Lecithin biosynthesis in a clonal line of lung adenoma cells with type II alveolar cell properties

Priming With Rhinovirus Protects Mice Against a Lethal Pulmonary Coronavirus Infection

Rhinoviruses (RV) have been shown to inhibit subsequent infection by heterologous respiratory viruses, including influenza viruses and severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). To better understand the mechanisms whereby RV protects against pulmonary coronavirus infection, we used a native murine virus, mouse hepatitis virus strain 1 (MHV-1), that causes severe disease in the lungs of infected mice. We found that priming of the respiratory tract with RV completely prevented mortality and reduced morbidity of a lethal MHV-1 infection. Replication of MHV-1 was reduced in RV-primed mouse lungs although expression of antiviral type I interferon, IFN-β, was more robust in mice infected with MHV-1 alone. We further showed that signaling through the type I interferon receptor was required for survival of mice given a non-lethal dose of MHV-1. RV-primed mice had reduced pulmonary inflammation and hemorrhage and influx of leukocytes, especially neutrophils, in the airways upon MHV-1 infection. Although MHV-1 replication was reduced in RV-primed mice, RV did not inhibit MHV-1 replication in coinfected lung epithelial cells in vitro. In summary, RV-mediated priming in the respiratory tract reduces viral replication, inflammation, and tissue damage, and prevents mortality of a pulmonary coronavirus infection in mice. These results contribute to our understanding of how distinct respiratory viruses interact with the host to affect disease pathogenesis, which is a critical step in understanding how respiratory viral coinfections impact human health.

Lung epithelial cells have virus-specific and shared gene expression responses to infection by diverse respiratory viruses

The severity of respiratory viral infections is partially determined by the cellular response mounted by infected lung epithelial cells. Disease prevention and treatment is dependent on our understanding of the shared and unique responses elicited by diverse viruses, yet few studies compare host responses to viruses from different families while controlling other experimental parameters. Murine models are commonly used to study the pathogenesis of respiratory viral infections, and in vitro studies using murine cells provide mechanistic insight into the pathogenesis observed in vivo. We used microarray analysis to compare changes in gene expression of murine lung epithelial cells infected individually by three respiratory viruses causing mild (rhinovirus, RV1B), moderate (coronavirus, MHV-1), and severe (influenza A virus, PR8) disease in mice. RV1B infection caused numerous gene expression changes, but the differential effect peaked at 12 hours post-infection. PR8 altered an intermediate number of genes whose expression continued to change through 24 hours. MHV-1 had comparatively few effects on host gene expression. The viruses elicited highly overlapping responses in antiviral genes, though MHV-1 induced a lower type I interferon response than the other two viruses. Signature genes were identified for each virus and included host defense genes for PR8, tissue remodeling genes for RV1B, and transcription factors for MHV-1. Our comparative approach identified universal and specific transcriptional signatures of virus infection that can be used to distinguish shared and virus-specific mechanisms of pathogenesis in the respiratory tract.

Strain a Mouse Lung Tumor Bioassay

This report summarizes data on the testing of 228 chemicals for carcinogenic activity by the strain A mouse lung adenoma bioassay. The assay is of six months duration and can distinguish two-fold dose differences in carcinogenic potential of compounds from a variety of chemical classes. Most compounds that induced lung tumors in strain A mice have also evoked a neoplastic response in other experimental animal bioassays and/or demonstrated mutagenic activity in various short-term tests. Recommendations are made for future studies on the: (a) distribution and metabolism of chemicals in strain A mouse lung tissue and in specific lung cell types, (b) ability of the lung adenoma bioassay to detect promoting agents, and (c) use of the bioassay to investigate the interactions of more than one chemical.

cDNA isolation, genomic structure, regulation, and chromosomal localization of human lung Kruppel-like factor

Lung Kruppel-like factor (LKLF) is a zinc finger transcription factor critical for embryonic development. We have previously identified and isolated the mouse LKLF gene and examined its role using gene targeting. In this report, we describe the isolation and molecular characterization of the human homolog of murine LKLF. The human and mouse LKLF homologs exhibit an 85% nucleotide identity and share 90% amino acid similarity. Furthermore, the 5' sequence in the proximal promoter region and 3' untranslated region are also conserved between the two species. Of particular interest is the finding that while sequences in the proximal promoter have diverged between mouse and human, a region of 75 nucleotides is essentially identical. Site-directed mutagenesis in this region impairs the ability of the LKLF promoter to drive reporter gene expression, indicating that it represents a novel transcriptional element important in the regulation of LKLF gene expression. The activation domain is highly proline-rich and, similar to mouse LKLF, contains 22% proline residues. The human LKLF transcriptional unit is located in a genomic region of approximately 3 kb on chromosome 19p13.1. This region of chromosome 19 is known to contain genes involved in various human diseases. Like mouse LKLF, human LKLF consists of three exons that are interrupted by two small introns. The locations of intron/exon boundaries and splice sites are conserved between two homologs. Northern analysis shows that LKLF is expressed in lung in addition to heart, skeletal muscle, placenta, and pancreas. The isolation and chromosomal mapping of human LKLF will make it possible to initiate studies devoted to assess the involvement of this gene in human disease(s).

Characterization of the lung Krüppel-like transcription factor gene and upstream regulatory elements

We previously described the isolation and characterization of the cDNA for lung Krüppel-like factor (LKLF), a zinc finger transcription factor that is predominately expressed in the lung of adult mice. In this study, we report the complete structure and nucleotide sequence of the mouse LKLF gene, which is comprised of three exons and two small introns. Moreover, the identification of critical sequence elements required for expression is described using reporter constructs with the LKLF promoter transfected into LA-4 lung cells. Results from these constructs reveal an important region for transcriptional activity that lies between the -490/-72bp upstream sequence. This region contains two canonical Sp1 binding sites that affect expression levels in a non tissue-specific manner. In addition, using a base-pair mutagenesis strategy, a region from -157/-72bp was found to be necessary for upregulating expression. In transfection assays, mutations of the -138/-111bp region resulted in approximately 70-80% loss of promoter activity. This cis-element does not appear to correspond to any known transcription factor consensus sequence. Moreover, mutations within this cis-region disrupt the binding of a protein complex from nuclear extracts of various tissues.

Introduction to mouse lung tumorigenesis

This article provides a brief overview of some of the characteristics of lung tumors in mice and their application for studies in both chemical and molecular carcinogenesis and in cancer chemoprevention. The reader is referred to the above-mentioned review articles, and the articles to follow in this issue, for more extensive discussions of mouse lung tumorigenesis. It has been very exciting and rewarding to observe the progress made by many dedicated scientists in the field of mouse lung tumorigenesis during the past several years, and I hope that the next few years will be even more exciting.

Mouse lung epithelial cell lines--tools for the study of differentiation and the neoplastic phenotype

Several dozen lung epithelial cell lines have been established in culture over the past 20 years from normal lung explants and their spontaneous transformants, and from lung tumors that arose spontaneously or were induced with chemicals, viruses, or oncogenic transgenes. To provide information from which to choose appropriate lines for investigating problems in lung cell biology and pulmonary neoplasia, this review describes the origins of these lines and some of their characteristics. These include growth, morphology, tumorigenicity, ability to metastasize, xenobiotic metabolism, mutational status, signal transducing activities, cytogenetics, ability to form domes, and electric conductance. In addition to collecting this information in a single place for the first time, we describe previously unpublished apoptosis features of some of these lines. An increasing number of investigations are beginning to use these lines and this review contains references into 1997.

Lung tumors in strain A mice: application for studies in cancer chemoprevention

Strain A mice develop a high incidence of spontaneous lung tumors during their lifetime. These tumors may be found in some animals as early as 3 to 4 weeks of age, increasing to nearly 100% by 24 months of age. The strain A mouse is also highly susceptible to the induction of lung tumors by several classes of chemical carcinogens and has been used extensively as a mouse lung tumor bioassay for assessing the carcinogenic activity of a variety of chemicals. In addition to its use in carcinogen detection, the strain A mouse lung tumor model has been employed extensively for the identification of inhibitors of chemical carcinogenesis. A number of chemopreventive agents including beta-naphthoflavone, butylated hydroxyanisole, ellagic acid, phenethyl isothiocyanate, phenylpropyl isothiocyanate, phenylbutyl isothiocyanate, phenylhexyl isothiocyanate, indole-3-carbinol, etc., have been shown to inhibit chemically induced lung tumors in strain A mice. In most instances, inhibition of lung tumorigenesis has been correlated with effects of the chemopreventive agent on the metabolic activation and/or detoxification of carcinogens. To date, no chemopreventive agent has been shown to inhibit lung tumorigenesis in strain A mice when administered after the carcinogen, i.e., during the promotion/progression stages of tumor development. Efforts should be made to develop a standardized protocol in strain A mice for evaluating chemopreventive agents as inhibitors of both the initiation and progression stages of lung tumor development.

Derivation of tumorigenic and non-tumorigenic mouse alveolar type-II cell lines from fetal type-II cells after a combined in vivo/in vitro carcinogen treatment

Alveolar type-II cells were isolated from the lungs of fetuses (day 18 of gestation) of the A/WySnAf (A/Sn) mouse strain, which were treated in utero at day 15 with the directly-acting carcinogen N-ethyl-N-nitrosourea (ENU). The isolated type-II cells were again treated with ENU during their initial growth in vitro. After a prolonged culture period, 5 cell lines were obtained, which were identified as type-II cell lines. Differences between cell lines were found with respect to contact-inhibited growth, cell doubling time and ability to grow in a serum-free medium. Two out of the 5 cell lines produced highly invasive type-II cell carcinomas after s.c. injection of 5 x 10(6) cells into nude mice. Thus, both tumorigenic and non-tumorigenic mouse alveolar type-II cell lines were derived after this combined in vivo and in vitro carcinogen treatment of fetal mouse alveolar type-II cells. This offers the possibility of studying in vitro the factors thought to influence lung tumorigenesis in vivo. In addition, our findings strongly suggest that alveolar type-II cells are the progenitor cells of malignant mouse lung tumors.

Phospholipid-transfer activities in cytosols from lung, isolated alveolar type II cells and alveolar type II cell-derived adenomas

We have examined phospholipid-transfer activities in cytosols from rat and mouse whole lung, isolated rat alveolar type II cells and alveolar type II cell-derived mouse pulmonary adenomas. We report an enrichment in phosphatidylcholine and phosphatidylglycerol (but not phosphatidylinositol) protein-catalysed transfer in the type II cell and adenoma cytosols compared with the whole-lung cytosols. The activities from these cytosols were resolved using column chromatofocusing, which clearly demonstrated the presence of a phosphatidylcholine-specific transfer protein in each of the four tissues. In addition, two proteins (rat) or three proteins (mouse) catalysing both phosphatidylcholine and phosphatidylglycerol transfer were resolved from whole lung, whereas in both the rat isolated alveolar type II cells and the mouse type II cell-derived adenomas one of these less specific proteins is not present.

Lymphocytic infiltration of bronchioloalveolar adenomas in mice

The proportion of mouse lung adenomas with associated lymphocytes was examined in relation to tumor histology, location within the lung, tumor invasiveness and surface lymphocyte markers. The highest proportion of lymphocyte positive tumors was found on the pleural surface in contact with lymphatics. Seventy eight percent of pleural Clara cell but only 16% of alveolar cell adenomas were positive for lymphocytes (P less than 0.001). The majority of tumor associated lymphocytes were Ig-positive, either IgG (53%) or IgA (45%). No correlation was found between lymphocytic infiltration and tumor invasiveness. Our data suggest that the affinity of lymphocytes for Clara cell adenomas may be determined by intrinsic differences between the two tumors rather than to biologic behavior.

Phospholipid composition and ultrastructure of A549 cells and other cultured pulmonary epithelial cells of presumed type II cell origin

In order to assess the usefulness of A549, L-2, and AK-D cell lines as model systems for alveolar type II cells, we compared their phospholipid composition to that of fibroblasts grown under similar conditions. The percentage of disaturated phosphatidylcholine and phosphatidylglycerol, key phospholipids of purified surface-active material, was the same in epithelial cells and fibroblasts. When A549 cells were maintained in serum-free media for two days, ultrastructural examination showed an increase in cytoplasmic lamellar inclusions but there was no change in the percentage of disaturated phosphatidylcholine or phosphatidylglycerol. Because the lipid content of these cultured cells was very different from that of freshly isolated rat type II cells, we conclude that their suitability as model cell systems for type II cells is questionable.