Analysis of Radiosensitivity Mechanisms by Calcium Imaging and Proteomics

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K08100
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 52040:Radiological sciences-related
• Research Institution: The University of Tokyo
• Principal Investigator: Enomoto Atsushi 東京大学, 大学院医学系研究科(医学部), 講師 (20323602)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: Calcium / Calpain / MAPK family / radio-sensitization

Outline of Final Research Achievements

The aim of this study was to clarify how biochemical changes triggered by heat and radiation stimulate antitumor activity. Hyperthermia decreased the expression levels of MAP3K such as TAK1, RAF1, and MEKK2 but not the downstream MAP2K and MAPK members. The hyperthermia-induced degradation of TAK1 and MEKK2 was rescued by either the proteasome inhibitor MG132 or the calpain inhibitor ALLN; however, RAF1 was not affected by the inhibitors. Heat induced downregulation of RAF1. X-irradiation
did not significantly change the expression of MAPK family members. Hyperthermia increased [Ca2+]i and calpain I expression. An in vitro cleavage assay demonstrated that TAK1 and MEKK2 are calpain I substrates. Knockdown of TAK1, RAF1, and MEKK2 suppressed cell proliferation and clonogenicity. MAP3Ks such as TAK1, RAF1, and/or MEKK2 play crucial roles in cell proliferation and clonogenicity and are potential molecular targets for hyperthermia-induced radiosensitizaion.

Free Research Field

放射線生物学

Academic Significance and Societal Importance of the Research Achievements

古くから温熱療法は抗腫瘍効果や放射線による治療効果を亢進させる働きがあることが知られている。温熱に関してはタンパク質の変性を誘導するものの、何故、再合成や再構成が可能なタンパク質の一時的な構造的変化が細胞致死あるいは放射線増感を引き起こすのかは未解明な点が多い。本研究により、放射線で活性化し、細胞増殖を正に制御するRAF1、MEKK2をはじめ複数のMAP3ksが温熱処理により発現や活性が低下することが判明した。この発見は温熱感受性の重要な標的分子となるだけではなく、ハイパーサーミアが有効ではない部位におけるがん治療や放射線増感に向けた分子標的薬の開発につながることが期待される。