The cytochrome P450 isoenzyme CYP1A1 is intimately involved in the metabolic activation of pulmonary procarcinogens, and its expression is induced by components found in tobacco smoke condensate. The CYP1A1 gene has been implicate as a risk factor in the etiology of lung cancer in heavy cigarette smokers. The role of human CYP1A1 in lung carcinogenesis was analyzed at the following levels: A. General regulatory patterns in neoplastic and non-neoplastic lung. Oligonucleotide directed mutagenesis (ODM) of regulatory region DNA and subsequent transfection experiments are being carried out with a panel of human non-small cell lung cancer (NSCLC) cell lines. Distinct patterns as well as strikingly different basal (non-induced) levels of CYP1A1 gene expression have been characterized, thus extending the observations by McLemore et al. To date, we have identified two potential classes of alteration that may account for the elevated basal levels of CYP1A1 gene expression observed in NSCLC. B. Activator-repressor interactions. We have identified one CYP1A1 gene regulatory element that, upon alteration via ODM, resulted in an increased level of expression of the gene--suggestive of an interaction with a repressor. Work is continuing on the identification of additional regulatory elements. C. Feedback modulation. In murine derived hepatoma cell lines, the CYP1A1 gene product, aromatic hydrocarbon hydroxylase (AHH) was shown to play an autoregulatory role in CYP1A1 gene expression. We are investigating the possibility that, in some NSCLC lines, the elevated basal levels of CYP1A1 gene expression observed may be due to a similar mechanism. D. Proto-oncogene interaction. Preliminary studies have identified a potential interaction between the regulatory region of the CYP1A1 gene and the proto-oncogenes c-fos and c-jun. The significance of the project is to elucidate the interactive role of genetically determined factors and chemical carcinogens in pulmonary carcinogenesis. The results will have diagnostic and prevention applications.
