-ODN treatment maintained deltapsi(m) at normoxic levels irrespective of hypoxia and caused a marked activation of glycolysis, destabilization energy charge, and cell death. Comparison with other cancer-derived (H441) or native tissue-derived (human bronchial epithelial; alveolar type II) lung epithelial cells revealed that the hypoxic suppression of deltapsi(m) was common to cells that expressed iNOS. The controlled dissipation of deltapsi(m), absence of an overt glycolytic activation, and conservation of viability suggest that A549 cells enter a state of metabolic suppression in hypoxia, which inherently depends on the activation of iNOS as Po2 falls.

A regulated apical Na(+) conductance in dexamethasone-treated H441 airway epithelial cells.

Treating H441 cells with dexamethasone raised the abundance of mRNA encoding the epithelial Na(+) channel alpha- and beta-subunits and increased transepithelial ion transport (measured as short-circuit current, I(sc)) from <4 microA.cm(-2) to 10-20 microA.cm(-2). This dexamethasone-stimulated ion transport was blocked by amiloride analogs with a rank order of potency of benzamil >or= amiloride > EIPA and can thus be attributed to active Na(+) absorption. Studies of apically permeabilized cells showed that this increased transport activity did not reflect a rise in Na(+) pump capacity, whereas studies of basolateral permeabilized cells demonstrated that dexamethasone increased apical Na(+) conductance (G(Na)) from a negligible value to 100-200 microS.cm(-2). Experiments that explored the ionic selectivity of this dexamethasone-induced conductance showed that it was equally permeable to Na(+) and Li(+) and that the permeability to these cations was approximately fourfold greater than to K(+). There was also a small permeability to N-methyl-d-glucammonium, a nominally impermeant cation. Forskolin, an agent that increases cellular cAMP content, caused an approximately 60% increase in I(sc), and measurements made after these cells had been basolaterally permeabilized demonstrated that this response was associated with a rise in G(Na). This cAMP-dependent control over G(Na) was disrupted by brefeldin A, an inhibitor of vesicular trafficking. Dexamethasone thus stimulates Na(+) transport in H441 cells by evoking expression of an amiloride-sensitive apical conductance that displays moderate ionic selectivity and is subject to acute control via a cAMP-dependent pathway.

Redox/ROS regulation of lipopolysaccharide-induced mitogen-activated protein kinase (MAPK) activation and MAPK-mediated TNF-alpha biosynthesis.

Redox and ROS regulation of MAPK-mediated TNF-alpha biosynthesis is not well characterized. It was hypothesized that the involvement of the MAPK pathway in regulating LPS-mediated TNF-alpha secretion is redox-dependent, NF-kappaB-sensitive and attenuated by N-acetyl-L-cysteine (NAC) and other antioxidants. In alveolar epithelial cells, LPS induced a time- and dose-dependent phosphorylation of MAPK(p38). This was associated with the activation of MAPK-activated protein kinase, which phosphorylated the small heat-shock protein, Hsp27. MAPK(p38) inhibition (SB-203580) abrogated LPS-induced TNF-alpha production. MAPK(ERK) blockade (PD-98059) attenuated TNF-alpha secretion, an effect synergistically amplified in the presence of SB-203580. Regulation of NF-kappaB by selective inhibitors revealed that this pathway is partially involved in regulating LPS-mediated TNF-alpha secretion. Whereas the proteasome inhibitor, MG-132, had no effect on LPS-mediated TNF-alpha production, CAPE, sulfasalazine and SN-50, a cell-permeant NF-kappaB inhibitor, attenuated but did not abrogate TNF-alpha biosynthesis. LPS up-regulated ROS, an effect abrogated by 4'-hydroxy-3'-methoxy-acetophenone and NAC, which reduced TNF-alpha secretion, induced the accumulation of GSH, reduced the concentration of GSSG, and blockaded the phosphorylation/activation of MAPK(p38) pathway. ROS induced MAPK(p38) phosphorylation and selective antioxidants, including the permeant GSH precursor, gamma-GCE, reduced ROS-dependent MAPK(p38) phosphorylation. These results indicate that the MAPK pathway and MAPK-mediated regulation of TNF-alpha production is redox-dependent, GSH-mediated and requires, at least in part, a NF-kappaB/ROS-sensitive mechanism.

A non-hypoxic, ROS-sensitive pathway mediates TNF-alpha-dependent regulation of HIF-1alpha.

A non-hypoxic, reactive oxygen species (ROS)-sensitive pathway mediating tumor necrosis factor-alpha (TNF-alpha)-dependent regulation of hypoxia-inducible factor-1alpha (HIF-alpha) was investigated in vitro. TNF-alpha mediated the translocation of HIF-1alpha, associated with up-regulating its activity under normoxia. Analysis of the mode of action of TNF-alpha revealed the accumulation of hydrogen peroxide (H2O2), superoxide anion (O(2-.)) and hydroxyl radical (.OH). Antioxidants purported as prototypical scavengers of H2O2 and .OH, attenuated TNF-alpha-induced HIF-1alpha activation, and blockading NADPH-oxidase by scavenging O(2-.) reduced the activity of HIF-1alpha. Inhibition of the mitochondrion complex I abrogated TNF-alpha-dependent activation of HIF-1alpha. Interrupting the respiratory chain reversed the excitatory effect of TNF-alpha on HIF-1alpha. These results indicate a non-hypoxic pathway mediating cytokine-dependent regulation of HIF-1alpha in a ROS-sensitive mechanism.

Hypoxic activation of an amiloride-sensitive cation conductance in alveolar epithelial cells.

Imposing hypoxia (P(O(2)) = 23 mmHg) upon A549 cells elicited increased G(amil) although previous work had predicted a fall in this parameter. G(amil) appeared to be dependent upon glucocorticoid-driven gene expression, a process inhibited by ERK, an enzyme activated by oxidative stress. However, hypoxia transiently activated this enzyme and the response was blocked by glucocorticoids, showing that the rise in G(amil) occurs only if ERK activation is suppressed. Fluorimetric assays showed that lowering P(O(2)) elicited H(2)O(2) formation indicating that this maneuver actually imposes oxidative stress, thus explaining how hypoxia can elicit responses normally associated with a rise in P(O(2)).

Nuclear factor-kappab blockade attenuates but does not abrogate lipopolysaccharide-dependent tumor necrosis factor-alpha biosynthesis in alveolar epithelial cells.

We have investigated the role that the nuclear factor (NF)-kappaB plays in regulating the biosynthesis of tumor necrosis factor (TNF)-alpha, an inflammatory cytokine. Irreversible inhibition of the proteasome complex by carbobenzoxy-l-leucyl-l-leucyl-l-leucinal (MG-132; 1-50 microM) had no inhibitory effect on LPS-mediated TNF-alpha biosynthesis. Furthermore, selective inhibition of NF-kappaB by the action of caffeic acid phenylethyl ester (CAPE; 1-100 microM) and sulfasalazine (SSA; 0.1-10 mM), a potent and irreversible inhibitor of NF-kappaB, partially attenuated, but did not abolish, LPS-dependent TNF-alpha secretion. Incorporation of a selectively permeant inhibitor of NF-kappaB, SN-50 (1-20 microM), a peptide which contains the nuclear localization sequence (NLS) for the p50 NF-kappaB subunit, and the amino-terminal sequence of Kaposi fibroblast growth factor to promote cell permeability, attenuated in a dose-dependent manner LPS-mediated release of TNF-alpha. It is concluded that the NF-kappaB pathway is partially implicated and that its blockade attenuates, but does not abrogate, LPS-dependent TNF-alpha biosynthesis in alveolar epithelial cells.

Oxygen-evoked Na+ transport in rat fetal distal lung epithelial cells.

Monolayer cultures of rat fetal distal lung epithelial (FDLE) cells generated larger spontaneous short circuit currents (ISC) when maintained (48 h) at neonatal alveolar PO2 (100 mmHg) than at fetal PO2 (23 mmHg). When cells were shifted between these atmospheres in order to impose a rise in PO2 equivalent to that seen at birth, no rise in ISC was seen after 6 h but the response was fully established by 24 h. Studies of basolaterally permeabilised cells revealed a small rise in apical Na+ conductance (GNa) 6 h after PO2 was raised but no further change had occurred by 24 h. A substantial rise was, however, seen after 48 h. Reporter gene assays showed that no activation of the -ENaC (epithelial Na+ channel -subunit) promoter was discernible 24 h after PO2 was raised but increased transcriptional activity was seen at 48 h. Studies of apically permeabilised cells showed that a small rise in Na+ pump capacity was evident 6 h after PO2 was raised and, in common with the rise in ISC, this effect was fully established by 24 h. The rise in ISC thus develops 6-24 h after PO2 is raised and is due, primarily, to increased Na+ pump capacity. The increase in GNa thus coincides with activation of the -ENaC promoter but these effects occur after the rise in ISC is fully established and so cannot underlie this physiological response. The increased transcription may be an adaptation to increased Na+ transport and not its cause.

The biphasic immunoregulation of pyrimidylpiperazine (Y-40138) is IL-10 sensitive and requires NF-kappa B targeting in the alveolar epithelium.

1. Pyrimidylpiperazine (Y-40138), a synthetic derivative of N-[1-(4-([4-(pyrimidin-2-yl)piperazin-1-yl]methyl)phenyl)cyclopropyl] acetamide, is a novel dual regulator of pro- and anti-inflammatory cytokines in vivo. The aim of the present study was to determine the signal transduction mechanisms implicated in vitro. 2. In alveolar epithelial cells, pre-treatment (30 min) with Y-40138 reduced LPS-induced biosynthesis of IL-1 beta, IL-6 and TNF-alpha, an effect paralleled by up-regulating an anti-inflammatory counter-loop mediated through IL-10. 3. This differential regulation of pro- and anti-inflammatory signals was accompanied by an inhibition of the nuclear localization of selective NF-kappa B subunits, particularly NF-kappa B(1) (p50), RelA (p65), the major transactivating member of the Rel family, RelB (p68) and c-Rel (p75). In addition, Y-40138 blockaded, in a dose-dependent manner, the LPS-induced nuclear activation of NF-kappa B. 4. Analysis of the upstream pathway involved in Y-40138-dependent retardation of LPS-induced NF-kappa B translocation/activation revealed the involvement of an I kappa B-alpha sensitive pathway. Pre-treatment with Y-40138 ameliorated LPS-induced degradation of I kappa B-alpha in the cytosolic compartment and retarded its phosphorylation, suggesting the involvement of an upstream kinase. 5. Recombinant IL-10 (0 -- 10 ng ml(-1)) blockaded, in a dose-dependent manner, LPS-induced biosynthesis of IL-1 beta, IL-6 and TNF-alpha. Furthermore, rhIL-10 reduced the DNA binding activity of NF-kappa B. Immunoneutralization of endogenous IL-10 by a polyclonal alpha IL-10 (5 microg ml(-1)) reversed the inhibitory effect of Y-40138 on pro-inflammatory cytokines and partially restored the DNA binding activity of NF-kappa B. 6. These results indicate that Y-40138 mediated dual immunoregulation of pro- and anti-inflammatory cytokines is IL-10 sensitive and mediated through the I kappa B-alpha/NF-kappa B signal transduction pathway.

Alpha-melanocyte-related tripeptide, Lys-d-Pro-Val, ameliorates endotoxin-induced nuclear factor kappaB translocation and activation: evidence for involvement of an interleukin-1beta193-195 receptor antagonism in the alveolar epithelium.

The potential anti-inflammatory role of alpha-melanocyte-stimulating hormone (alpha-MSH)-related tripeptide, lysine(11)-D-proline-valine(13) (KDPV), an analogue of interleukin (IL)-1beta(193-195) and an antagonist of IL-1beta/prostaglandin E(2), is not well characterized in the alveolar epithelium. In a model of foetal alveolar type II epithelial cells in vitro, we showed that lipopolysaccharide endotoxin (LPS) differentially, but selectively, induced the nuclear subunit composition of nuclear factor kappaB(1) (NF-kappaB(1)) (p50), RelA (p65) and c-Rel (p75), in parallel to up-regulating the DNA-binding activity (supershift indicating the presence of the p50-p65 complex). LPS accelerated the degradation of inhibitory kappaB-alpha (IkappaB-alpha), accompanied by enhancing its phosphorylation in the cytosolic compartment but not in the nucleus. KDPV suppressed, in a dose-dependent manner, the nuclear localization of p50, p65 and p75, an effect that led to the subsequent inhibition of NF-kappaB activation. Interleukin-1 receptor antagonist (IL-1ra) decreased the nuclear abundance of p50, p65 and p75, and subsequently depressed the DNA-binding activity induced by LPS. Analysis of the mechanism involved in the KDPV- and IL-1ra-mediated inhibition of NF-kappaB nuclear localization revealed a reversal in IkappaB-alpha phosphorylation and degradation, followed by cytosolic accumulation. LPS induced endogenous IL-1beta biosynthesis in a time-dependent manner; the administration of exogenous recombinant human interleukin 1 (rhIL-1) resulted in a dose-dependent activation of NF-kappaB. KDPV and IL-1ra abrogated the effect of rhIL-1. Pretreatment with the non-steroidal anti-inflammatory drug (NSAID) indomethacin, an inhibitor of cyclo-oxygenase, blocked the LPS-induced activation of NF-kappaB. These results indicate the involvement of prostanoid-dependent (NSAID-sensitive) and IL-1-dependent (IL-1ra-sensitive) mechanisms mediating LPS-induced NF-kappaB translocation and activation, a pathway that is regulated, in part, by a negative feedback mechanism transduced through IkappaB-alpha, the major cytosolic inhibitor of NF-kappaB.

NF-kappaB blockade reduces the O2-evoked rise in Na+ conductance in fetal alveolar cells.

Electrophoretic mobility shift assays revealed minimal levels of NF-kappaB activity in rat distal lung epithelial cells cultured at fetal (23 mmHg) or adult alveolar (100 mmHg) P(O2), but revealed significant activation of this transcription factor in cells exposed to a rise in P(O2) mimicking that experienced at birth. This response was entirely abolished by pretreating cells with 5 mM sulfasalazine (SSA). This shift in P(O2) also evoked a rise in apical Na+ conductance (G(Na+)) that may underlie the O2-evoked stimulation of Na+ transport seen in these cells. Pretreatment with SSA had no effect upon G(Na+) in cells cultured continually at adult or fetal P(O2) but did inhibit the increase in G(Na+) seen in cells that had experienced the rise in P(O2). O2-evoked activation of NF-kappaB may thus mediate the increased Na+ transport that occurs when the distal lung epithelial cells are exposed to a physiologically-relevant increase in P(O2).

Chemioxyexcitation (delta pO2/ROS)-dependent release of IL-1 beta, IL-6 and TNF-alpha: evidence of cytokines as oxygen-sensitive mediators in the alveolar epithelium.

The signalling mechanisms in oxidative stress mediated by cytokines in the perinatal alveolar epithelium are not well known. In an in vitro model of fetal alveolar type II epithelial cells, we investigated the profile of cytokines in response to ascending Deltap O(2)regimen (oxyexcitation). The peak of TNF-alpha (4 h) preceded IL-1beta and IL-6 (6-9 h), indicating a positive feedback autocrine loop confirmed by exogenous rmTNF-alpha. Reactive oxygen species (ROS) induced a dose-dependent release of cytokines, an effect specifically obliterated by selective antioxidants of the hydroxyl radical (*OH) and superoxide anion (O(2)-). Actinomycin and cycloheximide blocked the induced production of cytokines, implicating transcriptional and translational control. Whilst the dismutating enzymes superoxide dismutase (SOD) and catalase were ineffective in reducing ROS-induced cytokines, MnP, a cell-permeating SOD mimetic, abrogated xanthine/xanthine oxidase-dependent cytokine release. Desferrioxamine mesylate, which inhibits the iron-catalysed generation of *OH via the Fenton reaction, exhibited a mild effect on the release of cytokines. Dynamic variation in alveolar p O(2)constitutes a potential signalling mechanism within the perinatal lung allowing upregulation of cytokines in an ROS-dependent manner.

Thiol regulation of pro-inflammatory cytokines reveals a novel immunopharmacological potential of glutathione in the alveolar epithelium.

The therapeutic immunopharmacological potential of glutathione in the alveolar epithelium is not well characterized. We developed an in vitro model of fetal alveolar type II epithelial cells to investigate the effect of redox disequilibrium on chemioxyexcitation (DeltapO(2)/ROS) induced up-regulation of pro-inflammatory cytokines. Buthionine sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in glutathione (GSH) biosynthesis, induced intracellular reactive oxygen species (ROS) and the release of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha. Chloroethyl nitrosourea, which blocks the NADPH-dependent recycling of oxidized glutathione (GSSG), reduced ROS-induced cytokine production, similar to pyrrolidine dithiocarbamate, an antioxidant/pro-oxidant thiuram, which elevates GSSG. The antioxidant and GSH precursor, acetylcysteine, abrogated cytokine release concomitant with suppression of ROS, an effect mimicked by gamma-glutamylcysteinyl-ethyl ester, a cell permeant GSH. Cysteine, the rate-limiting amino acid in the de novo synthesis of GSH, administered as oxothiazolidine carboxylate and adenosylmethionine, mitigated the chemioxyexcitation-dependent cytokine release. Ebselen, an anti-inflammatory antioxidant, which mimics the effect of glutathione peroxidase, neutralized ROS by the GSH-peroxidase-coupled reaction, thereby blocking the pathway to cytokine enhancement. Our results indicate that modulating redox equilibrium by pharmacological thiols exhibits differential regulation on pro-inflammatory cytokines, thus bearing clinical consequences for the therapeutic treatment of pediatric distresses in pathophysiology.

The ex vivo differential expression of apoptosis signaling cofactors in the developing perinatal lung: essential role of oxygenation during the transition from placental to pulmonary-based respiration.

The signaling pathways implicated in regulating apoptosisin the perinatal developing lung are not well characterized. We have previously shown that apoptosis signaling cofactors in the fetal alveolar epithelium are redox-sensitive and differentially expressed in response to oxyexcitation (Haddad and Land, Biochem. Biophys. Res. Commun. 271, 257-267, 2000). In this report we investigated the role of oxygenation during the transition period from placental to pulmonary-based respiration in regulating the differential expression of apoptosis cofactors ex vivo. The antiapoptotic proto-oncogene, Bcl-2, exhibited suppressed abundance commencing after birth, an effect which was partially restored at a later stage of development. Oxygenation-mediated down-regulation of Bcl-2 was accompanied by suppression of Bax, such that Bcl-2/Bax equilibrium ratio remained steadily constant postnatally. Analysis of whether a Bax-independent pathway is involved in cell death in the perinatal lung revealed a novel role for p53, whose abundance predominated that of Bcl-2 and Bax at different stages of gestational development. We conclude that apoptosis ex vivo is partly Bax-insensitive and mediated by suppression of Bcl-2 in a p53-dependent mechanism.

Detection of Cl- flux in the apical microenvironment of cultured foetal distal lung epithelial cells.

A self-referencing Cl--selective microelectrode (Cl- SrE) was developed and used to detect changes in the direction and magnitude of the Cl- flux (J(Cl)) from the apical region of cultured foetal distal lung epithelial cells (FDLEs) as a function of external Cl- concentration ([Cl-]e) and in response to pharmacological challenges. The technique, which is similar to that developed for other ion-selective microelectrodes, centres on the oscillation of a Cl--selective microelectrode between known points, micrometres apart, orthogonal to the plasma membrane. Application of the Fick principle to the differential voltage obtained per excursion amplitude (the referenced signal) yields the Cl- flux (pmol x cm(-2) x s(-1)). A Cl- effusion gradient was used to confirm that empirical measurements of J(Cl) using the Cl- SrE were statistically similar to predicted flux values calculated from the fall in [Cl-] with distance from the tip of the effusion source. Apical J(Cl) was then measured as a function of [Cl-]e from polarised FDLE cultures grown on permeable supports. At [Cl-]e<50 mmol x l(-1), an apical-to-basolateral (inward) flux, maximal at 400 pmol x cm(-2 ) x s(-1), was observed; this reverted to a continuous basolateral-to-apical (outward) flux of 203 pmol x cm(-2 ) x s(-1) at [Cl]e>100 mmol x l(-1). At [Cl-]e>100 mmol x l(-1), isoproterenol (basolaterally applied, 10 micromol x l(-1)) activated a Cl- influx of 561 pmol x cm(-2 ) x s(-1), whereas UTP (apically applied, 100 micromol x l(-1)) stimulated a Cl- efflux of 300 pmol x cm(-2) x s(-1). In all cases, 50-70 % of J(Cl) was abolished by Cl- channel blockade using 10 micromol x l(-1) diphenylamine-2-carboxylic acid (DPC) or 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB). We conclude that the Cl- SrE resolves a Cl- gradient in the microenvironment of the apical region of lung epithelia that varies in both direction and magnitude as a function of external [Cl-]e and in response to Cl- channel blockade and to beta2 adrenoreceptor and P2Y receptor agonists.

Immunomodulatory potential of thymulin-Zn(2+) in the alveolar epithelium: amelioration of endotoxin-induced cytokine release and partial amplification of a cytoprotective IL-10-sensitive pathway.

The immunomodulatory potential of thymulin in the perinatal epithelium is not well characterized. In an in vitro model of fetal alveolar type II epithelial cells, we investigated the exhibition of an anti-inflammatory activity of this peptide hormone. Thymulin selectively ameliorated, in a dose-dependent manner, the endotoxin-induced release of IL-1 beta (IC(50) = 657 ng. ml(-1)), but showed no inhibitory effect on IL-6 and TNF-alpha. Zinc, an anti-inflammatory antioxidant, which is required for the biological activity of thymulin, reduced the secretion of IL-1 beta (IC(50) = 62 microM), TNF-alpha (IC(50) = 1000 microM), and, to a lesser extent, IL-6. This cation (100 microM) amplified the effect of thymulin on IL-1 beta and TNF-alpha (IC(50) < 0.1 ng. ml(-1)), but not on IL-6. Analysis of whether thymulin is up-regulating a counterpart anti-inflammatory signaling loop revealed the involvement of an IL-10-sensitive pathway. These results indicate that thymulin acts as a novel dual immunoregulator by enhancing an anti-inflammatory cytoprotective response and depressing an inflammatory signal, an effect synergistically amplified, in part, by cationic zinc.

Antioxidant/pro-oxidant equilibrium regulates HIF-1alpha and NF-kappa B redox sensitivity. Evidence for inhibition by glutathione oxidation in alveolar epithelial cells.

The O(2) and redox-sensitive transcription factors hypoxia inducible factor-1alpha (HIF-1alpha) and nuclear factor-kappaB (NF-kappaB) are differentially regulated in the alveolar epithelium over fetal to neonatal oxygen tensions. We have used fetal alveolar type II epithelial cells to monitor their regulation in association with redox responsiveness to antioxidant pretreatment in vitro. N-Acetyl-l-cysteine, a glutathione (GSH) precursor and a potent scavenger of reactive oxygen species, induced HIF-1alpha and ameliorated NF-kappaB nuclear abundance and DNA binding activity, respectively, in a dose-dependent manner. Analysis of variations in glutathione homeostasis at ascending DeltapO(2) regimen with N-acetyl-(L)-cysteine reveals increased GSH at the expense of the oxidized form of glutathione (GSSG), thereby shifting GSH/GSSG into reduction equilibrium. Pyrrolidine dithiocarbamate (PDTC), which exerts both antioxidant and pro-oxidant effects, provoked a substantial increase in HIF-1alpha nuclear abundance, with no apparent effect on its activation. PDTC reduced NF-kappaB nuclear abundance and its inhibitory effects on binding activity are dose-dependent. Assessment of glutathione homeostasis with PDTC shows increasing levels of GSSG at the expense of GSH, lowering GSH/GSSG in favor of an oxidative equilibrium. Our results indicate the hypoxic activation of HIF-1alpha and the hyperoxic induction of NF-kappaB in the fetal epithelium is redox-sensitive and, thus, tightly regulated by the GSH/GSSG equilibrium. This highlights glutathione as a key regulatory component for determining genetic responsiveness to oxidant/antioxidant imbalance in normal lung development and pathophysiological conditions.

The differential expression of apoptosis factors in the alveolar epithelium is redox sensitive and requires NF-kappaB (RelA)-selective targeting.

Fetal alveolar type II (fATII) epithelial cells were used to evaluate the role of signaling factors involved in oxidative stress-induced programmed cell death (PCD; apoptosis). Bcl-2, an antiapoptotic proto-oncogene, showed maximum abundance in hypoxia and mild reoxygenation, but declined thereafter. The Bcl-2 counterpart, Bax, which promotes PCD, displayed an increasing logarithmic profile with ascending DeltapO(2) regimen, such that the ratio of Bcl-2/Bax decreased as pO(2) increased. The expression of p53, a cell cycle regulator, paralleled Bax abundance. Pretreatment of fATII cells with l-buthionine-(S,R)-sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in the biosynthesis of glutathione (GSH), enhanced Bax and p53 expression over Bcl-2. The GSH analogue, gamma-glutamylcysteinyl-ethyl ester, down-regulated Bax/p53 abundance but restored that of Bcl-2, thereby increasing Bcl-2/Bax. The antioxidant and GSH precursor N-acetyl-l-cysteine favored Bcl-2 at the expense of Bax/p53, whereas pyrrolidine dithiocarbamate induced Bax against Bcl-2, with mild effect on p53. Sulfasalazine, a potent and specific inhibitor of NF-kappaB, induced Bax at the expense of Bcl-2, in a p53-dependent manner. We conclude that the differential expression of signaling factors involved in PCD in the alveolar epithelium is redox-sensitive and mediated, at least in part, by a negative feedback mechanism transduced by NF-kappaB.