Surfactant Biosynthesis Research Articles

Lost after translation: insights from pulmonary surfactant for understanding the role of alveolar epithelial dysfunction and cellular quality control in fibrotic lung disease.

Dating back nearly 35 years ago to the Witschi hypothesis, epithelial cell dysfunction and abnormal wound healing have reemerged as central concepts in the pathophysiology of idiopathic pulmonary fibrosis (IPF) in adults and in interstitial lung disease in children. Alveolar type 2 (AT2) cells represent a metabolically active compartment in the distal air spaces responsible for pulmonary surfactant biosynthesis and function as a progenitor population required for maintenance of alveolar integrity. Rare mutations in surfactant system components have provided new clues to understanding broader questions regarding the role of AT2 cell dysfunction in the pathophysiology of fibrotic lung diseases. Drawing on data generated from a variety of model systems expressing disease-related surfactant component mutations [surfactant proteins A and C (SP-A and SP-C); the lipid transporter ABCA3], this review will examine the concept of epithelial dysfunction in fibrotic lung disease, provide an update on AT2 cell and surfactant biology, summarize cellular responses to mutant surfactant components [including endoplasmic reticulum (ER) stress, mitochondrial dysfunction, and intrinsic apoptosis], and examine quality control pathways (unfolded protein response, the ubiquitin-proteasome system, macroautophagy) that can be utilized to restore AT2 homeostasis. This integrated response and its derangement will be placed in the context of cell stress and quality control signatures found in patients with familial or sporadic IPF as well as non-surfactant-related AT2 cell dysfunction syndromes associated with a fibrotic lung phenotype. Finally, the need for targeted therapeutic strategies for pulmonary fibrosis that address epithelial ER stress, its downstream signaling, and cell quality control are discussed.

Amniotic fluid LPCAT1 mRNA correlates with the lamellar body count.

Lysophosphatidylcholine acyltransferase 1 (LPCAT1) is required in the biosynthesis of pulmonary surfactant. This short communication describes our assessment of LPCAT1 mRNA levels in human amniotic fluid. We found a direct correlation between LPCAT1 mRNA copies and the amniotic fluid lamellar body count (LBC). This finding corroborates an association between LPCAT1 and surfactant phospholipid biosynthesis in humans. It may provide a model for future research in perinatal medicine.

Functional and molecular characterization of a lipopeptide surfactant from the marine sponge-associated eubacteria Bacillus licheniformis NIOT-AMKV06 of Andaman and Nicobar Islands, India

The production of a lipopeptide surfactant from the sponge-associated eubacteria Bacillus licheniformis NIOT-AMKV06 from the Andaman and Nicobar Islands was investigated. The highest production was attained with glucose and yeast extracts as the carbon and nitrogen sources (1.789mgmL−1), respectively. The surfactant was highly stable over a pH range of 5.0–10 and a temperature range of 20–70°C with high NaCl concentrations. Excellent emulsification activity was exhibited by the purified surfactant with crude oil, kerosene, and diesel. A two-fold increase in surfactant production (3.0mgmL−1) was observed using the newly formulated medium in this study. The surfactant biosynthesis gene cluster (sfp, sfpO, and srfA) from B. licheniformis NIOT-AMKV06 was heterologously expressed in Escherichia coli, and the production was increased three-fold (11.78gL−1) over the original strain. The results confirm the potential of the surfactant for use in bioremediation of hydrocarbons in a marine environment and for enhanced oil recovery. To our knowledge, this is the first report on the ability of a hydrocarbon to degrade B. licheniformis from marine sponges for the biosynthesis of a potent lipopeptide surfactant possessing characteristics of maximum stability, outstanding surfactant activity, and exceptional emulsifying capability.

Short-Term Cigarette Smoke Exposure Leads to Metabolic Alterations in Lung Alveolar Cells

Cigarette smoke (CS)-induced alveolar destruction and energy metabolism changes are known contributors to the pathophysiology of chronic obstructive pulmonary disease (COPD). This study examines the effect of CS exposure on metabolism in alveolar type II cells. Male A/J mice (8 wk old) were exposed to CS generated from a smoking machine for 4 or 8 weeks, and a recovery group was exposed to CS for 8 weeks and allowed to recover for 2 weeks. Alveolar type II cells were isolated from air- or CS- exposed mice. Acute CS exposure led to a reversible airspace enlargement in A/J mice as measured by the increase in mean linear intercept, indicative of alveolar destruction. The effect of CS exposure on cellular respiration was studied using the XF Extracellular Flux Analyzer. A decrease in respiration while metabolizing glucose was observed in the CS-exposed group, indicating altered glycolysis that was compensated by an increase in palmitate utilization; palmitate utilization was accompanied by an increase in the expression of CD36 and carnitine-palmitoyl transferase 1 in type II alveolar cells for the transport of palmitate into the cells and into mitochondria, respectively. The increase in palmitate use for energy production likely affects the surfactant biosynthesis pathway, as evidenced by the decrease in phosphatidylcholine levels and the increase in phospholipase A2 activity after CS exposure. These findings help our understanding of the mechanism underlying the surfactant deficiency observed in smokers and provide a target to delay the onset of COPD.

Metabolic shift in lung alveolar cell mitochondria following acrolein exposure

Acrolein, an α,β unsaturated electrophile, is an environmental pollutant released in ambient air from diesel exhausts and cooking oils. This study examines the role of acrolein in altering mitochondrial function and metabolism in lung-specific cells. RLE-6TN, H441, and primary alveolar type II (pAT2) cells were exposed to acrolein for 4 h, and its effect on mitochondrial oxygen consumption rates was studied by XF Extracellular Flux analysis. Low-dose acrolein exposure decreased mitochondrial respiration in a dose-dependent manner because of alteration in the metabolism of glucose in all the three cell types. Acrolein inhibited glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity, leading to decreased substrate availability for mitochondrial respiration in RLE-6TN, H441, and pAT2 cells; the reduced GAPDH activity was compensated in pAT2 cells by an increase in the activity of glucose-6-phosphate dehydrogenase, the regulatory control of the pentose phosphate pathway. The decrease in pyruvate from glucose metabolism resulted in utilization of alternative sources to support mitochondrial energy production: palmitate-BSA complex increased mitochondrial respiration in RLE-6TN and pAT2 cells. The presence of palmitate in alveolar cells for surfactant biosynthesis may prove to be the alternative fuel source for mitochondrial respiration. Accordingly, a decrease in phosphatidylcholine levels and an increase in phospholipase A2 activity were found in the alveolar cells after acrolein exposure. These findings have implications for understanding the decrease in surfactant levels frequently observed in pathophysiological situations with altered lung function following exposure to environmental toxicants.

Biosurfactants of Rhodococcus erythropolis IMV Ас-5017: Synthesis Intensification and Practical Application

Intensification of the surfactant synthesis by Rhodococcus erythropolis IMV Ac-5017 on different substrates, including industrial waste, as well as the use of surfactant preparations for oil degradation were studied. It was established that the addition of fumarate (0.2 %) and citrate (0.1 %) into the medium with ethanol, n-hexadecane, or glycerol (1-2 %) was accompanied by an increase of conditional surfactant concentration by 1.5-1.7 times compared to the indexes in the medium without organic acids. The intensification of surfactant synthesis in the presence of fumarate and citrate is caused by the increased activity of isocitrate lyase (by 1.2-15-fold) and enzymes of the surfactant biosynthesis (by 2-4.8-fold) compared to their activity in the medium without precursors. The possibility of surfactant synthesis intensification (by 3-4-fold) while cultivating of R. erythropolis IMV Ac-5017 in the medium with oil containing substrates (2 %) and glucose (0.1 %) was shown. The introduction of 0.01 mM Cu(2+) in the exponential growth phase of strain IMV Ac-5017 in the medium with ethanol accompanied by the increasing conditional surfactant concentration by 1.9 times. The highly efficient remediation (92-95 %) of oil (2-2.6 g/L) and Cu(2+) polluted water after treatment with surfactant preparations (native cultural liquid) at low concentrations (5 %) was determined.

Scaling of the process of biosynthesis of surfactants by Rhodococcus erythropolis EK-1 on hexadecane

Peculiarities of synthesis of surface-active substances (SAS) are studied at periodical cultivation of Rhodococcus erythropolis EK-1 in the AK-210 fermenter on medium containing n-hexadecane. Maximum indicators of SAS synthesis (concentration of extra cellular SAS is 7.2 g/l; factor of emulsification of the cultural liquid 50%; SAS yield from the substrate 50%) have been observed at 60-70% concentration of dissolved oxygen from the saturation level with aerial oxygen (pH 8.0) fractional supply of the substrate by portions each being 0.3-0.4% every 5-6 h to a final volume concentration of 2.4% and with the use of 10% inoculate grown until mid-exponential phase on the medium with 1.0 vol % of n-hexadecane. Implementation of the process of SAS biosynthesis with the fermentation equipment provided the possibility to increase almost two-fold the amount of the synthesized SAS and reduce 3.5-fold the time of cultivation of the producer strain compared with the growth in flasks at shake-flask propagator.

The Many Faces of Glutathione Transferase Pi

Glutathione transferase Pi (GST-pi, GSTP) is known to strongly affect human susceptibility to several cancers, asthma and neurodegenerative disorders. As with other glutathione transferases, it catalyses the addition of reduced glutathione to electrophilic species, and it is important in metabolite detoxification. It also was shown to bind proteins and compounds containing iron and nitric oxide. Some of these interactions have developed in the course of evolution into regulatory pathways that back up the GST's most ancient catalytic functions and provide precise and diverse responses to chemical and redox stresses. An aim of this review is to summarise recent knowledge on GSTP's complementary functions in crosstalking pathways of conventional glutathione transfer, nitric oxide and lipid metabolism and ASK1-dependent stress response. This review will describe how these complex interactions affect regulation of cell respiration, biosynthesis of lung surfactant, organism's immunity and circadian rhythms. Integration of the data leads to a new interpretation of the role of GSTP in normal human physiology, pathology and an organism's susceptibility to diseases.

Mechanisms and recent advances in biological control mediated through the potato rhizosphere

Potato cultivation has a strategic role as a food source for the human population. Its promising future development relies on improving the control of the numerous microbial diseases that affect its growth. Numerous and recent studies on the potato rhizosphere, mycorrhizosphere and endorhiza reveal the presence of a diverse and dense microbial community. This microbial community constitutes a rich source for plant growth-promoting rhizobacteria and biocontrol agents. So far, the beneficial effects achieved are related to microbial siderophores, antibiotics, biosynthesis of surfactants and phytohormones, nutrient and spatial competition, mycoparasitism, induced systemic resistance, phage therapy, quorum quenching and construction of transgenic lines. Considering the crucial role for food and the diversity of mechanisms involved in growth promotion and microbial protection, potato constitutes a historical and accurate model in developing new biocontrol strategies.

Biosurfactant Production by Halotolerant Rhodococcus fascians from Casey Station, Wilkes Land, Antarctica

Isolate A-3 from Antarctic soil in Casey Station, Wilkes Land, was characterized for growth on hydrocarbons. Use of glucose or kerosene as a sole carbon source in the culture medium favoured biosynthesis of surfactant which, by thin-layer chromatography, indicated the formation of a rhamnose-containing glycolipid. This compound lowered the surface tension at the air/water interface to 27 mN/m as well as inhibited the growth of B. subtilis ATCC 6633 and exhibited hemolytic activity. A highly hydrophobic surface of the cells suggests that uptake occurs via a direct cell-hydrocarbon substrate contact. Strain A-3 is Gram-positive, halotolerant, catalase positive, urease negative and has rod-coccus shape. Its cell walls contained meso-diaminopimelic acid. Phylogenetic analysis based on comparative analysis of 16S rRNA gene sequences revealed that strain A-3 is closely related to Rhodococcus fascians with which it shares 100% sequence similarity. This is the first report on rhamnose-containing biosurfactant production by Rhodococcus fascians isolated from Antarctic soil.

Cultural factors affecting biosurfactant production by Gordonia sp. BS29

Gordonia sp. BS29 is a hydrocarbon-degrading bacterium isolated from a site chronically contaminated by diesel. The strain produces extracellular bioemulsifiers, able to produce stable emulsions, and cell-bound glycolipid biosurfactants, able to reduce surface tension. The aims of this work were to investigate the cultural factors affecting the production of the cell-bound biosurfactants by Gordonia sp. BS29 and to find the optimal composition of growth medium for the production. The cultural factors which have a significant influence on surfactant biosynthesis, identified by a two level 2 (8-2) Fractional Factorial Design, were the type and concentration of the carbon source, the concentrations of phosphates and sodium chloride, and the interactions among these factors. On these factors, a flask-scale optimisation of cultural conditions was carried out. Then, a steepest ascent procedure and a Central Composite Design were applied to obtain a second order polynomial function fitting the experimental data near the optimum. In the optimised cultural condition we obtained a 5-fold increase in the biosurfactant concentration compared to the un-optimised medium (26.00), reaching a Critical Micelle Dilution value (129.43) among the highest in literature. The optimisation procedure did not change the number and type of the glycolipid biosurfactants produced by Gordonia sp. BS29.

Functional, genetic and chemical characterization of biosurfactants produced by plant growth-promotingPseudomonas putida267

Plant growth-promoting Pseudomonas putida strain 267, originally isolated from the rhizosphere of black pepper, produces biosurfactants that cause lysis of zoospores of the oomycete pathogen Phytophthora capsici. The biosurfactants were characterized, the biosynthesis gene(s) partially identified, and their role in control of Phytophthora damping-off of cucumber evaluated. The biosurfactants were shown to lyse zoospores of Phy. capsici and inhibit growth of the fungal pathogens Botrytis cinerea and Rhizoctonia solani. In vitro assays further showed that the biosurfactants of strain 267 are essential in swarming motility and biofilm formation. In spite of the zoosporicidal activity, the biosurfactants did not play a significant role in control of Phytophthora damping-off of cucumber, since both wild type strain 267 and its biosurfactant-deficient mutant were equally effective, and addition of the biosurfactants did not provide control. Genetic characterization revealed that surfactant biosynthesis in strain 267 is governed by homologues of PsoA and PsoB, two nonribosomal peptide synthetases involved in production of the cyclic lipopeptides (CLPs) putisolvin I and II. The structural relatedness of the biosurfactants of strain 267 to putisolvins I and II was supported by LC-MS and MS-MS analyses. The biosurfactants produced by Ps. putida 267 were identified as putisolvin-like CLPs; they are essential in swarming motility and biofilm formation, and have zoosporicidal and antifungal activities. Strain 267 provides excellent biocontrol activity against Phytophthora damping-off of cucumber, but the lipopeptide surfactants are not involved in disease suppression. Pseudomonas putida 267 suppresses Phy. capsici damping-off of cucumber and provides a potential supplementary strategy to control this economically important oomycete pathogen. The putisolvin-like biosurfactants exhibit zoosporicidal and antifungal activities, yet they do not contribute to biocontrol of Phy. capsici and colonization of cucumber roots by Ps. putida 267. These results suggest that Ps. putida 267 employs other, yet uncharacterized, mechanisms to suppress Phy. capsici.

Surfactant-Associated Protein B Is Critical to Survival in Nickel-Induced Injury in Mice

The etiology of acute lung injury is complex and associated with numerous, chemically diverse precipitating factors. During acute lung injury in mice, one key event is epithelial cell injury that leads to reduced surfactant biosynthesis. We have previously reported that transgenic mice that express transforming growth factor alpha (TGFA) in the lung were protected during nickel-induced lung injury. Here, we find that the mechanism by which TGFA imparts protection includes maintenance of surfactant-associated protein B (SFTPB) transcript levels and epidermal growth factor receptor-dependent signaling in distal pulmonary epithelial cells. This protection is complex and not accompanied by a diminution in inflammatory mediator transcripts or additional stimulation of antioxidant transcripts. In mouse lung epithelial (MLE-15) cells, microarray analysis demonstrated that nickel increased transcripts of genes enriched in MTF1, E2F-1, and AP-2 transcription factor-binding sites and decreased transcripts of genes enriched in AP-1-binding sites. Nickel also increased Jun transcript and DNA-binding activity, but decreased SFTPB transcript. Expression of SFTPB under the control of a doxycycline-sensitive promoter increased survival during nickel-induced injury as compared with control mice. Together, these findings support the idea that maintenance of SFTPB expression is critical to survival during acute lung injury.

15-Deoxy-Δ12,14-prostaglandin J2 Impairs Phosphatidylcholine Synthesis and Induces Nuclear Accumulation of Thiol-modified Cytidylyltransferase

Synthesis of phosphatidylcholine, the major phospholipid of animal cell membranes, requires the key enzyme cytidylyltransferase (CCTalpha). Cysteine sulfhydryls within CCTalpha are needed for full catalytic activity. Here we show that prostaglandin 15-deoxy-Delta12,14-PGJ2 (15d-PGJ2) inactivates CCTalpha by inducing generation of reactive oxidant species and the appearance of a cross-linked CCTalpha dimer in cells. N-Acetyl-l-cysteine reduced oxidative stress, prevented CCTalpha cross-linking, and restored CCT function in 15d-PGJ2-treated cells. 15d-PGJ2 modified critical cysteine residues within CCTalpha as determined by mutagenesis studies and by incorporation of biotin-15d-PGJ2 into CCTalpha. These effects of 15d-PGJ2 were associated with CCTalpha accumulation within the nucleus. The data indicate that bioactive prostanoids significantly impair membrane phospholipid production by promoting cysteine cross-bridging within CCTalpha.

Usual Interstitial Pneumonia in an Adolescent With ABCA3 Mutations*

Many diverse and frequently idiopathic disorders cause interstitial lung disease (ILD) in children. Although the histologic patterns of ILD in children and adults share similar features, important differences exist in etiology, clinical manifestations, and outcome. Usual interstitial pneumonia (UIP) is the most frequent histologic pattern in adult ILD; however, the characteristic histologic features of UIP have yet to be demonstrated in a child. We report a 15-year-old boy with the UIP pattern of pulmonary fibrosis who had mutations in the adenosine triphosphate-binding-cassette-A3 gene. Discovery of how genetic mutations of proteins involved in surfactant biosynthesis lead to progressive fibrosis will have implications for the understanding of the pathogenesis and clinical manifestations of ILD in both adults and children.

Integrated regulation involving quorum sensing, a two‐component system, a GGDEF/EAL domain protein and a post‐transcriptional regulator controls swarming and RhlA‐dependent surfactant biosynthesis in Serratia

Serratia sp. ATCC 39006 (Serratia 39006) is a Gram-negative bacterium which produces the secondary metabolite antibiotics, prodigiosin and 1-carbapen-2-em-3-carboxylic acid and secretes plant cell wall degrading enzymes. In this study we have identified mutations in the genes, pigX, rap and rsmA, which caused increased production of a previously unidentified surfactant and flagella-dependent swarming phenotype in Serratia 39006. Analysis of both the biosynthesis and regulation of surfactant production and swarming, revealed FlhC, quorum sensing, a GGDEF/EAL domain protein (PigX), a GacAS two-component system, an Rsm system and Rap as key regulators. In addition, surfactant biosynthesis required a protein similar to RhlA, involved in rhamnolipid synthesis in Pseudomonas aeruginosa. Homologues of RhlA have not previously been identified in members of the Enterobacteriaceae. Furthermore, we provide evidence that the surfactant may be responsible for dispersal of the antimicrobial pigment, prodigiosin. This study demonstrates the complex regulatory inputs into the coordinated multicellular swarming phenotype in Serratia.

Genetic Regulations of the Biosynthesis of Microbial Surfactants: An Overview

Microbial biosurfactants are surface active metabolites synthesized by microbes growing on a variety of substrates. In spite of having great potential for commercial, therapeutic and environmental applications, industrial level production has not been realized for their low yields and productivities. One vital factor determining their biosynthesis is the genetic makeup of the producer organisms. Studies on molecular genetics and biochemistry of the synthesis of several biosurfactants have revealed the operons, the enzymes and the metabolic pathways required for their extracellular production. Surfactin, a cyclic lipopeptide biosurfactant is a potent antimicrobial agent and is produced as a result of non-ribosomal biosynthesis catalyzed by a large multienzyme peptide synthetase complex called the surfactin synthetase. Pathways for the synthesis of other lipopeptides such as iturin, lichenysin and arthrofactin are also mediated by similar enzyme complexes. These non-ribosomal peptide synthetases (NRPSs) responsible for lipopeptide biosynthesis display a high degree of structural similarity among themselves even from distant microbial species. Plasmid-encoded- rhlA, B, R and I genes of rhl quorum sensing system are required for production of glycolipid biosurfactants by Pseudomonas species. Molecular genetics of biosynthesis of alasan and emulsan by Acinetobacter species and of the fungal biosurfactants such as mannosylerythritol lipids (MEL) and hydrophobins have been deciphered. However, limited genetic information is available about biosynthesis of other biosurfactants such as viscosin, amphisin and synthesized counterparts. As these molecules have emerged as potential agents in many industrial and environmental processes as well as in biomedical and therapeutic applications, it is essential to make them cost competitive. Genetically engineered hyper producing organisms giving high yields can bring the real breakthrough in the production process. This is possible only if the genetics of the microbial surfactant production is known in details. It is therefore desirable that the future research on biosurfactants be focused on the development and use of hyperproducers. The detailed knowledge of the genetics of microbial surfactant production should be used to produce organisms giving higher production with better product characteristics. With a better knowledge of the genes involved in this process, biosurfactant production can be realized in non-pathogenic industrial strains. The knowledge of expression of genes of a particular biosurfactant producer in a particular habitat will also throw light upon substrate dependence of production and preference for a particular substrate. Detailed description of the genetics of production of the newly identified biosurfactants like flavolipids, tensin and lokisin is not available. Efforts should be made by investigators to develop high yielding strains of microorganisms producing strong biosurfactants such as arthrofactin and lichenysin. A few marine biosurfactants have been discovered (Kalinovskaya et al. 2004) and there is high possibility of finding many other novel surface active compounds from the marine sources. Many of these are expected to possess interesting properties as pharmaceuticals and biomedical agents. The knowledge of molecular genetics of microbial surfactant production and its subsequent use to produce hyperproducers will determine the fate of biosurfactant industry.

Aberrant quality control in the endoplasmic reticulum impairs the biosynthesis of pulmonary surfactant in mice expressing mutant BiP

Accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces the unfolded protein response (UPR), which alleviates protein overload in the secretory pathway. Although the UPR is activated under diverse pathological conditions, its physiological role during development and in adulthood has not been fully elucidated. Binding immunoglobulin protein (BiP) is an ER chaperone, which is central to ER function. We produced knock-in mice expressing a mutant BiP lacking the retrieval sequence to cause a defect in ER function without completely eliminating BiP. In embryonic fibroblasts, the UPR compensated for mutation of BiP. However, neonates expressing mutant BiP suffered respiratory failure due to impaired secretion of pulmonary surfactant by alveolar type II epithelial cells. Expression of surfactant protein (SP)-C was reduced and the lamellar body was malformed, indicating that BiP plays a critical role in the biosynthesis of pulmonary surfactant. Because pulmonary surfactant requires extensive post-translational processing in the secretory pathway, these findings suggest that in secretory cells, such as alveolar type II cells, the UPR is essential for managing the normal physiological ER protein overload that occurs during development. Moreover, failure of this adaptive mechanism may increase pulmonary susceptibility to environmental insults, such as hypoxia and ischemia, ultimately leading to neonatal respiratory failure.

Evidence of defective surfactant biosynthesis in patients with Idiopathic Pulmonary Fibrosis (IPF)

Evidence of defective surfactant biosynthesis in patients with Idiopathic Pulmonary Fibrosis (IPF)

Glucocorticoids regulate expression of the fatty acid synthase gene in fetal rat type II cells

Fatty acids are integral components of pulmonary surfactant, a mixture of phospholipids and specific proteins that lines the alveolar surface and is essential for normal lung function. There are developmental increases in fatty acid biosynthesis and surfactant production in late-gestation fetal lung, and both processes are accelerated by glucocorticoids. Fatty acid synthase (FAS) is a key enzyme in de novo fatty acid biosynthesis, and increased FAS activity is responsible for the developmental and hormone-induced increases in fatty acid biosynthesis in fetal lung. Using cultured fetal lung explants, it has been reported that dexamethasone (Dex) increases FAS activity, protein content, mRNA content and rate of transcription. However, FAS expression has not been measured in isolated type II cells, the cellular source of surfactant within the lung. In the present study we measured parameters of FAS expression in type II cells isolated from the lungs of Dex-treated rats. Pregnant rats were injected with Dex or saline on days 18 and 19 of gestation and the fetuses delivered on day 20. Type II cells and fibroblasts were then isolated from the fetal lungs. Dex increased FAS activity, protein content, mRNA content and rate of transcription in the type II cells but not in the fibroblasts. Increased FAS expression in fetal type II cells in response to Dex is consistent with a critical role for FAS in the biosynthesis of lung surfactant.