Study Of The Relationship Between Ku Protein Expression And Lung Cancer Drug Resistance

Ku autoantigen, which was composed of Ku70 and Ku80 subunits, as a DNA banding protein located in cell nucleus, is widely expressed in normal and tumor tissues. The main biological function of Ku protein is to repair injured DNA. When DNA double-strand breaks (DSBs) are caused by radiation or cell toxicant drug which is analogous to radiation, Ku70 and Ku80 right away form a heterodimer that binds to the end of injured DNA and activates Non-homologous end-joining (NHEJ) pathway to repair DSBs.As a primary participator, Ku has been implicated to be involved directly or indirectly in many other important cellular metabolic processes, such as V(D)J recombination of immunoglobulins and T-cell receptor genes, immnunoglobulin type-switching, DNA replication and transcription regulaton, and so on. Noticeablely, Ku70 also plays a important role in apoptosis regulation. Ku is thought to play a crucial role in maintance of chromosomal integrity and cell survival. Recent reports suggest that there is a positive relationship between Ku and the development and progression of cancer. Specifically, prior studies suggest that a delicate balance exists in Ku expression, that over-expression of Ku proteins promotes oncogenic phenotypes, including hyper-proliferation and resistance to apoptosis, whereas deficient or low expression of Ku leads to genomic instability and tumorigenesis.Lung cancer is one of the diseases most harmful to human health in our country. Now it almost accounts for a quarter of the tumor, whose incidence is highest in all kinds of cancer. And as air pollution and other environmental carcinogenic factors increasing, the incidence of lung cancer continues to rise high.Modern medical research has showed that cancer is a gene disease. When cells are attacked by environmental factors, such as smoking and other physical or chemical carcinogenic factors, DNA damage occurs, such as DNA double-strand breaks, gene mutation or translocation. When DNA repair mechanism disfunctions, gene expression will be changed in large scale, that tumor suppressor gene expression may be reduced, while oncogenes may be activated, which leads to loss of control over the cell cloning proliferation. This is an important mechanism of tumorigenesis. The crucial role Ku protein plays in the DNA repair process, decides Ku protein has the closely relationship with tumorigenesis. Current studies have showed that the excessive Ku70/Ku80 expression played an important role in this process. In our preliminary studies, we detected and compared Ku70/Ku80 mRNA expression level in lung cancer and normal lung tissues with RT-PCR. It showed that the Ku70/Ku80 mRNA expression was significantly upregulated in lung cancer group, that suggessed Ku protein's excessive expression may have the closely relationship with the occurrence of lung cancer.Since the majority of lung cancer took on a concealed progress, more than eighty percent of lung cancer patients belonged to advanced stage when diagnosed, that missed the best time of surgical intervention.Thus, radiotherapy and chemotherapy become more important in lung cancer treatment. But so far, the therapeutic efficacy of lung cancer is still not ideal. One of the most important reasons is tumor cells radiotherapy and chemotherapy resistance. So it is more concerned how to increase the of cancer cells'chemotherapy and radiotherapy sensitivity.Past studies have shown that the main mechanism of lung cancer chemotherapy includs of DNA damage and promotion of apoptosis. Rudin inhibited Bcl-2 expression, using antisense oligonucleotide agents, and fund a significant increase in lung cancer cells'sensitivity to chemotherapeutic drug, which confirmed that Bcl-2 excessive expression and bax expression suppression play an important role in lung cancer chemotherapy resistance. Neeru Khanna, who enhanceed Bax, P53 expression and inhibited Bcl-2, Bcl-XL, and survivin expression with S29, promoted apoptosis and increased drug sensitivity in human non-small cell lung cancer H520 cells.In addition to a main component and regulator of human DNA double-strand break repair mechanism, Ku protein also has influence on apoptosis, and is considered a new apoptosis inhibitory factor. It has following functions: 1) strengthens DSBs repair,2) inhibits DSBs induced apoptosis ,3) combines with Bax, and inhibits its translocation to mitochondria, that thereby inhibits Bax-mediated apoptosis. So Ku protein may have something to do with cancer radiotherapy and chemotherapy resistance. Past studies have shown that Ku protein expression closely related to the tumor resistance to radiation, which acts the similar way with some kinds of chemotherapeutic drug to kill tumor cells by creating DSBs,such as Cisplatin, bleomycin,and so on. And radiotherapy resistance could be reversed by inhibiting Ku expression.So more and more researchers are concerned in the with the relationship of Ku and cancer chemotherapy resistance. Kim's study found that, Ku70-/- and Ku80-/- showed mice significantly higher sensitivity to Bleomycin, cytarabine and VCR's cell killing effect, and the cells with over- expression of Ku70 and Ku80 showed tolerance to bleomycin. Shen found that Ku70 expression levels were significantly increased in doxorubicin resistant cervical cancer cells. Kim found that Ku70 and Ku80 expression increased greatly in the VCR resistant human lymphocytic leukemia CEM cells. However, the relationship between Ku and the highest incidence tumor --lung cancer's chemotherapy resistance has still not been reported.This study is to detect and compare Ku70/Ku80 protein expression ratios in normal lung tissue, non-drug-resistant and drug-resistance lung cancer tissues using immunohisto -chemical staining technology, to comfirm the relationship between Ku expression and lung cancer chemotherapy resistance.Experimental Methods: Ku70/Ku80 protein expression status was tested using immunohistochemical staining technology, in 10 cases of normal lung tissue, 25 cases of non-drug-resistant lung cancer tissues from our hospital and 12 cases drug-resistant lung cancer tissues from Jilin Provincial Tumor Hospital. Ku70/80 staining positive cells in every 100 cells were counted. Experimental results:(1) Ku70 and Ku80 protein are expressed both in normal lung tissues and in lung cancer tissues, mainly distributed in the nucleus. (2) Compared to normal lung tissues, the number of Ku70/80 positive cells was markedly increased in lung cancer tissues, the difference is statistically significant, P <0.01; (3) Compared to non-resistant lung cancer, the number of Ku70/80 positive cells was markedly increased in drug resistant lung cancer tissues, the difference is statistically significant, P <0.01.Experimental conclusions: (1) Ku70/80 protein are expressed both in normal lung tissues and in lung cancer tissues. (2) Ku70/80 protein expressing ratio is significantly increased in lung cancer tissues than in normal lung tissues.It showed that increasing expression of Ku70/80 protein maybe one important mechanism of lung cancer genesis. (3) Ku70/80 protein expressing ratio is significantly increased in drug resistance lung cancer tussues than in non-resistance tissues, suggesting that Ku70/80 excessive expression has close relationship with lung cancer drug resistance. Therefore it may be helpful for lung cancer's early diagnosis, prognosis prospect, chemotherapy sensitivity monitoring and chemotherapy efficacy estimate, to test Ku protein expression quantity. It also may be helpful for clinical antitumor treatment select. It provides theoretical foundation for researches to reverse chemotherapy resistance by gene therapy taking Ku as target gene.