Relationship between thyroid tumor radiosensitivity and nuclear localization of DNA-dependent protein kinase catalytic subunit.

Ichiro Horie,Katsuya Matsuda,Kazuko Shichijo,Kiyoto Ashizawa,Makoto Ihara,Masahiro Nakashima,Ryota Otsubo,Takashi Kudo

doi:10.1093/jrr/rraa032

Abstract

Thyroid tumors are the most common types of endocrine malignancies and are commonly treated with radioactive iodine (RAI) to destroy remaining cancer cells following surgical intervention. We previously reported that the expression levels of double-stranded DNA-dependent protein kinase catalytic subunit (DNA-PKcs), which plays a key role in non-homologous end joining, are correlated with the radiosensitivity of cancer cells. Specifically, cells expressing high levels of DNA-PKcs exhibited radiation resistance, whereas cells expressing low levels were sensitive to radiation treatment. In this study, we observed full-length native DNA-PKcs (460 kDa) in radiation-resistant FRO and KTC-2 cells through western blot analysis using an antibody against the C-terminus of DNA-PKcs. In contrast, cleaved DNA-PKcs (175 kDa) were observed in radiation-sensitive TPC-1 and KTC-1 cells. Almost equal amounts of DNA-PKcs were observed in moderately radiation-sensitive WRO cells. We also describe a simple method for the prediction of radiation therapy efficacy in individual cases of thyroid cancers based on staining for DNA-PKcs in human cancer cell lines. Immunofluorescent staining showed that native DNA-PKcs was localized largely in the cytoplasm and only rarely localized in the nuclei of radiation-resistant thyroid cancer cells, whereas in radiation-sensitive cancer cells a 175-kDa cleaved C-terminal fragment of DNA-PKcs was localized mainly inside the nuclei. Therefore, DNA-PKcs moved to the nucleus after γ-ray irradiation. Our results suggest a new method for classifying human thyroid tumors based on their cellular distribution patterns of DNA-PKcs in combination with their radiosensitivity.

Highlights

Thyroid tumor cells have been shown to incorporate radioactive iodine for clinical purposes, no studies have reported the relationship between the clinical endpoint and expression of double-stranded DNA-dependent protein kinase (DNA-PK) in thyroid tumor cells
The concentration of native DNA-PKcs band differed between the five different thyroid cancer cell lines
A clear native DNA-PKcs band was observed in radiation-resistant FRO and KTC-2 cells, whereas only a weak band was observed in radiation-sensitive TPC-1 and KTC1 cells

Summary

Introduction

Thyroid tumor cells have been shown to incorporate radioactive iodine for clinical purposes, no studies have reported the relationship between the clinical endpoint and expression of double-stranded DNA-dependent protein kinase (DNA-PK) in thyroid tumor cells. Thyroid cancers are the most common endocrine malignancy and consist of three major types: papillary carcinoma, follicular carcinoma and anaplastic carcinoma. All of these malignancies are derived from thyroid follicular cells. Papillary carcinoma are the most common (80–90%), followed by follicular carcinoma (5–10%) [1, 2]. The prognosis and treatment of thyroid cancers depend on the tissues involved. Anaplastic carcinomas comprise only 1– 3% of all thyroid cancers, they account for 14–50% of all thyroid cancerrelated mortality [3]

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