Brpf-histone acetyltransferase (HAT) complexes have important roles in embryonic development and regulating differentiation in ESCs. Among Brpf family, Brpf3 is a scaffold protein of Myst2 histone acetyltransferase complex that plays crucial roles in gene regulation, DNA replication, development as well as maintaining pluripotency in embryonic stem cells (ESCs). However, its biological functions in ESCs are not elucidated. In this study, we find out that Brpf3 protein level is critical for Myst2 stability and E3 ligase Huwe1 functions as a novel negative regulator of Myst2 via ubiquitin-mediated degradation. Importantly, Brpf3 plays an antagonistic role in Huwe1-mediated degradation of Myst2, suggesting that protein–protein interaction between Brpf3 and Myst2 is required for retaining Myst2 stability. Further, Brpf3 overexpression causes the aberrant upregulation of Myst2 protein levels which in turn induces the dysregulated cell-cycle progression and also delay of early embryonic development processes such as embryoid-body formation and lineage commitment of mouse ESCs. The Brpf3 overexpression-induced phenotypes can be reverted by Huwe1 overexpression. Together, these results may provide novel insights into understanding the functions of Brpf3 in proper differentiation as well as cell-cycle progression of ESCs via regulation of Myst2 stability by obstructing Huwe1-mediated ubiquitination. In addition, we suggest that this is a useful report which sheds light on the function of an unknown gene in ESC field.

Brpf-组蛋白乙酰转移酶 (HAT) 复合物在胚胎发育和调节 ESC 分化中具有重要作用。在 Brpf 家族中，Brpf3 是 Myst2 组蛋白乙酰转移酶复合物的支架蛋白，在胚胎干细胞 (ESCs) 的基因调控、DNA 复制、发育以及维持多能性中起关键作用。然而，其在胚胎干细胞中的生物学功能尚未阐明。在这项研究中，我们发现 Brpf3 蛋白水平对 Myst2 的稳定性至关重要，而 E3 连接酶 Huwe1 通过泛素介导的降解作为 Myst2 的新型负调节因子。重要的是，Brpf3 在 Huwe1 介导的 Myst2 降解中起拮抗作用，表明 Brpf3 和 Myst2 之间的蛋白质-蛋白质相互作用是保持 Myst2 稳定性所必需的。更远，Brpf3 过表达导致 Myst2 蛋白水平异常上调，进而导致细胞周期进程失调，并延迟早期胚胎发育过程，如胚胎体形成和小鼠 ESC 的谱系定型。Brpf3 过表达诱导的表型可以通过 Huwe1 过表达来恢复。总之，这些结果可以通过阻碍 Huwe1 介导的泛素化来调节 Myst2 的稳定性，为理解 Brpf3 在适当分化中的功能以及 ESC 的细胞周期进程提供新的见解。此外，我们认为这是一份有用的报告，它阐明了 ESC 领域中未知基因的功能。