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DNA-PK is a nuclear protein with serine/threonine kinase activity and forms a complex consisting of the DNA-PKcs and a heterodimer of Ku70 and Ku80 proteins. Recent laboratory experiments have demonstrated that the DNA-PK complex formation is one of the major pathways by which mammalian cells respond to DNA double-strand breaks induced by ionizing radiation. In this study, we evaluated the relationship between expression levels of DNA-PKcs, Ku70 and Ku80 proteins and radiation sensitivity in oral squamous cell carcinoma (OSCC) cell lines and in OSCC patients treated with preoperative radiation therapy. The OSCC cell lines greatly differed in their response to irradiation, as assessed by a standard colony formation assay. However, the expression levels of the DNA-PK complex proteins were all similar, and there was no association between the magnitude of their expression and the tumor radiation sensitivity. Expression of DNA-PK complex proteins increased after radiation treatment, and the in- he DNA-PK complex is one of the major pathways by which cells respond to DNA double-strand breaks (DSBs). The DNA-PK complex consists of a heterodimer comprising 70-and 80-kDa proteins termed Ku and a 465-kDa serine/ threonine protein kinase catalytic subunit termed DNA-PKcs. 1)The Ku (p70/p80) component functions as an activator of the catalytic subunit, and also represents the major double-stranded DNA binding protein.1, 2) DNA-PK plays an important role in the repair of DSBs and in V(D)J recombination.3) Tumor cell lines defective in the expression of either Ku or DNA-PKcs exhibit marked radiation sensitivity. Cells lacking DNA-PK activity because of defects in DNA-PK components, such as human malignant glioma M059J cells and cells derived from scid mice, show hypersensitivity to ionizing radiation.3-7) These previous laboratory findings suggested that DNA-PK is a candidate as a predictor of cellular radiation sensitivity. There is, however, little information on the expression of DNA-PK in primary human tumors and the correlation, if any, with radiation sensitivity, though the results are not definitive. [8][9][10][11] Therefore, the aim of this study is to evaluate the relationship between expression levels of DNA-PK complex proteins and radiation sensitivity. Materials and MethodsCell culture. All SCC cell lines were grown in Ham/F12: DMEM (1:1) supplemented with 10% fetal bovine serum, 24 µg/ml adenine, 0.4 µg/ml hydrocortisone and 50 units/ml penicillin and streptomycin. The HSC2, HSC3 and HSC 4 cell lines were provided by Japanese Collection Research Bioresources. The SCC15, SCC25, SCC66 and SCC111 cell lines were provided by Dr.

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Cyclins and cyclin-dependent kinases (CDKs) play key roles in cell cycle regulation, a process of which dysregulation can lead to uncontrolled cell growth and hence to cancer. We have already reported the alteration of CDK4 and cyclin D1 expression in oral cancer. In this study, we examined by immunohistochemistry the expression of CDK2, and cyclins A and E in 20 normal oral mucosa, 42 dysplastic epithelia, and 103 oral squamous cell carcinomas (SCCs). The expressions of CDK2, and cyclins A and E were not detected in the normal epithelium and significantly altered from epithelial dysplasia to SCC. While there were no significant correlations between the expression of cyclins A, E and the patients' survival, CDK2 expression was significantly correlated with lymph node involvement (P = = = =0.025), tumor differentiation (P = = = =0.032), mode of tumor invasion (P = = = =0.017), and shorter survival period (P = = = =0.0173). These results suggest that the elevated expression of CDK2 is a critical factor in oral cancer progression and can be used as a negative predictive marker of the patients' prognosis. Key words: CDK2 -Cyclin A -Cyclin E -Oral cancer -PrognosisCell proliferation is ultimately dependent on cell cycle control, and the decision to continue to proliferate is made mainly during G1 phase as a result of the activities of G1 cyclins and cyclin-dependent kinases (CDKs) complexes.1-8) Among those kinases that regulate G1 progression, CDK4 and CDK6 are activated by association with cyclin D in the mid G1.9, 10) CDK2 is activated by binding to cyclin E, and its activity is essential for transition through the restriction point in the late G1. 7,8,11,12) Subsequently, cyclin A is expressed and is thought to be required, in association with CDK2, for progression through the S phase.13) Amplification and/or overexpression of cyclin E has been reported in colorectal, breast, lung, ovarian and uterus carcinomas.14-22) Overexpression of cyclin A has been reported in lung 20) and uterus carcinomas. 22) In the head and neck, amplification of cyclin D in oral squamous cell carcinoma (SCC) has recently been reported. 23,24) There are few reports on CDK2, and cyclins A and E in oral SCC, and the molecular events that underlie the histological progression are not well understood. In this study, we focused our attention on the G1/S and S to G2 transitions in the cell cycle and examined by immunohistochemistry the expression of CDK2, as well as its regulatory partners, cyclins A and E, in oral premalignant lesions and cancers. We also performed western blot analysis in matched sets of tumors and normal tissues. Furthermore, we analyzed the relationship between the expressions of CDK2 and cyclins A and E, and the clinicopathological parameters and patients' survival outcome. MATERIALS AND METHODSPatients Tissue samples of 20 normal oral mucosa specimens, 42 epithelial dysplasia specimens, and 103 oral SCC patients were investigated. The patients underwent surgery at the Department of Oral and Maxillofacial Surgery II, Okay...

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