A GT Box Element Is Essential for Basal and Cyclic Adenosine 3',5'-Monophosphate Regulation of the Human Surfactant Protein A2 Gene in Alveolar Type II Cells: Evidence for the Binding of Lung Nuclear Factors Distinct from Sp1

Direct exposure methods for testing native atmospheres

In vitro studies of adverse cellular effects induced by inhalable substances face a number of problems due to the difficulties in exposing cultured cells of the respiratory tract directly to test atmospheres composed of complex gases and particulate compounds. This paper discusses the characteristics of in vitro work and summarizes the use of different in vitro technologies to determine the adverse effects of inhaled pollutants. The exposure of cells to test atmospheres requires accurate control of the pollutant levels, as well as the close contact of cells and gas without interfering with the medium. Systems which rely on the solution of the gas in the medium overlay do not resemble the exposure conditions in vivo, and may not be suitable for studying, for example, the effects of poorly soluble gases. Exposure to gases or complex mixtures can be performed with roller bottles or flasks on rotating and rocking platforms and, using these techniques, the cells are periodically exposed to the test atmosphere. However, the most promising approach is based on a biphasic cell culture technique, where cells are grown on microporous membranes at an air-liquid interface. Here the cells are nutrified from the basal side of the membrane whilst the apical part with the cultivated cells is in direct contact with the test atmosphere. Based on this culture technique, different exposure systems have been developed and these are described and discussed. Exposure of cells from the respiratory tract to gases or particles is responsible for cell injury or cell activation associated with an overexpression of mRNA and the release of bioactive mediators. Therefore, in vitro studies using such a strategy, in combination with relevant and efficient exposure devices, open up new ways to test native complex gases and aerosols. Furthermore, such an experimental approach is not only suitable for cultivated cells, but it can also be used for exposing bacteria to inhalable test compounds. It is possible to analyze the mutagenic potency of in- and outdoor pollutants and several attempts have been made to determine the induction of revertants in a modified Ames assay after exposure to single gases or complex mixtures.

BR22, a novel protein, interacts with thyroid transcription factor-1 and activates the human surfactant protein B promoter

Surfactant protein (SP)-B expression is restricted to type II pneumocytes and Clara cells in the lung. Previously, a promoter region of human SP-B gene from -64 to -118 has been identified as critical for the tissue-specific expression of this gene. Two cis-elements for thyroid transcription factor (TTF)-1 and hepatocyte nuclear factor (HNF)-3alpha binding were found within this area. Using an oligonucleotide fragment, we incorporated this region sequence into the promoter of a HIS3 reporter gene in yeast. With this modified yeast a human lung complementary DNA (cDNA) library was screened for DNA-binding proteins, other than TTF-1 and HNF-3alpha, that interacted with this promoter segment. A cDNA clone encoding a novel polypeptide, BR22, was identified that activated the reporter gene expression in yeast. This gene is expressed in many tissues and encodes a protein with bipartite nuclear localization signals. Studies using in vivo yeast two-hybrid analysis, in vitro protein-protein interactions, and coimmunoprecipitation analyses demonstrated that BR22 formed a protein complex with TTF-1. In vivo cotransfection studies further indicated that BR22 could act with TTF-1 to synergistically activate the SP-B promoter in mammalian cells. Our data suggest that BR22 is a TTF-1-associated protein. Through a protein-protein interaction with TTF-1, BR22 can form a complex and activate the human SP-B promoter in vivo.

Involvement of Sp1 in the transcriptional regulation of the rat insulin-like growth factor-1 gene

Most insulin-like growth factor-I (IGF-I) transcripts are initiated in exon 1, but mechanisms of regulation are not well understood. Since potential Sp1 sites are found in footprinted regions within approximately 360 bp upstream and downstream from the major initiation sites in exon 1, we explored the involvement of Sp1 and Sp3 in regulation of IGF-1 expression. Gel shift assays showed strong Sp1 binding to the downstream site, but binding to the upstream site was weak; Sp1 bound to a CCTGCCCA sequence in downstream footprint region V, and Sp3 binding was centered on the same sequence. IGF-I basal promoter constructs containing a mutation in the downstream Sp1 site exhibited a 32% decrease in expression in CHO cells and a 75% decrease in HepG2 cells, indicating the importance of Sp1 for expression in vivo. Sp1 and Sp3 expression vectors provided three- to five-fold stimulation of wild-type IGF-I constructs, but had little effect on a construct containing a mutation in the downstream Sp1 site, and Sp1 had comparable effects in Drosophila SL2 cells. IGF-I heterologous promoter constructs exhibited similar responses: in both SL2 cells and CHO cells, stimulation by Sp1 was enhanced with constructs containing downstream region V. Since Sp1 also stimulated expression of concatamers of putative cis-acting sites fused to the SV40 promoter enhancer in pGL3, the results in combination indicate that the presence of IGF-I region V is sufficient to permit stimulation by Sp1.

CONCLUSION

Sp1 and related factors may play an important role in the regulation of IGF-I gene transcription, through interactions with region V downstream from the major initiation sites in exon 1.

Disruption of the klotho gene causes pulmonary emphysema in mice. Defect in maintenance of pulmonary integrity during postnatal life

Homozygous mutant klotho (KL(-/-)) mice exhibit multiple phenotypes resembling human aging. In the present study, we focused on examining the pathology of the lungs of klotho mice and found that it closely resembled pulmonary emphysema in humans both histologically and functionally. Histology of the lung of KL(-/-) mice was indistinguishable from those of wild-type littermates up to 2 wk of age. The first histologic changes appeared at 4 wk of age, showing enlargement of the air spaces accompanied by destruction of the alveolar walls, and progressed gradually with age. In addition to these changes, we observed calcium deposits in type I collagen fibers in alveolar septa and degeneration of type II pneumocytes in 8- to 10-wk-old KL(-/-) mice. Pulmonary function tests revealed prolonged expiration time in KL(-/-) mice, which is comparable with the pathophysiology of pulmonary emphysema. The expression level of messenger RNA for type IV collagen, surfactant protein-A and mitochondrial beta-adenosine triphosphatase was significantly increased in KL(-/-) mice, which may represent a compensatory response to alveolar destruction. Additionally, the heterozygous mutant klotho mice also developed pulmonary emphysema late in life, around 120 wk of age. These findings indicate that klotho gene expression is essential to maintaining pulmonary integrity during postnatal life. The klotho mutant mouse is a useful laboratory animal model for examining the relationship between aging and pulmonary emphysema.