Cellular functions of Rab GTPases at a glance

RabE1a- and SEC10b-mediated exocytosis and AP2β-mediated endocytosis are involved in the intracellular transport of tobamoviruses

To establish systemic infection, plant viruses must replicate, and conduct intra- and intercellular movement and long-distance movement, all of which require the participation of host factors. Tobamoviruses move in the form of movement protein (MP)-viral RNA complex and utilize endocytosis for intracellular movement. However, how tobamoviral MPs hijack host factors to reach the plasma membrane (PM) and then plasmodesmata (PD) is still largely unknown. Tomato brown rugose fruit virus (ToBRFV) is an emerging tobamovirus that mainly infects tomatoes and peppers. Here, we show that tomato RabE1a, a small Rab GTPase, interacts with ToBRFV MP and participates in the movement of ToBRFV. Knocking out RabE1a in tomatoes could inhibit infection by ToBRFV. RabE1a positively regulates MP transport to the PM, and this transport process is regulated by its nucleotide-binding state. Furthermore, RabE1a interacts with the exocyst subunit SEC10b to jointly regulate MP transport to the PM and intracellular movement of ToBRFV. The adaptor protein AP2β interacts with MP and transports MP from the PM to the PD for intercellular movement of ToBRFV. We further find that knocking out RabE1a could also inhibit the infection of other tobamoviruses. In summary, MP exocytosis is coregulated by RabE1a and the exocyst subunit SEC10b for transport to the PM, where it then uses AP2β-regulated endocytosis to PD. These results provide a comprehensive overview of tobamoviral MP intracellular transport and are insightful for breeding tomato plants resistant to ToBRFV and related tobamoviruses.

Role of the RAB27/SYTL Axis in Tumor Microenvironment Construction

Crosstalk between cancer cells and the tumor microenvironment (TME) is a key event in malignant progression and metastasis. The secretion of bioactive substances by cancer cells remodels the TME, affecting the activities of its components, including blood vessels, mesenchymal cells, and immune cells. These substances are effectively delivered through intracellular trafficking and exocytosis of cytoplasmic vesicles. The small guanosine triphosphatase (GTPase) RAB27 and its effectors, synaptotagmin-like (SYTL) family proteins, play essential roles in vesicle trafficking. Our recent research demonstrates the upregulation of RAB27A/B and SYTL1/2 in alveolar soft part sarcoma and acute myeloid leukemia. This enhanced trafficking promotes angiogenesis and the occupation of leukemia cells in the bone marrow niche. This review focuses on the role of the RAB27/SYTL axis in various cancer types associated with TME modifications, with a discussion on its importance as a therapeutic target.

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.

Proximal partners of the organellar N-terminal acetyltransferase NAA60: insights into Golgi structure and transmembrane protein topology

Biotin identification (BioID) is an interactomics approach that utilizes proximity labelling to map the local interactome or proxeome of proteins within a cell. This study applies BioID to investigate proteins proximal to NAA60 (N-alpha-acetyltransferase 60), an N-terminal acetyltransferase (NAT) of pathological significance in human disease, characterized by its unique Golgi localization. NAA60 is known to N-terminally acetylate transmembrane proteins that present their N-terminus on the cytosolic face of the membrane, and its involvement in maintaining Golgi structure has previously been established. Using a stable cell-line expressing an NAA60-BirA* fusion protein, we isolated biotinylated proteins through streptavidin affinity purification. Mass spectrometry analysis revealed over 100 proximal partners of NAA60, enriched in proteins localized on the trans-side of the Golgi apparatus. High-confidence proximity interactors included golgins and GRASP proteins, essential for Golgi integrity. Considering the transmembrane nature of NAA60, the identification of biotinylated peptides inferred the topology of transmembrane protein interactors within the secretory pathway. Subsequent suborganellar localization analysis revealed a more prominent medial/trans-Golgi localization of NAA60. Our findings underscore the role of NAA60 and its interactors in maintaining Golgi structural integrity and highlight the effectiveness of BioID in generating critical protein topology data, invaluable for enhancing the prediction of protein topology within cellular compartments.

tsCRISPR based identification of Rab proteins required for the recycling of Drosophila TRPL ion channel

In polarized cells, the precise regulation of protein transport to and from the plasma membrane is crucial to maintain cellular function. Dysregulation of intracellular protein transport in neurons can lead to neurodegenerative diseases such as Retinitis Pigmentosa, Alzheimer's and Parkinson's disease. Here we used the light-dependent transport of the TRPL (transient receptor potential-like) ion channel in Drosophila photoreceptor cells to study the role of Rab proteins in TRPL recycling. TRPL is located in the rhabdomeric membrane of dark-adapted flies, but it is transported out of the rhabdomere upon light exposure and localizes at the Endoplasmatic Reticulum within 12 h. Upon subsequent dark adaptation, TRPL is recycled back to the rhabdomeric membrane within 90 min. To screen for Rab proteins involved in TRPL recycling, we established a tissue specific (ts) CRISPR/Cas9-mediated knock-out of individual Rab genes in Drosophila photoreceptors and assessed TRPL localization using an eGFP tagged TRPL protein in the intact eyes of these mutants. We observed severe TRPL recycling defects in the knockouts of Rab3, Rab4, Rab7, Rab32, and RabX2. Using immunohistochemistry, we further showed that Rab3 and RabX2 each play a significant role in TRPL recycling and also influence TRPL transport. We localized Rab3 to the late endosome in Drosophila photoreceptors and observed disruption of TRPL transport to the ER in Rab3 knock-out mutants. TRPL transport from the ER to the rhabdomere ensues from the trans-Golgi where RabX2 is located. We observed accumulated TRPL at the trans-Golgi in RabX2 knock-out mutants. In summary, our study reveals the requirement of specific Rab proteins for different steps of TRPL transport in photoreceptor cells and provides evidence for a unique retrograde recycling pathway of TRPL from the ER via the trans-Golgi.

RalB uncoupled exocyst mediates endothelial Weibel-Palade body exocytosis

Ras-like (Ral) GTPases play essential regulatory roles in many cellular processes, including exocytosis. Cycling between GDP- and GTP-bound states, Ral GTPases function as molecular switches and regulate effectors, specifically the multi-subunit tethering complex exocyst. Here, we show that Ral isoform RalB controls regulated exocytosis of Weibel-Palade bodies (WPBs), the specialized endothelial secretory granules that store hemostatic protein von Willebrand factor. Remarkably, unlike typical small GTPase-effector interactions, RalB binds exocyst in its GDP-bound state in resting endothelium. Upon endothelial cell stimulation, exocyst is uncoupled from RalB-GTP resulting in WPB tethering and exocytosis. Furthermore, we report that PKC-dependent phosphorylation of the C-terminal hypervariable region (HVR) of RalB modulates its dynamic interaction with exocyst in endothelium. Exocyst preferentially interacts with phosphorylated RalB in resting endothelium. Dephosphorylation of RalB either by endothelial cell stimulation, or PKC inhibition, or expression of nonphosphorylatable mutant at a specific serine residue of RalB HVR, disengages exocyst and augments WPB exocytosis, resembling RalB exocyst-binding site mutant. In summary, it is the uncoupling of exocyst from RalB that mediates endothelial Weibel-Palade body exocytosis. Our data shows that Ral function may be more dynamically regulated by phosphorylation and may confer distinct functionality given high degree of homology and the shared set of effector protein between the two Ral isoforms.

Mechanisms of lysosomal tubulation and sorting driven by LRRK2

Lysosomes are dynamic cellular structures that adaptively remodel their membrane in response to stimuli, including membrane damage. Lysosomal dysfunction plays a central role in the pathobiology of Parkinson's disease (PD). Gain-of-function mutations in Leucine-rich repeat kinase 2 (LRRK2) cause familial PD and genetic variations in its locus increase the risk of developing the sporadic form of the disease. We previously uncovered a process we term LYTL (LYsosomal Tubulation/sorting driven by LRRK2), wherein membrane-damaged lysosomes generate tubules sorted into mobile vesicles. Subsequently, these vesicles interact with healthy lysosomes. LYTL is orchestrated by LRRK2 kinase activity, via the recruitment and phosphorylation of a subset of RAB GTPases. Here, we summarize the current understanding of LYTL and its regulation, as well as the unknown aspects of this process.

Dual Guardians of Immunity: FoRab10 and FoRab29 in Frankliniella occidentalis Confer Resistance to Tomato Spotted Wilt Orthotospovirus

Rab GTPase is critical for autophagy processes and is implicated in insect immunity against viruses. In this study, we aimed to investigate the role of FoRabs in the autophagic regulation of antiviral defense against tomato spotted wilt orthotospovirus (TSWV) in Frankliniella occidentalis. Transcriptome analysis revealed the downregulation of FoRabs in viruliferous nymph and adults of F. occidentalis in response to TSWV infection. Manipulation of autophagy levels with 3-MA and Rapa treatments resulted in a 5- to 15-fold increase and a 38-64% decrease in viral titers, respectively. Additionally, interference with FoRab10 in nymphs and FoRab29 in adults led to a 20-90% downregulation of autophagy-related genes, a decrease in ATG8-II (an autophagy marker protein), and an increase in the TSWV titers by 1.5- to 2.5-fold and 1.3- to 2.0-fold, respectively. In addition, the leaf disk and the living plant methods revealed increased transmission rates of 20.8-41.6 and 68.3-88.3%, respectively. In conclusion, FoRab10 and FoRab29 play a role in the autophagic regulation of the antiviral defense in F. occidentalis nymphs and adults against TSWV, respectively. These findings offer insights into the intricate immune mechanisms functional in F. occidentalis against TSWV, suggesting potential targeted strategies for F. occidentalis and TSWV management.

Rab5 Overcomes CAR T Cell Dysfunction Induced by Tumor-Mediated CAR Capture

Continuous interaction between chimeric antigen receptor (CAR) T cell (CART) and tumors often result in CART dysfunction and tumor escape. We observed that tumors can take up CAR molecules, leaving CARTs without surface-expressed CARs and thus unable to kill tumors after prolonged exposure. Overexpression of Rab5 resulted in augmented clathrin-independent endocytosis, preventing loss of surface-expressed CARs, and enhanced CART activity. Interestingly, we observed membrane protrusions on the CART cell surface which disappeared after multiple tumor challenges. Rab5 maintained these protrusions after repeated tumor engagements and their presence correlated with effective tumor clearance, suggesting a link between endocytosis, membrane protrusions, and cytolytic activity. In vivo , Rab5-expressing CARTs demonstrated improved activity and were able to clear an otherwise refractory mesothelin-expressing solid cancer in humanized mice by maintaining CAR surface expression within the tumor. Thus, pairing Rab5 with CAR expression could improve the clinical efficacy of CART therapy. Highlights "CAR-jacking" occurs when surface CAR is internalized by target tumor cells.Rab5 overexpression prevents "CAR-jacking" and enhances CART function.Rab5 promotes CAR endocytic recycling and maintains membrane protrusions.Rab5-expressing CARTs exhibit enhanced therapeutic efficacy against solid tumors.

Cucumber (Cucumis sativus L.) translationally controlled tumor protein interacts with CsRab11A and promotes activation of target of rapamycin in response to Podosphaera xanthii

The target of rapamycin (TOR) kinase serves as a central regulator that integrates nutrient and energy signals to orchestrate cellular and organismal physiology in both animals and plants. Despite significant advancements having been made in understanding the molecular and cellular functions of plant TOR kinases, the upstream regulators that modulate TOR activity are not yet fully elucidated. In animals, the translationally controlled tumor protein (TCTP) is recognized as a key player in TOR signaling. This study reveals that two TCTP isoforms from Cucumis sativus, when introduced into Arabidopsis, are instrumental in balancing growth and defense mechanisms against the fungal pathogen Golovinomyces cichoracearum. We hypothesize that plant TCTPs act as upstream regulators of TOR in response to powdery mildew caused by Podosphaera xanthii in Cucumis. Our research further uncovers a stable interaction between CsTCTP and a small GTPase, CsRab11A. Transient transformation assays indicate that CsRab11A is involved in the defense against P. xanthii and promotes the activation of TOR signaling through CsTCTP. Moreover, our findings demonstrate that the critical role of TOR in plant disease resistance is contingent upon its regulated activity; pretreatment with a TOR inhibitor (AZD-8055) enhances cucumber plant resistance to P. xanthii, while pretreatment with a TOR activator (MHY-1485) increases susceptibility. These results suggest a sophisticated adaptive response mechanism in which upstream regulators, CsTCTP and CsRab11A, coordinate to modulate TOR function in response to P. xanthii, highlighting a novel aspect of plant-pathogen interactions.

Rab GTPases, Active Members in Antigen-Presenting Cells, and T Lymphocytes

Processes such as cell migration, phagocytosis, endocytosis, and exocytosis refer to the intense exchange of information between the internal and external environment in the cells, known as vesicular trafficking. In eukaryotic cells, these essential cellular crosstalks are controlled by Rab GTPases proteins through diverse adaptor proteins like SNAREs complex, coat proteins, phospholipids, kinases, phosphatases, molecular motors, actin, or tubulin cytoskeleton, among others, all necessary for appropriate mobilization of vesicles and distribution of molecules. Considering these molecular events, Rab GTPases are critical components in specific biological processes of immune cells, and many reports refer primarily to macrophages; therefore, in this review, we address specific functions in immune cells, concretely in the mechanism by which the GTPase contributes in dendritic cells (DCs) and, T/B lymphocytes.

Roles of G proteins and their GTPase-activating proteins in platelets

Platelets are small anucleate blood cells supporting vascular function. They circulate in a quiescent state monitoring the vasculature for injuries. Platelets adhere to injury sites and can be rapidly activated to secrete granules and to form platelet/platelet aggregates. These responses are controlled by signalling networks that include G proteins and their regulatory guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Recent proteomics studies have revealed the complete spectrum of G proteins, GEFs, and GAPs present in platelets. Some of these proteins are specific for platelets and very few have been characterised in detail. GEFs and GAPs play a major role in setting local levels of active GTP-bound G proteins in response to activating and inhibitory signals encountered by platelets. Thus, GEFs and GAPs are highly regulated themselves and appear to integrate G protein regulation with other cellular processes. This review focuses on GAPs of small G proteins of the Arf, Rab, Ras, and Rho families, as well as of heterotrimeric G proteins found in platelets.

Function and regulation of Rab GTPases in cancers

The Rab small GTPases are characterized by the distinct intracellular localization and modulate various endocytic, transcytic and exocytic transport pathways. Rab proteins function as scaffolds that connect signaling pathways and intracellular membrane trafficking processes through the recruitment of effectors, such as tethering factors, phosphatases, motors and kinases. In different cancers, Rabs play as either an onco-protein or a tumor suppressor role, highly dependending on the context. The molecular mechanistic research has revealed that Rab proteins are involved in cancer progression through influences on migration, invasion, metabolism, exosome secretion, autophagy, and drug resistance of cancer cells. Therefore, targeting Rab GTPases to recover the dysregulated vesicle transport systems may provide potential strategy to restrain cancer progression. In this review, we discuss the regulation of Rab protein level and activity in modulating pathways involved in tumor progression, and propose that Rab proteins may serve as a prognostic factor in different cancers.

The Role of Rab GTPases in the development of genetic and malignant diseases

Small GTPases have been shown to play an important role in several cellular functions, including cytoskeletal remodeling, cell polarity, intracellular trafficking, cell-cycle, progression and lipid transformation. The Ras-associated binding (Rab) family of GTPases constitutes the largest family of GTPases and consists of almost 70 known members of small GTPases in humans, which are known to play an important role in the regulation of intracellular membrane trafficking, membrane identity, vesicle budding, uncoating, motility and fusion of membranes. Mutations in Rab genes can cause a wide range of inherited genetic diseases, ranging from neurodegenerative diseases, such as Parkinson's disease (PD) and Alzheimer's disease (AD) to immune dysregulation/deficiency syndromes, like Griscelli Syndrome Type II (GS-II) and hemophagocytic lymphohistiocytosis (HLH), as well as a variety of cancers. Here, we provide an extended overview of human Rabs, discussing their function and diseases related to Rabs and Rab effectors, as well as focusing on effects of (aberrant) Rab expression. We aim to underline their importance in health and the development of genetic and malignant diseases by assessing their role in cellular structure, regulation, function and biology and discuss the possible use of stem cell gene therapy, as well as targeting of Rabs in order to treat malignancies, but also to monitor recurrence of cancer and metastasis through the use of Rabs as biomarkers. Future research should shed further light on the roles of Rabs in the development of multifactorial diseases, such as diabetes and assess Rabs as a possible treatment target.

Pathomechanistic Networks of Motor System Injury in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is the most common, adult-onset, progressive motor neurodegenerative disorder that results in death within 3 years of the clinical diagnosis. Due to the clinicopathological heterogeneity, any reliable biomarkers for diagnosis or prognosis of ALS have not been identified till date. Moreover, the only three clinically approved treatments are not uniformly effective in slowing the disease progression. Over the last 15 years, there has been a rapid advancement in research on the complex pathomechanistic landscape of ALS that has opened up new avenues for successful clinical translation of targeted therapeutics. Multiple studies suggest that the age-dependent interaction of risk-associated genes with environmental factors and endogenous modifiers is critical to the multi-step process of ALS pathogenesis. In this review, we provide an updated discussion on the dysregulated cross-talk between intracellular homeostasis processes, the unique molecular networks across selectively vulnerable cell types, and the multisystemic nature of ALS pathomechanisms. Importantly, this work highlights the alteration in epigenetic and epitranscriptomic landscape due to gene-environment interactions, which have been largely overlooked in the context of ALS pathology. Finally, we suggest that precision medicine research in ALS will be largely benefitted from the stratification of patient groups based on the clinical phenotype, onset and progression, genome, exposome, and metabolic identities.

KIF16B drives MT1-MMP recycling in macrophages and promotes co-invasion of cancer cells

The matrix metalloproteinase MT1-MMP is a central effector of cellular proteolysis. Accordingly, regulation of the surface-localized pool of MT1-MMP is crucial for cell migration and invasion. Here, we identify the superprocessive kinesin KIF16B as a major driver of fast recycling of MT1-MMP to the surface of primary human macrophages. KIF16B associates with MT1-MMP on Rab14-positive vesicles, and its depletion results in strongly reduced MT1-MMP surface levels, as shown by microscopical, biochemical, and cell-sorting approaches. As a consequence, KIF16B-depleted macrophages exhibit strongly reduced matrix degradation and invasion. We further identify the cargo-binding C-terminus of KIF16B as a critical element of MT1-MMP transport, as its overexpression uncouples MT1-MMP vesicles from the endogenous motor, thus leading to a reduction of surface-associated MT1-MMP and to reduced matrix degradation and invasion. Importantly, depletion of KIF16B in primary macrophages also reduces the co-invasion of cancer cells from tumor spheroids, pointing to the KIF16B-driven recycling pathway in macrophages as an important regulatory element of the tumor microenvironment.

Ubiquitination in the regulation of autophagy

Autophagy, an efficient and effective approach to clear rapidly damaged organelles, macromolecules, and other harmful cellular components, enables the recycling of nutrient materials and supply of nutrients to maintain cellular homeostasis. Ubiquitination plays an important regulatory role in autophagy. This paper summarizes the most recent progress in ubiquitin modification in various stages of autophagy, including initiation, elongation, and termination. Moreover, this paper shows that ubiquitination is an important way through which selective autophagy achieves substrate specificity. Furthermore, we note the distinction between monoubiquitination and polyubiquitination in the regulation of autophagy. Compared with monoubiquitination, polyubiquitination is a more common strategy to regulate the activity of the autophagy molecular machinery. In addition, the role of ubiquitination in the closure and fusion of autophagosomes warrants further study. This article not only clarifies the regulatory mechanism of autophagy but also contributes to a deeper understanding of the importance of ubiquitination modification.

Decoding the crosstalk between mevalonate metabolism and T cell function

The mevalonate pathway is an essential metabolic pathway in T cells regulating development, proliferation, survival, differentiation, and effector functions. The mevalonate pathway is a complex, branched pathway composed of many enzymes that ultimately generate cholesterol and nonsterol isoprenoids. T cells must tightly control metabolic flux through the branches of the mevalonate pathway to ensure sufficient isoprenoids and cholesterol are available to meet cellular demands. Unbalanced metabolite flux through the sterol or the nonsterol isoprenoid branch is metabolically inefficient and can have deleterious consequences for T cell fate and function. Accordingly, there is tight regulatory control over metabolic flux through the branches of this essential lipid synthetic pathway. In this review we provide an overview of how the branches of the mevalonate pathway are regulated in T cells and discuss our current understanding of the relationship between mevalonate metabolism, cholesterol homeostasis and T cell function.

Vibrio MARTX toxin processing and degradation of cellular Rab GTPases by the cytotoxic effector Makes Caterpillars Floppy

Vibrio vulnificus causes life threatening infections dependent upon the effectors released from the Multifunctional-Autoprocessing Repeats-In-Toxin (MARTX) toxin. The Makes Caterpillars Floppy-like (MCF) cysteine protease effector is activated by host ADP ribosylation factors (ARFs), although the targets of processing activity were unknown. In this study we show MCF binds Ras-related proteins in brain (Rab) GTPases at the same interface occupied by ARFs and then cleaves and/or degrades 24 distinct members of the Rab GTPases family. The cleavage occurs in the C-terminal tails of Rabs. We determine the crystal structure of MCF as a swapped dimer revealing the open, activated state of MCF and then use structure prediction algorithms to show that structural composition, rather than sequence or localization, determine Rabs selected as MCF proteolytic targets. Once cleaved, Rabs become dispersed in cells to drive organelle damage and cell death to promote pathogenesis of these rapidly fatal infections.

Conserved but not critical: Trafficking and function of NaV1.7 are independent of highly conserved polybasic motifs

Non-addictive treatment of chronic pain represents a major unmet clinical need. Peripheral voltage-gated sodium (NaV) channels are an attractive target for pain therapy because they initiate and propagate action potentials in primary afferents that detect and transduce noxious stimuli. NaV1.7 sets the gain on peripheral pain-signaling neurons and is the best validated peripheral ion channel involved in human pain, and previous work has shown that it is transported in vesicles in sensory axons which also carry Rab6a, a small GTPase known to be involved in vesicular packaging and axonal transport. Understanding the mechanism of the association between Rab6a and NaV1.7 could inform therapeutic modalities to decrease trafficking of NaV1.7 to the distal axonal membrane. Polybasic motifs (PBM) have been shown to regulate Rab-protein interactions in a variety of contexts. In this study, we explored whether two PBMs in the cytoplasmic loop that joins domains I and II of human NaV1.7 were responsible for association with Rab6a and regulate axonal trafficking of the channel. Using site-directed mutagenesis we generated NaV1.7 constructs with alanine substitutions in the two PBMs. Voltage-clamp recordings showed that the constructs retain wild-type like gating properties. Optical Pulse-chase Axonal Long-distance (OPAL) imaging in live sensory axons shows that mutations of these PBMs do not affect co-trafficking of Rab6a and NaV1.7, or the accumulation of the channel at the distal axonal surface. Thus, these polybasic motifs are not required for interaction of NaV1.7 with the Rab6a GTPase, or for trafficking of the channel to the plasma membrane.

Vps9d1 regulates tubular endosome formation through specific activation of Rab22A

The small GTPase Rab22A is an important regulator of the formation of tubular endosomes, which are one of the types of recycling endosome compartments of the clathrin-independent endocytosis pathway. In order to regulate tubular endosome formation, Rab22A must be activated by a specific guanine-nucleotide-exchange factor (GEF); however, all of the GEFs that have been reported to exhibit Rab22A-GEF activity in vitro also activate Rab5A, an essential regulator of the clathrin-mediated endocytosis pathway, and no Rab22A-specific GEF has ever been identified. Here, we identified Vps9d1, a previously uncharacterized vacuolar protein sorting 9 (VPS9) domain-containing protein, as a novel Rab22A-GEF. The formation of tubular endosome structures was found to be severely impaired in Vps9d1-depleted HeLa cells, but Rab5A localization was unaffected. Expression of a constitutively active Rab22A mutant in Vps9d1-depleted HeLa cells restored tubular endosomes, but expression of a GEF-activity-deficient Vps9d1 mutant did not. Moreover, Vps9d1 depletion altered the distribution of clathrin-independent endocytosed cargos and impaired their recycling. Our findings indicate that Vps9d1 promotes tubular endosome formation by specifically activating Rab22A.

Rab10 regulates the sorting of internalised TrkB for retrograde axonal transport

Neurons process real-time information from axon terminals to coordinate gene expression, growth, and plasticity. Inputs from distal axons are encoded as a stream of endocytic organelles, termed signalling endosomes, targeted to the soma. Formation of these organelles depends on target-derived molecules, such as brain-derived neurotrophic factor (BDNF), which is recognised by TrkB receptors on the plasma membrane, endocytosed, and transported to the cell body along the microtubules network. Notwithstanding its physiological and neuropathological importance, the mechanism controlling the sorting of TrkB to signalling endosomes is currently unknown. In this work, we use primary mouse neurons to uncover the small GTPase Rab10 as critical for TrkB sorting and propagation of BDNF signalling from axon terminals to the soma. Our data demonstrate that Rab10 defines a novel membrane compartment that is rapidly mobilised towards the axon terminal upon BDNF stimulation, enabling the axon to fine-tune retrograde signalling depending on BDNF availability at the synapse. These results help clarifying the neuroprotective phenotype recently associated to Rab10 polymorphisms in Alzheimer's disease and provide a new therapeutic target to halt neurodegeneration.

The calcium-sensing receptor in inflammation: Recent updates

The Calcium-Sensing Receptor (CaSR) is a member of the class C of G-proteins coupled receptors (GPCRs), it plays a pivotal role in calcium homeostasis by directly controlling calcium excretion in the kidneys and indirectly by regulating parathyroid hormone (PTH) release from the parathyroid glands. The CaSR is found to be ubiquitously expressed in the body, playing a plethora of additional functions spanning from fluid secretion, insulin release, neuronal development, vessel tone to cell proliferation and apoptosis, to name but a few. The present review aims to elucidate and clarify the emerging regulatory effects that the CaSR plays in inflammation in several tissues, where it mostly promotes pro-inflammatory responses, with the exception of the large intestine, where contradictory roles have been recently reported. The CaSR has been found to be expressed even in immune cells, where it stimulates immune response and chemokinesis. On the other hand, CaSR expression seems to be boosted under inflammatory stimulus, in particular, by pro-inflammatory cytokines. Because of this, the CaSR has been addressed as a key factor responsible for hypocalcemia and low levels of PTH that are commonly found in critically ill patients under sepsis or after burn injury. Moreover, the CaSR has been found to be implicated in autoimmune-hypoparathyroidism, recently found also in patients treated with immune-checkpoint inhibitors. Given the tight bound between the CaSR, calcium and vitamin D metabolism, we also speculate about their roles in the pathogenesis of severe acute respiratory syndrome coronavirus-19 (SARS-COVID-19) infection and their impact on patients' prognosis. We will further explore the therapeutic potential of pharmacological targeting of the CaSR for the treatment and management of aberrant inflammatory responses.

V-ATPase a3 Subunit in Secretory Lysosome Trafficking in Osteoclasts

Vacuolar-type ATPase (V-ATPase) shares its structure and rotational catalysis with F-type ATPase (F-ATPase, ATP synthase). However, unlike subunits of F-ATPase, those of V-ATPase have tissue- and/or organelle-specific isoforms. Structural diversity of V-ATPase generated by different combinations of subunit isoforms enables it to play diverse physiological roles in mammalian cells. Among these various roles, this review focuses on the functions of lysosome-specific V-ATPase in bone resorption by osteoclasts. Lysosomes remain in the cytoplasm in most cell types, but in osteoclasts, secretory lysosomes move toward and fuse with the plasma membrane to secrete lysosomal enzymes, which is essential for bone resorption. Through this process, lysosomal V-ATPase harboring the a3 isoform of the a subunit is relocated to the plasma membrane, where it transports protons from the cytosol to the cell exterior to generate the acidic extracellular conditions required for secreted lysosomal enzymes. In addition to this role as a proton pump, we recently found that the lysosomal a3 subunit of V-ATPase is essential for anterograde trafficking of secretory lysosomes. Specifically, a3 interacts with Rab7, a member of the Rab guanosine 5'-triphosphatase (GTPase) family that regulates organelle trafficking, and recruits it to the lysosomal membrane. These findings revealed the multifunctionality of lysosomal V-ATPase in osteoclasts; V-ATPase is responsible not only for the formation of the acidic environment by transporting protons, but also for intracellular trafficking of secretory lysosomes by recruiting organelle trafficking factors. Herein, we summarize the molecular mechanism underlying secretory lysosome trafficking in osteoclasts, and discuss the possible regulatory role of V-ATPase in organelle trafficking.

Comparative Surfaceome Analysis of Clonal Histomonas meleagridis Strains with Different Pathogenicity Reveals Strain-Dependent Profiles

Histomonas meleagridis, a poultry-specific intestinal protozoan parasite, is histomonosis’s etiological agent. Since treatment or prophylaxis options are no longer available in various countries, histomonosis can lead to significant production losses in chickens and mortality in turkeys. The surfaceome of microbial pathogens is a crucial component of host–pathogen interactions. Recent proteome and exoproteome studies on H. meleagridis produced molecular data associated with virulence and in vitro attenuation, yet the information on proteins exposed on the cell surface is currently unknown. Thus, in the present study, we identified 1485 proteins and quantified 22 and 45 upregulated proteins in the virulent and attenuated strains, respectively, by applying cell surface biotinylation in association with high-throughput proteomic analysis. The virulent strain displayed upregulated proteins that could be linked to putative virulence factors involved in the colonization and establishment of infection, with the upregulation of two candidates being confirmed by expression analysis. In the attenuated strain, structural, transport and energy production proteins were upregulated, supporting the protozoan’s adaptation to the in vitro environment. These results provide a better understanding of the surface molecules involved in the pathogenesis of histomonosis, while highlighting the pathogen’s in vitro adaptation processes.

Extracellular vesicles and particles impact the systemic landscape of cancer

Intercellular cross talk between cancer cells and stromal and immune cells is essential for tumor progression and metastasis. Extracellular vesicles and particles (EVPs) are a heterogeneous class of secreted messengers that carry bioactive molecules and that have been shown to be crucial for this cell-cell communication. Here, we highlight the multifaceted roles of EVPs in cancer. Functionally, transfer of EVP cargo between cells influences tumor cell growth and invasion, alters immune cell composition and function, and contributes to stromal cell activation. These EVP-mediated changes impact local tumor progression, foster cultivation of pre-metastatic niches at distant organ-specific sites, and mediate systemic effects of cancer. Furthermore, we discuss how exploiting the highly selective enrichment of molecules within EVPs has profound implications for advancing diagnostic and prognostic biomarker development and for improving therapy delivery in cancer patients. Altogether, these investigations into the role of EVPs in cancer have led to discoveries that hold great promise for improving cancer patient care and outcome.

BAG3 Regulation of RAB35 Mediates the Endosomal Sorting Complexes Required for Transport/Endolysosome Pathway and Tau Clearance

BACKGROUND

Declining proteostasis with aging contributes to increased susceptibility to neurodegenerative diseases, including Alzheimer's disease (AD). Emerging studies implicate impairment of the endosome-lysosome pathway as a significant factor in the pathogenesis of these diseases. Previously, we demonstrated that BAG3 regulates phosphorylated tau clearance. However, we did not fully define how BAG3 regulates endogenous tau proteostasis, especially in the early stages of disease progression.

METHODS

Mass spectrometric analyses were performed to identify neuronal BAG3 interactors. Multiple biochemical assays were used to investigate the BAG3-HSP70-TBC1D10B (EPI64B)-RAB35-HRS regulatory networks. Live-cell imaging was used to study the dynamics of the endosomal pathway. Immunohistochemistry and immunoblotting were performed in human AD brains and in P301S tau transgenic mice with BAG3 overexpressed.

RESULTS

The primary group of neuronal BAG3 interactors identified are involved in the endocytic pathway. Among them were key regulators of small GTPases, such as the RAB35 GTPase-activating protein TBC1D10B. We demonstrated that a BAG3-HSP70-TBC1D10B complex attenuates the ability of TBC1D10B to inactivate RAB35. Thus, BAG3 interacts with TBC1D10B to support the activation of RAB35 and recruitment of HRS, initiating endosomal sorting complex required for transport-mediated endosomal tau clearance. Furthermore, TBC1D10B shows significantly less colocalization with BAG3 in AD brains than in age-matched controls. Overexpression of BAG3 in P301S tau transgenic mice increased the colocalization of phosphorylated tau with the endosomal sorting complex required for transport III protein CHMP2B and reduced the levels of the mutant human tau.

CONCLUSIONS

We identified a novel BAG3-TBC1D10B-RAB35 regulatory axis that modulates endosomal sorting complex required for transport-dependent protein degradation machinery and tau clearance. Dysregulation of BAG3 could contribute to the pathogenesis of AD.

Deletion in chromosome 6 spanning alpha-synuclein and multimerin1 loci in the Rab27a/b double knockout mouse

We report an incidental 358.5 kb deletion spanning the region encoding for alpha-synuclein (αsyn) and multimerin1 (Mmrn1) in the Rab27a/Rab27b double knockout (DKO) mouse line previously developed by Tolmachova and colleagues in 2007. Western blot and RT-PCR studies revealed lack of αsyn expression at either the mRNA or protein level in Rab27a/b DKO mice. PCR of genomic DNA from Rab27a/b DKO mice demonstrated at least partial deletion of the Snca locus using primers targeted to exon 4 and exon 6. Most genes located in proximity to the Snca locus, including Atoh1, Atoh2, Gm5570, Gm4410, Gm43894, and Grid2, were shown not to be deleted by PCR except for Mmrn1. Using whole genomic sequencing, the complete deletion was mapped to chromosome 6 (60,678,870–61,037,354), a slightly smaller deletion region than that previously reported in the C57BL/6J substrain maintained by Envigo. Electron microscopy of cortex from these mice demonstrates abnormally enlarged synaptic terminals with reduced synaptic vesicle density, suggesting potential interplay between Rab27 isoforms and αsyn, which are all highly expressed at the synaptic terminal. Given this deletion involving several genes, the Rab27a/b DKO mouse line should be used with caution or with appropriate back-crossing to other C57BL/6J mouse substrain lines without this deletion.

Megaviruses contain various genes encoding for eukaryotic vesicle trafficking factors

Many intracellular pathogens, such as bacteria and large viruses, enter eukaryotic cells via phagocytosis, then replicate and proliferate inside the host. To avoid degradation in the phagosomes, they have developed strategies to modify vesicle trafficking. Although several strategies of bacteria have been characterized, it is not clear whether viruses also interfere with the vesicle trafficking of the host. Recently, we came across SNARE proteins encoded in the genomes of several bacteria of the order Legionellales. These pathogenic bacteria may use SNAREs to interfere with vesicle trafficking, since SNARE proteins are the core machinery for vesicle fusion during transport. They assemble into membrane-bridging SNARE complexes that bring membranes together. We now have also discovered SNARE proteins in the genomes of diverse giant viruses. Our biochemical experiments showed that these proteins are able to form SNARE complexes. We also found other key trafficking factors that work together with SNAREs such as NSF, SM, and Rab proteins encoded in the genomes of giant viruses, suggesting that viruses can make use of a large genetic repertoire of trafficking factors. Most giant viruses possess different collections, suggesting that these factors entered the viral genome multiple times. In the future, the molecular role of these factors during viral infection need to be studied.

Integrating intracellular nanovesicles into integrin trafficking pathways and beyond

Membrane traffic controls the movement of proteins and lipids from one cellular compartment to another using a system of transport vesicles. Intracellular nanovesicles (INVs) are a newly described class of transport vesicles. These vesicles are small, carry diverse cargo, and are involved in multiple trafficking steps including anterograde traffic and endosomal recycling. An example of a biological process that they control is cell migration and invasion, due to their role in integrin recycling. In this review, we describe what is known so far about these vesicles. We discuss how INVs may integrate into established membrane trafficking pathways using integrin recycling as an example. We speculate where in the cell INVs have the potential to operate and we identify key questions for future investigation.

The roles and therapeutic approaches of MSC-derived exosomes in colorectal cancer

Colorectal cancer (CRC) is the third most common cancer in both men and women, accounting for 8% of all new cancer cases in both. CRC is typically diagnosed at advanced stages, which leads to a higher mortality rate. The 5-year survival rate for CRC is 64% in all cases and just 12% in metastatic cases. Mesenchymal stem cells (MSCs) are one of the most recent approaches for therapeutic interventions in cancer. MSCs have multiple properties, including paracrine signaling, immunologic functions, and the ability to migrate to the targeted tissue. MSCs can produce and secrete exosomes in tumor microenvironments. These exosomes can transfer compounds across tumor cells, stromal cells, fibroblasts, endothelial cells, and immune cells. Studies showed that modified MCS-derived exosomes have enhanced specificity, reduced immunogenicity, and better targeting capabilities in comparison to other frequently used delivery systems such as liposomes. Therefore, this study aimed to provide a comprehensive view of the role of natural MSC-derived exosomes in CRC, as well as the most current and prospective advancements in MSC-derived exosome therapeutic modifications.

Coxiella burnetii Plasmid Effector B Promotes LC3-II Accumulation and Contributes To Bacterial Virulence in a SCID Mouse Model

Coxiella burnetii, the causative agent of zoonotic Q fever, is characterized by replicating inside the lysosome-derived Coxiella-containing vacuole (CCV) in host cells. Some effector proteins secreted by C. burnetii have been reported to be involved in the manipulation of autophagy to facilitate the development of CCVs and bacterial replication. Here, we found that the Coxiella plasmid effector B (CpeB) localizes on vacuole membrane targeted by LC3 and LAMP1 and promotes LC3-II accumulation. Meanwhile, the C. burnetii strain lacking the QpH1 plasmid induced less LC3-II accumulation, which was accompanied by smaller CCVs and lower bacterial loads in THP-1 cells. Expression of CpeB in the strain lacking QpH1 led to restoration in LC3-II accumulation but had no effect on the smaller CCV phenotype. In the severe combined immune deficiency (SCID) mouse model, infections with the strain expressing CpeB led to significantly higher bacterial burdens in the spleen and liver than its parent strain devoid of QpH1. We also found that CpeB targets Rab11a to promote LC3-II accumulation. Intratracheally inoculated C. burnetii resulted in lower bacterial burdens and milder lung lesions in Rab11a conditional knockout (Rab11a^-/- CKO) mice. Collectively, these results suggest that CpeB promotes C. burnetii virulence by inducing LC3-II accumulation via a pathway involving Rab11a.

The lysosomal V-ATPase a3 subunit is involved in localization of Mon1-Ccz1, the GEF for Rab7, to secretory lysosomes in osteoclasts

We have shown previously that the lysosomal a3 isoform of the a subunit of vacuolar-type ATPase (V-ATPase) interacts with inactive (GDP-bound form) Rab7, a small GTPase that regulates late endosome/lysosome trafficking, and that a3 recruits Rab7 to secretory lysosomes in mouse osteoclasts. This is essential for outward trafficking of secretory lysosomes and thus for bone resorption. However, the molecular mechanism underlying the recruitment of Rab7 by a3 remains to be fully elucidated. Here, we showed that a3 interacts with the Mon1A-Ccz1 complex, a guanine nucleotide exchange factor (GEF) for Rab7, using HEK293T cells. The interaction was mediated by the amino-terminal half domain of a3 and the longin motifs of Mon1A and Ccz1. Exogenous expression of the GEF promoted the interaction between a3 and Rab7. Mon1A mutants that interact inefficiently with Rab7 interacted with a3 at a similar level to wild-type Mon1A. Lysosomal localization of endogenous Ccz1 was abolished in osteoclasts lacking a3. These results suggest that the lysosomal a3 isoform of V-ATPase interacts with Mon1A-Ccz1, and that a3 is important for Mon1A-Ccz1 localization to secretory lysosomes, which mediates Rab7 recruitment to the organelle.

Targeting Aβ and p-Tau Clearance in Methamphetamine-Induced Alzheimer’s Disease-Like Pathology: Roles of Syntaxin 17 in Autophagic Degradation in Primary Hippocampal Neurons

Methamphetamine (Meth), a central nervous system (CNS) stimulant with strong neurotoxicity, causes progressive cognitive impairment with characterized neurodegenerative changes. However, the mechanism underlying Meth-induced pathological changes remains poorly understood. In the current study, Meth elicited a striking accumulation of the pathological proteins hyperphosphorylated tau (p-tau) and amyloid beta (Aβ) in primary hippocampal neurons, while the activation of autophagy dramatically ameliorated the high levels of these pathological proteins. Interestingly, after the Meth treatment, Aβ was massively deposited in autophagosomes, which were remarkably trapped in early endosomes. Mechanistically, syntaxin 17 (Stx17), a key soluble n-ethylmaleimide-sensitive fusion protein (NSF) attachment protein receptor (SNARE) protein responsible for autophagosome and mature endosome/lysosome fusion, was significantly downregulated and hindered in combination with autophagosomes. Notably, adenovirus overexpression of Stx17 in primary neurons facilitated autophagosome-mature endosome/lysosome fusion, which dramatically reversed the Meth-induced increases in the levels of p-tau, Aβ, beta-secretase (Bace-1), and C-terminal fragments (CTFs). Immunofluorescence assays showed that Stx17 retarded the Meth-induced Aβ, p-tau, and Bace-1 accumulation in autophagosomes and facilitated the translocation of these pathological proteins to lysosomes, which indicated the importance of Stx17 via enhanced autophagosome-mature endosome/lysosome fusion. Therefore, the current study reveals a novel mechanism involving Meth-induced high levels of pathological proteins in neurons. Targeting Stx17 may provide a novel therapeutic strategy for Meth-induced neurodegenerative changes.

Typhoid toxin sorting and exocytic transport from Salmonella Typhi-infected cells

Typhoid toxin is an essential virulence factor for Salmonella Typhi, the cause of typhoid fever in humans. This toxin has an unusual biology in that it is produced by Salmonella Typhi only when located within host cells. Once synthesized, the toxin is secreted to the lumen of the Salmonella-containing vacuole from where it is transported to the extracellular space by vesicle carrier intermediates. Here, we report the identification of the typhoid toxin sorting receptor and components of the cellular machinery that packages the toxin into vesicle carriers, and exports it to the extracellular space. We found that the cation-independent mannose-6-phosphate receptor serves as typhoid toxin sorting receptor and that the coat protein COPII and the GTPase Sar1 mediate its packaging into vesicle carriers. Formation of the typhoid toxin carriers requires the specific environment of the Salmonella Typhi-containing vacuole, which is determined by the activities of specific effectors of its type III protein secretion systems. We also found that Rab11B and its interacting protein Rip11 control the intracellular transport of the typhoid toxin carriers, and the SNARE proteins VAMP7, SNAP23, and Syntaxin 4 their fusion to the plasma membrane. Typhoid toxin's cooption of specific cellular machinery for its transport to the extracellular space illustrates the remarkable adaptation of an exotoxin to exert its function in the context of an intracellular pathogen.

The pathological role of damaged organelles in renal tubular epithelial cells in the progression of acute kidney injury

Acute kidney injury (AKI) is a common clinical condition associated with high morbidity and mortality. The pathogenesis of AKI has not been fully elucidated, with a lack of effective treatment. Renal tubular epithelial cells (TECs) play an important role in AKI, and their damage and repair largely determine the progression and prognosis of AKI. In recent decades, it has been found that the mitochondria, endoplasmic reticulum (ER), lysosomes, and other organelles in TECs are damaged to varying degrees in AKI, and that they can influence each other through various signaling mechanisms that affect the recovery of TECs. However, the association between these multifaceted signaling platforms, particularly between mitochondria and lysosomes during AKI remains unclear. This review summarizes the specific pathophysiological mechanisms of the main TECs organelles in the context of AKI, particularly the potential interactions among them, in order to provide insights into possible novel treatment strategies.

KIF13A—A Key Regulator of Recycling Endosome Dynamics

Molecular motors of the kinesin superfamily (KIF) are a class of ATP-dependent motor proteins that transport cargo, including vesicles, along the tracks of the microtubule network. Around 45 KIF proteins have been described and are grouped into 14 subfamilies based on the sequence homology and domain organization. These motors facilitate a plethora of cellular functions such as vesicle transport, cell division and reorganization of the microtubule cytoskeleton. Current studies suggest that KIF13A, a kinesin-3 family member, associates with recycling endosomes and regulates their membrane dynamics (length and number). KIF13A has been implicated in several processes in many cell types, including cargo transport, recycling endosomal tubule biogenesis, cell polarity, migration and cytokinesis. Here we describe the recent advances in understanding the regulatory aspects of KIF13A motor in controlling the endosomal dynamics in addition to its structure, mechanism of its association to the membranes, regulators of motor activity, cell type-specific cargo/membrane transport, methods to measure its activity and its association with disease. Thus, this review article will provide our current understanding of the cell biological roles of KIF13A in regulating endosomal membrane remodeling.

Nuclear and Cytoplasmatic Players in Mitochondria-Related CNS Disorders: Chromatin Modifications and Subcellular Trafficking

Aberrant mitochondrial phenotypes are common to many central nervous system (CNS) disorders, including neurodegenerative and neurodevelopmental diseases. Mitochondrial function and homeostasis depend on proper control of several biological processes such as chromatin remodeling and transcriptional control, post-transcriptional events, vesicle and organelle subcellular trafficking, fusion, and morphogenesis. Mutation or impaired regulation of major players that orchestrate such processes can disrupt cellular and mitochondrial dynamics, contributing to neurological disorders. The first part of this review provides an overview of a functional relationship between chromatin players and mitochondria. Specifically, we relied on specific monogenic CNS disorders which share features with mitochondrial diseases. On the other hand, subcellular trafficking is coordinated directly or indirectly through evolutionarily conserved domains and proteins that regulate the dynamics of membrane compartments and organelles, including mitochondria. Among these “building blocks”, longin domains and small GTPases are involved in autophagy and mitophagy, cell reshaping, and organelle fusion. Impairments in those processes significantly impact CNS as well and are discussed in the second part of the review. Hopefully, in filling the functional gap between the nucleus and cytoplasmic organelles new routes for therapy could be disclosed.

Redox Control of Integrin-Mediated Hepatic Inflammation in Systemic Autoimmunity

Significance: Systemic autoimmunity affects 3%-5% of the population worldwide. Systemic lupus erythematosus (SLE) is a prototypical form of such condition, which affects 20-150 of 100,000 people globally. Liver dysfunction, defined by increased immune cell infiltration into the hepatic parenchyma, is an understudied manifestation that affects up to 20% of SLE patients. Autoimmunity in SLE involves proinflammatory lineage specification in the immune system that occurs with oxidative stress and profound changes in cellular metabolism. As the primary metabolic organ of the body, the liver is uniquely capable to encounter oxidative stress through first-pass derivatization and filtering of waste products. Recent Advances: The traffic of immune cells from their development through recirculation in the liver is guided by cell adhesion molecules (CAMs) and integrins, cell surface proteins that tightly anchor cells together. The surface expression of CAMs and integrins is regulated via endocytic traffic that is sensitive to oxidative stress. Reactive oxygen species (ROS) that elicit oxidative stress in the liver may originate from the mitochondria, the cytosol, or the cell membrane. Critical Issues: While hepatic ROS production is a source of vulnerability, it also modulates the development and function of the immune system. In turn, the liver employs antioxidant defense mechanisms to protect itself from damage that can be harnessed to serve as therapeutic mechanisms against autoimmunity, inflammation, and development of hepatocellular carcinoma. Future Directions: This review is aimed at delineating redox control of integrin signaling in the liver and checkpoints of regulatory impact that can be targeted for treatment of inflammation in systemic autoimmunity. Antioxid. Redox Signal. 36, 367-388.

The Role of RAB GTPases and Its Potential in Predicting Immunotherapy Response and Prognosis in Colorectal Cancer

Background: Colorectal cancer (CRC) is the third most common cancer worldwide, in which aberrant activation of the RAS signaling pathway appears frequently. RAB proteins (RABs) are the largest Ras small GTPases superfamily that regulates intracellular membrane trafficking pathways. The dysregulation of RABs have been found in various diseases including cancers. Compared with other members of Ras families, the roles of RABs in colorectal cancer are less well understood.

Methods: We analyzed the differential expression and clinicopathological association of RABs in CRC using RNA sequencing and genotyping datasets from TCGA samples. Moreover, the biological function of RAB17 and RAB34 were investigated in CRC cell lines and patient samples.

Results: Of the 62 RABs we analyzed in CRC, seven (RAB10, RAB11A, RAB15, RAB17, RAB19, RAB20, and RAB25) were significantly upregulated, while six (RAB6B, RAB9B, RAB12, RAB23, RAB31, and RAB34) were significantly downregulated in tumor tissues as compared to normal. We found that the upregulated-RABs, which were highly expressed in metabolic activated CRC subtype (CMS3), are associated with cell cycle related pathways enrichment and positively correlated with the mismatch repair (MMR) genes in CRC, implying their role in regulating cell metabolism and tumor growth. While, high expression of the downregulated-RABs were significantly associated with poor prognostic CRC mesenchymal subtypes (CMS4), immune checkpoint genes, and tumor infiltrating immune cells, indicating their role in predicting prognosis and immunotherapy efficacy. Interestingly, though RAB34 mRNA is downregulated in CRC, its high expression is significantly associated with poor prognosis. In vitro experiments showed that RAB17 overexpression can promote cell proliferation via cell cycle regulation. While, RAB34 overexpression can promote cell migration and invasion and is associated with PD-L1/PD-L2 expression increase in CRC cells.

Conclusions: Our study showed that RABs may play important roles in regulating cell cycle and immune-related pathways, therefore might be potential biomarkers in predicting prognosis and immunotherapy response in CRC.

G. Lahr D. Phylogenetic reconstruction and evolution of the Rab GTPase gene family in Amoebozoa

Rab GTPase is a paralog-rich gene family that controls the maintenance of the eukaryotic cell compartmentalization system. Diverse eukaryotes have varying numbers of Rab paralogs. Currently, little is known about the evolutionary pattern of Rab GTPase in most major eukaryotic 'supergroups'. Here, we present a comprehensive phylogenetic reconstruction of the Rab GTPase gene family in the eukaryotic 'supergroup' Amoebozoa, a diverse lineage represented by unicellular and multicellular organisms. We demonstrate that Amoebozoa conserved 20 of the 23 ancestral Rab GTPases predicted to be present in the last eukaryotic common ancestor and massively expanded several 'novel' in-paralogs. Due to these 'novel' in-paralogs, the Rab family composition dramatically varies between the members of Amoebozoa; as a consequence, 'supergroup'-based studies may significantly change our current understanding of the evolution and diversity of this gene family. The high diversity of the Rab GTPase gene family in Amoebozoa makes this 'supergroup' a key lineage to study and advance our knowledge of the evolution of Rab in Eukaryotes.

Rab31-dependent regulation of transforming growth factor ß expression in breast cancer cells

BACKGROUND

The small GTP-binding protein Rab31 plays an important role in the modulation of tumor biological-relevant processes, including cell proliferation, adhesion, and invasion. As an underlying mechanism, Rab31 is presumed to act as a molecular switch between a more proliferative and an invasive phenotype. This prompted us to analyze whether Rab31 overexpression in breast cancer cells affects expression of genes involved in epithelial-to-mesenchymal transition (EMT)-like processes when compared to Rab31 low-expressing cells.

METHODS

Commercially available profiler PCR arrays were applied to search for differentially expressed genes in Rab31 high- and low-expressing CAMA-1 breast cancer cells. Differential expression of selected candidate genes in response to Rab31 overexpression in CAMA-1 cells was validated by independent qPCR and protein assays.

RESULTS

Gene expression profiling of key genes involved in EMT, or its reciprocal process MET, identified 9 genes being significantly up- or down-regulated in Rab31 overexpressing CAMA-1 cells, with the strongest effects seen for TGFB1, encoding TGF-ß1 (> 25-fold down-regulation in Rab31 overexpressing cells). Subsequent validation analyses by qPCR revealed a strong down-regulation of TGFB1 mRNA levels in response to increased Rab31 expression not only in CAMA-1 cells, but also in another breast cancer cell line, MDA-MB-231. Using ELISA and Western blot analysis, a considerable reduction of both intracellular and secreted TGF-ß1 antigen levels was determined in Rab31 overexpressing cells compared to vector control cells. Furthermore, reduced TGF-ß activity was observed upon Rab31 overexpression in CAMA-1 cells using a sensitive TGF-ß bioassay. Finally, the relationship between Rab31 expression and the TGF-ß axis was analyzed by another profiler PCR array focusing on genes involved in TGF-ß signaling. We found 12 out of 84 mRNAs significantly reduced and 7 mRNAs significantly increased upon Rab31 overexpression.

CONCLUSIONS

Our results demonstrate that Rab31 is a potent modulator of the expression of TGF-ß and other components of the TGF-ß signaling pathway in breast cancer cells.

Regulation of Hook1-mediated endosomal sorting of clathrin-independent cargo by γ-taxilin

In clathrin-independent endocytosis, Hook1, a microtubule- and cargo-tethering protein, participates in sorting of cargo proteins such as CD98 and CD147 into recycling endosomes. However, the molecular mechanism that regulates Hook1-mediated endosomal sorting is not fully understood. Here, we found that γ-taxilin is a novel regulator of Hook1-mediated endosomal sorting. γ-Taxilin depletion promoted both CD98-positive tubular formation and CD98 recycling. Conversely, overexpression of γ-taxilin inhibited the CD98-positive tubular formation. Depletion of Hook1, or Rab10 or Rab22a (which are both involved in Hook1-mediated endosomal sorting), attenuated the effect of γ-taxilin depletion on the CD98-positive tubular formation. γ-Taxilin depletion promoted CD147-mediated spreading of HeLa cells, suggesting that γ-taxilin may be a pivotal player in various cellular functions in which Hook1-mediated cargo proteins are involved. γ-Taxilin bound to the C-terminal region of Hook1 and inhibited its interaction with CD98; the latter interaction is necessary for sorting CD98. We suggest that γ-taxilin negatively regulates the sorting of Hook1-mediated cargo proteins into recycling endosomes by interfering with the interactions between Hook1 and the cargo proteins.

Cooperation of cell adhesion and autophagy in the brain: Functional roles in development and neurodegenerative disease

Cellular adhesive connections directed by the extracellular matrix (ECM) and maintenance of cellular homeostasis by autophagy are seemingly disparate functions that are molecularly intertwined, each regulating the other. This is an emerging field in the brain where the interplay between adhesion and autophagy functions at the intersection of neuroprotection and neurodegeneration. The ECM and adhesion proteins regulate autophagic responses to direct protein clearance and guide regenerative programs that go awry in brain disorders. Concomitantly, autophagic flux acts to regulate adhesion dynamics to mediate neurite outgrowth and synaptic plasticity with functional disruption contributed by neurodegenerative disease. This review highlights the cooperative exchange between cellular adhesion and autophagy in the brain during health and disease. As the mechanistic alliance between adhesion and autophagy has been leveraged therapeutically for metastatic disease, understanding overlapping molecular functions that direct the interplay between adhesion and autophagy might uncover therapeutic strategies to correct or compensate for neurodegeneration.

AMPK-mediated phosphorylation enhances the auto-inhibition of TBC1D17 to promote Rab5-dependent glucose uptake

Dysregulation of glucose homeostasis contributes to insulin resistance and type 2 diabetes. Whilst exercise stimulated activation of AMP-activated protein kinase (AMPK), an important energy sensor, has been highlighted for its potential to promote insulin-stimulated glucose uptake, the underlying mechanisms for this remain largely unknown. Here we found that AMPK positively regulates the activation of Rab5, a small GTPase which is involved in regulating Glut4 translocation, in both myoblasts and skeletal muscles. We further verified that TBC1D17, identified as a potential interacting partner of Rab5 in our recent study, is a novel GTPase activating protein (GAP) of Rab5. TBC1D17-Rab5 axis regulates transport of Glut1, Glut4, and transferrin receptor. TBC1D17 interacts with Rab5 or AMPK via its TBC domain or N-terminal 1-306 region (N-Ter), respectively. Moreover, AMPK phosphorylates the Ser 168 residue of TBC1D17 which matches the predicted AMPK consensus motif. N-Ter of TBC1D17 acts as an inhibitory region by directly interacting with the TBC domain. Ser168 phosphorylation promotes intra-molecular interaction and therefore enhances the auto-inhibition of TBC1D17. Our findings reveal that TBC1D17 acts as a molecular bridge that links AMPK and Rab5 and delineate a previously unappreciated mechanism by which the activation of TBC/RabGAP is regulated.

Extracellular vesicles: General features and usefulness in diagnosis and therapeutic management of colorectal cancer

In the world, among all type of cancers, colorectal cancer (CRC) is the third most commonly diagnosed in males and the second in females. In most of cases, (RP1) patients’ prognosis limitation with malignant tumors can be attributed to delayed diagnosis of the disease. Identification of patients with early-stage disease leads to more effective therapeutic interventions. Therefore, new screening methods and further innovative treatment approaches are mandatory as they may lead to an increase in progression-free and overall survival rates. For the last decade, the interest in extracellular vesicles (EVs) research has exponentially increased as EVs generation appears to be a universal feature of every cell that is strongly involved in many mechanisms of cell-cell communication either in physiological or pathological situations. EVs can cargo biomolecules, such as lipids, proteins, nucleic acids and generate transmission signal through the intercellular transfer of their content. By this mechanism, tumor cells can recruit and modify the adjacent and systemic microenvironment to support further invasion and dissemination. This review intends to cover the most recent literature on the role of EVs production in colorectal normal and cancer tissues. Specific attention is paid to the use of EVs for early CRC diagnosis, follow-up, and prognosis as EVs have come into the spotlight of research as a high potential source of ‘liquid biopsies’. The use of EVs as new targets or nanovectors as drug delivery systems for CRC therapy is also summarized.

RNF13 Dileucine Motif Variants L311S and L312P Interfere with Endosomal Localization and AP-3 Complex Association

Developmental and epileptic encephalopathies (DEE) are rare and serious neurological disorders characterized by severe epilepsy with refractory seizures and a significant developmental delay. Recently, DEE73 was linked to genetic alterations of the RNF13 gene, which convert positions 311 or 312 in the RNF13 protein from leucine to serine or proline, respectively (L311S and L312P). Using a fluorescence microscopy approach to investigate the molecular and cellular mechanisms affected by RNF13 protein variants, the current study shows that wild-type RNF13 localizes extensively with endosomes and lysosomes, while L311S and L312P do not extensively colocalize with the lysosomal marker Lamp1. Our results show that RNF13 L311S and L312P proteins affect the size of endosomal vesicles along with the temporal and spatial progression of fluorescently labeled epidermal growth factor, but not transferrin, in the endolysosomal system. Furthermore, GST-pulldown and co-immunoprecipitation show that RNF13 variants disrupt association with AP-3 complex. Knockdown of AP-3 complex subunit AP3D1 alters the lysosomal localization of wild-type RNF13 and similarly affects the size of endosomal vesicles. Importantly, our study provides a first step toward understanding the cellular and molecular mechanism altered by DEE73-associated genetic variations of RNF13.

Role of HRTPT in kidney proximal epithelial cell regeneration: Integrative differential expression and pathway analyses using microarray and scRNA-seq

Damage to proximal tubules due to exposure to toxicants can lead to conditions such as acute kidney injury (AKI), chronic kidney disease (CKD) and ultimately end‐stage renal failure (ESRF). Studies have shown that kidney proximal epithelial cells can regenerate particularly after acute injury. In the previous study, we utilized an immortalized in vitro model of human renal proximal tubule epithelial cells, RPTEC/TERT1, to isolate HRTPT cell line that co‐expresses stem cell markers CD133 and CD24, and HREC24T cell line that expresses only CD24. HRTPT cells showed most of the key characteristics of stem/progenitor cells; however, HREC24T cells did not show any of these characteristics. The goal of this study was to further characterize and understand the global gene expression differences, upregulated pathways and gene interaction using scRNA‐seq in HRTPT cells. Affymetrix microarray analysis identified common gene sets and pathways specific to HRTPT and HREC24T cells analysed using DAVID, Reactome and Ingenuity software. Gene sets of HRTPT cells, in comparison with publicly available data set for CD133+ infant kidney, urine‐derived renal progenitor cells and human kidney‐derived epithelial proximal tubule cells showed substantial similarity in organization and interactions of the apical membrane. Single‐cell analysis of HRTPT cells identified unique gene clusters associated with CD133 and the 92 common gene sets from three data sets. In conclusion, the gene expression analysis identified a unique gene set for HRTPT cells and narrowed the co‐expressed gene set compared with other human renal–derived cell lines expressing CD133, which may provide deeper understanding in their role as progenitor/stem cells that participate in renal repair.

A novel function for Rab1 and Rab11 during secretory granule maturation

Regulated exocytosis is an essential process whereby specific cargo proteins are secreted in a stimulus-dependent manner. Cargo-containing secretory granules are synthesized in the trans-Golgi network (TGN); after budding from the TGN, granules undergo modifications, including an increase in size. These changes occur during a poorly understood process called secretory granule maturation. Here, we leverage the Drosophila larval salivary glands as a model to characterize a novel role for Rab GTPases during granule maturation. We find that secretory granules increase in size ∼300-fold between biogenesis and release, and loss of Rab1 or Rab11 reduces granule size. Surprisingly, we find that Rab1 and Rab11 localize to secretory granule membranes. Rab11 associates with granule membranes throughout maturation, and Rab11 recruits Rab1. In turn, Rab1 associates specifically with immature granules and drives granule growth. In addition to roles in granule growth, both Rab1 and Rab11 appear to have additional functions during exocytosis; Rab11 function is necessary for exocytosis, while the presence of Rab1 on immature granules may prevent precocious exocytosis. Overall, these results highlight a new role for Rab GTPases in secretory granule maturation.

From structure to ætiology: a new window on the biology of leucine-rich repeat kinase 2 and Parkinson's disease

Since the discovery of mutations in leucine-rich repeat kinase 2 (LRRK2) as an underlying genetic cause for the development of Parkinson's disease (PD) in 2004 (Neuron 44, 601-607; Neuron 44, 595-600), and subsequent efforts to develop LRRK2 kinase inhibitors as a therapy for Parkinson's (Expert Opin. Ther. Targets 21, 751-753), elucidating the atomic resolution structure of LRRK2 has been a major goal of research into this protein. At over 250 kDa, the large size and complicated domain organisation of LRRK2 has made this a highly challenging target for structural biologists, however, a number of recent studies using both in vitro and in situ approaches (Nature 588, 344-349; Cell 182, 1508-1518.e1516; Cell 184, 3519-3527.e3510) have provided important new insights into LRRK2 structure and the complexes formed by this protein.