The Affiliated Tumor Hospital of Xiangya Medical School, Central South University, Changsha, Hunan, 410013, People's Republic of China.
Cancer Research Institute, School of Basic Medical Sciences, Central South University, Changsha, Hunan, 410078, People's Republic of China.
J Exp Clin Cancer Res. 2020 Feb 7;39(1):30. doi: 10.1186/s13046-019-1493-4.
BRD7 is a tumor suppressor known to inhibit cell proliferation and cell cycle progression and initiate apoptosis in breast cancer. However, the function and underlying molecular events of BRD7 in tumor invasion and metastasis in breast cancer are not fully understood.
BRD7 expression was assessed in two stable cell lines MDA231 and MCF7 with BRD7 overexpression and one stable cell line MDA231 with BRD7 interference using qRT-PCR and western blotting. CCK8 assay was used to examine the proliferation ability of MDA231 and MCF7 cells. Scratch wound healing assay was used to evaluate cell migration in MDA231 and MCF7 cells. Both Matrigel and three-dimensional invasion assays were performed to investigate the cell invasion ability after BRD7 overexpression or silencing or YB1 restoration in MDA231 and MCF7 cells. The potential interacting proteins of BRD7 were screened using co-immunoprecipitation combined with mass spectrometry and verified by co-immunoprecipitation in HEK293T cells. Additionally, we confirmed the specific binding region between BRD7 and YB1 in HEK293T cells by constructing a series of deletion mutants of BRD7 and YB1 respectively. Finally, xenograft and metastatic mouse models using MDA231 cells were established to confirm the effect of BRD7 on tumor growth and metastasis.
Here, the results of a series of assays in vitro indicated that BRD7 has the ability to inhibit the mobility, migration and invasion of breast cancer cells. In addition, YB1 was identified as a novel interacting protein of BRD7, and BRD7 was found to associate with the C-terminus of YB1 via its N-terminus. BRD7 decreases the expression of YB1 through negatively regulating YB1 phosphorylation at Ser102, thereby promoting its proteasomal degradation. Furthermore, gene set enrichment analysis revealed that epithelial-mesenchymal transition (EMT) is the common change occurring with altered expression of either BRD7 or YB1 and that BRD7 represses mesenchymal genes and activates epithelial genes. Moreover, restoring the expression of YB1 antagonized the inhibitory effect of BRD7 on tumorigenicity, EMT, invasiveness and metastasis through a series of in vitro and in vivo experiments. Additionally, BRD7 expression was negatively correlated with the level of YB1 in breast cancer patients. The combination of low BRD7 and high YB1 expression was significantly associated with poor prognosis, distant metastasis and advanced TNM stage.
Collectively, these findings uncover that BRD7 blocks tumor growth, migration and metastasis by negatively regulating YB1-induced EMT, providing new insights into the mechanism by which BRD7 contributes to the progression and metastasis of breast cancer.
BRD7 是一种已知的肿瘤抑制因子，能够抑制乳腺癌细胞的增殖和细胞周期进程，并启动细胞凋亡。然而，BRD7 在乳腺癌肿瘤侵袭和转移中的功能和潜在分子事件尚不完全清楚。
使用 qRT-PCR 和 Western blot 评估两种稳定细胞系 MDA231 和 MCF7 中 BRD7 过表达和一种稳定细胞系 MDA231 中 BRD7 干扰的 BRD7 表达。CCK8 测定用于检测 MDA231 和 MCF7 细胞的增殖能力。划痕愈合试验用于评估 MDA231 和 MCF7 细胞的迁移能力。在 MDA231 和 MCF7 细胞中过表达或沉默 BRD7 或恢复 YB1 后，分别进行 Matrigel 和三维侵袭试验，以研究细胞侵袭能力。使用免疫共沉淀结合质谱筛选 BRD7 的潜在相互作用蛋白，并在 HEK293T 细胞中通过免疫共沉淀进行验证。此外，我们通过分别构建 BRD7 和 YB1 的一系列缺失突变体，证实了 BRD7 和 YB1 之间的特定结合区域。最后，使用 MDA231 细胞建立异种移植和转移小鼠模型，以证实 BRD7 对肿瘤生长和转移的影响。
本研究在体外进行的一系列实验结果表明，BRD7 具有抑制乳腺癌细胞迁移和侵袭的能力。此外，YB1 被鉴定为 BRD7 的一种新型相互作用蛋白，并且 BRD7 通过其 N 端与 YB1 的 C 端结合。BRD7 通过负调控 YB1 在 Ser102 处的磷酸化来降低 YB1 的表达，从而促进其蛋白酶体降解。此外，基因集富集分析表明，上皮-间充质转化 (EMT) 是 BRD7 或 YB1 表达改变时共同发生的变化，BRD7 抑制间充质基因并激活上皮基因。此外，通过一系列体外和体内实验，恢复 YB1 的表达可拮抗 BRD7 对肿瘤发生、EMT、侵袭和转移的抑制作用。此外，BRD7 的表达与乳腺癌患者 YB1 的水平呈负相关。低 BRD7 和高 YB1 表达的组合与不良预后、远处转移和晚期 TNM 分期显著相关。
总之，这些发现揭示了 BRD7 通过负调控 YB1 诱导的 EMT 来阻断肿瘤生长、迁移和转移，为 BRD7 促进乳腺癌进展和转移的机制提供了新的见解。
