Proteasomal deubiquitinase UCH37 inhibits degradation of β-catenin and promotes cell proliferation and motility

Novel curcumin derivatives N17 exert anti-cancer effects through the CSNK1G3/AKT axis in triple-negative breast cancer

Curcumin, extracted from Zingiberaceae and Araceae rhizomes, is clinically used for its anti-inflammatory, antibacterial, antioxidant, and anti-cancer properties. Its safety and potential make it a promising base for designing enhanced derivatives. The focus now is on optimizing curcumin and synthesizing more potent 1,4-pentadien-3-ones, which have anti-cancer activities. In the realm of triple-negative breast cancer (TNBC), an aggressive and invasive form with high metastatic potential, the need for innovative treatments is acute. The challenges posed by chemotherapy resistance, recurrence, and TNBC's heterogeneity have emphasized the necessity for novel therapeutic approaches. Our strategy involved the integration of a quinoxaline ring into 1,4-pentadien-3-one, followed by subsequent modifications. In this study, N17 demonstrated the ability to induce cell death and effectively suppress cell proliferation in breast cancer cells. These observed anti-cancer effects were attributed to the inhibition of p-AKT(S473), a key regulator implicated in both cell apoptosis and the modulation of epithelial-mesenchymal transition process in breast cancer cells. Furthermore, our investigation indicated N17 achieves its inhibitory effects on p-AKT(S473) by specifically targeting the CSNK1G3 protein. Remarkably, N17 not only impedes the EMT process but also triggers apoptosis through the CSNK1G3/AKT signaling axis. These findings provide the critical role of CSNK1G3 as an anti-cancer regulator in TNBC, establishing N17 as a pharmacological intervention with immense promise for treating cancer metastasis.

Deficiency of SIAH1 promotes the formation of filopodia by increasing the accumulation of FASN in liver cancer

It has been shown that the formation of filopodia is a key step in tumor cell metastasis, but there is limited research regarding its mechanism. In this study, we demonstrated that fatty acid synthase (FASN) promoted filopodia formation in liver cancer cells by regulating fascin actin-bundling protein 1 (FSCN1), a marker protein for filopodia. Mechanistically, on the one hand, the accumulation of FASN is caused by the enhanced deubiquitination of FASN mediated by UCHL5 (ubiquitin c-terminal hydrolase L5). In this pathway, low expression of SIAH1 (Seven in absentia homolog 1) can decrease the ubiquitination and degradation of ADRM1 (adhesion regulating molecule 1) thereby increasing its protein level, which will recruit and activate the deubiquitination enzyme UCHL5, leading to FASN undergo deubiquitination and escape from proteasomal degradation. On the other hand, the accumulation of FASN is related to its weakened ubiquitination, where SIAH1 directly acts as a ubiquitin ligase toward FASN, and low expression of SIAH1 reduces the ubiquitination and degradation of FASN. Both the two pathways are involved in the regulation of FASN in liver cancer. Our results reveal a novel mechanism for FASN accumulation due to the low expression of SIAH1 in human liver cancer and suggest an important role of FASN in filopodia formation in liver cancer cells.

UCHL5 promotes hepatocellular carcinoma progression by promoting glycolysis through activating Wnt/β-catenin pathway

BACKGROUND

Hepatocellular carcinoma (HCC) is highly malignant with a dismal prognosis, although the available therapies are insufficient. No efficient ubiquitinase has been identified as a therapeutic target for HCC despite the complicating role that of proteins ubiquitination plays in the malignant development of HCC.

METHODS

The expression of ubiquitin carboxyl terminal hydrolase L5 (UCHL5) in HCC tumor tissue and adjacent normal tissue was determined using the cancer genome atlas (TCGA) database and was validated using real-time quantitative polymerase chain reaction (RT-qRCR), Western blot and immunohistochemistry (IHC), and the relation of UCHL5 with patient clinical prognosis was explored. The expression of UCHL5 was knocked down and validated, and the effect of UCHL5 on the biological course of HCC was explored using cellular assays. To clarify the molecular mechanism of action of UCHL5 affecting HCC, expression studies of Adenosine triphosphate adenosine triphosphate (ATP), extracellular acidification (ECAR), and glycolysis-related enzymes were performed. The effects of UCHL5 on β-catenin ubiquitination and Wnt signaling pathways were explored in depth and validated using cellular functionalities. Validation was also performed in vivo.

RESULTS

In the course of this investigation, we discovered that UCHL5 was strongly expressed in HCC at both cellular and tissue levels. The prognosis of patients with high UCHL5 expression is considerably worse than that of those with low UCHL5 expression. UCHL5 has been shown to increase the degree of glycolysis in HCC cells with the impact of stimulating the proliferation and metastasis of HCC cells in both in vivo and in vitro. UCHL5 downregulates its degree of ubiquitination by binding to β-catenin, which activates the Wnt/β-catenin pathway and accelerates HCC cell glycolysis. Thereby promoting the growth of the HCC.

CONCLUSIONS

In summary, we have demonstrated for the first time that UCHL5 is a target of HCC and promotes the progression of hepatocellular carcinoma by promoting glycolysis through the activation of the Wnt/β-catenin pathway. UCHL5 may thus serve as a novel prognostic marker and therapeutic target for the treatment of HCC.

Branched ubiquitin chain binding and deubiquitination by UCH37 facilitate proteasome clearance of stress-induced inclusions

UCH37, also known as UCHL5, is a highly conserved deubiquitinating enzyme (DUB) that associates with the 26S proteasome. Recently, it was reported that UCH37 activity is stimulated by branched ubiquitin (Ub) chain architectures. To understand how UCH37 achieves its unique debranching specificity, we performed biochemical and Nuclear Magnetic Resonance (NMR) structural analyses and found that UCH37 is activated by contacts with the hydrophobic patches of both distal Ubs that emanate from a branched Ub. In addition, RPN13, which recruits UCH37 to the proteasome, further enhances branched-chain specificity by restricting linear Ub chains from having access to the UCH37 active site. In cultured human cells under conditions of proteolytic stress, we show that substrate clearance by the proteasome is promoted by both binding and deubiquitination of branched polyubiquitin by UCH37. Proteasomes containing UCH37(C88A), which is catalytically inactive, aberrantly retain polyubiquitinated species as well as the RAD23B substrate shuttle factor, suggesting a defect in recycling of the proteasome for the next round of substrate processing. These findings provide a foundation to understand how proteasome degradation of substrates modified by a unique Ub chain architecture is aided by a DUB.

Pyrvinium pamoate regulates MGMT expression through suppressing the Wnt/β-catenin signaling pathway to enhance the glioblastoma sensitivity to temozolomide

Temozolomide (TMZ) is the mainstream chemotherapeutic drug for treating glioblastoma multiforme (GBM), but the intrinsic or acquired chemoresistance to TMZ has become the leading clinical concern, which is related to the repair of DNA alkylation sites by O⁶-methylguanine-DNA methyltransferase (MGMT). Pyrvinium pamoate (PP), the FDA-approved anthelminthic drug, has been reported to inhibit the Wnt/β-catenin pathway within numerous cancer types, and Wnt/β-catenin signaling pathway can modulate the expression of MGMT gene. However, whether PP affects the expression of MGMT and enhances TMZ sensitivity in GBM cells remains unclear. In the present study, we found that PP and TMZ had synergistic effect on inhibiting the viability of GBM cells, and PP induced inhibition of MGMT and enhanced the TMZ chemosensitivity of GBM cells through down-regulating Wnt/β-catenin pathway. Moreover, the overexpression of MGMT or β-catenin weakened the synergy between PP and TMZ. The mechanism of PP in inhibiting the Wnt pathway was indicated that PP resulted in the degradation of β-catenin via the AKT/GSK3β/β-catenin signaling axis. Moreover, Ser552 phosphorylation in β-catenin, which promotes its nuclear accumulation and transcriptional activity, is blocked by PP that also inhibits the Wnt pathway to some extent. The intracranial GBM mouse model also demonstrated that the synergy between PP and TMZ could be achieved through down-regulating β-catenin and MGMT, which prolonged the survival time of tumor-bearing mice. Taken together, our data suggest that PP may serve as the prospect medicine to improve the chemotherapeutic effect on GBM, especially for chemoresistant to TMZ induced by MGMT overexpression.

Deubiquitination Reactions on the Proteasome for Proteasome Versatility

The 26S proteasome, a master player in proteolysis, is the most complex and meticulously contextured protease in eukaryotic cells. While capable of hosting thousands of discrete substrates due to the selective recognition of ubiquitin tags, this protease complex is also dynamically checked through diverse regulatory mechanisms. The proteasome's versatility ensures precise control over active proteolysis, yet prevents runaway or futile degradation of many essential cellular proteins. Among the multi-layered processes regulating the proteasome's proteolysis, deubiquitination reactions are prominent because they not only recycle ubiquitins, but also impose a critical checkpoint for substrate degradation on the proteasome. Of note, three distinct classes of deubiquitinating enzymes-USP14, RPN11, and UCH37-are associated with the 19S subunits of the human proteasome. Recent biochemical and structural studies suggest that these enzymes exert dynamic influence over proteasome output with limited redundancy, and at times act in opposition. Such distinct activities occur spatially on the proteasome, temporally through substrate processing, and differentially for ubiquitin topology. Therefore, deubiquitinating enzymes on the proteasome may fine-tune the degradation depending on various cellular contexts and for dynamic proteolysis outcomes. Given that the proteasome is among the most important drug targets, the biology of proteasome-associated deubiquitination should be further elucidated for its potential targeting in human diseases.

Ubiquitin C-Terminal Hydrolase L5 (UCHL5) Accelerates the Growth of Endometrial Cancer via Activating the Wnt/β-Catenin Signaling Pathway

Endometrial cancer (EC) is the most prevalent gynecological malignancy with high mortality. Chemotherapy plays a pivotal role both in an adjuvant setting and in exclusive treatment. However, current pharmacotherapies are limited and not ideal for improving the overall survival of EC patients. Thus, identification of the underlying molecular mechanisms responsible for initiation and progression of EC is imperative for developing novel therapeutic strategies. Ubiquitin C-terminal hydrolase L5 (UCHL5) has been found to aggravate tumor growth and metastasis in several different types of tumor models such as esophageal squamous cell carcinoma, hepatocellular carcinoma, and epithelial ovarian cancer. However, whether UCHL5 influences the growth of EC has not been elucidated. To expose the role of UCHL5 on EC, bioinformatics analysis was conducted, and it hinted that UCHL5 was overexpressed in EC tissues and associated with lower overall survival. Consistently, the overexpression of UCHL5 in EC tissues and cell lines was further confirmed by western blot (WB) and polymerase chain reaction (PCR) compared with non-tumor control. Lentivirus vectors carrying UCHL5 shRNA or CD sequences were used to reduce or overexpress the UCHL5 gene, respectively. Cell proliferation and cycle were facilitated, and cell apoptosis was decreased when the UCHL5 gene was overexpressed in EC cell lines. These results were opposite in UCHL5 knockdown EC cells. Additionally, the expression of β-catenin is positively related to UCHL5 levels and the tumorigenic effects of UCHL5 overexpression were reversed by the Wnt/β-catenin pathway inhibitor XAV939. Thus, Wnt/β-catenin pathway activation may be a partial mechanism responsible for the promoting effects of UCHL5 on EC growth. In conclusion, UCHL5 accelerated the growth of EC via the Wnt/β-catenin pathway and was expected to be an attractive target for EC treatment.