Dynamin inhibitors block activation of mTORC1 by amino acids independently of dynamin

Novel endocytosis inhibitors block entry of HIV-1 Tat into neural cells

Many pathogens including viruses enter cells by endocytosis. We identified and evaluated novel endocytosis inhibitors capable of blocking the entry of the HIV-1 Transactivation of Transcription protein (Tat) protein into neuronal cells and investigated their potential protective properties against Tat-induced neurotoxicity. In this study, the compounds Les-6631 and Les-6633 were synthesized and assessed. The effects of these compounds on the internalization of dextran and the cell-penetrating peptide (CPP) Tat-Cy5 complex in nerve cells were examined. In addition, the ability of these compounds to protect against oxidative stress and DNA damage induced by the full-length Tat protein was investigated. Les-6631 and Les-6633 were found to inhibit endocytosis better than the classical endocytosis inhibitor chlorpromazine, thereby effectively preventing the entry of the Tat protein into nerve cells. Moreover, compounds demonstrated the capacity to reduce oxidative stress and protect DNA from Tat-induced damage. In a neuro-AIDS model, both compounds proved effective in preventing neurotoxicity associated with HIV-1 infection, indicating its potential for therapeutic applications. Les-6631 and Les-6633 thus can protect cells from the harmful effects of pathogens. Their use in a neuro-AIDS model suggests a potential application in protective therapies for the nervous system in patients with HIV.NEW & NOTEWORTHY This study identifies novel rhodadyn-based inhibitors, Les-6631 and Les-6633, which selectively block dynamin's GTPase activity while sparing clathrin-mediated pathways. They effectively inhibit cellular uptake, protect neural cells from HIV-1 Tat-induced oxidative stress, and reduce mitochondrial and DNA damage. Their selective dynamin inhibition and antioxidant properties highlight their therapeutic potential for neurodegeneration and viral infections, offering cell protection without disrupting essential endocytic functions.

The orchestrated signaling by PI3Kα and PTEN at the membrane interface

The oncogene PI3Kα and the tumor suppressor PTEN represent two antagonistic enzymatic activities that regulate the interconversion of the phosphoinositide lipids PI(4,5)P2 and PI(3,4,5)P3 in membranes. As such, they are defining components of phosphoinositide-based cellular signaling and membrane trafficking pathways that regulate cell survival, growth, and proliferation, and are often deregulated in cancer. In this review, we highlight aspects of PI3Kα and PTEN interplay at the intersection of signaling and membrane trafficking. We also discuss the mechanisms of PI3Kα- and PTEN- membrane interaction and catalytic activation, which are fundamental for our understanding of the structural and allosteric implications on signaling at the membrane interface and may aid current efforts in pharmacological targeting of these proteins.

Effect of β-Glucan Supplementation on Growth Performance and Intestinal Epithelium Functions in Weaned Pigs Challenged by Enterotoxigenic Escherichia coli

Background: To examine the effect of β-glucan (BGL) supplementation on growth performance and intestinal epithelium functions in weaned pigs upon Enterotoxigenic Escherichia coli (ETEC) challenge. Methods: Thirty-two weaned pigs (Duroc × Landrace × Yorkshire) were assigned into four groups. Pigs fed with a basal diet or basal diet containing 500 mg/kg BGL were orally infused with ETEC or culture medium. Results: Results showed BGL tended to increase the average daily gain (ADG) in ETEC-challenged pigs (0.05 < p < 0.1). Dietary BGL supplementation had no significant influence on nutrient digestibility (p > 0.05). However, BGL improved the serum concentrations of immunoglobulin (Ig) A and IgG, and was beneficial to relieve the increasement of the concentrations of inflammatory cytokines such as the TNF-α and IL-6 upon ETEC-challenge (p < 0.05). Interestingly, BGL significantly increased the duodenal, jejunal and ileal villus height, and increased the jejunal ratio of villus height to crypt depth (V/C) upon ETEC challenge (p < 0.05). BGL also increased the activities of mucosal, sucrase and maltase in the ETEC-challenged pigs (p < 0.05). Moreover, BGL elevated the abundance of Lactobacillus and the concentration of propanoic acid in colon in the ETEC-challenged pigs (p < 0.05). Importantly, BGL elevated the expression levels of zonula occludins-1 (ZO-1) and mucin-2 (MUC-2) in the small intestinal mucosa upon ETEC challenge (p < 0.05). BGL also upregulated the expressions of functional genes such as the claudin-1, cationic amino acid transporter-1 (CAT-1), LAT-1, L amino acid transporter-1 (LAT1), fatty acid transport proteins (FATP1), FATP4, and sodium/glucose cotransporter-1 (SGLT-1) in the duodenum, and the occludin-1 and CAT-1 in the jejunum upon ETEC challenge (p < 0.05). Conclusions: These results suggested that BGL can attenuate intestinal damage in weaned pigs upon ETEC challenge, which was connected with the suppressed secretion of inflammatory cytokines and enhanced serum immunoglobulins, as well as improved intestinal epithelium functions and microbiota.

Role of Clathrin and Dynamin in Clathrin Mediated Endocytosis/Synaptic Vesicle Recycling and Implications in Neurological Diseases

Endocytosis is a process essential to the health and well-being of cell. It is required for the internalisation and sorting of “cargo”—the macromolecules, proteins, receptors and lipids of cell signalling. Clathrin mediated endocytosis (CME) is one of the key processes required for cellular well-being and signalling pathway activation. CME is key role to the recycling of synaptic vesicles [synaptic vesicle recycling (SVR)] in the brain, it is pivotal to signalling across synapses enabling intracellular communication in the sensory and nervous systems. In this review we provide an overview of the general process of CME with a particular focus on two key proteins: clathrin and dynamin that have a central role to play in ensuing successful completion of CME. We examine these two proteins as they are the two endocytotic proteins for which small molecule inhibitors, often of known mechanism of action, have been identified. Inhibition of CME offers the potential to develop therapeutic interventions into conditions involving defects in CME. This review will discuss the roles and the current scope of inhibitors of clathrin and dynamin, providing an insight into how further developments could affect neurological disease treatments.

Lysine-selective molecular tweezers are cell penetrant and concentrate in lysosomes

Lysine-selective molecular tweezers are promising drug candidates against proteinopathies, viral infection, and bacterial biofilm. Despite demonstration of their efficacy in multiple cellular and animal models, important questions regarding their mechanism of action, including cell penetrance and intracellular distribution, have not been answered to date. The main impediment to answering these questions has been the low intrinsic fluorescence of the main compound tested to date, called CLR01. Here, we address these questions using new fluorescently labeled molecular tweezers derivatives. We show that these compounds are internalized in neurons and astrocytes, at least partially through dynamin-dependent endocytosis. In addition, we demonstrate that the molecular tweezers concentrate rapidly in acidic compartments, primarily lysosomes. Accumulation of molecular tweezers in lysosomes may occur both through the endosomal-lysosomal pathway and via the autophagy-lysosome pathway. Moreover, by visualizing colocalization of molecular tweezers, lysosomes, and tau aggregates we show that lysosomes likely are the main site for the intracellular anti-amyloid activity of molecular tweezers. These findings have important implications for the mechanism of action of molecular tweezers in vivo, explaining how administration of low doses of the compounds achieves high effective concentrations where they are needed, and supporting the development of these compounds as drugs for currently cureless proteinopathies.

Chemical Inhibitors of Dynamin Exert Differential Effects in VEGF Signaling

VEGFR2 is the main receptor and mediator of the vasculogenic and angiogenic activity of VEGF. Activated VEGFR2 internalizes through clathrin-mediated endocytosis and macropinocytosis. As dynamin is a key regulator of the clathrin pathway, chemical inhibitors of dynamin are commonly used to assess the role of the clathrin route in receptor signaling. However, drugs may also exert off-target effects. Here, we compare the effects of three dynamin inhibitors, dynasore, dyngo 4a and dynole, on VEGFR2 internalization and signaling. Although these drugs consistently inhibit clathrin-mediated endocytosis of both transferrin (a typical cargo of this route) and VEGFR2, surprisingly, they exert contradictory effects in receptor signaling. Thus, while dynasore has no effect on phosphorylation of VEGFR2, the other two drugs are strong inhibitors. Furthermore, although dyngo does not interfere with phosphorylation of Akt, dynasore and dynole have a strong inhibitory effect. These inconsistent effects suggest that the above dynamin blockers, besides inhibiting dynamin-dependent endocytosis of VEGFR2, exert additional inhibitory effects on signaling that are independent of endocytosis; i.e., they are due to off-target effects. Using a recently developed protocol, we comparatively validate the specificity of two endocytic inhibitors, dynasore and EIPA. Our findings highlight the importance of assessing whether the effect of an endocytic drug on signaling is specifically due to its interference with endocytosis or due to off-targets.

Wbox2: A clathrin terminal domain-derived peptide inhibitor of clathrin-mediated endocytosis

Clathrin-mediated endocytosis (CME) occurs via the formation of clathrin-coated vesicles from clathrin-coated pits (CCPs). Clathrin is recruited to CCPs through interactions between the AP2 complex and its N-terminal domain, which in turn recruits endocytic accessory proteins. Inhibitors of CME that interfere with clathrin function have been described, but their specificity and mechanisms of action are unclear. Here we show that overexpression of the N-terminal domain with (TDD) or without (TD) the distal leg inhibits CME and CCP dynamics by perturbing clathrin interactions with AP2 and SNX9. TDD overexpression does not affect clathrin-independent endocytosis or, surprisingly, AP1-dependent lysosomal trafficking from the Golgi. We designed small membrane–permeant peptides that encode key functional residues within the four known binding sites on the TD. One peptide, Wbox2, encoding residues along the W-box motif binding surface, binds to SNX9 and AP2 and potently and acutely inhibits CME.

Metabolic compensation activates pro-survival mTORC1 signaling upon 3-phosphoglycerate dehydrogenase inhibition in osteosarcoma

Osteosarcoma is the most common pediatric and adult primary malignant bone cancer. Curative regimens target the folate pathway, downstream of serine metabolism, with high-dose methotrexate. Here, the rate-limiting enzyme in the biosynthesis of serine from glucose, 3-phosphoglycerate dehydrogenase (PHGDH), is examined, and an inverse correlation between PHGDH expression and relapse-free and overall survival in osteosarcoma patients is found. PHGDH inhibition in osteosarcoma cell lines attenuated cellular proliferation without causing cell death, prompting a robust metabolic analysis to characterize pro-survival compensation. Using metabolomic and lipidomic profiling, cellular response to PHGDH inhibition is identified as accumulation of unsaturated lipids, branched chain amino acids, and methionine cycle intermediates, leading to activation of pro-survival mammalian target of rapamycin complex 1 (mTORC1) signaling. Increased mTORC1 activation sensitizes cells to mTORC1 pathway inhibition, resulting in significant, synergistic cell death in vitro and in vivo. Identifying a therapeutic combination for PHGDH-high cancers offers preclinical justification for a dual metabolism-based combination therapy for osteosarcoma.

Dynasore protects ocular surface mucosal epithelia subjected to oxidative stress by maintaining UPR and calcium homeostasis

The mucosal epithelia of the ocular surface protect against external threats to the eye. Using a model of human stratified corneal epithelial cells with mucosal differentiation, we previously demonstrated that a small molecule inhibitor of dynamin GTPases, dynasore, prevents damage to cells and their transcellular barriers when subjected to oxidative stress. Investigating mechanisms, we now report the novel finding that dynasore acts by maintaining Ca+2 homeostasis, thereby inhibiting the PERK branch of the unfolded protein response (UPR) that promotes cell death. Dynasore was found to protect mitochondria by preventing mitochondrial permeability transition pore opening (mPTP), but, unlike reports using other systems, this was not mediated by dynamin family member DRP1. Necrostatin-1, an inhibitor of RIPK1 and lytic forms of programmed cell death, also inhibited mPTP opening and further protected the plasma membrane barrier. Significantly, necrostatin-1 did not protect the mucosal barrier. Oxidative stress increased mRNA for sXBP1, a marker of the IRE1 branch of the UPR, and CHOP, a marker of the PERK branch. It also stimulated phosphorylation of eIF2α, the upstream regulator of CHOP, as well as an increase in intracellular Ca2+. Dynasore selectively inhibited the increase in PERK branch markers, and also prevented the increase intracellular Ca2+ in response to oxidative stress. The increase in PERK branch markers were also inhibited when cells were treated with the cell permeable Ca2+ chelator, BAPTA-AM. To our knowledge, this is the first time that dynasore has been shown to have an effect on the UPR and suggests therapeutic applications.

Amino Acid Transporters as Targets for Cancer Therapy: Why, Where, When, and How

Amino acids are indispensable for the growth of cancer cells. This includes essential amino acids, the carbon skeleton of which cannot be synthesized, and conditionally essential amino acids, for which the metabolic demands exceed the capacity to synthesize them. Moreover, amino acids are important signaling molecules regulating metabolic pathways, protein translation, autophagy, defense against reactive oxygen species, and many other functions. Blocking uptake of amino acids into cancer cells is therefore a viable strategy to reduce growth. A number of studies have used genome-wide silencing or knock-out approaches, which cover all known amino acid transporters in a large variety of cancer cell lines. In this review, these studies are interrogated together with other databases to identify vulnerabilities with regard to amino acid transport. Several themes emerge, such as synthetic lethality, reduced redundancy, and selective vulnerability, which can be exploited to stop cancer cell growth.

Positive correlation of expression of L-type amino-acid transporter 1 with colorectal tumor progression and prognosis: Higher expression in sporadic colorectal tumors compared with ulcerative colitis-associated neoplasia

The role of L-type amino-acid transporter 1 (LAT1), an oncofetal protein, in tumor progression is not well known, although it is important for the survival and proliferation of cancer cells. LAT1 expression was immunohistochemically analyzed and compared in sporadic (conventional) colorectal tumors and ulcerative colitis (UC)-associated neoplasia development and progression. LAT1 expression showed a significant stepwise increase in the order: conventional low-grade tubular adenoma, high-grade tubular adenoma, and invasive adenocarcinoma. Similarly, the same increasing trend in LAT1 expression was found in UC-associated low-grade dysplasia, high-grade dysplasia, and adenocarcinoma, whereas expression was significantly lower compared with that in an adenoma-adenocarcinoma series. LAT1 expression was predominant in the upper half of mucosal lesions in low-grade adenoma. This localized difference in LAT1 expression between the upper and lower halves of mucosal lesions disappeared in conventional high-grade adenoma and adenocarcinoma. LAT1 expression in the colorectal mucosa was significantly increased in the order: nontumor mucosa, quiescent phase of UC, and active phase of UC. Considering the histological pattern of Ki-67 labeling, LAT1 expression appeared partly related to cell proliferation, but this was not significant. In relation to the prognosis of patients with sporadic phase IV colorectal adenocarcinoma, this was significantly poorer in the group with high LAT1 expression compared with that with low LAT1 expression. This suggests LAT1 expression may be used as a companion biomarker for anti-cancer therapy targeting the LAT1 molecule in colorectal cancers.

Spatial regulation of mTORC1 signalling: Beyond the Rag GTPases

The mechanistic (or mammalian) Target of Rapamycin Complex 1 (mTORC1) is a central regulator of cell growth and metabolism. By integrating mitogenic signals, mTORC1-dependent phosphorylation of substrates dictates the balance between anabolic, pro-growth and catabolic, recycling processes in the cell. The discovery that amino acids activate mTORC1 by promoting its translocation to the lysosome was a fundamental advance in the understanding of mTORC1 signalling. It has since become clear that the lysosome-cytoplasm shuttling of mTORC1 represents just one layer of spatial control of this signalling pathway. This review will focus on exploring the subcellular localisation of mTORC1 and its regulators to multiple sites within the cell. We will discuss how these spatially distinct regions such as endoplasmic reticulum, plasma membrane and the endosomal pathway co-operate to transduce nutrient availability to mTORC1, allowing for tight control of cell growth.

When trafficking and signaling mix: How subcellular location shapes G protein-coupled receptor activation of heterotrimeric G proteins

G protein-coupled receptors (GPCRs) physically connect extracellular information with intracellular signal propagation. Membrane trafficking plays a supportive role by "bookending" signaling events: movement through the secretory pathway delivers GPCRs to the cell surface where receptors can sample the extracellular environment, while endocytosis and endolysosomal membrane trafficking provide a versatile system to titrate cellular signaling potential and maintain homeostatic control. Recent evidence suggests that, in addition to these important effects, GPCR trafficking actively shapes the cellular signaling response by altering the location and timing of specific receptor-mediated signaling reactions. Here, we review key experimental evidence underlying this expanding view, focused on GPCR signaling mediated through activation of heterotrimeric G proteins located in the cytoplasm. We then discuss lingering and emerging questions regarding the interface between GPCR signaling and trafficking.

Ubiquitylation and endocytosis of the human LAT1/SLC7A5 amino acid transporter

The human L-type amino acid transporter 1 (LAT1), also known as SLC7A5, catalyzes the transport of large neutral amino acids across the plasma membrane. As the main transporter of several essential amino acids, notably leucine, LAT1 plays an important role in mTORC1 activation. Furthermore, it is overexpressed in various types of cancer cells, where it contributes importantly to sustained growth. Despite the importance of LAT1 in normal and tumor cells, little is known about the mechanisms that might control its activity, for example by promoting its downregulation via endocytosis. Here we report that in HeLa cells, activation of protein kinase C by phorbol 12-myristate 13-acetate (PMA) triggers efficient endocytosis and degradation of LAT1. Under these conditions we found LAT1 downregulation to correlate with increased LAT1 ubiquitylation. This modification was considerably reduced in cells depleted of the Nedd4-2 ubiquitin ligase. By systematically mutagenizing the residues of the LAT1 cytosolic tails, we identified a group of three close lysines (K19, K25, K30) in the N-terminal tail that are important for PMA-induced ubiquitylation and downregulation. Our study thus unravels a mechanism of induced endocytosis of LAT1 elicited by Nedd4-2-mediated ubiquitylation of the transporter's N-terminal tail.

CD98hc (SLC3A2) sustains amino acid and nucleotide availability for cell cycle progression

CD98 heavy chain (CD98hc) forms heteromeric amino acid (AA) transporters by interacting with different light chains. Cancer cells overexpress CD98hc-transporters in order to meet their increased nutritional and antioxidant demands, since they provide branched-chain AA (BCAA) and aromatic AA (AAA) availability while protecting cells from oxidative stress. Here we show that BCAA and AAA shortage phenocopies the inhibition of mTORC1 signalling, protein synthesis and cell proliferation caused by CD98hc ablation. Furthermore, our data indicate that CD98hc sustains glucose uptake and glycolysis, and, as a consequence, the pentose phosphate pathway (PPP). Thus, loss of CD98hc triggers a dramatic reduction in the nucleotide pool, which leads to replicative stress in these cells, as evidenced by the enhanced DNA Damage Response (DDR), S-phase delay and diminished rate of mitosis, all recovered by nucleoside supplementation. In addition, proper BCAA and AAA availability sustains the expression of the enzyme ribonucleotide reductase. In this regard, BCAA and AAA shortage results in decreased content of deoxynucleotides that triggers replicative stress, also recovered by nucleoside supplementation. On the basis of our findings, we conclude that CD98hc plays a central role in AA and glucose cellular nutrition, redox homeostasis and nucleotide availability, all key for cell proliferation.

Modulation of dynamin function by small molecules

Dynamins are essential as membrane remodelers in various cellular processes, like receptor-mediated endocytosis, synaptic vesicle recycling and spermatogenesis. Moreover, dynamin is involved in the internalization of numerous viruses and in the motility of several cancer cell lines. As tools for dissecting the underlying mechanisms of these important biological processes and as potential future therapeutics, small molecules have been developed in the last two decades that modulate the functions of dynamin. In this review we give an overview of the compound classes that are currently in use and describe how they affect dynamin function.

First person – Avinash Persaud

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Avinash Persaud is the first author on ‘Dynamin inhibitors block activation of mTORC1 by amino acids independently of dynamin’, published in Journal of Cell Science. Avinash is a research associate in the lab of Daniela Rotin at The Hospital for Sick Children, Toronto, Canada, investigating mTORC1 signaling and the function of the ubiquitin ligase Nedd4.

Dynasore suppresses proliferation and induces apoptosis of the non-small-cell lung cancer cell line A549

Lung cancer is the leading cause of cancer death worldwide, and most of all cases are non-small-cell lung cancer. Lung cancer is associated with dysregulation of mitochondrial fusion and fission, and inhibition of the fission regulator Dynamin-related protein 1 (Drp1) reduces proliferation and increases apoptosis of lung cancer cells. Dynasore is a small molecule non-selective inhibitor of the GTPase activity of dynamin 1, dynamin 2, and Drp1 in vivo and in vitro. Here, we investigated the effects of dynasore on the proliferation and apoptosis of A549 lung cancer cells, alone and in combination with the chemotherapeutic drug cisplatin. We found that cisplatin increased mitochondrial fission and dynamin 2 expression, whereas dynasore had the opposite effects. However, both cisplatin and dynasore independently induced mitochondrial oxidative stress, leading to mitochondrial dysfunction, reduced cell proliferation, and enhanced apoptosis. Importantly, dynasore significantly augmented the anti-cancer effects of cisplatin. To the best of our knowledge, this is the first report that dynasore inhibits proliferation and induces apoptosis of lung cancer cells, and enhances the inhibitory effects of cisplatin.