三阴性乳腺癌（TNBC）是乳腺癌（BC）的一种异质亚型，预后较差。内质网（ER）应激负责细胞过程并在细胞功能中起着关键作用。ER应激是一个复杂而动态的过程，可以诱导异常的凋亡和死亡。然而，TNBC中ER应激的潜在机制尚未明确。我们确定了泛素特异性蛋白酶19（USP19）作为TNBC负调控因子以进一步研究。通过体外增殖试验和细胞周期分析检测了USP19对BC增殖的影响，在体内使用小鼠肿瘤发生性模型检查了其在体内的影响。通过体外流式细胞学分析和体内TUNEL试验评估了细胞凋亡。利用蛋白质组学检测与USP19相互作用的蛋白质。多个体内外检测表明，USP19降低TNBC细胞增长，同时增加细胞凋亡。然后，我们证明USP19与解泛素化酶结合并随后稳定家族分子伴侣调节因子6（BAG6）。BAG6可增强B细胞淋巴瘤2（BCL2）的泛素化和降解，从而提高ER钙（Ca2+）水平，引起ER应激。我们还发现N6-甲基腺苷（m6 A）“编码者”甲基转移酶样蛋白14（METTL14）增加了全局m6 A修饰。我们的研究揭示了USP19通过调节BAG6和BCL2的稳定性，提高细胞内Ca2+浓度从而改变ER应激，可能成为TNBC治疗的可行靶点。 © 2023 The Authors. Clinical and Translational Medicine published by John Wiley & Sons Australia, Ltd on behalf of Shanghai Institute of Clinical Bioinformatics.

Triple-negative breast cancer (TNBC), a heterogeneous subtype of breast cancer (BC), had poor prognosis. Endoplasmic reticulum (ER) stress was responsible for cellular processes and played a crucial role in the cell function. ER stress is a complex and dynamic process that can induce abnormal apoptosis and death. However, the underlying mechanism of ER stress involved in TNBC is not well defined.We identified ubiquitin-specific protease 19 (USP19) as a TNBC negative regulator for further investigation. The effects of USP19 on BC proliferation were assessed in vitro using proliferation test and cell-cycle assays, while the effects in vivo were examined using a mouse tumorigenicity model. Through in vitro flow cytometric analyses and in vivo TUNEL assays, cell apoptosis was assessed. Proteomics was used to examine the proteins that interact with USP19.Multiple in vitro and in vivo tests showed that USP19 decreases TNBC cell growth while increasing apoptosis. Then, we demonstrated that USP19 interacts with deubiquitinates and subsequently stabilises family molecular chaperone regulator 6 (BAG6). BAG6 can boost B-cell lymphoma 2 (BCL2) ubiquitination and degradation, thereby raising ER calcium (Ca2+ ) levels and causing ER stress. We also found that the N6 -methyladenosine (m6 A) "writer" methyltransferase-like 14 (METTL14) increased global m6 A modification.Our study reveals that USP19 elevates the intracellular Ca2+ concentration to alter ER stress via regulation of BAG6 and BCL2 stability and may be a viable therapeutic target for TNBC therapy.© 2023 The Authors. Clinical and Translational Medicine published by John Wiley & Sons Australia, Ltd on behalf of Shanghai Institute of Clinical Bioinformatics.