IU1 and enzalutamide combination yields synergistic effects on castration-resistant prostate cancer.

BACKGROUND: Androgen deprivation therapy (ADT) is one of the main treatment modalities for prostate cancer (PCa); however, almost all patients treated with ADT eventually progress into castration-resistant PCa (CRPC). Although second-generation androgen receptor (AR) antagonists, such as enzalutamide, have been approved for CRPC treatment, AR signaling in CRPC cells is reactivated through multiple mechanisms, resulting in resistance to treatment and tumor progression with a very poor prognosis. The present study aimed to explore the anticancer effect of a treatment combining AR antagonist enzalutamide with AR degrader IU1 on PCa cells. METHODS: The joint effects of enzalutamide and IU1 on PCa cell proliferation and apoptosis and associated cell signaling were evaluated in vitro. Mechanistically, the ubiquitination level and half-life of AR were examined under the combination treatment. The binding of IU1 and enzalutamide to AR was further verified using cellular thermal shift analysis and isothermal dose-response curve fingerprinting. RESULTS: The combination of IU1 and three AR antagonists showed synergistic effects in different prostate cell lines. IU1 and enzalutamide synergistically promoted the degradation of AR and AR-V7 proteins, as well as suppressed the expression levels of AR and AR-V7 downstream target genes at the transcriptional and protein levels. The combination also synergistically blocked the PCa cell cycle and promoted apoptosis in PCa cell lines. Mechanistically, the combination promoted increased levels of AR ubiquitination. In CRPC cell lines and in the presence of increased androgen concentrations, enzalutamide was still able to bind AR competitively with androgens, reducing the stability of AR and thus promoting the degradation effect of IU1 on AR, synergistically producing an inhibitory effect on PCa cells. CONCLUSION: Taken together, our findings suggest that the combination of AR degrader and enzalutamide potentially represents a new therapeutic strategy for CRPC.

Examination of genetic and pharmacological tools to study the proteasomal deubiquitinating enzyme ubiquitin-specific protease 14 in the nervous system.

Strategies for enhancing protein degradation have been proposed for treating neurological diseases associated with a decline in proteasome activity. A proteasomal deubiquitinating enzyme that controls substrate entry into proteasomes, ubiquitin-specific protease 14 (USP14), is an attractive candidate for therapies that modulate proteasome activity. This report tests the validity of genetic and pharmacological tools to study USP14's role in regulating protein abundance. Although previous studies implicated USP14 in the degradation of microtubule associate protein tau, tar DNA binding protein, and prion protein, the levels of these proteins were similar in our neurons cultured from wild type and USP14-deficient mice. Neither loss nor over-expression of USP14 affected the levels of these proteins in mice, implying that modifying the amount of USP14 is not sufficient to alter their steady-state levels. However, neuronal over-expression of a catalytic mutant of USP14 showed that manipulating USP14's ubiquitin-hydrolase activity altered the levels of specific proteins in vivo. Although pharmacological inhibitors of USP14's ubiquitin-hydrolase activity reduced microtubule associate protein tau, tar DNA binding protein, and prion protein in culture, the effect was similar in wild type and USP14-deficient neurons, thus impacting their use for specifically evaluating USP14 in a therapeutic manner. While examining how targeting USP14 may affect other proteins in vivo, this report showed that fatty acid synthase, v-rel reticuloendotheliosis viral oncogene homolog, CTNNB1, and synaptosome associated protein 23 are reduced in USP14-deficient mice; however, loss of USP14 differentially altered the levels of these proteins in the liver and brain. As such, it is critical to more thoroughly examine how inhibiting USP14 alters protein abundance to determine if targeting USP14 will be a beneficial strategy for treating neurodegenerative diseases.

Small-Molecule Inhibitors Targeting Proteasome-Associated Deubiquitinases.

The 26S proteasome is the principal protease for regulated intracellular proteolysis. This multi-subunit complex is also pivotal for clearance of harmful proteins that are produced throughout the lifetime of eukaryotes. Recent structural and kinetic studies have revealed a multitude of conformational states of the proteasome in substrate-free and substrate-engaged forms. These conformational transitions demonstrate that proteasome is a highly dynamic machinery during substrate processing that can be also controlled by a number of proteasome-associated factors. Essentially, three distinct family of deubiquitinases-USP14, RPN11, and UCH37-are associated with the 19S regulatory particle of human proteasome. USP14 and UCH37 are capable of editing ubiquitin conjugates during the process of their dynamic engagement into the proteasome prior to the catalytic commitment. In contrast, RPN11-mediated deubiquitination is directly coupled to substrate degradation by sensing the proteasome's conformational switch into the commitment steps. Therefore, proteasome-bound deubiquitinases are likely to tailor the degradation events in accordance with substrate processing steps and for dynamic proteolysis outcomes. Recent chemical screening efforts have yielded highly selective small-molecule inhibitors for targeting proteasomal deubiquitinases, such as USP14 and RPN11. USP14 inhibitors, IU1 and its progeny, were found to promote the degradation of a subset of substrates probably by overriding USP14-imposed checkpoint on the proteasome. On the other hand, capzimin, a RPN11 inhibitor, stabilized the proteasome substrates and showed the anti-proliferative effects on cancer cells. It is highly conceivable that these specific inhibitors will aid to dissect the role of each deubiquitinase on the proteasome. Moreover, customized targeting of proteasome-associated deubiquitinases may also provide versatile therapeutic strategies for induced or repressed protein degradation depending on proteolytic demand and cellular context.

An inhibitor of the proteasomal deubiquitinating enzyme USP14 induces tau elimination in cultured neurons.

The ubiquitin-proteasome system (UPS) is responsible for most selective protein degradation in eukaryotes and regulates numerous cellular processes, including cell cycle control and protein quality control. A component of this system, the deubiquitinating enzyme USP14, associates with the proteasome where it can rescue substrates from degradation by removal of the ubiquitin tag. We previously found that a small-molecule inhibitor of USP14, known as IU1, can increase the rate of degradation of a subset of proteasome substrates. We report here the synthesis and characterization of 87 variants of IU1, which resulted in the identification of a 10-fold more potent USP14 inhibitor that retains specificity for USP14. The capacity of this compound, IU1-47, to enhance protein degradation in cells was tested using as a reporter the microtubule-associated protein tau, which has been implicated in many neurodegenerative diseases. Using primary neuronal cultures, IU1-47 was found to accelerate the rate of degradation of wild-type tau, the pathological tau mutants P301L and P301S, and the A152T tau variant. We also report that a specific residue in tau, lysine 174, is critical for the IU1-47-mediated tau degradation by the proteasome. Finally, we show that IU1-47 stimulates autophagic flux in primary neurons. In summary, these findings provide a powerful research tool for investigating the complex biology of USP14.

USP14 inhibitor attenuates cerebral ischemia/reperfusion-induced neuronal injury in mice.

Stroke is associated with over-production of misfolded and aggregating proteins. However, it remains largely unclear whether enhanced removal of protein aggregates following ischemic stroke is neuroprotective. Deubiquitinating enzymes (DUBs) are a large group of proteases that regulate protein degradation. The ubiquitin-specific protease 14 (USP14) is a DUB that is associated with the proteasome and negatively regulates proteasome activity. In this study, we examined the effect of 1-[1-(4-fluorophenyl)-2,5-dimethylpyrrol-3-yl]-2-pyrrolidin-1-ylethanone (IU1), a specific small molecule inhibitor of USP14, on mouse focal cerebral ischemic stroke-induced neuronal injury in mice. We found that IU1 treatment attenuated ischemic stroke-caused neuronal injury, which was reflected by increased survival rate, reduced infarct volume, as well as decreased neuronal loss in the IU1-treated mice compared to the control-treated mice. Additionally, IU1 treatment is associated with reduced protein aggregates and enhanced proteasome functionality. These data not only highlight the significance of protein homeostasis in cerebral ischemia/reperfusion-induced neuronal injury but also extend the therapeutic role of DUB inhibitors.

Inhibition of USP14 Suppresses ROS-dependent Ferroptosis and Alleviates Renal Ischemia/Reperfusion Injury.

The ubiquitin-specific protease 14 (USP14) is a deubiquitinating enzyme, its inhibitor was reported could alleviate the ischemia/reperfusion (I/R)-stimulated cerebral neuronal damage. However, its specific role in I/R-induced acute kidney injury (AKI) remains unclear. We established hypoxia/reoxygenation (H/R)-induced HK-2 cell injury model in vitro and I/R-induced kidney injury mice model in vivo. The expression or activity of USP14 was inhibited by siRNA or IU1, a small molecule inhibitor of USP14. ROS were scavenged by N-acetyl-cysteine (NAC). Biochemical index analysis and hematoxylin & eosin (H&E) staining were performed to evaluate renal injury. The results indicated that USP14 was upregulated in H/R-induced HK-2 cells and kidney tissues of I/R mice. Inhibition of USP14 suppressed the cell death, inflammatory, oxidative stress and reactive oxygen species (ROS)-dependent ferroptosis of H/R-induced HK-2 cells. What's more, IU1 and NAC effectively alleviated renal injury of I/R mice. In summary, this study suggested that inhibition of USP14 protected renal from I/R injury.

IU1 suppresses proliferation of cervical cancer cells through MDM2 degradation.

Previous studies have demonstrated that the antitumor potential of IU1 (a pharmacological compound), which was mediated by selective inhibition of proteasome-associated deubiquitinase ubiquitin-specific protease 14 (USP14). However, the underlying molecular mechanisms remain elusive. It has been well established that mdm2 (Murine double minute 2) gene was amplified and/or overexpressed in a variety of human neoplasms, including cervical cancer. Furthermore, MDM2 is critical to cervical cancer development and progression. Relatively studies have reported that USP15 and USP7 stabilized MDM2 protein levels by removing its ubiquitin chain. In the current study, we studied the cell proliferation status after IU1 treatment and the USP14-MDM2 protein interaction in cervical cancer cells. This study experimentally revealed that IU1 treatment reduced MDM2 protein expression in HeLa cervical cancer cells, along with the activation of autophagy-lysosomal protein degradation and promotion of ubiquitin-proteasome system (UPS) function, thereby blocked G0/G1 to S phase transition, decreased cell growth and triggered cell apoptosis. Thus, these results indicate that IU1 treatment simultaneously targets two major intracellular protein degradation systems, ubiquitin-proteasome and autophagy-lysosome systems, which leads to MDM2 degradation and contributes to the antitumor effect of IU1.