Glycosylation and raft endocytosis in cancer

De Novo Glycan Display on Cell Surfaces Using HaloTag: Visualizing the Effect of the Galectin Lattice on the Lateral Diffusion and Extracellular Vesicle Loading of Glycosylated Membrane Proteins

Glycans cover the cell surface to form the glycocalyx, which governs a myriad of biological phenomena. However, understanding and regulating glycan functions is extremely challenging due to the large number of heterogeneous glycans that engage in intricate interaction networks with diverse biomolecules. Glycocalyx-editing techniques offer potent tools to probe their functions. In this study, we devised a HaloTag-based technique for glycan manipulation, which enables the introduction of chemically synthesized glycans onto a specific protein (protein of interest, POI) and concurrently incorporates fluorescent units to attach homogeneous, well-defined glycans to the fluorescence-labeled POIs. Leveraging this HaloTag-based glycan-display system, we investigated the influence of the interactions between Gal-3 and various N-glycans on protein dynamics. Our analyses revealed that glycosylation modulates the lateral diffusion of the membrane proteins in a structure-dependent manner through interaction with Gal-3, particularly in the context of the Gal-3-induced formation of the glycan network (galectin lattice). Furthermore, N-glycan attachment was also revealed to have a significant impact on the extracellular vesicle-loading of membrane proteins. Notably, our POI-specific glycan introduction does not disrupt intact glycan structures, thereby enabling a functional analysis of glycans in the presence of native glycan networks. This approach complements conventional glycan-editing methods and provides a means for uncovering the molecular underpinnings of glycan functions on the cell surface.

Vaginal Ovule Loaded with Bismuth Lipophilic Nanoparticles and Cetylpyridinium Chloride Inhibits Human Cervical Carcinoma and Candida albicans Growth

Bismuth lipophilic nanoparticles (BisBAL NPs) and cetylpyridinium chloride (CPC) are antineoplastic and antimicrobial in vitro. As a next pre-clinical step, a clinically viable dosage form for vaginal application was developed. Compendial pharmacopeial tests (mass uniformity, disintegration, and compressive mechanics) and inductively coupled plasma optical emission spectroscopy were conducted on in-house developed glycerinated gelatin (60:15 v/w) vaginal ovules containing BisBAL NP-CPC. The antimycotic activity of BisBAL NP-CPC vaginal ovules was analyzed using disk diffusion and cell viability XTT assays. The antitumor properties of BisBAL NP-CPC vaginal ovules were assessed by cell viability MTT tests. BisBAL NP-CPC and drug-free vaginal ovules deposited into ex vivo porcine vaginas disaggregated without signs of adverse cytotoxicity within the timespan of clinical efficacy. BisBAL NP-CPC vaginal ovules demonstrated antifungal efficacy comparable to miconazole: C. albicans growth inhibition haloes in diffusion tests were 23 ± 0.968 mm (n = 3) for BisBAL NP-CPC and 20.35 ± 0.899 mm (n = 3) for miconazole. Likewise, BisBAL NP-CPC vaginal ovules reduced HeLa cell growth by 81%, outperforming the clinical reference of 500 μM 5-fluouracil, which induced a 70% growth inhibition. BisBAL NP-CPC incorporated into glycerinated gelatin vaginal ovules constitute an innovative drug delivery system for topical antimycotic and anti-cervical carcinoma treatments.

The diverse dependence of galectin-1 and -8 on multivalency for the modulation of FGFR1 endocytosis

Fibroblast growth factor receptor 1 (FGFR1) is a N-glycosylated cell surface receptor tyrosine kinase, which upon recognition of specific extracellular ligands, fibroblast growth factors (FGFs), initiates an intracellular signaling. FGFR1 signaling ensures homeostasis of cells by fine-tuning essential cellular processes, like differentiation, division, motility and death. FGFR1 activity is coordinated at multiple steps and unbalanced FGFR1 signaling contributes to developmental diseases and cancers. One of the crucial control mechanisms over FGFR1 signaling is receptor endocytosis, which allows for rapid targeting of FGF-activated FGFR1 to lysosomes for degradation and the signal termination. We have recently demonstrated that N-glycans of FGFR1 are recognized by a precise set of extracellular galectins, secreted and intracellular multivalent lectins implicated in a plethora of cellular processes and altered in immune responses and cancers. Specific galectins trigger FGFR1 clustering, resulting in activation of the receptor and in initiation of intracellular signaling cascades that shape the cell physiology. Although some of galectin family members emerged recently as key players in the clathrin-independent endocytosis of specific cargoes, their impact on endocytosis of FGFR1 was largely unknown.Here we assessed the contribution of extracellular galectins to the cellular uptake of FGFR1. We demonstrate that only galectin-1 induces internalization of FGFR1, whereas the majority of galectins predominantly inhibit endocytosis of the receptor. We focused on three representative galectins: galectin-1, -7 and -8 and we demonstrate that although all these galectins directly activate FGFR1 by the receptor crosslinking mechanism, they exert different effects on FGFR1 endocytosis. Galectin-1-mediated internalization of FGFR1 doesn't require galectin-1 multivalency and occurs via clathrin-mediated endocytosis, resembling in this way the uptake of FGF/FGFR1 complex. In contrast galectin-7 and -8 impede FGFR1 endocytosis, causing stabilization of the receptor on the cell surface and prolonged propagation of the signals. Furthermore, using protein engineering approaches we demonstrate that it is possible to modulate or even fully reverse the endocytic potential of galectins.

Molecular Regulation and Oncogenic Functions of TSPAN8

Tetraspanins, a superfamily of small integral membrane proteins, are characterized by four transmembrane domains and conserved protein motifs that are configured into a unique molecular topology and structure in the plasma membrane. They act as key organizers of the plasma membrane, orchestrating the formation of specialized microdomains called "tetraspanin-enriched microdomains (TEMs)" or "tetraspanin nanodomains" that are essential for mediating diverse biological processes. TSPAN8 is one of the earliest identified tetraspanin members. It is known to interact with a wide range of molecular partners in different cellular contexts and regulate diverse molecular and cellular events at the plasma membrane, including cell adhesion, migration, invasion, signal transduction, and exosome biogenesis. The functions of cell-surface TSPAN8 are governed by ER targeting, modifications at the Golgi apparatus and dynamic trafficking. Intriguingly, limited evidence shows that TSPAN8 can translocate to the nucleus to act as a transcriptional regulator. The transcription of TSPAN8 is tightly regulated and restricted to defined cell lineages, where it can serve as a molecular marker of stem/progenitor cells in certain normal tissues as well as tumors. Importantly, the oncogenic roles of TSPAN8 in tumor development and cancer metastasis have gained prominence in recent decades. Here, we comprehensively review the current knowledge on the molecular characteristics and regulatory mechanisms defining TSPAN8 functions, and discuss the potential and significance of TSPAN8 as a biomarker and therapeutic target across various epithelial cancers.

Identification of a novel endocytosis‑associated gene signature for prognostic prediction in lung adenocarcinoma

Lung cancer is one of the most common malignant solid tumors and the leading cause of cancer-associated mortality worldwide. Endocytosis is an essential physiological activity for cells to maintain membrane homeostasis, and has been reported to serve an important role in tumorigenesis and progression. In the present study, the aim was to construct a prognostic prediction model of endocytosis-associated genes for patients with lung adenocarcinoma (LUAD). The endocytosis-associated gene signature was established using Lasso Cox regression analysis using the training set of the LUAD cohort from The Cancer Genome Atlas (TCGA) database, and verified using two datasets from the Gene Expression Omnibus (GEO) database. Kaplan-Meier survival curves were used to evaluate the effectiveness of the prognostic evaluation of patients with LUAD. Differentially expressed genes were screened in the tumor tissue of patients compared with paired paracancerous tissues. A series of candidate genes associated to the prognosis of patients with LUAD was obtained using univariate Cox's regression analysis. Using the Lasso Cox regression analysis, an appropriate risk model with 18 endocytosis-associated genes was established. A high-risk score was positively correlated with a higher tumor stage and pathologic grade. Patients with LUAD and high-risk scores had shorter survival times, increased intratumor heterogeneities and immune cell infiltration into tumor tissues, compared with those patients with LUAD and low-risk scores. The endocytosis inhibitor chloroquine could repress proliferation and increase the apoptosis of lung cancer cells. In summary, a novel endocytosis-associated gene signature was constructed using TCGA and GEO datasets. Patients with LUAD and high-risk scores, as calculated by the signature, had a poor prognosis and short survival time.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

Sequential genome-wide CRISPR-Cas9 screens identify genes regulating cell-surface expression of tetraspanins

Tetraspanins, a superfamily of membrane proteins, mediate diverse biological processes through tetraspanin-enriched microdomains in the plasma membrane. However, how their cell-surface presentation is controlled remains unclear. To identify the regulators of tetraspanin trafficking, we conduct sequential genome-wide loss-of-function CRISPR-Cas9 screens based on cell-surface expression of a tetraspanin member, TSPAN8. Several genes potentially involved in endoplasmic reticulum (ER) targeting, different biological processes in the Golgi apparatus, and protein trafficking are identified and functionally validated. Importantly, we find that biantennary N-glycans generated by MGAT1/2, but not more complex glycan structures, are important for cell-surface tetraspanin expression. Moreover, we unravel that SPPL3, a Golgi intramembrane-cleaving protease reported previously to act as a sheddase of multiple glycan-modifying enzymes, controls cell-surface tetraspanin expression through a mechanism associated with lacto-series glycolipid biosynthesis. Our study provides critical insights into the molecular regulation of cell-surface presentation of tetraspanins with implications for strategies to manipulate their functions, including cancer cell invasion.

Optical Manipulation of Gb3 Enriched Lipid Domains: Impact of Isomerization on Gb3 -Shiga Toxin B Interaction

The plasma membrane is a complex assembly of proteins and lipids that can self-assemble in submicroscopic domains commonly termed "lipid rafts", which are implicated in membrane signaling and trafficking. Recently, photo-sensitive lipids were introduced to study membrane domain organization, and photo-isomerization was shown to trigger the mixing and de-mixing of liquid-ordered (lo ) domains in artificial phase-separated membranes. Here, we synthesized globotriaosylceramide (Gb3 ) glycosphingolipids that harbor an azobenzene moiety at different positions of the fatty acid to investigate light-induced membrane domain reorganization, and that serve as specific receptors for the protein Shiga toxin (STx). Using phase-separated supported lipid bilayers on mica surfaces doped with four different photo-Gb3 molecules, we found by fluorescence microscopy and atomic force microscopy that liquid disordered (ld ) domains were formed within lo domains upon trans-cis photo-isomerization. The fraction and size of these ld domains were largest for Gb3 molecules with the azobenzene group at the end of the fatty acid. We further investigated the impact of domain reorganization on the interaction of the B-subunits of STx with the photo-Gb3 . Fluorescence and atomic force micrographs clearly demonstrated that STxB binds to the lo phase if Gb3 is in the trans-configuration, whereas two STxB populations are formed if the photo-Gb3 is switched to the cis-configuration highlighting the idea of manipulating lipid-protein interactions with a light stimulus.

Comprehensive Evaluation of Multiple Approaches Targeting ABCB1 to Resensitize Docetaxel-Resistant Prostate Cancer Cell Lines

Docetaxel (DTX) is a mainstay in the treatment of metastatic prostate cancer. Failure of DTX therapy is often associated with multidrug resistance caused by overexpression of efflux membrane transporters of the ABC family such as the glycoprotein ABCB1. This study investigated multiple approaches targeting ABCB1 to resensitize DTX-resistant (DTXR) prostate cancer cell lines. In DU145 DTXR and PC-3 DTXR cells as well as age-matched parental controls, the expression of selected ABC transporters was analyzed by quantitative PCR, Western blot, flow cytometry and immunofluorescence. ABCB1 effluxing activity was studied using the fluorescent ABCB1 substrate rhodamine 123. The influence of ABCB1 inhibitors (elacridar, tariquidar), ABCB1-specific siRNA and inhibition of post-translational glycosylation on DTX tolerance was assessed by cell viability and colony formation assays. In DTXR cells, only ABCB1 was highly upregulated, which was accompanied by a strong effluxing activity and additional post-translational glycosylation of ABCB1. Pharmacological inhibition and siRNA-mediated knockdown of ABCB1 completely resensitized DTXR cells to DTX. Inhibition of glycosylation with tunicamycin affected DTX resistance partially in DU145 DTXR cells, which was accompanied by a slight intracellular accumulation and decreased effluxing activity of ABCB1. In conclusion, DTX resistance can be reversed by various strategies with small molecule inhibitors representing the most promising and feasible approach.

Galectin-3 Binding to α5β1 Integrin in Pore Suspended Biomembranes

Galectin-3 (Gal3) is a β-galactoside binding lectin that mediates many physiological functions, including the binding of cells to the extracellular matrix for which the glycoprotein α₅β₁ integrin is of critical importance. The mechanisms by which Gal3 interacts with membranes have not been widely explored to date due to the complexity of cell membranes and the difficulty of integrin reconstitution within model membranes. Herein, to study their interaction, Gal3 and α₅β₁ were purified, and the latter reconstituted into pore-suspended lipid bilayers comprised eggPC:eggPA. Using electrochemical impedance and fluorescence lifetime correlation spectroscopy, we found that on incubation with low nanomolar concentrations of wild-type Gal3, the membrane's admittance and fluidity, as well as integrin's lateral diffusivity, were enhanced. These effects were diminished in the following conditions: (i) absence of integrin, (ii) presence of lactose as a competitive inhibitor of glycan-Gal3 interaction, and (iii) use of a Gal3 mutant that lacked the N-terminal oligomerization domain (Gal3ΔNter). These findings indicated that WTGal3 oligomerized on α₅β₁ integrin in a glycan-dependent manner and that the N-terminal domain interacted directly with membranes in a way that is yet to be fully understood. At concentrations above 10 nM of WTGal3, membrane capacitance started to decrease and very slowly diffusing molecular species appeared, which indicated the formation of protein clusters made from WTGal3-α₅β₁ integrin assemblies. Overall, our study demonstrates the capacity of WTGal3 to oligomerize in a cargo protein-dependent manner at low nanomolar concentrations. Of note, these WTGal3 oligomers appeared to have membrane active properties that could only be revealed using our sensitive methods. At slightly higher WTGal3 concentrations, the capacity to generate lateral assemblies between cargo proteins was observed. In cells, this could lead to the construction of tubular endocytic pits according to the glycolipid-lectin (GL-Lect) hypothesis or to the formation of galectin lattices, depending on cargo glycoprotein stability at the membrane, the local Gal3 concentration, or plasma membrane intrinsic parameters. The study also demonstrates the utility of microcavity array-suspended lipid bilayers to address the biophysics of transmembrane proteins.

Nucleotide sugar transporter SLC35A2 is involved in promoting hepatocellular carcinoma metastasis by regulating cellular glycosylation

PURPOSE

Recently, aberrant glycosylation has been recognized to be relate to malignant behaviors of cancer and outcomes of patients with various cancers. SLC35A2 plays an indispensable role on glycosylation as a nucleotide sugar transporter. However, effects of SLC35A2 on malignant behaviors of cancer cells and alteration of cancer cells surface glycosylation profiles are still not fully understood, particularly in hepatocellular carcinoma (HCC). Hence, from a glycosylation perspective, we investigated the effects of SLC35A2 on metastatic behaviors of HCC cells.

METHODS

SLC35A2 expression in clinical samples and HCC cells was examined by immunohistochemical staining or Western blot/quantitative PCR and was regulated by RNA interference or vectors-mediated transfection. Effects of SLC35A2 expression alteration on metastatic behaviors and membrane glycan profile of HCC cells were observed by using respectively invasion, migration, cell adhesion assay, in vivo lung metastatic nude mouse model and lectins microarray. Co-location among proteins in HCC cells was observed by fluorescence microscope and detected by an in vitro co-immunoprecipitation assay.

RESULTS

SLC35A2 was upregulated in HCC tissues, and is associated with poor prognosis of HCC patients. SLC35A2 expression alteration significantly affected the invasion, adhesion, metastasis and membrane glycan profile and led to the dysregulated expressions or glycosylation of cell adhesion-related molecules in HCC cells. Mechanistically, the maintenance of SLC35A2 activity is critical for the recruitment of the key galactosyltransferase B4GalT1, which is responsible for complex glycoconjugate and lactose biosynthesis, to Golgi apparatus in HCC cells.

CONCLUSION

SLC35A2 plays important roles in promoting HCC metastasis by regulating cellular glycosylation modification and inducing the cell adhesive ability of HCC cells.

The Significance of Cell Surface N-Glycosylation for Internalization and Potency of Cytotoxic Conjugates Targeting Receptor Tyrosine Kinases

Precise anticancer therapies employing cytotoxic conjugates constitute a side-effect-limited, highly attractive alternative to commonly used cancer treatment modalities, such as conventional chemotherapy, radiotherapy or surgical interventions. Receptor tyrosine kinases are a large family of N-glycoproteins intensively studied as molecular targets for cytotoxic conjugates in various cancers. At the cell surface, these receptors are embedded in a dense carbohydrate layer formed by numerous plasma membrane glycoproteins. The complexity of the cell surface architecture is further increased by galectins, secreted lectins capable of recognizing and clustering glycoconjugates, affecting their motility and activity. Cell surface N-glycosylation is intensively remodeled by cancer cells; however, the contribution of this phenomenon to the efficiency of treatment with cytotoxic conjugates is largely unknown. Here, we evaluated the significance of N-glycosylation for the internalization and toxicity of conjugates targeting two model receptor tyrosine kinases strongly implicated in cancer: HER2 and FGFR1. We employed three conjugates of distinct molecular architecture and specificity: AffibodyHER2-vcMMAE (targeting HER2), vcMMAE-KCK-FGF1.E and T-Fc-vcMMAE (recognizing different epitopes within FGFR1). We demonstrated that inhibition of N-glycosylation reduced the cellular uptake of all conjugates tested and provided evidence for a role of the galectin network in conjugate internalization. In vitro binding studies revealed that the reduced uptake of conjugates is not due to impaired HER2 and FGFR1 binding. Importantly, we demonstrated that alteration of N-glycosylation can affect the cytotoxic potential of conjugates. Our data implicate a key role for cell surface N-glycosylation in the delivery of cytotoxic conjugates into cancer cells.

CD44 Glycosylation as a Therapeutic Target in Oncology

The interaction of non-kinase transmembrane glycoprotein CD44 with ligands including hyaluronic acid (HA) is closely related to the occurrence and development of tumors. Changes in CD44 glycosylation can regulate its binding to HA, Siglec-15, fibronectin, TM4SF5, PRG4, FGF2, collagen and podoplanin and activate or inhibit c-Src/STAT3/Twist1/Bmi1, PI3K/AKT/mTOR, ERK/NF-κB/NANOG and other signaling pathways, thereby having a profound impact on the tumor microenvironment and tumor cell fate. However, the glycosylation of CD44 is complex and largely unknown, and the current understanding of how CD44 glycosylation affects tumors is limited. These issues must be addressed before targeted CD44 glycosylation can be applied to treat human cancers.

Recent Progress in the Development of Opaganib for the Treatment of Covid-19

The Covid-19 pandemic driven by the SARS-CoV-2 virus continues to exert extensive humanitarian and economic stress across the world. Although antivirals active against mild disease have been identified recently, new drugs to treat moderate and severe Covid-19 patients are needed. Sphingolipids regulate key pathologic processes, including viral proliferation and pathologic host inflammation. Opaganib (aka ABC294640) is a first-in-class clinical drug targeting sphingolipid metabolism for the treatment of cancer and inflammatory diseases. Recent work demonstrates that opaganib also has antiviral activity against several viruses including SARS-CoV-2. A recently completed multinational Phase 2/3 clinical trial of opaganib in patients hospitalized with Covid-19 demonstrated that opaganib can be safely administered to these patients, and more importantly, resulted in a 62% decrease in mortality in a large subpopulation of patients with moderately severe Covid-19. Furthermore, acceleration of the clearance of the virus was observed in opaganib-treated patients. Understanding the biochemical mechanism for the anti-SARS-CoV-2 activity of opaganib is essential for optimizing Covid-19 treatment protocols. Opaganib inhibits three key enzymes in sphingolipid metabolism: sphingosine kinase-2 (SK2); dihydroceramide desaturase (DES1); and glucosylceramide synthase (GCS). Herein, we describe a tripartite model by which opaganib suppresses infection and replication of SARS-CoV-2 by inhibiting SK2, DES1 and GCS. The potential impact of modulation of sphingolipid signaling on multi-organ dysfunction in Covid-19 patients is also discussed.

Systematic Screening and Therapeutic Evaluation of Glyconanoparticles with Differential Cancer Affinities for Targeted Cancer Therapy

Cancer-targeting ligands used for nanomedicines have been limited mostly to antibodies, peptides, aptamers, and small molecules thus far. Here, a library of glycocalyx-mimicking nanoparticles as a platform to enable screening and identification of cancer-targeting nanomedicines is reported. Specifically, a library of 31 artificial glycopolymers composed of either homogeneous or heterogeneous display of five different sugar moieties (β-glucose, β-galactose, α-mannose, β-N-acetyl glucosamine, and β-N-acetyl galactosamine) is converted to a library of glyconanoparticles (GlyNPs). GlyNPs optimal for targeting CT26, DU145, A549, and PC3 tumors are systematically screened and identified. The cypate-conjugated GlyNP displaying α-mannose and β-N-acetyl glucosamine show selective targeting and potent photothermal therapeutic efficacy against A549 human lung tumors. The docetaxel-contained GlyNP displaying β-glucose, β-galactose, and α-mannose demonstrate targeted chemotherapy against DU145 human prostate tumors. The results presented herein collectively demonstrate that the GlyNP library is a versatile platform enabling the identification of cancer-targeting glyconanoparticles and suggest its potential applicability for targeting various diseased cells beyond cancer.

Loss of E-Cadherin Leads to Druggable Vulnerabilities in Sphingolipid Metabolism and Vesicle Trafficking

Simple Summary

Germline loss of the CDH1 gene is the primary genetic basis for hereditary diffuse gastric cancer, a disease resulting in elevated risk of both diffuse gastric cancer and lobular breast cancer. Current preventative treatment consists of prophylactic total gastrectomy, a therapy with several associated long-term morbidities. To address the lack of targeted molecular therapies for hereditary diffuse gastric cancer, we have utilized a synthetic lethal approach to identify candidate compounds that can specifically kill CDH1-null cells. Inhibitors of sphingolipid metabolism and vesicle trafficking pathways were identified as promising candidate compounds in a cell line model of CDH1 loss, then further validated in murine-derived organoid models of hereditary diffuse gastric cancer. With further research, these findings may lead to the development of novel chemoprevention strategies for the treatment of hereditary diffuse gastric cancer.

Abstract

Germline inactivating variants of CDH1 are causative of hereditary diffuse gastric cancer (HDGC), a cancer syndrome characterized by an increased risk of both diffuse gastric cancer and lobular breast cancer. Because loss of function mutations are difficult to target therapeutically, we have taken a synthetic lethal approach to identify targetable vulnerabilities in CDH1-null cells. We have previously observed that CDH1-null MCF10A cells exhibit a reduced rate of endocytosis relative to wildtype MCF10A cells. To determine whether this deficiency is associated with wider vulnerabilities in vesicle trafficking, we screened isogenic MCF10A cell lines with known inhibitors of autophagy, endocytosis, and sphingolipid metabolism. Relative to wildtype MCF10A cells, CDH1^−/− MCF10A cells showed significantly greater sensitivity to several drugs targeting these processes, including the autophagy inhibitor chloroquine, the endocytosis inhibitors chlorpromazine and PP1, and the sphingosine kinase 1 inhibitor PF-543. Synthetic lethality was confirmed in both gastric and mammary organoid models of CDH1 loss, derived from CD44-Cre/Cdh1^fl/fl/tdTomato mice. Collectively, these results suggest that both sphingolipid metabolism and vesicle trafficking represent previously unrecognised druggable vulnerabilities in CDH1-null cells and may lead to the development of new therapies for HDGC.

Recent advances in microscale separation techniques for lipidome analysis

This review paper highlights the recent research on liquid-phase microscale separation techniques for lipidome analysis over the last 10 years, mainly focusing on capillary liquid chromatography (LC) and capillary electrophoresis (CE) coupled with mass spectrometry (MS). Lipids are one of the most important classes of biomolecules which are involved in the cell membrane, energy storage, signal transduction, and so on. Since lipids include a variety of hydrophobic compounds including numerous structural isomers, lipidomes are a challenging target in bioanalytical chemistry. MS is the key technology that comprehensively identifies lipids; however, separation techniques like LC and CE are necessary prior to MS detection in order to avoid ionization suppression and resolve structural isomers. Separation techniques using μm-scale columns, such as a fused silica capillary and microfluidic device, are effective at realizing high-resolution separation. Microscale separation usually employs a nL-scale flow, which is also compatible with nanoelectrospray ionization-MS that achieves high sensitivity. Owing to such analytical advantages, microscale separation techniques like capillary/microchip LC and CE have been employed for more than 100 lipidome studies. Such techniques are still being evolved and achieving further higher resolution and wider coverage of lipidomes. Therefore, microscale separation techniques are promising as the fundamental technology in next-generation lipidome analysis.

Identification of a new regulation pathway of EGFR and E-cadherin dynamics

E-cadherin and EGFR are known to be closely associated hence regulating differentiation and proliferation notably in epithelia. We have previously shown that galectin-7 binds to E-cadherin and favors its retention at the plasma membrane. In this study, we shed in light that galectin-7 establishes a physical link between E-cadherin and EGFR. Indeed, our results demonstrate that galectin-7 also binds to EGFR, but unlike the binding to E-cadherin this binding is sugar dependent. The establishment of E-cadherin/EGFR complex and the binding of galectin-7 to EGFR thus lead to a regulation of its signaling and intracellular trafficking allowing cell proliferation and migration control. In vivo observations further support these results since an epidermal thickening is observed in galectin-7 deficient mice. This study therefore reveals that galectin-7 controls epidermal homeostasis through the regulation of E-cadherin/EGFR balance.

Cancer Cell Preferential Penetration and pH-Responsive Drug Delivery of Oligorutin

We report herein a novel delivery system, derived from the facile enzymatic synthesis of oligorutin (OR), for cancer cell targeting and pH-responsive drug delivery. In this study, we demonstrate that OR could preferentially penetrate cancer cells via the lipid raft-mediated endocytosis pathway, and cell membrane cholesterol was critical to the internalization of OR. The accumulation of OR in the tumor region was further confirmed by an in vivo biodistribution study. Considering the tumor-targeting property of OR, a pH-responsive drug delivery system (OR-BTZ) was developed by covalent conjugation of the catechol groups on OR with antitumor drug bortezomib (BTZ) through a pH-sensitive borate ester bond. OR-BTZ exerted cytotoxicity as well as inhibition of the migration and invasion to hepatoma carcinoma cells and showed no apparent cytotoxicity with liver normal cells. The OR-BTZs also presented significant therapeutic efficacy and low systematic toxicity in the murine hepatocellular carcinoma model. To our knowledge, this study presents the first attempt to exploit the potential of oligoflavonoids for cancer cell-targeted drug delivery and will motivate the development of flavonoids and their derivatives as a new type of biomaterials for tumor-targeted therapy.

Cholera Toxin as a Probe for Membrane Biology

Cholera toxin B-subunit (CTxB) has emerged as one of the most widely utilized tools in membrane biology and biophysics. CTxB is a homopentameric stable protein that binds tightly to up to five GM1 glycosphingolipids. This provides a robust and tractable model for exploring membrane structure and its dynamics including vesicular trafficking and nanodomain assembly. Here, we review important advances in these fields enabled by use of CTxB and its lipid receptor GM1.

Differential Glycosite Profiling-A Versatile Method to Compare Membrane Glycoproteomes

Glycosylation is the most prevalent and varied form of post-translational protein modifications. Protein glycosylation regulates multiple cellular functions, including protein folding, cell adhesion, molecular trafficking and clearance, receptor activation, signal transduction, and endocytosis. In particular, membrane proteins are frequently highly glycosylated, which is both linked to physiological processes and of high relevance in various disease mechanisms. The cellular glycome is increasingly considered to be a therapeutic target. Here we describe a new strategy to compare membrane glycoproteomes, thereby identifying proteins with altered glycan structures and the respective glycosites. The workflow started with an optimized procedure for the digestion of membrane proteins followed by the lectin-based isolation of glycopeptides. Since alterations in the glycan part of a glycopeptide cause mass alterations, analytical size exclusion chromatography was applied to detect these mass shifts. N-glycosidase treatment combined with nanoUPLC-coupled mass spectrometry identified the altered glycoproteins and respective glycosites. The methodology was established using the colon cancer cell line CX1, which was treated with 2-deoxy-glucose-a modulator of N-glycosylation. The described methodology is not restricted to cell culture, as it can also be adapted to tissue samples or body fluids. Altogether, it is a useful module in various experimental settings that target glycan functions.

The Cellular and Chemical Biology of Endocytic Trafficking and Intracellular Delivery-The GL-Lect Hypothesis

Lipid membranes are common to all forms of life. While being stable barriers that delimitate the cell as the fundamental organismal unit, biological membranes are highly dynamic by allowing for lateral diffusion, transbilayer passage via selective channels, and in eukaryotic cells for endocytic uptake through the formation of membrane bound vesicular or tubular carriers. Two of the most abundant fundamental fabrics of membranes-lipids and complex sugars-are produced through elaborate chains of biosynthetic enzymes, which makes it difficult to study them by conventional reverse genetics. This review illustrates how organic synthesis provides access to uncharted areas of membrane glycobiology research and its application to biomedicine. For this Special Issue on Chemical Biology Research in France, focus will be placed on synthetic approaches (i) to study endocytic functions of glycosylated proteins and lipids according to the GlycoLipid-Lectin (GL-Lect) hypothesis, notably that of Shiga toxin; (ii) to mechanistically dissect its endocytosis and intracellular trafficking with small molecule; and (iii) to devise intracellular delivery strategies for immunotherapy and tumor targeting. It will be pointed out how the chemical biologist's view on lipids, sugars, and proteins synergizes with biophysics and modeling to "look" into the membrane for atomistic scale insights on molecular rearrangements that drive the biogenesis of endocytic carriers in processes of clathrin-independent endocytosis.

Chemically synthesized Gb3 glycosphingolipids: tools to access their function in lipid membranes

Gb3 glycosphingolipids are the specific receptors for bacterial Shiga toxin. Whereas the trisaccharidic head group of Gb3 defines the specificity of Shiga toxin binding, the lipophilic part composed of sphingosine and different fatty acids is suggested to determine its localization within membranes impacting membrane organisation and protein binding eventually leading to protein internalisation. While most studies use Gb3 extracts, chemical synthesis provides a unique tool to access different tailor-made Gb3 glycosphingolipids. In this review, strategies to synthesize these complex glycosphingolipids are presented. Special emphasis is put on the preparation of Gb3 molecules differing only in their fatty acid part (saturated, unsaturated, α-hydroxylated and both, unsaturated and α-hydroxylated). With these molecules in hand, it became possible to investigate the phase behaviour of liquid ordered/liquid disordered supported membranes doped with the Gb3 species by means of fluorescence and atomic force microscopy. The results clearly highlight the influence of the different fatty acids of the Gb3 sphingolipids on the phase behaviour and the binding properties of Shiga toxin B subunits, even though the membranes were only doped with 5 mol% of the receptor lipid. To obtain fluorescent Gb3 derivatives, either fatty acid labelled Gb3 molecules or head group labelled ones were synthesized. These molecules enabled us to address the question, where the Gb3 sphingolipids are localized prior protein binding by means of fluorescence microscopy on giant unilamellar vesicles. The results again demonstrate that the fatty acid of Gb3 plays a pivotal role for the overall membrane organisation.

Vacuolin-1 inhibits endosomal trafficking and metastasis via CapZβ

Metastasis is the fundamental cause of cancer mortality, but there are still very few anti-metastatic drugs available. Endosomal trafficking has been implicated in tumor metastasis, and we have previously found that small chemical vacuolin-1 (V1) potently inhibits autophagosome-lysosome fusion and general endosomal-lysosomal degradation. Here, we assessed the anti-metastatic activity of V1 both in vitro and in vivo. V1 significantly inhibits colony formation, migration, and invasion of various cancer cells in vitro. It also compromises the assembly-disassembly dynamics of focal adhesions (FAs) by inhibiting the recycling and degradation of integrins. In various experimental or transgenic mouse models, V1 significantly suppresses the metastasis and/or tumor growth of breast cancer or melanoma. We further identified capping protein Zβ (CapZβ) as a V1 binding protein and showed that it is required for the V1-mediated inhibition of migration and metastasis of cancer cells. Collectively, our results indicate that V1 targets CapZβ to inhibit endosomal trafficking and metastasis.

In Vitro Studies to Define the Cell-Surface and Intracellular Targets of Polyarginine-Conjugated Sodium Borocaptate as a Potential Delivery Agent for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) requires pharmaceutical innovations and molecular-based evidence of effectiveness to become a standard cancer therapeutic in the future. Recently, in Japan, 4-borono-L-phenylalanine (BPA) was approved as a boron agent for BNCT against head and neck (H&N) cancers. H&N cancer appears to be a suitable target for BPA-BNCT, because the expression levels of L-type amino acid transporter 1 (LAT1), one of the amino acid transporters responsible for BPA uptake, are elevated in most cases of H&N cancer. However, in other types of cancer including malignant brain tumors, LAT1 is not always highly expressed. To expand the possibility of BNCT for these cases, we previously developed poly-arginine peptide (polyR)-conjugated mercaptoundecahydrododecaborate (BSH). PolyR confers the cell membrane permeability and tumor selectivity of BSH. However, the molecular determinants for the properties are not fully understood. In this present study, we have identified the cluster of differentiation 44 (CD44) protein and translational machinery proteins as a major cell surface target and intracellular targets of BSH-polyR, respectively. CD44, also known as a stem cell-associated maker in various types of cancer, is required for the cellular uptake of polyR-conjugated molecules. We showed that BSH-polyR was predominantly delivered to a CD44High cell population of cancer cells. Once delivered, BSH-polyR interacted with the translational machinery components, including the initiation factors, termination factors, and poly(A)-biding protein (PABP). As a proof of principle, we performed BSH-polyR-based BNCT against glioma stem-like cells and revealed that BSH-polyR successfully induced BNCT-dependent cell death specifically in CD44High cells. Bioinformatics analysis indicated that BSH-polyR would be suitable for certain types of malignant tumors. Our results shed light on the biochemical properties of BSH-polyR, which may further contribute to the therapeutic optimization of BSH-BNCT in the future.

Novel insights into the function of CD24: A driving force in cancer

CD24 is a highly glycosylated protein with a small protein core that is linked to the plasma membrane via a glycosyl-phosphatidylinositol anchor. CD24 is primarily expressed by immune cells but is often overexpressed in human tumors. In cancer, CD24 is a regulator of cell migration, invasion and proliferation. Its expression is associated with poor prognosis and it is used as cancer stemness marker. Recently, CD24 on tumor cells was identified as a phagocytic inhibitor ("do not eat me" signal) having a suppressive role in tumor immunity via binding to Siglec-10 on macrophages. This finding is reminiscent of the demonstration that soluble CD24-Fc can dampen the immune system in autoimmune disease. In the present review, we summarize recent progress on the role of the CD24-Siglec-10 binding axis at the interface between tumor cells and the immune system, and the role of CD24 genetic polymorphisms in cancer. We describe the specific function of cytoplasmic CD24 and discuss the presence of CD24 on tumor-released extracellular vesicles. Finally, we evaluate the potential of CD24-based immunotherapy.

Full-length galectin-8 and separate carbohydrate recognition domains: the whole is greater than the sum of its parts?

Galectin-8 (Gal-8) is a tandem-repeat type galectin with affinity for β-galactosides, bearing two carbohydrate recognition domains (CRD) connected by a linker peptide. The N- and C-terminal domains (Gal-8N and Gal-8C) share 35% homology, and their glycan ligand specificity is notably dissimilar: while Gal-8N shows strong affinity for α(2-3)-sialylated oligosaccharides, Gal-8C has higher affinity for non-sialylated oligosaccharides, including poly-N-acetyllactosamine and/ or A and B blood group structures. Particularly relevant for understanding the biological role of this lectin, full-length Gal-8 can bind cell surface glycoconjugates with broader affinity than the isolated Gal-8N and Gal-8C domains, a trait also described for other tandem-repeat galectins. Herein, we aim to discuss the potential use of separate CRDs in modelling tandem-repeat galectin-8 and its biological functions. For this purpose, we will cover several aspects of the structure-function relationship of this protein including crystallographic structures, glycan specificity, cell function and biological roles, with the ultimate goal of understanding the potential role of each CRD in predicting full-length Gal-8 involvement in relevant biological processes.