TRIB2 modulates proteasome function to reduce ubiquitin stability and protect liver cancer cells against oxidative stress

Abstract

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.

The Critical Role of TRIB2 in Cancer and Therapy Resistance

“…On the other hand, TRIB2 also modulates proteasome function via the proteasome subunit PSMB5 for which the PCBP2 protein is required. The DQLVPD sequence of TRIB2 binds to the KH3 domain of PCBP2 and PCBP2 interact with PSMB5, leading to the activation of PSMB5 and reducing Ub levels [ 48 ].…”

“…PCBP2 mediates degradation of some proteins and inhibits the production of reactive oxygen species (ROS), being implicated in development and progression of cancer. Mechanistically, TRIB2-PCBP2 interaction leads to a decrease in the ubiquitin pool by increasing the proteolytic efficiency of the proteasome and, consequently, maintains the viability of the liver cancer cells and promotes tumour growth [ 48 ].…”

TRIB2 desensitizes ferroptosis via βTrCP-mediated TFRC ubiquitiantion in liver cancer cells

“…Vast majority of studies have also suggested that TRIB2 can interact with a serial of E3s, such as βTrCP [ 2 ], SMAD specific E3 ubiquitin protein ligase 1 (Smurf1, [ 3 ]) and COP1 E3 ubiquitin ligase (COP1, [ 4 ]) at its C terminus. Recently, the roles of TRIB2 are expanded by our study demonstrating that TRIB2 can modulate proteasome function for the reduction of global Ub and protection of liver cancer cells against oxidative stress [ 5 ]. However, whether TRIB2 has other functions to boost tumorigenesis in liver cancer cells is still not very clear.…”

“…TRIB2 has been revealed as one of the key molecules stabilizing GPX4, the critical hydroperoxidase capable of converting lipid hydroperoxides into non-toxic lipid alcohols, thereby relieving cell damage under oxidative stress [ 5 ]. Inhibition of GPX4 either at genetic or pharmacological level causes ferroptosis [ 6 , 7 ].…”

Tribbles Pseudokinases in Colorectal Cancer

“…Recent work demonstrated that afatinib, an approved irreversible electrophilic covalent EGFR/HER2 inhibitor for lung cancer treatment, increased TRIB2 degradation in human acute myeloid leukemia (AML) cancer cells [ 93 ], demonstrating for the first time that TRIB2 might be a druggable protein. Early this year, others showed similar results in human hepatoma cell lines, where afatinib treatment (10 µM, 20 h) reduced TRIB2 protein levels and decreased cellular viability over 50% [ 94 ]. In SW-48, Colo205 and HT-29 CRC cell lines, though Tribbles levels were not investigated, afatinib treatment (1 or 10 µM, 48 h) also reduced cell viability [ 95 ], representing an opportunity for further studies, in order to establish TRIB2 targeting as a potential strategy for treating colon cancer.…”