DNA损伤应答（DDR）依赖于蛋白质翻译后修饰（PTM）来调控放射敏感性。棕榈酰化是一种重要的PTM，但在DDR及乳腺癌放射敏感性中的作用尚未见报道。Porcupine (PORCN) 是内质网膜O-棕榈酰转移酶，介导Wnt蛋白棕榈酰化。前期研究发现PORCN部分存在于细胞核中并参与DDR，同时发现PORCN核定位序列在DDR中起关键作用。PORCN可与非同源重组修复蛋白Ku70结合，并介导由辐射诱导的Ku70棕榈酰化。基于此，提出细胞核内PORCN通过棕榈酰化Ku70调控DNA损伤修复的科学设想。拟从Ku70是否为PORCN直接底物、Ku70棕榈酰化位点鉴定及其在DDR及乳腺癌放射敏感性的调控作用等方面，在细胞、荷瘤鼠、转基因鼠水平研究核内PORCN介导的棕榈酰化在DDR中的功能。本研究将深入了解棕榈酰化对乳腺癌基因组稳定性及放射敏感性的调控机制，并为乳腺癌放疗提供新的增敏靶点。

The DNA Damage Response (DDR), activation of which heavily relies on protein post translational modifications（PTMs）, controls cellular sensitivity to ionizing radiation (IR). Palmitoylation, a highly conserved PTM has recently shown to be abnormally regulated in breast cancer. However, it is not known whether palmitoylation is involved in the DDR and radiosensitivity. Porcupine (PORCN) is an O-palmitoleoyltransferase which resides on the Endoplasmic Reticulum (ER) membrane and it mediates activation of the Wnt pathway via palmitoylation. The stimulus for proposing this project was our preliminary findings that a fraction of the PORCN protein presents in the nucleus and that PORCN participates in the DDR. We identified the PORCN nuclear localization sequence domain and found that it was essential for DDR activation and radiosensitivity both in vitro and in vivo. Using a proteomic analysis, we identified a nuclear PORCN complex with DNA repair proteins involved, including Ku70, a Non-Homologous End Joining (NHEJ) repair protein. We further found palmitoylation was induced by IR in a PORCN-dependent manner. Based on these findings, our proposed studies will explore the role of PORCN-dependent palmitoylation in the DDR and breast cancer radiosensitivity. Three specific aims are proposed, including: 1) how PORCN palmiytolates Ku70; 2) what is the function of KU70 palmitoylation in the DDR and radiosensitivity; and 3) what is the nuclear PORCN palmitoylation function in a transgenic mouse model. This study will shed lights into the critical role of protein palmitoylation in the DDR and breast cancer radiosensitivity. Completion of this study will also have clinical impact as it will provide insights into novel targets for radiosensitization for breast cancer.