Up‐regulation of DNA‐dependent protein kinase correlates with radiation resistance in oral squamous cell carcinoma

Abstract

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.

Radioresistant cervical cancer shows upregulation of the NHEJ proteins DNA-PKcs, Ku70 and Ku86

“…An increased expression of DNA-PKcs and Ku70 was observed in residual tumour, whereas the percentage of the Ku80-positive cells was similar in tumour tissue pre-and post RT. The results reported by Shintani et al (2003) are partly in accordance with ours, suggesting that upregulation of DNA-PKcs and Ku70 associates with radioresistance. However, the discrepancy with respect to Ku80 between the studies is not clearly understood but may be related to differences in treatment type, intracavitary vs EBRT, or to the effect of chemotherapy, which was given to half of Prior RT After RT Figure 1 (A -C) Positive immunohistochemical staining of Ku70 (A) in poorly differentiated squamous cell carcinoma, Ku86 (B) in glassy cell adenocarcinoma and p21 (C) in moderately differentiated adenocarcinoma of the cervix.…”

“…the patients in the study of Shintani et al (2003) Moreover, differences in tumour type as well as in the time span between end of RT and surgery may contribute. Several studies have been performed with the aim of identifying molecular markers that could predict RT response in cervical cancer (Fyles et al, 1998;Haensgen et al, 2001;Lee et al, 2005;Kim et al, 2006).…”

“…To our knowledge this is the first study of clinical cervical cancer in which DNA-PK complex expression has been examined in both primary and residual tumour tissue after RT. There is one study analysing DNA-PK proteins in oral squamous cell carcinoma tumours pre-and post RT (Shintani et al, 2003). In that study, patients were treated with external beam radiotherapy (EBRT) with a total mean dose of 32.9 Gy followed by surgery performed after 2 -3 weeks.…”

The life and death of DNA-PK

“…DNA-PK may also play a vital role in cellular responses to low amounts of radiation-induced damage (Vaganay-Juery et al, 2000;Marples et al, 2002), which make it an attractive molecular target. This is especially true given that several studies have reported that components of the DNA-PK complex are upregulated in cancer cells (Sirzen et al, 1999;Wilson et al, 2000;Zhao et al, 2000;Shintani et al, 2003). Radiation remains a highly effective means to target human tumor-specific death.…”

Musashi1 Impacts Radio-Resistance in Glioblastoma by Controlling DNA-Protein Kinase Catalytic Subunit

“…32 In glioma specimens, hyperactivity of this protein was associated with tumor grading 33 and radio-resistance, 34 and its up-regulation after radiation treatment has been associated with radio-resistance in recurrent oral squamous cell carcinomas. 35 Using a DNA-PK kinase assay and assessing the phosphorylation status of replication protein A 2, a previous study demonstrated IR-induced DNA-PK activity in glioblastoma cell lines. 36 This increased activity was correlated with the survival fraction of those cells after a 5-Gy dose of irradiation, which suggests the role of DNA-PK in radiation resistance.…”