Type I collagen formation in rat type II alveolar cells immortalised by viral gene products

Abstract

Background - Alveolar type II (T2) cells synthesise matrix proteins such as type IV collagen and fibronectin. In contrast, a fetal rat T2 cell line has been shown to synthesise type I and III collagen as well as type IV collagen. To study regulation of collagen production in T2 cells, neonatal T2 cells immortalised by adenoviral 12SE1A gene transfer were used. It was previously reported that this immortalised cell line (E1A-T2) retains epithelial features such as tight junctions and cytokeratins but also expresses mesenchymal features such as vimentin. Methods - Collagen production was examined in E1A-T2 and primary neonatal T2 cells using polyacrylamide gel electrophoresis. Electron microscopy was used to examine collagen deposition in E1A-T2 cell culture. To define the mechanism by which α1(I) type I collagen gene expression was activated in E1A-T2 cells, a deletional analysis of α1(I) promoter constructs linked to the bacterial chloramphenicol acetyltransferase gene was performed. Results - E1A-T2 cells produced large amounts of type I collagen with a predominance of α1(I) homotrimers; α2(I) peptides were detected only in the cell layer. In contrast, primary neonatal rat T2 cell cultures produced a trace amount of type I collagen. Production of α1(I) peptide chains (per μg DNA) in E1A-T2 cell cultures was 30 times higher than that observed in primary neonatal T2 cell cultures. Electron microscopy showed deposition of type I collagen fibrils in the extracellular matrix of E1A-T2 cell cultures. Transfection studies suggested at least two cis-acting elements which mediate increased α1(I) gene expression in E1A-T2 cells. Conclusions - These studies indicate that the E1A-T2 cell line may be useful for studying type I collagen gene regulation in alveolar T2 cells. These findings also raise the possibility that viral activation of type I collagen genes in alveolar epithelium may be involved in certain forms of pulmonary fibrosis.