The nucleotide excision repair pathway in human peripheral blood lymphocytes as a potential market for cancer development

Exposure to cigarette smoke is a well established cause of lung cancer. Although significant progress has been made in treating many types of cancer, lung cancer remains among the most difficult to treat and is a leading cause of death in the world. This is a particular problem in Kentucky which has one of the highest rates of lung cancer in the nation. In the 5th congressional district in southeastem Kentucky, the high incidence of lung cancer does not appear to be explained by only exposure to cigarette smoke and other agents may act in concert with Cigarette smoke to elevate it (1).. One hypothesis is that interactions between carcinogens present in cigarette smoke and certain heavy metals present in contaminated drinking water (2, 3) playa role in the inordinately high incidence of lung cancer found in these regions of the state (4) .. Alternatively or perhaps in addition there may be genetiC components that interact with cigarette smoke to greatly elevate lung cancer incidence .. This area of research is a major focus of the Lung Cancer Initiatives Group in the Markey Cancer Center at the University of Kentucky. It is well established that compounds present in Cigarette smoke introduce DNA damage (5, 6) Many types of DNA damage that likely playa role in lung carcinogenesis are removed by the nucleotide excision repair (NER) pathway .. The NER pathway is an important cellular DNA repair pathway that recognizes and removes a wide spectrum of different modifications to DNA ranging from those introduced by carcinogens present in Cigarette smoke to those introduced by exposure to UV light (7). We have recently found that exposure of human lung cells in culture to either cigarette smoke condensate, an experimental surrogate for Cigarette smoke, or arsenic inhibits the NER pathway and significantly reduces the expression of XPC (detected at the level of protein and mRNA) that is required for DNA damage recognition during NER We hypothesize that cigarette smoke and specific heavy metals present in the environment such as arsenic inhibit the nucleotide excision repair pathway and this inhibitory effect is important in the etiology of lung cancer .. Reduced NER would increase the persistence of DNA adducts formed in the lung by exposure to cigarette smoke and therefore increase mutation formation which is a driving force in carcinogenesis .. We also hypothesize that chronic exposure to these agents results in systemic suppression of nucleotide excision repair that can be detected in peripheral lymphocytes isolated from blood samples .. Lastly, because XPC decreases in parallel with NER efficiency in cigarette smoke condensate- and arsenic-treated cells, we hypothesize that XPC might serve as a key biomarker for NER efficiency .. XPC protein has been found to be expressed approximately 10-fold less than several other key NER proteins and it has been suggested to be a rate limiting protein in NER (8). XPC is required at an early step of NER, DNA damage recognition, and hence, down regulation or limited availability of XPC would likely result in a reduction in NER efficiency. To begin to test these hypotheses we propose: Aim t To examine, in parallel, NER efficiency and XPC expression in lymphocytes obtained from a random human population. Aim 18. To standardize conditions to reproducibly measure NER efficiency and XPC protein and mRNA in human peripheral blood lymphocytes Aim 1b .. To compare NER efficiency with XPC protein and mRNA levels in 100·200 different lymphocyte samples.