NEOPLASTIC TRANSFORMATION BY CRYSTALLINE SILICA AND OTHER MINERALS

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Studies were continued on cells derived from the fetal rat lung alveolar epithelial cell line, FRLE, in which neoplastic transformation can be directly induced by quartz particles, without mediation by mesenchymal cells. The patterns of expression of TGF-beta mRNAs and proteins were reported in quartz-transformed cells and derived tumors. Additional tumorigenicity assays in nude mice were performed for quartz-treated and control cells. New studies were undertaken in order to investigate quartz-induced transformation mechanisms in mature alveolar epithelial cells derived from young adult rather than fetal rat lungs. Since rat alveolar type II cells usually cannot be maintained in culture for more than a few passages, they were transfected with plasmids containing immortalizing genes (either SV40 T antigen or adenovirus 2 E1A) and/or a selective marker. Transfected colonies, selected for morphological characteristics of epithelial polygonal cells forming pavement-like colonies, were expanded and cryopreserved at passage 5. These new cell lines have been passaged 15 times so far, and have maintained normal morphology. Characterization of the new cell lines and studies of quartz-induced cytotoxicity and transformation are under way. The SV40Tag-transfected cell line showed a much higher sensitivity to quartz-induced toxicity than the E1A-transfected cell line.