Initially identified as a key phosphoinositide that controls membrane trafficking at the Golgi complex, phosphatidylinositol‐4‐phosphate (PI4P) has emerged as a key molecule in the regulation of a ...diverse array of cellular functions. In this review we will discuss selected examples of the findings that in the last few years have significantly increased our awareness of the regulation and roles of PI4P in the Golgi complex and beyond. We will also highlight the role of PI4P in infection and cancer. We believe that, with the increasing number of regulators and effectors of PI4P identified, the time is ripe for a more integrated approach of study. A first step in this direction is the delineation of PI4P‐centered molecular networks that we provide using data from low and high throughput studies in yeast and mammals.
Intra‐ and extracellular stimuli generate localized pools of PI4P through the dynamic localization of PI4 kinases and PI4P phosphatases. PI4P recruits effector proteins, often in cooperation with accessory factors, to distinct membrane districts thus mediating multiple compartment‐specific cellular functions.
Retinal gene therapy with adeno-associated viral (AAV) vectors holds promises for treating inherited and noninherited diseases of the eye. Although clinical data suggest that retinal gene therapy is ...safe and effective, delivery of large genes is hindered by the limited AAV cargo capacity. Protein trans-splicing mediated by split inteins is used by single-cell organisms to reconstitute proteins. Here, we show that delivery of multiple AAV vectors each encoding one of the fragments of target proteins flanked by short split inteins results in protein trans-splicing and full-length protein reconstitution in the retina of mice and pigs and in human retinal organoids. The reconstitution of large therapeutic proteins using this approach improved the phenotype of two mouse models of inherited retinal diseases. Our data support the use of split intein-mediated protein trans-splicing in combination with AAV subretinal delivery for gene therapy of inherited blindness due to mutations in large genes.
Itraconazole (ITZ) is a well-known antifungal agent that also has anticancer activity. In this study, we identify ITZ as a broad-spectrum inhibitor of enteroviruses (e.g., poliovirus, coxsackievirus, ...enterovirus-71, rhinovirus). We demonstrate that ITZ inhibits viral RNA replication by targeting oxysterol-binding protein (OSBP) and OSBP-related protein 4 (ORP4). Consistently, OSW-1, a specific OSBP/ORP4 antagonist, also inhibits enterovirus replication. Knockdown of OSBP inhibits virus replication, whereas overexpression of OSBP or ORP4 counteracts the antiviral effects of ITZ and OSW-1. ITZ binds OSBP and inhibits its function, i.e., shuttling of cholesterol and phosphatidylinositol-4-phosphate between membranes, thereby likely perturbing the virus-induced membrane alterations essential for viral replication organelle formation. ITZ also inhibits hepatitis C virus replication, which also relies on OSBP. Together, these data implicate OSBP/ORP4 as molecular targets of ITZ and point to an essential role of OSBP/ORP4-mediated lipid exchange in virus replication that can be targeted by antiviral drugs.
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•ITZ, an antifungal and anticancer agent, is a broad-spectrum enterovirus inhibitor•OSBP and ORP4 are identified as novel targets of ITZ•ITZ binds OSBP and inhibits OSBP-mediated lipid exchange at membrane contact sites•ITZ also inhibits hepatitis C virus replication
Strating et al. present the antifungal drug itraconazole as a novel inhibitor of a broad range of viruses, including poliovirus and hepatitis C virus. Itraconazole acted on a novel target, the oxysterol-binding protein (OSBP), a protein that has an essential role in lipid transfer.
Batten diseases (BDs) are a group of lysosomal storage disorders characterized by seizure, visual loss, and cognitive and motor deterioration. We discovered increased levels of globotriaosylceramide ...(Gb3) in cellular and murine models of CLN3 and CLN7 diseases and used fluorescent‐conjugated bacterial toxins to label Gb3 to develop a cell‐based high content imaging (HCI) screening assay for the repurposing of FDA‐approved compounds able to reduce this accumulation within BD cells. We found that tamoxifen reduced the lysosomal accumulation of Gb3 in CLN3 and CLN7 cell models, including neuronal progenitor cells (NPCs) from CLN7 patient‐derived induced pluripotent stem cells (iPSC). Here, tamoxifen exerts its action through a mechanism that involves activation of the transcription factor EB (TFEB), a master gene of lysosomal function and autophagy. In vivo administration of tamoxifen to the CLN7Δex2 mouse model reduced the accumulation of Gb3 and SCMAS, decreased neuroinflammation, and improved motor coordination. These data strongly suggest that tamoxifen may be a suitable drug to treat some types of Batten disease.
SYNOPSIS
The neuronal ceroid lipofuscinoses (NCL), commonly known as Batten disease (BD), are a group of recessively inherited fatal diseases of the nervous system that typically arise in childhood. There is neither cure nor drugs to revert the course of these diseases.
Neural accumulation of lysosomal Gb3 is a novel hallmark of CLN3 and CLN7 batten diseases.
The FDA‐approved drug tamoxifen reverts pathological phenotype of CLN3 and CLN7 diseases in vitro and in vivo.
Tamoxifen effects are independent of the modulation of estrogen receptors but require the activation of TFEB.
The neuronal ceroid lipofuscinoses (NCL), commonly known as Batten disease (BD), are a group of recessively inherited fatal diseases of the nervous system that typically arise in childhood. There is neither cure nor drugs to revert the course of these diseases.
The activation state of the EGF receptor (EGF-R) is tightly controlled in the cell so as to prevent excessive signalling, with the dangerous consequences that this would have on cell growth and ...proliferation. This control occurs at different levels, with a key level being the trafficking and degradation of the EGF-R itself. Multiple guanosine triphosphatases belonging to the Arf, Rab and Rho families and their accessory proteins have key roles in these processes. In this study, we have identified ARAP1, a multidomain protein with both Arf GTPase-activating protein (GAP) and Rho GAP activities, as a novel component of the machinery that controls the trafficking and signalling of the EGF-R. We show that ARAP1 localizes to multiple cell compartments, including the Golgi complex, as previously reported, and endosomal compartments, where it is enriched in the internal membranes of multivesicular bodies. ARAP1 distribution is controlled by its phosphorylation and by its interactions with the 3- and 4-phosphorylated phosphoinositides through its five PH domains. We provide evidence that ARAP1 controls the late steps of the endocytic trafficking of the EGF-R, with ARAP1 knockdown leading to EGF-R accumulation in a sorting/late endosomal compartment and to the inhibition of EGF-R degradation that is accompanied by prolonged signalling.
Microsporidia are obligatory intracellular parasites, most species of which live in the host cell cytosol. They synthesize and then transport secretory proteins from the endoplasmic reticulum to the ...plasma membrane for formation of the spore wall and the polar tube for cell invasion. However, microsporidia do not have a typical Golgi complex. Here, using quick-freezing cryosubstitution and chemical fixation, we demonstrate that the Golgi analogs of the microsporidia Paranosema (Antonospora) grylli and Paranosema locustae appear as 300-nm networks of thin (25- to 40-nm diameter), branching or varicose tubules that display histochemical features of a Golgi, but that do not have vesicles. Vesicles are not formed even if membrane fusion is inhibited. These tubular networks are connected to the endoplasmic reticulum, the plasma membrane and the forming polar tube, and are positive for Sec13, γCOP and analogs of giantin and GM130. The spore-wall and polar-tube proteins are transported from the endoplasmic reticulum to the target membranes through these tubular networks, within which they undergo concentration and glycosylation. We suggest that the intracellular transport of secreted proteins in microsporidia occurs by a progression mechanism that does not involve the participation of vesicles generated by coat proteins I and II.
Close proximities between organelles have been described for decades. However, only recently a specific field dealing with organelle communication at membrane contact sites has gained wide ...acceptance, attracting scientists from multiple areas of cell biology. The diversity of approaches warrants a unified vocabulary for the field. Such definitions would facilitate laying the foundations of this field, streamlining communication and resolving semantic controversies. This opinion, written by a panel of experts in the field, aims to provide this burgeoning area with guidelines for the experimental definition and analysis of contact sites. It also includes suggestions on how to operationally and tractably measure and analyze them with the hope of ultimately facilitating knowledge production and dissemination within and outside the field of contact-site research.
Abstract Toxicity of silver nanoparticles (AgNPs) is supported by many observations in literature, but no mechanism details have been proved yet. Here we confirm and quantify the toxic potential of ...fully characterized AgNPs in HeLa and A549 cells. Notably, through a specific fluorescent probe, we demonstrate the intracellular release of Ag+ ions in living cells after nanoparticle internalization, showing that in-situ particle degradation is promoted by the acidic lysosomal environment. The activation of metallothioneins in response to AgNPs and the possibility to reverse the main toxic pathway by Ag+ chelating agents demonstrate a cause/effect relationship between ions and cell death. We propose that endocytosed AgNPs are degraded in the lysosomes and the release of Ag+ ions in the cytosol induces cell damages, while ions released in the cell culture medium play a negligible effect. These findings will be useful to develop safer-by-design nanoparticles and proper regulatory guidelines of AgNPs. From the Clinical Editor The authors describe the toxic potential of silver nanoparticles (AgNP) in human cancer cell lines. Cell death following the application of AgNPs is dose-dependent, and it is mostly due to Ag+ ions. Further in vivo studies should be performed to gain a comprehensive picture of AgNP-toxicity in mammals.
Adipose tissue expansion involves the enlargement of existing adipocytes, the formation of new cells from committed preadipocytes, and the coordinated development of the tissue vascular network. Here ...we find that murine endothelial cells (ECs) of classic white and brown fat depots share ultrastructural characteristics with pericytes, which are pluripotent and can potentially give rise to preadipocytes. Lineage tracing experiments using the VE-cadherin promoter reveal localization of reporter genes in ECs and also in preadipocytes and adipocytes of white and brown fat depots. Furthermore, capillary sprouts from human adipose tissue, which have predominantly EC characteristics, are found to express Zfp423, a recently identified marker of preadipocyte determination. In response to PPARγ activation, endothelial characteristics of sprouting cells are progressively lost, and cells form structurally and biochemically defined adipocytes. Together these data support an endothelial origin of murine and human adipocytes, suggesting a model for how adipogenesis and angiogenesis are coordinated during adipose tissue expansion.
► Progression of phenotypes from endothelial to preadipose seen in developing adipose tissues ► VE-cadherin promoter-driven tracers are found in adipocytes from white and brown adipose tissues ► Endothelial cells growing from human adipose tissue explants can develop mature adipocyte features ► A population of adipocyte stem cells from white and brown adipose tissue expresses VE-cadherin
Background
A remarkably high incidence of venous thromboembolism (VTE) has been reported among critically ill patients with COVID‐19 assisted in the intensive care unit (ICU). However, VTE burden ...among non‐ICU patients hospitalized for COVID‐19 that receive guideline‐recommended thromboprophylaxis is unknown.
Objectives
To determine the incidence of VTE among non‐ICU patients hospitalized for COVID‐19 that receive pharmacological thromboprophylaxis.
Methods
We performed a systematic screening for the diagnosis of deep vein thrombosis (DVT) by lower limb vein compression ultrasonography (CUS) in consecutive non‐ICU patients hospitalized for COVID‐19, independent of the presence of signs or symptoms of DVT. All patients were receiving pharmacological thromboprophylaxis with either enoxaparin or fondaparinux.
Results
The population that we screened consisted of 84 consecutive patients, with a mean age of 67.6 ± 13.5 years and a mean Padua Prediction Score of 5.1 ± 1.6. Seventy‐two patients (85.7%) had respiratory insufficiency, required oxygen supplementation, and had reduced mobility or were bedridden. In this cohort, we found 10 cases of DVT, with an incidence of 11.9% (95% confidence interval CI 4.98‐18.82). Of these, 2 were proximal DVT (incidence rate 2.4%, 95% CI −0.87‐5.67) and 8 were distal DVT (incidence rate 9.5%, 95% CI 3.23‐5.77). Significant differences between subjects with and without DVT were D‐dimer > 3000 µg/L (P < .05), current or previous cancer (P < .05), and need of high flow nasal oxygen therapy and/or non‐invasive ventilation (P < .01).
Conclusions
DVT may occur among non‐ICU patients hospitalized for COVID‐19, despite guideline‐recommended thromboprophylaxis.
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