Endothelial cell migration on fibronectin is regulated by syntaxin 6-mediated alpha5beta1 integrin recycling

Syntaxin6 contributes to hepatocellular carcinoma tumorigenesis via enhancing STAT3 phosphorylation

BACKGROUND

Syntaxin6 (STX6) is a SNARE (Soluble N-ethylmaleimide-sensitive factor attachment protein receptors) protein complex located in the trans-Golgi network and endosomes, which is closely associated with a variety of intracellular membrane transport events. STX6 has been shown to be overexpressed in a variety of human malignant tumors such as esophageal, colorectal, and renal cell carcinomas, and participates in tumorigenesis and development.

METHODS

Based on clinical public database and clinical liver samples analysis, the expression of STX6 in hepatocellular carcinoma (HCC) tissues was investigated. The effects of STX6 on proliferation, migration and invasion of HCC cell in vitro and in vivo were evaluated through gain- and loss-of-function studies. We further performed RNA-seq analysis and protein interactome analysis, to further decifer the detailed mechanisms of STX6 in the regulation of the JAK-STAT pathway in HCC.

RESULTS

STX6 expression was upregulated in HCC tissues and its expression was highly correlated with the high histological grade of the tumor. STX6 promoted HCC cell proliferation, migration and invasion both in vitro and in vivo. Mechanistically, STX6 mediated tumor progression depending on promoting the activation of JAK-STAT signaling pathway. Receptor for activated protein kinase C (RACK1) as an essential adaptor protein mediating STX6 regulation of JAK-STAT pathway. Specifically, STX6 interacted with RACK1 and then recruited signal transducer and activator of transcription 3 (STAT3) to form a protein-binding complex and activates STAT3 transcriptional activity.

CONCLUSIONS

This study provided a novel concept that STX6 exerted oncogenic effects by activating the STAT3 signaling pathway, and STX6 might be a promising therapeutic target for HCC.

Integrin-Dependent Cell-Matrix Adhesion in Endothelial Health and Disease

The endothelium is a dynamic, semipermeable layer lining all blood vessels, regulating blood vessel formation and barrier function. Proper composition and function of the endothelial barrier are required for fluid homeostasis, and clinical conditions characterized by barrier disruption are associated with severe morbidity and high mortality rates. Endothelial barrier properties are regulated by cell-cell junctions and intracellular signaling pathways governing the cytoskeleton, but recent insights indicate an increasingly important role for integrin-mediated cell-matrix adhesion and signaling in endothelial barrier regulation. Here, we discuss diseases characterized by endothelial barrier disruption, and provide an overview of the composition of endothelial cell-matrix adhesion complexes and associated signaling pathways, their crosstalk with cell-cell junctions, and with other receptors. We further present recent insights into the role of cell-matrix adhesions in the developing and mature/adult endothelium of various vascular beds, and discuss how the dynamic regulation and turnover of cell-matrix adhesions regulates endothelial barrier function in (patho)physiological conditions like angiogenesis, inflammation and in response to hemodynamic stress. Finally, as clinical conditions associated with vascular leak still lack direct treatment, we focus on how understanding of endothelial cell-matrix adhesion may provide novel targets for treatment, and discuss current translational challenges and future perspectives.

The Composites of PCL and Tetranuclear Titanium(IV)-Oxo Complex with Acetylsalicylate Ligands-Assessment of Their Biocompatibility and Antimicrobial Activity with the Correlation to EPR Spectroscopy

In our research, we have focused on the biological studies on composite materials produced by the dispersion of titanium(IV)-oxo complex (TOC) with acetylsalicylate ligands in a poly(ε-caprolactone) (PCL) matrix, which is a biodegradable thermoplastic polymer increasingly used in the production of medical devices. Using PCL as a matrix for the biologically active compounds, such as antimicrobial agents, antibiotics or other active medical substances, from which these individuals can be gradually released is fully understable. Composites of PCL + nTOC (n = 10, 15 and 20 wt.%) have been produced and, in such a form, the biological properties of TOCs have been estimated. Direct and indirect cytotoxicity studies have been performed in vitro on L929 and human umbilical vein endothelial cells (HUVEC) cell lines. The antibacterial and antifungal activity of the PCL + TOC samples have been assessed against two Staphylococcus aureus (ATCC 6538 and ATCC 25923) reference strains, two Escherichia coli (ATCC 8739 and ATCC 25922) reference strains and yeast of Candida albicans ATCC 10231. Obtained results have been correlated with electron paramagnetic resonance (EPR) spectroscopy data. We could conclude that photoexcitation by visible light of the surface of PCL + nTOC composite foils lead to the formation of different paramagnetic species, mainly O^-, which slowly disappears over time; however, their destructive effect on bacteria and cells has been proven.

Syntaxin-6, a Reliable Biomarker for Predicting the Prognosis of Patients with Cancer and the Effectiveness of Immunotherapy

Syntaxin-6 (STX6), a vesicular transport protein, is a direct target of the tumor suppressor gene P53, supporting cancer growth dependent on P53. However, STX6's function in the tumor microenvironment has yet to be reported. In this research, we comprehensively explored the role of the oncogene STX6 in pan-cancer by combining data from several databases, including the Cancer Genome Atlas, CPTAC, cBioPortal, and TIMER. Then, we verified the carcinogenic effect of STX6 in hepatocellular carcinoma (HCC) and colorectal cancer (CRC) through a series of experiments in vitro and in vivo. Bioinformatics analysis demonstrated that STX6 is an oncogene for several cancers and is mainly involved in the cell cycle, epithelial-mesenchymal transition, oxidative phosphorylation, and tumor immune modulation, especially for tumor-associated fibroblasts (CAFs) and NKT cells. Additionally, a high level of STX6 could indicate patients' resistance to immunotherapy. Our own data indicated that the STX6 level was upregulated in HCC and CRC. Knockdown of the STX6 levels could arrest the cell cycle and restrain cell proliferation, migration, and invasion. RNA-seq indicated that STX6 was significantly involved in pathways for cancer, such as the MAPK signal pathway. In a mouse model, knockdown of STX6 inhibited tumor growth and potentiated anti-PD-1 efficacy. In light of the essential roles STX6 plays in carcinogenesis and cancer immunology, it has the potential to be a predictive biomarker and a target for cancer immunotherapy.

Linking Late Endosomal Cholesterol with Cancer Progression and Anticancer Drug Resistance

Cancer cells undergo drastic metabolic adaptions to cover increased bioenergetic needs, contributing to resistance to therapies. This includes a higher demand for cholesterol, which often coincides with elevated cholesterol uptake from low-density lipoproteins (LDL) and overexpression of the LDL receptor in many cancers. This implies the need for cancer cells to accommodate an increased delivery of LDL along the endocytic pathway to late endosomes/lysosomes (LE/Lys), providing a rapid and effective distribution of LDL-derived cholesterol from LE/Lys to other organelles for cholesterol to foster cancer growth and spread. LDL-cholesterol exported from LE/Lys is facilitated by Niemann–Pick Type C1/2 (NPC1/2) proteins, members of the steroidogenic acute regulatory-related lipid transfer domain (StARD) and oxysterol-binding protein (OSBP) families. In addition, lysosomal membrane proteins, small Rab GTPases as well as scaffolding proteins, including annexin A6 (AnxA6), contribute to regulating cholesterol egress from LE/Lys. Here, we summarize current knowledge that links upregulated activity and expression of cholesterol transporters and related proteins in LE/Lys with cancer growth, progression and treatment outcomes. Several mechanisms on how cellular distribution of LDL-derived cholesterol from LE/Lys influences cancer cell behavior are reviewed, some of those providing opportunities for treatment strategies to reduce cancer progression and anticancer drug resistance.

TFEB controls integrin-mediated endothelial cell adhesion by the regulation of cholesterol metabolism

The dynamic integrin-mediated adhesion of endothelial cells (ECs) to the surrounding ECM is fundamental for angiogenesis both in physiological and pathological conditions, such as embryonic development and cancer progression. The dynamics of EC-to-ECM adhesions relies on the regulation of the conformational activation and trafficking of integrins. Here, we reveal that oncogenic transcription factor EB (TFEB), a known regulator of lysosomal biogenesis and metabolism, also controls a transcriptional program that influences the turnover of ECM adhesions in ECs by regulating cholesterol metabolism. We show that TFEB favors ECM adhesion turnover by promoting the transcription of genes that drive the synthesis of cholesterol, which promotes the aggregation of caveolin-1, and the caveolin-dependent endocytosis of integrin β1. These findings suggest that TFEB might represent a novel target for the pharmacological control of pathological angiogenesis and bring new insights in the mechanism sustaining TFEB control of endocytosis.

DisintegrinDB: The first integrated database resource of disintegrins from snake venoms

Nowadays, a large number of databases have been developed gathering different types of therapeutic peptides including antimicrobial, antiviral and scorpion toxins peptides facilitating the searching for these molecules and their structural characteristics and pharmacology. Disintegrins, a family of small non-enzymatic and cysteine-rich proteins found in the snake venom may have a potential role in terms of novel therapeutic leads for cancer treatment. Despite their therapeutic effect, no database dedicated to disintegrins is available yet. Indeed, accessible information related to disintegrins are either scattered or fragmented in different databases from which it becomes extremely difficult to collect all the properties related to a particular disintegrin without exploring numerous databases available through distinct websites. Here, we propose DisintegrinDB as a first unique resource centralizing data related to disintegrins from snake venom. DisintegrinDB aims to facilitate the search on a given disintegrin and centralizes all the information on these peptides, helping researchers to retrieve all relevant related information.

Efficient fabrication of monodisperse hepatocyte spheroids and encapsulation in hybrid hydrogel with controllable extracellular matrix effect

Three-dimensional (3D) culture techniques, such as spheroid and organoid cultures, have gained increasing interest in biomedical research. However, the understanding and control of extracellular matrix (ECM) effect in spheroid and organoid culture has been limited. Here, we report a biofabrication approach to efficiently form uniform-sized 3D hepatocyte spheroids and encapsulate them in a hybrid hydrogel composed of alginate and various ECM molecules. Cells were seeded in a microwell platform to form spheroid before being encapsulated directly in a hybrid hydrogel containing various ECM molecules, including collagen type I (COL1), collagen type IV (COL4), fibronectin (FN), and laminin (LM). A systematic analysis of the effect of ECM molecules on the primary mouse hepatocyte phenotype was then performed. Our results showed that hydrogel encapsulation of hepatocyte spheroid promoted hepatic marker expression and secretory functions. In addition, different ECM molecules elicited distinct effects on hepatic functions in 3D encapsulated hepatocyte spheroids, but not in 2D hepatocyte and 3D non-encapsulated spheroids. When encapsulated in hybrid hydrogel containing LM alone or COL1 alone, hepatocyte spheroids exhibited improved hepatic functions overall. Analysis of gene and protein expression showed an upregulation of integrinα1 and integrinα6 when LM was introduced in the hybrid hydrogel, suggesting a possible role of integrin signaling involved in the ECM effect. Finally, a combinatorial screening was performed to demonstrate the potential to screen a multitude of 3D microenvironments of varying ECM combinations that exhibited synergistic influence, indicating a strong positive effect of COL1 and a negative interaction effect of COL1·LM on both albumin and urea secretion. These findings illustrate the broad application potential of this biofabrication approach in identifying optimal ECM composition(s) for engineering 3D tissue, and elucidating defined ECM cues for tissue engineering and regenerative medicine.

Uremic endothelial-derived extracellular vesicles: Mechanisms of formation and their role in cell adhesion, cell migration, inflammation, and oxidative stress

p-Cresyl sulfate (PCS), indoxyl sulfate (IS), and inorganic phosphate (Pi) are uremic toxins found in chronic kidney disease (CKD) that are closely related to endothelial extracellular vesicles (EVs) formation. The present study aimed to understand the role of EVs and their role in cell adhesion and migration, inflammation, and oxidative stress. Human endothelial cells were treated with PCS, IS, and Pi in pre-established uremic and kinetic recommendations. EVs were characterized using scanning electron microscopy, flow cytometry, and NanoSight assays. The concentrations of EVs were established using Alamar Blue and MTT assays. Cell adhesion to extracellular matrix proteins was analyzed using an adhesion assay. Inflammation and oxidative stress were assessed by vascular cell adhesion molecule-1 expression/monocyte migration and reactive oxygen species production, respectively. The capacity of EVs to stimulate endothelial cell migration was evaluated using a wound-healing assay. Our data showed that endothelial cells stimulated with uremic toxins can induce the formation of EVs of different sizes, quantities, and concentrations, depending on the uremic toxin used. Cell adhesion was significantly (P < 0.01) stimulated in cells exposed to PCS-induced extracellular vesicles (PCSEVs) and inorganic phosphate-induced extracellular vesicles (PiEVs). Cell migration was significantly (P < 0.05) stimulated by PCSEVs. VCAM-1 expression was evident in cells treated with PCSEVs and IS-induced extracellular vesicles (ISEVs). EVs are not able to stimulate monocyte migration or oxidative stress. In conclusion, EVs may be a biomarker of endothelial injury and the inflammatory process, playing an important role in cell-to-cell communication and pathophysiological processes, although more studies are needed to better understand the mechanisms of EVs in uremia.

Triple co-culture and perfusion bioreactor for studying the interaction between Neisseria gonorrhoeae and neutrophils: A novel 3D tissue model for bacterial infection and immunity

Gonorrhea, a sexually transmitted disease caused by the bacteria Neisseria gonorrhoeae, is characterized by a large number of neutrophils recruited to the site of infection. Therefore, proper modeling of the N. gonorrhoeae interaction with neutrophils is very important for investigating and understanding the mechanisms that gonococci use to evade the immune response. We have used a combination of a unique human 3D tissue model together with a dynamic culture system to study neutrophil transmigration to the site of N. gonorrhoeae infection. The triple co-culture model consisted of epithelial cells (T84 human colorectal carcinoma cells), human primary dermal fibroblasts, and human umbilical vein endothelial cells on a biological scaffold (SIS). After the infection of the tissue model with N. gonorrhoeae, we introduced primary human neutrophils to the endothelial side of the model using a perfusion-based bioreactor system. By this approach, we were able to demonstrate the activation and transmigration of neutrophils across the 3D tissue model and their recruitment to the site of infection. In summary, the triple co-culture model supplemented by neutrophils represents a promising tool for investigating N. gonorrhoeae and other bacterial infections and interactions with the innate immunity cells under conditions closely resembling the native tissue environment.

Dynamins 2 and 3 control the migration of human megakaryocytes by regulating CXCR4 surface expression and ITGB1 activity

Megakaryocyte (MK) migration from the bone marrow periosteal niche toward the vascular niche is a prerequisite for proplatelet extension and release into the circulation. The mechanism for this highly coordinated process is poorly understood. Here we show that dynasore (DNSR), a small-molecule inhibitor of dynamins (DNMs), or short hairpin RNA knockdown of DNM2 and DNM3 impairs directional migration in a human MK cell line or MKs derived from cultured CD34⁺ cells. Because cell migration requires actin cytoskeletal rearrangements, we measured actin polymerization and the activity of cytoskeleton regulator RhoA and found them to be decreased after inhibition of DNM2 and DNM3. Because SDF-1α is important for hematopoiesis, we studied the expression of its receptor CXCR4 in DNSR-treated cells. CXCR4 expression on the cell surface was increased, at least partially because of slower endocytosis and internalization after SDF-1α treatment. Combined inhibition of DNM2 and DNM3 or forced expression of dominant-negative Dnm2-K44A or GTPase-defective DNM3 diminished β1 integrin (ITGB1) activity. DNSR-treated MKs showed an abnormally clustered staining pattern of Rab11, a marker of recycling endosomes. This suggests decreased recruitment of the recycling pathway in DNSR-treated cells. Altogether, we show that the GTPase activity of DNMs, which governs endocytosis and regulates cell receptor trafficking, exerts control on MK migration toward SDF-1α gradients, such as those originating from the vascular niche. DNMs play a critical role in MKs by triggering membrane-cytoskeleton rearrangements downstream of CXCR4 and integrins.

Integrin trafficking in cells and tissues

Cell adhesion to the extracellular matrix is fundamental to metazoan multicellularity and is accomplished primarily through the integrin family of cell-surface receptors. Integrins are internalized and enter the endocytic-exocytic pathway before being recycled back to the plasma membrane. The trafficking of this extensive protein family is regulated in multiple context-dependent ways to modulate integrin function in the cell. Here, we discuss recent advances in understanding the mechanisms and cellular roles of integrin endocytic trafficking.

A membrane fusion protein, Ykt6, regulates epithelial cell migration via microRNA-mediated suppression of Junctional Adhesion Molecule A

Vesicle trafficking regulates epithelial cell migration by remodeling matrix adhesions and delivering signaling molecules to the migrating leading edge. Membrane fusion, which is driven by soluble N-ethylmaleimide-sensitive factor associated receptor (SNARE) proteins, is an essential step of vesicle trafficking. Mammalian SNAREs represent a large group of proteins, but few have been implicated in the regulation of cell migration. Ykt6 is a unique SNARE existing in equilibrium between active membrane-bound and inactive cytoplasmic pools, and mediating vesicle trafficking between different intracellular compartments. The biological functions of this protein remain poorly understood. In the present study, we found that Ykt6 acts as a negative regulator of migration and invasion of human prostate epithelial cells. Furthermore, Ykt6 regulates the integrity of epithelial adherens and tight junctions. The observed anti-migratory activity of Ykt6 is mediated by a unique mechanism involving the expressional upregulation of microRNA 145, which selectively decreases the cellular level of Junctional Adhesion Molecule (JAM) A. This decreased JAM-A expression limits the activity of Rap1 and Rac1 small GTPases, thereby attenuating cell spreading and motility. The described novel functions of Ykt6 could be essential for the regulation of epithelial barriers, epithelial repair, and metastatic dissemination of cancer cells.

Fibronectin rescues estrogen receptor α from lysosomal degradation in breast cancer cells

Estrogen receptor α (ERα) is expressed in tissues as diverse as brains and mammary glands. In breast cancer, ERα is a key regulator of tumor progression. Therefore, understanding what activates ERα is critical for cancer treatment in particular and cell biology in general. Using biochemical approaches and superresolution microscopy, we show that estrogen drives membrane ERα into endosomes in breast cancer cells and that its fate is determined by the presence of fibronectin (FN) in the extracellular matrix; it is trafficked to lysosomes in the absence of FN and avoids the lysosomal compartment in its presence. In this context, FN prolongs ERα half-life and strengthens its transcriptional activity. We show that ERα is associated with β1-integrin at the membrane, and this integrin follows the same endocytosis and subcellular trafficking pathway triggered by estrogen. Moreover, ERα⁺ vesicles are present within human breast tissues, and colocalization with β1-integrin is detected primarily in tumors. Our work unravels a key, clinically relevant mechanism of microenvironmental regulation of ERα signaling.

PEGylated TiO2 nanoparticles mediated inhibition of cell migration via integrin beta 1

Nanoparticles (NPs) elicit various physiological responses in cellular environment, and the effect of NPs on cell migration is of high interest. In this work, the effects of NPs on cell migration and their possible mechanisms were studied. Here, we showed that after exposure to pegylated titanium dioxide nanoparticles (TiO₂-PEG NPs, where PEG stands for the polyethylene glycol), NCI-H292 cells exhibited slower migration than control cells. Furthermore, larger NPs inhibited cell migration much stronger than smaller NPs. Following NP exposure, the cells showed decreased expression of integrin beta 1 and phosphorylated focal adhesion kinase (pFAK), and disrupted F-actin structures. We demonstrated that a possible mechanism involved NP-mediated promotion of the lysosomal degradation of integrin beta 1, thus leading to reduced expression of pFAK and cytoskeletal disruption and inhibited cell migration. Therefore, our results showed that inhibition of NCI-H292 cell migration by NPs is mediated through integrin beta 1, which provides useful information for the application of NPs in cancer therapy and related fields.

α5β1 integrin trafficking and Rac activation are regulated by APPL1 in a Rab5-dependent manner to inhibit cell migration

Cell migration is a tightly coordinated process that requires the spatiotemporal regulation of many molecular components. Because adaptor proteins can serve as integrators of cellular events, they are being increasingly studied as regulators of cell migration. The adaptor protein containing a pleckstrin-homology (PH) domain, phosphotyrosine binding (PTB) domain, and leucine zipper motif 1 (APPL1) is a 709 amino acid endosomal protein that plays a role in cell proliferation and survival as well as endosomal trafficking and signaling. However, its function in regulating cell migration is poorly understood. Here, we show that APPL1 hinders cell migration by modulating both trafficking and signaling events controlled by Rab5 in cancer cells. APPL1 decreases internalization and increases recycling of α5β1 integrin, leading to higher levels of α5β1 integrin at the cell surface that hinder adhesion dynamics. Furthermore, APPL1 decreases the activity of the GTPase Rac and its effector PAK, which in turn regulate cell migration. Thus, we demonstrate a novel role for the interaction between APPL1 and Rab5 in governing crosstalk between signaling and trafficking pathways on endosomes to affect cancer cell migration.This article has an associated First Person interview with the first author of the paper.

Cullin-3 and its adaptor protein ANKFY1 determine the surface level of integrin β1 in endothelial cells

Angiogenesis, the formation of new blood vessels from the pre-existing vasculature, is related to numerous pathophysiological events. We previously reported that a RING ubiquitin ligase complex scaffold protein, cullin-3 (CUL3), and one of its adaptor proteins, BAZF, regulated angiogenesis in the mouse retina by suppressing Notch signaling. However, the degree of inhibition of angiogenesis was made greater by CUL3 depletion than by BAZF depletion, suggesting other roles of CUL3 in angiogenesis besides the regulation of Notch signaling. In the present study, we found that CUL3 was critical for the cell surface level of integrin β1, an essential cell adhesion molecule for angiogenesis in HUVECs. By siRNA screening of 175 BTBPs, a family of adaptor proteins for CUL3, we found that ANKFY1/Rabankyrin-5, an early endosomal BTBP, was also critical for localization of surface integrin β1 and angiogenesis. CUL3 interacted with ANKFY1 and was required for the early endosomal localization of ANKFY1. These data suggest that CUL3/ANKFY1 regulates endosomal membrane traffic of integrin β1. Our results highlight the multiple roles of CUL3 in angiogenesis, which are mediated through distinct CUL3-adaptor proteins.

Misdirection of endosomal trafficking mediated by herpes simplex virus-encoded glycoprotein B

Herpes simplex virus (HSV)-encoded glycoprotein B (gB) is the most abundant protein in the viral envelope and promotes fusion of the virus with the cellular membrane. In the present study, we found that gB impacts on the major histocompatibility complex (MHC)-II pathway of antigen presentation by fostering homotypic fusion of early endosomes and trapping MHC-II molecules in these altered endosomes. By using an overexpression approach, we demonstrated that transient expression of gB induces giant vesicles of early endosomal origin, which contained Rab5, early endosomal antigen 1 (EEA1), and large amounts of MHC-II molecules [human leukocyte antigen (HLA)-DR, and HLA-DM], but no CD63. In HSV-1-infected and stably transfected cell lines that expressed lower amounts of gB, giant endosomes were not observed, but strongly increased amounts of HLA-DR and HLA-DM were found in EEA1⁺ early endosomes. We used these giant vesicles as a model system and revealed that gB interacts with Rab5 and EEA1, and that gB-induced homotypic fusion of early endosomes to giant endosomes requires phosphatidylinositol 3-phosphate, the activity of soluble N-ethylmaleimide-sensitive factor attachment protein receptors, and the cytosolic gB sequence ⁸⁸⁹YTQVPN⁸⁹⁴ We conclude that gB expression alters trafficking of molecules of the HLA-II processing pathway, which leads to increased retention of MHC-II molecules in early endosomal compartments, thereby intercepting antigen presentation.-Niazy, N., Temme, S., Bocuk, D., Giesen, C., König, A., Temme, N., Ziegfeld, A., Gregers, T. F., Bakke, O., Lang, T., Eis-Hübinger, A. M., Koch, N. Misdirection of endosomal trafficking mediated by herpes simplex virus-encoded glycoprotein B.

Annexin A6-A multifunctional scaffold in cell motility

Annexin A6 (AnxA6) belongs to a highly conserved protein family characterized by their calcium (Ca²⁺)-dependent binding to phospholipids. Over the years, immunohistochemistry, subcellular fractionations, and live cell microscopy established that AnxA6 is predominantly found at the plasma membrane and endosomal compartments. In these locations, AnxA6 acts as a multifunctional scaffold protein, recruiting signaling proteins, modulating cholesterol and membrane transport and influencing actin dynamics. These activities enable AnxA6 to contribute to the formation of multifactorial protein complexes and membrane domains relevant in signal transduction, cholesterol homeostasis and endo-/exocytic membrane transport. Hence, AnxA6 has been implicated in many biological processes, including cell proliferation, survival, differentiation, inflammation, but also membrane repair and viral infection. More recently, we and others identified roles for AnxA6 in cancer cell migration and invasion. This review will discuss how the multiple scaffold functions may enable AnxA6 to modulate migratory cell behavior in health and disease.

Cordycepin inhibits migration of human glioblastoma cells by affecting lysosomal degradation and protein phosphatase activation

Cordycepin, a nucleoside-derivative-isolated form Cordyceps militaris, has been reported to suppress tumor cell proliferation and cause apoptosis. This study investigates the effect of cordycepin on the migration of human glioblastoma cells. Cordycepin suppressed the migration of the human glioblastoma cell lines U87MG and LN229 in transwell and wound healing assays. Cordycepin decreased protein expression of integrin α1, focal adhesion kinase (FAK), p-FAK, paxillin and p-paxillin. The lysosomal inhibitor NH₄Cl blocked the ability of cordycepin to inhibit focal adhesion protein expression and glioma cell migration. In addition, the protein phosphatase inhibitors calyculin A and okadaic acid blocked the cordycepin-mediated reduction in p-Akt, p-FAK and migration. Hematoxylin and eosin staining of mouse xenografts demonstrated that cordycepin reduced brain tumor size in vivo. In conclusion, cordycepin inhibited migration of human glioblastoma cells by affecting lysosomal degradation and protein phosphatase activation. This pathway may be a useful target for clinical therapy in the future.

PPFIA1 drives active α5β1 integrin recycling and controls fibronectin fibrillogenesis and vascular morphogenesis

Basolateral polymerization of cellular fibronectin (FN) into a meshwork drives endothelial cell (EC) polarity and vascular remodelling. However, mechanisms coordinating α5β1 integrin-mediated extracellular FN endocytosis and exocytosis of newly synthesized FN remain elusive. Here we show that, on Rab21-elicited internalization, FN-bound/active α5β1 is recycled to the EC surface. We identify a pathway, comprising the regulators of post-Golgi carrier formation PI4KB and AP-1A, the small GTPase Rab11B, the surface tyrosine phosphatase receptor PTPRF and its adaptor PPFIA1, which we propose acts as a funnel combining FN secretion and recycling of active α5β1 integrin from the trans-Golgi network (TGN) to the EC surface, thus allowing FN fibrillogenesis. In this framework, PPFIA1 interacts with active α5β1 integrin and localizes close to EC adhesions where post-Golgi carriers are targeted. We show that PPFIA1 is required for FN polymerization-dependent vascular morphogenesis, both in vitro and in the developing zebrafish embryo.

Endocytic Trafficking of Integrins in Cell Migration

Integrins are a family of heterodimeric receptors that bind to components of the extracellular matrix and influence cellular processes as varied as proliferation and migration. These effects are achieved by tight spatiotemporal control over intracellular signalling pathways, including those that mediate cytoskeletal reorganisation. The ability of integrins to bind to ligands is governed by integrin conformation, or activity, and this is widely acknowledged to be an important route to the regulation of integrin function. Over the last 15 years, however, the pathways that regulate endocytosis and recycling of integrins have emerged as major players in controlling integrin action, and studying integrin trafficking has revealed fresh insight into the function of this fascinating class of extracellular matrix receptors, in particular in the context of cell migration and invasion. Here, we review our current understanding of the contribution of integrin trafficking to cell motility.

Regulation of Cell Migration and β1 Integrin Trafficking by the Endosomal Adaptor GGA3

The integrin family of cell adhesion receptors link extracellular matrices to intracellular signaling pathways and the actin cytoskeleton; and regulate cell migration, proliferation and survival in normal and diseased tissues. The subcellular location of integrin receptors is critical for their function and deregulated trafficking is implicated in various human diseases. Here we identify a role for Golgi-localized gamma-ear containing Arf-binding protein 3 (GGA3), in regulating trafficking of β1 integrin. GGA3 knockdown reduces cell surface and total levels of α2, α5 and β1 integrin subunits, inhibits cell spreading, reduces focal adhesion number, as well as cell migration. In the absence of GGA3, integrins are increasingly retained inside the cell, traffic toward the perinuclear lysosomal compartment and their degradation is enhanced. Integrin traffic and maintenance of integrin levels are dependent on the integrity of the Arf binding site of GGA3. Furthermore, sorting nexin 17 (SNX17), a critical regulator of integrin recycling, becomes mislocalized to enlarged late endosomes upon GGA3 depletion. These data support a model whereby GGA3, through its ability to regulate SNX17 endosomal localization and through interaction with Arf6 diverts integrins from the degradative pathway supporting cell migration.

Glia Maturation Factor-γ Regulates Monocyte Migration through Modulation of β1-Integrin

Monocyte migration requires the dynamic redistribution of integrins through a regulated endo-exocytosis cycle, but the complex molecular mechanisms underlying this process have not been fully elucidated. Glia maturation factor-γ (GMFG), a novel regulator of the Arp2/3 complex, has been shown to regulate directional migration of neutrophils and T-lymphocytes. In this study, we explored the important role of GMFG in monocyte chemotaxis, adhesion, and β1-integrin turnover. We found that knockdown of GMFG in monocytes resulted in impaired chemotactic migration toward formyl-Met-Leu-Phe (fMLP) and stromal cell-derived factor 1α (SDF-1α) as well as decreased α5β1-integrin-mediated chemoattractant-stimulated adhesion. These GMFG knockdown impaired effects could be reversed by cotransfection of GFP-tagged full-length GMFG. GMFG knockdown cells reduced the cell surface and total protein levels of α5β1-integrin and increased its degradation. Importantly, we demonstrate that GMFG mediates the ubiquitination of β1-integrin through knockdown or overexpression of GMFG. Moreover, GMFG knockdown retarded the efficient recycling of β1-integrin back to the plasma membrane following normal endocytosis of α5β1-integrin, suggesting that the involvement of GMFG in maintaining α5β1-integrin stability may occur in part by preventing ubiquitin-mediated degradation and promoting β1-integrin recycling. Furthermore, we observed that GMFG interacted with syntaxin 4 (STX4) and syntaxin-binding protein 4 (STXBP4); however, only knockdown of STXBP4, but not STX4, reduced monocyte migration and decreased β1-integrin cell surface expression. Knockdown of STXBP4 also substantially inhibited β1-integrin recycling in human monocytes. These results indicate that the effects of GMFG on monocyte migration and adhesion probably occur through preventing ubiquitin-mediated proteasome degradation of α5β1-integrin and facilitating effective β1-integrin recycling back to the plasma membrane.

The macromolecular architecture of platelet-derived microparticles

Platelets are essential for hemostasis and wound healing. They are involved in fundamental processes of vascular biology such as angiogenesis, tissue regeneration, and tumor metastasis. Upon activation, platelets shed small plasma membrane vesicles termed platelet-derived microparticles (PMPs). PMPs include functional cell adhesion machinery that comprises transmembrane receptors (most abundant are the αIIbβ3 integrins), cytoskeletal systems and a large variety of adapter and signaling molecules. Glanzmann thrombasthenia (GT) is a condition characterized by platelets that are deficient of the integrin αIIbβ3 heterodimer. Here, we use cryo-electron tomography (cryo-ET) to study the structural organization of PMPs (in both healthy and GT patients), especially the cytoskeleton organization and receptor architecture. PMPs purified from GT patients show a significantly altered cytoskeletal organization, characterized by a reduced number of filaments present, compared to the healthy control. Furthermore, our results show that incubating healthy PMPs with manganese ions (Mn(2+)), in the presence of fibrinogen, induces a major conformational change of integrin receptors, whereas thrombin activation yields a moderate response. These results provide the first insights into the native molecular organization of PMPs.

Annexin A6 and Late Endosomal Cholesterol Modulate Integrin Recycling and Cell Migration

Annexins are a family of proteins that bind to phospholipids in a calcium-dependent manner. Earlier studies implicated annexin A6 (AnxA6) to inhibit secretion and participate in the organization of the extracellular matrix. We recently showed that elevated AnxA6 levels significantly reduced secretion of the extracellular matrix protein fibronectin (FN). Because FN is directly linked to the ability of cells to migrate, this prompted us to investigate the role of AnxA6 in cell migration. Up-regulation of AnxA6 in several cell models was associated with reduced cell migration in wound healing, individual cell tracking and three-dimensional migration/invasion assays. The reduced ability of AnxA6-expressing cells to migrate was associated with decreased cell surface expression of αVβ3 and α5β1 integrins, both FN receptors. Mechanistically, we found that elevated AnxA6 levels interfered with syntaxin-6 (Stx6)-dependent recycling of integrins to the cell surface. AnxA6 overexpression caused mislocalization and accumulation of Stx6 and integrins in recycling endosomes, whereas siRNA-mediated AnxA6 knockdown did not modify the trafficking of integrins. Given our recent findings that inhibition of cholesterol export from late endosomes (LEs) inhibits Stx6-dependent integrin recycling and that elevated AnxA6 levels cause LE cholesterol accumulation, we propose that AnxA6 and blockage of LE cholesterol transport are critical for endosomal function required for Stx6-mediated recycling of integrins in cell migration.

Interplay of Endosomal pH and Ligand Occupancy in Integrin α5β1 Ubiquitination, Endocytic Sorting, and Cell Migration

Membrane trafficking of integrins plays a pivotal role in cell proliferation and migration. How endocytosed integrins are targeted either for recycling or lysosomal delivery is not fully understood. Here, we show that fibronectin (FN) binding to α5β1 integrin triggers ubiquitination and internalization of the receptor complex. Acidification facilitates FN dissociation from integrin α5β1 in vitro and in early endosomes, promoting receptor complex deubiquitination by the USP9x and recycling to the cell surface. Depending on residual ligand occupancy of receptors, some α5β1 integrins remain ubiquitinated and are captured by ESCRT-0/I, containing histidine domain-containing protein tyrosine phosphatase (HD-PTP) and ubiquitin-associated protein 1 (UBAP1), and are directed for lysosomal proteolysis, limiting receptor downstream signaling and cell migration. Thus, HD-PTP or UBAP1 depletion confers a pro-invasive phenotype. Thus, pH-dependent FN-integrin dissociation and deubiquitination of the activated integrin α5β1 are required for receptor resensitization and cell migration, representing potential targets to modulate tumor invasiveness.

Quantitative and functional interrogation of parent-of-origin allelic expression biases in the brain

The maternal and paternal genomes play different roles in mammalian brains as a result of genomic imprinting, an epigenetic regulation leading to differential expression of the parental alleles of some genes. Here we investigate genomic imprinting in the cerebellum using a newly developed Bayesian statistical model that provides unprecedented transcript-level resolution. We uncover 160 imprinted transcripts, including 41 novel and independently validated imprinted genes. Strikingly, many genes exhibit parentally biased--rather than monoallelic--expression, with different magnitudes according to age, organ, and brain region. Developmental changes in parental bias and overall gene expression are strongly correlated, suggesting combined roles in regulating gene dosage. Finally, brain-specific deletion of the paternal, but not maternal, allele of the paternally-biased Bcl-x, (Bcl2l1) results in loss of specific neuron types, supporting the functional significance of parental biases. These findings reveal the remarkable complexity of genomic imprinting, with important implications for understanding the normal and diseased brain.

Role of SNARE proteins in tumourigenesis and their potential as targets for novel anti-cancer therapeutics

The function of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) in cellular trafficking, membrane fusion and vesicle release in synaptic nerve terminals is well characterised. Recent studies suggest that SNAREs are also important in the control of tumourigenesis through the regulation of multiple signalling and transportation pathways. The majority of published studies investigated the effects of knockdown/knockout or overexpression of particular SNAREs on the normal function of cells as well as their dysfunction in tumourigenesis promotion. SNAREs are involved in the regulation of cancer cell invasion, chemo-resistance, the transportation of autocrine and paracrine factors, autophagy, apoptosis and the phosphorylation of kinases essential for cancer cell biogenesis. This evidence highlights SNAREs as potential targets for novel cancer therapy. This is the first review to summarise the expression and role of SNAREs in cancer biology at the cellular level, their interaction with non-SNARE proteins and modulation of cellular signalling cascades. Finally, a strategy is proposed for developing novel anti-cancer therapeutics using targeted delivery of a SNARE-inactivating protease into malignant cells.

EARP is a multisubunit tethering complex involved in endocytic recycling

Recycling of endocytic receptors to the cell surface involves passage through a series of membrane-bound compartments by mechanisms that are poorly understood. In particular, it is unknown if endocytic recycling requires the function of multisubunit tethering complexes, as is the case for other intracellular trafficking pathways. Herein we describe a tethering complex named Endosome-Associated Recycling Protein (EARP) that is structurally related to the previously described Golgi-Associated Retrograde Protein (GARP) complex. Both complexes share the Ang2, Vps52 and Vps53 subunits, but EARP comprises an uncharacterized protein, Syndetin, in place of the Vps54 subunit of GARP. This change determines differential localization of EARP to recycling endosomes and GARP to the Golgi complex. EARP interacts with the target-SNARE Syntaxin 6 and various cognate SNAREs. Depletion of Syndetin or Syntaxin 6 delays recycling of internalized transferrin to the cell surface. These findings implicate EARP in canonical membrane-fusion events in the process of endocytic recycling.

Integrin traffic - the update

Integrins are a family of transmembrane cell surface molecules that constitute the principal adhesion receptors for the extracellular matrix (ECM) and are indispensable for the existence of multicellular organisms. In vertebrates, 24 different integrin heterodimers exist with differing substrate specificity and tissue expression. Integrin–extracellular-ligand interaction provides a physical anchor for the cell and triggers a vast array of intracellular signalling events that determine cell fate. Dynamic remodelling of adhesions, through rapid endocytic and exocytic trafficking of integrin receptors, is an important mechanism employed by cells to regulate integrin–ECM interactions, and thus cellular signalling, during processes such as cell migration, invasion and cytokinesis. The initial concept of integrin traffic as a means to translocate adhesion receptors within the cell has now been expanded with the growing appreciation that traffic is intimately linked to the cell signalling apparatus. Furthermore, endosomal pathways are emerging as crucial regulators of integrin stability and expression in cells. Thus, integrin traffic is relevant in a number of pathological conditions, especially in cancer. Nearly a decade ago we wrote a Commentary in Journal of Cell Science entitled ‘Integrin traffic’. With the advances in the field, we felt it would be appropriate to provide the growing number of researchers interested in integrin traffic with an update.

Role of cholesterol in SNARE-mediated trafficking on intracellular membranes

The cell surface delivery of extracellular matrix (ECM) and integrins is fundamental for cell migration in wound healing and during cancer cell metastasis. This process is not only driven by several soluble NSF attachment protein (SNAP) receptor (SNARE) proteins, which are key players in vesicle transport at the cell surface and intracellular compartments, but is also tightly modulated by cholesterol. Cholesterol-sensitive SNAREs at the cell surface are relatively well characterized, but it is less well understood how altered cholesterol levels in intracellular compartments impact on SNARE localization and function. Recent insights from structural biology, protein chemistry and cell microscopy have suggested that a subset of the SNAREs engaged in exocytic and retrograde pathways dynamically 'sense' cholesterol levels in the Golgi and endosomal membranes. Hence, the transport routes that modulate cellular cholesterol distribution appear to trigger not only a change in the location and functioning of SNAREs at the cell surface but also in endomembranes. In this Commentary, we will discuss how disrupted cholesterol transport through the Golgi and endosomal compartments ultimately controls SNARE-mediated delivery of ECM and integrins to the cell surface and, consequently, cell migration.

Regulation of the migration of endothelial cells by a gradient density of vascular endothelial growth factor

To investigate the effect of the surface gradient density of growth factor on the migration of endothelial cells (ECs), an approach to fabricate a gradient density of vascular endothelial growth factor (VEGF) onto silicon slides has been developed in this study. Our approach involves gradual injection of 3-glycidoxypropyltrimeth oxysilane (GPTMS) and then back filling with 3-triethoxysilylpropyl succinicanhydride (TESPSA) to produce a gradient density of carboxyl groups (-COOH) onto the silicon slides. The -COOH moieties were then activated for the immobilization of VEGF, which leading to a surface gradient density of VEGF. The successful formation of both carboxyl and VEGF gradient densities were confirmed by contact angle measurement, confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS), respectively. The treated silicon slide displayed a gradient density of VEGF from 54 to 132 ng/cm2 with a slope of 7.8 ng/cm2/mm. ECs cultured on the surface gradient density of VEGF demonstrated preferential orientation and an enhanced directional migration behavior. Up to 72% of cells migrated towards the region with high surface density of VEGF. However, the gradient density of VEGF had no significant effect on the cell migration rate. The study provides an alternative to explore chemical-directing cells migration, which is essentially important for understanding cell migration/in-growth behavior for angiogenesis involved in implant technology.

Cholesterol regulates Syntaxin 6 trafficking at trans-Golgi network endosomal boundaries

Inhibition of cholesterol export from late endosomes causes cellular cholesterol imbalance, including cholesterol depletion in the trans-Golgi network (TGN). Here, using Chinese hamster ovary (CHO) Niemann-Pick type C1 (NPC1) mutant cell lines and human NPC1 mutant fibroblasts, we show that altered cholesterol levels at the TGN/endosome boundaries trigger Syntaxin 6 (Stx6) accumulation into VAMP3, transferrin, and Rab11-positive recycling endosomes (REs). This increases Stx6/VAMP3 interaction and interferes with the recycling of αVβ3 and α5β1 integrins and cell migration, possibly in a Stx6-dependent manner. In NPC1 mutant cells, restoration of cholesterol levels in the TGN, but not inhibition of VAMP3, restores the steady-state localization of Stx6 in the TGN. Furthermore, elevation of RE cholesterol is associated with increased amounts of Stx6 in RE. Hence, the fine-tuning of cholesterol levels at the TGN-RE boundaries together with a subset of cholesterol-sensitive SNARE proteins may play a regulatory role in cell migration and invasion.

An RNAi screen identifies KIF15 as a novel regulator of the endocytic trafficking of integrin

α2β1 integrin is one of the most important collagen-binding receptors, and it has been implicated in numerous thrombotic and immune diseases. α2β1 integrin is a potent tumour suppressor, and its downregulation is associated with increased metastasis and poor prognosis in breast cancer. Currently, very little is known about the mechanism that regulates the cell-surface expression and trafficking of α2β1 integrin. Here, using a quantitative fluorescence-microscopy-based RNAi assay, we investigated the impact of 386 cytoskeleton-associated or -regulatory genes on α2 integrin endocytosis and found that 122 of these affected the intracellular accumulation of α2 integrin. Of these, 83 were found to be putative regulators of α2 integrin trafficking and/or expression, with no observed effect on the internalization of epidermal growth factor (EGF) or transferrin. Further interrogation and validation of the siRNA screen revealed a role for KIF15, a microtubule-based molecular motor, as a significant inhibitor of the endocytic trafficking of α2 integrin. Our data suggest a novel role for KIF15 in mediating plasma membrane localization of the alternative clathrin adaptor Dab2, thus impinging on pathways that regulate α2 integrin internalization.

N-ethylmaleimide-sensitive factor attachment protein α (αSNAP) regulates matrix adhesion and integrin processing in human epithelial cells

Integrin-based adhesion to the extracellular matrix (ECM) plays critical roles in controlling differentiation, survival, and motility of epithelial cells. Cells attach to the ECM via dynamic structures called focal adhesions (FA). FA undergo constant remodeling mediated by vesicle trafficking and fusion. A soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein α (αSNAP) is an essential mediator of membrane fusion; however, its roles in regulating ECM adhesion and cell motility remain unexplored. In this study, we found that siRNA-mediated knockdown of αSNAP induced detachment of intestinal epithelial cells, whereas overexpression of αSNAP increased ECM adhesion and inhibited cell invasion. Loss of αSNAP impaired Golgi-dependent glycosylation and trafficking of β1 integrin and decreased phosphorylation of focal adhesion kinase (FAK) and paxillin resulting in FA disassembly. These effects of αSNAP depletion on ECM adhesion were independent of apoptosis and NSF. In agreement with our previous reports that Golgi fragmentation mediates cellular effects of αSNAP knockdown, we found that either pharmacologic or genetic disruption of the Golgi recapitulated all the effects of αSNAP depletion on ECM adhesion. Furthermore, our data implicates β1 integrin, FAK, and paxillin in mediating the observed pro-adhesive effects of αSNAP. These results reveal novel roles for αSNAP in regulating ECM adhesion and motility of epithelial cells.

Derivation of human peripheral blood derived endothelial progenitor cells and the role of osteopontin surface modification and eNOS transfection

Endothelial coverage of blood-contacting biomaterial surfaces has been difficult to achieve. A readily available autologous source of endothelium combined with an appropriate attachment substrate would improve the chances of developing functional surfaces. Here we describe methods to derive high quantities of human endothelial progenitor cells (EPCs) from peripheral blood monocytes (PBMCs) obtained by leukapheresis. These cells are morphologically and phenotypically similar to human umbilical vein endothelial cells (HUVECs); however, their expression of the key vascular factor - endothelial nitric oxide synthase (eNOS) - is markedly lower than that observed in HUVECs. We demonstrate that eNOS levels can be restored with plasmid-based transfection. To promote EPC adherence we examined substrate enhancement with a matricellular protein associated with vascular repair, osteopontin (OPN). We observed dose- and time-dependent responses of OPN in EPC adhesion, spreading, and haptotactic migration of EPCs in Boyden chamber assays. In addition, the combination of the OPN coating and enhanced eNOS expression in EPCs maximally enhanced cell adhesion (39.6 ± 1.7 and 49.4 ± 2.4 cells/field for 0 and 1 nM OPN) and spreading (84.7 ± 3.5% and 92.1 ± 3.9% for 0 nM and 1 nM OPN). These data highlight the direct effects of OPN on peripheral blood derived EPCs, suggesting that OPN works by mediating progenitor cell adhesion during vascular injury. The combination of autologous EPCs and OPN coatings could be a promising method of developing functional endothelialized surfaces.

Intracellular trafficking of integrins in cancer cells

Integrins are heterodimeric cell surface receptors, which principally mediate the interaction between cells and their extracellular microenvironments. Because of their pivotal roles in cancer proliferation, survival, invasion and metastasis, integrins have been recognized as promising targets for cancer treatment. As is the case with other receptors, the localization of integrins on the cell surface has provided opportunities to block their functions by various inhibitory monoclonal antibodies. A number of small molecule agents blocking integrin-ligand binding have also been established, and some such agents are currently on the market or in clinical trials for some diseases including cancer. This review exclusively focuses on another strategy for cancer therapy, which comes from the obligate localization of integrins on the cell surface; targeting the intracellular trafficking of integrins. A number of studies have shown the essential roles of integrin trafficking in hallmarks of cancer, such as activation of oncogenic signaling pathways as well as acquisition of invasiveness. Recent findings have shown that increased integrin recycling activity is associated with some types of gain-of-function mutations of p53, a common feature of diverse types of cancers, which also indicates that targeting integrin recycling could be widely applicable and effective against many cancers. We also discuss possible therapeutic contexts where integrin trafficking can be effectively targeted, and what molecular interfaces may hopefully be druggable.

Syntaxin 16 regulates lumen formation during epithelial morphogenesis

The formation and maintenance of cell-cell junctions, both under physiological and pathological conditions, requires the targeting and trafficking of junctional proteins. Proteins of the syntaxin (Stx)-family localize to a variety of subcellular membranes and contribute to intracellular transport of cargo by regulating vesicle fusion events at these sites. Unlike plasma membrane localized Stxs, the roles of endosome- and Golgi-localized stx proteins in epithelial morphogenesis are less understood. Here we show that Stx16- an endosome- and Golgi-localized target-membrane soluble N-ethylmaleimide attachment protein receptor (t-SNARE) that plays a role in membrane trafficking between these compartments - is essential for lumen development. In cultured Madin Darby Canine Kidney (MDCK) cells, Stx16 was selectively upregulated as sparsely plated cells attained confluency. Stx16-depleted confluent monolayers consistently showed lower transepithelial resistance than control monolayers, and failed to maintain endogenous and ectopically expressed E-cadherin at the adherens junctions due to decreased recycling. We further found that whereas cysts formed by MDCK cells cultured in Matrigel have a single hollow lumen, those formed by stx16-depleted counterparts had multiple lumens, due to abnormal orientiation of the mitotic spindle. Finally, a similar role for stx16 function in vivo is indicated by our analysis of pronephric-duct development in zebrafish expressing the claudinB:lynGFP transgene; lack of stx16 function in this structure (in stx16-morphant embryos) led to the development of enlarged, torturous pronephric ducts with more than one lumen. Taken together, our in vitro and in vivo studies establish a role for Stx16 in maintaining the integrity of cell-cell junctions, and thereby in morphogenesis of the kidney epithelial lumen.

Late endosomal and lysosomal trafficking during integrin-mediated cell migration and invasion: cell matrix receptors are trafficked through the late endosomal pathway in a way that dictates how cells migrate

Recently it has become clear that trafficking of integrins to late endosomes is key to the regulation of integrin expression and function during cell migration. Here we discuss the molecular machinery that dictates whether integrins are sorted to recycling endosomes or are targeted to late endosomes and lysosomes. Integrins and other receptors that are sorted to late endosomes are not necessarily degraded and, under certain circumstances, can be spared destruction and returned to the cell surface to drive cell migration and invasion. We will discuss how the exchange of adhesion receptors and other key regulators of cell migration between late endosomes/lysosomes and the plasma membrane can promote dynamic turnover of adhesions during cell migration.

HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix interactions and intercellular adhesions

Restitution is a critical form of intestinal epithelial cell (IEC) healing. We have previously shown that heparin-binding epidermal-like growth factor (HB-EGF) is necessary for IEC restitution; however, the mechanisms by which HB-EGF promotes restitution remain poorly understood. This study was designed to investigate whether HB-EGF promotes intestinal restitution by affecting integrin-extracellular matrix (ECM) interactions and intercellular adhesions. The effect of HB-EGF administration was examined in a murine necrotizing enterocolitis (NEC) model in vivo and an IEC line scrape-wound healing model in vitro. We evaluated the effect of HB-EGF on the expression of integrins, E-cadherin/β-catenin, and integrin α5β1-dependent cell-ECM interactions. We found that HB-EGF promoted intestinal restitution and the expression of integrin α5β1. HB-EGF promoted integrin α5β1-dependent cell adhesion and spreading. In addition, HB-EGF decreased the expression E-cadherin/β-catenin, via the activation of v-erb-b2 erythroblastic leukemia viral oncogene homolog (ErbB-1). We conclude that HB-EGF promotes intestinal restitution by affecting integrin-ECM interactions and intercellular adhesions.

Notch signaling from the endosome requires a conserved dileucine motif

Notch signaling is reliant on γ-secretase–mediated processing, although the subcellular location where it cleaves Notch to initiate signaling remains unresolved. Findings here support a model in which Notch signaling in mammalian systems is initiated from either the plasma membrane or lysosome, but not the early endosome.

Notch signaling is reliant on γ-secretase–mediated processing, although the subcellular location where γ-secretase cleaves Notch to initiate signaling remains unresolved. Accumulating evidence demonstrates that Notch signaling is modulated by endocytosis and endosomal transport. In this study, we investigated the relationship between Notch transport itinerary and signaling capacity. In doing so, we discovered a highly conserved dileucine sorting signal encoded within the cytoplasmic tail that directs Notch to the limiting membrane of the lysosome for signaling. Mutating the dileucine motif led to receptor accumulation in cation-dependent mannose-phosphate receptor–positive tubular early endosomes and a reduction in Notch signaling capacity. Moreover, truncated receptor forms that mimic activated Notch were readily cleaved by γ-secretase within the endosome; however, the cleavage product was proteasome-sensitive and failed to contribute to robust signaling. Collectively these results indicate that Notch signaling from the lysosome limiting membrane is conserved and that receptor targeting to this compartment is an active process. Moreover, the data support a model in which Notch signaling in mammalian systems is initiated from either the plasma membrane or lysosome, but not the early endosome.

Regulation of intracellular membrane trafficking and cell dynamics by syntaxin-6

Intracellular membrane trafficking along endocytic and secretory transport pathways plays a critical role in diverse cellular functions including both developmental and pathological processes. Briefly, proteins and lipids destined for transport to distinct locations are collectively assembled into vesicles and delivered to their target site by vesicular fusion. SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins are required for these events, during which v-SNAREs (vesicle SNAREs) interact with t-SNAREs (target SNAREs) to allow transfer of cargo from donor vesicle to target membrane. Recently, the t-SNARE family member, syntaxin-6, has been shown to play an important role in the transport of proteins that are key to diverse cellular dynamic processes. In this paper, we briefly discuss the specific role of SNAREs in various mammalian cell types and comprehensively review the various roles of the Golgi- and endosome-localized t-SNARE, syntaxin-6, in membrane trafficking during physiological as well as pathological conditions.

Angiogenesis impairment in diabetes: role of methylglyoxal-induced receptor for advanced glycation endproducts, autophagy and vascular endothelial growth factor receptor 2

Diabetes impairs physiological angiogenesis by molecular mechanisms that are not fully understood. Methylglyoxal (MGO), a metabolite of glycolysis, is increased in patients with diabetes. This study defined the role of MGO in angiogenesis impairment and tested the mechanism in diabetic animals. Endothelial cells and mouse aortas were subjected to Western blot analysis of vascular endothelial growth factor receptor 2 (VEGFR2) protein levels and angiogenesis evaluation by endothelial cell tube formation/migration and aortic ring assays. Incubation with MGO reduced VEGFR2 protein, but not mRNA, levels in a time and dose dependent manner. Genetic knockdown of the receptor for advanced glycation endproducts (RAGE) attenuated the reduction of VEGFR2. Overexpression of Glyoxalase 1, the enzyme that detoxifies MGO, reduced the MGO-protein adducts and prevented VEGFR2 reduction. The VEGFR2 reduction was associated with impaired angiogenesis. Suppression of autophagy either by inhibitors or siRNA, but not of the proteasome and caspase, normalized both the VEGFR2 protein levels and angiogenesis. Conversely, induction of autophagy either by rapamycin or overexpression of LC3 and Beclin-1 reduced VEGFR2 and angiogenesis. MGO increased endothelial LC3B and Beclin-1, markers of autophagy, which were accompanied by an increase of both autophagic flux (LC3 punctae) and co-immunoprecipitation of VEGFR2 with LC3. Pharmacological or genetic suppression of peroxynitrite (ONOO(-)) generation not only blocked the autophagy but also reversed the reduction of VEGFR2 and angiogenesis. Like MGO-treated aortas from normglycemic C57BL/6J mice, aortas from diabetic db/db and Akita mice presented reductions of angiogenesis or VEGFR2. Administration of either autophagy inhibitor ex vivo or superoxide scavenger in vivo abolished the reductions. Taken together, MGO reduces endothelial angiogenesis through RAGE-mediated, ONOO(-)dependent and autophagy-induced VEGFR2 degradation, which may represent a new mechanism for diabetic angiogenesis impairment.

Secretion of soluble vascular endothelial growth factor receptor 1 (sVEGFR1/sFlt1) requires Arf1, Arf6, and Rab11 GTPases

The soluble form of vascular endothelial growth factor receptor 1 (sVEGFR-1/sFlt1) is generated by alternative splicing of the FLT1 gene. Secretion of sFlt1 from endothelial cells plays an important role in blood vessel sprouting and morphogenesis. However, excess sFlt1 secretion is associated with diseases such as preeclampsia and chronic kidney disease. To date, the secretory transport process involved in the secretion of sFlt1 is poorly understood. In the present study, we investigated the itinerary of sFlt1 trafficking along the secretory pathway. To understand the timecourse of sFlt1 secretion, endothelial cells stably expressing sFlt1 were metabolically radiolabeled with [(35)S]-methionine and cysteine. Our results indicate that after initial synthesis the levels of secreted [(35)S]-sFlt1 in the extracellular medium peaks at 8 hours. Treatment with brefeldin A (BFA), a drug which blocks trafficking between the endoplasmic reticulum (ER) and the Golgi complex, inhibited extracellular release of sFlt1 suggesting that ER to Golgi and intra-Golgi trafficking of sFlt1 are essential for its secretion. Furthermore, we show that ectopic expression of dominant-negative mutant forms of Arf1, Arf6, and Rab11 as well as siRNA-mediated knockdown of these GTPases block secretion of sFlt1 during normoxic and hypoxic conditions suggesting role for these small GTPases. This work is the first to report role of regulatory proteins involved in sFlt1 trafficking along the secretory pathway and may provide insights and new molecular targets for the modulation of sFlt-1 release during physiological and pathological conditions.

Regulation of integrin endocytic recycling and chemotactic cell migration by syntaxin 6 and VAMP3 interaction

Integrins are the primary receptors of cells adhering to the extracellular matrix, and play key roles in various cellular processes including migration, proliferation and survival. The expression and distribution of integrins at the cell surface is controlled by endocytosis and recycling. The present study examines the function of syntaxin 6 (STX6), a t-SNARE located in the trans-Golgi network, in integrin trafficking. STX6 is overexpressed in many types of human cancer. We show that depletion of STX6 inhibits chemotactic cell migration and the delivery of the laminin receptor α3β1 integrin to the cell surface, whereas STX6 overexpression stimulates chemotactic cell migration, integrin delivery, and integrin-initiated activation of focal adhesion kinase. These data indicate that STX6 plays a rate-limiting role in cell migration and integrin trafficking. In STX6-depleted cells, α3β1 integrin is accumulated in recycling endosomes that contain the v-SNARE VAMP3. Importantly, we show that STX6 and VAMP3 form a v-/t-SNARE complex, VAMP3 is required in α3β1 integrin delivery to the cell surface, and endocytosed α3β1 integrin traffics to both VAMP3 and STX6 compartments. Collectively, our data suggest a new integrin trafficking pathway in which endocytosed integrins are transported from VAMP3-containing recycling endosomes to STX6-containing trans-Golgi network before being recycled to the plasma membrane.