The ubiquitin-specific protease (USP) family is the largest and most diverse deubiquitinase (DUBs) family and plays a significant role in maintaining cell homeostasis. Dysregulation of USPs has been associated with carcinogenesis of various tumors. We identified that USP19 was downregulated in pancreatic tumor tissues and forced expression of USP19 diminished tumorigenicity of pancreatic cancer. Mechanistically, USP19 directly interacts with and stabilized NEK9 via inhibiting K48-specific polyubiquitination process on NEK9 protein at K525 site through its USP domain. Moreover, NEK9 phosphorylates the regulatory associated protein of mTOR (Raptor) at Ser792 and links USP19 to the inhibition of mTORC1 signaling pathway, which further leads to autophagic cell death of pancreatic cancer cells. Inhibition of autophagy by Atg5 knockdown or lysosome inhibitor bafilomycin A1 abolished the decreased malignant phenotype of USP19- and NEK9-overexpressing cancer cells. Importantly, USP19 expression exhibits a positive correlation with NEK9 expression in clinical samples, and low USP19 or NEK9 expression is associated with a worse prognosis. This study revealed that USP19-mediated NEK9 deubiquitylation is a regulatory mechanism for mTORC1 inhibition and provides a therapeutic target for diseases involving mTORC1 dysregulation.

泛素特异性蛋白酶 （USP） 家族是最大、最多样化的去泛素酶 （DUB） 家族，在维持细胞稳态中起着重要作用。USPs 失调与各种肿瘤的致癌作用有关。我们发现 USP19 在胰腺肿瘤组织中下调，USP19 的强制表达降低了胰腺癌的致瘤性。从机制上讲，USP19 通过其 USP 结构域抑制 K525 位点 NEK9 蛋白上的 K48 特异性多泛素化过程，直接与 NEK9 相互作用并稳定 NEK9。此外，NEK9 在 Ser792 位点磷酸化 mTOR （Raptor） 的调节相关蛋白，并将 USP19 与抑制 mTORC1 信号通路联系起来，从而进一步导致胰腺癌细胞的自噬细胞死亡。Atg5 敲低或溶酶体抑制剂巴弗洛霉素 A1 抑制自噬消除了 USP19 和 NEK9 过表达癌细胞的恶性表型降低。重要的是，USP19 表达与临床样本中的 NEK9 表达呈正相关，USP19 或 NEK9 低表达与较差的预后相关。本研究揭示了 USP19 介导的 NEK9 去泛素化是 mTORC1 抑制的一种调节机制，为涉及 mTORC1 失调的疾病提供了治疗靶点。