Transcriptional regulation of the gene encoding the major surfactant protein (SP-A) in rabbit fetal lung

Structure, genetics and function of the pulmonary associated surfactant proteins A and D: The extra-pulmonary role of these C type lectins

The collectins family encompasses several collagenous Ca²⁺-dependent defense lectins that are described as pathogen recognition molecules. They play an important role in both adaptive and innate immunity. Surfactant proteins A and D are two of these proteins which were initially discovered in association with surfactant in the pulmonary system. The structure, immune and inflammatory functions, and genetic variations have been well described in relation to their roles, function and pathophysiology in the pulmonary system. Subsequently, these proteins have been discovered in a wide range of other organs and organ systems. The role of these proteins outside the pulmonary system is currently an active area of research. This review intends to provide a current overview of the genetics, structure and extra-pulmonary functions of the surfactant collectin proteins.

Human SP-A1 (SFTPA1) variant-specific 3' UTRs and poly(A) tail differentially affect the in vitro translation of a reporter gene

Human surfactant protein A (SP-A) is encoded by two functional genes (SFTPA1, SFTPA2) with a high degree of sequence identity. Sequence differences among these genes and their genetic variants have been observed at the 5' and 3' untranslated regions (UTRs). In this work, we studied the impact on translation of the SFTPA1 (hSP-A1) and SFTPA2 (hSP-A2) gene 5' UTR splice variants and 3' UTR sequence variants, in the presence or absence of poly(A) tail. We generated constructs containing the luciferase reporter gene flanked upstream by one of the hSP-A 5' UTR splice variants and/or downstream by one hSP-A 3' UTR sequence variant. mRNA transcripts were prepared by in vitro transcription and used for either in vitro translation with a rabbit reticulocyte lysate or transient transfection of the lung adenocarcinoma cell line NCI-H441. The luciferase activity results indicate that hSP-A 5' UTR and 3' UTR together have an additive effect on translation. In this context, the hSP-A1 6A(3) and 6A(4) 3' UTR variants exhibited higher translation efficiency than the 6A(2) variant (P <0.05), whereas no significant difference was observed between the two hSP-A2 3' UTRs studied (1A(0), 1A(3)). Further sequence analysis revealed that a deletion of an 11-nucleotide (nt) element in both the 6A(3) and 6A(4) 3' UTR variants changes the predicted secondary structure stability and the number of putative miRNA binding sites. Removal of this 11-nt element in the 6A(2) 3' UTR resulted in increased translation, and the opposite effect was observed when the 11-nt element was cloned in a guest 3' UTR (6A(3), 6A(4)). These results indicate that sequence differences among hSP-A gene variants may account for differential regulation at the translational level.

TTF-1 response element is critical for temporal and spatial regulation and necessary for hormonal regulation of human surfactant protein-A2 promoter activity

Expression of the human surfactant protein-A2 (hSP-A2) gene is lung specific, occurs in type II and Clara cells, and is developmentally and hormonally regulated in fetal lung. Using transfected human fetal type II cells, we previously observed that approximately 300 bp of 5'-flanking DNA mediated cAMP and interleukin-1 (IL-1) stimulation and dexamethasone (Dex) inhibition of hSP-A2 promoter activity. This region contains response elements for estrogen-related receptor alpha element (ERRE, -241 bp), thyroid transcription factor (TTF)-1/Nkx2.1 (TTF-binding protein, -171 bp), upstream stimulatory factor 1/2 (E-box, -80 bp), and stimulatory protein (Sp) 1 (G/T-box, -62 bp), which are essential for basal and cAMP induction of hSP-A2 expression. To define genomic regions necessary for developmental, hormonal, and tissue-specific regulation of hSP-A2 expression in vivo, we analyzed transgenic mice carrying hGH reporter genes comprised of 313 bp of hSP-A2 gene 5'-flanking DNA +/- mutation in the TBE or 175 bp of 5'-flanking DNA, containing TBE, E-box and G/T-box, but lacking ERRE. Transgenes containing 313 or 175 bp of hSP-A2 5'-flanking DNA were expressed in a lung cell-specific manner and developmentally regulated in concert with the endogenous mouse SP-A gene. In cultured lung explants from hSP-A(-313):hGH transgenic fetal mice, cAMP and IL-1 induced and Dex inhibited transgene expression. However, the 175-bp hSP-A2 genomic region was insufficient to mediate hormonal regulation of hSP-A2 promoter activity. The finding that expression of the hSP-A(-313TBEmut):hGH transgene was essentially undetectable in fetal lung and was not hormonally regulated in transgenic fetal lung explants underscores the critical importance of the TBE in lung cell-specific, developmental, and hormonal regulation of hSP-A2 gene expression.

Leptin enhances lung maturity in the fetal rat

Pulmonary alveolar type II cells synthesize and secrete phospholipids and surfactant proteins. In most mammalian species, the synthesis of phospholipids and proteins of lung surfactant increases with fetal lung maturation, which occurs late in gestation. Factors that may promote lung maturation and surfactant production include the placental hormone, leptin, whose expression increases with advancing gestational age. We demonstrate that physiologic concentrations of leptin (1 and 10 ng/mL) increase the levels of surfactant proteins (SP) A, B, and C mRNA as well as SP-A and SP-B protein in d-17 fetal rat lung explants in vitro. To determine whether leptin exerts similar effects in vivo, we administered leptin antenatally to pregnant rats and compared its effects to that of dexamethasone, a known mediator of fetal lung development. Antenatal treatment with leptin for 2 d significantly increased the average weight of the fetal lungs in relation to their body weight. Histologic analysis revealed that the increase in fetal lung weight was accompanied by an increase in the number and maturation of type II alveolar cells and the expression of surfactant proteins B and C in these cells. Collectively, these results suggest that leptin is a cytokine regulator of rat fetal lung maturity.

Transcription Factors NF-κB and C/EBPδ and IL-1-Induced Expression of Surfactant Protein A in Lung Explants during the Perinatal Period

Interleukin-1 (IL-1) increases the expression of surfactant protein A (SP-A) in rabbit, lamb and human fetal lung. The upregulation disappears towards term. Among the transcription factors, IL-1 activates nuclear factor kappaB (NF-kappaB) and CCAAT/enhancer-binding protein delta (C/EBPdelta). NF-kappaB presumably has a role in IL-1-induced upregulation of SP-A. Also, C/EBPdelta may regulate SP-A expression. The aim was to study the role of these transcription factors in the induced effect of IL-1 on SP-A expression. Explants from fetal and neonatal rabbit lung were cultured in vitro followed by studies using immunohistochemistry, electrophoretic mobility shift assay and Northern analysis. We found gestation-dependent changes in IL-1-induced immunoreactivities of NF-kappaB and C/EBPdelta in the nuclei of alveolar cells. This increase in nuclear transcription factors correlated with IL-1-induced SP-A expression levels. As studied in the explants from fetal and newborn lung, the SP-A mRNA expression additionally associated with C/EBPdelta mRNA and with the binding of nuclear extracts from the lung explants to the C/EBP consensus probe. On the basis of the present and previous studies, we propose that NF-kappaB and C/EBPdelta have potential mediator roles in IL-1-induced upregulation of SP-A in immature lung.

Inflammatory and anti-inflammatory responsiveness of surfactant proteins in fetal and neonatal rabbit lung

Spontaneous preterm birth due to intrauterine infection is associated with increased concentrations of cytokines in amniotic fluid and in the airways at birth. Intra-amniotic IL-1 induces fetal lung maturity, consistent with the decrease in the incidence of respiratory distress syndrome (RDS) in intrauterine inflammation. On the other hand, antenatal corticosteroid decreases the incidence of RDS in infants born prematurely. The aim of the present study was to investigate the interaction between IL-1 and glucocorticoid in the expression of the surfactant proteins SP-A, -B, and -C. Lung explants from rabbit fetuses at 22 (immature), 27 (transitional), and 30 (mature) d of gestation (term, 30-31 d) and on d 1 after term birth were cultured with dexamethasone (Dx), IL-1alpha, or vehicle in the presence or absence of actinomycin D. According to the present results, IL-1alpha and Dx additively increased the expression of SP-A and SP-B on d 22. Later in gestation, SP-B and SP-C were suppressed by IL-1, whereas glucocorticoid tended to increase the expression of SP-B and SP-C and prevented the IL-1-induced suppression of SP. IL-1alpha and steroid interactively increased the stability of SP mRNA compared with the single agonist, possibly explaining the additive effects on the SP mRNA levels. The present results reveal beneficial additive effects of glucocorticoid and cytokine on lung surfactant. They may explain some of the acute beneficial effects of glucocorticoid therapy in chorioamnionitis before premature birth and in inflammatory lung disease after birth.

Glucocorticoid inhibition of SP-A gene expression in lung type II cells is mediated via the TTF-1-binding element

Induction of surfactant protein-A (SP-A) gene expression in fetal lung type II cells by cAMP and IL-1 is mediated by increased binding of thyroid transcription factor-1 (TTF-1) and NF-B proteins p50 and p65 to the TTF-1-binding element (TBE) at -183 bp. In type II cell transfections, dexamethasone (Dex) markedly inhibits cAMP-induced expression of rabbit SP-A:human growth hormone (hGH) fusion genes containing as little as 300 bp of the SP-A 5'-flanking sequence. Dex inhibition is blocked by RU-486, suggesting a role of the glucocorticoid receptor (GR). The present study was undertaken to define the mechanisms for GR inhibition of SP-A expression. Cotransfection of primary cultures of type II cells with a GR expression vector abrogated cAMP induction of SP-A promoter activity while, at the same time, causing a 60-fold induction of cotransfected mouse mammary tumor virus (MMTV) promoter. In lung cells transfected with a fusion gene containing three TBEs fused to the basal SP-A promoter, Dex prevented the stimulatory effect of IL-1 on TTF-1 induction of SP-A promoter activity, suggesting that the GR inhibits SP-A promoter activity through the TBE. In gel shift assays using nuclear extracts from human fetal type II cells cultured in the absence or presence of cAMP, Dex markedly reduced binding of nuclear proteins to the TBE and blocked the stimulatory effect of cAMP on TBE-binding activity. Our finding that Dex increased expression of the NF-kappaB inhibitory partner IkappaB-alpha suggests that the decrease in TBE-binding activity may be caused, in part, by GR inhibition of NF-kappaB interaction with this site.

Transcription factor USF2 is developmentally regulated in fetal lung and acts together with USF1 to induce SP-A gene expression

Expression of the pulmonary surfactant protein A (SP-A) gene is lung specific, developmentally regulated, and enhanced by hormones and factors that increase cAMP. We previously identified two E-box-like enhancers termed distal binding element (DBE) and proximal binding element (PBE) in the 5'-flanking region of the rabbit (r) SP-A gene that are essential for cAMP induction of rSP-A promoter activity (Gao E, Alcorn JL, and Mendelson CR. J Biol Chem 268: 19697-19709, 1993). We also found that DBE and PBE serve as binding sites for the basic helix-loop-helix-leucine zipper transcription factor, upstream stimulatory factor-1 (USF1) (Gao E, Wang Y, Alcorn JL, and Mendelson CR. J Biol Chem 272: 23398-23406, 1997). In the present study, PBE was used to screen a rabbit fetal lung cDNA expression library; a cDNA insert encoding the structurally related rabbit upstream stimulatory factor-2 (rUSF2) was isolated. The levels of rUSF2 mRNA reach peak levels in fetal rabbit lung at 28 days of gestation, in concert with the time of maximal induction of SP-A gene transcription. In yeast two-hybrid analysis, rUSF2 was found to preferentially form heterodimers, compared with homodimers, with rUSF1. Binding complexes of nuclear proteins isolated from fetal rabbit lung type II cells with the DBE and PBE were supershifted by anti-rUSF2 antibodies. Binding activity was enriched in nuclear proteins from type II cells compared with fibroblasts. Overexpression of rUSF2 in transfected lung A549 cells increased rSP-A promoter activity and acted synergistically with rUSF1. We suggest that heterodimers of USF2 and USF1 bound to two E-box elements in the SP-A gene 5'-flanking region serve a key role in developmental and hormonal regulation of SP-A gene expression in pulmonary type II cells.

Fetal lung maturation in estrogen-deprived baboons

We have previously shown that estrogen plays a central integrative role in regulating key aspects of fetal-placental development and that inhibition of estrogen production during the second half of baboon pregnancy suppressed fetal adrenal function. Because maturation of the fetal lung is dependent on cortisol of fetal adrenal origin, the current study determined whether lung development and expression of surfactant proteins (SPs) A and B were altered at term in estrogen-deprived baboons. Fetal lungs were obtained on d 100, 165, and 175 of gestation (term = d 184) from untreated baboons and on d 165 from animals treated daily during the second half of pregnancy either with the aromatase inhibitor CGS 20267 alone or with CGS 20267 and estradiol benzoate. Umbilical venous estradiol levels were suppressed by more than 95% by CGS 20267 and elevated by CGS 20267 and estrogen. Although umbilical serum cortisol levels were also suppressed by 35% by CGS 20267, cortisol levels in the fetal lung of estrogen-suppressed baboons were similar to values in untreated animals. Immunocytochemistry demonstrated that CGS 20267 treatment did not alter fetal lung expression of the 11 beta-hydroxysteroid dehydrogenase enzyme-1 enzyme catalyzing reduction of cortisone to cortisol. However, immunocytochemical expression of the 11 beta-hydroxysteroid dehydrogenase enzyme-2 catalyzing oxidation of cortisol to cortisone appeared lower in lungs of estrogen-deprived fetuses and restored to normal by CGS 20267 and estrogen. SP-A levels in fetal lungs of untreated baboons were increased 16- to 20-fold between d 100 and d 165-175 of gestation in untreated baboons and baboons treated with CGS 20267 or CGS 20267 and estrogen. Similarly, SP-B levels in fetal lungs of untreated baboons were increased 10-fold between d 100 and d 165-175 of gestation in untreated baboons and baboons treated with CGS 20267 or CGS 20267 and estrogen. Moreover, in estrogen-suppressed baboons, as in untreated animals, the fetal lung continued to grow and exhibited normal alveolarization on histology. We conclude that development of the primate fetal lung can occur in utero in baboons in which fetal serum cortisol levels have been suppressed by the relative absence of estrogen perhaps because of the ability of the lung to coordinate local production of cortisol.

Scar and pulmonary expression and shedding of ACE in rat myocardial infarction

We examined the topology of angiotensin-converting enzyme (ACE) mRNA expression, activity, and shedding in myocardial infarction-induced heart failure and sought to elucidate the source of the increased plasma ACE activity in this model. Three months after coronary ligature, lung, scar, and remaining viable left ventricular tissues were analyzed for ACE mRNA expression as well as tissue and solubilized ACE activity. ACE mRNA expression increased in the scar with respect to infarct severity, decreased in the lung, and remained unchanged in the left ventricle. ACE activity decreased in the lung and increased in the scar tissue and plasma. Shedding of ACE remained constant in the lung and increased in the scar. This study shows that ACE expression and activity is shifted from the pulmonary endothelium to the infarct scar tissue and that constancy of shedding in the lung and its increase in the scar are the source of the increased plasma ACE in congestive heart failure.

Regulation of surfactant proteins by LPS and proinflammatory cytokines in fetal and newborn lung

Intra-amniotic lipopolysaccharide (LPS) and cytokines may decrease respiratory distress syndrome (RDS) and increase chronic lung disease in the newborn. The aim was to identify the primary inflammatory mediators regulating the expression of surfactant proteins (SP) in explants from immature (22-day-old fetus) and mature (30-day term fetus and 2-day-old newborn) rabbits. In immature lung, interleukin (IL)-1alpha and IL-1beta upregulated the expression of SP-A and SP-B. These effects of IL-1 were diminished, and SP-C mRNA was suppressed additively in the presence of tumor necrosis factor (TNF)-alpha and either LPS or interferon (IFN)-gamma. LPS, TNF-alpha, or IFN-gamma had no effect alone. In explants from the term fetus and the newborn, LPS, IL-1alpha, and TNF-alpha additively suppressed the SPs. LPS acutely induced IL-1alpha in alveolar macrophages in mature lung but not in the immature lung. IFN-gamma that generally has low expression in intrauterine infection decreased the age dependence of the other agonists' effects on SPs. The present study serves to explain the variation of the pulmonary outcome after an inflammatory insult. We propose that IL-1 from extrapulmonary sources induces the SPs in premature lung and is responsible for the decreased risk of RDS in intra-amniotic infection.

Role of CBP/p300 and SRC-1 in transcriptional regulation of the pulmonary surfactant protein-A (SP-A) gene by thyroid transcription factor-1 (TTF-1)

Surfactant protein-A (SP-A) gene expression is developmentally regulated in fetal lung type II cells and is enhanced by cAMP. cAMP stimulation of SP-A gene expression is mediated by protein kinase A (PKA) phosphorylation of thyroid transcription factor 1 (TTF-1), expressed selectively in developing lung epithelium. In this study, we analyzed roles of CREB-binding protein (CBP) and steroid receptor coactivator-1 (SRC-1) in TTF-1 regulation of SP-A expression. Upon differentiation of human fetal lung in culture, nuclear localization of CBP, SRC-1, and TTF-1 increased in ductular epithelium in association with type II cell differentiation and induction of SP-A expression. In transient transfections, CBP and SRC-1 acted synergistically with TTF-1 to increase SP-A promoter activity. Overexpression of PKA catalytic subunit enhanced hSP-A promoter activation by SRC-1 plus TTF-1. Adenoviral E1A overexpression reduced TTF-1 +/- SRC-1 induction of SP-A promoter activity, suggesting a role of endogenous CBP/p300. TTF-1 interacted with SRC-1 and CBP in vitro. SRC-1 immunodepletion from type II cell nuclear extracts reduced binding to the TTF-1 binding element upstream of SP-A gene. In cultured type II cells, cAMP increased TTF-1 acetylation. This suggests that cAMP-mediated TTF-1 phosphorylation facilitates interaction with CBP and SRC-1, resulting in its hyperacetylation, further enhancing TTF-1 DNA-binding and transcriptional activity.

Role of transcription factors in fetal lung development and surfactant protein gene expression

Branching morphogenesis of the lung and differentiation of specialized cell populations is dependent upon reciprocal interactions between epithelial cells derived from endoderm of embryonic foregut and surrounding mesenchymal cells. These interactions are mediated by elaboration and concerted actions of a variety of growth and differentiation factors binding to specific receptors. Such factors include members of the fibroblast growth factor family, sonic hedgehog, members of the transforming growth factor-beta family, epidermal growth factor, and members of the platelet-derived growth factor family. Hormones that increase cyclic AMP formation, glucocorticoids, and retinoids also play important roles in branching morphogenesis, alveolar development, and cellular differentiation. Expression of the genes encoding these morphogens and their receptors is controlled by a variety of transcription factors that also are highly regulated. Several of these transcription factors serve dual roles as regulators of genes involved in early lung development and in specialized functions of differentiated cells. Targeted null mutations of genes encoding many of these morphogens and transcription factors have provided important insight into their function during lung development. In this chapter, the cellular and molecular mechanisms that control lung development are considered, as well as those that regulate expression of the genes encoding the surfactant proteins.

Hemodynamic stresses induce endothelial dysfunction and remodeling of pulmonary artery in experimental compensated heart failure

BACKGROUND

We hypothesized that, in compensated heart failure (HF), hemodynamic perturbations and their consequences exist in pulmonary artery (PA) despite the absence of any perturbation in thoracic aorta (TA).

METHODS AND RESULTS

The left coronary artery was ligated in 20 male Wistar rats with compensated HF. Four months after ligation, these rats were compared with 20 sham-operated control rats. Blood pressure, velocity, viscosity, luminal diameter, and wall tensile and shear stresses were determined in PA and TA. Arterial rings were mounted in a myograph for ex vivo study. Endothelial nitric oxide synthase (eNOS) mRNA expression was determined in lung and aorta. Sections of PA and TA were used for histomorphometric study. In PA from rats with compensated HF, (1) blood pressure and wall tensile stress increased, whereas blood velocity and wall shear stress decreased; (2) contractions to KCl were not altered, but maximal contraction to phenylephrine and EC(50) decreased; (3) endothelium-dependent relaxation to acetylcholine and basal NO activity were blunted, whereas endothelium-independent relaxation was preserved; (4) eNOS mRNA levels and eNOS transcription in lung nuclei decreased; and (5) medial cross-sectional area, thickness, smooth muscle cell number, elastin, and collagen contents increased. Conversely, no such changes were found in TA from rats with compensated HF.

CONCLUSIONS

In compensated HF induced by small myocardial infarction, hemodynamics, vascular wall function, and structure are altered in PA but preserved in TA. These results indicate that the pulmonary vascular bed is an early target of regional circulatory alterations in HF.

Characterization of rat CD14 promoter and its regulation by transcription factors AP1 and Sp family proteins in hepatocytes

CD14, a 55kDa glycoprotein, serves as a lipopolysaccharide (LPS) recognition molecule. CD14 is a monocyte differentiation antigen expressed by myeloid-derived cells, or other cells such as hepatocytes, as either a membrane-bound protein or a soluble serum protein. Increasing evidence indicates that soluble CD14 in plasma is an acute-phase protein derived, among other sources, from liver cells. Although information is available on the cellular expression of CD14, little is known about the cis- and trans-acting factors that regulate basal CD14 transcription in liver cells. We show here that liver cells have a relatively high basal CD14 transcription rate as determined by nuclear run-on assay. We cloned and sequenced an 883bp 5'-flanking region of the rat CD14 gene and demonstrated functional promoter activity in liver cells. Sequence analysis revealed that, like in the human and mouse CD14 genes, multiple Sp1 and AP1 binding elements exist in rat CD14. Site-directed mutagenesis and transient transfection assays demonstrated that an Sp1 element located at -836 and an AP1 element located at -270 are required for basal promoter activity in liver cells. Electrophoretic mobility shift assays indicate that both Sp1 and Sp3 nuclear factors interact with the -836 Sp1 element, while the AP1-related proteins Fra-2 and JunD bind to the AP1 motif. These data provide novel insights into the regulation of basal CD14 expression in liver cells.

Analysis of genomic regions involved in regulation of the rabbit surfactant protein A gene in transgenic mice

The gene encoding surfactant protein (SP) A, a developmentally regulated pulmonary surfactant-associated protein, is expressed in a lung-specific manner, primarily in pulmonary type II cells. SP-A gene transcription in the rabbit fetal lung is increased by cAMP. To delineate the genomic regions involved in regulation of SP-A gene expression, lines of transgenic mice carrying fusion genes composed of various amounts of 5'-flanking DNA from the rabbit SP-A gene linked to the human growth hormone structural gene as a reporter were established. We found that as little as 378 bp of 5'-flanking DNA was sufficient to direct appropriate lung cell-selective and developmental regulation of transgene expression. The same region was also sufficient to mediate cAMP induction of transgene expression. Mutagenesis or deletion of either of two DNA elements, proximal binding element and a cAMP response element-like sequence, previously found to be crucial for cAMP induction of SP-A promoter activity in transfected type II cells, did not affect lung-selective or temporal regulation of expression of the transgene; however, overall levels of fusion gene expression were reduced compared with those of wild-type transgenes.

Expression of CD14 by hepatocytes: upregulation by cytokines during endotoxemia

Studies were undertaken to examine hepatocyte CD14 expression during endotoxemia. Our results show that lipopolysaccharide (LPS) treatment in vivo caused a marked upregulation in CD14 mRNA and protein levels in rat hepatocytes. Detectable increases in mRNA were seen as early as 1.5 h after LPS treatment; these increases peaked at 20-fold by 3 h and returned to baseline levels by 24 h. In situ hybridization localized the CD14 mRNA expression to hepatocytes both in vitro and in vivo. Increases in hepatic CD14 protein levels were detectable by 3 h and peaked at 12 h. Hepatocytes from LPS-treated animals expressed greater amounts of cell-associated CD14 protein, and more of the soluble CD14 was released by hepatocytes from LPS-treated rats in vitro. The increases in hepatocyte CD14 expression during endotoxemia occurred in parallel to increases of CD14 levels in plasma. To provide molecular identification of the hepatocyte CD14, we cloned the rat liver CD14 cDNA. The longest clone consists of a 1,591-bp insert containing a 1,116-bp open reading frame. The deduced amino acid sequence is 372 amino acids long, has 81.8 and 62.8% homology to the amino acid sequences of mouse and human CD14, respectively, and is identical to the rat macrophage CD14. The expressed CD14 protein from this clone was functional, as indicated by NF-kappaB activation in response to LPS and fluorescein isothiocyanate-LPS binding in CHO cells stably transfected with rat CD14. A nuclear run-on assay showed that CD14 transcription rates were significantly increased in hepatocytes from LPS-treated animals, indicating that the upregulation in CD14 mRNA levels observed in rat hepatocytes after LPS treatment is dependent, in part, on increased transcription. In vitro and in vivo experiments indicated that interleukin-1beta and/or tumor necrosis factor alpha participate in the upregulation of CD14 mRNA levels in hepatocytes. Our data indicate that hepatocytes express CD14 and that hepatocyte CD14 mRNA and protein levels increase rapidly during endotoxemia. Our observations also support the idea that soluble CD14 is an acute-phase protein and that hepatocytes could be a source for soluble CD14 production.

Insulin inhibits surfactant protein A and B gene expression in the H441 cell line

Fetuses of mothers with uncontrolled gestational diabetes have an increased risk of developing neonatal respiratory distress syndrome and are frequently hyperinsulinemic, thus it has been proposed that high levels of insulin delay fetal lung maturation. We have shown previously that insulin inhibits the accumulation of mRNA for the surfactant-associated proteins A and B (SP-A and SP-B) in human fetal lung explants maintained in vitro. To test the hypothesis that the inhibitory effects of insulin on the surfactant proteins are the result of a direct action of insulin on the lung epithelial cell, we evaluated the effects of insulin in the H441 cell line, a human pulmonary adenocarcinoma cell line that expresses SP-A and SP-B mRNA. We observed that insulin treatment for 48 h decreased SP-A mRNA and protein levels in a concentration-dependent manner when compared to controls. The inhibitory effect of insulin on SP-A mRNA levels was apparent as early as after 4 h of exposure. SP-B mRNA levels were also significantly decreased by insulin in a concentration-dependent manner. Insulin, at 2.5 microg/ml, inhibited SP-A gene transcription by approx. 67%, and inhibited SP-B gene transcription by about 32%. There was no significant effect of insulin on SP-A or SP-B mRNA stability. Thus, we have observed a pattern of insulin inhibition of SP-A and SP-B gene expression in the H441 lung epithelial cell line similar to that previously observed in human fetal lung explants, which are comprised of both epithelial and mesenchymal cells. Our findings provide further evidence that insulin may delay fetal lung maturation by inhibiting SP-A and SP-B gene expression. Furthermore, our findings suggest that the inhibitory effects of insulin are, at least partially, the result of a direct action on the lung epithelial cell.

Mechanism of all trans-retinoic acid and glucocorticoid regulation of surfactant protein mRNA

The surfactant proteins (SPs) are required for the normal function of pulmonary surfactant, a lipoprotein substance that prevents alveolar collapse at end expiration. We characterized the effects of cortisol and all trans-retinoic acid (RA) on SP-A and SP-B gene expression in H441 cells, a human pulmonary adenocarcinoma cell line. Cortisol, at 10(-6) M, caused a significant inhibition of SP-A mRNA to levels that were 60-70% of controls and a five- to sixfold increase in the levels of SP-B mRNA. RA alone (10(-6) M) had no effect on SP-A mRNA levels and modestly reduced the inhibitory effect of cortisol. RA alone and the combination of cortisol and RA both significantly increased SP-B mRNA levels. RA had no effect on the rate of SP-A gene transcription or on SP-A mRNA stability. Cortisol alone and the combination of cortisol and RA significantly inhibited the rate of SP-A gene transcription but had no effect on SP-A mRNA half-life. RA at 10(-6) M had no effect on the rate of SP-B gene transcription but prolonged SP-B mRNA half-life. Cortisol alone and the combination of cortisol and RA caused a significant increase in the rate of SP-B gene transcription and also caused a significant increase in SP-B mRNA stability. We conclude that RA has no effect on SP-A gene expression and increases SP-B mRNA levels by an effect on SP-B mRNA stability and not on the rate of SP-B gene transcription. In addition, the effects of the combination of RA and cortisol were generally similar to those of cortisol alone.

O2 regulates surfactant protein A mRNA transcription and stability in human fetal lung in vitro

The effect of O2 on surfactant protein (SP) A mRNA transcription and half-life was determined in midtrimester human fetal lung tissue cultured in either 20 (control) or 70% O2. Incubation of tissues in 70% O2 resulted in a 133% increase in SP-A mRNA transcription rate compared with control tissues. The SP-A mRNA half-life was increased by 54% in lung tissues cultured in 70% O2 vs. control tissues. Western blot analysis indicated a threefold increase in SP-A in the 70% O2 condition, demonstrating that O2 regulation of SP-A mRNA levels results in corresponding changes in SP-A levels. Primer extension assays were performed to determine whether the observed increase in SP-A mRNA levels is secondary to the preferential expression of one of the human SP-A genes, SP-A1 or SP-A2. Transcripts of both the SP-A1 and SP-A2 genes were increased approximately 100% in tissues maintained in 70% O2 compared with control tissues. These data demonstrate that O2 regulates human SP-A mRNA levels by both transcriptional and posttranscriptional mechanisms. Furthermore, because there is no differential effect of O2 on the expression of SP-A1 vs. SP-A2 mRNA, the properties of these genes that mediate regulation by O2 must be conserved between the two genes.

Cyclic AMP-responsive expression of the surfactant protein-A gene is mediated by increased DNA binding and transcriptional activity of thyroid transcription factor-1

Surfactant protein (SP)-A gene transcription is stimulated by factors that increase cyclic AMP. In the present study, we observed that three thyroid transcription factor-1 (TTF-1) binding elements (TBEs) located within a 255 base pair region flanking the 5'-end of the baboon SP-A2 (bSP-A2) gene are required for maximal cyclic AMP induction of bSP-A2 promoter activity. We found that TTF-1 DNA binding activity was increased in nuclear extracts of pulmonary type II cells cultured in the presence of cyclic AMP. By contrast, the levels of immunoreactive TTF-1 protein were similar in nuclear extracts of control and cyclic AMP-treated type II cells. The incorporation of [32P]orthophosphate into immunoprecipitated TTF-1 protein also was markedly increased by cyclic AMP treatment. Moreover, exposure of nuclear extracts from cyclic AMP-treated type II cells either to potato acid phosphatase or alkaline phosphatase abolished the cyclic AMP-induced increase in TTF-1 DNA-binding activity. Interestingly, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), known to activate protein kinase C, also enhanced incorporation of [32P]orthophosphate into TTF-1 protein; however, the DNA binding activity of TTF-1 was decreased in nuclear extracts of TPA-treated type II cells. Expression vectors encoding TTF-1 and the catalytic subunit of protein kinase A (PKA-cat) were cotransfected into A549 lung adenocarcinoma cells together with an SPA:human growth hormone fusion gene (255 base pairs of 5'-flanking DNA from the baboon SP-A2 gene linked to human growth hormone, as reporter) containing TBEs, or with a reporter gene construct containing three tandem TBEs fused upstream of the bSP-A2 gene TATA box and the transcription initiation site. Coexpression of TTF-1 and PKA-cat increased fusion gene expression 3-4-fold as compared with expression of TTF-1 in the absence of PKA-cat. Moreover, the transcriptional activity of TTF-1 was suppressed by cotransfection of a dominant negative form of PKA regulatory subunit RIalpha. We suggest that a PKA-induced increase of TTF-1 phosphorylation and TBE binding activity mediates cyclic AMP-induced expression of the SP-A gene in lung type II cells.

Angiotensin I-converting enzyme genotype influences arterial response to injury in normotensive rats

Two normotensive strains of rat, the Lou and Brown Norway (BN) strains, have contrasting levels of plasma angiotensin-converting enzyme (ACE). To investigate the degree of genetic determination of ACE expression, a polymorphic marker of the ACE gene was analyzed in inbred rats of the two strains. The two inbred strains were shown to bear different alleles for a polymorphic marker at the ACE gene. The segregation of the alleles of this marker and the plasma ACE levels were studied in a group of F2 rats issued from a cross between Lou and BN rats. The degree of genetic determination of plasma ACE activity was estimated to be 94% in the F2 cohort. The ACE locus accounts for 74% of total plasma ACE variance. ACE activity and mRNA expression in lungs were also genetically determined. The difference observed in ACE mRNA accumulation in the lungs between the two strains was due to a difference in the transcriptional rate of the ACE gene, as shown in nuclear run-on experiments. No differences were observed in arterial blood pressure of homozygous F2 progeny. In these animals, ACE genotype did not interfere with the pressor or the depressor responses to ACE-dependent vasoactive peptides. There was a significant effect of strain on constitutive or inducible membrane or soluble ACE activity in primary cultures of vascular cells. Neointima formation in the carotid artery 14 days after balloon injury was also influenced by the genotype in F2 homozygous progeny, whereas the medial area was not. These results demonstrate that there is a close relationship between the genetically determined ACE expression and the inducibility of the ACE gene. The degree of genetic determination of ACE expression in inbred rat strains offers a unique opportunity to study the interaction between genetic and environmental determinants of ACE expression and its involvement in response to experimental cardiovascular and renal injury.

Primary cell culture of human type II pneumonocytes: maintenance of a differentiated phenotype and transfection with recombinant adenoviruses

Studies of the regulation of surfactant lipoprotein metabolism and secretion and surfactant protein gene expression have been hampered by the lack of a cell culture system in which the phenotypic properties of type II cells are maintained. We have developed a primary culture system that facilitates the maintenance of a number of morphologic and biochemical properties of type II pneumonocytes for up to 2 wk. Cells were isolated by collagenase digestion of midgestation human fetal lung tissue that had been maintained in organ culture in the presence of dibutyryl cyclic AMP (Bt2cAMP) for 5 days. The isolated cells were enriched for epithelial components by treatment with DEAE-dextran, plated on an extracellular matrix (ECM) derived from Madin-Darby canine kidney (MDCK) cells, and incubated at an air/liquid interface in a minimal amount of culture medium containing Bt2cAMP. The cell cultures were comprised of islands of round epithelial-like cells containing numerous dense osmiophilic granules, surrounded by sparse spindle-shaped cells with the appearance of fibroblasts. Ultrastructural examination revealed that the osmiophilic granules had the appearance of lamellar bodies, the distinguishing feature of type II pneumonocytes. Additionally, the cultures maintained elevated levels of SP-A gene expression for up to 2 wk. The expression of mRNAs encoding SP-A, SP-B, and SP-C were regulated in the cultured cells by glucocorticoids and cyclic AMP in a manner similar to that observed in fetal lung tissue in organ culture. The differentiated phenotype was most apparent when the cells were cultured at an air/liquid interface. In order to utilize the cultured type II cells for study of the effects of overexpression of various proteins and for promoter analysis, it is of essence to transfect DNA constructs into these cells with high efficiency. Unfortunately, we found the cells to be refractory to efficient transfer of DNA using conventional methods (i.e., lipofection, electroporation, or calcium phosphate-mediated transfection). However, replication-defective recombinant human adenoviruses were found to provide a highly efficient means of introducing DNA into the type II pneumonocytes. Furthermore, we observed in type II cell-enriched cultures infected with recombinant adenoviruses containing the lacZ gene under control of a cytomegalovirus promoter, that beta-galactosidase was expressed uniformly in the islands of type II cells and surrounding fibroblasts. By contrast, in cultures infected with recombinant adenoviruses containing the human growth hormone (hGH) gene under control of the SP-A gene promoter and 5'-flanking region, hGH was expressed only in the type II cells. Thus, this culture system provides an excellent means for identifying genomic elements that mediate type II cell-specific gene expression.

Transcription factor C/EBPdelta in fetal lung: developmental regulation and effects of cyclic adenosine 3',5'-monophosphate and glucocorticoids

Pulmonary surfactant is a developmentally and hormonally regulated lipoprotein synthesized exclusively in alveolar type II cells. Surfactant protein-A (SP-A) gene transcription in human fetal lung in culture is stimulated by glucocorticoids and cAMP; cAMP also enhances the rate of type II cell differentiation. The CCAAT/enhancer-binding protein (C/EBP) family of transcription factors serves an important role in the regulation of genes involved in energy metabolism, lipid biosynthesis, and cellular differentiation. The gene encoding C/EBPdelta, which is induced by glucocorticoids during the early phases of adipocyte differentiation, is expressed at relatively high levels in lung compared with other tissues. In the present study we have analyzed developmental changes in C/EBPdelta messenger RNA levels in fetal rabbit lung as well as changes in the levels of immunoreactive C/EBPdelta in human fetal lung during differentiation in organ culture and after treatment with cAMP and glucocorticoids. We observed that C/EBPdelta messenger RNA is detectable in fetal rabbit lung on day 19 of gestation and is increased approximately 3.7-fold to maximum levels on day 28 of gestation, the time when SP-A gene transcription increases to maximum levels. Immunohistochemical analysis of C/EBPdelta in midgestation human fetal lung before culture revealed trace nuclear staining in epithelial and occasional stromal cells. After 12 h of organ culture in serum-free medium, nuclear staining of C/EBPdelta was markedly increased in epithelial cells lining the prealveolar ducts of the human fetal lung tissue. By immunoblot analysis, it was found that C/EBPdelta levels were induced rapidly during organ culture in control medium and were increased further by treatment with dexamethasone and (Bt)2cAMP. C/EBPdelta levels were maximally induced during the first 24 h of culture and declined thereafter; after 72 h of incubation in control or cAMP-containing medium, C/EBPdelta was reduced markedly. By contrast, in fetal lung tissues incubated in medium containing dexamethasone or dexamethasone plus (Bt)2cAMP, the decline in C/EBPdelta was more modest, so that levels remained elevated throughout the 96-h culture period. Our findings that C/EBPdelta is localized primarily to alveolar epithelial cells, rapidly induced during differentiation of human fetal lung in culture, and increased by cAMP and glucocorticoids suggest a possible role in the regulation of type II cell differentiation and in the synthesis of surfactant phospholipids and proteins.

Glucocorticoid regulation of surfactant components in immature lambs

To assess effects of dose and duration of glucocorticoid exposure on maturation of the fetal lung, we administered single or multiple doses of betamethasone (0.5 mg/kg im) to pregnant sheep for 2 or 21 days before preterm delivery at 125 days of gestation. Lung function (compliance, lung volume at 40 cmH2O pressure, and ventilatory efficiency index) was increased after two to four weekly doses of glucocorticoid (2.5- to 4-fold increase) and after 48 h of exposure (1.4- to 2.3-fold). Total protein of lavage fluid decreased similarly with three doses, four doses, and 48 h of treatment. In lambs with long-term exposure to betamethasone, there was a similar, dose-dependent increase in concentrations of saturated phosphatidylcholine and surfactant proteins A (SP-A) and B (SP-B) (maximal 2- to 3-fold in tissue and 10- to 15-fold in lavage fluid). Levels of SP-A and SP-B were closely correlated in lavage fluid. In animals treated for 48 h, only tissue SP-B was increased (2.7-fold). We conclude that 48 h of glucocorticoid treatment improves lung function in the premature lamb without a detectable increase in lavage surfactant components and that longer exposure to antenatal glucocorticoid increases surfactant lipid and proteins in a coordinated fashion. The enhanced response with repetitive dosing indicates that the process of glucocorticoid-induced lung maturation is either reversible and/or gestational age dependent.

The basic helix-loop-helix-zipper transcription factor USF1 regulates expression of the surfactant protein-A gene

Expression of the rabbit pulmonary surfactant protein A (SP-A) gene is lung-specific, occurs primarily in type II cells, and is developmentally regulated. We previously identified two E-box-like enhancers, termed the distal binding element (DBE) and proximal binding element (PBE), in the 5'-flanking region of the rabbit SP-A gene. In the present study, the PBE was used to screen a rabbit fetal lung cDNA expression library; a cDNA insert was isolated which is highly similar in sequence to human upstream stimulatory factor 1 (hUSF1). By use of reverse transcription polymerase chain reaction, two isoforms of rabbit USF1 (rUSF1) mRNAs were identified in fetal rabbit lung and other tissues. The levels of rUSF1 mRNAs reach a peak in fetal rabbit lung at 23 days gestation, in concert with the time of initiation of SP-A gene transcription. Binding complexes of nuclear proteins obtained from fetal rabbit lung tissue and isolated type II cells with the DBE and PBE were supershifted by the addition of anti-rUSF1 IgG. Binding activity was enriched in type II cells compared with lung fibroblasts. Overexpression of rUSF1s in A549 adenocarcinoma cells positively regulated SP-A promoter activity of cotransfected reporter gene constructs. It is suggested that rUSF1s, which bind to two E-box elements in the SP-A gene 5'-flanking region, may serve a key role in the regulation of SP-A gene expression in pulmonary type II cells.

Peroxisome proliferator-activated receptor gamma1 expression is induced during cyclic adenosine monophosphate-stimulated differentiation of alveolar type II pneumonocytes

The primary function of lung alveolar type II cells is to synthesize pulmonary surfactant, a lipoprotein enriched in dipalmitoylphosphatidylcholine. Because type II pneumonocytes are highly lipogenic, we considered the possible role of the adipogenic nuclear hormone receptor, peroxisome proliferator-activated receptor gamma (PPARgamma), in their differentiation from epithelial cell precursors. A degenerate PCR-screening strategy revealed that multiple PPARs, including PPARgamma, are present in differentiated type II cells. A PCR-amplified PPARgamma DNA-binding domain was used to isolate a full-length PPARgamma1 complementary DNA clone from a rabbit type II cell complementary DNA library. Although another PPARgamma isoform, PPARgamma2, is known to be highly expressed in adipocytes, only PPARgamma1 was detected in rabbit type II cells by use of RT-PCR and by library screening. Rabbit PPARgamma1 has 90% nucleotide sequence identity and 95% amino acid identity to mouse PPARgamma1. PPARgamma1 messenger RNA was readily detected in total RNA isolated from rabbit type II pneumonocytes cultured in the presence of cAMP, which causes enlargement of the prealveolar ducts, accelerates the rate of type II cell differentiation, and induces transcription of the major surfactant associated protein, surfactant protein-A. PPARgamma1 messenger RNA also was detected in total RNA isolated from rabbit adipose tissue but not from whole adult or fetal lung, heart, or liver. By Western blot analysis, PPARgamma protein expression was found to occur coincidentally with surfactant protein-A expression during lung type II cell differentiation. In view of the role of PPARgamma in adipocyte differentiation and lipid homeostasis, we postulate that PPARgamma1 induction by cAMP plays a role in the differentiation and expression of lipogenic enzymes in lung type II cells.

Regulation of mRNA levels for pulmonary surfactant-associated proteins in developing rabbit lung

Gene transcriptional activities and steady-state mRNA levels have been examined for the surfactant-associated proteins SP-A, SP-B and SP-C in developing rabbit lung. It was observed SP-C mRNA levels increase early in gestation, while SP-A and SP-B mRNA levels increase rapidly between 26 and 30 days gestation. Transcriptional activities for all three surfactant apoproteins increase between 26 and 30 days. Studies conducted with fetal lung explants of 26 days gestation demonstrated exposure to low doses of dexamethasone increases SP-A and SP-C mRNA levels, while high doses stimulate transcription, although this only significant for SP-C. Time course studies revealed different temporal patterns and glucocorticoid responses for SP-A and SP-C mRNAs. SP-A and SP-C mRNA production and steady-state levels were reduced after treatment with cycloheximide. In contrast, SP-B gene transcription was selectively stimulated, suggesting involvement of a labile negative regulatory factory. It is concluded that expression of the three surfactant apoproteins is independently regulated. Early in gestation, SP-C mRNA levels may be regulated in vivo through message stabilization. Glucocorticoids can affect SP-A and SP-C mRNA levels in culture at both transcriptional and post-transcriptional levels. The ability of glucocorticoids to influence these processes declines during fetal development.

Exposure of rabbit fetal lung to glucocorticoids in vitro does not enhance transcription of the gene encoding pulmonary surfactant-associated protein-B (SP-B)

We have investigated the ontogeny and hormonal regulation of both synthesis rates and cellular accumulation of the mRNA for surfactant-associated protein B (SP-B) in rabbit fetal lung. The developmental pattern for SP-B mRNA synthesis increased as a function of gestational age and paralleled that for SP-B mRNA levels except on days 22-26 of gestation where relatively higher levels of gene transcription were observed. Time-course studies with explants from 26- and 30-day fetal lung maintained in culture revealed a gradual increase in mRNA levels and a much smaller increase in gene transcription relative to adult values. Within 48 h of exposure of 26-day explants to dexamethasone at 10(-8) M there was a rapid increase in SP-B mRNA levels to 7-fold adult levels. A similar overall although somewhat slower and attenuated pattern was observed with 30-day explants. Dexamethasone at 10(-8) M had no effect on SP-B gene transcription with explants of either gestational age. We conclude that the major effect of dexamethasone treatment in vitro on SP-B mRNA levels appears to be post-transcriptional and there are small but distinct differences in the effects of glucocorticoids on SP-B mRNA levels with explant cultures from early and late stages of fetal lung maturation.

Dexamethasone up-regulates mannose receptor activity by increasing mRNA levels

The macrophage mannose receptor is highly susceptible to modulation by a variety of inflammatory and anti-inflammatory agents. Previous studies have demonstrated that mannose receptor activity is dramatically enhanced in rat bone marrow macrophages following treatment with dexamethasone. In the present study we have investigated potential mechanisms that might be involved in this up-regulation. Uptake of ligands by the mannose receptor was increased 2.5-fold in a dose- and time-dependent manner. Maximal stimulation was seen following treatment of macrophages with 0.1-1.0 microgram/ml of dexamethasone for 24-48 h. Dexamethasone treatment increased both the number of cell surface binding sites and total cellular binding activity to 250% of control levels. In addition, total receptor protein as measured by immunoprecipitation was increased 2.5-fold. Neither the maturation rate nor the turnover rate of the protein was altered by dexamethasone treatment. Using an oligonucleotide probe derived from sequence data from the cloned human receptor cDNA, we investigated the effect of dexamethasone on the expression of mannose receptor mRNA. Following incubation with dexamethasone for 12-24 h, the level of mRNA was significantly increased. These results demonstrate that dexamethasone treatment of rat bone marrow macrophages induces synthesis of new receptor protein through an increase in the level of mannose receptor mRNA.

Hormonal and developmental regulation of pulmonary surfactant synthesis in fetal lung

Pulmonary surfactant, a unique developmentally regulated, phospholipid-rich lipoprotein, is synthesized by the type II cells of the pulmonary alveolus, where it is stored in organelles termed lamellar bodies. The principal surface-active component of surfactant, dipalmitoylphosphatidylcholine, a disaturated form of phosphatidylcholine, acts in concert with the surfactant-associated proteins to reduce alveolar surface tension. Relatively large amounts of phosphatidylglycerol also are present in lung surfactants of a number of species, including man. The role of phosphatidylglycerol in surfactant function has not been elucidated; however, its presence in increased amounts in pulmonary surfactant is correlated with enhanced fetal lung maturity. Surfactant glycerophospholipid synthesis in fetal lung tissue is regulated by a number of hormones and factors, including glucocorticoids, prolactin, insulin, oestrogens, androgens, thyroid hormones, and catecholamines acting through cyclic AMP. In studies with human fetal lung in organ culture, we have observed that glucocorticoids, in combination with prolactin and/or insulin, increase the rate of lamellar body phosphatidylcholine synthesis and alter lamellar body glycerophospholipid composition to one reflective of surfactant secreted by the human fetal lung at term. Four surfactant-associated proteins, SP-A, SP-B, SP-C and SP-D, have recently been characterized. Recognition of their potential importance in the reduction of alveolar surface tension and in endocytosis and reutilization of secreted surfactant by type II cells has stimulated rapid advancement of knowledge concerning the structures of the surfactant proteins and their genes, as well as their developmental and hormonal regulation in fetal lung tissue. The genes encoding SP-A, SP-B and SP-C are expressed in a cell-specific manner and are independently regulated in fetal lung tissue during development. SP-A gene expression occurs exclusively in the type II cell and is initiated after 75% of gestation is complete. In the human fetus, expression of the SP-B and SP-C genes is detectable much earlier in development than SP-A, before the time of appearance of differentiated type II cells. It is apparent from studies using human and rabbit fetal lung in culture that cyclic AMP and glucocorticoids serve important roles in the regulation of SP-A gene expression. While the effects of cyclic AMP are exerted primarily at the level of gene transcription in human fetal lung tissue, glucocorticoids have stimulatory effects on SP-A gene transcription and inhibitory effects on SP-A mRNA stability. In addition, cyclic AMP and glucocorticoids act synergistically to increase SP-A gene transcription in human fetal lung in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of pulmonary surfactant protein synthesis in fetal lung: a major role of glucocorticoids and cyclic AMP

Augmented synthesis of the lipoprotein, pulmonary surfactant, is initiated in fetal lung toward the end of-gestation. Inadequate surfactant synthesis by the lungs of premature infants can result in respiratory distress syndrome, the leading cause of neonatal morbidity and mortality in developed countries. The surfactant-associated proteins act with surfactant glycerophospholipids to reduce alveolar surface tension, and mediate the reutilization of secreted surfactant components by type II cells. Genes encoding the surfactant proteins SP-A, SP-B, and SP-C have been isolated and characterized. Recent findings suggest that surfactant protein gene expression in fetal lung is under multifactortal control and is regulated by glucocorticoids, cAMP, growth factors, and insulin.

Analysis of parvovirus infections using strand-specific hybridization probes

The autonomous parvoviruses cause a broad spectrum of acute and chronic infections of animals and man. The discrimination of sites of viral replication from sites of viral sequestration is an important goal in elucidating the pathogenesis of these diseases. It is possible to employ strand-specific RNA hybridization probes in such analyses because a 'plus' sense probe will react with single stranded virion DNA and duplex replicative form DNA, but a 'minus' sense probe will react preferentially with obligate replicative intermediates (duplex replicative form DNA and mRNA). Strand-specific RNA hybridization probes were developed for the Aleutian mink disease parvovirus (ADV) and were used to study acute and chronic infections of mink. Such probes were capable of differentiating replicative intermediates (duplex replicative form DNA and mRNA) from single-stranded virion DNA in Southern blot analysis and in strand-specific in situ hybridization. ADV infection of seronegative newborn mink kits causes an acute, cytopathic infection of type II alveolar cells. Replication in these cells is highly permissive and is characterized by high levels of replicative intermediates and virion DNA. A fatal respiratory distress syndrome and hyaline membrane formation result from impaired surfactant production by the infected type II cells. On the other hand, ADV infection of adult mink is associated with a persistent infection and a disorder of the immune regulation. The target cells for viral replication in adult mink are confined to the lymphoid system and the bone marrow. Replication in these cells, which are probably lymphocytes, is restricted, and characterized by greatly reduced levels of replicative intermediates and virion DNA. It, therefore, seems that disease in the infected adult mink results from a restricted infection by ADV. Large amounts of virion DNA can also be demonstrated in locations where replication cannot be detected and apparently represents sequestration of virion particles by elements of the reticuloendothelial system. Thus, replication and sequestration can, in fact, be distinguished by the strand-specific in situ hybridization. These studies indicate that strand-specific in situ hybridization is a potentially valuable method for studying the pathogenesis of parvovirus infections.