Radioresistance limits the efficacy of radiotherapy against breast cancer, especially the most lethal subtype of breast cancer, triple-negative breast cancer (TNBC). Epithelial-to-mesenchymal transition (EMT) is closely related to tumor radioresistance. In this work, we attempted to identify the key EMT-related transcription factor(s) that can induce radioresistance in breast cancer cells. A set of 44 EMT transcription factors were analyzed in parental and radioresistant TNBC cell lines. The function of FOXQ1, a differentially expressed transcription factor, was determined in TNBC radioresistance. FOXQ1-interacting proteins were identified by co-immunoprecipitation and mass spectrometry. Compared with parental cells, FOXQ1 was significantly upregulated in radioresistant TNBC cells. Silencing of FOXQ1 increased the radiosensitiviy of radioresistant TNBC cells both in vitro and in vivo. FOXQ1 associated with a nuclear isoform of RAPH1 (named RAPH1-i3) in radioresistant TNBC cells. Overexpression of RAPH1-i3 enhanced TNBC cell proliferation and migration, and most interestingly, induced radioresistance in parental TNBC cells when co-expressed with FOXQ1. Similar findings were observed in estrogen receptor-positive breast cancer cell lines that had co-expression of RAPH1-i3 and FOXQ1. Mechanistically, co-expression of RAPH1-i3 and FOXQ1 activated STAT3 signaling and increased the expression of CCND1, MCL1, Bcl-XL, and MMP2. Depletion of RAPH1-i3 impaired the radioresistance of radioresistant TNBC cells. Additionally, RAPH1-i3 upregulation was associated with advanced tumor stage and reduced disease-free survival in TNBC patients. These results collectively show that RAPH1-i3 interacts with FOXQ1 to promote breast cancer progression and radioresistance. RAPH1-i3 and FOXQ1 represent therapeutic targets for the treatment of breast cancer including TNBC.

放射抗性限制了放射治疗对乳腺癌的疗效，尤其是乳腺癌中最致命的亚型三阴性乳腺癌（TNBC）。上皮间质转化（EMT）与肿瘤放射抵抗密切相关。在这项工作中，我们试图鉴定能够诱导乳腺癌细胞放射抗性的关键 EMT 相关转录因子。在亲本和抗辐射 TNBC 细胞系中分析了一组 44 个 EMT 转录因子。 FOXQ1（一种差异表达的转录因子）在 TNBC 放射抗性中的功能被确定。通过免疫共沉淀和质谱法鉴定了 FOXQ1 相互作用蛋白。与亲代细胞相比，FOXQ1 在抗辐射 TNBC 细胞中显着上调。 FOXQ1 沉默可增加体外和体内抗辐射 TNBC 细胞的放射敏感性。 FOXQ1 与抗辐射 TNBC 细胞中的 RAPH1 核亚型（称为 RAPH1-i3）相关。 RAPH1-i3 的过度表达增强了 TNBC 细胞的增殖和迁移，最有趣的是，当与 FOXQ1 共表达时，会诱导亲代 TNBC 细胞的放射抗性。在共表达 RAPH1-i3 和 FOXQ1 的雌激素受体阳性乳腺癌细胞系中也观察到了类似的结果。从机制上讲，RAPH1-i3 和 FOXQ1 的共表达激活 STAT3 信号传导并增加 CCND1、MCL1、Bcl-XL 和 MMP2 的表达。 RAPH1-i3 的耗竭会损害抗辐射 TNBC 细胞的抗辐射能力。此外，RAPH1-i3 上调与 TNBC 患者的晚期肿瘤分期和无病生存率降低相关。这些结果共同表明 RAPH1-i3 与 FOXQ1 相互作用，促进乳腺癌进展和放射抗性。 RAPH1-i3 和 FOXQ1 代表治疗乳腺癌（包括 TNBC）的治疗靶点。