The ER-embedded UBE2J1/RNF26 ubiquitylation complex exerts spatiotemporal control over the endolysosomal pathway

The role of ubiquitin-conjugating enzyme in the process of spermatogenesis

The ubiquitination is crucial for controlling cellular homeostasis and protein modification, in which ubiquitin-conjugating enzyme (E2) acts as the central player in the ubiquitination system. Ubiquitin-conjugating enzymes, which have special domains that catalyse substrates, have sequence discrepancies and modulate various pathophysiological processes in different cells of multiple organisms. E2s take part in the mitosis of primordial germ cells, meiosis of spermatocytes and the formation of mature haploid spermatids to maintain normal male fertility. In this review, we summarize the various types of E2s and their functions during distinct stages of spermatogenesis.

RNF26-mediated ubiquitination of TRIM21 promotes bladder cancer progression

RNF26 is an important E3 ubiquitin ligase that has been associated with poor prognosis in bladder cancer. However, the underlying mechanisms of RNF26 in bladder cancer tumorigenesis are not fully understood. In the present study, we found that RNF26 expression level was significantly upregulated in the bladder cancer tissues, and higher RNF26 expression is closely associated with poorer prognosis, lower immune cell infiltration, and more sensitive to immune checkpoint blockade drugs and chemotherapy drugs, including cisplatin, VEGFR-targeting drugs and MET-targeting drugs. RNF26 knockdown in UMUC3 and T24 cell lines inhibited cell growth, colony formation and migratory capacity. Meanwhile, RNF26 overexpression had the opposite effects. Mechanistically, RNF26 exerts its oncogenic function by binding to TRIM21 and promoting its ubiquitination and subsequent degradation. Moreover, we revealed ZHX3 as a downstream target of RNF26/TRIM21 pathway in bladder cancer. Taken together, we identified a novel RNF26/TRIM21/ZHX3 axis that promotes bladder cancer progression. Thus, the RNF26/TRIM21/ZHX3 axis constitutes a potential efficacy predictive marker and may serve as a therapeutic target for the treatment of bladder cancer.

CDK4/6 inhibitors dephosphorylate RNF26 to stabilize TSC1 and increase the sensitivity of ccRCC to mTOR inhibitors

BACKGROUND

The combined use of CDK4/6 inhibitors and mTOR inhibitors has achieved some clinical success in ccRCC. Exploring the underlying mechanism of the CDK4/6 pathway in cancer cells and the drug interactions of CDK4/6 inhibitors in combination therapy could help identify new therapeutic strategies for ccRCC. Notably, CDK4/6 inhibitors inactivate the mTOR pathway by increasing the protein levels of TSC1, but the mechanism by which CDK4/6 inhibitors regulate TSC1 is still unclear.

METHODS

Mass spectrometry analysis, coimmunoprecipitation analysis, GST pull-down assays, immunofluorescence assays, Western blot analysis and RT‒qPCR analysis were applied to explore the relationships among CDK4, RNF26 and TSC1. Transwell assays, tube formation assays, CCK-8 assays, colony formation assays and xenograft assays were performed to examine the biological role of RNF26 in renal cancer cells.TCGA-KIRC dataset analysis and RT‒qPCR analysis were used to examine the pathways affected by RNF26 silencing.

RESULTS

CDK4/6 inhibitors stabilized TSC1 in cancer cells. We showed that CDK4 enhances the interaction between TSC1 and RNF26 and that RNF26 activates the mTOR signaling pathway in ccRCC, contributes to ccRCC progression and angiogenesis, and promotes tumorigenesis. We then found that RNF26 functions as an E3 ligase of TSC1 to regulate CDK4-induced TSC1. This finding suggested that RNF26 promotes ccRCC progression and angiogenesis to some extent by negatively regulating TSC1.

CONCLUSION

Our results revealed a novel CDK4/RNF26/TSC1 axis that regulates the anticancer efficacy of CDK4/6 inhibitors and mTOR inhibitors in ccRCC.

Trichinella spiralis inhibits myoblast differentiation by targeting SQSTM1/p62 with a secreted E3 ubiquitin ligase

Trichinella spiralis infection is associated with the formation of cysts within host skeletal muscle cells, thereby enabling immune evasion and subsequent growth and development; however, the pathogenic factors involved in this process and their mechanisms remain elusive. Here, we found that Ts-RNF secreted by T. spiralis is required for its growth and development in host cells. Further study revealed that Ts-RNF functions as an E3 ubiquitin ligase that targets the UBA domain of SQSTM1/p62 by forming K63-type ubiquitin chains. This modification interferes with autophagic flux, leading to impaired mitochondrial clearance and abnormal myotube differentiation and fusion. Our results established that T. spiralis increases its escape by interfering with host autophagy via the secretion of an E3 ubiquitin ligase.

Mechanisms of substrate processing during ER-associated protein degradation

Maintaining proteome integrity is essential for long-term viability of all organisms and is overseen by intrinsic quality control mechanisms. The secretory pathway of eukaryotes poses a challenge for such quality assurance as proteins destined for secretion enter the endoplasmic reticulum (ER) and become spatially segregated from the cytosolic machinery responsible for disposal of aberrant (misfolded or otherwise damaged) or superfluous polypeptides. The elegant solution provided by evolution is ER-membrane-bound ubiquitylation machinery that recognizes misfolded or surplus proteins or by-products of protein biosynthesis in the ER and delivers them to 26S proteasomes for degradation. ER-associated protein degradation (ERAD) collectively describes this specialized arm of protein quality control via the ubiquitin-proteasome system. But, instead of providing a single strategy to remove defective or unwanted proteins, ERAD represents a collection of independent processes that exhibit distinct yet overlapping selectivity for a wide range of substrates. Not surprisingly, ER-membrane-embedded ubiquitin ligases (ER-E3s) act as central hubs for each of these separate ERAD disposal routes. In these processes, ER-E3s cooperate with a plethora of specialized factors, coordinating recognition, transport and ubiquitylation of undesirable secretory, membrane and cytoplasmic proteins. In this Review, we focus on substrate processing during ERAD, highlighting common threads as well as differences between the many routes via ERAD.

RNF26 binds perinuclear vimentin filaments to integrate ER and endolysosomal responses to proteotoxic stress

Proteotoxic stress causes profound endoplasmic reticulum (ER) membrane remodeling into a perinuclear quality control compartment (ERQC) for the degradation of misfolded proteins. Subsequent return to homeostasis involves clearance of the ERQC by endolysosomes. However, the factors that control perinuclear ER integrity and dynamics remain unclear. Here, we identify vimentin intermediate filaments as perinuclear anchors for the ER and endolysosomes. We show that perinuclear vimentin filaments engage the ER-embedded RING finger protein 26 (RNF26) at the C-terminus of its RING domain. This restricts RNF26 to perinuclear ER subdomains and enables the corresponding spatial retention of endolysosomes through RNF26-mediated membrane contact sites (MCS). We find that both RNF26 and vimentin are required for the perinuclear coalescence of the ERQC and its juxtaposition with proteolytic compartments, which facilitates efficient recovery from ER stress via the Sec62-mediated ER-phagy pathway. Collectively, our findings reveal a scaffolding mechanism that underpins the spatiotemporal integration of organelles during cellular proteostasis.

EGFR trafficking: effect of dimerization, dynamics, and mutation

Spontaneous dimerization of EGF receptors (EGFR) and dysregulation of EGFR signaling has been associated with the development of different cancers. Under normal physiological conditions and to maintain homeostatic cell growth, once EGFR signaling occurs, it needs to be attenuated. Activated EGFRs are rapidly internalized, sorted through early endosomes, and ultimately degraded in lysosomes by a process generally known as receptor down-regulation. Through alterations to EGFR trafficking, tumors develop resistance to current treatment strategies, thus highlighting the necessity for combination treatment strategies that target EGFR trafficking. This review covers EGFR structure, trafficking, and altered surface expression of EGFR receptors in cancer, with a focus on how therapy targeting EGFR trafficking may aid tyrosine kinase inhibitor treatment of cancer.

Super-resolution proximity labeling reveals anti-viral protein network and its structural changes against SARS-CoV-2 viral proteins

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replicates in human cells by interacting with host factors following infection. To understand the virus and host interactome proximity, we introduce a super-resolution proximity labeling (SR-PL) method with a "plug-and-playable" PL enzyme, TurboID-GBP (GFP-binding nanobody protein), and we apply it for interactome mapping of SARS-CoV-2 ORF3a and membrane protein (M), which generates highly perturbed endoplasmic reticulum (ER) structures. Through SR-PL analysis of the biotinylated interactome, 224 and 272 peptides are robustly identified as ORF3a and M interactomes, respectively. Within the ORF3a interactome, RNF5 co-localizes with ORF3a and generates ubiquitin modifications of ORF3a that can be involved in protein degradation. We also observe that the SARS-CoV-2 infection rate is efficiently reduced by the overexpression of RNF5 in host cells. The interactome data obtained using the SR-PL method are presented at https://sarscov2.spatiomics.org. We hope that our method will contribute to revealing virus-host interactions of other viruses in an efficient manner.

Homotypic SCOTIN assemblies form ER-endosome membrane contacts and regulate endosome dynamics

The ER regulates the spatiotemporal organization of endolysosomal systems by membrane contact. In addition to tethering via heterotypic interactions on both organelles, we present a novel ER-endosome tethering mechanism mediated by homotypic interactions. The single-pass transmembrane protein SCOTIN is detected in the membrane of the ER and endosomes. In SCOTIN-knockout (KO) cells, the ER-late endosome contacts are reduced, and the perinuclear positioning of endosomes is disturbed. The cytosolic proline-rich domain (PRD) of SCOTIN forms homotypic assemblies in vitro and is necessary for ER-endosome membrane tethering in cells. A region of 28 amino acids spanning 150-177 within the SCOTIN PRD is essential to elicit membrane tethering and endosomal dynamics, as verified by reconstitution in SCOTIN-KO cells. The assembly of SCOTIN (PRD) is sufficient to mediate membrane tethering, as purified SCOTIN (PRD), but not SCOTIN (PRDΔ150-177), brings two different liposomes closer in vitro. Using organelle-specific targeting of a chimeric PRD domain shows that only the presence on both organellar membranes enables the ER-endosome membrane contact, indicating that the assembly of SCOTIN on heterologous membranes mediates organelle tethering.

An E2-E3 pair contributes to seed size control in grain crops

Understanding the molecular mechanisms that regulate grain yield is important for improving agricultural productivity. Protein ubiquitination controls various aspects of plant growth but lacks understanding on how E2-E3 enzyme pairs impact grain yield in major crops. Here, we identified a RING-type E3 ligase SGD1 and its E2 partner SiUBC32 responsible for grain yield control in Setaria italica. The conserved role of SGD1 was observed in wheat, maize, and rice. Furthermore, SGD1 ubiquitinates the brassinosteroid receptor BRI1, stabilizing it and promoting plant growth. Overexpression of an elite SGD1 haplotype improved grain yield by about 12.8% per plant, and promote complex biological processes such as protein processing in endoplasmic reticulum, stress responses, photosystem stabilization, and nitrogen metabolism. Our research not only identifies the SiUBC32-SGD1-BRI1 genetic module that contributes to grain yield improvement but also provides a strategy for exploring key genes controlling important traits in Poaceae crops using the Setaria model system.

Genetic disruption of mammalian endoplasmic reticulum-associated protein degradation: Human phenotypes and animal and cellular disease models

Endoplasmic reticulum-associated protein degradation (ERAD) is a stringent quality control mechanism through which misfolded, unassembled and some native proteins are targeted for degradation to maintain appropriate cellular and organelle homeostasis. Several in vitro and in vivo ERAD-related studies have provided mechanistic insights into ERAD pathway activation and its consequent events; however, a majority of these have investigated the effect of ERAD substrates and their consequent diseases affecting the degradation process. In this review, we present all reported human single-gene disorders caused by genetic variation in genes that encode ERAD components rather than their substrates. Additionally, after extensive literature survey, we present various genetically manipulated higher cellular and mammalian animal models that lack specific components involved in various stages of the ERAD pathway.

UBE2J1 knockdown promotes cell apoptosis in endometrial cancer via regulating PI3K/AKT and MDM2/p53 signaling

Emerging evidence has demonstrated that ubiquitin conjugating enzyme E2 J1 (UBE2J1) exerts pivotal function in many cancers. UBE2J1 was reported to be dysregulated in endometrial cancer (EC). This study was designed to further investigate the regulatory character and mechanism of UBE2J1 in EC. Bioinformatic tools and databases were used to analyze gene expression pattern and gene expression correlation in EC tissues, and the prognosis of EC patients. Gene expression was evaluated by reverse-transcription quantitative polymerase chain reaction. Western blot was used for protein level detection. In vitro cell apoptosis was detected by flow cytometry analyses and TUNEL assays. In vivo cell apoptosis was evaluated by detecting Bax and Bcl-2 expression in tumor tissues via immunohistochemical and western blot analyses. In this study, UBE2J1 knockdown promoted cell apoptosis in EC cells and in mouse models of EC. PI3K and AKT expression is positively correlated with UBE2J1 level and is related to poor prognosis of EC patients. UBE2J1 knockdown repressed the PI3K/AKT pathway both in vitro and in vivo. UBE2J1 downregulation decreased MDM2 expression, but increased p53 expression. MDM2 overexpression reverses the promotion of UBE2J1 knockdown on cell apoptosis in EC. Overall, UBE2J1 knockdown induces cell apoptosis in EC by inactivating the PI3K/AKT signaling and suppressing the MDM2/p53 signaling.

Ubiquitin and its relatives as wizards of the endolysosomal system

The endolysosomal system comprises a dynamic constellation of vesicles working together to sense and interpret environmental cues and facilitate homeostasis. Integrating extracellular information with the internal affairs of the cell requires endosomes and lysosomes to be proficient in decision-making: fusion or fission; recycling or degradation; fast transport or contacts with other organelles. To effectively discriminate between these options, the endolysosomal system employs complex regulatory strategies that crucially rely on reversible post-translational modifications (PTMs) with ubiquitin (Ub) and ubiquitin-like (Ubl) proteins. The cycle of conjugation, recognition and removal of different Ub- and Ubl-modified states informs cellular protein stability and behavior at spatial and temporal resolution and is thus well suited to finetune macromolecular complex assembly and function on endolysosomal membranes. Here, we discuss how ubiquitylation (also known as ubiquitination) and its biochemical relatives orchestrate endocytic traffic and designate cargo fate, influence membrane identity transitions and support formation of membrane contact sites (MCSs). Finally, we explore the opportunistic hijacking of Ub and Ubl modification cascades by intracellular bacteria that remodel host trafficking pathways to invade and prosper inside cells.

Endosome biogenesis is controlled by ER and the cytoskeleton at tripartite junctions

The plasma membrane (PM) and its associated cargo are internalized into small vesicles via endocytosis funneling cargo into endosomes. The endosomal system must efficiently deliver cargos, as well as recycle cargo receptors and membrane to maintain homeostasis. In animal cells, endosome trafficking, maturation, and cargo recycling rely on the actin and microtubule cytoskeleton. Microtubules and their associated motor proteins provide the roads on which endosomes move and fuse during cargo sorting and delivery. In addition, highly dynamic assemblies of actin adjust the shape of the endosomal membrane to promote cargo segregation into budding domains allowing for receptor recycling. Recent work has revealed that the endoplasmic reticulum (ER) frequently acts as an intermediary between endosomes and their cytoskeletal regulators via membrane contact sites (MCSs). This review will discuss the factors which form these tripartite junction between the ER, endosomes, and the cytoskeleton as well as their function.

Transcription factor EB regulates phosphatidylinositol-3-phosphate levels that control lysosome positioning in the bladder cancer model

Lysosomes orchestrate degradation and recycling of exogenous and endogenous material thus controlling cellular homeostasis. Little is known how this organelle changes during cancer. Here we investigate the intracellular landscape of lysosomes in a cellular model of bladder cancer. Employing standardized cell culture on micropatterns we identify a phenotype of peripheral lysosome positioning prevailing in bladder cancer cell lines but not normal urothelium. We show that lysosome positioning is controlled by phosphatidylinositol-3-phosphate (PtdIns3P) levels on endomembranes which recruit FYVE-domain containing proteins for lysosomal dispersion. We identify transcription factor EB (TFEB) as an upstream regulator of PtdIns3P production by VPS34 that is activated in aggressive bladder cancer cells with peripheral lysosomes. This conceptually clarifies the dual role of TFEB as regulator of endosomal maturation and autophagy, two distinct processes controlled by PtdIns3P. Altogether, our findings uncover peripheral lysosome positioning, resulting from PtdIns3P production downstream of TFEB activation, as a potential biomarker for bladder cancer.

UBE2J1 inhibits colorectal cancer progression by promoting ubiquitination and degradation of RPS3

Ubiquitin-conjugating enzyme E2 J1 (UBE2J1) has been proven to participate in the ubiquitination of multiple substrate proteins. However, the underlying mechanisms of UBE2J1 as a ubiquitin-conjugating enzyme participating in cancer development and progression remain largely unknown. Here, we identified that UBE2J1 is downregulated in colorectal cancer (CRC) tissues and cell lines which are mediated by DNA hypermethylation of its promoter, and decreased UBE2J1 is associated with poor prognosis. Functionally, UBE2J1 serving as a suppressor gene inhibits the proliferation and metastasis of CRC cells. Mechanistically, UBE2J1-TRIM25, forming an E2-E3 complex, physically interacts with and targets RPS3 for ubiquitination and degradation at the K214 residue. The downregulated RPS3 caused by UBE2J1 overexpression restrains NF-κB translocation into the nucleus and therefore inactivates the NF-κB signaling pathway. Our study revealed a novel role of UBE2J1-mediated RPS3 poly-ubiquitination and degradation in disrupting the NF-κB signaling pathway, which may serve as a novel and promising biomarker and therapeutic target for CRC.

Membrane compartmentalisation of the ubiquitin system

We now have a comprehensive inventory of ubiquitin system components. Understanding of any system also needs an appreciation of how components are organised together. Quantitative proteomics has provided us with a census of their relative populations in several model cell types. Here, by examining large scale unbiased data sets, we seek to identify and map those components, which principally reside on the major organelles of the endomembrane system. We present the consensus distribution of > 50 ubiquitin modifying enzymes, E2s, E3s and DUBs, that possess transmembrane domains. This analysis reveals that the ER and endosomal compartments have a diverse cast of resident E3s, whilst the Golgi and mitochondria operate with a more restricted palette. We describe key functions of ubiquitylation that are specific to each compartment and relate this to their signature complement of ubiquitin modifying components.

Choreographing the motor-driven endosomal dance

The endosomal system orchestrates the transport of lipids, proteins and nutrients across the entire cell. Along their journey, endosomes mature, change shape via fusion and fission, and communicate with other organelles. This intriguing endosomal choreography, which includes bidirectional and stop-and-go motions, is coordinated by the microtubule-based motor proteins dynein and kinesin. These motors bridge various endosomal subtypes to the microtubule tracks thanks to their cargo-binding domain interacting with endosome-associated proteins, and their motor domain interacting with microtubules and associated proteins. Together, these interactions determine the mobility of different endosomal structures. In this Review, we provide a comprehensive overview of the factors regulating the different interactions to tune the fascinating dance of endosomes along microtubules.

Controlling contacts-Molecular mechanisms to regulate organelle membrane tethering

In recent years, membrane contact sites (MCS), which mediate interactions between virtually all subcellular organelles, have been extensively characterized and shown to be essential for intracellular communication. In this review essay, we focus on an emerging topic: the regulation of MCS. Focusing on the tether proteins themselves, we discuss some of the known mechanisms which can control organelle tethering events and identify apparent common regulatory hubs, such as the VAP interface at the endoplasmic reticulum (ER). We also highlight several currently hypothetical concepts, including the idea of tether oligomerization and redox regulation playing a role in MCS formation. We identify gaps in our current understanding, such as the identity of the majority of kinases/phosphatases involved in tether modification and conclude that a holistic approach-incorporating the formation of multiple MCS, regulated by interconnected regulatory modulators-may be required to fully appreciate the true complexity of these fascinating intracellular communication systems.

RNF185 regulates proteostasis in Ebolavirus infection by crosstalk between the calnexin cycle, ERAD, and reticulophagy

Virus infection affects cellular proteostasis and provides an opportunity to study this cellular process under perturbation. The proteostasis network in the endoplasmic reticulum (ER) is composed of the calnexin cycle, and the two protein degradation pathways ER-associated protein degradation (ERAD) and ER-to-lysosome-associated degradation (ERLAD/ER-phagy/reticulophagy). Here we show that calnexin and calreticulin trigger Zaire Ebolavirus (EBOV) glycoprotein GP_1,2 misfolding. Misfolded EBOV-GP_1,2 is targeted by ERAD machinery, but this results in lysosomal instead of proteasomal degradation. Moreover, the ER Ub ligase RNF185, usually associated with ERAD, polyubiquitinates EBOV-GP_1,2 on lysine 673 via ubiquitin K27-linkage. Polyubiquinated GP_1,2 is subsequently recruited into autophagosomes by the soluble autophagy receptor sequestosome 1 (SQSTM1/p62), in an ATG3- and ATG5-dependent manner. We conclude that EBOV hijacks all three proteostasis mechanisms in the ER to downregulate GP_1,2 via polyubiquitination and show that this increases viral fitness. This study identifies linkages among proteostasis network components previously thought to function independently.

Little is known about how proteostasis is maintained during viral infection. Here, the authors identify unexpected crosstalk between the calnexin cycle, ERAD, and reticulophagy, resulting in suppression of ebolavirus glycoprotein expression.

ER as master regulator of membrane trafficking and organelle function

The endoplasmic reticulum (ER), which occupies a large portion of the cytoplasm, is the cell's main site for the biosynthesis of lipids and carbohydrate conjugates, and it is essential for folding, assembly, and biosynthetic transport of secreted proteins and integral membrane proteins. The discovery of abundant membrane contact sites (MCSs) between the ER and other membrane compartments has revealed that, in addition to its biosynthetic and secretory functions, the ER plays key roles in the regulation of organelle dynamics and functions. In this review, we will discuss how the ER regulates endosomes, lysosomes, autophagosomes, mitochondria, peroxisomes, and the Golgi apparatus via MCSs. Such regulation occurs via lipid and Ca2+ transfer and also via control of in trans dephosphorylation reactions and organelle motility, positioning, fusion, and fission. The diverse controls of other organelles via MCSs manifest the ER as master regulator of organelle biology.

USP17 is required for peripheral trafficking of lysosomes

Expression of the deubiquitinase USP17 is induced by multiple stimuli, including cytokines (IL‐4/6), chemokines (IL‐8, SDF1), and growth factors (EGF), and several studies indicate it is required for cell proliferation and migration. However, the mechanisms via which USP17 impacts upon these cellular functions are unclear. Here, we demonstrate that USP17 depletion prevents peripheral lysosome positioning, as well as trafficking of lysosomes to the cell periphery in response to EGF stimulation. Overexpression of USP17 also increases secretion of the lysosomal protease cathepsin D. In addition, USP17 depletion impairs plasma membrane repair in cells treated with the pore‐forming toxin streptolysin O, further indicating that USP17 is required for lysosome trafficking to the plasma membrane. Finally, we demonstrate that USP17 can deubiquitinate p62, and we propose that USP17 can facilitate peripheral lysosome trafficking by opposing the E3 ligase RNF26 to untether lysosomes from the ER and facilitate lysosome peripheral trafficking, lysosome protease secretion, and plasma membrane repair.

Order through destruction: how ER-associated protein degradation contributes to organelle homeostasis

The endoplasmic reticulum (ER) is a large, dynamic, and multifunctional organelle. ER protein homeostasis is essential for the coordination of its diverse functions and depends on ER-associated protein degradation (ERAD). The latter process selects target proteins in the lumen and membrane of the ER, promotes their ubiquitination, and facilitates their delivery into the cytosol for degradation by the proteasome. Originally characterized for a role in the degradation of misfolded proteins and rate-limiting enzymes of sterol biosynthesis, the many branches of ERAD now appear to control the levels of a wider range of substrates and influence more broadly the organization and functions of the ER, as well as its interactions with adjacent organelles. Here, we discuss recent mechanistic advances in our understanding of ERAD and of its consequences for the regulation of ER functions.

Non-proteolytic ubiquitylation in cellular signaling and human disease

Ubiquitylation is one of the most common post-translational modifications (PTMs) of proteins that frequently targets substrates for proteasomal degradation. However it can also result in non-proteolytic events which play important functions in cellular processes such as intracellular signaling, membrane trafficking, DNA repair and cell cycle. Emerging evidence demonstrates that dysfunction of non-proteolytic ubiquitylation is associated with the development of multiple human diseases. In this review, we summarize the current knowledge and the latest concepts on how non-proteolytic ubiquitylation pathways are involved in cellular signaling and in disease-mediating processes. Our review, may advance our understanding of the non-degradative ubiquitylation process.

Evanthia Pangou and co-authors review recent insights into the important roles of non-proteolytic ubiquitylation in cellular signaling as well as in physiology and disease.

Perinuclear positioning of endosomes can affect PS-ASO activities

Phosphorothioate (PS) modified antisense oligonucleotide (ASO) drugs that act on cellular RNAs must enter cells and be released from endocytic organelles to elicit antisense activity. It has been shown that PS-ASOs are mainly released by late endosomes. However, it is unclear how endosome movement in cells contributes to PS-ASO activity. Here, we show that PS-ASOs in early endosomes display Brownian type motion and migrate only short distances, whereas PS-ASOs in late endosomes (LEs) move linearly along microtubules with substantial distances. In cells with normal microtubules and LE movement, PS-ASO-loaded LEs tend to congregate perinuclearly. Disruption of perinuclear positioning of LEs by reduction of dynein 1 decreased PS-ASO activity, without affecting PS-ASO cellular uptake. Similarly, disruption of perinuclear positioning of PS-ASO-LE foci by reduction of ER tethering proteins RNF26, SQSTM1 and UBE2J1, or by overexpression of P50 all decreased PS-ASO activity. However, enhancing perinuclear positioning through reduction of USP15 or over-expression of RNF26 modestly increased PS-ASO activity, indicating that LE perinuclear positioning is required for ensuring efficient PS-ASO release. Together, these observations suggest that LE movement along microtubules and perinuclear positioning affect PS-ASO productive release.