Molecular imaging analysis of Rab GTPases in the regulation of phagocytosis and macropinocytosis

Invasion by exogenous RNA: cellular defense strategies and implications for RNA inference

Exogenous RNA poses a continuous threat to genome stability and integrity across various organisms. Accumulating evidence reveals complex mechanisms underlying the cellular response to exogenous RNA, including endo-lysosomal degradation, RNA-dependent repression and innate immune clearance. Across a variety of mechanisms, the natural anti-sense RNA-dependent defensive strategy has been utilized both as a powerful gene manipulation tool and gene therapy strategy named RNA-interference (RNAi). To optimize the efficiency of RNAi silencing, a comprehensive understanding of the whole life cycle of exogenous RNA, from cellular entry to its decay, is vital. In this paper, we review recent progress in comprehending the recognition and elimination of foreign RNA by cells, focusing on cellular entrance, intracellular transportation, and immune-inflammatory responses. By leveraging these insights, we highlight the potential implications of these insights for advancing RNA interference efficiency, underscore the need for future studies to elucidate the pathways and fates of various exogenous RNA forms, and provide foundational information for more efficient RNA delivery methods in both genetic manipulation and therapy in different organisms.

Advanced Strategies for Overcoming Endosomal/Lysosomal Barrier in Nanodrug Delivery

Nanocarriers have therapeutic potential to facilitate drug delivery, including biological agents, small-molecule drugs, and nucleic acids. However, their efficiency is limited by several factors; among which, endosomal/lysosomal degradation after endocytosis is the most important. This review summarizes advanced strategies for overcoming endosomal/lysosomal barriers to efficient nanodrug delivery based on the perspective of cellular uptake and intracellular transport mechanisms. These strategies include promoting endosomal/lysosomal escape, using non-endocytic methods of delivery to directly cross the cell membrane to evade endosomes/lysosomes and making a detour pathway to evade endosomes/lysosomes. On the basis of the findings of this review, we proposed several promising strategies for overcoming endosomal/lysosomal barriers through the smarter and more efficient design of nanodrug delivery systems for future clinical applications.

Characterization of the Gene Repertoire and Environmentally Driven Expression Patterns in Tanner Crab (Chionoecetes bairdi)

Tanner crab (Chionoecetes bairdi) is an economically important species that is threatened by ocean warming and bitter crab disease, which is caused by an endoparasitic dinoflagellate, Hematodinium. Little is known about disease transmission or its link to host mortality, or how ocean warming will affect pathogenicity or host susceptibility. To provide a transcriptomic resource for the Tanner crab, we generated a suite of RNA-seq libraries encompassing pooled hemolymph samples from crab displaying differing infection statuses and maintained at different temperatures (ambient (7.5˚C), elevated (10˚C), or decreased (4˚C)). After assembling a transcriptome and performing a multifactor differential gene expression analysis, we found genes influenced by temperature in relation to infection and detected some of those genes over time at the individual level using RNA-seq data from one crab. Biological processes associated with those genes include lipid storage, transcription, response to oxidative stress, cell adhesion, and morphogenesis. Alteration in lipid storage and transcription provide insight into how temperature impacts energy allocation in Hematodinium infected crabs. Alteration in expression patterns in genes associated with morphogenesis could suggest that hemocytes were changing morphology and/or type in response to temperature. This project provides insight into how Hematodinium infection could influence crab physiology as oceans warm.

Downregulation of beclin 1 restores arsenite-induced impaired autophagic flux by improving the lysosomal function in the brain

Arsenite is a toxic metalloid that causes various adverse effects in the brain. However, the underlying mechanisms of arsenite-induced neurotoxicity remain poorly understood. In this study, both adult beclin 1^+/+ and beclin 1^+/- mice were employed to establish a model of chronic arsenite exposure by treating with arsenite via drinking water for 6 months. The results clearly demonstrated that exposure to arsenite profoundly caused damage to the cerebral cortex, induced autophagy and impaired autophagic flux in the cerebral cortex. Heterozygous disruption of beclin 1 in animals remarkably alleviated the neurotoxic effects of arsenite. To verify the results obtained in the animals, a permanent U251 cell line was used. After treating of cells with arsenite, similar phenomenon was also observed, showing the significant elevation in the expression levels of autophagy-related genes. Importantly, lysosomal dysfunction caused by arsenite was observed in vitro and in vivo. Either knockdown of beclin 1 in cells or heterozygous disruption of beclin 1 in animals remarkably alleviated the lysosomal dysfunction induced by arsenite. These findings indicate that downregulation of beclin 1 could restore arsenite-induced impaired autophagic flux possibly through improving lysosomal function, and correct that regulation of autophagy via beclin 1 would be an alternative approach for the treatment of arsenite neurotoxicity.

Arf6-mediated macropinocytosis-enhanced suicide gene therapy of C16TAB-condensed Tat/pDNA nanoparticles in ovarian cancer

The use of cell-penetrating peptides (CPPs), typically HIV-Tat, to deliver therapeutic genes for cancer treatment is hampered by the inefficient delivery and complicated uptake route of plasmid DNA (pDNA). On the one hand, surface charges, particle size and shape essentially contribute to the endocytosis pathway of Tat/pDNA nanocomplexes, and on the other hand, endogenous cellular factors dominantly determine their intracellular trafficking fate and biological outcome. Recent advances in surfactant-modified nanomaterial and dual molecular imaging technology have offered new opportunities for suicide gene therapy. In this study, we employed the cationic surfactant C16TAB to further condense Tat/pDNA nanocomplexes for improving their delivery efficiency and tested the therapeutic effect of Tat/pDNA/C16TAB (T-P-C) nanoparticles carrying the GCV-converted HSV-ttk suicide gene for ovarian cancer. The cellular endocytosis pathway and underlying signal mechanism of T-P-C nanoparticles were further determined. The obtained T-P-C nanoparticles exhibited a small size, positive surface charge, irregular granular shape and high pDNA encapsulation efficiency. The in vitro experiments showed that T-P-C nanoparticles mainly used the macropinocytosis pathway for uptake in ovarian cancer cells. Their internalization and payload gene expression were controlled by the Arf6 GTPase-dependent, Rab GTPase-activated signal axis. Further in vivo molecular imaging based on DF (Fluc-eGFP)-TF (RFP-Rluc-HSV-ttk) system showed that T-P-C nanoparticles significantly increased the targeted delivery and suicide gene therapy in a mouse model xenografted with human ovarian cancer. More importantly, Arf6-mediated macropinocytosis remarkably enhanced the delivery efficiency and suicide gene therapy effect of T-P-C nanoparticles. Therefore, these C16TAB-condensed Tat/pDNA nanoparticles combined with the dual molecular imaging strategy provides a novel intracellular delivery platform for high-efficient, precise suicide gene therapy of ovarian cancer.

Macrophage-Regulatory T Cell Interactions Promote Type 2 Immune Homeostasis Through Resistin-Like Molecule α

RELMα is a small, secreted protein expressed by type 2 cytokine-activated “M2” macrophages in helminth infection and allergy. At steady state and in response to type 2 cytokines, RELMα is highly expressed by peritoneal macrophages, however, its function in the serosal cavity is unclear. In this study, we generated RELMα TdTomato (Td) reporter/knockout (Rα^Td) mice and investigated RELMα function in IL-4 complex (IL-4c)-induced peritoneal inflammation. We first validated the RELMα^Td/Td transgenic mice and showed that IL-4c injection led to the significant expansion of large peritoneal macrophages that expressed Td but not RELMα protein, while RELMα^+/+ mice expressed RELMα and not Td. Functionally, RELMα^Td/Td mice had increased IL-4 induced peritoneal macrophage responses and splenomegaly compared to RELMα^+/+ mice. Gene expression analysis indicated that RELMα^Td/Td peritoneal macrophages were more proliferative and activated than RELMα^+/+ macrophages, with increased genes associated with T cell responses, growth factor and cytokine signaling, but decreased genes associated with differentiation and maintenance of myeloid cells. We tested the hypothesis that Rα^Td/Td macrophages drive aberrant T cell activation using peritoneal macrophage and T cell co-culture. There were no differences in CD4⁺ T cell effector responses when co-cultured with RELMα^+/+ or RELMα^Td/Td macrophages, however, RELMα^Td/Td macrophages were impaired in their ability to sustain proliferation of FoxP3⁺ regulatory T cells (Treg). Supportive of the in vitro results, immunofluorescent staining of the spleens revealed significantly decreased FoxP3⁺ cells in the RELMα^Td/Td spleens compared to RELMα^+/+ spleens. Taken together, these studies identify a new RELMα regulatory pathway whereby RELMα-expressing macrophages directly sustain Treg proliferation to limit type 2 inflammatory responses.

Ubiquitination-Dependent Regulation of Small GTPases in Membrane Trafficking: From Cell Biology to Human Diseases

Membrane trafficking is critical for cellular homeostasis, which is mainly carried out by small GTPases, a class of proteins functioning in vesicle budding, transport, tethering and fusion processes. The accurate and organized membrane trafficking relies on the proper regulation of small GTPases, which involves the conversion between GTP- and GDP-bound small GTPases mediated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Emerging evidence indicates that post-translational modifications (PTMs) of small GTPases, especially ubiquitination, play an important role in the spatio-temporal regulation of small GTPases, and the dysregulation of small GTPase ubiquitination can result in multiple human diseases. In this review, we introduce small GTPases-mediated membrane trafficking pathways and the biological processes of ubiquitination-dependent regulation of small GTPases, including the regulation of small GTPase stability, activity and localization. We then discuss the dysregulation of small GTPase ubiquitination and the associated human membrane trafficking-related diseases, focusing on the neurological diseases and infections. An in-depth understanding of the molecular mechanisms by which ubiquitination regulates small GTPases can provide novel insights into the membrane trafficking process, which knowledge is valuable for the development of more effective and specific therapeutics for membrane trafficking-related human diseases.

From Pinocytosis to Methuosis-Fluid Consumption as a Risk Factor for Cell Death

The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell's surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and-most importantly-shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement.

The role of endolysosomal trafficking in anticancer drug resistance

Multidrug resistance (MDR) remains a major obstacle towards curative treatment of cancer. Despite considerable progress in delineating the basis of intrinsic and acquired MDR, the underlying molecular mechanisms remain to be elucidated. Emerging evidences suggest that dysregulation in endolysosomal compartments is involved in mediating MDR through multiple mechanisms, such as alterations in endosomes, lysosomes and autophagosomes, that traffic and biodegrade the molecular cargo through macropinocytosis, autophagy and endocytosis. For example, altered lysosomal pH, in combination with transcription factor EB (TFEB)-mediated lysosomal biogenesis, increases the sequestration of hydrophobic anti-cancer drugs that are weak bases, thereby producing an insufficient and off-target accumulation of anti-cancer drugs in MDR cancer cells. Thus, the use of well-tolerated, alkalinizing compounds that selectively block Vacuolar H⁺-ATPase (V-ATPase) may be an important strategy to overcome MDR in cancer cells and increase chemotherapeutic efficacy. Other mechanisms of endolysosomal-mediated drug resistance include increases in the expression of lysosomal proteases and cathepsins that are involved in mediating carcinogenesis and chemoresistance. Therefore, blocking the trafficking and maturation of lysosomal proteases or direct inhibition of cathepsin activity in the cytosol may represent novel therapeutic modalities to overcome MDR. Furthermore, endolysosomal compartments involved in catabolic pathways, such as macropinocytosis and autophagy, are also shown to be involved in the development of MDR. Here, we review the role of endolysosomal trafficking in MDR development and discuss how targeting endolysosomal pathways could emerge as a new therapeutic strategy to overcome chemoresistance in cancer.

The Dual Role of Macropinocytosis in Cancers: Promoting Growth and Inducing Methuosis to Participate in Anticancer Therapies as Targets

Macropinocytosis is an important mechanism of internalizing extracellular materials and dissolved molecules in eukaryotic cells. Macropinocytosis has a dual effect on cancer cells. On the one hand, cells expressing RAS genes (such as K-RAS, H-RAS) under the stress of nutrient deficiency can spontaneously produce constitutive macropinocytosis to promote the growth of cancer cells by internalization of extracellular nutrients (like proteins), receptors, and extracellular vesicles(EVs). On the other hand, abnormal expression of RAS genes and drug treatment (such as MOMIPP) can induce a novel cell death associated with hyperactivated macropinocytosis: methuosis. Based on the dual effect, there is immense potential for designing anticancer therapies that target macropinocytosis in cancer cells. In view of the fact that there has been little review of the dual effect of macropinocytosis in cancer cells, herein, we systematically review the general process of macropinocytosis, its specific manifestation in cancer cells, and its application in cancer treatment, including anticancer drug delivery and destruction of macropinocytosis. This review aims to serve as a reference for studying macropinocytosis in cancers and designing macropinocytosis-targeting anticancer drugs in the future.

Recruitment of monocytes and mature macrophages in mouse pubic symphysis relaxation during pregnancy and postpartum recovery†

Appropriate remodeling of the female lower reproductive tract and pelvic floor is essential during normal mammalian pregnancy, labor, and postpartum recovery. During mouse pregnancy, in addition to reproductive tract modifications, the pubic symphysis (PS) is remodeled into a soft interpubic ligament (IpL) to provide safe delivery of the offspring and fast postpartum recovery. Although temporal changes in the phenotypes of myeloid cells, such as mononuclear phagocytes, are crucial to remodeling the lower reproductive tract organs in preparation for a safe delivery, little is known about the involvement of recruited monocytes or macrophages in mouse PS remodeling. We used combined light microscopy, electron microscopy, and qPCR analysis to investigate the profile of recruited monocytes and macrophage polarization markers in C57Bl6 mouse interpubic tissues during pregnancy (D12, D18, and D19) and early days postpartum (1 dpp and 3 dpp) to better identify their presence in proper remodeling of the mouse PS. Our morphological data show that the number of recruited monocytes is increased in interpubic tissues and that recruited monocytes differentiate into proinflammatory or anti-inflammatory macrophage phenotypes from D18 to 3 dpp, which may contribute to dynamic changes in the gene expression of specific inflammatory mediators involved in interpubic tissue remodeling at these time points. Therefore, our morphological and quantitative gene expression data suggest that both differentiated macrophages from recruited monocytes and polarized macrophages may collaborate for IpL relaxation at labor and the appropriate repair of the PS after the first pregnancy.

Regulatory Mechanism of SNAP23 in Phagosome Formation and Maturation

Synaptosomal associated protein of 23 kDa (SNAP23), a plasma membrane-localized soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE), is a ubiquitously expressed protein that is generally involved in fusion of the plasma membrane and secretory or endosomal recycling vesicles during several types of exocytosis. SNAP23 is expressed in phagocytes, such as neutrophils, macrophages, and dendritic cells, and functions in both exocytosis and phagocytosis. This review focuses on the function of SNAP23 in immunoglobulin G Fc receptor-mediated phagocytosis by macrophages. SNAP23 and its partner SNAREs mediate fusion of the plasma membrane with intracellular organelles or vesicles to form phagosomes as well as the fusion of phagosomes with endosomes or lysosomes to induce phagosome maturation, characterized by reactive oxygen species production and acidification. During these processes, SNAP23 function is regulated by phosphorylation. In addition, microtubule-associated protein 1A/1B light chain 3 (LC3)-associated phagocytosis, which tightly promotes or suppresses phagosome maturation depending on the foreign target, requires SNAP23 function. SNAP23 that is enriched on the phagosome membrane during LC3-associated phagocytosis may be phosphorylated or dephosphorylated, thereby enhancing or inhibiting subsequent phagosome maturation, respectively. These findings have increased our understanding of the SNAP23-associated membrane trafficking mechanism in phagocytes, which has important implications for microbial pathogenesis and innate and adaptive immune responses.

Rab7 controls innate immunity by regulating phagocytosis and antimicrobial peptide expression in Chinese mitten crab

The Rab family is the most significant subfamily of small GTP-binding proteins. These proteins have widespread intracellular localization and play an important role in many biological processes. Rab7 plays a crucial role in the innate immune system of crustaceans. In the present study, we cloned and characterized Rab7 from Chinese mitten crab (Eriocheir sinensis), designated EsRab7. The full-length of the EsRab7 cDNA sequence is 1,257 bp and contains a 618-bp open reading frame encoding a 205-amino acid polypeptide. Bioinformatics analysis showed that the Rab7 protein was highly conserved during evolution. Quantitative real-time PCR showed the highest tissue expression in muscle, followed by hepatopancreas. EsRab7 was significantly upregulated in hemocytes after stimulation by Gram-positive Staphylococcus aureus or Gram-negative Vibrio parahaemolyticus. Further studies showed that EsRab7 knockdown during bacterial stimulation resulted in decreased bacterial phagocytosis. In addition, EsRab7 regulated the expression of antimicrobial peptides via the Toll signaling pathway. Collectively, these results demonstrate that EsRab7 plays critical roles in antimicrobial function in the Chinese mitten crab.

Endosomes and Autophagy: Regulators of Pulmonary Endothelial Cell Homeostasis in Health and Disease

Significance: Alterations in oxidant/antioxidant balance injure pulmonary endothelial cells and are important in the pathogenesis of lung diseases, such as Acute Respiratory Distress Syndrome (ARDS), ischemia/reperfusion injury, pulmonary arterial hypertension (PAH), and emphysema. Recent Advances: The endosomal and autophagic pathways regulate cell homeostasis. Both pathways support recycling or degradation of macromolecules or organelles, targeted to endosomes or lysosomes, respectively. Thus, both processes promote cell survival. However, with environmental stress or injury, imbalance in endosomal and autophagic pathways may enhance macromolecular or organelle degradation, diminish biosynthetic processes, and cause cell death. Critical Issues: While the role of autophagy in cellular homeostasis in pulmonary disease has been investigated, the role of the endosome in the lung vasculature is less known. Furthermore, autophagy can either decrease or exacerbate endothelial injury, depending upon inciting insult and disease process. Future Directions: Diseases affecting the pulmonary endothelium, such as emphysema, ARDS, and PAH, are linked to altered endosomal or autophagic processing, leading to enhanced degradation of macromolecules and potential cell death. Efforts to target this imbalance have yielded limited success as treatments for lung injuries, which may be due to the complexity of both processes. It is possible that endosomal trafficking proteins, such as Rab GTPases and late endosomal/lysosomal adaptor, MAPK and MTOR activator 1, may be novel therapeutic targets. While endocytosis or autophagy have been linked to improved function of the pulmonary endothelium in vitro and in vivo, further studies are needed to identify targets for modulating cellular homeostasis in the lung.

Differential proteomic profiles and characterizations between hyalinocytes and granulocytes in ivory shell Babylonia areolata

The haemocytes of the ivory shell, Babylonia areolata are classified by morphologic observation into the following types: hyalinocytes (H) and granulocytes (G). Haemocytes comprise diverse cell types with morphological and functional heterogene and play indispensable roles in immunological homeostasis of invertebrates. In the present study, two types of haemocytes were morphologically identified and separated as H and G by Percoll density gradient centrifugation. The differentially expressed proteins were investigated between H and G using mass spectrometry. The results showed that total quantitative proteins between H and G samples were 1644, the number of up-regulated proteins in G was 215, and the number of down-regulated proteins in G was 378. Among them, cathepsin, p38 MAPK, toll-interacting protein-like and beta-adrenergic receptor kinase 2-like were up-regulated in G; alpha-2-macroglobulin-like protein, C-type lectin, galectin-2-1, galectin-3, β-1,3-glucan-binding protein, ferritin, mega-hemocyanin, mucin-17-like, mucin-5AC-like and catalytic subunit of protein kinase A were down-regulated in G. The results showed that the most significantly enriched KEGG pathways were the pathways related to ribosome, phagosome, endocytosis, carbon metabolism, protein processing in endoplasmic reticulum and oxidative phosphorylation. For phagosome and endocytosis pathway, the number of down-regulation proteins in G was more than that of up-regulation proteins. For lysosome pathway, the number of up-regulation proteins in G was more than that of down-regulation proteins. These results suggested that two sub-population haemocytes perform the different immune functions in B. areolata.

Rab32 GTPase, as a direct target of miR-30b/c, controls the intracellular survival of Burkholderia pseudomallei by regulating phagosome maturation

Burkholderia pseudomallei is a gram-negative, facultative intracellular bacterium, which causes a disease known as melioidosis. Professional phagocytes represent a crucial first line of innate defense against invading pathogens. Uptake of pathogens by these cells involves the formation of a phagosome that matures by fusing with early and late endocytic vesicles, resulting in killing of ingested microbes. Host Rab GTPases are central regulators of vesicular trafficking following pathogen phagocytosis. However, it is unclear how Rab GTPases interact with B. pseudomallei to regulate the transport and maturation of bacterial-containing phagosomes. Here, we showed that the host Rab32 plays an important role in mediating antimicrobial activity by promoting phagosome maturation at an early phase of infection with B. pseudomallei. And we demonstrated that the expression level of Rab32 is increased through the downregulation of the synthesis of miR-30b/30c in B. pseudomallei infected macrophages. Subsequently, we showed that B. pseudomallei resides temporarily in Rab32-positive compartments with late endocytic features. And Rab32 enhances phagosome acidification and promotes the fusion of B. pseudomallei-containing phagosomes with lysosomes to activate cathepsin D, resulting in restricted intracellular growth of B. pseudomallei. Additionally, Rab32 mediates phagosome maturation depending on its guanosine triphosphate/guanosine diphosphate (GTP/GDP) binding state. Finally, we report the previously unrecognized role of miR-30b/30c in regulating B. pseudomallei-containing phagosome maturation by targeting Rab32 in macrophages. Altogether, we provide a novel insight into the host immune-regulated cellular pathway against B. pseudomallei infection is partially dependent on Rab32 trafficking pathway, which regulates phagosome maturation and enhances the killing of this bacterium in macrophages.

Bullous Pemphigoid IgG Induces Cell Dysfunction and Enhances the Motility of Epidermal Keratinocytes via Rac1/Proteasome Activation

Bullous pemphigoid (BP) is an autoimmune disease characterized by the formation of blisters, in which autoantibodies mainly target type XVII collagen (ColXVII) expressed in basal keratinocytes. BP IgG is known to induce the internalization of ColXVII from the plasma membrane of keratinocytes through macropinocytosis. However, the cellular dynamics following ColXVII internalization have not been completely elucidated. BP IgG exerts a precise effect on cultured keratinocytes, and the morphological/functional changes in BP IgG-stimulated cells lead to the subepidermal blistering associated with BP pathogenesis. Based on the electron microscopy examination, BP IgG-stimulated cells exhibit alterations in the cell membrane structure and the accumulation of intracellular vesicles. These morphological changes in the BP IgG-stimulated cells are accompanied by dysfunctional mitochondria, increased production of reactive oxygen species, increased motility, and detachment. BP IgG triggers the cascade leading to metabolic impairments and stimulates cell migration in the treated keratinocytes. These cellular alterations are reversed by pharmacological inhibitors of Rac1 or the proteasome pathway, suggesting that Rac1 and proteasome activation are involved in the effects of BP IgG on cultured keratinocytes. Our study highlights the role of keratinocyte kinetics in the direct functions of IgG in patients with BP.

The origins and evolution of macropinocytosis

In macropinocytosis, cells take up micrometre-sized droplets of medium into internal vesicles. These vesicles are acidified and fused to lysosomes, their contents digested and useful compounds extracted. Indigestible contents can be exocytosed. Macropinocytosis has been known for approaching 100 years and is described in both metazoa and amoebae, but not in plants or fungi. Its evolutionary origin goes back to at least the common ancestor of the amoebozoa and opisthokonts, with apparent secondary loss from fungi. The primary function of macropinocytosis in amoebae and some cancer cells is feeding, but the conserved processing pathway for macropinosomes, which involves shrinkage and the retrieval of membrane to the cell surface, has been adapted in immune cells for antigen presentation. Macropinocytic cups are large actin-driven processes, closely related to phagocytic cups and pseudopods and appear to be organized around a conserved signalling patch of PIP3, active Ras and active Rac that directs actin polymerization to its periphery. Patches can form spontaneously and must be sustained by excitable kinetics with strong cooperation from the actin cytoskeleton. Growth-factor signalling shares core components with macropinocytosis, based around phosphatidylinositol 3-kinase (PI3-kinase), and we suggest that it evolved to take control of ancient feeding structures through a coupled growth factor receptor. This article is part of the Theo Murphy meeting issue 'Macropinocytosis'.

The Phosphoinositide Kinase PIKfyve Promotes Cathepsin-S-Mediated Major Histocompatibility Complex Class II Antigen Presentation

Antigen presentation to T cells in major histocompatibility complex class II (MHC class II) requires the conversion of early endo/phagosomes into lysosomes by a process called maturation. Maturation is driven by the phosphoinositide kinase PIKfyve. Blocking PIKfyve activity by small molecule inhibitors caused a delay in the conversion of phagosomes into lysosomes and in phagosomal acidification, whereas production of reactive oxygen species (ROS) increased. Elevated ROS resulted in reduced activity of cathepsin S and B, but not X, causing a proteolytic defect of MHC class II chaperone invariant chain Ii processing. We developed a novel universal MHC class II presentation assay based on a bio-orthogonal "clickable" antigen and showed that MHC class II presentation was disrupted by the inhibition of PIKfyve, which in turn resulted in reduced activation of CD4⁺ T cells. Our results demonstrate a key role of PIKfyve in the processing and presentation of antigens, which should be taken into consideration when targeting PIKfyve in autoimmune disease and cancer.

Hypoxia in Combination With Muscle Contraction Improves Insulin Action and Glucose Metabolism in Human Skeletal Muscle via the HIF-1α Pathway

Skeletal muscle insulin resistance is the hallmark of type 2 diabetes and develops long before the onset of the disease. It is well accepted that physical activity improves glycemic control, but the knowledge on underlying mechanisms mediating the beneficial effects remains incomplete. Exercise is accompanied by a decrease in intramuscular oxygen levels, resulting in induction of HIF-1α. HIF-1α is a master regulator of gene expression and might play an important role in skeletal muscle function and metabolism. Here we show that HIF-1α is important for glucose metabolism and insulin action in skeletal muscle. By using a genome-wide gene expression profiling approach, we identified RAB20 and TXNIP as two novel exercise/HIF-1α-regulated genes in skeletal muscle. Loss of Rab20 impairs insulin-stimulated glucose uptake in human and mouse skeletal muscle by blocking the translocation of GLUT4 to the cell surface. In addition, exercise/HIF-1α downregulates the expression of TXNIP, a well-known negative regulator of insulin action. In conclusion, we are the first to demonstrate that HIF-1α is a key regulator of glucose metabolism in skeletal muscle by directly controlling the transcription of RAB20 and TXNIP These results hint toward a novel function of HIF-1α as a potential pharmacological target to improve skeletal muscle insulin sensitivity.

Clathrin-mediated endocytosis is required for ANE 30-100K-induced autophagy

BACKGROUND

We identified an autophagy-inducing areca nut (AN) ingredient (AIAI) in the 30-100 kDa fraction of AN extract (ANE 30-100K). This study was to analyze the role of endocytosis in ANE 30-100K-induced autophagy.

METHODS

We used benzyl alcohol, dynasore, and shRNA of clathrin and dynamin to assess whether ANE 30-100K-induced cytotoxicity and accumulation of microtubule-associated protein 1 light chain 3 (LC3)-II were affected in oral (OECM-1) and esophageal (CE81T/VGH) carcinoma cells.

RESULTS

Both benzyl alcohol and dynasore effectively reduced ANE 30-100K-induced cytotoxicity and LC3-II accumulation in OECM-1 and CE81T/VGH cells. Downregulated protein expression of both clathrin and dynamin by their shRNA also significantly attenuated ANE 30-100K-induced elevation of LC3-II levels in CE81T/VGH cells.

CONCLUSIONS

These results indicate that AIAI may be engulfed by cells through clathrin-mediated endocytosis, which promotes the execution of the following autophagy program.

Comprehensive Transcriptome Analysis Provides Evidence of Local Thermal Adaptation in Three Loaches (Genus: Misgurnus)

The geographic distribution of three Misgurnus species, M. anguillicaudatus, M. bipartitus, and M. mohoity, displays a specific pattern in China, coincident with temperature zones. In this study, we sequenced the transcriptomes of these three species and used the sequences to investigate the lineage-specific adaptations within the genus Misgurnus. In total, 51 orphan genes (19 in M. anguillicaudatus, 18 in M. bipartitus, and 14 in M. mohoity) that may contribute to the species-specific adaptations were identified. An analysis of 1392 one-to-one orthologous genes revealed significantly higher ratios of nonsynonymous-to-synonymous substitutions in the M. mohoity lineage than in M. anguillicaudatus. The genes displaying signatures of positive selection and rapid evolution in Misgurnus were involved in four function categories, (1) energy metabolism; (2) signal transduction; (3) membrane; and (4) cell proliferation or apoptosis, implying that these candidate genes play critical roles in the thermal adaptation of the fish to their living environments. We also detected more than five positively selected sites in cldn15lb and isca1, which function as important factors in paracellular Na⁺ transport and Fe/S cluster assembly, respectively. Overall, our study provides valuable insights into the adaptive evolution of loaches from different temperature zones in China and is a foundation for future studies to clarify the genetic basis of temperature adaptation in fishes.