Construction of a DNA double-strand break model and its application to studies of DNA repair and low dose irradiation effects

2018 Fiscal Year Final Research Report

• Project/Area Number: 25340044
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Risk sciences of radiation and chemicals
• Research Institution: National Institute of Health Sciences
• Principal Investigator: Honma Masamitsu 国立医薬品食品衛生研究所, 変異遺伝部, 部長 (30250179)
• Research Collaborator: Yasui Manabu ; Suzuki Tetsuya ; Sassa Akira
• Project Period (FY): 2013-04-01 – 2019-03-31
• Keywords: DNA修復 / 放射線防護 / 低線量モデル / 発がん

Outline of Final Research Achievements

As a model for low dose radiation, I developed a system that generates only one DNA double-strand breaks (DSB)DSB in the human cell genome using a restriction enzyme I-SceI site. This system revealed that a DSB mainly causes small deletions by non-homologous end joining (NHEJ). Involvement of homologous recombination (HR) was less than 10% of the whole. In addition, in order to elucidate the mechanism of genome integrity, I focused on recombination repair between chromosomes. I constructed BLM knocked out (KO) cells using genome editing technology in the system. In BLM-KO cells, the enhancement of spontaneous HR frequency, cross-type gene conversion, non-cross-type long gene conversion, and deletion were frequently observed. BLM was considered to be involved in the maintenance of Holliday structure, and the defect destabilizes Holliday structure, leading to the deletion and recombination of the genome in a large area.

Free Research Field

放射線生物学

Academic Significance and Societal Importance of the Research Achievements

放射線はゲノムに対して最も重篤であるDNA二本鎖切断（DSB）を誘発し、それが、がんの主たる要因と考えられているが、放射線はそれ以外の損傷（酸化ストレス、一本鎖切断等）も引き起こすため、DSBの修復機構や、がん化への関与の研究は非常に困難である。本研究では制限酵素に注目し、たった一つのDSBをヒト細胞のゲノム中に発生させる究極の低線量モデルを世界で始めて構築した。これによりDSBには閾値が存在せず、高い確率で突然変異を誘発することを明らかにし、放射線のリスク評価の考えを前進させた。