Crystalline silica-induced lung carcinomas in rats (a unique model for fibrosis-associated lung cancer) originate from alveolar type II epithelial cells. In order to study the effects of silica in these target cells, a recently developed cell line of fetal rat lung alveolar type II epithelium (FRLE/2G3) was chosen. This line was obtained from Dr. M. A. Haralson, Dept. of Pathology, Vanderbilt University, in whose laboratory it was established by outgrowth from lung explants of 20-day fetal Sprague-Dawley rats, followed by two subsequent cloning procedures (Leheup, B.P. et al., Lab. Invest. 60:791-807, 1989). In present studies, this line was found to grow well in various culture conditions and under exposure to silica and other dusts. The cells formed colonies of tightly juxtaposed polygonal cells, grew rapidly to confluent monolayers and then developed discrete areas of multilayered elevated ridges. Different samples of crystalline silica induced low toxicity, but marked inhibition of growth rate. By scanning and transmission electron microscopy, untreated and silica-treated FRLE cells showed characteristic lamellar bodies of alveolar type II epithelia, desmosomes and a few surface villi. The distribution of the lamellar bodies was shown by localization of the specific fluorescent dye Phosphine 3R. Penetration of silica particles occurred directly through gaps in the cell membrane and by internalization in the cytoplasm, mostly in membrane-bound vesicles. Destruction of cytoplasmic organelles was found around some particles. Some particles were found adjacent to the nuclear membrane or to mitochondria. Cytogenetic analysis and karyotypes of the FRLE/2G3 cells showed a ploidy distribution of 85% with 70-80 chromosomes and 15% with 140 or more chromosomes. Two marker chromosomes were present in all karyotypes. No significant differences from controls were found in the karyotypes of cells exposed to silica for 5 weeks. These silica-treated cells were not tumorigenic in nude mice. A selective transformation assay is being developed with these cells following their transfection with oncogenes.
