The regulation of homeostasis in the Ubiquitin (Ub) proteasome system (UPS) is likely to be important for the development of liver cancer. Tribbles homolog 2 (TRIB2) is known to affect Ub E3 ligases (E3s) in liver cancer. However, whether TRIB2 regulates the UPS in other ways and the relevant mechanisms are still unknown. Here, we reveal that TRIB2 decreased Ub levels largely by stimulating proteasome degradation of Ub. In the proteasome, proteasome 20S subunit beta 5 (PSMB5) was critical for the function of TRIB2, although it did not directly interact with TRIB2. However, poly (rC) binding protein 2 (PCBP2), which was identified by mass spectrometry, directly interacted with both TRIB2 and PSMB5. PCBP2 was a prerequisite for the TRIB2 induction of PSMB5 activity and decreased Ub levels. A significant correlation between TRIB2 and PCBP2 was revealed in liver cancer specimens. Interestingly, TRIB2 suppressed the K48-ubiquitination of PCBP2 to increase its level. Therefore, a model showing that TRIB2 cooperates and stimulates PCBP2 to reduce Ub levels was established. Additionally, the reduction in Ub levels induced by TRIB2 and PCBP2 was dependent on K48-ubiquitination. PCBP2 was one of the possible downstream factors of TRIB2 and their interaction relied on the DQLVPD element of TRIB2 and the KH3 domain of PCBP2. This interaction was necessary to maintain the viability of the liver cancer cells and promote tumor growth. Mechanistically, glutathione peroxidase 4 functioned as one of the terminal effectors of TRIB2 and PCBP2 to protect liver cancer cells from oxidative damage. Taken together, the data indicate that, in addition to affecting E3s, TRIB2 plays a critical role in regulating UPS by modulating PSMB5 activity in proteasome to reduce Ub flux, and that targeting TRIB2 might be helpful in liver cancer treatments by enhancing the oxidative damage induced by therapeutic agents.

泛素 (Ub) 蛋白酶体系统 (UPS) 中稳态的调节可能对肝癌的发展很重要。已知 Tribbles 同源物 2 (TRIB2) 会影响肝癌中的 Ub E3 连接酶 (E3s)。然而，TRIB2是否以其他方式调节UPS以及相关机制尚不清楚。在这里，我们揭示了 TRIB2 主要通过刺激 Ub 的蛋白酶体降解来降低 Ub 水平。在蛋白酶体中，蛋白酶体 20S 亚基 beta 5 (PSMB5) 对 TRIB2 的功能至关重要，尽管它不直接与 TRIB2 相互作用。然而，通过质谱鉴定的聚 (rC) 结合蛋白 2 (PCBP2) 直接与 TRIB2 和 PSMB5 相互作用。PCBP2 是 TRIB2 诱导 PSMB5 活性和降低 Ub 水平的先决条件。在肝癌标本中揭示了TRIB2和PCBP2之间的显着相关性。有趣的是，TRIB2 抑制了 PCBP2 的 K48 泛素化以提高其水平。因此，建立了显示TRIB2协同并刺激PCBP2降低Ub水平的模型。此外，TRIB2 和 PCBP2 诱导的 Ub 水平降低取决于 K48 泛素化。PCBP2 是 TRIB2 可能的下游因子之一，它们的相互作用依赖于 TRIB2 的 DQLVPD 元件和 PCBP2 的 KH3 结构域。这种相互作用对于维持肝癌细胞的活力和促进肿瘤生长是必要的。从机制上讲，谷胱甘肽过氧化物酶 4 作为 TRIB2 和 PCBP2 的末端效应物之一，保护肝癌细胞免受氧化损伤。综合起来，数据表明，