TBC1D5 controls the GTPase cycle of Rab7b

VPS34 Governs Oocyte Developmental Competence by Regulating Mito/Autophagy: A Novel Insight into the Significance of RAB7 Activity and Its Subcellular Location

Asynchronous nuclear and cytoplasmic maturation in human oocytes is believed to cause morphological anomalies after controlled ovarian hyperstimulation. Vacuolar protein sorting 34 (VPS34) is renowned for its pivotal role in regulating autophagy and endocytic trafficking. To investigate its impact on oocyte development, oocyte-specific knockout mice (ZcKO) are generated, and these mice are completely found infertile, with embryonic development halted at 2- to 4-cell stage. This infertility is related with a disruption on autophagic/mitophagic flux in ZcKO oocytes, leading to subsequent failure of zygotic genome activation (ZGA) in derived 2-cell embryos. The findings further elucidated the regulation of VPS34 on the activity and subcellular translocation of RAS-related GTP-binding protein 7 (RAB7), which is critical not only for the maturation of late endosomes and lysosomes, but also for initiating mitophagy via retrograde trafficking. VPS34 binds directly with RAB7 and facilitates its activity conversion through TBC1 domain family member 5 (TBC1D5). Consistent with the cytoplasmic vacuolation observed in ZcKO oocytes, defects in multiple vesicle trafficking systems are also identified in vacuolated human oocytes. Furthermore, activating VPS34 with corynoxin B (CB) treatment improved oocyte quality in aged mice. Hence, VPS34 activation may represent a novel approach to enhance oocyte quality in human artificial reproduction.

CRISPR/CasRx-Mediated Knockdown of Rab7B Restores Incomplete Cell Shape Induced by Pelizaeus-Merzbacher Disease-Associated PLP1 p.Ala243Val

Pelizaeus-Merzbacher disease (PMD, currently known as hypomyelinating leukodystrophy type 1 [HLD1]) is a hereditary hypomyelinating and/or demyelinating disease associated with the proteolipid protein 1 (plp1) gene in the central nervous system (CNS). One of the major causes of this condition is incomplete or defective oligodendroglial cell myelin sheath formation triggered by endoplasmic reticulum (ER) stress and subsequent unfolded protein response (UPR). The HLD1-associated Ala-243-to-Val mutation (p.Ala243Val) of PLP1 is widely recognized to trigger defective oligodendroglial cell morphological differentiation, primarily due to ER stress. We have previously reported that knockdown of Rab7B (also known as Rab42), a small GTP/GDP-binding protein involved in intracellular vesicle trafficking around the lysosome, can recover chemical ER stress-induced incomplete cell shapes in the FBD-102b cell line, a model of oligodendroglial cell morphological differentiation. Here, we present findings indicating that incomplete cell shapes induced by PLP1 p.Ala243Val can be restored by knockdown of Rab7B using the clustered regularly interspaced short palindromic repeats (CRISPR) and CasRx (also known as Cas13d) system. Also, the knockdown promoted the trafficking of PLP1 p.Ala243Val to lysosome-associated membrane protein 1 (LAMP1)-positive organelles. These results highlight the unique role of Rab7B knockdown in modulating oligodendroglial cell morphological changes and potentially facilitating the transport of mutated PLP1 to LAMP1-positive organelles, suggesting its potential as a therapeutic target for alleviating HLD1 phenotypes, at least in part, at the molecular and cellular levels.

Autophagy as a dual-faced host response to viral infections

Autophagy selectively degrades viral particles or cellular components, either facilitating or inhibiting viral replication. Conversely, most viruses have evolved strategies to escape or exploit autophagy. Moreover, autophagy collaborates with the pattern recognition receptor signaling, influencing the expression of adaptor molecules involved in the innate immune response and regulating the expression of interferons (IFNs). The intricate relationship between autophagy and IFNs plays a critical role in the host cell defense against microbial invasion. Therefore, it is important to summarize the interactions between viral infections, autophagy, and the host defense mechanisms against viruses. This review specifically focuses on the interactions between autophagy and IFN pathways during viral infections, providing a comprehensive summary of the molecular mechanisms utilized or evaded by different viruses.

Cell-specific secretory granule sorting mechanisms: the role of MAGEL2 and retromer in hypothalamic regulated secretion

Intracellular protein trafficking and sorting are extremely arduous in endocrine and neuroendocrine cells, which synthesize and secrete on-demand substantial quantities of proteins. To ensure that neuroendocrine secretion operates correctly, each step in the secretion pathways is tightly regulated and coordinated both spatially and temporally. At the trans-Golgi network (TGN), intrinsic structural features of proteins and several sorting mechanisms and distinct signals direct newly synthesized proteins into proper membrane vesicles that enter either constitutive or regulated secretion pathways. Furthermore, this anterograde transport is counterbalanced by retrograde transport, which not only maintains membrane homeostasis but also recycles various proteins that function in the sorting of secretory cargo, formation of transport intermediates, or retrieval of resident proteins of secretory organelles. The retromer complex recycles proteins from the endocytic pathway back to the plasma membrane or TGN and was recently identified as a critical player in regulated secretion in the hypothalamus. Furthermore, melanoma antigen protein L2 (MAGEL2) was discovered to act as a tissue-specific regulator of the retromer-dependent endosomal protein recycling pathway and, by doing so, ensures proper secretory granule formation and maturation. MAGEL2 is a mammalian-specific and maternally imprinted gene implicated in Prader-Willi and Schaaf-Yang neurodevelopmental syndromes. In this review, we will briefly discuss the current understanding of the regulated secretion pathway, encompassing anterograde and retrograde traffic. Although our understanding of the retrograde trafficking and sorting in regulated secretion is not yet complete, we will review recent insights into the molecular role of MAGEL2 in hypothalamic neuroendocrine secretion and how its dysregulation contributes to the symptoms of Prader-Willi and Schaaf-Yang patients. Given that the activation of many secreted proteins occurs after they enter secretory granules, modulation of the sorting efficiency in a tissue-specific manner may represent an evolutionary adaptation to environmental cues.

Receptor Recycling by Retromer

The highly conserved retromer complex controls the fate of hundreds of receptors that pass through the endolysosomal system and is a central regulatory node for diverse metabolic programs. More than 20 years ago, retromer was discovered as an essential regulator of endosome-to-Golgi transport in yeast; since then, significant progress has been made to characterize how metazoan retromer components assemble to enable its engagement with endosomal membranes, where it sorts cargo receptors from endosomes to the trans-Golgi network or plasma membrane through recognition of sorting motifs in their cytoplasmic tails. In this review, we examine retromer regulation by exploring its assembled structure with an emphasis on how a range of adaptor proteins shape the process of receptor trafficking. Specifically, we focus on how retromer is recruited to endosomes, selects cargoes, and generates tubulovesicular carriers that deliver cargoes to target membranes. We also examine how cells adapt to distinct metabolic states by coordinating retromer expression and function. We contrast similarities and differences between retromer and its related complexes: retriever and commander/CCC, as well as their interplay in receptor trafficking. We elucidate how loss of retromer regulation is central to the pathology of various neurogenerative and metabolic diseases, as well as microbial infections, and highlight both opportunities and cautions for therapeutics that target retromer. Finally, with a focus on understanding the mechanisms that govern retromer regulation, we outline new directions for the field moving forward.

Relating enhancer genetic variation across mammals to complex phenotypes using machine learning

Protein-coding differences between species often fail to explain phenotypic diversity, suggesting the involvement of genomic elements that regulate gene expression such as enhancers. Identifying associations between enhancers and phenotypes is challenging because enhancer activity can be tissue-dependent and functionally conserved despite low sequence conservation. We developed the Tissue-Aware Conservation Inference Toolkit (TACIT) to associate candidate enhancers with species' phenotypes using predictions from machine learning models trained on specific tissues. Applying TACIT to associate motor cortex and parvalbumin-positive interneuron enhancers with neurological phenotypes revealed dozens of enhancer-phenotype associations, including brain size-associated enhancers that interact with genes implicated in microcephaly or macrocephaly. TACIT provides a foundation for identifying enhancers associated with the evolution of any convergently evolved phenotype in any large group of species with aligned genomes.

The role of autophagy in viral infections

Autophagy is an evolutionarily conserved catabolic cellular process that exerts antiviral functions during a viral invasion. However, co-evolution and co-adaptation between viruses and autophagy have armed viruses with multiple strategies to subvert the autophagic machinery and counteract cellular antiviral responses. Specifically, the host cell quickly initiates the autophagy to degrade virus particles or virus components upon a viral infection, while cooperating with anti-viral interferon response to inhibit the virus replication. Degraded virus-derived antigens can be presented to T lymphocytes to orchestrate the adaptive immune response. Nevertheless, some viruses have evolved the ability to inhibit autophagy in order to evade degradation and immune responses. Others induce autophagy, but then hijack autophagosomes as a replication site, or hijack the secretion autophagy pathway to promote maturation and egress of virus particles, thereby increasing replication and transmission efficiency. Interestingly, different viruses have unique strategies to counteract different types of selective autophagy, such as exploiting autophagy to regulate organelle degradation, metabolic processes, and immune responses. In short, this review focuses on the interaction between autophagy and viruses, explaining how autophagy serves multiple roles in viral infection, with either proviral or antiviral functions.

The emerging roles of retromer and sorting nexins in the life cycle of viruses

Retromer and sorting nexins (SNXs) transport cargoes from endosomes to the trans-Golgi network or plasma membrane. Recent studies have unveiled the emerging roles for retromer and SNXs in the life cycle of viruses, including members of Coronaviridae, Flaviviridae and Retroviridae. Key components of retromer/SNXs, such as Vps35, Vps26, SNX5 and SNX27, can affect multiple steps of the viral life cycle, including facilitating the entry of viruses into cells, participating in viral replication, and promoting the assembly of virions. Here we present a comprehensive updated review on the interplay between retromer/SNXs and virus, which will shed mechanistic insights into controlling virus infection.

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Retromer/SNXs could regulate viral infection directly or indirectly.

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Retromer/SNXs plays an important role for SARS-CoV-2 infection.

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HPV entry is mediated by retromer/SNXs.

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Retromer is required for HCV replication.

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Retromer affects the late step of HIV replication.

Impaired Retrograde Transport Due to Lack of TBC1D5 Contributes to the Trafficking Defect of Lysosomal Cathepsins in Ischemic/Hypoxic Cardiomyocytes

Lysosomal dysfunction has been found in many pathological conditions, and methods to improve lysosomal function have been reported to be protective against infarcted hearts. However, the mechanisms underlying lysosomal dysfunction caused by ischemic injury are far less well-established. The retromer complex is implicated in the trafficking of cation-independent mannose 6-phosphate receptor (CI-MPR), which is an important protein tag for the proper transport of lysosomal contents and therefore is important for the maintenance of lysosomal function. In this study, we found that the function of retrograde transport in cardiomyocytes was impaired with ischemia/hypoxia (I/H) treatment, which resulted in a decrease in CI-MPR and an abnormal distribution of lysosomal cathepsins. I/H treatment caused a reduction in TBC1D5 and a blockade of the Rab7 membrane cycle, which impeded retromer binding to microtubules and motor proteins, resulting in an impairment of retrograde transport and a decrease in CI-MPR. We also established that TBC1D5 was an important regulator of the distribution of lysosomal cathepsins. Our findings shed light on the regulatory role of retromer in ischemic injury and uncover the regulatory mechanism of TBC1D5 over retromer.

Traptamer screening: a new functional genomics approach to study virus entry and other cellular processes

Historically, the genetic analysis of mammalian cells entailed the isolation of randomly arising mutant cell lines with altered properties, followed by laborious genetic mapping experiments to identify the mutant gene responsible for the phenotype. In recent years, somatic cell genetics has been revolutionized by functional genomics screens, in which expression of every protein-coding gene is systematically perturbed, and the phenotype of the perturbed cells is determined. We outline here a novel functional genomics screening strategy that differs fundamentally from commonly used approaches. In this strategy, we express libraries of artificial transmembrane proteins named traptamers and select rare cells with the desired phenotype because, by chance, a traptamer specifically perturbs the expression or activity of a target protein. Active traptamers are then recovered from the selected cells and can be used as tools to dissect the biological process under study. We also briefly describe how we have used this new strategy to provide insights into the complex process by which human papillomaviruses enter cells.

Assessing the Genetic Background and Selection Signatures of Huaxi Cattle Using High-Density SNP Array

Huaxi cattle, a specialized beef cattle breed in China, has the characteristics of fast growth, high slaughter rate, and net meat rate, good reproductive performance, strong stress resistance, and wide adaptability. In this study, we evaluated the genetic diversity, population structure, and genetic relationships of Huaxi cattle and its ancestor populations at the genome-wide level, as well as detecting the selection signatures of Huaxi cattle. Principal component analysis (PCA) and phylogenetic analysis revealed that Huaxi cattle were obviously separated from other cattle populations. The admixture analysis showed that Huaxi cattle has distinct genetic structures among all populations at K = 4. It can be concluded that Huaxi cattle has formed its own unique genetic features. Using integrated haplotype score (iHS) and composite likelihood ratio (CLR) methods, we identified 143 and 199 potentially selected genes in Huaxi cattle, respectively, among which nine selected genes (KCNK1, PDLIM5, CPXM2, CAPN14, MIR2285D, MYOF, PKDCC, FOXN3, and EHD3) related to ion binding, muscle growth and differentiation, and immunity were detected by both methods. Our study sheds light on the unique genetic feature and phylogenetic relationship of Huaxi cattle, provides a basis for the genetic mechanism analysis of important economic traits, and guides further intensive breeding improvement of Huaxi cattle.

Rab7b regulates dendritic cell migration by linking lysosomes to the actomyosin cytoskeleton

Lysosomal signaling facilitates the migration of immune cells by releasing Ca²⁺ to activate the actin-based motor myosin II at the cell rear. However, how the actomyosin cytoskeleton physically associates to lysosomes is unknown. We have previously identified myosin II as a direct interactor of Rab7b, a small GTPase that mediates the transport from late endosomes/lysosomes to the trans-Golgi network (TGN). Here, we show that Rab7b regulates the migration of dendritic cells (DCs) in one- and three-dimensional environments. DCs are immune sentinels that transport antigens from peripheral tissues to lymph nodes to activate T lymphocytes and initiate adaptive immune responses. We found that the lack of Rab7b reduces myosin II light chain phosphorylation and the activation of the transcription factor EB (TFEB), which controls lysosomal signaling and is required for fast DC migration. Furthermore, we demonstrate that Rab7b interacts with the lysosomal Ca²⁺ channel TRPML1 (also known as MCOLN1), enabling the local activation of myosin II at the cell rear. Taken together, our findings identify Rab7b as the missing physical link between lysosomes and the actomyosin cytoskeleton, allowing control of immune cell migration through lysosomal signaling.

This article has an associated First Person interview with the first author of the paper.

Summary: The small GTPase Rab7b bridges the lysosomal Ca²⁺ channel TRPML1 to myosin II, thus enabling the local activation of myosin II at the cell rear and promoting fast migration of dendritic cells.

Who's in control? Principles of Rab GTPase activation in endolysosomal membrane trafficking and beyond

The eukaryotic endomembrane system consists of multiple interconnected organelles. Rab GTPases are organelle-specific markers that give identity to these membranes by recruiting transport and trafficking proteins. During transport processes or along organelle maturation, one Rab is replaced by another, a process termed Rab cascade, which requires at its center a Rab-specific guanine nucleotide exchange factor (GEF). The endolysosomal system serves here as a prime example for a Rab cascade. Along with endosomal maturation, the endosomal Rab5 recruits and activates the Rab7-specific GEF Mon1-Ccz1, resulting in Rab7 activation on endosomes and subsequent fusion of endosomes with lysosomes. In this review, we focus on the current idea of Mon1-Ccz1 recruitment and activation in the endolysosomal and autophagic pathway. We compare identified principles to other GTPase cascades on endomembranes, highlight the importance of regulation, and evaluate in this context the strength and relevance of recent developments in in vitro analyses to understand the underlying foundation of organelle biogenesis and maturation.

Thiazole-Based Thiosemicarbazones: Synthesis, Cytotoxicity Evaluation and Molecular Docking Study

INTRODUCTION

Hybrid drug design has developed as a prime method for the development of novel anticancer therapies that can theoretically solve much of the pharmacokinetic disadvantages of traditional anticancer drugs. Thus a number of studies have indicated that thiazole-thiophene hybrids and their bis derivatives have important anticancer activity. Mammalian Rab7b protein is a member of the Rab GTPase protein family that controls the trafficking from endosomes to the TGN. Alteration in the Rab7b expression is implicated in differentiation of malignant cells, causing cancer.

METHODS

1-(4-Methyl-2-(2-(1-(thiophen-2-yl) ethylidene) hydrazinyl) thiazol-5-yl) ethanone was used as building block for synthesis of novel series of 5-(1-(2-(thiazol-2-yl) hydrazono) ethyl) thiazole derivatives. The bioactivities of the synthesized compounds were evaluated with respect to their antitumor activities against MCF-7 tumor cells using MTT assay. Computer-aided docking protocol was performed to study the possible molecular interactions between the newly synthetic thiazole compounds and the active binding site of the target protein Rab7b. Moreover, the in silico prediction of adsorption, distribution, metabolism, excretion (ADME) and toxicity (T) properties of synthesized compounds were carried out using admetSAR tool.

RESULTS

The results obtained showed that derivatives 9 and 11b have promising activity (IC50 = 14.6 ± 0.8 and 28.3 ± 1.5 µM, respectively) compared to Cisplatin (IC50 = 13.6 ± 0.9 µM). The molecular docking analysis reveals that the synthesized compounds are predicted to be fit into the binding site of the target Rab7b. In summary, the synthetic thiazole compounds 1-17 could be used as potent inhibitors as anticancer drugs.

CONCLUSION

Promising anticancer activity of compounds 9 and 11 compared with cisplatin reference drug suggests that these ligands may contribute as lead compounds in search of new anticancer agents to combat chemo-resistance.

Novel autophagic vacuolar myopathies: Phenotype and genotype features

BACKGROUND

Autophagic vacuolar myopathies (AVMs) are an emerging group of heterogeneous myopathies sharing histopathological features on muscle pathology, in which autophagic vacuoles are the pathognomonic morphologic hallmarks. Glycogen storage disease type II (GSDII) caused by lysosomal acid α-glucosidase (GAA) deficiency is the best-characterised AVM.

AIMS

This study aimed to investigate the mutational profiling of seven neuromuscular outpatients sharing clinical, myopathological and biochemical findings with AVMs.

METHODS

We applied a diagnostic protocol, recently published by our research group for suspected late-onset GSDII (LO-GSDII), including counting PAS-positive lymphocytes on blood smears, dried blood spot (DBS)-GAA, muscle biopsy histological and immunofluorescence studies, GAA activity assay and expression studies on muscle homogenate, GAA sequencing, GAA multiplex ligation-dependent probe amplification (MLPA) and whole exome sequencing (WES).

RESULTS

The patients had a limb girdle-like muscular pattern with persistent hyperCKaemia; vacuolated PAS-positive lymphocytes, glycogen accumulation and impaired autophagy at muscle biopsy. Decreased GAA activity was also measured. While GAA sequencing identified no pathogenic mutations, WES approach allowed us to identify for each patient an unexpected mutational pattern in genes cooperating in lysosomal-autophagic machinery, some of which have never been linked to human diseases.

CONCLUSIONS

Our data suggest that reduced GAA activity may occur in any condition of impaired autophagy and that WES approach is advisable in all genetically undefined cases of autophagic myopathy. Therefore, deficiency of GAA activity and PAS-positive lymphocytes should be considered as AVM markers together with LC3/p62-positive autophagic vacuoles.

Specific TBC Domain-Containing Proteins Control the ER-Golgi-Plasma Membrane Trafficking of GPCRs

G-protein-coupled receptors (GPCRs) constitute the largest superfamily of cell surface signaling proteins. However, the molecular mechanisms underlying their cell surface delivery after synthesis remain poorly understood. Here, we screen the TBC domain-containing proteins, putative Rab GTPase-activating proteins (GAPs), in the intracellular trafficking of GPCRs and identify several TBC proteins that activity-dependently regulate the anterograde transport, en route from the endoplasmic reticulum to the Golgi or from the Golgi to the cell surface, of several prototypic GPCR members without affecting other plasma membrane proteins. We also show that TBC1D6 functions as a GAP for Rab26, physically associates with Rab26, and attenuates Rab26 interaction with GPCRs. Furthermore, both overexpression and depletion of TBC1D6 inhibit the post-Golgi traffic of GPCRs. These data demonstrate important roles of the TBC proteins in forward trafficking of nascent GPCRs and reveal regulatory mechanisms of GPCR targeting to the functional destination.

Wei et al. report that several TBC proteins specifically and activity-dependently regulate ER-Golgi-plasma membrane transport of nascent GPCRs. They also show that TBC1D6 is a GAP for Rab26 and controls GPCR post-Golgi traffic. Their results reveal crucial roles of TBC proteins in and provide regulatory mechanisms of GPCR trafficking.

TBC1D5-Catalyzed Cycling of Rab7 Is Required for Retromer-Mediated Human Papillomavirus Trafficking during Virus Entry

During virus entry, human papillomaviruses are sorted by the cellular trafficking complex, called retromer, into the retrograde transport pathway to traffic from the endosome to downstream cellular compartments, but regulation of retromer activity during HPV entry is poorly understood. Here we selected artificial proteins that modulate cellular proteins required for HPV infection and discovered that entry requires TBC1D5, a retromer-associated, Rab7-specific GTPase-activating protein. Binding of retromer to the HPV L2 capsid protein recruits TBC1D5 to retromer at the endosome membrane, which then stimulates hydrolysis of Rab7-GTP to drive retromer disassembly from HPV and delivery of HPV to the retrograde pathway. Although the cellular retromer cargos CIMPR and DMT1-II require only GTP-bound Rab7 for trafficking, HPV trafficking requires cycling between GTP- and GDP-bound Rab7. Thus, ongoing cargo-induced membrane recruitment, assembly, and disassembly of retromer complexes drive HPV trafficking.

Structure of TBC1D23 N-terminus reveals a novel role for rhodanese domain

Members of the Tre2-Bub2-Cdc16 (TBC) family often function to regulate membrane trafficking and to control signaling transductions pathways. As a member of the TBC family, TBC1D23 is critical for endosome-to-Golgi cargo trafficking by serving as a bridge between Golgi-bound golgin-97/245 and the WASH/FAM21 complex on endosomal vesicles. However, the exact mechanisms by which TBC1D23 regulates cargo transport are poorly understood. Here, we present the crystal structure of the N-terminus of TBC1D23 (D23N), which consists of both the TBC and rhodanese domains. We show that the rhodanese domain is unlikely to be an active sulfurtransferase or phosphatase, despite containing a putative catalytic site. Instead, it packs against the TBC domain and forms part of the platform to interact with golgin-97/245. Using the zebrafish model, we show that impacting golgin-97/245-binding, but not the putative catalytic site, impairs neuronal growth and brain development. Altogether, our studies provide structural and functional insights into an essential protein that is required for organelle-specific trafficking and brain development.

The secreted protein kinase CstK from Coxiella burnetii influences vacuole development and interacts with the GTPase-activating host protein TBC1D5

The intracellular bacterial pathogen Coxiella burnetii is the etiological agent of the emerging zoonosis Q fever. Crucial to its pathogenesis is type 4b secretion system-mediated secretion of bacterial effectors into host cells that subvert host cell membrane trafficking, leading to the biogenesis of a parasitophorous vacuole for intracellular replication. The characterization of prokaryotic serine/threonine protein kinases in bacterial pathogens is emerging as an important strategy to better understand host-pathogen interactions. In this study, we investigated CstK (for Coxiella Ser/Thr kinase), a protein kinase identified in C. burnetii by in silico analysis. We demonstrate that this putative protein kinase undergoes autophosphorylation on Thr and Tyr residues and phosphorylates a classical eukaryotic protein kinase substrate in vitro This dual Thr-Tyr kinase activity is also observed for a eukaryotic dual-specificity Tyr phosphorylation-regulated kinase class. We found that CstK is translocated during infections and localizes to Coxiella-containing vacuoles (CCVs). Moreover, a CstK-overexpressing C. burnetii strain displayed a severe CCV development phenotype, suggesting that CstK fine-tunes CCV biogenesis during the infection. Protein-protein interaction experiments identified the Rab7 GTPase-activating protein TBC1D5 as a candidate CstK-specific target, suggesting a role for this host GTPase-activating protein in Coxiella infections. Indeed, CstK co-localized with TBC1D5 in noninfected cells, and TBC1D5 was recruited to CCVs in infected cells. Accordingly, TBC1D5 depletion from infected cells significantly affected CCV development. Our results indicate that CstK functions as a bacterial effector protein that interacts with the host protein TBC1D5 during vacuole biogenesis and intracellular replication.

Papillomaviruses Go Retro

Human papillomaviruses are important pathogens responsible for approximately 5% of cancer as well as other important human diseases, but many aspects of the papillomavirus life cycle are poorly understood. To undergo genome replication, HPV DNA must traffic from the cell surface to the nucleus. Recent findings have revolutionized our understanding of HPV entry, showing that it requires numerous cellular proteins and proceeds via a series of intracellular membrane-bound vesicles that comprise the retrograde transport pathway. This paper reviews the evidence supporting this unique entry mechanism with a focus on the crucial step by which the incoming virus particle is transferred from the endosome into the retrograde pathway. This new understanding provides novel insights into basic cellular biology and suggests novel rational approaches to inhibit HPV infection.

Endosome-to-TGN Trafficking: Organelle-Vesicle and Organelle-Organelle Interactions

Retrograde transport from endosomes to the trans-Golgi network (TGN) diverts proteins and lipids away from lysosomal degradation. It is essential for maintaining cellular homeostasis and signaling. In recent years, significant advancements have been made in understanding this classical pathway, revealing new insights into multiple steps of vesicular trafficking as well as critical roles of ER-endosome contacts for endosomal trafficking. In this review, we summarize up-to-date knowledge about this trafficking pathway, in particular, mechanisms of cargo recognition at endosomes and vesicle tethering at the TGN, and contributions of ER-endosome contacts.

PEBP1/RKIP behavior: a mirror of actin-membrane organization

Phosphatidylethanolamine-binding protein 1 (PEBP1), a small 21 kDa protein, is implicated in several key processes of the living cell. The deregulation of PEBP1, especially its downregulation, leads to major diseases such as cancer and Alzheimer's disease. PEBP1 was found to interact with numerous proteins, especially kinases and GTPases, generally inhibiting their activity. To understand the basic functionality of this amazing small protein, we have considered several known processes that it modulates and we have discussed the role of each molecular target in these processes. Here, we propose that cortical actin organization, associated with membrane changes, is involved in the majority of the processes modulated by PEBP1. Furthermore, based on recent data, we summarize some key PEBP1-interacting proteins, and we report their respective functions and focus on their relationships with actin organization. We suggest that, depending on the cell status and environment, PEBP1 is an organizer of the actin-membrane composite material.

Screening and analysis of small molecular peptides in urine of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is a common clinical disease with complicated clinical process and harmful effects on pregnant women and fetus. The purpose of this study is to use the convenient urine samples in combination with glucose levels to detect or predict GDM. In this study, urine samples of non-pregnant women, normal pregnant women and GDM patients were collected. The peptides in urine were enriched by weak cationic exchange magnetic beads (MB-WCX) and analyzed by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). 46 polypeptide peaks with statistical difference (P < 0.01) were screened out by using Bioexplorer analysis software. The level of molecules with mass-to-charge ratio of 1079.2, 1290.6 and 1500.7 was higher in the GDM group than the other two groups. Through the analysis of differential molecules by liquid chromatography tandem mass spectrometry (LC-MS), the above molecules were identified as coagulation factor IX, TBC1 family member 5 isoform a [Homo sapiens] (TBC1D5a) and immunoglobulin kappa constant. The discovery of polypeptides provides the research basis for further primary screening and assistant diagnosis of GDM through urine samples.

Lysosomal size matters

Lysosomes are key cellular catabolic centers that also perform fundamental metabolic, signaling and quality control functions. Lysosomes are not static and they respond dynamically to intra‐ and extracellular stimuli triggering changes in organelle numbers, size and position. Such physical changes have a strong impact on lysosomal activity ultimately influencing cellular homeostasis. In this review, we summarize the current knowledge on lysosomal size regulation, on its physiological role(s) and association to several disease conditions.

Interaction between VPS35 and RABG3f is necessary as a checkpoint to control fusion of late compartments with the vacuole

Vacuoles are essential organelles in plants, playing crucial roles, such as cellular material degradation, ion and metabolite storage, and turgor maintenance. Vacuoles receive material via the endocytic, secretory, and autophagic pathways. Membrane fusion is the last step during which prevacuolar compartments (PVCs) and autophagosomes fuse with the vacuole membrane (tonoplast) to deliver cargoes. Protein components of the canonical intracellular fusion machinery that are conserved across organisms, including Arabidopsis thaliana, include complexes, such as soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), that catalyze membrane fusion, and homotypic fusion and vacuole protein sorting (HOPS), that serve as adaptors which tether cargo vesicles to target membranes for fusion under the regulation of RAB-GTPases. The mechanisms regulating the recruitment and assembly of tethering complexes are not well-understood, especially the role of RABs in this dynamic regulation. Here, we report the identification of the small synthetic molecule Endosidin17 (ES17), which interferes with synthetic, endocytic, and autophagic traffic by impairing the fusion of late endosome compartments with the tonoplast. Multiple independent target identification techniques revealed that ES17 targets the VPS35 subunit of the retromer tethering complex, preventing its normal interaction with the Arabidopsis RAB7 homolog RABG3f. ES17 interference with VPS35-RABG3f interaction prevents the retromer complex to endosome anchoring, resulting in retention of RABG3f. Using multiple approaches, we show that VPS35-RABG3f-GTP interaction is necessary to trigger downstream events like HOPS complex assembly and fusion of late compartments with the tonoplast. Overall, our results support a role for the interaction of RABG3f-VPS35 as a checkpoint in the control of traffic toward the vacuole.

VPS29, a tweak tool of endosomal recycling

The endolysosomal system is a highly dynamic network of membranes for degradation and recycling. During endosomal maturation, cargo molecules destined for lysosomal degradation are progressively concentrated through continuous rounds of fusion and fission reactions concomitant with inbound and outbound membrane fluxes. Of the cargo molecules delivered to endosomes, about two-thirds are rescued from degradation and recycled for reuse. This balance between degradation and recycling is essential to preserve the proteostatic plasticity of the cell under variable physiological demands. Cargo retrieval from endosomes involves several sorting complexes with stable core compositions that associate with multidomain regulatory proteins, consequently displaying complex interaction networks. The vacuolar protein sorting 29 (VPS29) has emerged as a central scaffold that coordinates the physical assembly of retrieval complexes with regulatory components in what appears to be an elegant solution for regulating distinct retrieval stations. This review summarizes the VPS29-binding partners and its integration into retrieval complexes for endosomal sorting and trafficking.

Rab regulation by GEFs and GAPs during membrane traffic

Rab GTPases and their regulatory proteins play a crucial role in vesicle-mediated membrane trafficking. During vesicle membrane tethering Rab GTPases are activated by GEFs (guanine nucleotide exchange factors) and then inactivated by GAPs (GTPase activating proteins). Recent evidence shows that in addition to activating and inactivating Rab GTPases, both Rab GEFs and GAPs directly contribute to membrane tethering events during vesicle traffic. Other studies have extended the range of processes, in which Rabs function, and revealed roles for Rabs and their GAPs in the regulation of autophagy. Here, we will discuss these advances and the emerging relationship between the domain architectures of Rab GEFs and vesicle coat protein complexes linked with GTPases of the Sar, ARF and Arl families in animal cells.

Multiple Roles of Rab GTPases at the Golgi

The Golgi apparatus is a central sorting station in the cell. It receives newly synthesized molecules from the endoplasmic reticulum and directs them to different subcellular destinations, such as the plasma membrane or the endocytic pathway. Importantly, in the last few years, it has emerged that the maintenance of Golgi structure is connected to the proper regulation of membrane trafficking. Rab proteins are small GTPases that are considered to be the master regulators of the intracellular membrane trafficking. Several of the over 60 human Rabs are involved in the regulation of transport pathways at the Golgi as well as in the maintenance of its architecture. This chapter will summarize the different roles of Rab GTPases at the Golgi, both as regulators of membrane transport, scaffold, and tethering proteins and in preserving the structure and function of this organelle.

First person – Marita Borg Distefano

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Marita Borg Distefano is the first author on ‘TBC1D5 controls the GTPase cycle of Rab7b’, published in Journal of Cell Science. Marita is a researcher in the labs of Oddmund Bakke and Cinzia Progida at the University of Oslo, Norway, investigating intracellular trafficking, Rab proteins and cell migration.