DESCRIPTION Exposure of the human lung to environmental particulates and gases contributes to a variety of diseases, including pulmonary fibrosis and cancer. Previous work in our research group has shown that asbestos, reactive oxygen species (ROS), and reactive nitrogen species (RNS) trigger specific cell signaling pathways in target cells of the lung, leading to activation of transcription factors such as AP-1 and NF-KB. These and other transcription factors are involved in cellular decisions leading to phenotypic changes involved in the initiation of lung disease. To extend our understanding of cellular responses to mixtures of chemical and physical agents, we propose to study the effects of chrysotile asbestos and nitrogen dioxide (NO2), either alone or together, on three endpoints of exposure: cell survival, cell cycle progression, and apoptosis. First, we will characterize the responses of rat lung epithelial (RLE) cells and rat lung fibroblasts (RLF) to asbestos and/or N02, in regard to the activation of the transcription factors AP-1, NF-KB, and E2F and their downstream target genes. Activation of cyclin-dependent kinases (CDKs), metabolism of their protein inhibitors (i.e., CKIs p15, pl6, pl8, p2l, and p27),and phosphorylation of retinoblastoma family proteins (pRB and pl3O) will be studied as regulators of cell cycle progression. Cell imaging techniques, flow cytometry and activation of proteases will be used to measure apoptotic responses. Transient expression of dominantnegative regulatory molecules will be used to dissect mechanisms of exposure responses. For physiological relevance, results from experiments using models for cell cycle control and apoptosis in Vitro will be verified by inhalation studies using mice. Finally, to test the contributions of specific proteins such as p53, CKIS, and other candidate cell cycle regulators in cell cycle activation and/or apoptosis by asbestos and N02, inhalation studies will be performed in transgenic mice lacking specific genes of interest. Dissection of the role of cell cycle and survival regulators in proliferative and apoptotic responses to the combined effects of asbestos and N02 may lead to new biomarkers for exposure of the human lung to chemical mixtures.