Endocytic Pathway Research Articles

Outer membrane vesicles derived from gut microbiota mediate tubulointerstitial inflammation: a potential new mechanism for diabetic kidney disease.

Rationale: Chronic tubulointerstitial inflammation is a common pathological process in diabetic kidney disease (DKD). However, its underlying mechanism is largely unknown. This study aims at investigating the role of gut microbiota-derived outer membrane vesicles (OMVs) in tubulointerstitial inflammation in DKD. Methods: Gut microbiota in diabetes mellitus rats was manipulated by microbiota depletion and fecal microbiota transplantation to explore its role in tubulointerstitial inflammation. To check the direct effects of OMVs, fecal bacterial extracellular vesicles (fBEVs) were administrated to mice orally and HK-2 cells in vitro. For mechanistic investigations, HK-2 cells were treated with small interfering RNA against caspase-4 and fBEVs pre-neutralized by polymyxin B. Results: By performing gut microbiota manipulation, it was confirmed that gut microbiota mediated tubulointerstitial inflammation in DKD. In diabetic rats, gut microbiota-derived OMVs were increased and were clearly detected in distant renal tubulointerstitium. Diabetic fBEVs directly administered by gavage translocated into tubular epithelial cells and induced tubulointerstitial inflammation and kidney injury. In vitro, OMVs were internalized through various endocytic pathways and triggered cellular inflammatory response. Mechanistically, it was revealed that OMVs-derived lipopolysaccharide induced tubular inflammation, which was mediated by the activation of the caspase-11 pathway. Conclusions: Increased OMVs due to dysbiosis translocated through leaky gut barrier into distant tubulointerstitium and induced cellular inflammation and renal tubulointerstitial injury in DKD. These findings enrich the mechanism understanding of how gut microbiota and its releasing OMVs influence the development and progression of kidney disease.

Delivery of siRNA using cationic rosette nanotubes for gene silencing.

The quest for new therapeutic treatments for hereditary diseases has led to many advances in RNA interference (RNAi) and gene silencing. While this technique has the potential to address many problems, the key to its continued use is the development of effective delivery strategies that would reduce cellular toxicity and increase silencing efficiency. Rosette nanotubes (RNTs) are biomimetic supramolecular nanostructures formed through the self-assembly of hybrid guanine-cytosine (G∧C) DNA bases. Here, we used bioactive RNTs for siRNA delivery and gene silencing. Fifteen lysine-functionalized twin-G∧C motifs (KnT, n = 1 to 15) were synthesized using solid phase peptide synthesis to produce building blocks that self-assembled to produce cationic RNTs under physiological conditions. The intracellular uptake of siRNA delivered by the oligo-L-lysine RNTs was examined and it was found that the complexation of siRNA was affected by the cationic charges from the lysine residues and the length of RNTs formed, with the higher charged KnT RNTs delivering siRNA to the cells at a faster rate. In addition, by protecting siRNA from serum degradation, KnT RNTs were shown to deliver their cargo to the cells effectively via the endocytic pathway. A reduction in the expression (∼70%) of the target stat3 protein was observed during gene expression analysis in HCT116 and A549 cell lines.

Rhenium(I) Block Copolymers Based on Polyvinylpyrrolidone: A Successful Strategy to Water-Solubility and Biocompatibility

A series of diphosphine Re(I) complexes Re1-Re4 have been designed via decoration of the archetypal core {Re(CO)2(N^N)} through the installations of the phosphines P0 and P1 bearing the terminal double bond, where N^N = 2,2'-bipyridine (N^N1), 4,4'-di-tert-butyl-2,2'-bipyridine (N^N2) or 2,9-dimethyl-1,10-phenanthroline (N^N3) and P0 = diphenylvinylphosphine, and P1 = 4-(diphenylphosphino)styrene. These complexes were copolymerized with the corresponding N-vinylpyrrolidone-based Macro-RAFT agents of different polymer chain lengths to give water-soluble copolymers of low-molecular p(VP-l-Re) and high-molecular p(VP-h-Re) block-copolymers containing rhenium complexes. Compounds Re1-Re4, as well as the copolymers p(VP-l-Re) and p(VP-h-Re), demonstrate phosphorescence from a 3MLCT excited state typical for this type of chromophores. The copolymers p(VP-l-Re#) and p(VP-h-Re#) display weak sensitivity to molecular oxygen in aqueous and buffered media, which becomes almost negligible in the model physiological media. In cell experiments with CHO-K1 cell line, p(VP-l-Re2) and p(VP-h-Re2) displayed significantly reduced toxicity compared to the initial Re2 complex and internalized into cells presumably by endocytic pathways, being eventually accumulated in endosomes. The sensitivity of the copolymers to oxygen examined in CHO-K1 cells via phosphorescence lifetime imaging microscopy (PLIM) proved to be inessential.

Using Ion Substitution and Fluid Indicators to Monitor Macropinosome Dynamics in Live Cells.

All forms of endocytosis involve the incidental uptake of fluid (pinocytosis). Macropinocytosis is a specialized type of endocytosis that results in the bulk ingestion of extracellular fluid via large (>0.2μm) vacuoles called macropinosomes. The process is a means of immune surveillance, a point of entry for intracellular pathogens, and a source of nutrients for proliferating cancer cells. Macropinocytosis has also recently emerged as a tractable system that can be experimentally exploited to understand fluid handling in the endocytic pathway. In this chapter, we describe how stimulating macropinocytosis in the presence of extracellular fluids of a defined ionic composition can be combined with high-resolution microscopy to understand the role of ion transport in controlling membrane traffic.

Negatively charged Cu1.33S nanochains: endocytic pathway, photothermal therapy and toxic effect in vivo.

Negatively charged nanomaterials have good biocompatibility and low cytotoxicity, but the efficiency of their entry into cells is relatively low. Thus, striking a balance between cell transport efficiency and cytotoxicity is a challenging problem in the field of nanomedicine. In this work, negatively charged Cu1.33S nanochains have shown a higher cellular uptake level in 4T1 cells than Cu1.33S nanoparticles with a similar diameter and surface charge. Inhibition experiments indicate that the cellular uptake of the nanochains depends principally on the lipid-raft protein (i.e. caveolin-1) mediated pathway, although the role of clathrin cannot be ruled out. Caveolin-1 can provide short-range attraction at the membrane interface. Furthermore, by using biochemical analysis, blood routine examination and histological evaluation on healthy Sprague Dawley rats, it is found that the Cu1.33S nanochains have no obvious toxic effect. The Cu1.33S nanochains have an effective photothermal therapy effect of tumor ablation in vivo under low injection dosage and laser intensity. As for the best performing group (20 μg + 1 W cm-2), the temperature of the tumor site rapidly increases within the initial 3 min and rises to a plateau of 79 °C (ΔT = 46 °C) at 5 min. These results reveal the feasibility of the Cu1.33S nanochains as a photothermal agent.

Detection by super-resolution microscopy of viral proteins inside bloodborne extracellular vesicles

Aim: Extracellular vesicles (EVs) are small particles released by all cells, including virally infected cells, into the extracellular space. They play a role in various cellular processes, including intercellular communication, signaling, and immunity, and carry several biomolecules like proteins, lipids, and nucleic acids that can modulate cellular functions mostly by releasing their cargo inside the target cells via the endocytic pathway. One of the most exciting aspects of EV physiology is its potential in liquid biopsy as a diagnostic and prognostic marker. However, due to their extremely small size and lack of a molecular approach to examine intravesicular content or cargo, we cannot fully utilize their potential in healthcare. Methods: Here, we present a novel approach that allows examining bloodborne EVs at a single-particle level with the ability to examine their cargo without disrupting structural integrity. Our technique utilizes super-resolution microscopy and a unique permeabilization process that maintains structural integrity while facilitating the examination of EV cargo. We used a mild-detergent-based permeabilization buffer that protects the integrity of EVs, minimizes background, and improves detection. Results: Utilizing this approach, we were able to recognize viral proteins of SARS-CoV-2 virus in COVID-19 patients, including spike and nucleocapsid. Surprisingly, we found an almost equal amount of spike protein inside and on the surface of bloodborne EVs. This would have proven difficult to determine using other conventional methods. Conclusion: To summarize, we have developed an easy-to-perform, sensitive, and highly efficient method that offers a mechanism to examine bloodborne EV cargo without disrupting their structural integrity.

The logistics of Wnt production and delivery.

Wnts are secreted proteins that control stem cell maintenance, cell fate decisions, and growth during development and adult homeostasis. Wnts carry a post-translational modification not seen in any other secreted protein: during biosynthesis, they are appended with a palmitoleoyl moiety that is required for signaling but also impairs solubility and hence diffusion in the extracellular space. In some contexts, Wnts act only in a juxtacrine manner but there are also instances of long range action. Several proteins and processes ensure that active Wnts reach the appropriate target cells. Some, like Porcupine, Wntless, and Notum are dedicated to Wnt function; we describe their activities in molecular detail. We also outline how the cell infrastructure (secretory, endocytic, and retromer pathways) contribute to the progression of Wnts from production to delivery. We then address how Wnts spread in the extracellular space and form a signaling gradient despite carrying a hydrophobic moiety. We highlight particularly the role of lipid-binding Wnt interactors and heparan sulfate proteoglycans. Finally, we briefly discuss how evolution might have led to the emergence of this unusual signaling pathway.

Recombinant IL-37 Exerts an Anti-inflammatory Effect on Human Aortic Valve Interstitial Cells through Extracellular and Intracellular Actions.

Calcific aortic valve disease (CAVD) is a chronic inflammatory disease with slow progression that involves soluble extracellular matrix (ECM) proteins. Previously, we found that recombinant interleukin (IL)-37 suppresses aortic valve interstitial cells (AVIC) inflammatory response through the interaction with IL-18 receptor α-chain (IL-18Rα) on the cell surface. Endogenous IL-37 can be retained in the cytoplasm or released into extracellular spaces. It remains unknown whether recombinant IL-37 exerts the anti-inflammatory effect through intracellular action. Here, we found that recombinant IL-37 suppressed AVIC inflammatory response to soluble ECM proteins. Interestingly, recombinant IL-37 was internalized by human AVICs in an IL-18Rα-independent fashion. Blocking endocytic pathways reduced the internalization and anti-inflammatory potency of recombinant IL-37. Overexpression of IL-37 in human AVICs suppressed soluble ECM proteins-induced NF-κB activation and the production of ICAM-1 and VCAM-1. However, IL-37D20A (mutant IL-37 lacking nucleus-targeting sequences) overexpression had no such effect, and the inflammatory response to soluble ECM proteins was essentially intact in AVICs from transgenic mice expressing IL-37D20A. Together, recombinant IL-37 can be internalized by human AVICs through endocytosis. Intracellular IL-37 exerts an anti-inflammatory effect through a nucleus-targeting mechanism. This study highlights the potent anti-inflammatory effect of recombinant IL-37 in both extracellular and intracellular compartments through distinct mechanisms.

Canonical and Non-Canonical Roles of SNX1 and SNX2 in Endosomal Membrane Dynamics.

Sorting nexins (SNXs) are a family of membrane-binding proteins known to play a critical role in regulating endocytic pathway sorting and endosomal membrane trafficking. Among them, SNX1 and SNX2 are members of the SNX-BAR subfamily and possess a membrane-curvature domain and a phosphoinositide-binding domain, which enables their stabilization at the phosphatidylinositol-3-phosphate (PI3P)-positive surface of endosomes. While their binding to PI3P-positive platforms facilitates interaction with endosomal partners and stabilization at the endosomal membrane, their SNX-BAR region is pivotal for generating membrane tubulation from endosomal compartments. In this context, their primary identified biological roles-and their partnership-are tightly associated with the retromer and endosomal SNX-BAR sorting complex for promoting exit 1 complex trafficking, facilitating the transport of cargoes from early endosomes to the secretory pathway. However, recent literature indicates that these proteins also possess biological functions in other aspects of endosomal features and sorting processes. Notably, SNX2 has been found to regulate endosome-endoplasmic reticulum (ER) contact sites through its interaction with VAP proteins at the ER membrane. Furthermore, data from our laboratory show that SNX1 and SNX2 are involved in the tubulation of early endosomes toward ER sites associated with autophagy initiation during starvation. These findings shed light on a novel role of SNXs in inter-organelle tethering and communication. In this concise review, we will explore the non-retromer functions of SNX1 and SNX2, specifically focusing on their involvement in endosomal membrane dynamics during stress sensing and autophagy-associated processes.

Insights into the function of ESCRT complex and LBPA in ASFV infection.

The African swine fever virus (ASFV) is strongly dependent on an intact endocytic pathway and a certain cellular membrane remodeling for infection, possibly regulated by the endosomal sorting complexes required for transport (ESCRT). The ESCRT machinery is mainly involved in the coordination of membrane dynamics; hence, several viruses exploit this complex and its accessory proteins VPS4 and ALIX for their own benefit. In this work, we found that shRNA-mediated knockdown of VPS4A decreased ASFV replication and viral titers, and this silencing resulted in an enhanced expression of ESCRT-0 component HRS. ASFV infection slightly increased HRS expression but not under VPS4A depletion conditions. Interestingly, VPS4A silencing did not have an impact on ALIX expression, which was significantly overexpressed upon ASFV infection. Further analysis revealed that ALIX silencing impaired ASFV infection at late stages of the viral cycle, including replication and viral production. In addition to ESCRT, the accessory protein ALIX is involved in endosomal membrane dynamics in a lysobisphosphatydic acid (LBPA) and Ca2+-dependent manner, which is relevant for intraluminal vesicle (ILV) biogenesis and endosomal homeostasis. Moreover, LBPA interacts with NPC2 and/or ALIX to regulate cellular cholesterol traffic, and would affect ASFV infection. Thus, we show that LBPA blocking impacted ASFV infection at both early and late infection, suggesting a function for this unconventional phospholipid in the ASFV viral cycle. Here, we found for the first time that silencing of VPS4A and ALIX affects the infection later on, and blocking LBPA function reduces ASFV infectivity at early and later stages of the viral cycle, while ALIX was overexpressed upon infection. These data suggested the relevance of ESCRT-related proteins in ASFV infection.

Fusogenic liposome-coated nanoparticles for rapid internalization into donor corneal endothelial tissue to enable prophylaxis before transplantation.

Cold stress (hypothermia) during storage and cytokine stress due to acute allograft rejection adversely affect the donor corneal endothelium in the short term. Pharmacological pre-treatment (before transplantation) of the donor corneal endothelium or cells (propagated in vitro for cell injection therapy) with microtubule stabilizers, cold stress protectants, and other molecules is an attractive strategy to tackle damage caused by hypothermia and cytokine stress. These molecules can be delivered intracellularly to the donor corneal endothelium or cells at controlled rates for desired periods and with one-time administration using nanoparticles. However, the death-to-preservation time of donor corneas of more than 4 to 6 h significantly decreases endothelial cell density and increases the risk of microbial contamination. Therefore, we have developed fusogenic liposome-coated nanoparticles for rapid internalization of nanoparticles into cultured corneal endothelial cells and ex vivo corneal endothelial tissue. Here, we have shown that the fusogenic liposome-coated nanoparticles have the intrinsic ability to efficiently and rapidly internalize into cultured corneal endothelial cells and ex vivo corneal tissue within 3 h by possibly fusing with the cell membrane and bypassing the endocytic pathway. Lactate dehydrogenase assay showed that the internalized fusogenic liposome-coated nanoparticles did not cause cytotoxicity in endothelial cells associated with the ex vivo cornea for at least up to 2 days. Thus, fusogenic liposome-coated nanoparticles have great potential as a platform for engineering cells and endothelial tissue of donor corneas to facilitate prophylactic drug delivery during storage and after transplantation.

Lassa Virus Structural Biology and Replication.

Lassa virus (LASV) is the causative agent of Lassa fever, an often-fatal hemorrhagic feverthat is endemic in West Africa. LASV virions are enveloped and contain two single-stranded RNA genome segments. Both segments are ambisense and encode two proteins. The nucleoprotein associates with viral RNAs forming ribonucleoprotein complexes. The glycoprotein complex mediates viral attachment and entry. The Zinc protein serves as the matrix protein. Large is a polymerase that catalyzes viral RNA transcription and replication. LASV virion entry occurs via a clathrin-independent endocytic pathway usually involving alpha-dystroglycan and lysosomal associated membrane protein 1 as surface and intracellular receptors, respectively. Advances in understanding LASV structural biology and replication have facilitated development of promising vaccine and drug candidates.

Transmembrane kinase 1-mediated auxin signal regulates membrane-associated clathrin in Arabidopsis roots.

Clathrin-mediated endocytosis (CME) is the major endocytic pathway in eukaryotic cells that directly regulates abundance of plasma membrane proteins. Clathrin triskelia are composed of clathrin heavy chains (CHCs) and light chains (CLCs), and the phytohormone auxin differentially regulates membrane-associated CLCs and CHCs, modulating the endocytosis and therefore the distribution of auxin efflux transporter PIN-FORMED2 (PIN2). However, the molecular mechanisms by which auxin regulates clathrin are still poorly understood. Transmembrane kinase (TMKs) family proteins are considered to contribute to auxin signaling and plant development; it remains unclear whether they are involved in PIN transport by CME. We assessed TMKs involvement in the regulation of clathrin by auxin, using genetic, pharmacological, and cytological approaches including live-cell imaging and immunofluorescence. In tmk1 mutant seedlings, auxin failed to rapidly regulate abundance of both CHC and CLC and to inhibit PIN2 endocytosis, leading to an impaired asymmetric distribution of PIN2 and therefore auxin. Furthermore, TMK3 and TMK4 were shown not to be involved in regulation of clathrin by auxin. In summary, TMK1 is essential for auxin-regulated clathrin recruitment and CME. TMK1 therefore plays a critical role in the establishment of an asymmetric distribution of PIN2 and an auxin gradient during root gravitropism.

Surface morphology live-cell imaging reveals how macropinocytosis inhibitors affect membrane dynamics

Macropinocytosis is a unique endocytic pathway that involves dynamic membrane ruffling and is important in various cellular functions beyond nutrient uptake. Due to its impact, macropinocytosis has been the subject of various studies and macropinocytosis inhibitors have been widely used. However, inhibitors exhibit offtarget effects and could be less specific for macropinocytosis, thereby affecting various cellular mechanisms with effects on nanoscale membrane dynamics that remain elusive. In this study, we revealed how five different inhibitors affect membrane dynamics before and after treatment using scanning ion conductance microscopic imaging on living cells. Our results indicated that cytochalasins and sodium azide exhibited similar slowing effects on horizontal ruffle movements, even though their inhibitory mechanisms are different. In contrast, ruffle deformation and elongation were less strongly inhibited compared to the movements along cell membrane direction. These results suggested the involvement of mechanisms beyond actin polymerization. The ruffles disappeared and the cell surface smoothened upon the 5-(N-ethyl-N-isopropyl)-Amiloride treatment. In the presence of wortmannin, we observed active ruffles but no cup-like structures. These findings and scanning ion conductance microscopy live-cell imaging would potentially contribute to a better understanding of inhibitor effects.

Molecular mechanism underlying desensitization of the proton-activated chloride channel PAC.

Desensitization is a common property of membrane receptors, including ion channels. The newly identified proton-activated chloride (PAC) channel plays an important role in regulating the pH and size of organelles in the endocytic pathway, and is also involved in acid-induced cell death. However, how the PAC channel desensitizes is largely unknown. Here, we show by patch-clamp electrophysiological studies that PAC (also known as TMEM206/ASOR) undergoes pH-dependent desensitization upon prolonged acid exposure. Through structure-guided and comprehensive mutagenesis, we identified several residues critical for PAC desensitization, including histidine (H) 98, glutamic acid (E) 94, and aspartic acid (D) 91 at the extracellular extension of the transmembrane helix 1 (TM1), as well as E107, D109, and E250 at the extracellular domain (ECD)-transmembrane domain (TMD) interface. Structural analysis and molecular dynamic simulations revealed extensive interactions between residues at the TM1 extension and those at the ECD-TMD interface. These interactions likely facilitate PAC desensitization by stabilizing the desensitized conformation of TM1, which undergoes a characteristic rotational movement from the resting and activated states to the desensitized state. Our studies establish a new paradigm of channel desensitization in this ubiquitously expressed ion channel and pave the way for future investigation of its relevance in cellular physiology and disease.

CCDC22 and CCDC93, two potential retriever-interacting proteins, are required for root and root hair growth in Arabidopsis.

Endomembrane trafficking is essential for plant growth and often depends on a balance between secretory and endocytic pathways. VPS26C is a component of the retriever complex which has been shown to function in the recycling of integral plasma membrane proteins in human cell culture and is part of a core retriever complex in Arabidopsis that is required for root hair growth. In this work, we report a characterization of the Arabidopsis homologues of CCDC22 and CCDC93, two additional proteins required for retriever function in humans. Phylogenetic analysis indicates that CCDC22 (AT1G55830) and CCDC93 (AT4G32560) are single copy genes in plants that are present across the angiosperms, but like VPS26C, are absent from the grasses. Both CCDC22 and CCDC93 are required for root and root hair growth in Arabidopsis and localize primarily to the cytoplasm in root epidermal cells. Previous work has demonstrated a genetic interaction between VPS26C function and a VTI13-dependent trafficking pathway to the vacuole. To further test this model, we characterized the vti13 ccdc93 double mutant and show that like vps26c, ccdc93 is a suppressor of the vti13 root hair phenotype. Together this work identifies two new proteins essential for root and root hair growth in plants and demonstrate that the endosomal pathway(s) in which CCDC93 functions is genetically linked to a VTI13-dependent trafficking pathway to the vacuole.

Capturing and Quantifying Particle Transcytosis with Microphysiological Intestine-on-Chip Models.

Understanding the intestinal transport of particles is critical in several fields ranging from optimizing drug delivery systems to capturing health risks from the increased presence of nano- and micro-sized particles in human environment. While Caco-2 cell monolayers grown on permeable supports are the traditional in vitro model used to probe intestinal absorption of dissolved molecules, they fail to recapitulate the transcytotic activity of polarized enterocytes. Here, an intestine-on-chip model is combined with in silico modeling to demonstrate that the rate of particle transcytosis is ≈350× higher across Caco-2 cell monolayers exposed to fluid shear stress compared to Caco-2 cells in standard "static" configuration. This relates to profound phenotypical alterations and highly polarized state of cells grown under mechanical stimulation and it is shown that transcytosis in the microphysiological model is energy-dependent and involves both clathrin and macropinocytosis mediated endocytic pathways. Finally, it is demonstrated that the increased rate of transcytosis through cells exposed to flow is explained by a higher rate of internal particle transport (i.e., vesicular cellular trafficking and basolateral exocytosis), rather than a change in apical uptake (i.e., binding and endocytosis). Taken together, thefindings have important implications for addressing research questions concerning intestinal transport of engineered and environmental particles.

SIDT2 Inhibits Phosphorothioate Antisense Oligonucleotide Activity by Regulating Cellular Localization of Lysosomes.

Phosphorothioate (PS)-modified antisense oligonucleotide (ASO) drugs enter cells through endocytic pathways where a majority are entrapped within membrane-bound endosomes and lysosomes, representing a limiting step for antisense activity. While late endosomes have been identified as a major site for productive PS-ASO release, how lysosomes regulate PS-ASO activity beyond macromolecule degradation remains not fully understood. In this study, we reported that SID1 transmembrane family, member 2 (SIDT2), a lysosome transmembrane protein, can robustly regulate PS-ASO activity. We showed that SIDT2 is required for the proper colocalization between PS-ASO and lysosomes, suggesting an important role of SIDT2 in the entrapment of PS-ASOs in lysosomes. Mechanistically, we revealed that SIDT2 regulates lysosome cellular location. Lysosome location is largely determined by its movement along microtubules. Interestingly, we also observed an enrichment of proteins involved in microtubule function among SIDT2-binding proteins, suggesting that SIDT2 regulates lysosome location via its interaction with microtubule-related proteins. Overall, our data suggest that lysosome protein SIDT2 inhibits PS-ASO activity potentially through its interaction with microtubule-related proteins to place lysosomes at perinuclear regions, thus, facilitating PS-ASO's localization to lysosomes for degradation.

Lomasomes and Other Fungal Plasma Membrane Macroinvaginations Have a Tubular and Lamellar Genesis.

The plasma membrane of filamentous fungi forms large-sized invaginations, which are either tubes or parietal vesicles. Vesicular macroinvaginations at the ultrastructural level correspond to classical lomasomes. There is an assumption that vesicular macroinvaginations/lomasomes may be involved in macrovesicular endocytosis. The original aim of this study was to test for the presence of macroendocytosis in xylotrophic basidiomycetes using time-lapse and Z-stacks fluorescent microscopic technologies. However, the results were unexpected since most of the membrane structures labeled by the endocytic tracer (FM4-64 analog) are various types of plasma membrane macroinvaginations and not any endomembranes. All of these macroinvaginations have a tubular or lamellar genesis. Moreover, under specific conditions of a microscopic preparation, the diameter of the tubes forming the macroinvaginations increases with the time of the sample observation. In addition, the morphology and successive formation of the macroinvaginations mimic the endocytic pathway; these invaginations can easily be mistaken for endocytic vesicles, endosomes, and vacuole-lysosomes. The paper analyzes the various macroinvagination types, suggests their biological functions, and discusses some features of fungal endocytosis. This study is a next step toward understanding complex fungal physiology and is a presentation of a new intracellular tubular system in wood-decaying fungi.

Volleying plasma membrane proteins from birth to death: Role of J-domain proteins.

The function, stability, and turnover of plasma membrane (PM) proteins are crucial for cellular homeostasis. Compared to soluble proteins, quality control of plasma membrane proteins is extremely challenging. Failure to meet the high quality control standards is detrimental to cellular and organismal health. J-domain proteins (JDPs) are among the most diverse group of chaperones that collaborate with other chaperones and protein degradation machinery to oversee cellular protein quality control (PQC). Although fragmented, the available literature from different models, including yeast, mammals, and plants, suggests that JDPs assist PM proteins with their synthesis, folding, and trafficking to their destination as well as their degradation, either through endocytic or proteasomal degradation pathways. Moreover, some JDPs interact directly with the membrane to regulate the stability and/or functionality of proteins at the PM. The deconvoluted picture emerging is that PM proteins are relayed from one JDP to another throughout their life cycle, further underscoring the versatility of the Hsp70:JDP machinery in the cell.