Rab Proteins, Connecting Transport and Vesicle Fusion

Tight junction proteins in glial tumors development and progression

Tight junctions form a paracellular barrier in epithelial and endothelial cells, and they regulate the diffusion of fluids, molecules, and the penetration of cells across tissue compartments. Tight junctions are composed of a group of integral membrane proteins, which include the claudin family, tight junction-associated Marvel protein family, junctional adhesion molecule family, and proteins that anchor the cytoskeleton, such as zonula occludens proteins and the cingulin family. Several factors, such as neurotransmitters or cytokines, and processes like ischemia/hypoxia, inflammation, tumorigenesis, phosphorylation/dephosphorylation, ubiquitination, and palmitoylation, regulate tight junction proteins. Claudins are involved in tumorigenesis processes that lead to glioma formation. In gliomas, there is a noticeable dysregulation of claudins, occludin, and zonula occludens-1 abundance, and their dislocation has been observed. The weakening of intercellular adhesion and cell detachment is responsible for glioma infiltration into surrounding tissues. Furthermore, the paracellular permeability of the blood-brain barrier, formed with the involvement of tight junction proteins, influences the development of peritumoral edema - and, simultaneously, the rate of drug delivery to the glial tumor. Understanding the junctional and paracellular environments in brain tumors is crucial to predicting glial tumor progression and the feasibility of chemotherapeutic drug delivery. This knowledge may also illuminate differences between high and low-grade gliomas.

Bactericidal ability of target acidic phospholipids and phagocytosis of CDC42 GTPase-mediated cytoskeletal rearrangement underlie functional conservation of CXCL12 in vertebrates

Chemokine CXCL12 plays a crucial role in both direct bactericidal activity and phagocytosis in humans. However, the mechanisms and evolutionary functions of these processes in vertebrates remain largely unknown. In this study, we found that the direct bactericidal activity of CXCL12 is highly conserved across various vertebrate lineages, including Arctic lamprey (Lampetra japonica), Basking shark (Cetorhinus maximus), grass carp (Ctenopharyngodon idella), Western clawed frog (Xenopus tropicalis), Green anole (Anolis carolinensis), chicken (Gallus gallus), and human (Homo sapiens). CXCL12 also has been shown to promote phagocytosis in lower and higher vertebrates. We then employed C. idella CXCL12a (CiCXCL12a) as a model to further investigate its immune functions and underlying mechanisms. CiCXCL12a exerts direct broad-spectrum antibacterial activity by targeting bacterial acidic phospholipids, resulting in bacterial cell membrane perforation, and eventual lysis. Monocytes/macrophages are attracted to the infection sites for phagocytosis through the rapid production of CiCXCL12a during bacterial infection. CiCXCL12a induces CDC42 and CDC42 GTPase activation, which in turn mediates F-actin polymerization and cytoskeletal rearrangement. The interaction between F-actin and Aeromonas hydrophila facilitates bacterial internalization into monocytes/macrophages. Additionally, A. hydrophila is colocalized within early endosomes, late endosomes and lysosomes, ultimately degrading within phagolysosomes. CiCXCL12a also activates PI3K-AKT, JAK-STAT5 and MAPK-ERK signaling pathways. Notably, only the PI3K-AKT signaling pathway inhibits LPS-induced monocyte/macrophage apoptosis. Thus, CiCXCL12a plays key roles in reducing tissue bacterial loads, attenuating organ injury, and decreasing mortality rates. Altogether, our findings elucidate the conserved mechanisms underlying CXCL12-mediated bactericidal activity and phagocytosis, providing novel perspectives into the immune functions of CXCL12 in vertebrates.

Rab7 GTPase, a direct target of miR-131-3p, limits intracellular Spiroplasma eriocheiris infection by modulating phagocytosis

Spiroplasma eriocheiris is a kind of intracellular pathogen without cell wall and the causative agent of Chinese mitten crab Eriocheir sinensis "tremor disease", which causes significant economic losses in the crustacean aquaculture. However, little is known about the intracellular transport of this pathogen and host innate immune response to this pathogen. Rab GTPases are key regulators for endocytosis and intracellular pathogen trafficking. In this study, we showed that S. eriocheiris infection upregulated the transcription of Rab7 through the downregulation of miR-131-3p. Subsequently, both hemocytes transfected with miR-131-3p mimics and hemocytes derived from Rab7 knockdown crabs exhibited reduced phagocytic activities and increased susceptibility to S. eriocheiris infection. Additionally, Rab7 could interact with the cell shape-determining protein MreB3 of S. eriocheiris, and its overexpression promoted S. eriocheiris internalization and fusion with lysosomes, thereby limiting S. eriocheiris replication in Drosophila S2 cells. Overall, these results demonstrated that Rab7 facilitated host cell phagocytosis and interacted with MreB3 of S. eriocheiris to prevent S. eriocheiris infection. Moreover, miR-131-3p was identified as a negative regulator of this process through its targeting of Rab7. Therefore, targeting miR-131-3p might be an effective strategy for controlling S. eriocheiris in crab aquaculture.

Rab4b Promotes Cytolethal Distending Toxin from Glaesserella parasuis-Induced Cytotoxicity in PK-15 Cells

Glaesserella parasuis cytolethal distending toxin (GpCDT) can induce cell cycle arrest and apoptosis. Our laboratory's previous work demonstrated that GTPase 4b (Rab4b) is a key host protein implicated in GpCDT-induced cytotoxicity. This study investigated the probable involvement of Rab4b in the process. Our study used CRISPR/Cas9 technology to create a Rab4b-knockout cell line. The results showed greater resistance to GpCDT-induced cell cytotoxicity. In contrast, forced Rab4b overexpression increased GpCDT-induced cytotoxicity. Further immunoprecipitation study reveals that GpCDT may bind with Rab4b. In PK-15 cells, GpCDT is transported to the early endosomes and late endosomes, while after knocking out Rab4b, GpCDT cannot be transported to the early endosome via vesicles. Rab4b appears essential for GpCDT-induced cytotoxicity in PK-15 cells.

The Rab6 post-Golgi secretory pathway contributes to herpes simplex virus 1 (HSV-1) egress

Herpes simplex virus 1 (HSV-1) is an alpha herpesvirus that infects a majority of the world population. The mechanisms and cellular host factors involved in the intracellular transport and exocytosis of HSV-1 particles are not fully understood. To elucidate these late steps in the replication cycle, we developed a live-cell fluorescence microscopy assay of HSV-1 virion intracellular trafficking and exocytosis. This method allows us to track individual virus particles and identify the precise moment and location of particle exocytosis using a pH-sensitive reporter. We show that HSV-1 uses the host cell's post-Golgi secretory pathway during egress. The small GTPase, Rab6, binds to nascent secretory vesicles at the trans-Golgi network and plays important, but non-essential, roles in vesicle traffic and exocytosis at the plasma membrane, therefore making it a useful marker of the Golgi and post-Golgi secretory pathway. We show that HSV-1 particles colocalize with Rab6a in the region of the Golgi, cotraffic with Rab6a to the cell periphery, and undergo exocytosis from Rab6a vesicles. Consistent with previous reports, we find that HSV-1 particles accumulate at preferential egress sites in infected cells. The secretory pathway mediates this preferential/polarized egress, since Rab6a vesicles accumulate near the plasma membrane similarly in uninfected cells. These data suggest that, following particle envelopment, HSV-1 egress follows a pre-existing cellular secretory pathway to exit infected cells rather than novel, virus-induced mechanisms.

IMPORTANCE

Herpes simplex virus 1 (HSV-1) infects a majority of people. It establishes a life-long latent infection and occasionally reactivates, typically causing characteristic oral or genital lesions. Rarely in healthy natural hosts, but more commonly in zoonotic infections and in elderly, newborn, or immunocompromised patients, HSV-1 can cause severe herpes encephalitis. The precise cellular mechanisms used by HSV-1 remain an important area of research. In particular, the egress pathways that newly assembled virus particles use to exit from infected cells are unclear. In this study, we used fluorescence microscopy to visualize individual virus particles exiting from cells and found that HSV-1 particles use the pre-existing cellular secretory pathway.

Potential Effects of Hyperglycemia on SARS-CoV-2 Entry Mechanisms in Pancreatic Beta Cells

The COVID-19 pandemic has revealed a bidirectional relationship between SARS-CoV-2 infection and diabetes mellitus. Existing evidence strongly suggests hyperglycemia as an independent risk factor for severe COVID-19, resulting in increased morbidity and mortality. Conversely, recent studies have reported new-onset diabetes following SARS-CoV-2 infection, hinting at a potential direct viral attack on pancreatic beta cells. In this review, we explore how hyperglycemia, a hallmark of diabetes, might influence SARS-CoV-2 entry and accessory proteins in pancreatic β-cells. We examine how the virus may enter and manipulate such cells, focusing on the role of the spike protein and its interaction with host receptors. Additionally, we analyze potential effects on endosomal processing and accessory proteins involved in viral infection. Our analysis suggests a complex interplay between hyperglycemia and SARS-CoV-2 in pancreatic β-cells. Understanding these mechanisms may help unlock urgent therapeutic strategies to mitigate the detrimental effects of COVID-19 in diabetic patients and unveil if the virus itself can trigger diabetes onset.

A novel noncanonical function for IRF6 in the recycling of E-cadherin

Interferon Regulatory Factor 6 (IRF6) is a transcription factor essential for keratinocyte cell-cell adhesions. Previously, we found that recycling of E-cadherin was defective in the absence of IRF6, yet total E-cadherin levels were not altered, suggesting a previously unknown, nontranscriptional function for IRF6. IRF6 protein contains a DNA binding domain (DBD) and a protein binding domain (PBD). The transcriptional function of IRF6 depends on its DBD and PBD, however, whether the PBD is necessary for the interaction with cytoplasmic proteins has yet to be demonstrated. Here, we show that an intact PBD is required for recruitment of cell-cell adhesion proteins at the plasma membrane, including the recycling of E-cadherin. Colocalizations and coimmunoprecipitations reveal that IRF6 forms a complex in recycling endosomes with Rab11, Myosin Vb, and E-cadherin, and that the PBD is required for this interaction. These data indicate that IRF6 is a novel effector of the endosomal recycling of E-cadherin and demonstrate a non-transcriptional function for IRF6 in regulating cell-cell adhesions.

Deacylases-structure, function, and relationship to diseases

Reversible S-acylation plays a pivotal role in various biological processes, modulating protein functions such as subcellular localization, protein stability/activity, and protein-protein interactions. These modifications are mediated by acyltransferases and deacylases, among which the most abundant modification is S-palmitoylation. Growing evidence has shown that this rivalrous pair of modifications, occurring in a reversible cycle, is essential for various biological functions. Aberrations in this process have been associated with various diseases, including cancer, neurological disorders, and immune diseases. This underscores the importance of studying enzymes involved in acylation and deacylation to gain further insights into disease pathogenesis and provide novel strategies for disease treatment. In this Review, we summarize our current understanding of the structure and physiological function of deacylases, highlighting their pivotal roles in pathology. Our aim is to provide insights for further clinical applications.

Salvia miltiorrhiza polysaccharide promotes the health of crayfish (Procambarus clarkii) by promoting hemocyte phagocytosis, protecting hepatopancreas and enhancing intestinal barrier function

Plant polysaccharides as immunomodulators are considered one of the effective measures to reduce antibiotic therapy in aquaculture. The immunomodulatory function of Salvia miltiorrhiza polysaccharides (SMP) has been demonstrated and begun to be applied in vertebrates, but its potential effect on crustaceans is unclear. In this study, crayfish (Procambarus clarkii) was fed with 0 %, 0.3 %, 0.7 %, 1.1 %, and 1.5 % SMP for 4 weeks to investigate the effects of SMP on hemocytes phagocytosis, hepatopancreatic function, and intestinal barrier function. The results revealed that hemocyte phagocytic activity was increased in all SMP groups. During the process of hemocytes phagocytic recognition and formation of phagosomes and phagolysosomes, the mRNA expression levels of mas, hem, rab3, ctsb, and lamp-1 were up-regulated mainly in the 0.3 % SMP group. During the clearance phase of phagocytosis, respiratory burst activity, ROS level, T-SOD, CAT, GST, and LZM activities were mainly increased in the 1.5 % SMP group. Hepatopancreas AKP and GOT activity were no significant change in all SMP groups. ACP activity was significantly enhanced in the 1.1 % SMP group. The GPT activity of 0.3-0.7 % SMP group was significantly decreased. The 0.7 % SMP group had the highest intestinal fold height. The highest index values of OTUs, Ace, Chao, and Shannon were in the 0.3 % SMP group. The dietary addition of 0.3 % SMP led to a tendency of increased relative abundance of Firmicutes and Bacteroidota at the phylum level, while the relative abundance of Proteobacteria at the phylum level decreased. In conclusion, dietary SMP could promote crayfish health by enhancing phagocytosis, protecting hepatopancreas and enhancing intestinal barrier function. This study contributes to the theoretical foundation for exploring the potential application of plant polysaccharides in crustaceans.

Herpes Simplex Virus 1 (HSV-1) Uses the Rab6 Post-Golgi Secretory Pathway For Viral Egress

Herpes Simplex Virus 1 (HSV-1) is an alpha herpesvirus that infects a majority of the world population. The mechanisms and cellular host factors involved in the intracellular transport and exocytosis of HSV-1 particles are not fully understood. To elucidate these late steps in the replication cycle, we developed a live-cell fluorescence microscopy assay of HSV-1 virion intracellular trafficking and exocytosis. This method allows us to track individual virus particles, and identify the precise moment and location of particle exocytosis using a pH-sensitive reporter. We show that HSV-1 uses the host Rab6 post-Golgi secretory pathway during egress. The small GTPase, Rab6, binds to nascent secretory vesicles at the trans-Golgi network and regulates vesicle trafficking and exocytosis at the plasma membrane. HSV-1 particles colocalize with Rab6a in the region of the Golgi, cotraffic with Rab6a to the cell periphery, and undergo exocytosis from Rab6a vesicles. Consistent with previous reports, we find that HSV-1 particles accumulate at preferential egress sites in infected cells. The Rab6a secretory pathway mediates this preferential/polarized egress, since Rab6a vesicles accumulate near the plasma membrane similarly in uninfected cells. These data suggest that, following particle envelopment, HSV-1 egress follows a pre-existing cellular secretory pathway to exit infected cells rather than novel, virus-induced mechanisms.

Altered G-Protein Transduction Protein Gene Expression in the Testis of Infertile Patients with Nonobstructive Azoospermia

Recent studies have shown that several members of the G-protein-coupled receptors (GPCR) superfamily play crucial roles in the maintenance of ion-water homeostasis of the sperm and Sertoli cells, development of the germ cells, formation of the blood barrier, and maturation of sperm. The GPCR, guanyl-nucleotide exchange factor, membrane traffic protein, and small GTPase genes were analyzed by microarray and bioinformatics (3513 sperm and Sertoli cell genes). In the microarray analyses of three human cases with different nonobstructive azoospermia sperm, the expression of GOLGA8IP, OR2AT4, PHKA1, A2M, OR56A1, SEMA3G, LRRC17, APP, ARHGAP33, RABGEF1, NPY2R, GHRHR, LTB4R2, GRIK5, OR6K6, NAPG, OR6C65, VPS35, FPR3, and ARL4A was upregulated, while expression of MARS, SIRPG, OGFR, GPR150, LRRK1, and NGEF was downregulated. There was an increase in GBP3, GBP3, TNF, TGFB3, and CLTC expression in the Sertoli cells of three human cases with NOA, whereas expression of PAQR4, RRAGD, RAC2, SERPINB8, IRPB1, MRGPRF, RASA2, SIRPG, RGS2, RAP2A, RAB2B, ARL17, SERINC4, XIAP, DENND4C, ANKRA2, CSTA, STX18, and SNAP23 were downregulated. A combined analysis of Enrich Shiny Gene Ontology (GO), STRING, and Cytoscape was used to predict proteins' molecular interactions and then to recognize master pathways. Functional enrichment analysis showed that the biological process (BP), regulation of protein metabolic process, regulation of small GTPase-mediated signal transduction were significantly expressed in up-/downregulated differentially expressed genes (DEGs) in sperm. In molecular function (MF) experiments of DEGs that were up-/downregulated, it was found that GPCR activity, guanyl ribonucleotide binding, GTPase activity and nucleoside-triphosphatase activity were overexpressed. An analysis of GO enrichment findings of Sertoli cells showed BP and MF to be common DEGs. When these gene mutations have been validated, they can be used to create new GPCR antagonists or agonists that are receptor-selective.

Influence of EGF and pro-NGF on EGFR/SORTILIN interaction and clinical impact in head and neck squamous cell carcinoma

Head and Neck Squamous Cell Carcinoma (HNSCC) remains a cancer with a poor prognosis, with a 5-year survival rate of less than 50%. Although epidermal growth factor receptor (EGFR) is almost always overexpressed, targeted anti-EGFR therapies have modest efficacy and are mainly used in palliative care. Growth factors such as Nerve Growth Factor (NGF) and its precursor proNGF have been shown in our laboratory to play a role in tumor growth and aggressiveness. Interestingly, an interaction between Sortilin, a proNGF receptor, and EGFR has been observed. This interaction appears to interfere with the pro-oncogenic signaling of EGF and modulate the membrane expression of EGFR. The aim of this study was to characterize this interaction biologically, to assess its impact on clinical prognosis and to analyze its role in the cellular trafficking of EGFR. Using immunohistochemical staining on tumor sections from patients treated at our university center and PLA (Proximity Ligation Assay) labeling, we showed that Sortilin expression is significantly associated with reduced 5-year survival. However, when Sortilin was associated with EGFR, this association was not found. Using the Cal-27 and Cal-33 cancer cell lines, we observed that proNGF reduces the effects of EGF on cell growth by inducing the internalization of its receptor. These results therefore suggest a regulatory role for Sortilin in the degradation or renewal of EGFR on the membrane. It would be interesting in future work to show the intracellular fate of EGFR and the role of (pro)neurotrophins in these mechanisms.

Paxillin regulates Rab5-mediated vesicle motility through modulating microtubule acetylation

Rab GTPase-mediated vesicle trafficking of cell surface proteins, including integrins, through endocytic and recycling pathways is important in controlling cell-extracellular matrix interactions during cell migration. The focal adhesion adaptor protein, paxillin, plays a central role in regulating adhesion dynamics and was previously shown to promote anterograde vesicle trafficking through modulation of microtubule acetylation via its inhibition of the deacetylase HDAC6. The role of paxillin in retrograde trafficking is unknown. Herein, we identified a role for paxillin in the modulation of the Rab5 GTPase, which is necessary for regulating early endosome dynamics and focal adhesion turnover. Using MDA-MB-231 breast cancer cells and paxillin (-/-) fibroblasts, paxillin was shown to impact Rab5-associated vesicle size and distribution, as well as Rab5 GTPase activity, through its modulation of HDAC6. Using a combination of real-time imaging and particle tracking analysis, paxillin was shown to promote Rab5-associated vesicle motility through inhibition of HDAC6-mediated micro-tubule deacetylation, along with the localization of active integrin to focal adhesions.

Lack of Rab27a attenuates foam cell formation and macrophage inflammation in uremic apolipoprotein E knockout mice

As the most common cardiovascular disease, atherosclerosis (AS), is a leading cause of high mortality in patients with chronic renal failure. Rab27a has been reported to regulate the progression of cardiovascular and renal diseases. Nevertheless, little studies investigated the role and mechanism of Rab27a in uremic-accelerated AS (UAAS). An animal model of UAAS was established in apolipoprotein E knockout (apoE^-/-) mice using 5/6 nephrectomy (NX). We conducted in vitro and in vivo functional experiments to explore the role of Rab27a in UAAS, including the presence of oxidized low-density lipoprotein (ox-LDL). Rab27a expression was upregulated in the plaque tissues of NX apoE^-/- mice. The knockout of Rab27a (Rab27a^-/-) reduced AS-induced artery injury, as manifested by the reductions of plaque area, collagen deposition, inflammation and lipid droplet. Besides, cholesterol efflux was increased, while the expression of lipid metabolism-related proteins and the secretions of pro-inflammatory factors were decreased in ox-LDL-induced NX Rab27a^-/- apoE^-/- mice group. Further, Rab27a deletion inhibited the activation of nuclear factor κB (NF-κB) pathway. In conclusion, our study indicated that Rab27a deficiency attenuated foam cell formation and macrophage inflammation, depending on the NF-κB pathway activation, to inhibit AS progression in uremic apoE^-/- mice. This finding may provide a new targeting strategy for UAAS therapy.

Elucidation of the Cellular Interactome of African Swine Fever Virus Fusion Proteins and Identification of Potential Therapeutic Targets

African swine fever virus (ASFV) encodes more than 150 proteins, most of them of unknown function. We used a high-throughput proteomic analysis to elucidate the interactome of four ASFV proteins, which potentially mediate a critical step of the infection cycle, the fusion and endosomal exit of the virions. Using affinity purification and mass spectrometry, we were able to identify potential interacting partners for those ASFV proteins P34, E199L, MGF360-15R and E248R. Representative molecular pathways for these proteins were intracellular and Golgi vesicle transport, endoplasmic reticulum organization, lipid biosynthesis, and cholesterol metabolism. Rab geranyl geranylation emerged as a significant hit, and also Rab proteins, which are crucial regulators of the endocytic pathway and interactors of both p34 and E199L. Rab proteins co-ordinate a tight regulation of the endocytic pathway that is necessary for ASFV infection. Moreover, several interactors were proteins involved in the molecular exchange at ER membrane contacts. These ASFV fusion proteins shared interacting partners, suggesting potential common functions. Membrane trafficking and lipid metabolism were important categories, as we found significant interactions with several enzymes of the lipid metabolism. These targets were confirmed using specific inhibitors with antiviral effect in cell lines and macrophages.

Porcine Enteric Alphacoronavirus Entry through Multiple Pathways (Caveolae, Clathrin, and Macropinocytosis) Requires Rab GTPases for Endosomal Transport

Porcine enteric alphacoronavirus (PEAV) is a new bat HKU2-like porcine coronavirus, and its endemic outbreak has caused severe economic losses to the pig industry. Its broad cellular tropism suggests a potential risk of cross-species transmission. A limited understanding of PEAV entry mechanisms may hinder a rapid response to potential outbreaks. This study analyzed PEAV entry events using chemical inhibitors, RNA interference, and dominant-negative mutants. PEAV entry into Vero cells depended on three endocytic pathways: caveolae, clathrin, and macropinocytosis. Endocytosis requires dynamin, cholesterol, and a low pH. Rab5, Rab7, and Rab9 GTPases (but not Rab11) regulate PEAV endocytosis. PEAV particles colocalize with EEA1, Rab5, Rab7, Rab9, and Lamp-1, suggesting that PEAV translocates into early endosomes after internalization, and Rab5, Rab7, and Rab9 regulate trafficking to lysosomes before viral genome release. PEAV enters porcine intestinal cells (IPI-2I) through the same endocytic pathway, suggesting that PEAV may enter various cells through multiple endocytic pathways. This study provides new insights into the PEAV life cycle. IMPORTANCE Emerging and reemerging coronaviruses cause severe human and animal epidemics worldwide. PEAV is the first bat-like coronavirus to cause infection in domestic animals. However, the PEAV entry mechanism into host cells remains unknown. This study demonstrates that PEAV enters into Vero or IPI-2I cells through caveola/clathrin-mediated endocytosis and macropinocytosis, which does not require a specific receptor. Subsequently, Rab5, Rab7, and Rab9 regulate PEAV trafficking from early endosomes to lysosomes, which is pH dependent. The results advance our understanding of the disease and help to develop potential new drug targets against PEAV.

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.

The endocytosis of foot-and mouth disease virus requires clathrin and caveolin and is dependent on the existence of Rab5 and Rab7 in CHO-677 cells

Foot-and-mouth disease virus (FMDV) is a highly contagious virus that causes severe vesicular disease of cloven-hoofed animals. Various endocytosis mechanisms are involved in the entry of FMDV after binding to the integrin and heparan sulfate (HS) receptors. However, the mechanism of FMDV using other unknown receptors to enter the cells remains unclear. Here, we reported that the endocytosis and endosomal pathways are employed by FMDV to invade the Chinese hamster ovary cell line (CHO-677) without the integrin and HS receptors. We demonstrated that the internalization of FMDV into CHO-677 cells was abrogated by chlorpromazine, an inhibitor of clathrin-mediated endocytosis. Knockdown of the clathrin heavy chain decreased the viral protein abundance. Incubation of the CHO-677 cells with the inhibitors of caveolae-mediated endocytosis or transfection by caveolin-1 siRNA also limited FMDV replication. In addition, we determined that the acidic environment and the existence of dynamin were essential for FMDV infection in CHO-677 cells. The endosomal proteins Rab5 (early endosome) and Rab7 (late endosome), but not Rab11 (recycling endosome), were utilized by FMDV during infection. These data provide a new entry model of FMDV by unknown receptors which will help to better understand the pathogenesis mediated by FMDV.

BRAF-V600E utilizes posttranscriptional mechanisms to amplify LPS-induced TNFα production in dendritic cells in a mouse model of Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is an inflammatory disease characterized by abnormal dendritic cells (DCs) with hyperactive ERK signaling, called "LCH cells." Since DCs rely on ERK signaling to produce inflammatory molecules in response to pathogenic cues, we hypothesized that hyperactive ERK enhances DCs inflammatory responses. We specifically investigated TLR4-induced TNFα production in LCH cells by utilizing the BRAF-V600Efl/+ :CD11c-Cre mouse model of LCH, which hyperactivates ERK in DCs. We measured LPS-induced TNFα production both in vivo and in vitro using splenic CD11c+ cells and bone marrow-derived DCs with or without pharmacologic BRAFV600E inhibition. We observed a reversible increase in secreted TNFα and a partially reversible increase in TNFα protein per cell, despite a decrease in TLR4 signaling and Tnfa transcripts compared with controls. We examined ERK-driven, posttranscriptional mechanisms that contribute to TNFα production and secretion using biochemical and cellular assays. We identified a reversible increase in TACE activation, the enzyme required for TNFα secretion, and most strikingly, an increase in protein translation, including TNFα. Defining the translatome through polysome-bound RNA sequencing revealed up-regulated translation of the LPS-response program. These data suggest hyperactive ERK signaling utilizes multiple posttranscriptional mechanisms to amplify inflammatory responses in DCs, advancing our understanding of LCH and basic DC biology.

Vesicle trafficking and vesicle fusion: mechanisms, biological functions, and their implications for potential disease therapy

Intracellular vesicle trafficking is the fundamental process to maintain the homeostasis of membrane-enclosed organelles in eukaryotic cells. These organelles transport cargo from the donor membrane to the target membrane through the cargo containing vesicles. Vesicle trafficking pathway includes vesicle formation from the donor membrane, vesicle transport, and vesicle fusion with the target membrane. Coat protein mediated vesicle formation is a delicate membrane budding process for cargo molecules selection and package into vesicle carriers. Vesicle transport is a dynamic and specific process for the cargo containing vesicles translocation from the donor membrane to the target membrane. This process requires a group of conserved proteins such as Rab GTPases, motor adaptors, and motor proteins to ensure vesicle transport along cytoskeletal track. Soluble N-ethyl-maleimide-sensitive factor (NSF) attachment protein receptors (SNARE)-mediated vesicle fusion is the final process for vesicle unloading the cargo molecules at the target membrane. To ensure vesicle fusion occurring at a defined position and time pattern in eukaryotic cell, multiple fusogenic proteins, such as synaptotagmin (Syt), complexin (Cpx), Munc13, Munc18 and other tethering factors, cooperate together to precisely regulate the process of vesicle fusion. Dysfunctions of the fusogenic proteins in SNARE-mediated vesicle fusion are closely related to many diseases. Recent studies have suggested that stimulated membrane fusion can be manipulated pharmacologically via disruption the interface between the SNARE complex and Ca²⁺ sensor protein. Here, we summarize recent insights into the molecular mechanisms of vesicle trafficking, and implications for the development of new therapeutics based on the manipulation of vesicle fusion.

TFAM expression in brown adipocytes confers obesity resistance by secreting extracellular vesicles that promote self-activation

The occurrence of diet-induced obesity has been increasing worldwide and has become a major health concern. Mitochondria are densely distributed in brown adipose tissue and are involved in lipid consumption. Therefore, increasing energy expenditure through the activation of brown adipocytes may be a potential therapy for obesity. Our findings showed that mitochondrial transcription factor A (TFAM) homozygous transgenic (TgTg) mice had highly activated brown adipocytes and increased expression of oxidative phosphorylation, leading to resistance to obesity. Transplantation models of TFAM-expressing brown adipocytes could mimic the phenotype of TFAM TgTg mice, and proving their anti-obesity effect. We found that brown adipocytes secrete exosomes which enable self-activation in an autocrine and paracrine manner. The secretion was enhanced in TFAM TgTg brown adipocytes, resulting in a higher activation. These findings may lead to a promising treatment strategy for obesity through selective stimulation of exosome secretion.

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Human TFAM overexpression in BAT promotes strong anti-obesity effects

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Increasing mitochondrial function in hTFAM TgTg mice facilitates EVs secretion

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Enhanced EV released in TgTg brown adipocytes induce self-differentiation/activation

The KASH5 protein involved in meiotic chromosomal movements is a novel dynein activating adaptor

Dynein harnesses ATP hydrolysis to move cargo on microtubules in multiple biological contexts. Dynein meets a unique challenge in meiosis by moving chromosomes tethered to the nuclear envelope to facilitate homolog pairing essential for gametogenesis. Though processive dynein motility requires binding to an activating adaptor, the identity of the activating adaptor required for dynein to move meiotic chromosomes is unknown. We show that the meiosis-specific nuclear-envelope protein KASH5 is a dynein activating adaptor: KASH5 directly binds dynein using a mechanism conserved among activating adaptors and converts dynein into a processive motor. We map the dynein-binding surface of KASH5, identifying mutations that abrogate dynein binding in vitro and disrupt recruitment of the dynein machinery to the nuclear envelope in cultured cells and mouse spermatocytes in vivo. Our study identifies KASH5 as the first transmembrane dynein activating adaptor and provides molecular insights into how it activates dynein during meiosis.

Analysis insights for three FRET pairs of chemically unlinked two-molecule FRET cytometry

Förster resonance energy transfer (FRET) is the direct energy exchange between two-component fluorescent molecules. FRET methods utilize chemically linked molecules or unlinked fluorescence protein-protein interactions. FRET is therefore a powerful indicator of molecular proximity, but standardized determination of FRET efficiency is challenged when investigating natural (chemically unlinked) interactions. In this paper, we have examined the interactions of tumor necrosis factor receptor-1 (TNFR1) molecules expressed as recombinant fusion proteins of cyan, yellow, or red fluorescent protein (-CFP, -YFP, or -RFP) to evaluate two-molecule chemically unlinked FRET by flow cytometry. We demonstrate three independent FRET pairs CFP→YFP (FRET-1), YFP→RFP (FRET-2) and CFP→RFP (FRET-3), comparing TNFR1+TNFR1 with non-interacting TNFR1+CD27 proteins, on both LSR-II and Fortessa X-20 cytometers. We describe genuine FRET activities reflecting TNFR1 homotypic interactions. FRET events can be visualized during sample acquisition via the use of "spiked" FRET donor cells, together with TNFR1+TNFR1 co-transfected cells, as FRET channel MFI overlays. FRET events are subsequentially indicated by comparing concatenated files of cells expressing either FRET positive events (TNFR1+TNFR1) or FRET negative events (TNFR1+CD27) to generate single-cell scatter plots showing loss of FRET donor brightness. Robust determination of FRET efficiency is then confirmed at the single-cell level by applying matrix calculations based on the measurements of FRET donor, acceptor and FRET fluorescent intensities (I), detector channel emission coefficient (S), fluorescent protein extinction coefficients (ε) and α factor. In this TNFR based system, the mean CFP→YFP FRET-1 efficiency is 0.43 (LSR-II) and 0.41 (Fortessa), the mean YFP→RFP FRET-2 efficiency is 0.30 (LSR-II) and 0.29 (Fortessa), and the mean CFP→RFP FRET-3 efficiency is 0.56 (LSR-II) and 0.54 (Fortessa). This study also embraces multidimensional clustering using t-SNE, Fit-SNE, UMAP, Tri-Map and PaCMAP to further demonstrate FRET. These approaches establish a robust system for standardized detection of chemically unlinked TNFR1 homotypic interactions with three individual FRET pairs.

Dvl2 facilitates the coordination of NF-κB and Wnt signaling to promote colitis-associated colorectal progression

Colitis‐associated colorectal cancer (CAC) arises due to prolonged inflammation and has distinct molecular events compared with sporadic colorectal cancer (CRC). Although inflammatory NF‐κB signaling was activated by pro‐inflammatory cytokines (such as TNFα) in early stages of CAC, Wnt/β‐catenin signaling later appears to function as a key regulator of CAC progression. However, the exact mechanism responsible for the cross‐regulation between these 2 pathways remains unclear. Here, we found reciprocal inhibition between NF‐κB and Wnt/β‐catenin signaling in CAC samples, and the Dvl2, an adaptor protein of Wnt/β‐catenin signaling, is responsible for NF‐κB inhibition. Mechanistically, Dvl2 interacts with the C‐terminus of tumor necrosis factor receptor 1 (TNFRI) and mediates TNFRI endocytosis, leading to NF‐κB signal inhibition. In addition, increased infiltration of the pro‐inflammatory cytokine interleukin‐13 (IL‐13) is responsible for upregulating Dvl2 expression through STAT6. Targeting STAT6 effectively decreases Dvl2 levels and restrains colony formation of cancer cells. These findings demonstrate a unique role for Dvl2 in TNFRI endocytosis, which facilitates the coordination of NF‐κB and Wnt to promote CAC progression.

The thermal proteome stability profile of Trypanosoma cruzi in epimastigote and trypomastigote life stages

Trypanosoma cruzi is a flagellate protozoa being the etiological agent of Chagas disease, a neglected tropical disease, which still poses a public health problem worldwide. The intricate molecular changes during T. cruzi-host interaction have been explored using different largescale omics techniques. However, protein stability is largely unknown. Thermal proteome profiling (TPP) methodology has the potential to characterize proteome-wide stability highlighting key proteins during T. cruzi infection and life stage transition from the invertebrate to the mammalian host. In the present work, T. cruzi epimastigotes and trypomastigotes cell lysates were subjected to TPP workflow and analyzed by quantitative large-scale mass spectrometry-based proteomics to fit a melting profile for each protein. A total of 2884 proteins were identified and associated to 1741 melting curves being 1370 in trypomastigotes (Tm_AVG 53.53 °C) and 1279 in epimastigotes (Tm_AVG 50.89 °C). A total of 453 proteins were identified with statistically different melting profiles between the two life stages. Proteins associated to pathogenesis and intracellular transport had regulated melting temperatures. Membrane and glycosylated proteins had a higher average Tm in trypomastigotes compared to epimastigotes. This study represents the first large-scale comparison of parasite protein stability between life stages. SIGNIFICANCE: Trypanosoma cruzi, a unicellular flagellate parasite, is the etiological agent of Chagas disease, endemic in South America and affecting more that 7 million people worldwide. There is an intense research to identify novel chemotherapeutic and diagnostic targets of Chagas disease. Proteomic approaches have helped in elucidating the quantitative proteome and PTMs changes of T. cruzi during life cycle transition and upon different biotic and abiotic stimuli. However, a comprehensive knowledge of the protein-protein interaction and protein conformation is still missing. In order to fill this gap, this manuscript elucidates the T. cruzi Y strain proteome-wide thermal stability map in the epimastigote and trypomastigote life stages. Comparison between life stages showed a higher average melting temperature stability for trypomastigotes than epimastigotes indicating a host temperature adaptation. Both presented a selective thermal stability shift for cellular compartments, molecular functions and biological processes based on the T. cruzi life stage. Membrane and glycosylated proteins presented a higher thermal stability in trypomastigotes when compared to the epimastigotes.

The multiple roles of RAB GTPases in female and male meiosis

BACKGROUND

RAB GTPases constitute the largest family of small GTPases and are found in all eukaryotes. RAB GTPases regulate components of the endomembrane system, the nucleus and the plasma membrane, and are involved in intracellular actin/tubulin-dependent vesicle movement, membrane fusion and cell growth in mitosis.

OBJECTIVE AND RATIONALE

RAB GTPases play multiple critical roles during both female and male meiosis. This review summarizes the progress made in our understanding of the role of RAB GTPases in female and male meiosis in different species. We also discuss the potential relationship between RAB GTPases and oocyte/sperm quality, which may help in understanding the mechanisms underlying oogenesis and spermatogenesis and potential genetic causes of infertility.

SEARCH METHODS

The PubMed database was searched for articles published between 1991 and 2020 using the following terms: 'RAB', 'RAB oocyte', 'RAB sperm' and 'RAB meiosis'.

OUTCOMES

An analysis of 126 relevant articles indicated that RAB GTPases are present in all eukaryotes, and ten subfamilies (almost 70 members) are expressed in human cells. The roles of 25 RAB proteins and orthologues in female meiosis and 12 in male meiosis have been reported. RAB proteins are essential for the accurate continuity of genetic material, successful fertilization and the normal growth of offspring. Distinct and crucial functions of RAB GTPases in meiosis have been reported. In oocytes, RAB GTPases are involved in spindle organization, kinetochore-microtubule attachment, chromosome alignment, actin filament-mediated spindle migration, cytokinesis, cell cycle and oocyte-embryo transition. RAB GTPases function in mitochondrial processes and Golgi-mediated vesicular transport during female meiosis, and are critical for cortical granule transport during fertilization and oocyte-embryo transition. In sperm, RAB GTPases are vital for cytoskeletal organization and successful cytokinesis, and are associated with Golgi-mediated acrosome formation, membrane trafficking and morphological changes of sperm cells, as well as the exocytosis-related acrosome reaction and zona reaction during fertilization.

WIDER IMPLICATIONS

Abnormal expression of RAB GTPases disrupts intracellular systems, which may induce diverse diseases. The roles of RAB proteins in female and male reproductive systems, thus, need to be considered. The mechanisms underlying the function of RAB GTPases and the binding specificity of their effectors during oogenesis, spermatogenesis and fertilization remain to be studied. This review should contribute to our understanding of the molecular mechanisms of oogenesis and spermatogenesis and potential genetic causes of infertility.

The nanoscale molecular morphology of docked exocytic dense-core vesicles in neuroendocrine cells

Rab-GTPases and their interacting partners are key regulators of secretory vesicle trafficking, docking, and fusion to the plasma membrane in neurons and neuroendocrine cells. Where and how these proteins are positioned and organized with respect to the vesicle and plasma membrane are unknown. Here, we use correlative super-resolution light and platinum replica electron microscopy to map Rab-GTPases (Rab27a and Rab3a) and their effectors (Granuphilin-a, Rabphilin3a, and Rim2) at the nanoscale in 2D. Next, we apply a targetable genetically-encoded electron microscopy labeling method that uses histidine based affinity-tags and metal-binding gold-nanoparticles to determine the 3D axial location of these exocytic proteins and two SNARE proteins (Syntaxin1A and SNAP25) using electron tomography. Rab proteins are distributed across the entire surface and t-SNARE proteins at the base of docked vesicles. We propose that the circumferential distribution of Rabs and Rab-effectors could aid in the efficient transport, capture, docking, and rapid fusion of calcium-triggered exocytic vesicles in excitable cells.

Mechanisms and Regulation of Cardiac CaV1.2 Trafficking

During cardiac excitation contraction coupling, the arrival of an action potential at the ventricular myocardium triggers voltage-dependent L-type Ca²⁺ (Ca_V1.2) channels in individual myocytes to open briefly. The level of this Ca²⁺ influx tunes the amplitude of Ca²⁺-induced Ca²⁺ release from ryanodine receptors (RyR2) on the junctional sarcoplasmic reticulum and thus the magnitude of the elevation in intracellular Ca²⁺ concentration and ultimately the downstream contraction. The number and activity of functional Ca_V1.2 channels at the t-tubule dyads dictates the amplitude of the Ca²⁺ influx. Trafficking of these channels and their auxiliary subunits to the cell surface is thus tightly controlled and regulated to ensure adequate sarcolemmal expression to sustain this critical process. To that end, recent discoveries have revealed the existence of internal reservoirs of preformed Ca_V1.2 channels that can be rapidly mobilized to enhance sarcolemmal expression in times of acute stress when hemodynamic and metabolic demand increases. In this review, we provide an overview of the current thinking on Ca_V1.2 channel trafficking dynamics in the heart. We highlight the numerous points of control including the biosynthetic pathway, the endosomal recycling pathway, ubiquitination, and lysosomal and proteasomal degradation pathways, and discuss the effects of β-adrenergic and angiotensin receptor signaling cascades on this process.

FOXO regulates the expression of antimicrobial peptides and promotes phagocytosis of hemocytes in shrimp antibacterial immunity

Invertebrates rely on innate immunity, including humoral and cellular immunity, to resist pathogenic infection. Previous studies showed that forkhead box transcription factor O (FOXO) participates in mucosal immune responses of mammals and the gut humoral immune regulation of invertebrates. However, whether FOXO is involved in systemic and cellular immunity regulation in invertebrates remains unknown. In the present study, we identified a FOXO from shrimp (Marsupenaeus japonicus) and found that it was expressed at relatively basal levels in normal shrimp, but was upregulated significantly in shrimp challenged by Vibrio anguillarum. FOXO played a critical role in maintaining hemolymph and intestinal microbiota homeostasis by promoting the expression of Relish, the transcription factor of the immune deficiency (IMD) pathway for expression of antimicrobial peptides (AMPs) in shrimp. We also found that pathogen infection activated FOXO and induced its nuclear translocation by reducing serine/threonine kinase AKT activity. In the nucleus, activated FOXO directly regulated the expression of its target Amp and Relish genes against bacterial infection. Furthermore, FOXO was identified as being involved in cellular immunity by promoting the phagocytosis of hemocytes through upregulating the expression of the phagocytotic receptor scavenger receptor C (Src), and two small GTPases, Rab5 and Rab7, which are related to phagosome trafficking to the lysosome in the cytoplasm. Taken together, our results indicated that FOXO exerts its effects on homeostasis of hemolymph and the enteric microbiota by activating the IMD pathway in normal shrimp, and directly or indirectly promoting AMP expression and enhancing phagocytosis of hemocytes against pathogens in bacteria-infected shrimp. This study revealed the different functions of FOXO in the mucosal (local) and systemic antibacterial immunity of invertebrates.

Microtubules and motor proteins support zebrafish neuronal migration by directing cargo

Neuronal migration during development is necessary to form an ordered and functional brain. Postmitotic neurons require microtubules and dynein to move, but the mechanisms by which they contribute to migration are not fully characterized. Using tegmental hindbrain nuclei neurons in zebrafish embryos together with subcellular imaging, optogenetics, and photopharmacology, we show that, in vivo, the centrosome's position relative to the nucleus is not linked to greatest motility in this cell type. Nevertheless, microtubules, dynein, and kinesin-1 are essential for migration, and we find that interference with endosome formation or the Golgi apparatus impairs migration to a similar extent as disrupting microtubules. In addition, an imbalance in the traffic of the model cargo Cadherin-2 also reduces neuronal migration. These results lead us to propose that microtubules act as cargo carriers to control spatiotemporal protein distribution, which in turn controls motility. This adds crucial insights into the variety of ways that microtubules can support successful neuronal migration in vivo.

Porcine Circovirus Type 3 Enters Into PK15 Cells Through Clathrin- and Dynamin-2-Mediated Endocytosis in a Rab5/Rab7 and pH-Dependent Fashion

Porcine circovirus type 3 (PCV3) invades multiple tissues and organs of pigs of different ages and are widely spread throughout pig farms, emerging as an important viral pathogen that can potentially damage the pig industry worldwide. Since PCV3 is a newly discovered virus, many aspects of its life cycle remain unknown. Porcine kidney epithelial cells are important host targets for PCV3. Here, we used systematic approaches to dissect the molecular mechanisms underlying the cell entry and intracellular trafficking of PCV3 in PK15 cells, a cell line of porcine kidney epithelial origin. A large number of PCV3 viral particles were found to colocalize with clathrin but not caveolin-1 after entry, and PCV3 infection was significantly decreased when treated with chlorpromazine, dynasore, knockdown of clathrin heavy chain expression via RNA interference, or overexpression of a dominant-negative mutant of EPS15 in PCV3-infected cells. After internalization, the viral particles were further observed to colocalize with Rab5 and Rab7, and knockdown of both expression by RNA interference significantly inhibited PCV3 replication. We also found that PCV3 infection was impeded by ammonium chloride treatment, which indicated the requirement of an acidic environment for viral entry. Taken together, our findings demonstrate that PCV3 enters PK15 cells through a clathrin- and dynamin-2-mediated endocytic pathway, which requires early and late endosomal trafficking, as well as an acidic environment, providing an insightful theoretical basis for further understanding the PCV3 life cycle and its pathogenesis.

Hypoxic exosomes orchestrate tumorigenesis: molecular mechanisms and therapeutic implications

The solid tumor microenvironment possesses a hypoxic condition, which promotes aggressiveness and resistance to therapies. Hypoxic tumor cells undergo broadly metabolic and molecular adaptations and communicate with surrounding cells to provide conditions promising for their homeostasis and metastasis. Extracellular vesicles such as exosomes originating from the endosomal pathway carry different types of biomolecules such as nucleic acids, proteins, and lipids; participate in cell-to-cell communication. The exposure of cancer cells to hypoxic conditions, not only, increases exosomes biogenesis and secretion but also alters exosomes cargo. Under the hypoxic condition, different signaling pathways such as HIFs, Rab-GTPases, NF-κB, and tetraspanin are involved in the exosomes biogenesis. Hypoxic tumor cells release exosomes that induce tumorigenesis through promoting metastasis, angiogenesis, and modulating immune responses. Exosomes from hypoxic tumor cells hold great potential for clinical application and cancer diagnosis. Besides, targeting the biogenesis of these exosomes may be a therapeutic opportunity for reducing tumorigenesis. Exosomes can serve as a drug delivery system transferring therapeutic compounds to cancer cells. Understanding the detailed mechanisms involved in biogenesis and functions of exosomes under hypoxic conditions may help to develop effective therapies against cancer.

Oncolytic H-1 Parvovirus Enters Cancer Cells through Clathrin-Mediated Endocytosis

H-1 protoparvovirus (H-1PV) is a self-propagating virus that is non-pathogenic in humans and has oncolytic and oncosuppressive activities. H-1PV is the first member of the Parvoviridae family to undergo clinical testing as an anticancer agent. Results from clinical trials in patients with glioblastoma or pancreatic carcinoma show that virus treatment is safe, well-tolerated and associated with first signs of efficacy. Characterisation of the H-1PV life cycle may help to improve its efficacy and clinical outcome. In this study, we investigated the entry route of H-1PV in cervical carcinoma HeLa and glioma NCH125 cell lines. Using electron and confocal microscopy, we detected H-1PV particles within clathrin-coated pits and vesicles, providing evidence that the virus uses clathrin-mediated endocytosis for cell entry. In agreement with these results, we found that blocking clathrin-mediated endocytosis using specific inhibitors or small interfering RNA-mediated knockdown of its key regulator, AP2M1, markedly reduced H-1PV entry. By contrast, we found no evidence of viral entry through caveolae-mediated endocytosis. We also show that H-1PV entry is dependent on dynamin, while viral trafficking occurs from early to late endosomes, with acidic pH necessary for a productive infection. This is the first study that characterises the cell entry pathways of oncolytic H-1PV.

Novel Intrinsic Mechanisms of Active Drug Extrusion at the Blood-Brain Barrier: Potential Targets for Enhancing Drug Delivery to the Brain?

The blood-brain barrier (BBB) limits the pharmacotherapy of several brain disorders. In addition to the structural and metabolic characteristics of the BBB, the ATP-driven, drug efflux transporter P-glycoprotein (Pgp) is a selective gatekeeper of the BBB; thus, it is a primary hindrance to drug delivery into the brain. Here, we review the complex regulation of Pgp expression and functional activity at the BBB with an emphasis on recent studies from our laboratory. In addition to traditional processes such as transcriptional regulation and posttranscriptional or posttranslational modification of Pgp expression and functionality, novel mechanisms such as intra- and intercellular Pgp trafficking and intracellular Pgp-mediated lysosomal sequestration in BBB endothelial cells with subsequent disposal by blood neutrophils are discussed. These intrinsic mechanisms of active drug extrusion at the BBB are potential therapeutic targets that could be used to modulate P-glycoprotein activity in the treatment of brain diseases and enhance drug delivery to the brain.

The Role of Exosomes in the Crosstalk between Adipocytes and Liver Cancer Cells

Exosomes are membrane-bound extracellular vesicles (EVs) that transport bioactive materials between cells and organs. The cargo delivered by exosomes can alter a wide range of cellular responses in recipient cells and play an important pathophysiological role in human cancers. In hepatocellular carcinoma (HCC), for example, adipocyte- and tumor-secreted factors contained in exosomes contribute to the creation of a chronic inflammatory state, which contributes to disease progression. The exosome-mediated crosstalk between adipocytes and liver cancer cells is a key aspect of a dynamic tumor microenvironment. In this review, we summarize the role of increased adiposity and the role of adipocyte-derived exosomes (AdExos) and HCC-derived exosomes (HCCExos) in the modulation of HCC progression. We also discuss recent advances regarding how malignant cells interact with the surrounding adipose tissue and employ exosomes to promote a more aggressive phenotype.

Rac1-dependent endocytosis and Rab5-dependent intracellular trafficking are required by Enterovirus A71 and Coxsackievirus A10 to establish infections

Enterovirus A71 (EVA71) and Coxsackievirus A10 (CVA10) are representative types of Enterovirus A. Dependent on the host cell types, the EVA71 entry may utilize clathrin-, caveola-, and endophilin-A2-mediated endocytosis. However, the cell-entry and intracellular trafficking pathways of CVA10, using KREMEN1 as its receptor, are unclear. Here, we tested the relevant mechanisms through RNA interference (RNAi) and chemical inhibitors. We found that endocytosis of EVA71 and CVA10 in rhabdomyosarcoma (RD) cells engaged multiple pathways, and both viruses required Rac1. Interestingly, while CDC42 and Pak1 participated in EVA71 infection, PI3K played a role in CVA10 infection. The functions of Rab proteins in intracellular trafficking of CVA10 and EVA71 were examined by RNAi. Knockdown of Rab5 and Rab21 significantly reduced CVA10 infectivity, while knockdown of Rab5, Rab7 and Rab9 reduced EVA71 infectivity. Confocal microscopy confirmed the colocalization of CVA10 virions with Rab5 or Rab21, and colocalization of EVA71 virions with Rab5 or Rab7. Additionally, we observed that both CVA10 and EVA71 infections were inhibited by endosome acidification inhibitors, bafilomycin-A1 and NH₄Cl. Together, our findings comparatively illustrate the entry and intracellular trafficking processes of representative Enterovirus A types and revealed novel enterovirus intervention targets.

Changes in the proteome of sea urchin Paracentrotus lividus coelomocytes in response to LPS injection into the body cavity

Background

The immune system of echinoderm sea urchins is characterised by a high degree of complexity that is not completely understood. The Mediterranean sea urchin Paracentrotus lividus coelomocytes mediate immune responses through phagocytosis, encapsulation of non-self particles, and production of diffusible factors including antimicrobial molecules. Details of these processes, and molecular pathways driving these mechanisms, are still to be fully elucidated.

Principal findings

In the present study we treated the sea urchin P. lividus with the bacterial lipopolysaccharide (LPS) and collected coelomocytes at different time-points (1, 3, 6 and 24 hours). We have shown, using label-free quantitative mass spectrometry, how LPS is able to modulate the coelomocyte proteome and to effect cellular pathways, such as endocytosis and phagocytosis, as soon as the immunomodulating agent is injected. The present study has also shown that treatment can modulate various cellular processes such as cytoskeleton reorganisation, and stress and energetic homeostasis.

Conclusions

Our data demonstrates, through mass spectrometry and the following functional annotation bioinformatics analysis, how the bacterial wall constituent is sufficient to set off an immune response inducing cytoskeleton reorganisation, the appearance of clusters of heat shock proteins (Hsp) and histone proteins and the activation of the endocytic and phagocytic pathways. Data are available via ProteomeXchange with identifier PXD008439.

3-O-acetylrubianol C (3AR-C) induces RIPK1-dependent programmed cell death by selective inhibition of IKKβ

In tumor necrosis factor (TNF) signaling, phosphorylation and activation of receptor interacting protein kinase 1 (RIPK1) by upstream kinases is an essential checkpoint in the suppression of TNF-induced cell death. Thus, discovery of pharmacological agents targeting RIPK1 may provide new strategies for improving the therapeutic efficacy of TNF. In this study, we found that 3-O-acetylrubianol C (3AR-C), an arborinane triterpenoid isolated from Rubia philippinesis, promoted TNF-induced apoptotic and necroptotic cell death. To identify the molecular mechanism, we found that in mouse embryonic fibroblasts, 3AR-C drastically upregulated RIPK1 kinase activity by selectively inhibiting IKKβ. Notably, 3AR-C did not interfere with IKKα or affect the formation of the TNF receptor1 (TNFR1) complex-I. Moreover, in human cancer cells, 3AR-C was only sufficient to sensitize TNF-induced cell death when c-FLIP_L expression was downregulated to facilitate the formation of TNFR1 complex-II and necrosome. Taken together, our study identified a novel arborinane triterpenoid 3AR-C as a potent activator of TNF-induced cell death via inhibition of IKKβ phosphorylation and promotion of the cytotoxic potential of RIPK1, thus providing a rationale for further development of 3AR-C as a selective IKKβ inhibitor to overcome TNF resistance in cancer therpay.

ER morphology and endo-lysosomal crosstalk: Functions and disease implications

The endoplasmic reticulum (ER) is a continuous endomembrane system comprising the nuclear envelope, ribosome-studded sheets, dense peripheral matrices, and an extensive polygonal network of interconnected tubules. In addition to performing numerous critical cellular functions, the ER makes extensive contacts with other organelles, including endosomes and lysosomes. The molecular and functional characterization of these contacts has advanced significantly over the past several years. These contacts participate in key functions such as cholesterol transfer, endosome tubule fission, and Ca²⁺ exchange. Disruption of key proteins at these sites can result in often severe diseases, particularly those affecting the nervous system.

Intracellular Trafficking Network and Autophagy of PHBHHx Nanoparticles and their Implications for Drug Delivery

3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBHHx), which is naturally generated by biodegradable polyhydroxyalkanoates synthesized by bacteria, is an attractive material for drug delivery due to its controllable physical properties, non-toxicity, environmental friendliness, degradable properties and good biocompatibility. However, the intracellular trafficking network pathways, especially the autophagy mechanism of PHBHHx nanoparticles (NPs), have rarely been investigated. In this paper, we successfully prepared the NPs used solvent displacement method and investigated the autophagy pathways and other intracellular trafficking mechanisms based on NPs with the assistance of Rab proteins. We found that NPs were internalized in cells mainly via clathrin endocytosis and caveolin endocytosis. Beside the classical pathways, we discovered two new pathways: the micropinocytosis early endosome (EEs)-micropinocytosis-lysosome pathway and the EEs-liposome-lysosome pathway. NPs were delivered to cells through endocytosis recycling vesicles and GLUT4 exocytosis vesicles. Similar to other nanoparticles, NPs also induced intracellular autophagy and were then degraded via endolysosomal pathways. 3-MA and CQ were used as autophagy inhibitors to avoid the degradation of NPs through lysosomes by blocking endolysosomal pathways. Tumor volumes and weights were significantly decreased when autophagy inhibitors and chemical drugs packaged in NPs were cooperatively used.

Type II Diabetes Mellitus Accelerates Age-Dependent Aβ Pathology in Cynomolgus Monkey Brain

Accumulating evidence suggests that diabetes mellitus (DM) is one of the strongest risk factors for developing Alzheimer's disease (AD). However, it remains unclear how DM accelerates AD pathology in the brain. Cynomolgus monkey (Macaca fascicularis) is one of the nonhuman primates used for biomedical research, and we can observe spontaneous formation of AD pathology, such as senile plaques (SPs) and neurofibrillary tangles (NFTs), with the advance of aging. Furthermore, obesity is occasionally observed and frequently leads to development of type II DM (T2DM) in laboratory-housed cynomolgus monkeys. These findings suggest that cynomolgus monkey is a useful species to study the relationship between T2DM and AD pathology. In T2DM-affected monkey brains, SPs were observed in frontal and temporal lobe cortices almost 5 years earlier than healthy control monkeys. Moreover, age-related endocytic pathology, such as intraneuronal accumulation of enlarged endosomes, was exacerbated in T2DM-affected monkey brains. Since accumulating evidences suggest that endocytic dysfunction is involved in Aβ pathology, T2DM may aggravate age-related endocytic dysfunction, leading to the acceleration of Aβ pathology.

Systematic investigation of intracellular trafficking behavior of one-dimensional alumina nanotubes

Nanotube materials exhibit high drug loading capacity and controlled drug release properties, providing new opportunities for drug delivery. However, the intracellular trafficking paths of 1-dimensional (1D) nanostructured materials are poorly understood compared to their spherical counterparts, impeding the broad application of 1D materials as drug carriers. Here, we report the intracellular trafficking mechanism of nontoxic and biocompatible nanomaterials called anodic alumina nanotubes (AANTs), a model for 1D materials with a geometry that can be precisely engineered. The results indicated that AANTs enter the cells mainly by caveolin endocytosis and micropinocytosis and that cells use a novel macropinocytosis-late endosomes (LEs)-lysosomes route to transport AANTs. Moreover, liposomes (marked by DsRed-Rab18) are fully involved in the classical pathway of early endosomes (EEs)/LEs developing into lysosomes. The AANTs were delivered to the cells via two pathways: slow endocytosis recycling and GLUT4 exocytosis vesicles. The AANTs also induced intracellular autophagy and then degraded via the endolysosomal pathway. Blocking endolysosomal pathways using autophagy inhibitors prevented the degradation of AANTs through lysosomes. Our results add new insights into the pathways and mechanisms of intracellular trafficking of AANTs, and suggest that intracellular trafficking and lysosomal degradation are highly interdependent and important for efficient drug delivery, and should be evaluated together for drug carrier development.

The integral function of the endocytic recycling compartment is regulated by RFFL-mediated ubiquitylation of Rab11 effectors

Endocytic trafficking is regulated by ubiquitylation (also known as ubiquitination) of cargoes and endocytic machineries. The role of ubiquitylation in lysosomal delivery has been well documented, but its role in the recycling pathway is largely unknown. Here, we report that the ubiquitin (Ub) ligase RFFL regulates ubiquitylation of endocytic recycling regulators. An RFFL dominant-negative (DN) mutant induced clustering of endocytic recycling compartments (ERCs) and delayed endocytic cargo recycling without affecting lysosomal traffic. A BioID RFFL interactome analysis revealed that RFFL interacts with the Rab11 effectors EHD1, MICALL1 and class I Rab11-FIPs. The RFFL DN mutant strongly captured these Rab11 effectors and inhibited their ubiquitylation. The prolonged interaction of RFFL with Rab11 effectors was sufficient to induce the clustered ERC phenotype and to delay cargo recycling. RFFL directly ubiquitylates these Rab11 effectors in vitro, but RFFL knockout (KO) only reduced the ubiquitylation of Rab11-FIP1. RFFL KO had a minimal effect on the ubiquitylation of EHD1, MICALL1, and Rab11-FIP2, and failed to delay transferrin recycling. These results suggest that multiple Ub ligases including RFFL regulate the ubiquitylation of Rab11 effectors, determining the integral function of the ERC.

Rab5, Rab7, and Rab11 Are Required for Caveola-Dependent Endocytosis of Classical Swine Fever Virus in Porcine Alveolar Macrophages

The members of Flaviviridae utilize several endocytic pathways to enter a variety of host cells. Our previous work showed that classical swine fever virus (CSFV) enters porcine kidney (PK-15) cells through a clathrin-dependent pathway that requires Rab5 and Rab7. The entry mechanism for CSFV into other cell lines remains unclear, for instance, porcine alveolar macrophages (3D4/21 cells). More importantly, the trafficking of CSFV within endosomes controlled by Rab GTPases is unknown in 3D4/21 cells. In this study, entry and postinternalization of CSFV were analyzed using chemical inhibitors, RNA interference, and dominant-negative (DN) mutants. Our data demonstrated that CSFV entry into 3D4/21 cells depends on caveolae, dynamin, and cholesterol but not clathrin or macropinocytosis. The effects of DN mutants and knockdown of four Rab proteins that regulate endosomal trafficking were examined on CSFV infection, respectively. The results showed that Rab5, Rab7, and Rab11, but not Rab9, regulate CSFV endocytosis. Confocal microscopy showed that virus particles colocalize with Rab5, Rab7, or Rab11 within 30 min after virus entry and further with lysosomes, suggesting that after internalization CSFV moves to early, late, and recycling endosomes and then into lysosomes before the release of the viral genome. Our findings provide insights into the life cycle of pestiviruses in macrophages.IMPORTANCE Classical swine fever, is caused by classical swine fever virus (CSFV). The disease is notifiable to World Organisation for Animal Health (OIE) in most countries and causes significant financial losses to the pig industry globally. Understanding the processes of CSFV endocytosis and postinternalization will advance our knowledge of the disease and provide potential novel drug targets against CSFV. With this objective, we used systematic approaches to dissect these processes in CSFV-infected 3D4/21 cells. The data presented here demonstrate for the first time to our knowledge that CSFV is able to enter cells via caveola-mediated endocytosis that requires Rab5, Rab7 and Rab11, in addition to the previously described classical clathrin-dependent pathway that requires Rab5 and Rab7. The characterization of CSFV entry will further promote our current understanding of Pestivirus cellular entry pathways and provide novel targets for antiviral drug development.