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To study mechanisms of cell proliferation by asbestos and nonasbestos fibers, we examined the effects of these agents on the mRNA levels of c-fos and c-jun and ornithine decarboxylase (ODC) in hamster tracheal epithelial (HTE) cells and rat pleural mesothelial (RPM) cells, the progenitor cells of bronchogenic carcinoma and mesothelioma, respectively. In comparison with crocidolite asbestos, increases in c-jun mRNA were less striking in HTE cells after exposure to man-made vitreous fiber-10 (MMVF-10) or refractory ceramic fiber-1 (RCF-1). No c-fos mRNA was detected in HTE cells after exposure to particulates, but exposure of HTE cells to H2O2 caused striking increases in c-fos and c-jun, which preceded increases in ODC mRNA. Increases in ODC mRNA were also observed in HTE cells after exposure to nonasbestos fibers, whereas only crocidolite asbestos caused elevations in ODC mRNA in RPM cells. In RPM cells, crocidolite and chrysotile asbestos caused increases in mRNA levels of both c-fos and c-jun. No increases in proto-oncogene induction were observed using MMVF-10 or RCF-1 at nontoxic concentrations (< or = 5 micrograms/cm2 dish). Moreover, erionite, a fiber extremely potent in the causation of mesothelioma in humans, caused more dramatic elevations in c-fos and c-jun. Nonfibrous particles (riebeckite, polystyrene beads) did not alter proto-oncogene expression in these cell types, suggesting that the fibrous geometry of particulates is critical in the induction of c-fos and c-jun.