USP14 inhibition regulates tumorigenesis by inducing apoptosis in gastric cancer

Deubiquitinases (DUBs) are an essential component of the ubiquitin-proteasome system (UPS). They trim ubiquitin from substrate proteins, thereby preventing them from degradation, and modulate different cellular processes. Ubiquitin-specific protease 14 (USP14) is a DUB that has mainly been studied for its role in tumorigenesis in several cancers. In the present study, we found that the protein levels of USP14 were remarkably higher in gastric cancer tissues than in the adjacent normal tissues. We also demonstrated that the inhibition of USP14 activity using IU1 (an USP14 inhibitor) or the inhibition of USP14 expression using USP14-specific siRNA markedly reduced the viability of gastric cancer cells and suppressed their migratory and invasive abilities. The reduction in gastric cancer cell proliferation due to the inhibition of USP14 activity was a result of the increase in the degree of apoptosis, as evidenced by the increased expression levels of cleaved caspase-3 and cleaved PARP. Furthermore, an experiment using the USP14 inhibitor IU1 revealed that the inhibition of USP14 activity suppressed 5-fluorouracil (5-FU) resistance in GC cells. Collectively, these findings indicate that USP14 plays critical roles in gastric cancer progression and suggest its potential to serve as a novel therapeutic target for gastric cancer treatment. [BMB Reports 2023; 56(8): 451-456].

USP14 inhibition regulates tumorigenesis by inducing apoptosis in gastric cancer

Deubiquitinases (DUBs) are an essential component of the ubiquitin-proteasome system (UPS). They trim ubiquitin from substrate proteins, thereby preventing them from degradation, and modulate different cellular processes. Ubiquitin-specific protease 14 (USP14) is a DUB that has mainly been studied for its role in tumorigenesis in several cancers. In the present study, we found that the protein levels of USP14 were remarkably higher in gastric cancer tissues than in the adjacent normal tissues. We also demonstrated that the inhibition of USP14 activity using IU1 (an USP14 inhibitor) or the inhibition of USP14 expression using USP14-specific siRNA markedly reduced the viability of gastric cancer cells and suppressed their migratory and invasive abilities. The reduction in gastric cancer cell proliferation due to the inhibition of USP14 activity was a result of the increase in the degree of apoptosis, as evidenced by the increased expression levels of cleaved caspase-3 and cleaved PARP. Furthermore, an experiment using the USP14 inhibitor IU1 revealed that the inhibition of USP14 activity suppressed 5-fluorouracil (5-FU) resistance in GC cells. Collectively, these findings indicate that USP14 plays critical roles in gastric cancer progression and suggest its potential to serve as a novel therapeutic target for gastric cancer treatment. [BMB Reports 2023; 56(8): 451-456].

USP14: Structure, Function, and Target Inhibition

Ubiquitin-specific protease 14 (USP14), a deubiquitinating enzyme (DUB), is associated with proteasomes and exerts a dual function in regulating protein degradation. USP14 protects protein substrates from degradation by removing ubiquitin chains from proteasome-bound substrates, whereas promotes protein degradation by activating the proteasome. Increasing evidence have shown that USP14 is involved in several canonical signaling pathways, correlating with cancer, neurodegenerative diseases, autophagy, immune responses, and viral infections. The activity of USP14 is tightly regulated to ensure its function in various cellular processes. Structural studies have demonstrated that free USP14 exists in an autoinhibited state with two surface loops, BL1 and BL2, partially hovering above and blocking the active site cleft binding to the C-terminus of ubiquitin. Hence, both proteasome-bound and phosphorylated forms of USP14 require the induction of conformational changes in the BL2 loop to activate its deubiquitinating function. Due to its intriguing roles in the stabilization of disease-causing proteins and oncology targets, USP14 has garnered widespread interest as a therapeutic target. In recent years, significant progress has been made on identifying inhibitors targeting USP14, despite the complexity and challenges in improving their selectivity and affinity for USP14. In particular, the crystal structures of USP14 complexed with IU1-series inhibitors revealed the underlying allosteric regulatory mechanism and enabled the further design of potent inhibitors. In this review, we summarize the current knowledge regarding the structure, regulation, pathophysiological function, and selective inhibition of USP14, including disease associations and inhibitor development.

USP14 Inhibition Regulates Tumorigenesis by Inducing Autophagy in Lung Cancer In Vitro

The ubiquitin–proteasome system is an essential regulator of several cellular pathways involving oncogenes. Deubiquitination negatively regulates target proteins or substrates linked to both hereditary and sporadic forms of cancer. The deubiquitinating enzyme ubiquitin-specific protease 14 (USP14) is associated with proteasomes where it trims the ubiquitin chain on the substrate. Here, we found that USP14 is highly expressed in patients with lung cancer. We also demonstrated that USP14 inhibitors (IU1-47 and siRNA-USP14) significantly decreased cell proliferation, migration, and invasion in lung cancer. Remarkably, we found that USP14 negatively regulates lung tumorigenesis not only through apoptosis but also through the autophagy pathway. Our findings suggest that USP14 plays a crucial role in lung tumorigenesis and that USP14 inhibitors are potent drugs in lung cancer treatment.