Role Of DNA Repair Proteins In Lung Cancerogenesis

Lung cancer, one of the most common malignant tumor in the world, is the main reason of deaths caused by cancers in patients, especially in males. Datas published by WHO show that lung cancer is a globally important cancer either in morbility or in mortality. Also our country is predicted to be a leading country of lung cancers in the 21st country. Lung cancers include tumors derived from tracheas, bronchias and pulmonary epithelium, and its pathological types include squamous carcinoma, adenocarcinoma, large cell carcinoma (generally called non-small cell lung carcinoma, NSCLC) and small cell lung carcinoma. Besides smoking, lung cancer positive family history is considered to be a risk factor. The transformations of genes include the frequent mutation of p53 gene, the activating point mutation of KRAS oncogene, the frequent deletion and abnormal transcription of FHIT gene heterozygote, also the deletion and transcriptional silence of P16 homozygote, which is a CDK repressor. The increasing risk of lung cancers is related to the polymorphism of specific cytochrome P450 genes, the defect of DNA repair ability including DNA bases excision repair genes XRCC1, PARP-1 and ERCC4.DNA is the most important hereditary substance in living creatures. The cellular stress response caused by DNA damage has a significance for protecting DNA stability, repressing gene mutations and maintaining cells' life span. Like other malignant tumors, the generating process of NSCLC is a complex process with mutiple factors, mutiple stages and mutiple steps. Its main machanisms result from the combined action of the activation of oncogenes and the inactivation of tumor suppressor genes, the hypofunction and deletion of DNA damage repair genes, and some signaling pathways caused by a variety of factors.DNA damage repair genes play an important role in maintaining the integrity and stability of hereditary genes, and also preventing cell cancerization. Our study mainly discusses the relativity between lung cancer patients and the expressions of DNA damage repair proteins such as Mre11 and Ku80. Moreover, we construct a mouse lung cancer cell line deleting DNA damage repair protein PARP-1 and then develop a cell evaluating platform for further studies of clinically anticarcinoma drugs.Methods:1. We test the expressions of DNA damage repair proteins in human lung cancer tissues by immunohistochemistry, do the statistical analysis by the non-parametric test and then evaluate the relativity between the expressions of protein Mre11, Ki67 and the patients' sexes, ages, clinical stages and pathological classifications.2. We use the PARP-1 knocked-off mouse lung cancer model to do the primary culture, and then identify this PARP-1 knocked-off cell line by morphological observation, the analysis of immunofluorescence and tumorigenicity.Results:1. By the analysis of immunohistochemistry and statistics, there is no apparent relativity (P>0.05) between the expressions of protein Mrell, Ki67 and the patients' sexes, ages, pathological classifications and tumor sizes(TNM classification). However, the expressions of those proteins become lower in stage I lung adenocarcinoma organization, and then their expressions become higher with the progression of the tumor. The peak values of the expression of protein Mre11 and Ki67 are at stage II lung adenocarcinoma organization, and then their expressions become lower again in stage III lung adenocarcinoma organization. These datas show a significant difference in statistics (P<0.05), and suggest that DNA damage repair protein Mre11 is related to the generating process of lung cancers.2. We establish an effective method of primary culture in mouse lung cancer cells.3. We successfully aquire two primary lung adenocarcinoma cell lines in mice, with a typical character of epithelium in both light and electron microscope. Transplant tumor inoculation test in nude mice shows that those epithelial origin of cells have tumorigenicity.Conclusions:1. By the analysis of immunohistochemistry, it indicates that there is a notable relativity (P<0.05) between the expression of DNA damage repair protein Mrell and the clinical stages in human lung adenocarcinoma. According to the expression rule in every stage, it's suggested that Mre11 may repress the process of lung adenocarcinoma; however, there is no apparent relativity (P>0.05) between the expressions of protein Ki67 and the patients' sexes, ages, clinical stages, TNM classification and pathological differentiation degree.2. We successfully establish a primary lung adenocarcinoma cell line deleted PARP-1 in mice, and prove the cause of tumorigenicity. The establishment of this cell line provides a platform for studying clinically anticarcinoma drugs.