USP42 protects ZNRF3/RNF43 from R-spondin-dependent clearance and inhibits Wnt signalling

New insights in ubiquitin-dependent Wnt receptor regulation in tumorigenesis

Wnt signaling plays a crucial role in embryonic development and homeostasis maintenance. Delicate and sensitive fine-tuning of Wnt signaling based on the proper timings and positions is required to balance cell proliferation and differentiation and maintain individual health. Therefore, homeostasis is broken by tissue hypoplasia or tumor formation once Wnt signal dysregulation disturbs the balance of cell proliferation. The well-known regulatory mechanism of Wnt signaling is the molecular reaction associated with the cytoplasmic accumulation of effector β-catenin. In addition to β-catenin, most Wnt effector proteins are also regulated by ubiquitin-dependent modification, both qualitatively and quantitatively. This review will explain the regulation of the whole Wnt signal in four regulatory phases, as well as the different ubiquitin ligases and the function of deubiquitinating enzymes in each phase. Along with the recent results, the mechanism by which RNF43 negatively regulates the surface expression of Wnt receptors, which has recently been well understood, will be detailed. Many RNF43 mutations have been identified in pancreatic and gastrointestinal cancers and examined for their functional alteration in Wnt signaling. Several mutations facilitate or activate the Wnt signal, reversing the RNF43 tumor suppressor function into an oncogene. RNF43 may simultaneously play different roles in classical multistep tumorigenesis, as both wild-type and mutant RNF43 suppress the p53 pathway. We hope that the knowledge obtained from further research in RNF43 will be applied to cancer treatment in the future despite the fully unclear function of RNF43.

Effects of Helicobacter pylori and Moluodan on the Wnt/β-catenin signaling pathway in mice with precancerous gastric cancer lesions

BACKGROUND

Helicobacter pylori (H. pylori) is the primary risk factor for gastric cancer (GC), the Wnt/β-Catenin signaling pathway is closely linked to tumourigenesis. GC has a high mortality rate and treatment cost, and there are no drugs to prevent the progression of gastric precancerous lesions to GC. Therefore, it is necessary to find a novel drug that is inexpensive and preventive to against GC.

AIM

To explore the effects of H. pylori and Moluodan on the Wnt/β-Catenin signaling pathway and precancerous lesions of GC (PLGC).

METHODS

Mice were divided into the control, N-methyl-N-nitrosourea (MNU), H. pylori + MNU, and Moluodan groups. We first created an H. pylori infection model in the H. pylori + MNU and Moluodan groups. A PLGC model was created in the remaining three groups except for the control group. Moluodan was fed to mice in the Moloudan group ad libitum. The general condition of mice were observed during the whole experiment period. Gastric tissues of mice were grossly and microscopically examined. Through quantitative real-time PCR (qRT-PCR) and Western blotting analysis, the expression of relevant genes were detected.

RESULTS

Mice in the H. pylori + MNU group showed the worst performance in general condition, gastric tissue visual and microscopic observation, followed by the MNU group, Moluodan group and the control group. QRT-PCR and Western blotting analysis were used to detect the expression of relevant genes, the results showed that the H. pylori + MNU group had the highest expression, followed by the MNU group, Moluodan group and the control group.

CONCLUSION

H. pylori can activate the Wnt/β-catenin signaling pathway, thereby facilitating the development and progression of PLGC. Moluodan suppressed the activation of the Wnt/β-catenin signaling pathway, thereby decreasing the progression of PLGC.

Comprehensive analysis of zinc and ring finger 3 in prognostic value and pan-cancer immunity

Zinc and ring finger 3 (ZNRF3) is a negative suppressor of Wnt signal and newly identified as an important regulator in tumorigenesis and development. However, the pan-cancer analysis of ZNRF3 has not been reported. We found that ZNRF3 was significantly decreased in six tumors including CESC, KIRP, KIRC, SKCM, OV, and ACC, but increased in twelve tumors, namely LGG, ESCA, STES, COAD, STAD, LUSC, LIHC, THCA, READ, PAAD, TGCT, and LAML. Clinical outcomes of cancer patients were closely related to ZNRF3 expression in ESCA, GBM, KIRC, LUAD, STAD, UCEC, LGG, and SARC. The highest genetic alteration frequency of ZNRF3 occurred in ACC. Abnormal expression of ZNRF3 could be attributed to the differences of copy number variation (CNV) and DNA methylation as well as ZNRF3-interacting proteins. Besides, ZNRF3 were strongly associated with tumor heterogeneity, tumor stemness, immune score, stromal score and ESTIMATE score in certain cancers. In terms of immune cell infiltration, ZNRF3 was positively correlated to infiltration of cancer-associated fibroblasts in CESC, HNSC, OV, PAAD, PRAD, and THYM, but negatively associated with infiltration of CD8 T cells in HNSC, KIRC, KIRP and THYM. Moreover, ZNRF3 expression was correlated with most immune checkpoint genes in SARC, LUSC, LUAD, PRAD, THCA, UVM, TGCT, and OV, and associated with overwhelming majority of immunoregulatory genes in almost all cancers. Most RNA modification genes were also remarkably related to ZNRF3 level in KIRP, LUAD, LUSC, THYM, UVM, PRAD, and UCEC, indicating that ZNRF3 might have an important effect on cancer epigenetic regulation. Finally, we verified the expression and role of ZNRF3 in clinical specimens and cell lines of renal cancer and liver cancer. This study provides a comprehensive pan-cancer analysis of ZNRF3 and reveals the complexity of its carcinogenic effect.

Friend or foe? Reciprocal regulation between E3 ubiquitin ligases and deubiquitinases

Protein ubiquitination is a post-translational modification that entails the covalent attachment of the small protein ubiquitin (Ub), which acts as a signal to direct protein stability, localization, or interactions. The Ub code is written by a family of enzymes called E3 Ub ligases (∼600 members in humans), which can catalyze the transfer of either a single ubiquitin or the formation of a diverse array of polyubiquitin chains. This code can be edited or erased by a different set of enzymes termed deubiquitinases (DUBs; ∼100 members in humans). While enzymes from these distinct families have seemingly opposing activities, certain E3-DUB pairings can also synergize to regulate vital cellular processes like gene expression, autophagy, innate immunity, and cell proliferation. In this review, we highlight recent studies describing Ub ligase-DUB interactions and focus on their relationships.

[Ubiquitin-specific protease 42 regulates osteogenic differentiation of human adipose-derived stem cells]

OBJECTIVE

To explore the effect of ubiquitin-specific protease 42 (USP42) on osteogenic differentiation of human adipose-derived stem cells (hASCs) in vivo and in vitro.

METHODS

A combination of experiments was carried out with genetic depletion of USP42 using a lentiviral strategy. Alkaline phosphatase (ALP) staining and quantification, alizarin red S (ARS) staining and quantification were used to determine the osteogenic differentiation ability of hASCs under osteogenic induction between the experimental group (knockdown group and overexpression group) and the control group. Quantitative reverse transcription PCR (qRT-PCR) was used to detect the expression levels of osteogenesis related genes in the experimental group and control group, and Western blotting was used to detect the expression levels of osteogenesis related proteins in the experimental group and control group. Nude mice ectopic implantation experiment was used to evaluate the effect of USP42 on the osteogenic differentiation of hASCs in vivo.

RESULTS

The mRNA and protein expressions of USP42 in knockdown group were significantly lower than those in control group, and those in overexpression group were significantly higher than those in control group. After 7 days of osteogenic induction, the ALP activity in the knockdown group was significantly higher than that in the control group, and ALP activity in overexpression group was significantly lower than that in control group. After 14 days of osteogenic induction, ARS staining was significantly deeper in the knockdown group than in the control group, and significantly lighter in overexpression group than in the control group. The results of qRT-PCR showed that the mRNA expression levels of ALP, osterix (OSX) and collagen type Ⅰ (COLⅠ) in the knockdown group were significantly higher than those in the control group after 14 days of osteogenic induction, and those in overexpression group were significantly lower than those in control group. The results of Western blotting showed that the expression levels of runt-related transcription factor 2 (RUNX2), OSX and COLⅠ in the knockout group were significantly higher than those in the control group at 14 days after osteogenic induction, while the expression levels of RUNX2, OSX and COLⅠ in the overexpression group were significantly lower than those in the control group. Hematoxylin-eosin staining of subcutaneous grafts in nude mice showed that the percentage of osteoid area in the knockdown group was significantly higher than that in the control group.

CONCLUSION

Knockdown of USP42 can significantly promote the osteogenic differentiation of hASCs in vitro and in vivo, and overexpression of USP42 significantly inhibits in vivo osteogenic differentiation of hASCs, and USP42 can provide a potential therapeutic target for bone tissue engineering.

Comprehensive analysis of the role of ubiquitin-specific peptidases in colorectal cancer: A systematic review

BACKGROUND

Colorectal cancer (CRC) is the third most frequent and the second most fatal cancer. The search for more effective drugs to treat this disease is ongoing. A better understanding of the mechanisms of CRC development and progression may reveal new therapeutic strategies. Ubiquitin-specific peptidases (USPs), the largest group of the deubiquitinase protein family, have long been implicated in various cancers. There have been numerous studies on the role of USPs in CRC; however, a comprehensive view of this role is lacking.

AIM

To provide a systematic review of the studies investigating the roles and functions of USPs in CRC.

METHODS

We systematically queried the MEDLINE (via PubMed), Scopus, and Web of Science databases.

RESULTS

Our study highlights the pivotal role of various USPs in several processes implicated in CRC: Regulation of the cell cycle, apoptosis, cancer stemness, epithelial-mesenchymal transition, metastasis, DNA repair, and drug resistance. The findings of this study suggest that USPs have great potential as drug targets and noninvasive biomarkers in CRC. The dysregulation of USPs in CRC contributes to drug resistance through multiple mechanisms.

CONCLUSION

Targeting specific USPs involved in drug resistance pathways could provide a novel therapeutic strategy for overcoming resistance to current treatment regimens in CRC.

The involvement of E3 ubiquitin ligases in the development and progression of colorectal cancer

To date, colorectal cancer (CRC) still has limited therapeutic efficacy and poor prognosis and there is an urgent need for novel targets to improve the outcome of CRC patients. The highly conserved ubiquitination modification mediated by E3 ubiquitin ligases is an important mechanism to regulate the expression and function of tumor promoters or suppressors in CRC. In this review, we provide an overview of E3 ligases in modulating various biological processes in CRC, including proliferation, migration, stemness, metabolism, cell death, differentiation and immune response of CRC cells, emphasizing the pluripotency of E3 ubiquitin ligases. We further focus on the role of E3 ligases in regulating vital cellular signal pathways in CRC, such as Wnt/β-catenin pathway and NF-κB pathway. Additionally, considering the potential of E3 ligases as novel targets in the treatment of CRC, we discuss what aspects of E3 ligases can be utilized and exploited for efficient therapeutic strategies.

Intestinal Paneth cell differentiation relies on asymmetric regulation of Wnt signaling by Daam1/2

The mammalian intestine is one of the most rapidly self-renewing tissues, driven by stem cells residing at the crypt bottom. Paneth cells form a major element of the niche microenvironment providing various growth factors to orchestrate intestinal stem cell homeostasis, such as Wnt3. Different Wnt ligands can selectively activate β-catenin-dependent (canonical) or -independent (noncanonical) signaling. Here, we report that the Dishevelled-associated activator of morphogenesis 1 (Daam1) and its paralogue Daam2 asymmetrically regulate canonical and noncanonical Wnt (Wnt/PCP) signaling. Daam1/2 interacts with the Wnt inhibitor RNF43, and Daam1/2 double knockout stimulates canonical Wnt signaling by preventing RNF43-dependent degradation of the Wnt receptor, Frizzled (Fzd). Single-cell RNA sequencing analysis revealed that Paneth cell differentiation is impaired by Daam1/2 depletion because of defective Wnt/PCP signaling. Together, we identified Daam1/2 as an unexpected hub molecule coordinating both canonical and noncanonical Wnt, which is fundamental for specifying an adequate number of Paneth cells.

The USP46 complex deubiquitylates LRP6 to promote Wnt/β-catenin signaling

The relative abundance of Wnt receptors plays a crucial role in controlling Wnt signaling in tissue homeostasis and human disease. While the ubiquitin ligases that ubiquitylate Wnt receptors are well-characterized, the deubiquitylase that reverses these reactions remains unclear. Herein, we identify USP46, UAF1, and WDR20 (USP46 complex) as positive regulators of Wnt signaling in cultured human cells. We find that the USP46 complex is similarly required for Wnt signaling in Xenopus and zebrafish embryos. We demonstrate that Wnt signaling promotes the association between the USP46 complex and cell surface Wnt coreceptor, LRP6. Knockdown of USP46 decreases steady-state levels of LRP6 and increases the level of ubiquitylated LRP6. In contrast, overexpression of the USP46 complex blocks ubiquitylation of LRP6 by the ubiquitin ligases RNF43 and ZNFR3. Size exclusion chromatography studies suggest that the size of the USP46 cytoplasmic complex increases upon Wnt stimulation. Finally, we show that USP46 is essential for Wnt-dependent intestinal organoid viability, likely via its role in LRP6 receptor homeostasis. We propose a model in which the USP46 complex increases the steady-state level of cell surface LRP6 and facilitates the assembly of LRP6 into signalosomes via a pruning mechanism that removes sterically hindering ubiquitin chains.

The WNT/β-catenin system in chronic kidney disease-mineral bone disorder syndrome

BACKGROUND

The WNT/β-catenin system is an evolutionarily conserved signaling pathway that plays a crucial role in morphogenesis and cell tissue formation during embryogenesis. Although usually suppressed in adulthood, it can be reactivated during organ damage and regeneration. Transient activation of the WNT/β-catenin pathway stimulates tissue regeneration after acute kidney injury, while persistent (uncontrolled) activation can promote the development of chronic kidney disease (CKD). CKD-MBD is a clinical syndrome that develops with systemic mineral and bone metabolism disorders caused by CKD, characterized by abnormal bone mineral metabolism and/or extraosseous calcification, as well as cardiovascular disease associated with CKD, including vascular stiffness and calcification.

OBJECTIVE

This paper aims to comprehensively review the WNT/β-catenin signaling pathway in relation to CKD-MBD, focusing on its components, regulatory molecules, and regulatory mechanisms. Additionally, this review highlights the challenges and opportunities for using small molecular compounds to target the WNT/β-catenin signaling pathway in CKD-MBD therapy.

METHODS

We conducted a comprehensive literature review using various scientific databases, including PubMed, Scopus, and Web of Science, to identify relevant articles. We searched for articles that discussed the WNT/β-catenin signaling pathway, CKD-MBD, and their relationship. We also reviewed articles that discussed the components of the WNT/β-catenin signaling pathway, its regulatory molecules, and regulatory mechanisms.

RESULTS

The WNT/β-catenin signaling pathway plays a crucial role in CKD-MBD by promoting vascular calcification and bone mineral metabolism disorders. The pathway's components include WNT ligands, Frizzled receptors, and LRP5/6 co-receptors, which initiate downstream signaling cascades leading to the activation of β-catenin. Several regulatory molecules, including GSK-3β, APC, and Axin, modulate β-catenin activation. The WNT/β-catenin signaling pathway also interacts with other signaling pathways, such as the BMP pathway, to regulate CKD-MBD.

CONCLUSIONS

The WNT/β-catenin signaling pathway is a potential therapeutic target for CKD-MBD. Small molecular compounds that target the components or regulatory molecules of the pathway may provide a promising approach to treat CKD-MBD. However, more research is needed to identify safe and effective compounds and to determine the optimal dosages and treatment regimens.

RNF43 induces the turnover of protease-activated receptor 2 in colon cancer

Post-translational modification of G-protein coupled receptors (GPCRs) plays a central role in tissue hemostasis and cancer. The molecular mechanism of post-translational regulation of protease-activated receptors (PARs), a subgroup of GPCRs is yet understudied. Here we show that the cell-surface transmembrane E3 ubiquitin ligase ring finger 43 (RNF43) is a negative feedback regulator of PAR₂ , impacting PAR₂ -induced signaling and colon cancer growth. RNF43 co-associates with PAR₂ , promoting its membrane elimination and degradation as shown by reduced cell surface biotinylated PAR₂ levels and polyubiquitination. PAR₂ degradation is rescued by R-spondin2 in the presence of leucine-rich repeat-containing G-protein-coupled receptor5 (LGR5). In fact, PAR₂ acts jointly with LGR5, as recapitulated by increased β-catenin levels, transcriptional activity, phospho-LRP6, and anchorage-independent colony growth in agar. Animal models of the chemically induced AOM/DSS colon cancer of wt versus Par2/f2rl1 KO mice as also the 'spleen-liver' colon cancer metastasis, allocated a central role for PAR₂ in colon cancer growth and development. RNF43 is abundantly expressed in the Par2/f2rl1 KO-treated AOM/DSS colon tissues while its level is very low to nearly null in colon cancer adenocarcinomas of the wt mice. The same result is obtained in the 'spleen-liver' model of spleen-inoculated cells, metastasized to the liver. High RNF43 expression is observed in the liver upon shRNA -Par2 silencing. "Limited-dilution-assay" performed in mice in-vivo, assigned PAR₂ as a member of the cancer stem cell niche compartment. Collectively, we elucidate an original regulation of PAR₂ oncogene, a member of cancer stem cells, by RNF43 ubiquitin ligase. It impacts β-catenin signaling and colon cancer growth.

Ubiquitin modification in osteogenic differentiation and bone formation: From mechanisms to clinical significance

The ubiquitin-proteasome system is an important pathway for mediating posttranslational modification and protein homeostasis and exerts a wide range of functions in diverse biological processes, including stem cell differentiation, DNA repair, and cell cycle regulation. Many studies have shown that ubiquitination modification plays a critical role in regulating the osteogenic differentiation of stem cells and bone formation through various mechanisms. This review summarizes current progress on the effects and mechanisms of ubiquitin modification on transcription factors and signaling pathways involved in osteogenic differentiation. Moreover, the review highlights the latest advances in the clinical application of drugs in bone tissue engineering. A thorough understanding of ubiquitin modifications may provide promising therapeutic targets for stem cell-based bone tissue engineering.

Molecular regulation after mucosal injury and regeneration in ulcerative colitis

Ulcerative colitis (UC) is a chronic nonspecific inflammatory disease with a complex etiology. Intestinal mucosal injury is an important pathological change in individuals with UC. Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5+) intestinal stem cells (ISCs) exhibit self-renewal and high differentiation potential and play important roles in the repair of intestinal mucosal injury. Moreover, LGR5+ ISCs are intricately regulated by both the Wnt/β-catenin and Notch signaling pathways, which jointly maintain the function of LGR5+ ISCs. Combination therapy targeting multiple signaling pathways and transplantation of LGR5+ ISCs may lead to the development of new clinical therapies for UC.

Nuclear Dishevelled: An enigmatic role in governing cell fate and Wnt signaling

The Dishevelled gene was first identified in Drosophila mutants with disoriented hair and bristle polarity and subsequent work has now demonstrated its importance in critical and diverse aspects of biology. Since those early discoveries, Dishevelled has been shown to coordinate a plethora of developmental and cellular processes that range from controlling cell polarity during gastrulation to partnering with chromatin modifying enzymes to regulate histone methylation at genomic loci. While the role of DVL in development is well-respected and the cytosolic function of DVL has been studied more extensively, its nuclear role continues to remain murky. In this review we highlight some of the seminal discoveries that have contributed to the field, but the primary focus is to discuss recent advances with respect to the nuclear role of Dishevelled. This nuclear function of Dishevelled is a dimension which is proving to be increasingly important yet remains enigmatic.

Clone wars: From molecules to cell competition in intestinal stem cell homeostasis and disease

The small intestine is among the fastest self-renewing tissues in adult mammals. This rapid turnover is fueled by the intestinal stem cells residing in the intestinal crypt. Wnt signaling plays a pivotal role in regulating intestinal stem cell renewal and differentiation, and the dysregulation of this pathway leads to cancer formation. Several studies demonstrate that intestinal stem cells follow neutral drift dynamics, as they divide symmetrically to generate other equipotent stem cells. Competition for niche space and extrinsic signals in the intestinal crypt is the governing mechanism that regulates stemness versus cell differentiation, but the underlying molecular mechanisms are still poorly understood, and it is not yet clear how this process changes during disease. In this review, we highlight the mechanisms that regulate stem cell homeostasis in the small intestine, focusing on Wnt signaling and its regulation by RNF43 and ZNRF3, key inhibitors of the Wnt pathway. Furthermore, we summarize the evidence supporting the current model of intestinal stem cell regulation, highlighting the principles of neutral drift at the basis of intestinal stem cell homeostasis. Finally, we discuss recent studies showing how cancer cells bypass this mechanism to gain a competitive advantage against neighboring normal cells.

Stem cells in the gut rapidly renew themselves through processes that cancer cells co-opt to trigger tumor development. Gabriele Colozza from the Institute of Molecular Biotechnology in Vienna, Austria, and colleagues review how a network of critical molecular signals and competition for limited space help to regulate the dynamics of stem cells in the intestines. The correct balance between self-renewal and differentiation is tightly controlled by the so-called Wnt signaling pathway and its inhibitors. Competition between dividing cells in the intestinal crypts, the locations between finger-like protrusions in the gut where stem cells are found, provides another protective mechanism against runaway stem cell growth. However, intestinal cancer cells, thanks to their activating mutations, bypass these safeguards to gain a survival advantage. Drugs that target these ‘super-competitive’ behaviors could therefore help combat tumor proliferation.

Recombinant Porcine R-Spondin 1 Facilitates Intestinal Stem Cell Expansion along the Crypt-Villus Axis through Potentiating Wnt/β-Catenin Signaling in Homeostasis and Deoxynivalenol Injury

R-spondin 1 (RSPO1) is a ligand for the intestinal stem cell (ISC) marker Lgr5 in the crypt, which functions to amplify canonical Wnt signaling to stimulate the division of ISCs. Despite the crucial role of recombinant human RSPO1 (rhRSPO1) in homeostasis and regeneration, little is known about RSPO1 among different species. Here, we cloned the porcine RSPO1 (pRSPO1) gene and obtained rpRSPO1 protein through the expression system of the recombinant Escherichia coli Rosetta (DE3) chemical competent cells. Using the in vitro IPEC-J2 model that combines cell proliferation evaluation approaches, we identified the rpRSPO1 activity in stimulating jejunal epithelial cells. And upon deoxynivalenol challenge in mice, we found that rpRSPO1 ameliorated their growth retardation and jejunal epithelial integrity. Importantly, the ISCs in the jejunum had greater proliferation and differentiation potential that was accompanied by Wnt/β-catenin pathway activation after rpRSPO1 modulation. Subsequently, the jejunal organoids expanded from these ISCs ex vivo presented robust growth advantages. And the rpRSPO1 was able to guide Wnt/β-catenin activity to increase ISC activity. Our work systematically demonstrates that rpRSPO1 facilitates ISC expansion by potentiating Wnt/β-catenin signaling during homeostasis and responding to deoxynivalenol perturbations.

Superresolution microscopy localizes endogenous Dvl2 to Wnt signaling-responsive biomolecular condensates

Wnt signaling governs cell fate and tissue polarity across species. The Dishevelled proteins are central to Wnt signaling cascades. Wnt-mediated multiprotein complexes such as the “signalosome” and the “destruction complex” have been proposed to represent biomolecular condensates. These nonmembranous, specialized compartments have been suggested to form through liquid–liquid phase separation and ensure correctly proceeding physiological reactions. Although biomolecular condensates have increasingly been studied, key questions remain regarding, for example, their architecture and physiological regulation. Here, superresolution microscopy after endogenous labeling of Dishevelled-2 gives insights into protein functions and Wnt signaling at physiological levels. It reveals the distinct molecular architecture of endogenous Wnt condensates at single-molecule resolution and illustrates close interactions at the centrosome.

During organismal development, homeostasis, and disease, Dishevelled (Dvl) proteins act as key signaling factors in beta-catenin–dependent and beta-catenin–independent Wnt pathways. While their importance for signal transmission has been genetically demonstrated in many organisms, our mechanistic understanding is still limited. Previous studies using overexpressed proteins showed Dvl localization to large, punctate-like cytoplasmic structures that are dependent on its DIX domain. To study Dvl’s role in Wnt signaling, we genome engineered an endogenously expressed Dvl2 protein tagged with an mEos3.2 fluorescent protein for superresolution imaging. First, we demonstrate the functionality and specificity of the fusion protein in beta-catenin–dependent and beta-catenin–independent signaling using multiple independent assays. We performed live-cell imaging of Dvl2 to analyze the dynamic formation of the supramolecular cytoplasmic Dvl2_mEos3.2 condensates. While overexpression of Dvl2_mEos3.2 mimics the previously reported formation of abundant large “puncta,” supramolecular condensate formation at physiological protein levels is only observed in a subset of cells with approximately one per cell. We show that, in these condensates, Dvl2 colocalizes with Wnt pathway components at gamma-tubulin and CEP164-positive centrosomal structures and that the localization of Dvl2 to these condensates is Wnt dependent. Single-molecule localization microscopy using photoactivated localization microscopy (PALM) of mEos3.2 in combination with DNA-PAINT demonstrates the organization and repetitive patterns of these condensates in a cell cycle–dependent manner. Our results indicate that the localization of Dvl2 in supramolecular condensates is coordinated dynamically and dependent on cell state and Wnt signaling levels. Our study highlights the formation of endogenous and physiologically regulated biomolecular condensates in the Wnt pathways at single-molecule resolution.

Deubiquitinases in Cancers: Aspects of Proliferation, Metastasis, and Apoptosis

Simple Summary

This review summarizes the current DUBs findings that correlate with the most common cancers in the world (liver, breast, prostate, colorectal, pancreatic, and lung cancers). The DUBs were further classified by their biological functions in terms of proliferation, metastasis, and apoptosis. The work provides an updated of the current findings, and could be used as a quick guide for researchers to identify target DUBs in cancers.

Abstract

Deubiquitinases (DUBs) deconjugate ubiquitin (UBQ) from ubiquitylated substrates to regulate its activity and stability. They are involved in several cellular functions. In addition to the general biological regulation of normal cells, studies have demonstrated their critical roles in various cancers. In this review, we evaluated and grouped the biological roles of DUBs, including proliferation, metastasis, and apoptosis, in the most common cancers in the world (liver, breast, prostate, colorectal, pancreatic, and lung cancers). The current findings in these cancers are summarized, and the relevant mechanisms and relationship between DUBs and cancers are discussed. In addition to highlighting the importance of DUBs in cancer biology, this study also provides updated information on the roles of DUBs in different types of cancers.

Receptor control by membrane-tethered ubiquitin ligases in development and tissue homeostasis

Paracrine cell-cell communication is central to all developmental processes, ranging from cell diversification to patterning and morphogenesis. Precise calibration of signaling strength is essential for the fidelity of tissue formation during embryogenesis and tissue maintenance in adults. Membrane-tethered ubiquitin ligases can control the sensitivity of target cells to secreted ligands by regulating the abundance of signaling receptors at the cell surface. We discuss two examples of this emerging concept in signaling: (1) the transmembrane ubiquitin ligases ZNRF3 and RNF43 that regulate WNT and bone morphogenetic protein receptor abundance in response to R-spondin ligands and (2) the membrane-recruited ubiquitin ligase MGRN1 that controls Hedgehog and melanocortin receptor abundance. We focus on the mechanistic logic of these systems, illustrated by structural and protein interaction models enabled by AlphaFold. We suggest that membrane-tethered ubiquitin ligases play a widespread role in remodeling the cell surface proteome to control responses to extracellular ligands in diverse biological processes.

Lysosomal degradation of the maternal dorsal determinant Hwa safeguards dorsal body axis formation

The Spemann and Mangold Organizer (SMO) is of fundamental importance for dorsal ventral body axis formation during vertebrate embryogenesis. Maternal Huluwa (Hwa) has been identified as the dorsal determinant that is both necessary and sufficient for SMO formation. However, it remains unclear how Hwa is regulated. Here, we report that the E3 ubiquitin ligase zinc and ring finger 3 (ZNRF3) is essential for restricting the spatial activity of Hwa and therefore correct SMO formation in Xenopus laevis. ZNRF3 interacts with and ubiquitinates Hwa, thereby regulating its lysosomal trafficking and protein stability. Perturbation of ZNRF3 leads to the accumulation of Hwa and induction of an ectopic axis in embryos. Ectopic expression of ZNRF3 promotes Hwa degradation and dampens the axis-inducing activity of Hwa. Thus, our findings identify a substrate of ZNRF3, but also highlight the importance of the regulation of Hwa temporospatial activity in body axis formation in vertebrate embryos.

A MET-PTPRK kinase-phosphatase rheostat controls ZNRF3 and Wnt signaling

Zinc and ring finger 3 (ZNRF3) is a transmembrane E3 ubiquitin ligase that targets Wnt receptors for ubiquitination and lysosomal degradation. Previously, we showed that dephosphorylation of an endocytic tyrosine motif (4Y motif) in ZNRF3 by protein tyrosine phosphatase receptor-type kappa (PTPRK) promotes ZNRF3 internalization and Wnt receptor degradation (Chang et al 2020). However, a responsible protein tyrosine kinase(s) (PTK) phosphorylating the 4Y motif remained elusive. Here we identify the proto-oncogene MET (mesenchymal-epithelial transition factor) as a 4Y kinase. MET binds to ZNRF3 and induces 4Y phosphorylation, stimulated by the MET ligand HGF (hepatocyte growth factor, scatter factor). HGF-MET signaling reduces ZNRF3-dependent Wnt receptor degradation thereby enhancing Wnt/β-catenin signaling. Conversely, depletion or pharmacological inhibition of MET promotes the internalization of ZNRF3 and Wnt receptor degradation. We conclude that HGF-MET signaling phosphorylates- and PTPRK dephosphorylates ZNRF3 to regulate ZNRF3 internalization, functioning as a rheostat for Wnt signaling that may offer novel opportunities for therapeutic intervention.

Organoids and Colorectal Cancer

Organoids were first established as a three-dimensional cell culture system from mouse small intestine. Subsequent development has made organoids a key system to study many human physiological and pathological processes that affect a variety of tissues and organs. In particular, organoids are becoming very useful tools to dissect colorectal cancer (CRC) by allowing the circumvention of classical problems and limitations, such as the impossibility of long-term culture of normal intestinal epithelial cells and the lack of good animal models for CRC. In this review, we describe the features and current knowledge of intestinal organoids and how they are largely contributing to our better understanding of intestinal cell biology and CRC genetics. Moreover, recent data show that organoids are appropriate systems for antitumoral drug testing and for the personalized treatment of CRC patients.

USP42 protects ZNRF3/RNF43 from R-spondin-dependent clearance and inhibits Wnt signalling

The tumour suppressors RNF43 and ZNRF3 play a central role in development and tissue homeostasis by promoting the turnover of the Wnt receptors LRP6 and Frizzled (FZD). The stem cell growth factor R‐spondin induces auto‐ubiquitination and membrane clearance of ZNRF3/RNF43 to promote Wnt signalling. However, the deubiquitinase stabilising ZNRF3/RNF43 at the plasma membrane remains unknown. Here, we show that the USP42 antagonises R‐spondin by protecting ZNRF3/RNF43 from ubiquitin‐dependent clearance. USP42 binds to the Dishevelled interacting region (DIR) of ZNRF3 and stalls the R‐spondin‐LGR4‐ZNRF3 ternary complex by deubiquitinating ZNRF3. Accordingly, USP42 increases the turnover of LRP6 and Frizzled (FZD) receptors and inhibits Wnt signalling. Furthermore, we show that USP42 functions as a roadblock for paracrine Wnt signalling in colon cancer cells and mouse small intestinal organoids. We provide new mechanistic insights into the regulation R‐spondin and conclude that USP42 is crucial for ZNRF3/RNF43 stabilisation at the cell surface.