The ubiquitin-proteasome pathway in adult and pediatric brain tumors: biological insights and therapeutic opportunities

Zonisamide attenuates pressure overload-induced myocardial hypertrophy in mice through proteasome inhibition

Myocardial hypertrophy is a pathological thickening of the myocardium which ultimately results in heart failure. We previously reported that zonisamide, an antiepileptic drug, attenuated pressure overload-caused myocardial hypertrophy and diabetic cardiomyopathy in murine models. In addition, we have found that the inhibition of proteasome activates glycogen synthesis kinase 3 (GSK-3) thus alleviates myocardial hypertrophy, which is an important anti-hypertrophic strategy. In this study, we investigated whether zonisamide prevented pressure overload-caused myocardial hypertrophy through suppressing proteasome. Pressure overload-caused myocardial hypertrophy was induced in mice by trans-aortic constriction (TAC) surgery. Two days after the surgery, the mice were administered zonisamide (10, 20, 40 mg·kg-1·d-1, i.g.) for four weeks. We showed that zonisamide administration significantly mitigated impaired cardiac function. Furthermore, zonisamide administration significantly inhibited proteasome activity as well as the expression levels of proteasome subunit beta types (PSMB) of the 20 S proteasome (PSMB1, PSMB2 and PSMB5) and proteasome-regulated particles (RPT) of the 19 S proteasome (RPT1, RPT4) in heart tissues of TAC mice. In primary neonatal rat cardiomyocytes (NRCMs), zonisamide (0.3 μM) prevented myocardial hypertrophy triggered by angiotensin II (Ang II), and significantly inhibited proteasome activity, proteasome subunits and proteasome-regulated particles. In Ang II-treated NRCMs, we found that 18α-glycyrrhetinic acid (18α-GA, 2 mg/ml), a proteasome inducer, eliminated the protective effects of zonisamide against myocardial hypertrophy and proteasome. Moreover, zonisamide treatment activated GSK-3 through inhibiting the phosphorylated AKT (protein kinase B, PKB) and phosphorylated liver kinase B1/AMP-activated protein kinase (LKB1/AMPKα), the upstream of GSK-3. Zonisamide treatment also inhibited GSK-3's downstream signaling proteins, including extracellular signal-regulated kinase (ERK) and GATA binding protein 4 (GATA4), both being the hypertrophic factors. Collectively, this study highlights the potential of zonisamide as a new therapeutic agent for myocardial hypertrophy, as it shows potent anti-hypertrophic potential through the suppression of proteasome.

Identification of ubiquitin-specific protease 32 as an oncogene in glioblastoma and the underlying mechanisms

Glioblastoma (GBM) patients present poor prognosis. Deubiquitination by deubiquitinating enzymes (DUBs) is a critical process in cancer progression. Ubiquitin-specific proteases (USPs) constitute the largest sub-family of DUBs. Evaluate the role of USP32 in GBM progression and provide a potential target for GBM treatment. Clinical significance of USP32 was investigated using Gene Expression Omnibus databases. Effects of USP32 on cell growth and metastasis were studied in vitro and in vivo. Differentially expressive genes between USP32-knockdown U-87 MG cells and negative control cells were detected using RNA sequencing and used for Gene Ontology and Kyoto Encyclopedia of Genes and Genomic pathway enrichment analyses. Finally, RT-qPCR was used to validate the divergent expression of genes involved in the enriched pathways. USP32 was upregulated in GBM patients, being correlated to poor prognosis. USP32 downregulation inhibited cell growth and metastasis in vitro. Furthermore, USP32 knockdown inhibited tumorigenesis in vivo. In addition, UPS32 was identified as a crucial regulator in different pathways including cell cycle, cellular senescence, DNA replication, base excision repair, and mismatch repair pathways. USP32 acts as an oncogene in GBM through regulating several biological processes/pathways. It could be a potential target for GBM treatment.

Exploring the role and clinical implications of proteasome inhibition in medulloblastoma

Ubiquitin proteasome-mediated protein degradation has been implicated in posttranslational oncogenesis in medulloblastoma. Current research is evaluating the clinical implications of proteasome inhibition as a therapeutic target. In medulloblastoma cell lines, proteasome inhibitors induce apoptosis and inhibit cell proliferation via multiple pathways involving activation of caspase pathways, NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells) pathway inhibition, reduced AKT/mTOR pathway activity, and pro-apoptotic protein expression. Second-generation proteasome inhibitors demonstrate blood-brain barrier penetration while maintaining antitumor effect. This review summarizes the ubiquitin-proteasome system in the pathogenesis of medulloblastoma and the potential clinical implications.

The Role of the Ubiquitin Proteasome System in Glioma: Analysis Emphasizing the Main Molecular Players and Therapeutic Strategies Identified in Glioblastoma Multiforme

Gliomas constitute the most frequent tumors of the brain. High-grade gliomas are characterized by a poor prognosis caused by a set of attributes making treatment difficult, such as heterogeneity and cell infiltration. Additionally, there is a subgroup of glioma cells with properties similar to those of stem cells responsible for tumor recurrence after treatment. Since proteasomal degradation regulates multiple cellular processes, any mutation causing disturbances in the function or expression of its elements can lead to various disorders such as cancer. Several studies have focused on protein degradation modulation as a mechanism of glioma control. The ubiquitin proteasome system is the main mechanism of cellular proteolysis that regulates different events, intervening in pathological processes with exacerbating or suppressive effects on diseases. This review analyzes the role of proteasomal degradation in gliomas, emphasizing the elements of this system that modulate different cellular mechanisms in tumors and discussing the potential of distinct compounds controlling brain tumorigenesis through the proteasomal pathway.

Carnosine suppresses human glioma cells under normoxic and hypoxic conditions partly via inhibiting glutamine metabolism

L-Carnosine (β-alanyl-L-histidine) is a naturally occurring dipeptide, which has shown broad-spectrum anticancer activity. But the anticancer mechanisms and regulators remain unknown. In this study, we investigated the effects of carnosine on human glioma U87 and U251 cell lines under normoxia (21% O2) and hypoxia (1% O2). We showed that carnosine (25-75 mM) dose-dependently inhibited the proliferation of the glioma cells; carnosine (50 mM) inhibited their colony formation, migration, and invasion capacity. But there was no significant difference in the inhibitory effects of carnosine under normoxia and hypoxia. Treatment with carnosine (50 mM) significantly decreased the expression of glutamine synthetase (GS) at the translation level rather than the transcription level in U87 and U251 cells, both under normoxia and hypoxia. Furthermore, the silencing of GS gene with shRNA and glutamine (Gln) deprivation significantly suppressed the growth, migratory, and invasive potential of the glioma cells. The inhibitory effect of carnosine on U87 and U251 cells was partly achieved by inhibiting the Gln metabolism pathway. Carnosine reduced the expression of GS in U87 and U251 cells by promoting the degradation of GS through the proteasome pathway, shortening the protein half-life, and reducing its stability. Given that targeting tumor metabolism is a proven efficient therapeutic tactic, our results may present new treatment strategies and drugs for improving the prognosis of gliomas.

First Whole Transcriptome RNAseq on CHD8 Haploinsufficient Patient and Meta-Analyses Across Cellular Models Uncovers Likely Key Pathophysiological Target Genes

In 2019, we confirmed that the haploinsufficiency of CHD8 does indeed cause the novel syndromic neurodevelopmental disease we first discovered a dozen years before. Here, we report the first whole transcriptome RNAseq gene expression profiling for a patient with this new syndrome, as a preliminary exploration of potential pathophysiological mechanisms. We compared our patient transcriptome profile with that of all publicly available RNAseq datasets from human cellular models including neuronal progenitor cells, neurons and organoids. We compared differential gene expression profiles overall and conducted phenotype-informed data filtration based on the characteristic syndrome presentation. We found that concordance among differential gene expression profiles was poor across all datasets. Nevertheless, remarkably, we show that the patient blood differential gene expression profile most resembled that of the neuronal cell model, a finding that encourages further transcriptome profiling using patient blood samples. In addition, our custom phenotype-informed analyses yielded important, differentially expressed syndrome pathophysiology target genes. Finally, we note that genes dysregulated due to CHD8 heterozygous deletion are linked to known neurological as well as oncological pathways.

Bortezomib inhibits growth and sensitizes glioma to temozolomide (TMZ) via down-regulating the FOXM1-Survivin axis

Background

High-grade glioma (HGG) is a fatal human cancer. Bortezomib, a proteasome inhibitor, has been approved for the treatment of multiple myeloma but its use in glioma awaits further investigation. This study aimed to explore the chemotherapeutic effect and the underlying mechanism of bortezomib on gliomas.

Methods

U251 and U87 cell viability and proliferation were detected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, tumor cell spheroid growth, and colony formation assay. Cell apoptosis and cell cycle were detected by flow cytometry. Temozolomide (TMZ)-insensitive cell lines were induced by long-term TMZ treatment, and cells with stem cell characteristics were enriched with stem cell culture medium. The mRNA levels of interested genes were measured via reverse transcription-quantitative polymerase chain reaction, and protein levels were determined via Western blotting/immunofluorescent staining in cell lines and immunohistochemical staining in paraffin-embedded sections. Via inoculating U87 cells subcutaneously, glioma xenograft models in nude mice were established for drug experiments. Patient survival data were analyzed using the Kaplan–Meier method.

Results

Bortezomib inhibited the viability and proliferation of U251 and U87 cells in a dose- and time-dependent manner by inducing apoptosis and cell cycle arrest. Bortezomib also significantly inhibited the spheroid growth, colony formation, and stem-like cell proliferation of U251 and U87 cells. When administrated in combination, bortezomib showed synergistic effect with TMZ in vitro and sensitized glioma to TMZ treatment both in vitro and in vivo. Bortezomib reduced both the mRNA and protein levels of Forkhead Box M1 (FOXM1) and its target gene Survivin. The FOXM1–Survivin axis was markedly up-regulated in established TMZ-insensitive glioma cell lines and HGG patients. Expression levels of FOXM1 and Survivin were positively correlated with each other and both related to poor prognosis in glioma patients.

Conclusions

Bortezomib was found to inhibit glioma growth and improved TMZ chemotherapy efficacy, probably via down-regulating the FOXM1–Survivin axis. Bortezomib might be a promising agent for treating malignant glioma, alone or in combination with TMZ.