Data Sheet 1_IGF1R promotes radiation-induced HSCs activation by regulating DNA-PKcs-mediated DNA damage repair.docx

Introduction Ionizing radiation (IR)-induced liver fibrosis is one of the most serious complications of radiotherapy for liver cancer, and the core of its development lies in the activation of hepatic stellate cells (HSCs). The insulin-like growth factor 1 receptor (IGF1R) is commonly known as a growth-promoting kinase receptor that plays a critical role in cell differentiation and tissue reorganization, as well as in promoting the activation of HSCs, tentatively. Additionally, there has been a resurgence of interest in its role in DNA damage repair; nevertheless, the underlying mechanism remains poorly understood. Considering that DNA damage and repair are the most serious radiation injury events, the aim of this study was to explore the mechanism of IGF1R in the activation of HSCs by regulating DNA damage repair.
Method and resultsIn this study, we first confirmed that IR induced the activation of HSCs, along with DNA damage and the upregulation of DNAdependent protein kinase catalytic subunit (DNA-PKcs) and IGF1R expressions. Then we indicated that the radiation-induced activation of HSCs and DNA damage repair were promoted by the activation or overexpression of IGF1R, either alone or together with DNA-PKcs activation, mechanistically through IGF1R–DNAPKcs interactions. The process is primarily facilitated by the nuclear translocation of IGF1R, which promotes PRKDC transcription at the mRNA level. Moreover, it involves an interaction with DNA-PKcs in the cytoplasm at the protein level, which, in turn, facilitates the entry of DNA-PKcs into the nucleus and subsequent promotion of DNA damage repair.
DiscussionOur findings suggest that the inhibition of the IGF1R-promoted, DNA-PKcs-dependent non-homologous end joining (NHEJ) repair mode is a promising strategy to prevent the activation of HSCs. To the best of our knowledge, the present study is pioneering in its exploration of the mechanism by which IGF1R mediates radiation-induced activation of HSCs by regulating DNA-PKcs.

【引言】电离辐射（Ionizing radiation, IR）诱导的肝纤维化是肝癌放疗最严重的并发症之一，其发病核心为肝星状细胞（hepatic stellate cells, HSCs）的活化。胰岛素样生长因子1受体（insulin-like growth factor 1 receptor, IGF1R）是公认的促生长激酶受体，在细胞分化、组织重构中发挥关键作用，且初步研究显示其可促进HSCs活化。此外，学界近年重新关注其在DNA损伤修复中的功能，但其具体调控机制仍未明确。鉴于DNA损伤与修复是辐射损伤最核心的事件，本研究旨在探讨IGF1R通过调控DNA损伤修复介导HSCs活化的具体机制。
【方法与结果】本研究首先证实，电离辐射可诱导HSCs活化，同时引发DNA损伤，并上调DNA依赖蛋白激酶催化亚基（DNA-dependent protein kinase catalytic subunit, DNA-PKcs）与IGF1R的表达水平。随后研究表明，单独激活或过表达IGF1R，或联合激活DNA-PKcs，均可通过IGF1R与DNA-PKcs的相互作用，促进辐射诱导的HSCs活化及DNA损伤修复进程。该过程主要依赖IGF1R的核转位：IGF1R可在mRNA水平促进PRKDC基因的转录；同时在蛋白质层面，IGF1R可与细胞质中的DNA-PKcs发生相互作用，进而促进DNA-PKcs入核，最终加速DNA损伤修复。
【讨论】本研究结果显示，抑制IGF1R介导的、依赖DNA-PKcs的非同源末端连接（non-homologous end joining, NHEJ）修复通路，是阻断HSCs活化的潜在有效策略。据我们所知，本研究首次探索了IGF1R通过调控DNA-PKcs介导辐射诱导HSCs活化的具体机制，具有开创性意义。