Endometrial cancer (EC) stands as one of the most prevalent malignancies affecting the female genital tract, witnessing a rapid surge in incidence globally. Despite the well-established association of histone methyltransferase SMYD3 with the development and progression of various cancers, its specific oncogenic role in endometrial cancer remains unexplored. In the present study, we report that the expression level of SMYD3 is significantly upregulated in EC samples and associated with EC progression. Through meticulous in vivo and in vitro experiments, we reveal that depletion of SMYD3 curtails cell proliferation, migration, and invasion capabilities, leading to compromised non-homologous end joining repair (NHEJ) and heightened sensitivity of EC cells to radiation. Furthermore, our pathway enrichment analysis underscores the pivotal involvement of the DNA damage repair pathway in regulating EC progression. Mechanistically, in response to DNA damage, SMYD3 is recruited to these sites in a PARP1-dependent manner, specifically methylating LIG4. This methylation sets off a sequential assembly of the LIG4/XRCC4/XLF complex, actively participating in the NHEJ pathway and thereby fostering EC progression. Notably, our findings highlight the promise of SMYD3 as a crucial player in NHEJ repair and its direct correlation with EC progression. Intriguingly, pharmacological intervention targeting SMYD3 with its specific inhibitor, BCI-121, emerges as a potent strategy, markedly suppressing the tumorigenicity of EC cells and significantly enhancing the efficacy of radiotherapy. Collectively, our comprehensive data position SMYD3 as a central factor in NHEJ repair and underscore its potential as a promising pharmacological target for endometrial cancer therapy, validated through both in vitro and in vivo systems.

子宫内膜癌（EC）是影响女性生殖道最常见的恶性肿瘤之一，全球发病率急剧上升。尽管组蛋白甲基转移酶 SMYD3 与各种癌症的发生和进展之间存在明确的关联，但其在子宫内膜癌中的具体致癌作用仍有待探索。在本研究中，我们报告 EC 样本中 SMYD3 的表达水平显着上调，并且与 EC 进展相关。通过细致的体内和体外实验，我们发现 SMYD3 的缺失会抑制细胞增殖、迁移和侵袭能力，导致非同源末端连接修复 (NHEJ) 受损并提高 EC 细胞对辐射的敏感性。此外，我们的通路富集分析强调了 DNA 损伤修复通路在调节 EC 进展中的关键参与。从机制上讲，为了响应 DNA 损伤，SMYD3 以 PARP1 依赖性方式被招募到这些位点，特别是甲基化 LIG4。这种甲基化引发了 LIG4/XRCC4/XLF 复合物的顺序组装，积极参与 NHEJ 途径，从而促进 EC 进展。值得注意的是，我们的研究结果强调了 SMYD3 作为 NHEJ 修复中关键参与者的前景及其与 EC 进展的直接相关性。有趣的是，针对SMYD3及其特异性抑制剂BCI-121的药物干预成为一种有效的策略，显着抑制EC细胞的致瘤性并显着增强放疗的疗效。总的来说，我们的综合数据将 SMYD3 定位为 NHEJ 修复的核心因素，并强调其作为子宫内膜癌治疗的有前途的药理学靶点的潜力，并通过体外和体内系统进行验证。