Deubiquitinating Enzyme USP20 Regulates Extracellular Signal-Regulated Kinase 3 Stability and Biological Activity

A novel PDIA3/FTO/USP20 positive feedback regulatory loop induces osteogenic differentiation of preosteoblast in osteoporosis

Osteoporosis is a chronic skeletal disease and the major source of risk for fractures in aged people. It is urgent to investigate the mechanism regulating osteoporosis for developing potential treatment and prevention strategies. Osteogenic differentiation of preosteoblast enhances bone formation, which might be a promising strategy for treatment and prevention of osteoporosis. Protein disulfide isomerase family A, member 3 (PDIA3) could induce bone formation, yet the role of PDIA3 in osteogenic differentiation of preosteoblast remains unknown. In this study, m6 A RNA methylation was detected by methylated RNA immunoprecipitation (MeRIP), while mRNA stability was identified by RNA decay assay. Besides, protein-protein interaction and protein phosphorylation were determined using co-immunoprecipitation (Co-IP). Herein, results revealed that PDIA3 promoted osteogenic differentiation of preosteoblast MC3T3-E1. Besides, PDIA3 mRNA methylation was suppressed by FTO alpha-ketoglutarate dependent dioxygenase (FTO) as RNA methylation reduced PDIA3 mRNA stability during osteogenic differentiation of MC3T3-E1 cells. Moreover, ubiquitin specific peptidase 20 (USP20) improved FTO level through inhibiting FTO degradation while PDIA3 increased FTO level by enhancing USP20 phosphorylation during osteogenic differentiation of MC3T3-E1 cells, suggesting a positive feedback regulatory loop between PDIA3 and FTO. In summary, these findings indicated the mechanism of PDIA3 regulating osteogenic differentiation of preosteoblast and provided potential therapeutic targets for osteoporosis.

Role of the Atypical MAPK ERK3 in Cancer Growth and Progression

Extracellular signal-regulated kinase 3 (ERK3) is an atypical mitogen-activated protein kinase (MAPK) whose structural and regulatory features are distinct from those of conventional MAPKs, such as ERK1/2. Since its identification in 1991, the regulation, substrates and functions of ERK3 have remained largely unknown. However, recent years have witnessed a wealth of new findings about ERK3 signaling. Several important biological functions for ERK3 have been revealed, including its role in neuronal morphogenesis, inflammation, metabolism, endothelial cell tube formation and epithelial architecture. In addition, ERK3 has been recently shown to play important roles in cancer cell proliferation, migration, invasion and chemoresistance in multiple types of cancers. Furthermore, accumulating studies have uncovered various molecular mechanisms by which the expression level, protein stability and activity of ERK3 are regulated. In particular, several post-translational modifications (PTMs), including ubiquitination, hydroxylation and phosphorylation, have been shown to regulate the stability and activity of ERK3 protein. In this review, we discuss recent findings regarding biochemical and cellular functions of ERK3, with a main focus on its roles in cancers, as well as the molecular mechanisms of regulating its expression and activity.

Phosphoproteomic analysis identifies supervillin as an ERK3 substrate regulating cytokinesis and cell ploidy

Extracellular signal-regulated kinase 3 (ERK3) is a poorly characterized member of the mitogen-activated protein (MAP) kinase family. Functional analysis of the ERK3 signaling pathway has been hampered by a lack of knowledge about the substrates and downstream effectors of the kinase. Here, we used large-scale quantitative phosphoproteomics and targeted gene silencing to identify direct ERK3 substrates and gain insight into its cellular functions. Detailed validation of one candidate substrate identified the gelsolin/villin family member supervillin (SVIL) as a bona fide ERK3 substrate. We show that ERK3 phosphorylates SVIL on Ser245 to regulate myosin II activation and cytokinesis completion in dividing cells. Depletion of SVIL or ERK3 leads to increased cytokinesis failure and multinucleation, a phenotype rescued by wild type SVIL but not by the non-phosphorylatable S245A mutant. Our results unveil a new function of the atypical MAP kinase ERK3 in cell division and the regulation of cell ploidy.

Emerging roles of deubiquitinating enzymes in actin cytoskeleton and tumor metastasis

BACKGROUND

Metastasis accounts for the majority of cancer-related deaths. Actin dynamics and actin-based cell migration and invasion are important factors in cancer metastasis. Metastasis is characterized by actin polymerization and depolymerization, which are precisely regulated by molecular changes involving a plethora of actin regulators, including actin-binding proteins (ABPs) and signalling pathways, that enable cancer cell dissemination from the primary tumour. Research on deubiquitinating enzymes (DUBs) has revealed their vital roles in actin dynamics and actin-based migration and invasion during cancer metastasis.

CONCLUSION

Here, we review how DUBs drive tumour metastasis by participating in actin rearrangement and actin-based migration and invasion. We summarize the well-characterized and essential actin cytoskeleton signalling molecules related to DUBs, including Rho GTPases, Src kinases, and ABPs such as cofilin and cortactin. Other DUBs that modulate actin-based migration signalling pathways are also discussed. Finally, we discuss and address therapeutic opportunities and ongoing challenges related to DUBs with respect to actin dynamics.

Phosphorylation of USP20 on Ser334 by IRAK1 promotes IL-1β-evoked signaling in vascular smooth muscle cells and vascular inflammation

Reversible lysine-63 (K63) polyubiquitination regulates proinflammatory signaling in vascular smooth muscle cells (SMCs) and plays an integral role in atherosclerosis. Ubiquitin-specific peptidase 20 (USP20) reduces NFκB activation triggered by proinflammatory stimuli, and USP20 activity attenuates atherosclerosis in mice. The association of USP20 with its substrates triggers deubiquitinase activity; this association is regulated by phosphorylation of USP20 on Ser334 (mouse) or Ser333 (human). USP20 Ser333 phosphorylation was greater in SMCs of atherosclerotic segments of human arteries as compared with nonatherosclerotic segments. To determine whether USP20 Ser334 phosphorylation regulates proinflammatory signaling, we created USP20-S334A mice using CRISPR/Cas9-mediated gene editing. USP20-S334A mice developed ∼50% less neointimal hyperplasia than congenic WT mice after carotid endothelial denudation. WT carotid SMCs showed substantial phosphorylation of USP20 Ser334, and WT carotids demonstrated greater NFκB activation, VCAM-1 expression, and SMC proliferation than USP20-S334A carotids. Concordantly, USP20-S334A primary SMCs in vitro proliferated and migrated less than WT SMCs in response to IL-1β. An active site ubiquitin probe bound to USP20-S334A and USP20-WT equivalently, but USP20-S334A associated more avidly with TRAF6 than USP20-WT. IL-1β induced less K63-linked polyubiquitination of TRAF6 and less downstream NFκB activity in USP20-S334A than in WT SMCs. Using in vitro phosphorylation with purified IRAK1 and siRNA-mediated gene silencing of IRAK1 in SMCs, we identified IRAK1 as a novel kinase for IL-1β-induced USP20 Ser334 phosphorylation. Our findings reveal novel mechanisms regulating IL-1β-induced proinflammatory signaling: by phosphorylating USP20 Ser334, IRAK1 diminishes the association of USP20 with TRAF6 and thus augments NFκB activation, SMC inflammation, and neointimal hyperplasia.

ERK3 and DGKζ interact to modulate cell motility in lung cancer cells

Extracellular signal-regulated kinase 3 (ERK3) promotes cell migration and tumor metastasis in multiple cancer types, including lung cancer. The extracellular-regulated kinase 3 protein has a unique structure. In addition to the N-terminal kinase domain, ERK3 includes a central conserved in extracellular-regulated kinase 3 and ERK4 (C34) domain and an extended C-terminus. However, relatively little is known regarding the role(s) of the C34 domain. A yeast two-hybrid assay using extracellular-regulated kinase 3 as bait identified diacylglycerol kinase ζ (DGKζ) as a binding partner. DGKζ was shown to promote migration and invasion in some cancer cell types, but its role in lung cancer cells is yet to be described. The interaction of extracellular-regulated kinase 3 and DGKζ was confirmed by co-immunoprecipitation and in vitro binding assays, consistent with their co-localization at the periphery of lung cancer cells. The C34 domain of ERK3 was sufficient for binding to DGKζ, while extracellular-regulated kinase 3 bound to the N-terminal and C1 domains of DGKζ. Surprisingly, in contrast to extracellular-regulated kinase 3, DGKζ suppresses lung cancer cell migration, suggesting DGKζ might inhibit ERK3-mediated cell motility. Indeed, co-overexpression of exogenous DGKζ and extracellular-regulated kinase 3 completely blocked the ability of ERK3 to promote cell migration, but DGKζ did not affect the migration of cells with stable ERK3 knockdown. Furthermore, DGKζ had little effect on cell migration induced by overexpression of an ERK3 mutant missing the C34 domain, suggesting DGKζ requires this domain to prevent ERK3-mediated increase in cell migration. In summary, this study has identified DGKζ as a new binding partner and negative regulator of extracellular-regulated kinase 3 in controlling lung cancer cell migration.

The emerging role of ubiquitin-specific protease 20 in tumorigenesis and cancer therapeutics

As a critical member of the ubiquitin-specific proteolytic enzyme family, ubiquitin-specific peptidase 20 (USP20) regulates the stability of proteins via multiple signaling pathways. In addition, USP20 upregulation is associated with various cellular biological processes, such as cell cycle progression, proliferation, migration, and invasion. Emerging studies have revealed the pivotal role of USP20 in the tumorigenesis of various cancer types, such as breast cancer, colon cancer, lung cancer, gastric cancer and adult T cell leukemia. In our review, we highlight the different mechanisms of USP20 in various tumor types and demonstrate that USP20 regulates the stability of multiple proteins. Therefore, regulating the activity of USP20 is a novel tumor treatment. However, the clinical significance of USP20 in cancer treatment merits more evidence. Finally, different prospects exist for the continued research focus of USP20.

USP20 regulates the stability of EMT transcription factor SOX4 and influences colorectal cancer metastasis

BACKGROUND

Colorectal cancer (CRC) is a familiar malignancy accompanied by higher morbidity and mortality. The deubiquitination enzyme USP20 has been discovered to be one key factor in several cancers progression. SOX4 is a critical transcription factor to regulate the expression of various genes, and participates into the occurrence and progression of cancers. In this study, it was aimed to illustrate the role of USP20 and the regulatory relationship between USP20 and SOX4 in CRC.

METHODS

The protein expressions of USP20, SOX4, E-cadherin, N-cadherin, Snail and slug were tested through western blot. The cell proliferation ability was verified through CCK-8 assay. The migration and invasion abilities were detected through Transwell assay. The mRNA expression of SOX4 was confirmed through RT-qPCR. The interaction between USP20 and SOX4 was notarized through Co-IP assay.

RESULT

Our study demonstrated that USP20 displayed higher expression, and facilitated CRC progression through regulating cell proliferation, migration, invasion and EMT process markers. USP20 was found to modulate SOX4 protein expression. Next, it was verified that USP20 regulated SOX4 degradation through deubiquitination. Finally, through rescue assays, we revealed that USP20 mediated SOX4 expression to accelerate CRC progression.

CONCLUSIONS

In this study, USP20 regulated the stability of EMT transcription factor SOX4 and aggravated colorectal cancer metastasis. This finding might highlight the function of USP20 in the treatment of CRC.

MAPK-Activated Protein Kinases: Servant or Partner?

Mitogen-activated protein kinase (MAPK)-activated protein kinases (MAPKAPKs) are defined by their exclusive activation by MAPKs. They can be activated by classical and atypical MAPKs that have been stimulated by mitogens and various stresses. Genetic deletions of MAPKAPKs and availability of highly specific small-molecule inhibitors have continuously increased our functional understanding of these kinases. MAPKAPKs cooperate in the regulation of gene expression at the level of transcription; RNA processing, export, and stability; and protein synthesis. The diversity of stimuli for MAPK activation, the cross talk between the different MAPKs and MAPKAPKs, and the specific substrate pattern of MAPKAPKs orchestrate immediate-early and inflammatory responses in space and time and ensure proper control of cell growth, differentiation, and cell behavior. Hence, MAPKAPKs are promising targets for cancer therapy and treatments for conditions of acute and chronic inflammation, such as cytokine storms and rheumatoid arthritis. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

FBXW7-mediated ERK3 degradation regulates the proliferation of lung cancer cells

Extracellular signal-regulated kinase 3 (ERK3) is an atypical member of the mitogen-activated protein kinase (MAPK) family, members of which play essential roles in diverse cellular processes during carcinogenesis, including cell proliferation, differentiation, migration, and invasion. Unlike other MAPKs, ERK3 is an unstable protein with a short half-life. Although deubiquitination of ERK3 has been suggested to regulate the activity, its ubiquitination has not been described in the literature. Here, we report that FBXW7 (F-box and WD repeat domain-containing 7) acts as a ubiquitination E3 ligase for ERK3. Mammalian two-hybrid assay and immunoprecipitation results demonstrated that ERK3 is a novel binding partner of FBXW7. Furthermore, complex formation between ERK3 and the S-phase kinase-associated protein 1 (SKP1)-cullin 1-F-box protein (SCF) E3 ligase resulted in the destabilization of ERK3 via a ubiquitination-mediated proteasomal degradation pathway, and FBXW7 depletion restored ERK3 protein levels by inhibiting this ubiquitination. The interaction between ERK3 and FBXW7 was driven by binding between the C34D of ERK3, especially at Thr417 and Thr421, and the WD40 domain of FBXW7. A double mutant of ERK3 (Thr417 and Thr421 to alanine) abrogated FBXW7-mediated ubiquitination. Importantly, ERK3 knockdown inhibited the proliferation of lung cancer cells by regulating the G₁/S-phase transition of the cell cycle. These results show that FBXW7-mediated ERK3 destabilization suppresses lung cancer cell proliferation in vitro.

Regulation of Mitogen-Activated Protein Kinase Signaling Pathways by the Ubiquitin-Proteasome System and Its Pharmacological Potential

Mitogen-activated protein kinase (MAPK) cascades are evolutionarily conserved signaling pathways that play essential roles in transducing extracellular environmental signals into diverse cellular responses to maintain homeostasis. These pathways are classically organized into an architecture of three sequentially acting protein kinases: a MAPK kinase kinase that phosphorylates and activates a MAPK kinase, which in turn phosphorylates and activates the effector MAPK. The activity of MAPKs is tightly regulated by phosphorylation of their activation loop, which can be modulated by positive and negative feedback mechanisms to control the amplitude and duration of the signal. The signaling outcomes of MAPK pathways are further regulated by interactions of MAPKs with scaffolding and regulatory proteins. Accumulating evidence indicates that, in addition to these mechanisms, MAPK signaling is commonly regulated by ubiquitin-proteasome system (UPS)-mediated control of the stability and abundance of MAPK pathway components. Notably, the biologic activity of some MAPKs appears to be regulated mainly at the level of protein turnover. Recent studies have started to explore the potential of targeted protein degradation as a powerful strategy to investigate the biologic functions of individual MAPK pathway components and as a new therapeutic approach to overcome resistance to current small-molecule kinase inhibitors. Here, we comprehensively review the mechanisms, physiologic importance, and pharmacological potential of UPS-mediated protein degradation in the control of MAPK signaling. SIGNIFICANCE STATEMENT: Accumulating evidence highlights the importance of targeted protein degradation by the ubiquitin-proteasome system in regulating and fine-tuning the signaling output of mitogen-activated protein kinase (MAPK) pathways. Manipulating protein levels of MAPK cascade components may provide a novel approach for the development of selective pharmacological tools and therapeutics.

Expression, purification and characterization of the second DUSP domain of deubiquitinase USP20/VDU2

Deubiquitinase USP20/VDU2 (VHL-interacting Deubiquitinating Enzyme 2) has been proved to play vital roles in multiple cellular processes by controlling the life-span of substrate proteins including hypoxia-inducible factor HIF1α, β2-adrenergic receptor, and type 2 iodothyronine deiodinase etc. USP20 contains four distinct structural domains, which include the N-terminal zinc-finger ubiquitin binding domain (ZnF-UBP), the catalytic domain (USP domain), and two tandem DUSP domains (DUSP1 and DUSP2). Here in this study, we report the setting up of the production approach for USP20 DUSP2, and the NMR characterization of the produced target protein. With the assistance of GB1 tag and glycerol, both the solubility and stability of USP20 DUSP2 are significantly enhanced. And by using the optimized protein production procedure, monomeric and stable ¹⁵N, ¹³C-labeled USP20 DUSP2 sample for NMR data acquisition was obtained. The secondary structural elements of USP20 DUSP2 were then revealed by the analysis of recorded NMR spectra, and USP20 DUSP2 forms an AB3 fold in solution. The production protocol and NMR characterization results reported in this manuscript could be utilized in the extended structural and functional studies of USP20 DUSP2.

ERK3/MAPK6 controls IL-8 production and chemotaxis

ERK3 is a ubiquitously expressed member of the atypical mitogen activated protein kinases (MAPKs) and the physiological significance of its short half-life remains unclear. By employing gastrointestinal 3D organoids, we detect that ERK3 protein levels steadily decrease during epithelial differentiation. ERK3 is not required for 3D growth of human gastric epithelium. However, ERK3 is stabilized and activated in tumorigenic cells, but deteriorates over time in primary cells in response to lipopolysaccharide (LPS). ERK3 is necessary for production of several cellular factors including interleukin-8 (IL-8), in both, normal and tumorigenic cells. Particularly, ERK3 is critical for AP-1 signaling through its interaction and regulation of c-Jun protein. The secretome of ERK3-deficient cells is defective in chemotaxis of neutrophils and monocytes both in vitro and in vivo. Further, knockdown of ERK3 reduces metastatic potential of invasive breast cancer cells. We unveil an ERK3-mediated regulation of IL-8 and epithelial secretome for chemotaxis.

The atypical MAPK ERK3 potently suppresses melanoma cell growth and invasiveness

Mitogen-activated protein kinase 6 (MAPK6) represents an atypical MAPK also known as extracellular signal-regulated kinase 3 (ERK3), which has been shown to play roles in cell motility and metastasis. ERK3 promotes migration and invasion of lung cancer cells and head and neck cancer cells by regulating the expression and/or activity of proteins involved in cancer progression. For instance, ERK3 upregulates matrix metallopeptidases and thereby promotes cancer cell invasiveness, and it phosphorylates tyrosyl-DNA phosphodiesterase 2, thereby enhancing chemoresistance in lung cancer. Here we discovered that ERK3 plays a converse role in melanoma. We observed that BRAF, an oncogenic Ser/Thr kinase, upregulates ERK3 expression levels by increasing both ERK3 messenger RNA levels and protein stability. Interestingly, although BRAF's kinase activity was required for upregulating ERK3 gene transcription, BRAF stabilized ERK3 protein in a kinase-independent fashion. We further demonstrate that ERK3 inhibits the migration, proliferation and colony formation of melanoma cells. In line with this, high level of ERK3 predicted increased survival among patients with melanomas. Taken together, these results indicate that ERK3 acts as a potent suppressor of melanoma cell growth and invasiveness.

Network Analysis of UBE3A/E6AP-Associated Proteins Provides Connections to Several Distinct Cellular Processes

Perturbations in activity and dosage of the UBE3A ubiquitin-ligase have been linked to Angelman syndrome and autism spectrum disorders. UBE3A was initially identified as the cellular protein hijacked by the human papillomavirus E6 protein to mediate the ubiquitylation of p53, a function critical to the oncogenic potential of these viruses. Although a number of substrates have been identified, the normal cellular functions and pathways affected by UBE3A are largely unknown. Previously, we showed that UBE3A associates with HERC2, NEURL4, and MAPK6/ERK3 in a high-molecular-weight complex of unknown function that we refer to as the HUN complex (HERC2, UBE3A, and NEURL4). In this study, the combination of two complementary proteomic approaches with a rigorous network analysis revealed cellular functions and pathways in which UBE3A and the HUN complex are involved. In addition to finding new UBE3A-associated proteins, such as MCM6, SUGT1, EIF3C, and ASPP2, network analysis revealed that UBE3A-associated proteins are connected to several fundamental cellular processes including translation, DNA replication, intracellular trafficking, and centrosome regulation. Our analysis suggests that UBE3A could be involved in the control and/or integration of these cellular processes, in some cases as a component of the HUN complex, and also provides evidence for crosstalk between the HUN complex and CAMKII interaction networks. This study contributes to a deeper understanding of the cellular functions of UBE3A and its potential role in pathways that may be affected in Angelman syndrome, UBE3A-associated autism spectrum disorders, and human papillomavirus-associated cancers.

The deubiquitinating enzyme USP20 stabilizes ULK1 and promotes autophagy initiation

Autophagy begins with the formation of autophagosomes, a process that depends on the activity of the serine/threonine kinase ULK1 (hATG1). Although earlier studies indicated that ULK1 activity is regulated by dynamic polyubiquitination, the deubiquitinase involved in the regulation of ULK1 remained unknown. In this study, we demonstrate that ubiquitin-specific protease 20 (USP20) acts as a positive regulator of autophagy initiation through stabilizing ULK1. At basal state, USP20 binds to and stabilizes ULK1 by removing the ubiquitin moiety, thereby interfering with the lysosomal degradation of ULK1. The stabilization of basal ULK1 protein levels is required for the initiation of starvation-induced autophagy, since the depletion of USP20 by RNA interference inhibits LC3 puncta formation, a marker of autophagic flux. At later stages of autophagy, USP20 dissociates from ULK1, resulting in enhanced ULK1 degradation and apoptosis. Taken together, our findings provide the first evidence that USP20 plays a crucial role in autophagy initiation by maintaining the basal expression level of ULK1.

L290P/V mutations increase ERK3's cytoplasmic localization and migration/invasion-promoting capability in cancer cells

Protein kinases are frequently mutated in human cancers, which leads to altered signaling pathways and contributes to tumor growth and progression. ERK3 is an atypical mitogen-activated protein kinase (MAPK) containing an S-E-G activation motif rather than the conserved T-X-Y motif in conventional MAPKs such as ERK1/2. Recent studies have revealed important roles for ERK3 in cancers. ERK3 promotes cancer cell migration/invasion and tumor metastasis, and its expression is upregulated in multiple cancers. Little is known, however, regarding ERK3 mutations in cancers. In the present study, we functionally and mechanistically characterized ERK3 L290P/V mutations, which are located within ERK3’s kinase domain, and are shown to exist in several cancers including lung cancer and colon cancer. We found that in comparison with wild type ERK3, both L290P and L290V mutants have greatly increased activity in promoting cancer cell migration and invasion, but have little impact on ERK3’s role in cell proliferation. Mechanistically, while they have no clear effect on kinase activity, L290P/V mutations enhance ERK3’s cytoplasmic localization by increasing the interaction with the nuclear export factor CRM1. Our findings suggest that L290P/V mutations of ERK3 may confer increased invasiveness to cancers.