BRD4 promotes the stemness of gastric cancer cells via attenuating miR-216a-3p-mediated inhibition of Wnt/β-catenin signaling

The bromodomain and extra-terminal domain (BET) protein BRD4 is emerging as a potential target for cancer therapy. However, BRD4 roles in regulating the stemness of gastric cancer cells are unclear. Here, we demonstrated that BRD4 expression was significantly increased in gastric cancer tissues, cell spheroids, and BRD4 knockdown attenuated the stemness of gastric cancer cells characterized as the decrease of stemness markers expression, capacity of cells spheroids formation and ALDH1 activity. Importantly, BRD4 expression was negatively correlated with overall survival, first progression survival and post progression survival of gastric cancer patients. Mechanistic investigations revealed that miR-216a-3p was the most remarkably upregulated miRNA in response to BRD4 knockdown and Wnt/beta-catenin signaling was necessary for BRD4-mediated promotion on the stemness of gastric cancer cells. Additionally, BRD4 directly bound to the promoter and promoted the methylation level of MIR216A promoter, thus decreasing miR-216a-3p level. Notably, Wnt3a was identified as the direct target of miR-216a-3p in gastric cancer cells. Therefore, our results defined a BRD4/miR-216a-3p/Wnt/beta-catenin pathway in regulating the stemness of gastric cancer cells.

含溴结构域和额外末端结构域（BET）的蛋白BRD4正在成为癌症治疗的一个潜在靶点。然而，BRD4在调控胃癌细胞干性方面的作用尚不清楚。在此，我们证明了BRD4在胃癌组织、细胞球状体中的表达显著增加，并且BRD4的敲低减弱了胃癌细胞的干性，其表现为干性标志物表达降低、细胞球状体形成能力和乙醛脱氢酶1（ALDH1）活性下降。重要的是，BRD4的表达与胃癌患者的总生存期、首次进展生存期和进展后生存期呈负相关。机制研究表明，miR - 216a - 3p是在BRD4敲低时上调最显著的微小RNA（miRNA），并且Wnt/β - 连环蛋白信号通路对于BRD4介导的对胃癌细胞干性的促进是必需的。此外，BRD4直接结合到启动子上并提高了MIR216A启动子的甲基化水平，从而降低了miR - 216a - 3p的水平。值得注意的是，在胃癌细胞中Wnt3a被确定为miR - 216a - 3p的直接靶标。因此，我们的研究结果明确了一个在调控胃癌细胞干性方面的BRD4/miR - 216a - 3p/Wnt/β - 连环蛋白通路。