Despite three decades of advancement in cancer treatment modalities, lung cancer remains a devastating disease with a 5 year survival rate of 10%. These grim facts point out the need for a radical change in our approach to this disease. Lung cancer "chemoprevention" is an exciting new strategy, and recent chemoprevention trials have revealed that retinoids are active in the prevention of lung cancer. This proposal will begin to examine mechanisms of retinoid-induced lung cancer chemoprevention. The hypotheses to be tested are: 1) retinoid receptor expression and function are altered in premalignant and malignant human bronchial epithelial (HBE) cells; 2) Retinoids induce different biologic effects in normal, premalignant, and malignant HBE cells; 3) Retinoid receptors mediate the effects of retinoids in HBE cells. These hypotheses will be tested through the completion of the following Specific Aims: 1) to study the expression and function of retinoid receptors (RAR and RXR gene families) in normal, premalignant, and malignant HBE cell lines and in biopsies of benign, dysplastic, and malignant bronchial tissue from patients. 2) to examine retinoid-induced changes in the growth and squamous differentiation of normal, premalignant, and malignant HBE cells; 3) to investigate the role of specific receptors in mediating retinoid actions in HBE cells. This proposal will involve the study of normal HBE cells grown from bronchial explants, a premalignant, virally- immortalized HBE cell line (BEAS-2B), and malignant HBE cell lines derived from BEAS-2B cells exposed to cigarette smoke condensate. To correlate findings from this carcinogenesis model to cancer patients, these studies will also involve lung tumor biopsies and adjacent benign lung as well as bronchial biopsies obtained from patients before and during retinoid treatment. Expression of receptors and squamous markers will be examined at the RNA and protein levels. To investigate receptor function, assays of receptor:DNA binding (gel shift analysis), transcriptional activation (transient transfection assays), and activated expression of receptor-controlled genes (Northern analysis) will be performed. Changes in cell growth will be investigated by measurements of S phase fraction (flow cytometry and incorporation of 3H-thymidine and bromodeoxyuridine). The role of specific receptors will be examined by transfection of expression vectors containing receptor cDNAs. Clinical studies have revealed exciting potential for retinoids as cancer preventive agents. To improve on the clinical outcome so far obtained with retinoid therapy, insights into mechanisms of retinoid-induced lung cancer chemoprevention must be developed. Preliminary data presented here demonstrate that alterations in receptor expression are associated with HBE neoplastic transformation. Completion of these Specific Aims will further reveal the role of receptors in the control of HBE cellular growth, differentiation, and tumorigenicity. These studies will provide a rationale for the development of new strategies for the prevention or treatment of lung cancer which are based on insight into mechanisms of retinoid effects in HBE cells.