Inhibition of Ubiquitin-specific Peptidase 8 Suppresses Growth of Gefitinib-resistant Non-small Cell Lung Cancer Cells by Inducing Apoptosis

Inhibition of ubiquitin specific peptidase 8 is effective against 5-fluorouracil resistance in colon cancer via suppressing EGFR and EGFR-mediated signaling pathways

BACKGROUND

The identification of a sensitizing strategy to overcome 5-fluorouracil (5-FU) therapeutic resistance is needed in colon cancer. Recent studies highlight the oncogenic role of ubiquitin specific peptidase 8 (USP8) in many cancers. In line with these efforts, this work investigated the therapeutic potential of targeting USP8 in colon cancer.

METHODS

Immunohistochemistry was performed to determine USP8 expression level in colon cancer tissues and their adjacent normal tissues. Gain-of-function analysis via plasmid overexpression and loss-of-function analysis via siRNA knockdown were applied on cellular assays. The combinatory effects of USP8 inhibitor and cisplatin were determined using a colon xenograft mouse model. Immunoblotting was performed to investigate the molecular mechanism of USP8 inhibition in colon cancer cells.

RESULTS

Compared to normal counterparts, we showed that USP8 protein level was significantly higher in colon cancer tissues and cells. In addition, USP8 expression was not affected by prolonged exposure of colon cancer cells to 5-FU. USP8 was important for colon cancer cell growth and survival but not migration as assessed by loss-of-function and gain-of-function approaches. Pharmacological inhibition of USP8 using USP8 inhibitor is active against both sensitive and 5-FU-resistant colon cancer cells. Of note, USP8 inhibitor significantly inhibited colon cancer formation and growth, and augmented in vivo efficacy of 5-FU without causing toxicity in mice. Mechanistic studies showed that USP8 inhibitor acted on colon cancer cells through suppressing EGFR and EGFR-mediated signalling pathways.

CONCLUSIONS

Our work is the first to reveal the essential role of USP8 in colon cancer via EGFR oncogenic signalling pathways. Our findings provide a proof-of-concept that USP8 inhibitors are promising candidates to overcome 5-FU resistance in colon cancer.

Central role of ubiquitin-specific protease 8 in leptin signaling pathway in pulmonary arterial hypertension

BACKGROUND

Leptin receptor (ObR-b) is overexpressed in pulmonary artery smooth muscle cells (PA-SMCs) from patients with pulmonary arterial hypertension (PAH) and is implicated in both mechanisms that contribute to pulmonary vascular remodeling: hyperproliferation and inflammation. Our aim was to investigate the role of ubiquitin-specific peptidase 8 (USP8) in ObR-b overexpression in PAH.

METHODS

We performed in situ and in vitro experiments in human lung specimens and isolated PA-SMCs combined with 2 different in vivo models in rodents and we generated a mouse with an inducible USP8 deletion specifically in smooth muscles.

RESULTS

Our results showed an upregulation of USP8 in the smooth muscle layer of distal pulmonary arteries from patients with PAH, and upregulation of USP8 expression in PAH PA-SMCs, compared to controls. USP8 inhibition in PAH PA-SMCs significantly blocked both ObR-b protein expression level at the cell surface as well as ObR-b-dependant intracellular signaling pathway as shown by a significant decrease in pSTAT3 expression. USP8 was required for ObR-b activation in PA-SMCs and its inhibition prevented Ob-mediated cell proliferation through STAT3 pathway. USP8 inhibition by the chemical inhibitor DUBs-IN-2 protected against the development of experimental PH in the 2 established experimental models of PH. Targeting USP8 specifically in smooth muscle cells in a transgenic mouse model also protected against the development of experimental PH.

CONCLUSIONS

Our findings highlight the role of USP8 in ObR-b overexpression and pulmonary vascular remodeling in PAH.

Functionalized Gold Nanoparticles Suppress the Proliferation of Human Lung Alveolar Adenocarcinoma Cells by Deubiquitinating Enzymes Inhibition

Functionalized gold nanoparticles (AuNPs) are widely used in therapeutic applications, but little is known regarding the impact of their surface functionalization in the process of toxicity against cancer cells. This study investigates the anticancer effects of 5 nm spherical AuNPs functionalized with tannate, citrate, and PVP on deubiquitinating enzymes (DUBs) in human lung alveolar adenocarcinoma (A549) cells. Our findings show that functionalized AuNPs reduce the cell viability in a concentration- and time-dependent manner as measured by modified lactate dehydrogenase (mLDH) and 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays. An increased generation of intracellular reactive oxygen species (ROS) and depletion of glutathione (GSH/GSSG) ratio was observed with the highest AuNP concentration of 10 μg/mL. The expression of DUBs such as ubiquitin specific proteases (USP7, USP8, and USP10) was slightly inhibited when treated with concentrations above 2.5 μg/mL. Moreover, functionalized AuNPs showed an inhibitory effect on protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) and wingless-related integration site (Wnt) signaling proteins, and this could further trigger mitochondrial related-apoptosis by the upregulation of caspase-3, caspase-9, and PARP in A549 cells. Furthermore, our study shows a mechanistic understanding of how functionalized AuNPs inhibit the DUBs, consequently suppressing cell proliferation, and can be modulated as an approach toward anticancer therapy. The study also warrants the need for future work to investigate the effect of functionalized AuNPs on DUB on other cancer cell lines both in vitro and in vivo.

USP8 inhibitor-induced DNA damage activates cell cycle arrest, apoptosis, and autophagy in esophageal squamous cell carcinoma

Increasing evidence suggests that targeting ubiquitin-specific peptidase 8 (USP8) serves as an attractive anti-cancer strategy. However, the role of USP8 inhibitor, DUB-IN-1, in esophageal squamous cell carcinoma (ESCC) cells still needs to be explored. Here, immunohistochemistry was employed to examine the expression of USP8 in ESCC tissues. Cell Counting Kit-8 (CCK-8) was used to evaluate cell proliferation ability, and propidium iodide (PI) was selected to test the effect of DUB-IN-1 on cell cycle. AnnexinV-FITC/PI staining and the activity of caspase 3 were detedcted to evaluate apoptosis. Transmission electron microscope, microtubule-associated protein 1 light-chain 3 (LC3) expression, and acridine orange (AO) staining were selected to check if there was autophagy. Comet assay and γ-H2AX immunofluorescence was used to monitor DNA damage. Rescue experiment was used to determine the key role of of p53 in cell cycle, apoptosis, and autophagy. Results revealed that the leve of USP8 was higher in ESCC tissues than that in tissues adjacent to carcinoma. DUB-IN-1, an USP8 inhibitor, caused DNA damage, led to G2/M phase block by p53-p21 axis, and triggered apoptosis by regulating the p53 target proteins including Bax, Noxa, and Puma. Besides, DUB-IN-1 could stimulate autophagy through p53-dependent adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activation. Taken together, this study revealed the cytotoxic effects and the mechanism of DUB-IN-1, which indicated that DUB-IN-1 may be a novel inhibitor targeting USP8 that can kill ESCC cells. USP8 inhibitor, DUB-IN-1, treatment could inhibit esophageal squamous cell carcinoma cell growth and induce G2/M cell cycle arrest, apoptosis, and autophagy by DNA damage-induced p53 activation. DUB-IN-1 treatment led to G2/M cell cycle arrest by upregulating the protein level of p21 and triggered apoptosis by modulating the p53 target proteins including Bax, Noxa, and Puma. Meanwhile, DUB-IN-1 treatment stimulated protective autophagy through p53-dependent AMPK activation. Collectively, these findings suggested that DNA damage-triggered p53 activation, p53-Puma/Noxa/Bax, p53-p21, and p53-AMPK pathways were all involved in the effect of DUB-IN-1.

Advances in Molecular Pathophysiology and Targeted Therapy for Cushing's Disease

Cushing's disease is caused by autonomous secretion of adrenocorticotropic hormone (ACTH) from corticotroph pituitary neuroendocrine tumors. As a result, excess cortisol production leads to the overt manifestation of the clinical features of Cushing's syndrome. Severe complications have been reported in patients with Cushing's disease, including hypertension, menstrual disorders, hyperglycemia, osteoporosis, atherosclerosis, infections, and mental disorders. Cushing's disease presents with a variety of clinical features, ranging from overt to subtle. In this review, we explain recent advances in molecular insights and targeted therapy for Cushing's disease. The pathophysiological characteristics of hormone production and pituitary tumor cells are also explained. Therapies to treat the tumor growth in the pituitary gland and the autonomous hypersecretion of ACTH are discussed. Drugs that target corticotroph pituitary neuroendocrine tumors have been effective, including cabergoline, a dopamine receptor type 2 agonist, and pasireotide, a multi-receptor-targeted somatostatin analog. Some of the drugs that target adrenal hormones have shown potential therapeutic benefits. Advances in potential novel therapies for Cushing's disease are also introduced.

Identification of chemicals breaking the USP8 interaction with its endocytic substrate CHMP1B

The ubiquitin-specific protease USP8 plays a major role in controlling the stability and intracellular trafficking of numerous cell surface proteins among which the EGF receptor that regulates cell growth and proliferation in many physio-pathological processes. The function of USP8 at the endocytic pathway level partly relies on binding to and deubiquitination of the Endosomal Sorting Complex Required for Transport (ESCRT) protein CHMP1B. In the aim of finding chemical inhibitors of the USP8::CHMP1B interaction, we performed a high-throughput screening campaign using an HTRF® assay to monitor the interaction directly in lysates of cells co-expressing both partners. The assay was carried out in an automated format to screen the academic Fr-PPIChem library (Bosc N et al., 2020), which includes 10,314 compounds dedicated to the targeting of protein-protein interactions (PPIs). Eleven confirmed hits inhibited the USP8::CHMP1B interaction within a range of 30% to 70% inhibition at 50 µM, while they were inactive on a set of other PPI interfaces demonstrating the feasibility of specifically disrupting this particular interface. In parallel, we adapted this HTRF® assay to compare the USP8 interacting capacity of CHMP1B variants. As anticipated from earlier studies, a deletion of the MIM (Microtubule Interacting and Trafficking domain Interacting Motif) domain or mutation of two conserved leucine residues, L192 and L195, in this domain respectively abolished or strongly impeded the USP8::CHMP1B interaction. By contrast, a CHMP1B mutant that displays a highly decreased ubiquitination level following mutation of four lysine residues in arginine interacted at a similar level as the wild-type form with USP8. Therefore, conserved leucine residues within the MIT domain rather than its ubiquitinated status triggers CHMP1B substrate recognition by USP8.

Molecular mechanism of lncRNA SNHG12 in immune escape of non-small cell lung cancer through the HuR/PD-L1/USP8 axis

Background

The pivotal role of long noncoding RNAs (lncRNAs) in cancer immune responses has been well established. This study was conducted with the aim of exploring the molecular mechanism of lncRNA small nucleolar RNA host gene 12 (SNHG12) in immune escape of non-small cell lung cancer (NSCLC).

Methods

Expression of lncRNA SNHG12, programmed cell death receptor ligand 1 (PD-L1), ubiquitin-specific protease 8 (USP8), and human antigen R (HuR) in NSCLC tissues and cells was measured, and their binding relationship was determined. NSCLC cell proliferation and apoptosis were assessed. Peripheral blood mononuclear cells (PBMCs) were co-cultured with NSCLC cells. The ratio of CD8⁺ T cells, PBMC proliferation, and inflammatory factors were determined. lncRNA SNHG12 localization was assessed via subcellular fractionation assay. The half-life period of mRNA was determined using actinomycin D. Xenograft tumor models were established to confirm the role of lncRNA SNHG12 in vivo.

Results

LncRNA SNHG12 was found to be prominently expressed in NSCLC tissues and cells, which was associated with a poor prognosis. Silencing lncRNA SNHG12 resulted in the reduction in proliferation and the promotion of apoptosis of NSCLC cells, while simultaneously increasing PBMC proliferation and the ratio of CD8⁺ T cells. Mechanically, the binding of lncRNA SNHG12 to HuR improved mRNA stability and expression of PD-L1 and USP8, and USP8-mediated deubiquitination stabilized the protein level of PD-L1. Overexpression of USP8 or PD-L1 weakened the inhibition of silencing lncRNA SNHG12 on the immune escape of NSCLC. Silencing lncRNA SNHG12 restricted tumor growth and upregulated the ratio of CD8⁺ T cells by decreasing USP8 and PD-L1.

Conclusion

LncRNA SNHG12 facilitated the immune escape of NSCLC by binding to HuR and increasing PD-L1 and USP8 levels.

Inhibiting USP8 overcomes hepatocellular carcinoma resistance via suppressing receptor tyrosine kinases

The ubiquitin-specific protease 8 (USP8) is a prototypic multidomain deubiquitinating enzyme with pleiotropic functions. We investigated the role of USP8 in hepatocellular carcinoma (HCC) by analyzing expression patterns of USP8 in HCC patients, and evaluating its functions and underlying signaling. Among 20 HCC patients investigated, we found that USP8 protein upregulation was a common phenomenon (17 out of 20) in HCC compared to normal liver tissue. Furthermore, the upregulation of USP8 was not associated with any clinicopathology. USP8 inhibition via genetic and pharmacological approaches resulted in growth inhibition and apoptosis induction in both sensitive and doxorubicin-resistant HCC cells. Of note, USP8 inhibition significantly enhanced doxorubicin or sorafenib's efficacy in HCC cells and mouse models. We further found that USP8 inhibition decreased levels of multiple receptor tyrosine kinases (RTKs) by ~90%, such as epidermal growth factor receptor (EGFR) and c-Met. Consistently, the downstream signaling regulated by RTKs was disrupted in HCC cells after USP8 inhibition, as shown by the decreased p-Akt, p-STAT3 and p-Raf. Our findings demonstrate that USP8 is a novel therapeutic target in HCC. Inhibiting USP8 has potential to overcome current drug resistance, particularly on HCC patients with high USP8 expression.

USP8 is a Novel Therapeutic Target in Melanoma Through Regulating Receptor Tyrosine Kinase Levels

Introduction

The hyperactivation of receptor tyrosine kinase (RTK)-mediated pathways plays an important role in melanoma progression and resistance to therapy. The ubiquitin-specific protease 8 (USP8) is a deubiquitinating enzyme and its inhibition induces degradation of RTKs. This work explored the expression and role of USP8 in melanoma.

Methods

ELISA and qPCR were performed to assess USP8 expression in melanoma tissues and cells, as well as their normal counterparts. Cellular proliferation, migration and apoptosis assays were performed to determine USP8 functions in three melanoma cell lines. Western blot was performed to analyze RTK signaling in melanoma cells after USP8 inhibition.

Results

mRNA and protein level of USP8 were higher in melanoma cells than normal melanocytes. Higher USP8 expression was also found in tumors in the majority of melanoma patients. USP8 expression was not associated with clinicopathological features, such as age, disease stage, histology, ulceration and BRAF status. Functional analysis demonstrated that USP8 overexpression promoted melanoma cell activities and alleviated the inhibitory effects of therapeutic drugs. In contrast, USP8 knockdown suppressed melanoma cell growth, survival and migration, and augmented the inhibitory effects of therapeutic drugs. Mechanism studies revealed that USP8 inhibition remarkably reduced the expression level of multiple oncogenic RTKs, including c-Met, Kit, EGFR and GPCR. Consistently, RTK-mediated downstream pathways were disrupted in USP8-depleted cells, leading to the increased level of pro-apoptotic proteins and decreased level of anti-apoptotic proteins.

Conclusion

Inhibition of USP8 activity is a novel sensitizing strategy to overcome therapy resistance in melanoma.

Knockdown of USP8 Inhibits the Growth of Lung Cancer Cells

Purpose

Lung cancer is the deadliest tumor in the world. This study aimed to investigate the effection of USP8 on the proliferation and growth of NSCLC cells.

Methods

The proliferation, migration, invasion, cell cycle progression, and apoptosis of A549 and H1299 cells were evaluated with CCK8, colony formation, scratch, transwell, and flow cytometry experiments. Furthermore, the expression of cell cycle- and apoptosis-related proteins was detected by western blot.

Results

Knockdown of USP8 inhibited the proliferation, migration, invasion, and cell cycle progression of A549 and H1299 cells, and promoted the apoptosis. The results of western blot indicated that knockdown of USP8 down-regulated the expression of Cyclin D1, CDK4, CDK6, p-AKT, and Bcl2, and up-regulated the expression of Bax.

Conclusion

Knockdown of USP8 inhibited the proliferation of human lung cancer cells by regulating cell cycle- and apoptosis-related proteins. USP8 may be a therapeutic target for lung cancer.

Ubiquitin-specific peptidase 8 regulates the trafficking and stability of the human organic anion transporter 1

Background Organic anion transporter 1 (OAT1) plays a vital role in avoiding the potential toxicity of various anionic drugs through the involvement of kidney elimination. We previously demonstrated that ubiquitin conjugation to OAT1 led to OAT1 internalization from cell surface, followed by degradation. Ubiquitination is a dynamic process, where deubiquitination is catalyzed by a class of ubiquitin-specific peptidases. Methods The role of ubiquitin-specific peptidase 8 (USP8) in hOAT1 function, expression and ubiquitination was assessed by conducting transporter uptake assay, biotinylation assay and ubiquitination assay. Results We demonstrated that USP8 overexpression in hOAT1-expressing cells led to an increased hOAT1 transporter activity and expression, which correlated well with a reduced hOAT1 ubiquitination. Such phenomenon was not observed in inactive USP8 mutant-transfected cells. In addition, the knockdown of endogenous USP8 by USP8-specific siRNA resulted in an increased hOAT1 ubiquitination, which correlated well with a decrease in hOAT1 expression and transport activity. Biotinylation experiments demonstrated that USP8-induced increase in hOAT1 expression and transport activity occurred through a deceleration of the rates of hOAT1 internalization and degradation. Conclusions These results indicated the regulatory role of USP8 in OAT1 function, expression, trafficking, and stability. General significance USP8 could be a new target for modulating OAT1-mediated drug transport.

Ubiquitin-specific protease 8 inhibitor suppresses adrenocorticotropic hormone production and corticotroph tumor cell proliferation

Cushing's disease is primarily caused by autonomic hypersecretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma. In Cushing's disease, mutations in the ubiquitin-specific protease 8 (USP8) have been detected. These mutations are associated with hyperactivation of USP8 that prevent epidermal growth factor receptor (EGFR) degradation. This leads to increased EGFR stability and results in the maintenance of EGFR signaling in Cushing's disease. USP8 inhibitors can suppress the growth of various tumors. In this study, the effects of a potent USP8 inhibitor, DUBs-IN-2, on ACTH production and cell proliferation were examined in mouse corticotroph tumor (AtT-20) cells. Proopiomelanocortin (Pomc) mRNA levels and ACTH levels were decreased in AtT-20 cells by DUBs-IN-2. Further, cell proliferation was inhibited, and apoptosis was induced by DUBs-IN-2. Transcript levels of pituitary tumor-transforming gene 1 (Pttg1), a pituitary tumor growth marker, were increased; and transcript levels of stress response growth arrest and DNA damage-inducible 45 (Gadd45β) and Cdk5 and ABL enzyme substrate 1 (Cables1) mRNA levels were increased in response to the drug. Gadd45β or Cables1 knockdown partially inhibited the DUBs-IN-2-induced decrease in cell proliferation, but not Pomc mRNA levels. Both GADD45β and CABLES1 may be responsible, at least in part, for the USP8-induced suppression of corticotroph tumor cell proliferation. USP-8 may be a new treatment target in Cushing's disease.

Ubiquitin-specific protease 8 (USP8/UBPy): a prototypic multidomain deubiquitinating enzyme with pleiotropic functions

Protein modification by ubiquitin is one of the most versatile posttranslational regulations and counteracted by almost 100 deubiquitinating enzymes (DUBs). USP8 was originally identified as a growth regulated ubiquitin-specific protease and is like many other DUBs characterized by its multidomain architecture. Besides the catalytic domain, specific protein-protein interaction modules were characterized which contribute to USP8 substrate recruitment, regulation and targeting to distinct protein complexes. Studies in mice and humans impressively showed the physiological relevance and non-redundant function of USP8 within the context of the whole organism. USP8 knockout (KO) mice exhibit early embryonic lethality while induced deletion in adult animals rapidly causes lethal liver failure. Furthermore, T-cell specific ablation disturbs T-cell development and function resulting in fatal autoimmune inflammatory bowel disease. In human patients, somatic mutations in USP8 were identified as the underlying cause of adrenocorticotropic hormone (ACTH) releasing pituitary adenomas causing Cushing's disease (CD). Here we provide an overview of the versatile molecular, cellular and pathology associated function and regulation of USP8 which appears to depend on specific protein binding partners, substrates and the cellular context.

The New Genetic Landscape of Cushing's Disease: Deubiquitinases in the Spotlight

Cushing’s disease (CD) is a rare condition caused by adrenocorticotropic hormone (ACTH)-producing adenomas of the pituitary, which lead to hypercortisolism that is associated with high morbidity and mortality. Treatment options in case of persistent or recurrent disease are limited, but new insights into the pathogenesis of CD are raising hope for new therapeutic avenues. Here, we have performed a meta-analysis of the available sequencing data in CD to create a comprehensive picture of CD’s genetics. Our analyses clearly indicate that somatic mutations in the deubiquitinases are the key drivers in CD, namely USP8 (36.5%) and USP48 (13.3%). While in USP48 only Met415 is affected by mutations, in USP8 there are 26 different mutations described. However, these different mutations are clustering in the same hotspot region (affecting in 94.5% of cases Ser718 and Pro720). In contrast, pathogenic variants classically associated with tumorigenesis in genes like TP53 and BRAF are also present in CD but with low incidence (12.5% and 7%). Importantly, several of these mutations might have therapeutic potential as there are drugs already investigated in preclinical and clinical setting for other diseases. Furthermore, network and pathway analyses of all somatic mutations in CD suggest a rather unified picture hinting towards converging oncogenic pathways.

Transcriptome analysis of peripheral blood mononuclear cells from chronic hepatitis B and hepatocellular carcinoma patients: a network-based attitude

Aim: The aim of the study was constructing a protein–protein interaction network for chronic hepatitis B (CHB) and hepatocellular carcinoma (HCC) patients. Materials & methods: Comprehensive gene expression profile of peripheral blood mononuclear cells of CHB and HCC were obtained from Gene Expression Omnibus/NCBI database. Differentially expressed genes (DEGs) of samples were analyzed using GEO2R web application. Results: The majority of DEGs in both CHB and HCC has been enriched in immune system responses. However, there was a significant disparity between the enrichment of these genes (especially genes associated with Toll-like receptor-and-TNF) in CHB-HCC compared with normal-CHB. Conclusion: The transcriptome properties of peripheral blood mononuclear cells are changed in patients with HBV-HCC. The immune response genes are the most deregulated genes in HCC patients.

[Formula: see text]

Downregulation of USP32 inhibits cell proliferation, migration and invasion in human small cell lung cancer

OBJECTIVES

Ubiquitin specific protease 32 (USP32) is a highly conserved but uncharacterized gene, which has been reported to be associated with growth of breast cancer cells. However, the role of USP32 in human small cell lung cancer (SCLC) has not been uncovered. The aim of this study was to investigate and evaluate the clinical significance of USP32 in patients with SCLC.

MATERIALS AND METHODS

Expression of USP32 was firstly investigated using public online data sets and then determined in SCLC tissues and cell lines using quantitative real-time PCR, Western blotting and immunohistochemical staining. SCLC cells were transfected with a small-interfering RNA targeting USP32 mRNA and analysed for cell viability, proliferation ability, cell cycle distribution, apoptosis and invasion.

RESULTS

USP32 was found to be overexpressed in SCLC tissues compared with normal tissues. High USP32 expression was significantly correlated with disease stage and invasion. In vitro experiments demonstrated that silencing of USP32 caused a significant decrease in the proliferation and migration rate of cells. Furthermore, USP32 silencing arrested cell cycle progression at G0/G1 phase via decreasing CDK4/Cyclin D1 complex and elevating p21. In addition, downregulation of USP32 significantly induced cell apoptosis by activating cleaved caspase-3 and cleaved PARP, as well as inhibiting cell invasiveness via altering epithelial mesenchymal transition expression.

CONCLUSIONS

Our results suggest for the first time that USP32 is important for SCLC progression and might be a potential target for molecular therapy of SCLC.

Deubiquitinating enzyme USP22 positively regulates c-Myc stability and tumorigenic activity in mammalian and breast cancer cells

The proto-oncogene c-Myc has a pivotal function in growth control, differentiation, and apoptosis and is frequently affected in human cancer, including breast cancer. Ubiquitin-specific protease 22 (USP22), a member of the USP family of deubiquitinating enzymes (DUBs), mediates deubiquitination of target proteins, including histone H2B and H2A, telomeric repeat binding factor 1, and cyclin B1. USP22 is also a component of the mammalian SAGA transcriptional co-activating complex. In this study, we explored the functional role of USP22 in modulating c-Myc stability and its physiological relevance in breast cancer progression. We found that USP22 promotes deubiquitination of c-Myc in several breast cancer cell lines, resulting in increased levels of c-Myc. Consistent with this, USP22 knockdown reduces c-Myc levels. Furthermore, overexpression of USP22 stimulates breast cancer cell growth and colony formation, and increases c-Myc tumorigenic activity. In conclusion, the present study reveals that USP22 in breast cancer cell lines increases c-Myc stability through c-Myc deubiquitination, which is closely correlated with breast cancer progression.

Inhibition of Ubiquitin-specific Peptidase 8 Suppresses Adrenocorticotropic Hormone Production and Tumorous Corticotroph Cell Growth in AtT20 Cells

BACKGROUND

Two recent whole-exome sequencing researches identifying somatic mutations in the ubiquitin-specific protease 8 (USP8) gene in pituitary corticotroph adenomas provide exciting advances in this field. These mutations drive increased epidermal growth factor receptor (EGFR) signaling and promote adrenocorticotropic hormone (ACTH) production. This study was to investigate whether the inhibition of USP8 activity could be a strategy for the treatment of Cushing's disease (CD).

METHODS

The anticancer effect of USP8 inhibitor was determined by testing cell viability, colony formation, apoptosis, and ACTH secretion. The immunoblotting and quantitative reverse transcription polymerase chain reaction were conducted to explore the signaling pathway by USP8 inhibition.

RESULTS

Inhibition of USP8-induced degradation of receptor tyrosine kinases including EGFR, EGFR-2 (ERBB2), and Met leading to a suppression of AtT20 cell growth and ACTH secretion. Moreover, treatment with USP8 inhibitor markedly induced AtT20 cells apoptosis.

CONCLUSIONS

Inhibition of USP8 activity could be an effective strategy for CD. It might provide a novel pharmacological approach for the treatment of CD.

DUBs, New Members in the Hypoxia Signaling clUb

Cellular protein homeostasis is tightly regulated by ubiquitination. Responsible for target protein ubiquitination is a class of enzymes, the so-called ubiquitin E3 ligases. They are opposed to a second class of enzymes, called deubiquitinating enzymes (DUBs), which can remove polyubiquitin chains from their specific target proteins. The coaction of the two sets of enzymes allows the cell to adapt its overall protein content and the abundance of particular proteins to a variety of cellular and environmental stresses, including hypoxia. In recent years, DUBs have been highlighted to play major roles in many diseases, including cancer, both as tumor suppressors and oncogenes. Therefore, DUBs are emerging as promising targets for cancer-cell specific treatment. Here, we will review the current understanding of DUBs implicated in the control of hypoxia-inducible factor, the regulation of DUBs by hypoxia, and the use of DUB-specific drugs to target tumor hypoxia-signaling.