Cell-specific and developmental regulation of rabbit surfactant protein B promoter in transgenic mice

Regulation of lung injury and fibrosis by p53-mediated changes in urokinase and plasminogen activator inhibitor-1

Alveolar type II epithelial cell (ATII) apoptosis and proliferation of mesenchymal cells are the hallmarks of idiopathic pulmonary fibrosis, a devastating disease of unknown cause characterized by alveolar epithelial injury and progressive fibrosis. We used a mouse model of bleomycin (BLM)-induced lung injury to understand the involvement of p53-mediated changes in urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1) levels in the regulation of alveolar epithelial injury. We found marked induction of p53 in ATII cells from mice exposed to BLM. Transgenic mice expressing transcriptionally inactive dominant negative p53 in ATII cells showed augmented apoptosis, whereas those deficient in p53 resisted BLM-induced ATII cell apoptosis. Inhibition of p53 transcription failed to suppress PAI-1 or induce uPA mRNA in BLM-treated ATII cells. ATII cells from mice with BLM injury showed augmented binding of p53 to uPA, uPA receptor (uPAR), and PAI-1 mRNA. p53-binding sequences from uPA, uPAR, and PAI-1 mRNA 3' untranslated regions neither interfered with p53 DNA binding activity nor p53-mediated promoter transactivation. However, increased expression of p53-binding sequences from uPA, uPAR, and PAI-1 mRNA 3' untranslated regions in ATII cells suppressed PAI-1 and induced uPA after BLM treatment, leading to inhibition of ATII cell apoptosis and pulmonary fibrosis. Our findings indicate that disruption of p53-fibrinolytic system cross talk may serve as a novel intervention strategy to prevent lung injury and pulmonary fibrosis.

Transcriptional regulation of SP-B gene expression by nitric oxide in H441 lung epithelial cells

Surfactant protein B (SP-B) is essential for the surface tension-lowering function of pulmonary surfactant. Surfactant dysfunction and reduced SP-B levels are associated with elevated nitric oxide (NO) in inflammatory lung diseases, such as acute respiratory distress syndrome. We previously found that NO donors decreased SP-B expression in H441 and MLE-12 lung epithelial cells by reducing SP-B promoter activity. In this study, we determined the roles of DNA elements and interacting transcription factors necessary for NO inhibition of SP-B promoter activity in H441 cells. We found that the NO donor diethylenetriamine-nitric oxide adduct (DETA-NO) decreased SP-B promoter thyroid transcription factor 1 (TTF-1), hepatocyte nuclear factor 3 (HNF-3), and Sp1 binding activities but increased activator protein 1 (AP-1) binding activity. DETA-NO decreased TTF-1, but not Sp1, levels, suggesting that reduced TTF-1 expression contributes to reduced TTF-1 binding activity. Lack of effect on Sp1 levels suggested that DETA-NO inhibits Sp1 binding activity per se. Overexpression of Sp1, but not TTF-1, blocked DETA-NO inhibition of SP-B promoter activity. DETA-NO inhibited SP-B promoter induction by exogenous TTF-1 without altering TTF-1 levels. DETA-NO decreased TTF-1 mRNA levels and gene transcription rate, indicating that DETA-NO inhibits TTF-1 expression at the transcriptional level. We conclude that NO inhibits SP-B promoter by decreasing TTF-1, Sp1, and HNF-3 binding activities and increasing AP-1 binding activity. NO inhibits TTF-1 levels and activity to decrease SP-B expression. NO inhibition of SP-B expression could be a mechanism by which surfactant dysfunction occurs in inflammatory lung diseases.

Rat aquaporin-5 4.3-kb 5'-flanking region differentially regulates expression in salivary gland and lung in vivo

We previously cloned a 4.3-kb genomic fragment encompassing 5'-flanking regulatory elements of rat aquaporin-5 (Aqp5) that demonstrated preferential transcriptional activity in lung and salivary cells in vitro. To investigate the ability of Aqp5 regulatory elements to direct transgene expression in vivo, transgenic (TG) mice and rats were generated in which the 4.3-kb Aqp5 fragment directed the expression of enhanced green fluorescent protein (EGFP). RT-PCR revealed relative promoter specificity for the lung and salivary glands in TG mice. Immunofluorescence microscopy showed strong EGFP expression in salivary acinar cells but not in lung type I (AT1) cells, both known sites of endogenous AQP5 expression. Similar results were obtained in TG rats generated by lentiviral transgenesis. EGFP mRNA was detected in both salivary glands and lung. Robust EGFP fluorescence was observed in frozen sections of the rat salivary gland but not in the lung or other tested tissues. The percentage of EGFP-positive acinar cells was increased in parotid and submandibular glands of TG rats receiving a chronic injection of the beta-adrenergic receptor agonist isoproterenol. EGFP-positive cells in the lung that were also reactive with the AT1-cell specific monoclonal antibody VIIIB2 were identified by flow cytometry. These findings demonstrate that the 4.3-kb Aqp5 promoter/enhancer directs strong cell-specific transgene expression in salivary gland and low-level AT1 cell-specific expression in the lung. While these Aqp5 regulatory elements should be useful for functional studies in salivary glands, additional upstream or intronic cis-active elements are likely required for robust expression in the lung.

The murine SP-C promoter directs type II cell-specific expression in transgenic mice

Genomic DNA from the mouse pulmonary surfactant protein C (SP-C) gene was analyzed in transgenic mice to identify DNA essential for alveolar type II cell-specific expression. SP-C promoter constructs extending either 13 or 4.8 kb upstream of the transcription start site directed lung-specific expression of the bacterial chloramphenicol acetyl transferase (CAT) reporter gene. In situ hybridization analysis demonstrated alveolar cell-specific expression in the lungs of adult transgenic mice, and the pattern of 4.8 SP-C-CAT expression during development paralleled that of the endogenous SP-C gene. With the use of deletion constructs, lung-specific, low-level CAT activity was detected in tissue assays of SP-C-CAT transgenic mice retaining 318 bp of the promoter. In transient and stable cell transfection experiments, the 4.8-kb SP-C promoter was 90-fold more active as a stably integrated gene. These findings indicate that 1) the 4.8-kb SP-C promoter is sufficient to direct cell-specific and developmental expression, 2) an enhancer essential for lung-specific expression maps to the proximal 318-bp promoter, and 3) the activity of the 4.8-kb SP-C promoter construct is highly dependent on its chromatin environment.

The CCT promoter directs high-level transgene expression in distal lung epithelial cell lines

Gene therapy requires the presence of a robust and yet small promoter to drive high-level expression of desired proteins. In comparative analysis, we investigated the promoter strength of the CTP:phosphocholine cytidylyltransferase promoter (CCT alpha) with other commonly used promoters, which were all cloned into a similar background vector (PGL3 basic). Transient promoter-reporter assays in murine lung epithelial (MLE-12) cells revealed that the core CCT alpha promoter (240 bp) was observed to exhibit a 40-fold, 8-fold, and 3-fold higher level of activity compared with the simian virus 40, human cytomegalovirus, and Rous sarcoma virus promoters, respectively. The CCT alpha promoter was significantly more active than the Clara cell 10, thymidine kinase, and phosphoglycerate kinase promoters. This pattern of high-level expression for CCT alpha was detected primarily in cell lines of distal lung epithelial origin (MLE-12, RLE, H441) and was reduced in other cell lines (A549, CHO, HepG 2). CCT alpha promoter-reporter activity, CCT alpha transcript levels, and immunoreactive protein levels increased significantly in the presence of all-trans retinoic acid. The CCT alpha promoter, in a retinoic acid-inducible manner, efficiently directed expression of murine erythropoietin in MLE-12 cells. Collectively, these observations suggest that the CCT alpha construct might be useful to drive high-level, regulatable expression of heterologous proteins in alveolar epithelia.

Nitric oxide inhibits surfactant protein B gene expression in lung epithelial cells

Surfactant protein B (SP-B) is an essential constituent of pulmonary surfactant. In a number of inflammatory diseases of the lung, elevated nitric oxide (NO) levels are associated with decreased SP-B levels, suggesting that reduced SP-B levels contribute to lung injury. In this study, we investigated the effects of NO on SP-B gene expression in H441 and MLE-12 cells, cell lines with characteristics of bronchiolar (Clara) and alveolar type II epithelial cells, respectively. Results show that NO donors decreased SP-B mRNA levels in a concentration- and time-dependent manner in H441 and MLE-12 cells. The NO donors also antagonized dexamethasone induction of SP-B mRNA in H441 cells. NO donor inhibition of SP-B mRNA was blocked by the transcriptional inhibitor 5,6-dichloro-1-beta-D-ribofuranozyl-benzimidazole. NO donors decreased luciferase expression from a reporter plasmid containing -911/+41 bp of human SP-B 5'-flanking DNA in H441 and MLE-12 cells, indicating inhibitory effects on SP-B promoter activity. NO inhibition of SP-B mRNA levels was not blocked by LY-83583 and KT-5823, inhibitors of soluble guanylate cyclase and protein kinase G, respectively. Furthermore, cell-permeable cGMP analog 8-bromo-cGMP had no effect on SP-B mRNA levels. These data indicate that elevated NO levels negatively regulate SP-B gene expression by inhibiting gene transcription and that NO inhibits SP-B gene expression independently of cGMP levels. These data imply that reduced SP-B expression due to elevated NO levels can contribute to lung injury.

Human surfactant protein B promoter in transgenic mice: temporal, spatial, and stimulus-responsive regulation

Surfactant protein B (SP-B) is a developmentally and hormonally regulated lung protein that is required for normal surfactant function. We generated transgenic mice carrying the human SP-B promoter (-1,039/+431 bp) linked to chloramphenicol acetyltransferase (CAT). CAT activity was high in lung and immunoreactive protein localized to alveolar type II and bronchiolar epithelial cells. In addition, thyroid, trachea, and intestine demonstrated CAT activity, and each of these tissues also expressed low levels of SP-B mRNA. Developmental expression of CAT activity and SP-B mRNA in fetal lung were similar and both increased during explant culture. SP-B mRNA but not CAT activity decreased during culture of adult lung, and both were reduced by transforming growth factor (TGF)-beta(1). Treatment of adult mice with intratracheal bleomycin caused similar time-dependent decreases in lung SP-B mRNA and CAT activity. These findings indicate that the human SP-B promoter fragment directs tissue- and lung cell-specific transgene expression and contains cis-acting elements involved in regulated expression during development, fetal lung explant culture, and responsiveness to TGF-beta and bleomycin-induced lung injury.

Lung surfactant protein B promoter function is dependent on the helical phasing, orientation and combinatorial actions of cis-DNA elements

Surfactant protein B (SP-B), a hydrophobic protein of lung surfactant, is essential for surfactant function, normal respiration and survival. SP-B is expressed in a cell-type specific manner by the alveolar type II and bronchiolar (Clara) epithelial cells of the lung and is developmentally induced. Our previous studies showed that the activity of the rabbit SP-B minimal promoter (-236/+39 bp) is dependent on the binding of an array of transcription factors including Sp1, Sp3, thyroid transcription factor 1, hepatocyte nuclear factor 3 and activating transcription factor/cyclic AMP response element binding protein. The SP-B minimal promoter sequence as well as the spacing and orientations of cis-DNA elements are conserved in human, rabbit and mouse SP-B genes. In the present study, we investigated the importance of spacing and orientation of cis-DNA elements on SP-B promoter function in NCI-H441 cells, a human cell line of Clara cell lineage. Further we investigated the effects of transcription factors on SP-B promoter expression by co-transfection experiments. Results showed that disruptions of helical phasing and orientation of cis-DNA elements reduced SP-B promoter activity indicating that proper alignment and orientation of cis-DNA elements are necessary for SP-B promoter function. Co-transfection experiments showed that transcription factors function in a combinatorial rather than in a synergistic manner to enhance SP-B promoter activity.

Identification of a novel DNA regulatory element in the rabbit surfactant protein B (SP-B) promoter that is a target for ATF/CREB and AP-1 transcription factors

Surfactant protein B (SP-B) is required for the maintenance of biophysical properties and physiological function of pulmonary surfactant. SP-B is expressed in a cell/tissue-specific manner by the alveolar type II and bronchiolar (Clara) epithelial cells of the lung and is developmentally and hormonally regulated. We previously identified a minimal promoter region containing -236/+39 base pairs (bp) of rabbit SP-B gene that is necessary and sufficient for high level promoter activity in NCI-H441 cells, a cell line with characteristics of Clara cells. In this study, we have characterized the functional importance of a novel DNA regulatory element, termed SP-B CRE, with the sequence TGAGGTCA in the SP-B minimal promoter. The SP-B CRE sequence shared homology to cyclic AMP responsive element (CRE) binding sequence and contained an overlapping nuclear receptor element binding half-site. Mutation of SP-B CRE into a scrambled sequence reduced promoter activity by greater than 70%, whereas mutation into a palindromic consensus CRE increased the promoter activity by 100%. Electrophoretic mobility shift assay (EMSA) and Western immunoblot analysis of affinity purified proteins interacting with SP-B CRE showed that it is a target for binding of members of the activating transcription factor (ATF)/cyclic AMP response element binding protein (CREB) family of transcription factors, such as CREB, CREM, ATF-1, ATF-2 as well as c-Jun and TTF-1. Overexpression of CREB, ATF-2 and c-Jun inhibited SP-B promoter activity in NCI-H441 cells. These data have shown that members of the ATF/CREB family of transcription factors and c-Jun play important roles in mediating the transcriptional regulation of the SP-B gene.