USP8: a novel therapeutic target for Cushing's disease

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.

Genetic Basis of ACTH-Secreting Adenomas

Cushing's disease represents 60-70% of all cases of Cushing's syndrome, presenting with a constellation of clinical features associated with sustained hypercortisolism. Molecular alterations in corticotrope cells lead to the formation of ACTH-secreting adenomas, with subsequent excessive production of endogenous glucocorticoids. In the last few years, many authors have contributed to analyzing the etiopathogenesis and pathophysiology of corticotrope adenomas, which still need to be fully clarified. New molecular modifications such as somatic mutations of USP8 and other genes have been identified, and several case series and case reports have been published, highlighting new molecular alterations that need to be explored. To investigate the current knowledge of the genetics of ACTH-secreting adenomas, we performed a bibliographic search of the recent scientific literature to identify all pertinent articles. This review presents the most recent updates on somatic and germline mutations underlying Cushing's disease. The prognostic implications of these mutations, in terms of clinical outcomes and therapeutic scenarios, are still debated. Further research is needed to define the clinical features associated with the different genotypes and potential pharmacological targets.

Quantitative Real-Time Analysis of Differentially Expressed Genes in Peripheral Blood Samples of Hypertension Patients

Hypertension (HTN) is considered one of the most important and well-established reasons for cardiovascular abnormalities, strokes, and premature mortality globally. This study was designed to explore possible differentially expressed genes (DEGs) that contribute to the pathophysiology of hypertension. To identify the DEGs of HTN, we investigated 22 publicly available cDNA Affymetrix datasets using an integrated system-level framework. Gene Ontology (GO), pathway enrichment, and transcriptional factors were analyzed to reveal biological information. From 50 DEGs, we ranked 7 hypertension-related genes (p-value < 0.05): ADM, ANGPTL4, USP8, EDN, NFIL3, MSR1, and CEBPD. The enriched terms revealed significant functional roles of HIF-1-α transcription; endothelin; GPCR-binding ligand; and signaling pathways of EGF, PIk3, and ARF6. SP1 (66.7%), KLF7 (33.3%), and STAT1 (16.7%) are transcriptional factors associated with the regulatory mechanism. The expression profiles of these DEGs as verified by qPCR showed 3-times higher fold changes (2−ΔΔCt) in ADM, ANGPTL4, USP8, and EDN1 genes compared to control, while CEBPD, MSR1 and NFIL3 were downregulated. The aberrant expression of these genes is associated with the pathophysiological development and cardiovascular abnormalities. This study will help to modulate the therapeutic strategies of hypertension.

USP8 Inhibitor Suppresses HER-2 Positive Gastric Cancer Cell Proliferation and Metastasis via the PI3K/AKT Signaling Pathway

Purpose

Referring to global cancer statistics, the incidence of gastric cancer (GC) was ranked sixth; however, detailed mechanisms underlying its development were not thoroughly investigated. Previous studies have reported that inhibition of ubiquitin-specific peptidase 8 (USP8) induced degradation of several receptor tyrosine kinases, such as epidermal growth factor receptor (EGFR), embryonic stem cells (ESCs), etc. Nevertheless, the regulation of HER-2 by USP8 and the molecular mechanisms controlling their role in the pathogenesis of GC remain unknown.

Patients and Methods

A total of 69 patients with histologically confirmed GC were recruited to satisfy the purpose of this study. Initially, tumor samples and GC cell lines were used to detect USP8 and HER-2 levels. Next, MTT and colony formation assays were applied to analyze cell proliferation capability. Cell migration and invasion ability were examined by transwell assays. To examine related mRNA and protein expressions, Western blot assays and quantitative real-time PCR (qRT-PCR) were performed. Immunofluorescence was used to detect the effect of USP8 inhibitor on GC cells. Finally, in vivo experiments were used to examine the effect of USP8 inhibitor.

Results

Patients with USP8 high-expression tumors have shown worse overall survival while opposite results found in patients with low USP8 expressions. Regarding disease prognosis, patients with low expression of USP8 and HER-2 were performed better prognosis, whereas those with overexpression of USP8 and HER-2 shown poor prognosis. USP8 inhibitor significantly inhibited HER-2 positive cell NCI-N87 proliferation and metastasis. In addition, USP8 stabilizes HER-2, preventing it from ubiquitin proteasome-mediated degradation. In vivo studies confirmed that the USP8 inhibitor inhibited HER-2 positive cell NCI-N87 tumor growth. However, it did not affect the HER2-negative cell MGC-803. Careful investigation unraveled that the USP8 inhibitor significantly inhibited NCI-N87 cell proliferation and metastasis via phosphatidylinositol-3-kinases/protein-serine-threonine kinase (PI3K/AKT) pathway.

Conclusion

The USP8 inhibited HER-2 positive GC cell proliferation and migration in vivo and in vitro and probably served as a novel potential therapeutic biomarker for HER-2 positive GC.

The role of deubiquitinating enzymes in gastric cancer

The epigenetic regulation of gene expression (via DNA methylation, histone modification and microRNA interference) contributes to a variety of diseases, particularly cancer. Protein deubiquitination serves a key role in the mechanism underlying histone modification, and consequently influences tumor development and progression. Improved characterization of the role of ubiquitinating enzymes has led to the identification of numerous deubiquitinating enzymes (DUBs) with various functions. Gastric cancer (GC) is a highly prevalent cancer type that exhibits a high mortality rate. Latest analysis about cancer patient revealed that GC is sixth deadliest cancer type, which frequently occur in male (7.2%) than female (4.1%). Complex associations between DUBs and GC progression have been revealed in multiple studies; however, the molecular mechanism underpinning the metastasis and recurrence of GC is yet to be elucidated. Generally, DUBs were upregulated in gastric cancer. The relation of DUBs and tumor size, classification and staging was observed in GC. Besides, 5-yar survival rate of patients with GC is effeccted by expression level of DUBs. Among the highly expressed DUBs, specifically six DUBs namely UCHs, USPs, OTUs, MJDs, JAMMs and MCPIPs effect on this survival rate. Consequently, the association between GC and DUBs has received increasing attention in recent years. Therefore, in the present review, literature investigating the association between DUBs and GC pathophysiology was analyzed and critically appraised.

Rapid Covalent-Probe Discovery by Electrophile-Fragment Screening

Covalent probes can display unmatched potency, selectivity, and duration of action; however, their discovery is challenging. In principle, fragments that can irreversibly bind their target can overcome the low affinity that limits reversible fragment screening, but such electrophilic fragments were considered nonselective and were rarely screened. We hypothesized that mild electrophiles might overcome the selectivity challenge and constructed a library of 993 mildly electrophilic fragments. We characterized this library by a new high-throughput thiol-reactivity assay and screened them against 10 cysteine-containing proteins. Highly reactive and promiscuous fragments were rare and could be easily eliminated. In contrast, we found hits for most targets. Combining our approach with high-throughput crystallography allowed rapid progression to potent and selective probes for two enzymes, the deubiquitinase OTUB2 and the pyrophosphatase NUDT7. No inhibitors were previously known for either. This study highlights the potential of electrophile-fragment screening as a practical and efficient tool for covalent-ligand discovery.

EB 2017 Article: Soy protein isolate feeding does not result in reproductive toxicity in the pre-pubertal rat testis

The isoflavone phytoestrogens found in the soy protein isolate used in soy infant formulas have been shown to have estrogenic actions in the developing male reproductive tract resulting in reproductive toxicity. However, few studies have examined potential estrogenicity of soy protein isolate as opposed to that of pure isoflavones. In this study, we fed weanling male Sprague-Dawley rats a semi-purified diet with casein or soy protein isolate as the sole protein source from postnatal day 21 to 33. Additional groups were fed casein or soy protein isolate and treated s.c. with 10 µg/kg/d estradiol via osmotic minipump. Estradiol treatment reduced testis, prostate weights, and serum androgen concentrations ( P < 0.05). Soy protein isolate had no effect. Estradiol up-regulated 489 and down-regulated 1237 testicular genes >1.5-fold ( P < 0.05). In contrast, soy protein isolate only significantly up-regulated expression of 162 genes and down-regulated 16 genes. The top 30 soy protein isolate-up-regulated genes shared 93% concordance with estradiol up-regulated genes. There was little overlap between soy protein isolate down-regulated genes and those down-regulated by estradiol treatment. Functional annotation analysis revealed significant differences in testicular biological processes affected by estradiol or soy protein isolate. Estradiol had major actions on genes involved in reproductive processes including down-regulation of testicular steroid synthesis and expression of steroid receptor activated receptor (Star) and cytochrome P450 17α-hydroxylase/(Cyp17a1). In contrast, soy protein isolate primarily affected pathways associated with macromolecule modifications including ubiquitination and histone methylation. Our results indicate that rather than acting as a weak estrogen in the developing testis, soy protein isolate appears to act as a selective estrogen receptor modulator with little effect on reproductive processes. Impact statement Soy protein isolate (SPI) is the sole protein used to make soy-based infant formulas. SPI contains phytoestrogens, which are structurally similar to estradiol. These phytoestrogens, daidzein, genistein, and equol, fit the definition of endocrine-disrupting compounds, and at high concentrations, have estrogenic actions resulting in reproductive toxicity in the developing male, when provided as isolated chemicals. However, few animal studies have examined the potential estrogenicity of SPI as opposed to pure isoflavones. In this study, SPI feeding did not elicit an estrogenic response in the testis nor any adverse outcomes including reduced testicular growth, or androgen production during early development in rats when compared to those receiving estradiol. These findings are consistent with emerging data showing no differences in reproductive development in males and female children that received breast milk, cow's milk formula, or soy infant formula during the postnatal feeding period.

New Molecular Targets for Treatment of Cushing's Disease

Despite the best outcomes from trans-sphenoidal surgery, approximately one-third of patients with Cushing's disease will need medical therapy. Current treatments have drawbacks and there is a clear clinical need for new therapies. Recent understanding of molecular pathways leading to excess ACTH secretion has identified key components that may be targeted with the aim to provide novel effective treatment for this devastating disease. These include testicular orphan nuclear receptor 4, heat shock protein 90, and epidermal growth factor receptor. Based on data from preclinical studies, clinical trials are seeking to assess whether targeting these novel pathways can translate into patient benefit.

Receptor Tyrosine Kinase Ubiquitination and De-Ubiquitination in Signal Transduction and Receptor Trafficking

Receptor tyrosine kinases (RTKs) are membrane-based sensors that enable rapid communication between cells and their environment. Evidence is now emerging that interdependent regulatory mechanisms, such as membrane trafficking, ubiquitination, proteolysis and gene expression, have substantial effects on RTK signal transduction and cellular responses. Different RTKs exhibit both basal and ligand-stimulated ubiquitination, linked to trafficking through different intracellular compartments including the secretory pathway, plasma membrane, endosomes and lysosomes. The ubiquitin ligase superfamily comprising the E1, E2 and E3 enzymes are increasingly implicated in this post-translational modification by adding mono- and polyubiquitin tags to RTKs. Conversely, removal of these ubiquitin tags by proteases called de-ubiquitinases (DUBs) enables RTK recycling for another round of ligand sensing and signal transduction. The endocytosis of basal and activated RTKs from the plasma membrane is closely linked to controlled proteolysis after trafficking and delivery to late endosomes and lysosomes. Proteolytic RTK fragments can also have the capacity to move to compartments such as the nucleus and regulate gene expression. Such mechanistic diversity now provides new opportunities for modulating RTK-regulated cellular responses in health and disease states.

Animal models of pituitary neoplasia

Pituitary neoplasias can occur as part of a complex inherited disorder, or more commonly as sporadic (non-familial) disease. Studies of the molecular and genetic mechanisms causing such pituitary tumours have identified dysregulation of >35 genes, with many revealed by studies in mice, rats and zebrafish. Strategies used to generate these animal models have included gene knockout, gene knockin and transgenic over-expression, as well as chemical mutagenesis and drug induction. These animal models provide an important resource for investigation of tissue-specific tumourigenic mechanisms, and evaluations of novel therapies, illustrated by studies into multiple endocrine neoplasia type 1 (MEN1), a hereditary syndrome in which ∼ 30% of patients develop pituitary adenomas. This review describes animal models of pituitary neoplasia that have been generated, together with some recent advances in gene editing technologies, and an illustration of the use of the Men1 mouse as a pre clinical model for evaluating novel therapies.