Rab GTPases as coordinators of vesicle traffic. Nat Rev Mol Cell Biol. 2009;10:513-525. [PMID: 19603039 DOI: 10.1038/nrm2728]

Homeostasis and metabolism of iron and other metal ions in neurodegenerative diseases

As essential micronutrients, metal ions such as iron, manganese, copper, and zinc, are required for a wide range of physiological processes in the brain. However, an imbalance in metal ions, whether excessive or insufficient, is detrimental and can contribute to neuronal death through oxidative stress, ferroptosis, cuproptosis, cell senescence, or neuroinflammation. These processes have been found to be involved in the pathological mechanisms of neurodegenerative diseases. In this review, the research history and milestone events of studying metal ions, including iron, manganese, copper, and zinc in neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), will be introduced. Then, the upstream regulators, downstream effector, and crosstalk of mental ions under both physiologic and pathologic conditions will be summarized. Finally, the therapeutic effects of metal ion chelators, such as clioquinol, quercetin, curcumin, coumarin, and their derivatives for the treatment of neurodegenerative diseases will be discussed. Additionally, the promising results and limitations observed in clinical trials of these metal ion chelators will also be addressed. This review will not only provide a comprehensive understanding of the role of metal ions in disease development but also offer perspectives on their modulation for the prevention or treatment of neurodegenerative diseases.

The prognostic and immune significance of Rab11A in pan-cancer and its function and mechanism underlying estrogen receptor targeting in breast cancer

OBJECTIVE

Rab11A is an important molecule for recycling endosomes and is closely related to the proliferation, invasion, and metastasis of tumors. This study investigated the prognostic and immune significance of Rab11A and validated its potential function and mechanism in breast cancer (BRCA).

METHODS

RNA sequencing data for 33 tumors were downloaded from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression databases. Correlation analysis was used to evaluate the relationship between Rab11A expression and immune characteristics. Potential pathways were identified using the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analysis. Immunohistochemical analysis, colony formation assay, bromodeoxyuridine incorporation assay, immunofluorescence, and Western blot were used to explore potential function and mechanism.

RESULTS

Analysis of the TCGA database showed significant upregulation of Rab11A expression in a variety of cancers. Rab11A was up-regulated in 82.4% of BRCA. High Rab11A expression is associated with poor survival in cancer patients and is a predictor of poor prognosis. CIBERSORT analysis showed that Rab11A was negatively associated with almost all immune cycle activity scores pan-cancer. The results of the TCGA-BRCA cohort were further confirmed by using pathological samples from clinical BRCA patients. The results showed that Rab11A expression was correlated with estrogen receptor (ER) and progesterone receptor expression in BRCA (p < 0.05). Knockdown and overexpression of Rab11A affected the proliferation of BRCA cells. Further mechanistic studies revealed that down-regulation of ER alpha (ERα) and up-regulation of ER beta (ERβ) mediated Rab11A-induced inhibition of BRCA cell proliferation.

CONCLUSION

Rab11A expression in pan-cancer is associated with poor prognosis and immune profile. In particular, in BRCA, Rab11A expression regulates cell proliferation by targeting ERα and ERβ. High Rab11A expression is tightly associated with immune characteristics, tumor microenvironment, and genetic mutations. These results provide a reference for exploring the role of Rab11A in pan-cancer and provide a new perspective for revealing potential therapeutic targets in BRCA.

Hypoxia as a critical player in extracellular vesicles-mediated intercellular communication between tumor cells and their surrounding microenvironment

In the past years, increasing attention has been paid to the role of extracellular vesicles (EVs) as mediators of intercellular communication in cancer. These small size particles mediate the intercellular transfer of important bioactive molecules involved in malignant initiation and progression. Hypoxia, or low partial pressure of oxygen, is recognized as a remarkable feature of solid tumors and has been demonstrated to exert a profound impact on tumor prognosis and therapeutic efficacy. Indeed, the high-pitched growth rate and chaotic neovascular architecture that embodies solid tumors results in a profound reduction in oxygen pressure within the tumor microenvironment (TME). In response to oxygen-deprived conditions, tumor cells and their surrounding milieu develop homeostatic adaptation mechanisms that contribute to the establishment of a pro-tumoral phenotype. Latest evidence suggests that the hypoxic microenvironment that surrounds the tumor bulk may be a clincher for the observed elevated levels of circulating EVs in cancer patients. Thus, it is proposed that EVs may play a role in mediating intercellular communication in response to hypoxic conditions. This review focuses on the EVs-mediated crosstalk that is established between tumor cells and their surrounding immune, endothelial, and stromal cell populations, within the hypoxic TME.

Intracellular mechanistic insights into cRGD-modified Bi2Se3 nanofoams for enhanced photothermal therapy via exocytosis inhibition

The cRGD peptide surface coating strategy for photothermal therapy nanoplatforms shows great promise in developing safe and effective cancer therapies. However, the precise intracellular mechanisms of these platforms remain unclear due to the complexity of intracellular trafficking and nano-bio interactions. This study investigates the nano-bio interactions of Bi2Se3 nanofoams, a representative photothermal therapy nanoplatform, coated with cRGD peptide in cancer cells, focusing on endocytosis, exocytosis, and cellular trafficking. Our findings reveal that the cRGD-coated Bi2Se3 nanofoams are internalized through three distinct endocytosis pathways: Rab34-mediated macropinocytosis, caveolae-dependent, and clathrin-dependent endocytosis. These nanofoams then accumulate in lysosomes via autophagy. Furthermore, inhibiting exocytosis reduces the loss of these nanofoams from cancer cells, enhancing photothermal and chemotherapy effects. This exocytosis-inhibiting strategy demonstrates significant potential for cancer therapy, validated by successful in vitro and in vivo results.

Skeletal and dental tissue mineralization: The potential role of the endoplasmic reticulum/Golgi complex and the endolysosomal and autophagic transport systems

This paper presents a review of the potential role of the endoplasmic reticulum/Golgi complex and intracellular vesicles in mediating events leading to or associated with vertebrate tissue mineralization. The possible importance of these organelles in this process is suggested by observations that calcium ions accumulate in the tubules and lacunae of the endoplasmic reticulum and Golgi. Similar levels of calcium ions (approaching millimolar) are present in vesicles derived from endosomes, lysosomes and autophagosomes. The cellular level of phosphate ions in these organelles is also high (millimolar). While the source of these ions for mineral formation has not been identified, there are sound reasons for considering that they may be liberated from mitochondria during the utilization of ATP for anabolic purposes, perhaps linked to matrix synthesis. Published studies indicate that calcium and phosphate ions or their clusters contained as cargo within the intracellular organelles noted above lead to formation of extracellular mineral. The mineral sequestered in mitochondria has been documented as an amorphous calcium phosphate. The ion-, ion cluster- or mineral-containing vesicles exit the cell in plasma membrane blebs, secretory lysosomes or possibly intraluminal vesicles. Such a cell-regulated process provides a means for the rapid transport of ions or mineral particles to the mineralization front of skeletal and dental tissues. Within the extracellular matrix, the ions or mineral may associate to form larger aggregates and potential mineral nuclei, and they may bind to collagen and other proteins. How cells of hard tissues perform their housekeeping and other biosynthetic functions while transporting the very large volumes of ions required for mineralization of the extracellular matrix is far from clear. Addressing this and related questions raised in this review suggests guidelines for further investigations of the intracellular processes promoting the mineralization of the skeletal and dental tissues.

Lipid droplets in central nervous system and functional profiles of brain cells containing lipid droplets in various diseases

Lipid droplets (LDs), serving as the convergence point of energy metabolism and multiple signaling pathways, have garnered increasing attention in recent years. Different cell types within the central nervous system (CNS) can regulate energy metabolism to generate or degrade LDs in response to diverse pathological stimuli. This article provides a comprehensive review on the composition of LDs in CNS, their generation and degradation processes, their interaction mechanisms with mitochondria, the distribution among different cell types, and the roles played by these cells-particularly microglia and astrocytes-in various prevalent neurological disorders. Additionally, we also emphasize the paradoxical role of LDs in post-cerebral ischemia inflammation and explore potential underlying mechanisms, aiming to identify novel therapeutic targets for this disease.

A review on evolution, structural characteristics, interactions, and regulation of the membrane transport protein: The family of Rab proteins

Rab proteins are a key family of small GTPases that play crucial roles in vesicular trafficking, membrane dynamics, and maintaining cellular homeostasis. Studying this family of proteins is interesting as having many structural isoforms with variable evolutionary trends and wide distribution in cells. The proteins are renowned for their unique structural characteristics, which support their functional adaptability and specificity. Based on these features these proteins show different regulatory pathways and show involvement in dynamic protein-protein interactions, which is essential for intracellular signaling processes and in maintaining cellular functionality and balance. Notably, it is the first review to compile such extensive information about Rabs. Such information related to these proteins explores the molecular mechanisms in medicine based on their phylogenetic development, structural conformation changes, interaction networks, distribution, and regulation-dysregulations discussed in this review. Moreover, this review offers a consolidated resource for researchers and clinicians to understand the Rabs in different magnitudes.

Nationwide multi-centric prospective study for the identification of biomarkers to predict the treatment responses of nivolumab through comprehensive analyses of pretreatment plasma exosome mRNAs from head and neck cancer patients (BIONEXT study)

Background

Nivolumab paved a new way in the treatment of patients with recurrent or metastatic (RM) head and neck squamous cell carcinoma (RM-HNSCC). However, the limited rates of long-term survivors (< 20%) demand a robust prognostic biomarker. This nationwide multi-centric prospective study aimed to identify a plasma exosome (PEX) mRNA signature, which serves as a companion diagnostic of nivolumab and provides a biological clue to develop effective therapies for a majority of non-survivors.

Methods

Pre-treatment plasmas (N = 104) of RM-HNSCC patients were subjected to comprehensive PEX mRNA analyses for prognostic marker discovery and validation. In parallel, paired treatment-naïve tumor and plasma samples (N = 20) were assayed to elucidate biological implications of the PEX mRNA signature.

Results

Assays for pre-treatment blood samples (N = 104) demonstrated that a combination of 6 candidate PEX mRNAs plus neutrophil-to-lymphocyte ratio precisely distinguished non-survivors from >2-year survivors (2-year OS; 0% vs 57.7%; P = 0.000124) with a high hazard ratio of 2.878 (95% CI 1.639-5.055; P = 0.0002348). Parallel biological assays demonstrated that in the paired treatment-naïve HNSCC tumor and plasma samples (N = 20), PEX HLA-E mRNA (a non-survivor-predicting marker) was positively corelated with overexpression of HLA-E protein (P = 0.0191) and the dense population of tumor-infiltrating NK cells (P = 0.024) in the corresponding tumor, suggesting that the HLA-E-NKG2A immune checkpoint may inhibit the antitumor effect of PD-1blockade.

Conclusion

The PEX mRNA signature could be useful as a companion diagnostic of nivolumab. The combination of an anti-NKG2A antibody (i.e., monalizumab) and nivolumab may serve as a treatment option for non-survivors predicted by a RT-qPCR-based pre-treatment measurement of PEX mRNAs.

Lipophagy: exploring its association with male reproductive system disorders and investigating potential mechanisms

BACKGROUND

Lipid metabolism, one of the three major metabolic processes, plays a crucial role in male fertility, particularly when lipid homeostasis is disrupted. Lipid droplets (LDs), cellular organelles that store lipids primarily in the form of triglycerides and cholesterol esters, serve as central hubs in lipid metabolism.The degradation of LDs is regulated by lipases and lipophagy.

OBJECTIVE: 

This review explores the various forms of lipophagy, its molecular mechanisms, and its critical role in male fertility. Specifically, it examines the association between lipophagy and male infertility, sexual dysfunction, and reproductive cancers.

METHODS: 

This review synthesizes current research on the molecular pathways regulating lipophagy, focusing on its impact on male reproductive health.

RESULTS: 

Lipophagy is essential for maintaining lipid homeostasis in male reproductive tissues. Dysfunction of lipophagy is associated with impaired sperm function, infertility, sexual dysfunction, and an increased risk of reproductive cancers in men.

CONCLUSION: 

Lipophagy plays a pivotal role in regulating lipid metabolism and maintaining male fertility. It may serve as a potential therapeutic target for treating male reproductive disorders.

The Molecular Biology of Placental Transport of Calcium to the Human Foetus

From fertilisation to delivery, calcium must be transported into and within the foetoplacental unit for intracellular signalling. This requires very rapid, precisely located Ca2+ transfers. In addition, from around the eighth week of gestation, increasing amounts of calcium must be routed directly from maternal blood to the foetus for bone mineralisation through a flow-through system, which does not impact the intracellular Ca2+ concentration. These different processes are mediated by numerous membrane-sited Ca2+ channels, transporters, and exchangers. Understanding the mechanisms is essential to direct interventions to optimise foetal development and postnatal bone health and to protect the mother and foetus from pre-eclampsia. Ethical issues limit the availability of human foetal tissue for study. Our insight into the processes of placental Ca2+ handling is advancing rapidly, enabled by developing genetic, analytical, and computer technology. Because of their diverse sources, the reports of new findings are scattered. This review aims to pull the data together and to highlight areas of uncertainty. Areas needing clarification include trafficking, membrane expression, and recycling of channels and transporters in the placental microvilli; placental metabolism of vitamin D in gestational diabetes and pre-eclampsia; and the vascular effects of increased endothelial Orai expression by pregnancy-specific beta-1-glycoproteins PSG1 and PSG9.

Rational Design of Biocompatible Ir(III) Photosensitizer to Overcome Drug-Resistant Cancer via Oxidative Autophagy Inhibition

Autophagy is a crucial quality control mechanism that degrades damaged cellular components through lysosomal fusion with autophagosomes. However, elevated autophagy levels can promote drug resistance in cancer cells, enhancing their survival. Downregulation of autophagy through oxidative stress is a clinically promising strategy to counteract drug resistance, yet precise control of oxidative stress in autophagic proteins remains challenging. Here, a molecular design strategy of biocompatible neutral Ir(III) photosensitizers is demonstrated, B2 and B4, for precise reactive oxygen species (ROS) control at lysosomes to inhibit autophagy. The underlying molecular mechanisms for the biocompatibility and lysosome selectivity of Ir(III) complexes are explored by comparing B2 with the cationic or the non-lysosome-targeting analogs. Also, the biological mechanisms for autophagy inhibition via lysosomal oxidation are explored. Proteome analyses reveal significant oxidation of proteins essential for autophagy, including lysosomal and fusion-mediator proteins. These findings are verified in vitro, using mass spectrometry, live cell imaging, and a model SNARE complex. The anti-tumor efficacy of the precise lysosomal oxidation strategy is further validated in vivo with B4, engineered for red light absorbance. This study is expected to inspire the therapeutic use of spatiotemporal ROS control for sophisticated modulation of autophagy.

Rab11b promotes M1-like macrophage polarization by restraining autophagic degradation of NLRP3 in alcohol-associated liver disease

Macrophage polarization is vital to mounting a host defense or repairing tissue in various liver diseases. Excessive activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome is related to the orchestration of inflammation and alcohol-associated liver disease (ALD) pathology. Rab GTPases play critical roles in regulating vesicular transport. In this study we investigated the role of Rab11b in ALD, aiming to identify effective therapeutic targets. Here, we first demonstrated a decreased expression of Rab11b in macrophages from ALD mice. Knockdown of Rab11b by macrophage-specific adeno-associated virus can alleviate alcohol induced liver inflammation, injury and steatosis. We found that LPS and alcohol stimulation promoted Rab11b transferring from the nucleus to the cytoplasm in bone marrow-derived macrophages (BMDM) cells. Rab11b specifically activated the NLRP3 inflammasome in BMDMs and RAW264.7 cells to induce M1 macrophage polarization. Rab11b overexpression in BMDMs inhibited autophagic flux, leading to the suppression of LC3B-mediated NLRP3 degradation. We conclude that impaired Rab11b could alleviate alcohol-induced liver injury via autophagy-mediated NLRP3 degradation.

Comprehensive knockout analysis of the RAB family small GTPases reveals an overlapping role of RAB2 and RAB14 in autophagosome maturation

Macroautophagy, simply referred to below as autophagy, is an intracellular degradation system that is highly conserved in eukaryotes. Since the processes involved in autophagy are accompanied by membrane dynamics, RAB small GTPases, key regulators of membrane trafficking, are generally thought to regulate the membrane dynamics of autophagy. Although more than half of the mammalian RABs have been reported to be involved in canonical and selective autophagy, no consensus has been reached in regard to the role of RABs in mammalian autophagy. Here, we comprehensively analyzed a rab-knockout (KO) library of MDCK cells to reevaluate the requirement for each RAB isoform in basal and starvation-induced autophagy. The results revealed clear alteration of the MAP1LC3/LC3-II level in only four rab-KO cells (rab1-KO, rab2-KO, rab7a-KO, and rab14-KO cells) and identified RAB14 as a new regulator of autophagy, specifically at the autophagosome maturation step. The autophagy-defective phenotype of two of these rab-KO cells, rab2-KO and rab14-KO cells, was very mild, but double KO of rab2 and rab14 caused a severer autophagy-defective phenotype (greater LC3 accumulation than in single-KO cells, indicating an overlapping role of RAB2 and RAB14 during autophagosome maturation. We also found that RAB14 is phylogenetically similar to RAB2 and that it possesses the same properties as RAB2, i.e. autophagosome localization and interaction with the HOPS subunits VPS39 and VPS41. Our findings suggest that RAB2 and RAB14 overlappingly regulate the autophagosome maturation step through recruitment of the HOPS complex to the autophagosome.Abbreviation: AID2: auxin-inducible degron 2; ATG: autophagy related; BafA1: bafilomycin A1; CKO: conditional knockout; EBSS: Earle's balanced salt solution; EEA1: early endosome antigen 1; HOPS: homotypic fusion and protein sorting; HRP: horseradish peroxidase; IP: immunoprecipitation; KD: knockdown; KO: knockout; LAMP2: lysosomal-associated membrane protein 2; MDCK: Madin-Darby canine kidney; mAb: monoclonal antibody; MEF: mouse embryonic fibroblast; MTORC1: mechanistic target of rapamycin kinase complex 1; 5-Ph-IAA: 5-phenyl-indole-3-acetic acid; pAb: polyclonal antibody; siRNA: small interfering RNA; SNARE: soluble NSF-attachment protein receptor; TF: transferrin; WT: wild-type.

Structural basis for Rab23 activation and a loss-of-function mutation in Carpenter syndrome

Rab23 is a member of the Rab family of small GTPases. It plays crucial roles in Hedgehog signaling, ciliary transport, and embryonic development. As a small GTPase, Rab23 cycles between the GDP-bound inactivated state and the GTP-bound activated state. Mutations in Rab23 are directly implicated in Carpenter syndrome, a development disorder characterized by deformed skulls, abnormal fingers or toes, and intellectual disabilities. Several clinical point mutations, for example, M12K, C85R, and Y79del, have been found to occur within the GTPase domain. However, the mechanisms of activation of Rab23 and pathogenesis of its clinical mutants are still unclear with limited structural information. So far, there are only two reported crystal structures of mouse Rab23 in complex with GDP. Here, we determined high-resolution crystal structures of human Rab23 and the human Rab23 Y79del clinical mutant, in complex with GDP and GMPPNP, a nonhydrolysable GTP analog, respectively. Supported by in vitro biochemical and functional analyses, we demonstrated that the Y79 deletion mutant exhibited structural distortions in the switch II region relative to that of the WT. The structural changes potentially disrupted the binding of Rab23 Y79del to its interacting partners, thus leading to a loss-of-function and the development of Carpenter syndrome.

RHO subfamily of small GTPases in the development and function of hematopoietic cells

RHOA, RHOB, and RHOC comprise a subfamily of RHO GTPase proteins famed for controlling cytoskeletal dynamics. RHO proteins operate downstream of multiple signals emerging from the microenvironment, leading to diverse cell responses, such as proliferation, adhesion, and migration. Therefore, RHO signaling has been centrally placed in the regulation of blood cells. Despite their high homology, unique roles of RHOA, RHOB, and RHOC have been described in hematopoietic cells. In this article, we overview the contribution of RHO proteins in the development and function of each blood cell lineage. Additionally, we highlight the aberrations of the RHO signaling pathways found in hematological malignancies, providing clues for the identification of new therapeutic targets.

Chloroquine Affects Presynaptic Membrane Retrieval in Diaphragm Neuromuscular Junctions of Old Mice

Aging disrupts multiple homeostatic processes, including autophagy, a cellular process for the recycling and degradation of defective cytoplasmic structures. Acute treatment with the autophagy inhibitor chloroquine blunts the maximal forces generated by the diaphragm muscle, but the mechanisms underlying neuromuscular dysfunction in old age remain poorly understood. We hypothesized that chloroquine treatment increases the presynaptic retention of the styryl dye FM 4-64 following high-frequency nerve stimulation, consistent with the accumulation of unprocessed bulk endosomes. Diaphragm-phrenic nerve preparations from 24-month-old male and female C57BL/6 × 129 J mice were incubated with FM 4-64 (5 µM) and either chloroquine (50 µM) or vehicle during 80 Hz phrenic nerve stimulation. Acute chloroquine treatment significantly decreased FM 4-64 intensity at diaphragm neuromuscular junctions following 80 Hz phrenic nerve stimulation, consistent with disrupted synaptic vesicle recycling. A similar reduction was evident in regions with the greatest FM 4-64 fluorescence intensity, which most likely surround synaptic vesicle release sites. In the absence of nerve stimulation, chloroquine treatment significantly increased FM 4-64 intensity at diaphragm neuromuscular junctions. These findings highlight the importance of autophagy in regulating presynaptic vesicle retrieval (including vesicle recycling and endosomal processing) and support the role of autophagy impairments in age-related neuromuscular dysfunction.

Legionella uses host Rab GTPases and BAP31 to create a unique ER niche

The bacterium Legionella pneumophila secretes numerous effector proteins that manipulate endoplasmic reticulum (ER)-derived vesicles to form the Legionella-containing vacuole (LCV). Despite extensive studies, whether the LCV membrane is separate from or connected to the host ER network remains unclear. Here, we show that the smooth ER (sER) is closely associated with the LCV early in infection. Remarkably, Legionella forms a distinct rough ER (rER) niche at later stages, disconnected from the host ER network. We discover that host small GTPases Rab10 and Rab4 and an ER protein, BAP31, play crucial roles in transitioning the LCV from an sER to an rER. Additionally, we have identified a Legionella effector, Lpg1152, that binds to BAP31. Interestingly, the optimal growth of Legionella is dependent on both BAP31 and Lpg1152. These findings detail the complex interplay between host and pathogen in transforming the LCV membrane from a host-associated sER to a distinct rER.

Mapping the Protein Phosphatase 1 Interactome in Human Cytomegalovirus Infection

Protein phosphorylation is a crucial regulatory mechanism in cellular homeostasis. The human cytomegalovirus (HCMV) incorporates protein phosphatase 1 (PP1) into its tegument, yet the biological relevance and mechanisms of this incorporation remain unclear. Our study offers the first characterization of the PP1 interactome during HCMV infection and its alterations. Using co-immunoprecipitation, mass spectrometry, and quantitative proteomics, we identified 159 high-confidence interacting proteins (HCIPs) in the PP1 interactome, consisting of 126 human and 33 viral proteins. We observed significant temporal changes in the PP1 interactome following HCMV infection, including the altered interactions of PP1 regulatory subunits. Further analysis highlighted the central roles of these PP1 interacting proteins in intracellular trafficking, with particular emphasis on the trafficking protein particle complex and Rab GTPases, which are crucial for the virus's manipulation of host cellular processes in virion assembly and egress. Additionally, our study on the noncatalytic PP1 inhibitor 1E7-03 revealed a decrease in PP1's interaction with key HCMV proteins, supporting its potential as an antiviral agent. Our findings suggest that PP1 docking motifs are critical in viral-host interactions and offer new insights for antiviral strategies.

Flow-Dependent Modulation of Endothelial Ca2+ Dynamics by Small Conductance Ca2+-Activated K+ Channels in Mouse Carotid Arteries

BACKGROUND

Small conductance Ca2+ activated K+ channels (KCa2.3) are important regulators of vascular function. They provide Ca2+-dependent hyperpolarization of the endothelial membrane potential, promoting agonist-induced vasodilation. Another important mechanism of influence may occur through positive feedback regulation of endothelial Ca2+ signals, likely via amplification of influx through membrane cation channels. KCa2.3 channels have recently been implicated in flow-mediated dilation of the arterial vasculature and may contribute to the crucial homeostatic role of shear stress in preventing vascular wall remodeling and progressive vascular disease (i.e., atherosclerosis). The impact of KCa2.3 channels on endothelial Ca2+ signaling under physiologically relevant shear stress conditions remains unknown.

METHODS

In the current study, we employ mice expressing an endothelium-specific Ca2+ fluorophore (cdh5-GCaMP8) to characterize the KCa2.3 channel influence on the dynamic Ca2+ signaling profile along the arterial endothelium in the presence and absence of shear-stress.

RESULTS

Our data indicate KCa2.3 channels have a minimal influence on basal Ca2+ signaling in the carotid artery endothelium in the absence of flow, but they contribute substantially to amplification of Ca2+ dynamics in the presence of flow and their influence can be augmented through exogenous positive modulation.

CONCLUSIONS

The findings suggest a pivotal role for KCa2.3 channels in adjusting the profile of homeostatic dynamic Ca2+ signals along the arterial intima under flow.

A trafficking regulatory subnetwork governs αVβ6 integrin-HER2 cross-talk to control breast cancer invasion and drug resistance

HER2 and αVβ6 integrin are independent predictors of breast cancer survival and metastasis. We identify an αVβ6/HER2 cross-talk mechanism driving invasion, which is dysregulated in drug-resistant HER2+ breast cancer cells. Proteomic analyses reveal ligand-bound αVβ6 recruits HER2 and a trafficking subnetwork, comprising guanosine triphosphatases RAB5 and RAB7A and the Rab regulator guanine nucleotide dissociation inhibitor 2 (GDI2). The RAB5/RAB7A/GDI2 functional module mediates direct cross-talk between αVβ6 and HER2, affecting receptor trafficking and signaling. Acute exposure to trastuzumab increases recruitment of the subnetwork to αVβ6, but trastuzumab resistance decouples GDI2 recruitment. GDI2, RAB5, and RAB7A cooperate to regulate migration and transforming growth factor-β activation to promote invasion. However, these mechanisms are dysregulated in trastuzumab-resistant cells. In patients, RAB5A, RAB7A, and GDI2 expression correlates with patient survival and αVβ6 expression predicts relapse following trastuzumab treatment. Thus, the RAB5/RAB7A/GDI2 subnetwork regulates αVβ6-HER2 cross-talk to drive breast cancer invasion but is subverted in trastuzumab-resistant cells to drive αVβ6-independent and HER2-independent tumor progression.

Role of Redox Homeostasis in the Communication Between Brain and Liver Through Extracellular Vesicles

Extracellular vesicles (EVs) are small, membrane-bound particles secreted by cells into the extracellular environment, playing an increasingly recognized role in inter-organ communication and the regulation of various physiological processes. Regarding the redox homeostasis context, EVs play a pivotal role in propagating and mitigating oxidative stress signals across different organs. Cells under oxidative stress release EVs containing signaling molecules that can influence the redox status of distant cells and tissues. EVs are starting to be recognized as contributors to brain-liver communication. Therefore, in this review, we show how redox imbalance can affect the release of EVs in the brain and liver. We propose EVs as mediators of redox homeostasis in the brain-liver axis.

The potential mechanisms underlying phthalate-induced hypospadias: a systematic review of rodent model studies

Objectives

Maternal exposure to environmental endocrine disruptors, such as phthalates, during pregnancy is a significant risk factor for the development of hypospadias. By consolidating existing research on the mechanisms by which phthalates induce hypospadias in rodent models, this systematic review aims to organize and analyze the discovered mechanisms and their potential connections.

Methods

The study involved all articles that explored the mechanisms of phthalate-induced hypospadias using rodent models. A comprehensive search of the PubMed and Web of Science databases was conducted using the terms "hypospadias" and "phthalates" before January 20, 2024. Then, two investigators screened for studies worthy of inclusion by setting inclusion and exclusion criteria.

Results

Of the initial 326 search results, 22 were included in the subsequent analysis. Based on the commonalities among different results, the mechanisms of phthalate-induced hypospadias could be categorized into the following five groups: sex steroids-related signaling pathways (n=10), epithelial-mesenchymal transition (n=6), autophagy (n=5), apoptosis (n=4) and angiogenesis (n=2). Among these, sex steroids-related signaling pathways might serve as a central regulator among all mechanisms, and reactive oxygen species (ROS) also played an important mediating role.

Conclusion

The systematic review indicates that phthalates may initially disrupt the balance of sex steroids-related pathways, leading to abnormally elevated levels of ROS and subsequently to other functional abnormalities, ultimately resulting in the development of hypospadias. All these findings will help to improve prevention strategies during pregnancy to reduce the adverse effects of phthalates on the offspring.

BEACH domain proteins function as cargo-sorting adaptors in secretory and endocytic pathways

We identify BEACH domain-containing proteins (BDCPs) as novel membrane coat proteins involved in the sorting of transmembrane proteins (TMPs) on the trans-Golgi network and tubular sorting endosomes. The seven typical mammalian BDCPs share a predicted alpha-solenoid-beta propeller structure, suggesting they have a protocoatomer origin and function. We map the subcellular localization of seven BDCPs based on their dynamic colocalization with RAB and ARF small GTPases and identify five typical BDCPs on subdomains of dynamic tubular-vesicular compartments on the intersection of endocytic recycling and post-Golgi secretory pathways. We demonstrate that BDCPs interact directly with the cytosolic tails of selected TMPs and identify a subset of TMPs, whose trafficking to the plasma membrane is affected in cells lacking BDCP. We propose that the competitive binding of BDCPs and clathrin coat adaptors to the cytosolic tails of TMPs, followed by their clustering to distinct subdomains of secretory/recycling tubules function as a mechanism for sorting of TMPs in pleomorphic tubular-vesicular compartments that lack a clathrin coat.

Hijacking host cell vesicular transport: New insights into the nutrient acquisition mechanism of Chlamydia

Chlamydia infection is an important cause of public health diseases, and no effective vaccine is currently available. Owing to its unique intracellular lifestyle, Chlamydia requires a variety of nutrients and substrates from host cells, particularly sphingomyelin, cholesterol, iron, amino acids, and the mannose-6-phosphate receptor, which are essential for inclusion development. Here, we summarize the recent advances in Chlamydia nutrient acquisition mechanism by hijacking host cell vesicular transport, which plays an important role in chlamydial growth and development. Chlamydia obtains the components necessary to complete its intracellular developmental cycle by recruiting Rab proteins (major vesicular trafficking regulators) and Rab effector proteins to the inclusion, interfering with Rab-mediated multivesicular trafficking, reorienting the nutrition of host cells, and reconstructing the intracellular niche environment. Consequently, exploring the role of vesicular transport in nutrient acquisition offers a novel perspective on new approaches for preventing and treating Chlamydia infection.

An RXLR effector disrupts vesicle trafficking at ER-Golgi interface for Phytophthora capsici pathogenicity

Phytophthora species, an oomycete plant pathogen, secrete effectors into plant cells throughout their life cycle for manipulating host immunity to achieve successful colonization. However, the molecular mechanisms underlying effector-triggered necrotic cell death remain elusive. In this study, we identified an RXLR (amino acid residue; Arginine-Any amino acid-Leucine-Arginine motif) effector (Pc12) from Phytophthora capsici, which contributes to virulence and induces necrosis by triggering a distinct endoplasmic reticulum (ER) stress response through its interaction with Rab13-2. The necrotic cell death induced by Pc12 did not exhibit conventional effector-triggered immunity-mediated hypersensitive cell death, including the involvement of nucleotide-binding site leucine-rich repeat downstream signaling components and transcriptional reprogramming of defense-related genes. Instead, it alters the localization of ER-resident proteins and confines secretory proteins within the ER. Pc12 directly interacts with Rab13-2, which is primarily localized to the ER and Golgi apparatus, resulting in a diminished Rab13-2 signal on the Golgi apparatus. Furthermore, Rab13-2 exhibits increased affinity for its interactor, Rab escort protein 1, in the presence of Pc12. Structural predictions revealed that a specific residue of Rab13-2 is crucial for binding to the C-terminus of Pc12. Substitution of this residue reduced its interaction with Pc12 and impaired P. capsici infection while maintaining its interaction with Rab escort protein 1 and prenylated Rab acceptor 1. These findings provide insight into how a pathogen effector induces a distinct form of necrotic cell death to facilitate colonization of the host plant by disrupting the recycling of Rab13-2, a protein involved in vesicle trafficking at the ER-Golgi interface.

Precise Control of Intracellular Trafficking and Receptor-Mediated Endocytosis in Living Cells and Behaving Animals

Intracellular trafficking, an extremely complex network, dynamically orchestrates nearly all cellular activities. A versatile method that enables the manipulation of target transport pathways with high spatiotemporal accuracy in vitro and in vivo is required to study how this network coordinates its functions. Here, a new method called RIVET (Rapid Immobilization of target Vesicles on Engaged Tracks) is presented. Utilizing inducible dimerization between target vesicles and selective cytoskeletons, RIVET can spatiotemporally halt numerous intracellular trafficking pathways within seconds in a reversible manner. Its highly specific perturbations allow for the real-time dissection of the dynamic relationships among different trafficking pathways. Moreover, RIVET is capable of inhibiting receptor-mediated endocytosis. This versatile system can be applied from the cellular level to whole organisms. RIVET opens up new avenues for studying intracellular trafficking under various physiological and pathological conditions and offers potential strategies for treating trafficking-related disorders.

Differential Expression Spectrum of circRNA in Plasma Exosomes in Dilated Cardiomyopathy With Heart Failure

Dilated cardiomyopathy (DCM), a form of non-ischaemic myocardial disease, is characterised by structural and functional cardiac abnormalities. As defined by the World Health Organisation, DCM constitutes a significant cardiac pathology, leading to increased morbidity and mortality due to complications such as heart failure and arrhythmias. The diagnostic process for DCM predominantly employs echocardiography and MRI, with biomarkers like NT-pro BNP and troponin providing supportive, yet non-specific, evidence. Exosomes, small extracellular vesicles, play a critical role in intercellular communications by transferring biomolecules including lipids, proteins, messenger RNA (mRNA) and non-coding RNA (ncRNA) to target cells, thereby influencing key cellular processes such as proliferation, differentiation, apoptosis, angiogenesis and immune modulation. Within the ncRNA category, circular RNAs (circRNAs) are notable for their cellular specificity and evolutionary conservation and are often implicated in the regulatory mechanisms underlying DCM and heart failure. This investigation employed next-generation sequencing technology to analyse plasma exosomal circRNA profiles in DCM patients with chronic heart failure (CHF), compared to healthy controls. The analysis revealed distinct circRNA expression patterns, identifying 49 uniquely expressed circRNAs in the DCM cohort with CHF. These circRNAs were associated with several critical biological pathways, including the sequestration of extracellular ligands from receptors, N-acetyltransferase activity, histone acetyltransferase activity and endocytic vesicle membrane composition. The findings of this study provide valuable insights into the pathophysiological mechanisms of DCM and offer evidence for improving clinical diagnostic methodologies.

Rab2A-mediated Golgi-lipid droplet interactions support very-low-density lipoprotein secretion in hepatocytes

Lipid droplets (LDs) serve as crucial hubs for lipid trafficking and metabolic regulation through their numerous interactions with various organelles. While the interplay between LDs and the Golgi apparatus has been recognized, their roles and underlying mechanisms remain poorly understood. Here, we reveal the role of Ras-related protein Rab-2A (Rab2A) in mediating LD-Golgi interactions, thereby contributing to very-low-density lipoprotein (VLDL) lipidation and secretion in hepatocytes. Mechanistically, our findings identify a selective interaction between Golgi-localized Rab2A and 17-beta-hydroxysteroid dehydrogenase 13 (HSD17B13) protein residing on LDs. This complex facilitates dynamic organelle communication between the Golgi apparatus and LDs, thus contributing to lipid transfer from LDs to the Golgi apparatus for VLDL2 lipidation and secretion. Attenuation of Rab2A activity via AMP-activated protein kinase (AMPK) suppresses the Rab2A-HSD17B13 complex formation, impairing LD-Golgi interactions and subsequent VLDL secretion. Furthermore, genetic inhibition of Rab2A and HSD17B13 in the liver reduces the serum triglyceride and cholesterol levels. Collectively, this study provides a new perspective on the interactions between the Golgi apparatus and LDs.

RAB37-mediated autophagy guards ovarian homeostasis and function

Loss of ovarian homeostasis is associated with ovary dysfunction and female diseases; however, the underlying mechanisms responsible for the establishment of homeostasis and its function in the ovary have not been fully elucidated. Here, we showed that conditional knockout of Rab37 in oocytes impaired macroautophagy/autophagy proficiency in the ovary and interfered with follicular homeostasis and ovary development in mice. Flunarizine treatment upregulated autophagy, thus rescuing the impairment of follicular homeostasis and ovarian dysfunction in rab37 knockout mice by reprogramming of homeostasis. Notably, both the E2F1 and EGR2 transcription factors synergistically activated Rab37 transcription and promoted autophagy. Thus, RAB37-mediated autophagy ensures ovary function by maintaining ovarian homeostasis.Abbreviations: AMH: anti-Mullerian hormone; ATG: autophagy related; BECN1: beclin 1; cKO: conditional knockout; Cre: cyclization recombination enzyme; dpp: days postpartum; E2: estradiol; E2F1: E2F transcription factor 1; EBF1: EBF transcription factor 1; EGR2: early growth response 2; FSH: follicle stimulating hormone; LH: luteinizing hormone; mpp: months postpartum; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; RAB37: RAB37, member RAS oncogene family; SQSTM1: sequestosome 1; TFEB: transcription factor EB; Zp3: zona pellucida glycoprotein 3.

The dual role of autophagy during porcine reproductive and respiratory syndrome virus infection: A review

Autophagy is a highly conserved catabolic process that transports cellular components to lysosomes for degradation and reuse. It impacts various cellular functions, including innate and adaptive immunity. It can exhibit a dual role in viral infections, either promoting or inhibiting viral replication depending on the virus and the stage of the infection cycle. Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant pathogen impacting the sustainable development of the global pork industry. Recent research has shown that PRRSV has evolved specific mechanisms to facilitate or impede autophagosome maturation, thereby evading innate and adaptive immune responses. These primary mechanisms involve viral proteins that target multiple regulators of autophagosome formation, including autophagy receptors, tethering proteins, autophagy-related (ATG) genes, as well as the functional proteins of autophagosomes and late endosomes/lysosomes. Additionally, these mechanisms are related to the post-translational modification of key components, viral antigens for presentation to T lymphocytes, interferon production, and the biogenesis and function of lysosomes. This review discusses the specific mechanisms by which PRRSV targets autophagy in host defence and virus survival, summarizes the role of viral proteins in subverting the autophagic process, and examines how the host utilizes the antiviral functions of autophagy to prevent PRRSV infection.

RAB32 promotes glioma cell progression by activating the JAK/STAT3 signaling pathway

OBJECTIVE

This study aimed to investigate the role of RAB32 in glioblastomas and its molecular mechanisms that regulate gliomas.

METHODS

The expression and prognostic value of RAB32 were evaluated using western blotting and the Gene Expression Profiling Interactive, Chinese Glioma Genome Atlas, and The Cancer Genome Atlas databases. Lentivirus containing sh-RAB32 or OE-RAB32 was used to manipulate RAB32 expression in glioma cells. The effects of RAB32 on cell proliferation, migration, and invasion were determined by western blotting, cell counting kit-8, plate cloning, wound healing, and transwell assays. Gene set enrichment analysis was used to screen for associations between the JAK/STAT3 signaling pathway and RAB32. The role of this pathway was verified using JAK/STAT3 inhibitors.

RESULTS

RAB32 expression was significantly upregulated in patients with glioma and in glioma cell lines. The expression level was positively correlated with the glioma grade and served as an independent prognostic factor. In vitro experiments revealed that RAB32 knockdown inhibited glioblastoma cell proliferation, migration, and invasion, while the opposite effects were observed with overexpression and could be inhibited by the JAK/STAT3 inhibitor BP-1-102.

CONCLUSION

RAB32 promotes malignant progression of glioblastoma cells through the JAK/STAT signaling pathway, providing new possibilities for therapeutic targets for glioblastoma.

Novel Interacting Partners of MGP-40, a Chitinase-Like Protein in Buffalo Mammary Epithelial Cells

Mammary Gland Protein-40 (MGP-40), also known as chitinase-3-like protein 1 (CHI3L1), is involved in critical biological processes such as inflammation, tissue remodeling, and cell proliferation, especially during the involution phase of the mammary gland. This study aimed to explore the molecular mechanisms of MGP-40 by identifying its novel interacting partners in buffalo mammary epithelial cells (BuMECs). Stable overexpression of MGP-40 in BuMECs was achieved through transfection with the pCIneo-MGP-40 vector, followed by G418 selection and confirmation by Western blot analysis. To identify interacting proteins, Co-immunoprecipitation (Co-IP) of BuMEC lysate using an anti-YKL-40 antibody was performed, and the eluted proteins were analyzed using SDS-PAGE and mass spectrometry (MALDI-TOF/TOF). The analysis revealed several interacting proteins, including synaptotagmin-like 3, Ras-related Rab19, RIB34A-like protein with coiled coils, and ATP synthase subunit g. These interacting partners suggest that MGP-40 is involved in crucial cellular processes like vesicle trafficking, cytoskeletal organization, and energy metabolism, extending its known functions in inflammation and tissue remodeling. Notably, the interactions with synaptotagmin-like 3 and Rab proteins emphasize MGP-40's potential role in vesicular transport, essential for milk production in mammary epithelial cells, while the association with ATP synthase subunit g links MGP-40 to energy regulation during lactation. These findings provide preliminary insights into the potential roles of MGP-40 in mammary gland physiology, particularly in cellular processes such as vesicle trafficking and energy metabolism. Further studies, including in vivo validation, are essential to confirm these interactions and clarify their relevance to mammary gland function and pathology.

Spatiotemporal recruitment of the ubiquitin-specific protease USP8 directs endosome maturation

The spatiotemporal transition of small GTPase Rab5 to Rab7 is crucial for early-to-late endosome maturation, yet the precise mechanism governing Rab5-to-Rab7 switching remains elusive. USP8, a ubiquitin-specific protease, plays a prominent role in the endosomal sorting of a wide range of transmembrane receptors and is a promising target in cancer therapy. Here, we identified that USP8 is recruited to Rab5-positive carriers by Rabex5, a guanine nucleotide exchange factor (GEF) for Rab5. The recruitment of USP8 dissociates Rabex5 from early endosomes (EEs) and meanwhile promotes the recruitment of the Rab7 GEF SAND-1/Mon1. In USP8-deficient cells, the level of active Rab5 is increased, while the Rab7 signal is decreased. As a result, enlarged EEs with abundant intraluminal vesicles accumulate and digestive lysosomes are rudimentary. Together, our results reveal an important and unexpected role of a deubiquitinating enzyme in endosome maturation.

A novel SBF1 missense mutation causes autosomal dominant Charcot-Marie-Tooth disease type 4B3

Introduction

We present a case of autosomal dominant Charcot-Marie-Tooth disease type 4B3 (CMT4B3) in a family caused by a novel SBF1 missense mutation.

Methods

Two patients, a mother and daughter, were recruited from our hospital. Both exhibited early-onset symptoms, including distal muscle atrophy of the limbs, without cranial nerve involvement. Electromyography was performed to assess nerve amplitudes and conduction velocities. Whole-exome sequencing (WES) and Sanger sequencing were performed to identify genetic mutations.

Results

Electromyography revealed a significant decline in nerve amplitudes, while the nerve conduction velocities (NCVs) remained normal in the extremities. Sequencing identified a novel missense mutation (c.1398C > A, p.H466Q) in exon 13 of the SET binding factor 1 (SBF1) gene in both patients, indicating an autosomal dominant inheritance pattern.

Discussion

Pathogenicity and protein predictions suggest that the myotubularin-related protein 5 (MTMR5), encoded by the mutated SBF1, may possess an altered structure, resulting in disease. These findings will help expand the phenotypic and genetic spectrum of CMT4B3.

Impact of Rab27 on Melanoma Cell Invasion and sEV Secretion

The migratory and invasive capabilities of melanoma cells contribute to metastasis. Therefore, targeting the genes driving these processes can support melanoma therapy. Rab27A and Rab27B contribute to tumor formation progression in many types of cancer through various mechanisms, including the secretion of small extracellular vesicles (sEVs). We explored the role of these GTPases in melanoma cell functioning in three RAB27A knockout (KO) cell lines (A375, DMBC12, and SkMel28) and a double RAB27A/B KO A375 cell line. The loss of RAB27A impaired the migration and invasion of DMBC12 and SkMel28 cells; however, the behavior of highly aggressive A375 cells was unaffected. The RAB27A/B double knockout moderately decreased the migratory capacity of A375 cells without disturbing their invasiveness. Additionally, the silencing of RAB27A did not affect the number and mean size of the sEVs, despite some alterations in the protein content of the vesicles. Both Rab27 isoforms can, at least partially, act independently. The potential role of Rab27A in the functioning of melanoma cells depends on the individual character of the cell line, but not on its basal expression, and seems to be unrelated to the secretion of sEVs.

Molecular Basis of the Recognition of the Active Rab8a by Optineurin

Optineurin (OPTN), a multifunctional adaptor protein in mammals, plays critical roles in many cellular processes, such as vesicular trafficking and autophagy. Notably, mutations in optineurin are directly associated with many human diseases, such as amyotrophic lateral sclerosis (ALS). OPTN can specifically recognize Rab8a and the GTPase-activating protein TBC1D17, and facilitate the inactivation of Rab8a mediated by TBC1D17, but with poorly understood mechanism. Here, using biochemical and structural approaches, we systematically characterize the interaction between OPTN and Rab8a, revealing that OPTN selectively recognizes the GTP-bound active Rab8a through its leucine-zipper domain (LZD). The determined crystal structure of OPTN LZD in complex with the active Rab8a not only elucidates the detailed binding mechanism of OPTN with Rab8a but also uncovers a unique binding mode of Rab8a with its effectors. Furthermore, we demonstrate that the central coiled-coil domain of OPTN and the active Rab8a can simultaneously interact with the TBC domain of TBC1D17 to form a ternary complex. Finally, based on the OPTN LZD/Rab8a complex structure and relevant biochemical analyses, we also evaluate several known ALS-associated mutations found in the LZD of OPTN. Collectively, our findings provide mechanistic insights into the interaction of OPTN with Rab8a, expanding our understanding of the binding modes of Rab8a with its effectors and the potential etiology of diseases caused by OPTN mutations.

Rab6a enables BICD2/dynein-mediated trafficking of human papillomavirus from the trans-Golgi network during virus entry

Rab GTPases control intracellular vesicular transport, including retrograde trafficking of human papillomavirus (HPV) during cell entry, guiding the virus from the endosome to the trans-Golgi network (TGN), the Golgi apparatus, and eventually the nucleus. Rab proteins have been identified that act prior to the arrival of HPV at the TGN, but Rab proteins operating in later stages of entry remain elusive. Here, we report that knockdown of Rab6a impairs HPV entry by preventing HPV exit from the TGN and impeding intra-Golgi transport of the incoming virus. Rab6a supports HPV trafficking by facilitating the association of HPV with dynein, a motor protein complex, and BICD2, a dynein adaptor, in the TGN. L2 can bind directly to GTP-Rab6a in vitro, and excess of either GTP-Rab6a or GDP-Rab6 inhibits HPV entry, suggesting that cycling between GDP-Rab6 and GTP-Rab6 is critical. Notably, Rab6a is crucial for HPV-BICD2 and HPV-dynein association in the TGN of infected cells but not in the endosome. Our findings reveal important features of the molecular basis of HPV infection, including the discovery that HPV uses different mechanisms to engage dynein at different times during entry, and identify potential targets for therapeutic approaches to inhibit HPV infection.

IMPORTANCE

Human papillomaviruses (HPVs) are small, non-enveloped DNA viruses that cause approximately 5% of human cancer. Like most other DNA viruses, HPV traffics to the nucleus during virus entry to successfully infect cells. We show here that HPV utilizes a cellular enzyme, Rab6a, during virus entry to engage the dynein molecular motor for transport along microtubules. Rab6a is required for complex formation between the HPV L2 capsid protein, dynein, and the dynein adaptor BICD2 in the trans-Golgi network (TGN). This complex is required for transport of the incoming virus out of the TGN as it journeys to the nucleus. Our findings identify potential targets for therapeutic approaches.

Role of Rab35 in modulating lipid metabolism and viral entry during pseudorabies virus infection

Pseudorabies virus (PRV), the causative agent of Aujeszky's disease in swine, is a significant pathogen in veterinary medicine. Rab35 is a key regulatory GTPase involved in diverse cellular functions, including endocytic recycling, cytokinesis, and the regulation of the actin cytoskeleton. Although Rab35's roles in these processes are well-documented, its contribution to PRV replication dynamics had not been previously elucidated. Our study demonstrated that PRV infection led to an increase in Rab35 expression at both the mRNA and protein levels in both in vitro cell culture and in vivo models. Elevated Rab35 expression was associated with an acceleration of PRV replication, whereas knocking down Rab35 expression significantly impeded viral proliferation. Further investigation revealed that while Rab35 depletion did not impact the initial attachment of PRV to host cells, it critically suppressed subsequent viral entry and effectively obstructed the transcription of early PRV genes. The downregulation of Rab35 disrupted the expression of enzymes critical to lipid synthesis, which are upregulated during PRV infection. Moreover, Rab35 knockdown disrupted lipid dynamics necessary for the virus to integrate into clathrin-coated pits, a pivotal mechanism for PRV cellular entry. These findings collectively suggest that Rab35 plays a facilitatory role in PRV infection by modulating lipid metabolism and the viral entry process, thereby offering new insights into the complex intracellular mechanisms underlying PRV replication.

Visualization of endogenous G proteins on endosomes and other organelles

Classical G-protein-coupled receptor (GPCR) signaling takes place in response to extracellular stimuli and involves receptors and heterotrimeric G proteins located at the plasma membrane. It has recently been established that GPCR signaling can also take place from intracellular membrane compartments, including endosomes that contain internalized receptors and ligands. While the mechanisms of GPCR endocytosis are well understood, it is not clear how well internalized receptors are supplied with G proteins. To address this gap, we use gene editing, confocal microscopy, and bioluminescence resonance energy transfer to study the distribution and trafficking of endogenous G proteins. We show here that constitutive endocytosis is sufficient to supply newly internalized endocytic vesicles with 20-30% of the G protein density found at the plasma membrane. We find that G proteins are present on early, late, and recycling endosomes, are abundant on lysosomes, but are virtually undetectable on the endoplasmic reticulum, mitochondria, and the medial-trans Golgi apparatus. Receptor activation does not change heterotrimer abundance on endosomes. Our findings provide a subcellular map of endogenous G protein distribution, suggest that G proteins may be partially excluded from nascent endocytic vesicles, and are likely to have implications for GPCR signaling from endosomes and other intracellular compartments.

Increased Rab1a accelerates osteoarthritis by inhibiting autophagy via activation of the mTORC1-S6K pathway

INTRODUCTION

Cartilage degradation is a critical alteration in the progression of osteoarthritis (OA) due to the disorder of chondrocyte metabolic homeostasis. Autophagy plays an important role in maintaining intracellular homeostasis. Recent investigations have increasingly underscored the importance of autophagy in modulating the pathological mechanisms underlying OA. Ras-related protein Rab-1a (Rab1a) has been illustrated to regulate autophagy in many diseases but not in OA.

OBJECTIVES

This study aims to elucidate whether Rab1a could regulate the development of OA through modulation of chondrocyte autophagy and apoptosis.

METHODS

Proteomic sequencing, Western blotting, and immunohistochemistry were applied to detect the expression level of Rab1a in vitro and in vivo. Gene Ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways were rigorously identified. The effects of Rab1a and the interaction between Rab1a, mTORC1, autophagy and apoptosis were explored by qPCR, Western blotting, and immunofluorescence. An experimental mouse OA model was also performed to confirm the role of Rab1a in OA pathogenesis in vivo. Histological analysis was employed to demonstrate cartilage damage.

RESULTS

Rab1a expression was significantly upregulated in inflamed chondrocytes and knee OA cartilage. Inhibition of Rab1a partially attenuated the degradation of the extracellular matrix and cell apoptosis both in vitro and in vivo, whereas overexpression of Rab1a intensified cartilage matrix degradation and cellular apoptosis. Additionally, elevated Rab1a levels were observed to suppress autophagy and activate the mTORC1-S6K signaling pathway, thereby aggravating OA pathogenesis.

CONCLUSION

The augmentation of Rab1a expression impairs autophagy and promotes apoptosis through the activation of the mTORC1-S6K signaling pathway, further exacerbating OA pathogenesis. This finding suggests that Rab1a serves as a promising and innovative therapeutic target for the prevention and treatment of OA.

Rab40 GTPases regulate AMBRA1-mediated transcription and cell migration

The Rab40 subfamily are unique small monomeric GTPases that form CRL5-based ubiquitin E3 ligase complex and regulate ubiquitylation of specific target proteins. Recent studies have shown that Rab40s play an important role in regulating cell migration, but the underlying mechanisms of Rab40/CRL5 complex function are still not fully understood. In this study we identified AMBRA1 as a novel binding partner of Rab40 GTPases and showed that this interaction mediates a bi-directional crosstalk between CRL4 and CRL5 E3 ligases. Importantly, we found that Rab40/CRL5 ubiquitylates AMBRA1, which does not result in AMBRA1 degradation, but instead it seems to induce AMBRA1-dependent regulation of gene transcription. The global transcriptional profiles identified by RNA-seq showed that AMBRA1 regulates transcription of genes related to cell adhesion and migration. Additionally, we have shown that AMBRA1-dependent transcription regulation does not require the enzymatic activity of AMBRA1/CRL4, and that Rab40-induced AMBRA1 ubiquitylation leads to dissociation of AMBRA1/CRL4 complex. Taken together, our findings reveal a novel function of Rab40/CRL5 complex as an important regulator for AMBRA1-dependent transcription of genes involved in cell migration.

Host restriction factor Rab11a limits porcine epidemic diarrhea virus invasion of cells via fusion peptide-mediated membrane fusion

Porcine epidemic diarrhea virus (PEDV) causes enormous economic losses to the pork industry, and its extensive cell tropism poses a substantial challenge to public health and safety. However, the invasion mechanisms and relevant host factors of PEDV remain poorly understood. In this study, we identified 422 differentially expressed genes related to PEDV infection through transcriptome analysis. Among these, Annexin A2 (ANXA2), Prohibitin-2 (PHB2), and Caveolin-2 (CAV2) were identified through screening and verifying as having a specific interaction with the PEDV S protein, and positive regulation of PEDV internalization was validated by siRNA and overexpression tests. Subsequently, using host membrane protein interaction networks and co-immunoprecipitation analysis, we found that ANXA2 PHB2 or CAV2 directly interact with Rab11a. Next, we constructed a pseudovirus model (LV-PEDV S-GFP) to further confirm that the downregulation of Rab11a could promote PEDV invasion. In detail, ANXA2, PHB2, or CAV2 promoted PEDV invasion via downregulating Rab11a. Furthermore, we showed that the S-protein fusion peptide (FP) was sufficient for S-protein interaction with ANXA2, PHB2, CAV2, and Rab11a, and the addition of exogenous GTP could regulate the efficiency of PEDV invasion. Collectively, ANXA2, PHB2, or CAV2 influenced the membrane fusion of PEDV with host cells through the host restriction factor Rab11a. This study could be targeted for future research to develop strategies for the control of PEDV.

Systematical characterization of Rab7 gene family in Gossypium and potential functions of GhRab7B3-A gene in drought tolerance

BACKGROUND

Cotton serves as a primary source of natural fibers crucial for the textile industry. However, environmental elements such as drought have posed challenges to cotton cultivation, resulting in adverse impacts on both production and fiber quality. Improving cotton's resilience to drought could mitigate yield losses and foster the expansion of cotton farming. Rab7 protein, widely present in organisms, controls the degradation and recycling of cargo, and has a potential role in biotic and abiotic tolerance. However, comprehensive exploration of the Rab7 gene family in Gossypium remains scarce.

RESULTS

Herein, we identified a total of 10, 10, 20, and 20 Rab7 genes through genome-wide analysis in Gossypium arboreum, Gossypium raimondii, Gossypium hirsutum, and Gossypium barbadense, respectively. Collinearity analysis unveiled the pivotal role of whole genome or segmental duplication events in the expansion of GhRab7s. Study of gene architecture, conserved protein motifs, and domains suggested the conservation of structure and function throughout evolution. Exploration of cis-regulatory elements revealed the responsiveness of GhRab7 genes to abiotic stress, corroborated by transcriptome analysis under diverse environmental stresses. Notably, the greatly induced expression of GhRab7B3-A under drought treatment prompted us to investigate its function through virus-induced gene silencing (VIGS) assays. Silencing GhRab7B3-A led to exacerbated dehydration and wilting compared with the control. Additionally, inhibition of stomatal closure, antioxidant enzyme activities and expression patterns of genes responsive to abiotic stress were observed in GhRab7B3-A silenced plants.

CONCLUSIONS

This study sheds light on Rab7 members in cotton, identifies a gene linked to drought stress, and paves the way for additional investigation of Rab7 genes associated with drought stress tolerance.

Extracellular Vesicles as Potential Biomarkers in Addictive Disorders

Small extracellular vesicles (sEVs) and their role in mental and addictive disorders are extremely promising research areas. Because of their small size, sEVs can pass through the blood-brain barrier. The membrane of sEVs contain proteins that protect them against destruction by the organism's immune system. Due to these properties, sEVs circulating in the blood can be used as potential biomarkers of processes occurring in the brain. Exposure to psychoactive substances in vitro and in vivo affects sEV biogenesis and significantly alters the amount of sEVs and chemical composition of their cargo. Based on the published reports, sEVs carry numerous potential biomarkers of addictive pathologies, although the diagnostic significance of these markers still has to be evaluated. A large body of evidence indicates that psychoactive substances influence Rab family GTPases, Toll-like receptors, complement system components, and cytokines. In some studies, the effect of psychoactive substances on sEVs was found to be sex-dependent. It has become commonly accepted that sEVs are involved in the regulation of neuroinflammation and interaction between glial cells and neurons, as well as between peripheral cells and cells of the central nervous system. Here, we formulated a hypothesis on the existence of two mechanisms/stages involved in the effect of psychoactive substances on sEVs: the "fast" mechanism that provides neuroplasticity, and the "slow" one, resulting from the impaired biogenesis of sEVs and formation of aberrant vesicles.

Targeting Ras-, Rho-, and Rab-family GTPases via a conserved cryptic pocket

The family of Ras-like GTPases consists of over 150 different members, regulated by an even larger number of guanine exchange factors (GEFs) and GTPase-activating proteins (GAPs) that comprise cellular switch networks that govern cell motility, growth, polarity, protein trafficking, and gene expression. Efforts to develop selective small molecule probes and drugs for these proteins have been hampered by the high affinity of guanosine triphosphate (GTP) and lack of allosteric regulatory sites. This paradigm was recently challenged by the discovery of a cryptic allosteric pocket in the switch II region of K-Ras. Here, we ask whether similar pockets are present in GTPases beyond K-Ras. We systematically surveyed members of the Ras, Rho, and Rab family of GTPases and found that many GTPases exhibit targetable switch II pockets. Notable differences in the composition and conservation of key residues offer potential for the development of optimized inhibitors for many members of this previously undruggable family.

Rab11 suppresses neuronal stress signaling by localizing dual leucine zipper kinase to axon terminals for protein turnover

Dual leucine zipper kinase (DLK) mediates multiple neuronal stress responses, and its expression levels are constantly suppressed to prevent excessive stress signaling. We found that Wallenda (Wnd), the Drosophila ortholog of DLK, is highly enriched in the axon terminals of Drosophila sensory neurons in vivo and that this subcellular localization is necessary for Highwire-mediated Wnd protein turnover under normal conditions. Our structure-function analysis found that Wnd palmitoylation is essential for its axon terminal localization. Palmitoylation-defective Wnd accumulated in neuronal cell bodies, exhibited dramatically increased protein expression levels, and triggered excessive neuronal stress responses. Defective intracellular transport is implicated in neurodegenerative conditions. Comprehensive dominant-negative Rab protein screening identified Rab11 as an essential factor for Wnd localization in axon terminals. Consequently, Rab11 loss-of-function increased the protein levels of Wnd and induced neuronal stress responses. Inhibiting Wnd activity significantly ameliorated neuronal loss and c-Jun N-terminal kinase signaling triggered by Rab11 loss-of-function. Taken together, these suggest that DLK proteins are constantly transported to axon terminals for protein turnover and a failure of such transport can lead to neuronal loss. Our study demonstrates how subcellular protein localization is coupled to protein turnover for neuronal stress signaling.

RAB4A is a master regulator of cancer cell stemness upstream of NUMB-NOTCH signaling

Cancer stem cells (CSCs) are a group of specially programmed tumor cells that possess the characteristics of perpetual cell renewal, increased invasiveness, and often, drug resistance. Hence, eliminating CSCs is a major challenge for cancer treatment. Understanding the cellular programs that maintain CSCs, and identifying the critical regulators for such programs, are major undertakings in both basic and translational cancer research. Recently, we have reported that RAB4A is a major regulator of epithelial-to-mesenchymal transition (EMT) and it does so mainly through regulating the activation of RAC1 GTPase. In the current study, we have delineated a new signaling circuitry through which RAB4A transmits its control of cancer stemness. Using in vitro and in vivo studies, we show that RAB4A, as the upstream regulator, relays signal stepwise to NUMB, NOTCH1, RAC1, and then SOX2 to control the self-renewal property of multiple cancer cells of diverse tissue origins. Knockdown of NUMB, or overexpression of NICD (the active fragment NOTCH1) or SOX2, rescued the in vitro sphere-forming and in vivo tumor-forming abilities that were lost upon RAB4A knockdown. Furthermore, we discovered that the chain of control is mostly through transcriptional regulation at every step of the pathway. The discovery of the novel signaling axis of RAB4A-NUMB-NOTCH-SOX2 opens the path for further expansion of the signaling chain and for the identification of new regulators and interacting proteins important for CSC functions, which can be explored to develop new and effective therapies.

Distinct trafficking routes of polarized and non-polarized membrane cargoes in Aspergillus nidulans

Membrane proteins are sorted to the plasma membrane via Golgi-dependent trafficking. However, our recent studies challenged the essentiality of Golgi in the biogenesis of specific transporters. Here, we investigate the trafficking mechanisms of membrane proteins by following the localization of the polarized R-SNARE SynA versus the non-polarized transporter UapA, synchronously co-expressed in wild-type or isogenic genetic backgrounds repressible for conventional cargo secretion. In wild-type, the two cargoes dynamically label distinct secretory compartments, highlighted by the finding that, unlike SynA, UapA does not colocalize with the late-Golgi. In line with early partitioning into distinct secretory carriers, the two cargoes collapse in distinct ER-Exit Sites (ERES) in a sec31ts background. Trafficking via distinct cargo-specific carriers is further supported by showing that repression of proteins essential for conventional cargo secretion does not affect UapA trafficking, while blocking SynA secretion. Overall, this work establishes the existence of distinct, cargo-dependent, trafficking mechanisms, initiating at ERES and being differentially dependent on Golgi and SNARE interactions.

RABIF promotes hepatocellular carcinoma progression through regulation of mitophagy and glycolysis

The RAB interacting factor (RABIF) is a putative guanine nucleotide exchange factor that also functions as a RAB-stabilizing holdase chaperone. It has been implicated in pathogenesis of several cancers. However, the functional role and molecular mechanism of RABIF in hepatocellular carcinoma (HCC) are not entirely known. Here, we demonstrate an upregulation of RABIF in patients with HCC, correlating with a poor prognosis. RABIF inhibition results in decreased HCC cell growth both in vitro and in vivo. Our study reveals that depleting RABIF attenuates the STOML2-PARL-PGAM5 axis-mediated mitophagy. Consequently, this reduction in mitophagy results in diminished mitochondrial reactive oxygen species (mitoROS) production, thereby alleviating the HIF1α-mediated downregulation of glycolytic genes HK1, HKDC1, and LDHB. Additionally, we illustrate that RABIF regulates glucose uptake by controlling RAB10 expression. Importantly, the knockout of RABIF or blockade of mitophagy sensitizes HCC cells to sorafenib. This study uncovers a previously unrecognized role of RABIF crucial for HCC growth and identifies it as a potential therapeutic target.

RABR-1, an atypical Rab-related GTPase, cell-nonautonomously restricts somatosensory dendrite branching

Neurons are highly polarized cells with dendrites and axons. Dendrites, which receive sensory information or input from other neurons, often display elaborately branched morphologies. While mechanisms that promote dendrite branching have been widely studied, less is known about the mechanisms that restrict branching. Using the nematode Caenorhabditis elegans, we identify rabr-1 (for Rab-related gene 1) as a factor that restricts branching of the elaborately branched dendritic trees of PVD and FLP somatosensory neurons. Animals mutant for rabr-1 show excessively branched dendrites throughout development and into adulthood in areas where the dendrites overlay epidermal tissues. Phylogenetic analyses show that RABR-1 displays similarity to small GTPases of the Rab-type, although based on sequence alone, no clear vertebrate ortholog of RABR-1 can be identified. We find that rabr-1 is expressed and can function in epidermal tissues, suggesting that rabr-1 restricts dendritic branching cell-nonautonomously. Genetic experiments further indicate that for the formation of ectopic branches rabr-1 mutants require the genes of the Menorin pathway, which have been previously shown to mediate dendrite morphogenesis of somatosensory neurons. A translational reporter for RABR-1 reveals a subcellular localization to punctate, perinuclear structures, which correlates with endosomal and autophagosomal markers, but anticorrelates with lysosomal markers suggesting an amphisomal character. Point mutations in rabr-1 analogous to key residues of small GTPases suggest that rabr-1 functions in a GTP-bound form independently of GTPase activity. Taken together, rabr-1 encodes for an atypical small GTPase of the Rab-type that cell-nonautonomously restricts dendritic branching of somatosensory neurons, likely independently of GTPase activity.