Adenocarcinoma is the major histologic type of lung cancer diagnosed. However, identification of the genes and pathways underlying the development of this tumor type lags behind knowledge for other histologic types of lung cancers. The major hypothesis of this proposal is that tumor suppressor genes (TSGs) shown to be inactivated by CpG island promoter methylation are involved in the initiation and development of adenocarcinoma. Furthermore, the frequency for inactivation and thus, the involvement of specific TSGs will vary depending on carcinogen exposure. These hypothesis will be tested by examining adenocarcinomas associated with exposure to cigarette smoke either directly or through environmental tobacco smoke and radiation in the form of radon progeny and arising in the central or peripheral lung, locations where carcinogen deposition may differ. The fact that the type of damage inflicted on DNA differs between these exposures as well as the deposition patterns within the lung suggests that the mechanisms for tumor induction may also be divergent. This supposition has been confirmed in our laboratory; inactivation of the estrogen receptor by CpG island methylation was greater in never-smokers than smokers and greater in rodent tumors induced by radiation than by the tobacco-specific nitrosamine NNK, while inactivation of the p16/INK4a (p16) gene by methylation was greater in rodent tumors induced by NNK than by radiation. Our studies also indicated that alterations in expression of cytosine DNA-methyltransferase (DNA-MTase) may be integrally linked to the aberrant CpG island methylation and may play a critical role in neoplastic development. The samples selected to test our hypothesis are 240 adenocarcinomas located either centrally or peripherally within the lung from smokers, former uranium miners, or never smokers. The four TSGs selected p16, ER, HIC-1, and E-cadherin, are all inactivated by methylation and involved in adenocarcinoma. Gene status will be evaluated at the protein (immunohistochemistry) and gene level (copy number and methylation state). Expression levels of DNA-MTase will be determined and related to methylation status of these four TSGs. Our studies have also detected p16 methylation in pre-malignant lesions indicating that silencing of these gene may be one of the initiating steps in adenocarcinoma development. Thus, we will also test in a more mechanistic manner the hypothesis of this proposal. The timing for increased DNA-Mtase activity and methylation of the p16 and ER genes will be directly examined in a target cells (alveolar type II) for adenocarcinoma following exposure of rats to specific carcinogens. These studies will identify genes involved in adenocarcinoma., time key methylation changes during adenocarcinoma, and provide an animal model in which to test intervention and prevention therapies directed against these genetic changes.
Showing the most recent 10 out of 33 publications
