Normal human keratinocytes bind to the alpha3LG4/5 domain of unprocessed laminin-5 through the receptor syndecan-1

Subpopulation commensalism promotes Rac1-dependent invasion of single cells via laminin-332

Phenotypic heterogeneity poses a significant hurdle for cancer treatment but is under-characterized in the context of tumor invasion. Amidst the range of phenotypic heterogeneity across solid tumor types, collectively invading cells and single cells have been extensively characterized as independent modes of invasion, but their intercellular interactions have rarely been explored. Here, we isolated collectively invading cells and single cells from the heterogeneous 4T1 cell line and observed extensive transcriptional and epigenetic diversity across these subpopulations. By integrating these datasets, we identified laminin-332 as a protein complex exclusively secreted by collectively invading cells. Live-cell imaging revealed that laminin-332 derived from collectively invading cells increased the velocity and directionality of single cells. Despite collectively invading and single cells having similar expression of the integrin α6β4 dimer, single cells demonstrated higher Rac1 activation upon laminin-332 binding to integrin α6β4. This mechanism suggests a novel commensal relationship between collectively invading and single cells, wherein collectively invading cells promote the invasive potential of single cells through a laminin-332/Rac1 axis.

The basement membrane in epidermal polarity, stemness, and regeneration

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function.

Gene expression profiling of laminin α3-blocked keratinocytes reveals an immune-independent mechanism of blistering

Laminin-332 pemphigoid is a rare and chronic autoimmune blistering disease which results in subepidermal blisters and erosive lesions predominantly localized to mucous membranes. As histologic inflammation is variable and non-complement-fixing IgG antibodies against laminin-332 are the predominant class of autoantibodies deposited at the epidermal basement membrane zone, we hypothesized that complement-independent pro-inflammatory and blistering pathways existed similarly to that previously shown in bullous pemphigoid. As autoantibodies to laminin α3 are most prevalent, we studied the major cellular response to blockade of laminin α3 using a well-characterized monoclonal antibody (P3H9-2). RNA-seq revealed upregulation of numerous desmosomal genes (DSG1, DSG3, DSC1, DSC3 and DSP) as well as KRT1 and KRT10. Additionally, P3H9-2-treated cells demonstrated downregulation of most hemidesmosomal genes. A pro-inflammatory response was not appreciated. Using pharmacological inhibitors, we identified both protein kinase C and NOTCH as key regulators of P3H9-2 induced differentiation. We lastly utilized 3D human skin equivalents to determine whether blockade of laminin α3 would lead to delayed blistering, consistent with keratinocyte differentiation. Significant blistering was noted after 72 h of treatment, with only minimal separation at 24 h. In summary, blockade of laminin α3 alters keratinocyte differentiation, representing a potential complement-independent mechanism of blistering.

Coreceptor Functions of Cell Surface Heparan Sulfate Proteoglycans

Receptor-ligand interactions play an important role in many biological processes by triggering specific cellular responses. These interactions are frequently regulated by coreceptors that facilitate, alter, or inhibit signaling. Coreceptors work in parallel with other specific and accessory molecules to coordinate receptor-ligand interactions. Cell surface heparan sulfate proteoglycans (HSPGs) function as unique coreceptors because they can bind to many ligands and receptors through their HS and core protein motifs. Cell surface HSPGs are typically expressed in abundance of the signaling receptors and, thus, are capable of mediating the initial binding of ligands to the cell surface. HSPG coreceptors do not possess kinase domains or intrinsic enzyme activities and, for the most part, binding to cell surface HSPGs does not directly stimulate intracellular signaling. Because of these features, cell surface HSPGs primarily function as coreceptors for many receptor-ligand interactions. Given that cell surface HSPGs are widely conserved, they likely serve fundamental functions to preserve basic physiological processes. Indeed, cell surface HSPGs can support specific cellular interactions with growth factors, morphogens, chemokines, extracellular matrix (ECM) components, and microbial pathogens and their secreted virulence factors. Through these interactions, HSPG coreceptors regulate cell adhesion, proliferation, migration and differentiation, and impact the onset, progression, and outcome of pathophysiological processes, such as development, tissue repair, inflammation, infection, and tumorigenesis. This review seeks to provide an overview of the various mechanisms of how cell surface HSPGs function as coreceptors.

Heparan sulfate proteoglycans serve as alternative receptors for low affinity LCMV variants

Members of the Old World Arenaviruses primarily utilize α-dystroglycan (α-DAG1) as a cellular receptor for infection. Mutations within the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV) reduce or abrogate the binding affinity to α-DAG1 and thus influence viral persistence, kinetics, and cell tropism. The observation that α-DAG1 deficient cells are still highly susceptible to low affinity variants, suggests the use of an alternative receptor(s). In this study, we used a genome-wide CRISPR Cas9 knockout screen in DAG1 deficient 293T cells to identify host factors involved in α-DAG1-independent LCMV infection. By challenging cells with vesicular stomatitis virus (VSV), pseudotyped with the GP of LCMV WE HPI (VSV-GP), we identified the heparan sulfate (HS) biosynthesis pathway as an important host factor for low affinity LCMV infection. These results were confirmed by a genetic approach targeting EXTL3, a key factor in the HS biosynthesis pathway, as well as by enzymatic and chemical methods. Interestingly, a single point mutation within GP1 (S153F or Y155H) of WE HPI is sufficient for the switch from DAG1 to HS binding. Furthermore, we established a simple and reliable virus-binding assay, using directly labelled VSV-GP by intramolecular fusion of VSV-P and mWasabi, demonstrating the importance of HS for virus attachment but not entry in Burkitt lymphoma cells after reconstitution of HS expression. Collectively, our study highlights the essential role of HS for low affinity LCMV infection in contrast to their high affinity counterparts. Residual LCMV infection in double knockouts indicate the use of (a) still unknown entry receptor(s).

Therapeutic potential of targeting membrane-spanning proteoglycan SDC4 in hepatocellular carcinoma

Syndecan-4 (SDC4) functions as a major endogenous membrane-associated receptor and widely regulates cytoskeleton, cell adhesion, and cell migration in human tumorigenesis and development, which represents a charming anti-cancer therapeutic target. Here, SDC4 was identified as a direct cellular target of small-molecule bufalin with anti-hepatocellular carcinoma (HCC) activity. Mechanism studies revealed that bufalin directly bond to SDC4 and selectively increased SDC4 interaction with substrate protein DEAD-box helicase 23 (DDX23) to induce HCC genomic instability. Meanwhile, pharmacological promotion of SDC4/DDX23 complex formation also inactivated matrix metalloproteinases (MMPs) and augmented p38/JNK MAPKs phosphorylation, which are highly associated with HCC proliferation and migration. Notably, specific knockdown of SDC4 or DDX23 markedly abolished bufalin-dependent inhibition of HCC proliferation and migration, indicating SDC4/DDX23 signaling axis is highly involved in the HCC process. Our results indicate that membrane-spanning proteoglycan SDC4 is a promising druggable target for HCC, and pharmacological regulation of SDC4/DDX23 signaling axis with small-molecule holds great potential to benefit HCC patients.

Circulating Heparan Sulfate Proteoglycans as Biomarkers in Health and Disease

Cell-surface heparan sulfate proteoglycans (HSPGs) play key roles in regulating cell behavior, cell signaling, and cell matrix interactions in both physiological and pathological conditions. Their soluble forms from glycocalyx shedding are not merely waste products, but, rather, bioactive molecules, detectable in serum, which may be useful as diagnostic and prognostic markers. In addition, as in the case of glypican-3 in hepatocellular carcinoma, they may be specifically expressed by pathological tissue, representing promising targets for immunotherapy. The primary goal of this comprehensive review is to critically survey the main findings of the clinical data from the last 20 years and provide readers with an overall picture of the diagnostic and prognostic value of circulating HSPGs. Moreover, issues related to the involvement of HSPGs in various pathologies, including cardiovascular disease, thrombosis, diabetes and obesity, kidney disease, cancer, trauma, sepsis, but also multiple sclerosis, preeclampsia, pathologies requiring surgery, pulmonary disease, and others will be discussed.

Syndecan receptors: pericellular regulators in development and inflammatory disease

The syndecans are the major family of transmembrane proteoglycans, usually bearing multiple heparan sulfate chains. They are present on virtually all nucleated cells of vertebrates and are also present in invertebrates, indicative of a long evolutionary history. Genetic models in both vertebrates and invertebrates have shown that syndecans link to the actin cytoskeleton and can fine-tune cell adhesion, migration, junction formation, polarity and differentiation. Although often associated as co-receptors with other classes of receptors (e.g. integrins, growth factor and morphogen receptors), syndecans can nonetheless signal to the cytoplasm in discrete ways. Syndecan expression levels are upregulated in development, tissue repair and an array of human diseases, which has led to the increased appreciation that they may be important in pathogenesis not only as diagnostic or prognostic agents, but also as potential targets. Here, their functions in development and inflammatory diseases are summarized, including their potential roles as conduits for viral pathogen entry into cells.

A novel mechanism in wound healing: Laminin 332 drives MMP9/14 activity by recruiting syndecan-1 and CD44

Re-epithelialization describes the resurfacing of a skin wound with new epithelium. In response to various stimuli including that of growth factors, cytokines and extracellular matrix (ECM), wound edge epidermal keratinocytes undergo cytoskeleton rearrangements compatible with their motile behavior and develop protrusive adhesion contacts. Matrix metalloproteinases (MMP) expression is crucial for proper cell movement and ECM remodeling; however, their deposition mechanism is unknown in keratinocytes. Here, we show that similar to cytokine IL-1ß, the precursor laminin 332 pro-migratory fragment G45 induces expression of the MMP-9 pro-enzyme, which together with MMP-14, further exerts its proteolytic activity within epithelial podosomes. This event strictly depends on the expression of the proteoglycan receptor syndecan-1 that was found in a ring surrounding the podosome core, co-localised with CD44. Our findings uncover that by directly recruiting both syndecan-1 and CD44, the laminin-332 G45 domain plays a major role in regulating mechanisms underlying keratinocyte / ECM remodeling during wound repair.

Interplay between Cell-Surface Receptors and Extracellular Matrix in Skin

Skin consists of the epidermis and dermis, which are connected by a specialized basement membrane-the epidermal basement membrane. Both the epidermal basement membrane and the underlying interstitial extracellular matrix (ECM) created by dermal fibroblasts contain distinct network-forming macromolecules. These matrices play various roles in order to maintain skin homeostasis and integrity. Within this complex interplay of cells and matrices, cell surface receptors play essential roles not only for inside-out and outside-in signaling, but also for establishing mechanical and biochemical properties of skin. Already minor modulations of this multifactorial cross-talk can lead to severe and systemic diseases. In this review, major epidermal and dermal cell surface receptors will be addressed with respect to their interactions with matrix components as well as their roles in fibrotic, inflammatory or tumorigenic skin diseases.

Laminin 332 in cancer: When the extracellular matrix turns signals from cell anchorage to cell movement

Laminin 332 is crucial in the biology of epithelia. This large extracellular matrix protein consists of the heterotrimeric assembly of three subunits - α3, β3, and γ2 - and its multifunctionality relies on a number of extracellular proteolytic processing events. Laminin 332 is central to normal epithelium homeostasis by sustaining cell adhesion, polarity, proliferation, and differentiation. It also supports a major function in epithelial tissue formation, repair, and regeneration by buttressing cell migration and survival and basement membrane assembly. Interest in this protein increased after the discovery that its expression is perturbed in tumor cells, cancer-associated fibroblasts, and the tumor microenvironment. This review summarizes current knowledge regarding the established involvement of the laminin 332 γ2 chain in tumor invasiveness and discusses the role of its α3 and β3 subunits.

Mechanism of anchorage-independency and tumor formation of cancer cells: possible involvement of cell membrane-bound laminin-332

Cancer cells are characterized by anchorage-independency and tumor formation. Involvement of laminin-332 in the pathogenesis of cancer has also been reported. I present a theory that can explain these characteristics together. Proliferating keratinocytes in wound healing produce and deposit laminin-332, which is shown in the provisional basement membrane of a wound. In association with wound closure, expression of LG4/5 domain on the α3 chain of laminin-332 disappears, implicating cleavage of LG4/5 domain. LG4/5 domain expression indicates that laminin-332 prior to the cleavage is bound to the cell membrane, because LG4/5 domain is a cell binding site. In this binding, heparan sulfate proteoglycan on the cell surface seems to be the acceptor for LG4/5 domain. I named this laminin "cell membrane-bound laminin-332" (ML332). ML332 would then bind to integrin α3β1 via LG1-3 domain, the integrin binding site, and activate FAK and the following Ras/MAPK pathway. Therefore, ML332 eliminates the need for proliferating keratinocytes to bind to processed laminin-332 secreted and deposited into the basement membrane for their proliferation (anchorage-independency). This may hold true of every proliferating epithelial cell, either benign or malignant. Whereas wound closure deprives keratinocytes of anchorage-independency, such events do not occur in cancer cells, and cancer cells maintain anchorage-independency. In the basement membrane formation by epithelial cells, short arms of laminin-332 anchored to the cell membrane bind each other and generate a meshwork polymer. This is the three-arm interaction model. In a similar manner, short-arm interactions between adjacent cancer cells may occur and induce tumor formation.

Developing defined substrates for stem cell culture and differentiation

Over the past few decades, a variety of different reagents for stem cell maintenance and differentiation have been commercialized. These reagents share a common goal in facilitating the manufacture of products suitable for cell therapy while reducing the amount of non-defined components. Lessons from developmental biology have identified signalling molecules that can guide the differentiation process in vitro, but less attention has been paid to the extracellular matrix used. With the introduction of more biologically relevant and defined matrices, that better mimic specific cell niches, researchers now have powerful resources to fine-tune their in vitro differentiation systems, which may allow the manufacture of therapeutically relevant cell types. In this review article, we revisit the basics of the extracellular matrix, and explore the important role of the cell-matrix interaction. We focus on laminin proteins because they help to maintain pluripotency and drive cell fate specification.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

The Interaction between Laminin-332 and α3β1 Integrin Determines Differentiation and Maintenance of CAFs, and Supports Invasion of Pancreatic Duct Adenocarcinoma Cells

Ranking among the most lethal tumour entities, pancreatic duct adenocarcinoma cells invade neighbouring tissue resulting in high incidence of metastasis. They are supported by tumour stroma fibroblasts which have undergone differentiation into cancer-associated fibroblasts (CAFs). Stiffness of cell substratum, cytokines, such as transforming growth factor-β (TGF-β), and stromal matrix proteins, such as laminin-332, are factors which promote CAF differentiation. In a spheroid culture system, differentiation of CAFs was analysed for laminin-332 production, laminin-binding integrin repertoire, adhesion and migration behaviour, and, in heterospheroids, for their interplay with the pancreatic duct adenocarcinoma AsPC-I cells. Our data reveal that CAFs produce laminin-332 thus contributing to its ectopic deposition within the tumour stroma. Moreover, CAF differentiation correlates with an increased expression of α3β1 integrin, the principal laminin-332-receptor. Beyond its role as novel CAF marker protein, integrin α3β1 crucially determines differentiation and maintenance of the CAF phenotype, as knock-out of the integrin α3 subunit reversed the CAF differentiated state. AsPC-I cells co-cultured in heterospheroids with integrin α3-deficient CAFs invaded less than from heterospheroids with wild-type CAFs. This study highlights the role of integrin α3β1 integrin-laminin-332 interaction of CAFs which promotes and sustains differentiation of CAFs and promotes carcinoma invasion.

Differential Distribution of Laminin N-Terminus α31 Across the Ocular Surface: Implications for Corneal Wound Repair

Purpose

Laminin N-terminus (LaNt) α31 is a relatively unstudied protein derived from the laminin α3 gene but structurally similar to netrins. LaNt α31 has, to date, been investigated only in two-dimensional (2D) keratinocyte culture where it influences cell migration and adhesion, processes integral to wound repair. Here we investigated LaNt α31 distribution in ocular surface epithelium, during limbal stem cell activation, and corneal wound healing.

Methods

Human, mouse, and pig eyes, ex vivo limbal explant cultures, and alkali burn wounds were processed for immunohistochemistry with antibodies against LaNt α31 along with progenitor cell-associated proteins. LaNt α31 expression was induced via adenoviral transduction into primary epithelial cells isolated from limbal explants, and cell spreading and migration were analyzed using live imaging.

Results

LaNt α31 localized to the basal layer of the conjunctival, limbal, and corneal epithelial cells. However, staining was nonuniform with apparent subpopulation enrichment, and some suprabasal reactivity was also noted. This LaNt α31 distribution largely matched that of keratin 15, epidermal growth factor receptor, and transformation-related protein 63α (p63α), and displayed similar increases in expression in activated limbal explants. During active alkali burn wound repair, LaNt α31 displayed increased expression in limbal regions and loss of basal restriction within the cornea. Distribution returned to predominately basal cell restricted once the wounded epithelium matured. Cultured corneal epithelial cells expressing LaNt α31 displayed increased 2D area and reduced migration, suggesting a functional link between this protein and key wound repair activities.

Conclusions

These data place LaNt α31 in position to influence laminin-dependent processes including wound repair and stem cell activation.

Extracellular matrix contribution to skin wound re-epithelialization

The ability of skin to act as a barrier is primarily determined by cells that maintain the continuity and integrity of skin and restore it after injury. Cutaneous wound healing in adult mammals is a complex multi-step process that involves overlapping stages of blood clot formation, inflammation, re-epithelialization, granulation tissue formation, neovascularization, and remodeling. Under favorable conditions, epidermal regeneration begins within hours after injury and takes several days until the epithelial surface is intact due to reorganization of the basement membrane. Regeneration relies on numerous signaling cues and on multiple cellular processes that take place both within the epidermis and in other participating tissues. A variety of modulators are involved, including growth factors, cytokines, matrix metalloproteinases, cellular receptors, and extracellular matrix components. Here we focus on the involvement of the extracellular matrix proteins that impact epidermal regeneration during wound healing.

Dually modified transmembrane proteoglycans in development and disease

Aberrant cell signaling in response to secreted growth factors has been linked to the development of multiple diseases, including cancer. As such, understanding mechanisms that control growth factor availability and receptor-growth factor interaction is vital. Dually modified transmembrane proteoglycans (DMTPs), which are classified as cell surface macromolecules composed of a core protein decorated with covalently linked heparan sulfated (HS) and/or chondroitin sulfated (CS) glycosaminoglycan (GAG) chains, provide one type of regulatory mechanism. Specifically, DMTPs betaglycan and syndecan-1 (SDC1) play crucial roles in modulating key cell signaling pathways, such as Wnt, transforming growth factor-β and fibroblast growth factor signaling, to affect epithelial cell biology and cancer progression. This review outlines current and potential functions for betaglycan and SDC1, with an emphasis on comparing individual roles for HS and CS modified DMTPs. We highlight the mutual dependence of DMTPs' GAG chains and core proteins and provide comprehensive knowledge on how these DMTPs, through regulation of ligand availability and receptor internalization, control cell signaling pathways involved in development and disease.

Perlecan expression influences the keratin 15-positive cell population fate in the epidermis of aging skin

The epidermis is continuously renewed by stem cell proliferation and differentiation. Basal keratinocytes append the dermal‐epidermal junction, a cell surface‐associated, extracellular matrix that provides structural support and influences their behaviour. It consists of laminins, type IV collagen, nidogens, and perlecan, which are necessary for tissue organization and structural integrity. Perlecan is a heparan sulfate proteoglycan known to be involved in keratinocyte survival and differentiation. Aging affects the dermal epidermal junction resulting in decreased contact with keratinocytes, thus impacting epidermal renewal and homeostasis. We found that perlecan expression decreased during chronological skin aging. Our in vitro studies revealed reduced perlecan transcript levels in aged keratinocytes. The production of in vitro skin models revealed that aged keratinocytes formed a thin and poorly organized epidermis. Supplementing these models with purified perlecan reversed the phenomenon allowing restoration of a well‐differentiated multi‐layered epithelium. Perlecan down‐regulation in cultured keratinocytes caused depletion of the cell population that expressed keratin 15. This phenomenon depended on the perlecan heparan sulphate moieties, which suggested the involvement of a growth factor. Finally, we found defects in keratin 15 expression in the epidermis of aging skin. This study highlighted a new role for perlecan in maintaining the self‐renewal capacity of basal keratinocytes.

Fundamentals of protein and cell interactions in biomaterials

The extracellular matrix (ECM) is an active and complex microenvironment with outstanding biomechanical, biophysical, and biochemical characteristics, which can indirectly or directly controls cell adhesion, migration, proliferation, and differentiation, as well as partaking in regeneration and homeostasis of organs and tissues. The ECM has captivated a great deal of attention with the rapid progress of tissue engineering (TE) in the field of regenerative medicine (RM). Approaches to TE, RM and cancer therapy center on the necessity to deliver cell signals to direct cell proliferation and differentiation. These "external signals" are induced from cell-cell, and cell-ECM, interactions, as well as from physico-chemical, mechanical stimuli and growth factors. With the advent of new biomaterials such as casein, we gave a general insight into cell-ECM protein interactions in biomaterials and their applications in TE, RM and cancer therapy. An account of the main ECM molecules and cellular receptors with emphasis on integrins and its ligands was given, their effect on the induction of particular signal transduction pathways is also elucidated.

Molecular and clinical profiles of syndecan-1 in solid and hematological cancer for prognosis and precision medicine

Syndecan-1 (SDC1, CD138) is a key cell surface adhesion molecule essential for maintaining cell morphology and interaction with the surrounding microenvironment. Deregulation of SDC1 contributes to cancer progression by promoting cell proliferation, metastasis, invasion and angiogenesis, and is associated with relapse through chemoresistance. SDC1 expression level is also associated with responses to chemotherapy and with prognosis in multiple solid and hematological cancers, including multiple myeloma and Hodgkin lymphoma. At the tissue level, the expression levels of SDC1 and the released extracellular domain of SDC1 correlate with tumor malignancy, phenotype, and metastatic potential for both solid and hematological tumors in a tissue-specific manner. The SDC1 expression profile varies among cancer types, but the differential expression signatures between normal and cancer cells in epithelial and stromal compartments are directly associated with aggressiveness of tumors and patient's clinical outcome and survival. Therefore, relevant biomarkers of SDC signaling may be useful for selecting patients that would most likely respond to a particular therapy at the time of diagnosis or perhaps for predicting relapse. In addition, the reciprocal expression signature of SDC between tumor epithelial and stromal compartments may have synergistic value for patient selection and the prediction of clinical outcome.

Molecular Basis of Laminin-Integrin Interactions

Laminins are composed of three polypeptide chains, designated as α, β, and γ. The C-terminal region of laminin heterotrimers, containing coiled-coil regions, short tails, and laminin globular (LG) domains, is necessary and sufficient for binding to integrins, which are the major laminin receptor class. Laminin recognition by integrins critically requires the α chain LG domains and a glutamic acid residue of the γ chain at the third position from the C-terminus. Furthermore, the C-terminal region of the β chain contains a short amino acid sequence that modulates laminin affinity for integrins. Thus, all three of the laminin chains act cooperatively to facilitate integrin binding. Mammals possess 5 α (α1-5), 3 β (β1-3), and 3 γ (γ1-3) chains, combinations of which give rise to 16 distinct laminin isoforms. Each isoform is expressed in a tissue-specific and developmental stage-specific manner, exerting its functions through binding of integrins. In this review, we detail the current knowledge surrounding the molecular basis and physiological relevance of specific interactions between laminins and integrins, and describe the mechanisms underlying laminin action through integrins.

Interaction of human papillomavirus type 16 particles with heparan sulfate and syndecan-1 molecules in the keratinocyte extracellular matrix plays an active role in infection

Oncogenic human papillomaviruses (HPVs) attach predominantly to extracellular matrix (ECM) components during infection of cultured keratinocytes and in the rodent vaginal challenge model in vivo. However, the mechanism of virion transfer from the ECM to receptors that mediate entry into host cells has not been determined. In this work we strove to assess the role of heparan sulfate (HS) chains in HPV16 binding to the ECM and determine how HPV16 release from the ECM is regulated. We also assessed the extent to which capsids released from the ECM are infectious. We show that a large fraction of HPV16 particles binds to the ECM via HS chains, and that syndecan-1 (snd-1) molecules present in the ECM are involved in virus binding. Inhibiting the normal processing of snd-1 and HS molecules via matrix metalloproteinases and heparanase dramatically reduces virus release from the ECM, cellular uptake and infection. Conversely, exogenous heparinase activates each of these processes. We confirm that HPV16 released from the ECM is infectious in keratinocytes. Use of a specific inhibitor shows furin is not involved in HPV16 release from ECM attachment factors and corroborates other studies showing only the intracellular activity of furin is responsible for modulating HPV infectivity. These data suggest that our recently proposed model, describing the action of HS proteoglycan processing enzymes in releasing HPV16 from the cell surface in complex with the attachment factor snd-1, is also relevant to the release of HPV16 particles from the ECM to promote efficient infection of keratinocytes.

Cytoplasmic domain interactions of syndecan-1 and syndecan-4 with α6β4 integrin mediate human epidermal growth factor receptor (HER1 and HER2)-dependent motility and survival

Epithelial cells are highly dependent during wound healing and tumorigenesis on the α6β4 integrin and its association with receptor tyrosine kinases. Previous work showed that phosphorylation of the β4 subunit upon matrix engagement depends on the matrix receptor syndecan (Sdc)-1 engaging the cytoplasmic domain of the β4 integrin and coupling of the integrin to human epidermal growth factor receptor-2 (HER2). In this study, HER2-dependent migration activated by matrix engagement is compared with migration stimulated by EGF. We find that whereas HER2-dependent migration depends on Sdc1, EGF-dependent migration depends on a complex consisting of human epidermal growth factor receptor-1 (HER1, commonly known as EGFR), α6β4, and Sdc4. The two syndecans recognize distinct sites at the extreme C terminus of the β4 integrin cytoplasmic domain. The binding motif in Sdc1 is QEEXYX, composed in part by its syndecan-specific variable (V) region and in part by the second conserved (C2) region that it shares with other syndecans. A cell-penetrating peptide containing this sequence competes for HER2-dependent epithelial migration and carcinoma survival, although it is without effect on the EGFR-stimulated mechanism. β4 mutants bearing mutations specific for Sdc1 and Sdc4 recognition act as dominant negative mutants to block cell spreading or cell migration that depends on HER2 or EGFR, respectively. The interaction of the α6β4 integrin with the syndecans appears critical for it to be utilized as a signaling platform; migration depends on α3β1 integrin binding to laminin 332 (LN332; also known as laminin 5), whereas antibodies that block α6β4 binding are without effect. These findings indicate that specific syndecan family members are likely to have key roles in α6β4 integrin activation by receptor tyrosine kinases.

The NTR domain of procollagen C-proteinase enhancer-1 (PCPE-1) mediates PCPE-1 binding to syndecans-1, -2 and -4 as well as fibronectin

Procollagen C-proteinase enhancer 1 (PCPE-1) is an extracellular matrix glycoprotein that can stimulate procollagen processing by procollagen C-proteinases (PCPs) such as bone morphogenetic protein-1 (BMP-1). PCPE-1 consists of two CUB domains that bind to the procollagen C-propeptide and are responsible for enhancing activity and a netrin-like (NTR) domain that binds to BMP-1 as well as heparin and heparan sulfate. The NTR domain also mediates binding of PCPE-1 to cells, an interaction inhibited by heparin, thus suggesting involvement of cell membrane heparan-sulfate proteoglycans (HSPGs). Using pull-down experiments and an ELISA type binding assay we show here that PCPE-1 binds to three cell membrane HSPGs, syndecans-1, -2 and -4. We also demonstrate that this binding is mediated by the NTR domain and depends on the glycosaminoglycan chains of the syndecans. Using co-immunoprecipitation and an ELISA type binding assay we show that PCPE-1 can also bind fibronectin (an established binding partner of BMP-1), another interaction involving the NTR domain. Consistently, fibronectin inhibits cell attachment to PCPE-1 although it does not affect PCPE-1 enhancing activity. PCPE-1 is not an adhesive protein since cell attachment to PCPE-1 is not associated with cell spreading and/or actin filaments formation. The results suggest that PCPE-1 binding to syndecans and/or fibronectin may control collagen fibril assembly on the cell surface. Further characterization of these interactions may pave the way for future design of new means to modulate collagen deposition in pathological conditions such as fibrosis.

A Comprehensive Review of Dysregulated miRNAs Involved in Cervical Cancer

MicroRNAs(miRNAs) have become the center of interest in oncology. In recent years, various studies have demonstrated that miRNAs regulate gene expression by influencing important regulatory genes and thus are responsible for causing cervical cancer. Cervical cancer being the third most diagnosed cancer among the females worldwide, is the fourth leading cause of cancer related mortality. Prophylactic human papillomavirus (HPV) vaccines and new HPV screening tests, combined with traditional Pap test screening have greatly reduced cervical cancer. Yet, thousands of women continue to be diagnosed with and die of this preventable disease annually. This has necessitated the scientists to ponder over ways of evolving new methods and chalk out novel treatment protocols/strategies. As miRNA deregulation plays a key role in malignant transformation of cervical cancer along with its targets that can be exploited for both prognostic and therapeutic strategies, we have collected and reviewed the role of miRNA in cervical cancer. A systematic search was performed using PubMed for articles that report aberrant expression of miRNA in cervical cancer. The present review provides comprehensive information for 246 differentially expressed miRNAs gathered from 51 published articles that have been implicated in cervical cancer progression. Of these, more than 40 miRNAs have been reported in the literature in several instances signifying their role in the regulation of cancer. We also identified 40 experimentally validated targets, studied the cause of miRNAs dysregulation along with its mechanism and role in different stages of cervical cancer. We also identified and analysed miRNA clusters and their expression pattern in cervical cancer. This review is expected to further enhance our understanding in this field and serve as a valuable reference resource.

Integrin Regulation of Epidermal Functions in Wounds

Significance: Integrins are bidirectional signaling receptors for extracellular matrix that regulate both inside-out signaling that controls keratinocyte-mediated changes to the wound microenvironment and outside-in signaling that controls keratinocyte responses to microenvironmental changes. As such, integrins represent attractive therapeutic targets for treatment of chronic wounds or general promotion of wound healing. Advances in wound management are particularly important as the elderly and diabetic populations within the United States continue to grow. Recent Advances: Although integrins are best known for mediating cell adhesion and migration, integrins in wound epidermis also control cell survival, proliferation, matrix remodeling, and paracrine crosstalk to other cellular compartments of the wound. Importantly, the concept of targeting integrins in the clinic has been established for treatment of certain cancers and other diseases, laying the groundwork for similar exploitation of integrins as targets to treat chronic wounds. Critical Issues: Despite their attractiveness as therapeutic targets, integrins have complex roles in wound healing that are impacted by both their own expression and a highly dynamic wound microenvironment that determines ligand availability. Therefore, identifying relevant integrin ligands in the wound and understanding both distinct and overlapping functions that different integrins play in the epidermis will be critical to determine their precise roles in wound healing. Future Directions: Future research should focus on gaining a thorough understanding of the highly coordinated functions of different integrins in wound epidermis, and on determining which of these functions go awry in pathological wounds. This focus should facilitate development of integrin-targeting therapeutics for treating chronic wounds.

Processing of laminin α chains generates peptides involved in wound healing and host defense

Laminins play a fundamental role in basement membrane architecture and function in human skin. The C-terminal laminin G domain-like (LG) modules of laminin α chains are modified by proteolysis to generate LG1-3 and secreted LG4-5 tandem modules. In this study, we provide evidence that skin-derived cells process and secrete biologically active peptides from the LG4-5 module of the laminin α3, α4 and α5 chain in vitro and in vivo. We show enhanced expression and processing of the LG4-5 module of laminin α3 in keratinocytes after infection and in chronic wounds in which the level of expression and further processing of the LG4-5 module correlated with the speed of wound healing. Furthermore, bacterial or host-derived proteases promote processing of laminin α3 LG4-5. On a functional level, we show that LG4-5-derived peptides play a role in wound healing. Moreover, we demonstrate that LG4-derived peptides from the α3, α4 and α5 chains have broad antimicrobial activity and possess strong chemotactic activity to mononuclear cells. Thus, the data strongly suggest a novel multifunctional role for laminin LG4-5-derived peptides in human skin and its involvement in physiological processes and pathological conditions such as inflammation, chronic wounds and skin infection.

Tumor suppressive microRNA-218 inhibits cancer cell migration and invasion by targeting focal adhesion pathways in cervical squamous cell carcinoma

Cervical cancer is one of the most common cancers in women. More than 275,100 women die from cervical cancer each year. Cervical squamous cell carcinoma (cervical SCC), one of the most frequent types of cervical cancers, is associated with high-risk human papilloma virus (HPV), although HPV infection alone may not be enough to induce malignant transformation. MicroRNAs (miRNAs), a class of small non-coding RNAs, regulate protein-coding gene expression by repressing translation or cleaving RNA transcripts in a sequence-specific manner. A growing body of evidence suggests that miRNAs contribute to cervical SCC progression, development and metastasis. miRNA expression signatures in SCC (hypopharyngeal SCC and esophageal SCC) revealed that miR-218 expression was significantly reduced in cancer tissues compared with adjacent non-cancerous epithelium, suggesting that miR-218 is a candidate tumor suppressor. The aim of this study was to investigate the functional significance of miR-218 in cervical SCC and to identify novel miR‑218-mediated cancer pathways in cervical SCC. Restoration of miR-218 significantly inhibited cancer cell migration and invasion in both HPV-positive and HPV-negative cervical SCC cell lines. These data indicated that miR-218 acts as a tumor suppressor in cervical SCC. Our in silico analysis showed that miR-218 appeared to be an important modulator of tumor cell processes through suppression of many targets, particularly those involved in focal adhesion signaling pathways. Gene expression data indicated that LAMB3, a laminin protein known to influence cell differentiation, migration, adhesion, proliferation and survival, was upregulated in cervical SCC clinical specimens, and silencing studies demonstrated that LAMB3 functioned as an oncogene in cervical SCC. The identification of novel tumor-suppressive miR-218-mediated molecular pathways has provided new insights into cervical SCC oncogenesis and metastasis.

Laminin 332 processing impacts cellular behavior

Laminin 332, composed of the α3, β3 and γ2 chains, is an epithelial-basement membrane specific laminin variant. Its main role in normal tissues is the maintenance of epithelial-mesenchymal cohesion in tissues exposed to external forces, including skin and stratified squamous mucosa. After being secreted and deposited in the extracellular matrix, laminin 332 undergoes physiological maturation processes consisting in the proteolytic processing of domains located within the α3 and the γ2 chains. These maturation events are essential for laminin 332 integration into the basement membrane where it plays an important function in the nucleation and maintenance of anchoring structures. Studies in normal and pathological situations have revealed that laminin 332 can trigger distinct cellular events depending on the level of its proteolytic cleavages. In this review, the biological and structural characteristics of laminin 332 domains are presented and we discuss whether they trigger specific functions.

Tumor suppressive microRNA-218 inhibits cancer cell migration and invasion through targeting laminin-332 in head and neck squamous cell carcinoma

Recent our microRNA (miRNA) expression signature revealed that expression of microRNA-218 (miR-218) was reduced in cancer tissues, suggesting a candidate of tumor suppressor in head and neck squamous cell carcinoma (HNSCC). The aim of this study was to investigate the functional significance of miR-218 and its mediated moleculer pathways in HNSCC. Restoration of miR-218 in cancer cells led to significant inhibition of cell migration and invasion activities in HNSCC cell lines (FaDu and SAS). Genome-wide gene expression analysis of miR-218 transfectants and in silico database analysis showed that focal adhesion pathway was a promising candidate of miR-218 target pathways. The laminins are an important and biologically active part of the basal lamina, the function of that are various such as influencing cell differentiation, migration and adhesion as well as proliferation and cell survival. Interestingly, all components of laminin-332 (LAMA3, LAMB3 and LAMC2) are listed on the candidate genes in focal adhesion pathway. Furthermore, we focused on LAMB3 which has a miR-218 target site and gene expression studies and luciferase reporter assays showed that LAMB3 was directly regulated by miR-218. Silencing study of LAMB3 demonstrated significant inhibition of cell migration and invasion. In clinical specimens with HNSCC, the expression levels of laminin-332 were significantly upregulated in cancer tissues compared to adjacent non-cancerous tissues. Our analysis data showed that tumor suppressive miR-218 contributes to cancer cell migration and invasion through regulating focal adhesion pathway, especially laminin-332. Tumor suppressive miRNA-mediated novel cancer pathways provide new insights into the potential mechanisms of HNSCC oncogenesis.

The mutual impact of syndecan-1 and its glycosaminoglycan chains--a multivariable puzzle

Proteoglycans, with their core proteins and attached glycosaminoglycan chains, are recognized as important partners in many biological processes, yet often experimental analysis of their molecular action is considered for only part of these molecules: either the protein or the carbohydrate unit. In this article, we have tried to summarize, with an example of the syndecan family in general and more specifically with syndecan-1, what is known considering the mutual influence of these different components, and we follow whether the nature of the glycosaminoglycan chains matters for these effects.

Cell surface proteoglycans syndecan-1 and -4 bind overlapping but distinct sites in laminin α3 LG45 protein domain

Keratinocyte migration during epidermal repair depends on interactions between cellular heparan sulfate proteoglycan receptors, syndecan-1 and -4, and the C-terminal globular domains (LG45) of the extracellular matrix protein laminin 332. This study investigates the molecular basis of the binding specificity of the syndecan-1 and -4 receptors expressed by human keratinocytes. We used site-directed mutagenesis to alter a recombinant LG45 protein by substituting the most critical basic residues with glutamine. All proteins were expressed in mammalian cells, purified, and characterized biochemically. We used in vitro binding assays, including surface plasmon resonance, to examine interactions between mutated LG45 and heparan sulfates, syndecan-1 and -4. We identify a major heparin binding domain on the outer edge of a β-strand of LG45 surrounded by a track of converging low affinity residues. This domain harbors distinctive syndecan-1 and -4 binding-specific sequences. This is the first study to demonstrate a binding specificity of two proteoglycans produced by a single cell type. In addition, we found that although syndecan-1 interacts exclusively through its glycosaminoglycan chains, syndecan-4 binding relies on both its core protein and its heparan sulfate chains. These results suggest that LG45 may trigger different signals toward keratinocytes depending on its interaction with syndecan-1 or -4.

Epitope mapping of function-blocking monoclonal antibody CM6 suggests a "weak" integrin binding site on the laminin-332 LG2 domain

Laminin-332 (Ln-332) is an extracellular matrix molecule that regulates cell adhesion, spreading, and migration by interaction with cell surface receptors such as alpha3beta1 and alpha6beta4. Previously, we developed a function-blocking monoclonal antibody against rat Ln-332, CM6, which blocks hemidesmosome assembly induced by Ln-332-alpha6beta4 interactions. However, the location of its epitope on Ln-332 has remained unclear. In this study, we show that the CM6 epitope is located on the laminin G-like (LG)2 module of the Ln-332 alpha3 chain. To specify the residues involved in this epitope, we produced a series of GST-fused alpha3 LG2 mutant proteins in which rat-specific acids were replaced with human acids by a site-directed mutagenesis strategy. CM6 reactivity against these proteins showed that CM6 binds to the (1089)NERSVR(1094) sequence of rat Ln-332 LG2 module. In a structural model, this sequence maps to an LG2 loop sequence that is exposed to solvent according to predictions, consistent with its accessibility to antibody. CM6 inhibits integrin-dependent cell adhesion on Ln-332 and inhibits cell spreading on both Ln-332 and recombinant LG2 (rLG2; but not rLG3), suggesting the presence of an alpha3beta1 binding site on LG2. However, we were unable to show that rLG2 supports adhesion in standard assays, suggesting that LG2 may contain a "weak" integrin binding site, only detectable in spreading assays that do not require washes. These results, together with our previous findings, indicate that binding sites for alpha3beta1 and alpha6beta4 are closely spaced in the Ln-332 LG domains where they regulate alternative cell functions, namely adhesion/migration or hemidesmosome anchoring.

Interaction of syndecan and alpha6beta4 integrin cytoplasmic domains: regulation of ErbB2-mediated integrin activation

The alpha6beta4 integrin is a laminin 332 (LN332) receptor central to the formation of hemidesmosomes in epithelial layers. However, the integrin becomes phosphorylated by keratinocytes responding to epidermal growth factor in skin wounds or by squamous cell carcinomas that overexpress/hyperactivate the tyrosine kinase ErbB2, epidermal growth factor receptor, or c-Met. We show here that the beta4-dependent signaling in A431 human squamous carcinoma cells is dependent on the syndecan family of matrix receptors. Yeast two-hybrid analysis identifies an interaction within the distal third (amino acids 1473-1752) of the beta4 cytoplasmic domain and the conserved C2 region of the syndecan cytoplasmic domain. Via its C2 region, Sdc1 forms a complex with the alpha6beta4 integrin along with the receptor tyrosine kinase ErbB2 and the cytoplasmic kinase Fyn in A431 cells. Engagement of LN332 or clustering of the alpha6beta4 integrin with integrin-specific antibodies causes phosphorylation of ErbB2, Fyn, and the beta4 subunit as well as activation of phosphatidylinositol 3-kinase and Akt and their assimilation into this complex. This leads to phosphatidylinositol 3-kinase-dependent cell spreading and Akt-dependent protection from apoptosis. This is disrupted by RNA interference silencing of Sdc1 but can be rescued by mouse Sdc1 or Sdc4 but not by syndecan mutants lacking their C-terminal C2 region. This disruption does not prevent the phosphorylation of ErbB2 or Fyn but blocks the Fyn-mediated phosphorylation of the beta4 tail. We propose that syndecans engage the distal region of the beta4 cytoplasmic domain and bring it to the plasma membrane, where it can be acted upon by Src family kinases.

Dermatopontin promotes epidermal keratinocyte adhesion via alpha3beta1 integrin and a proteoglycan receptor

Dermatopontin, an extracellular matrix component initially purified from bovine dermis, promoted cell adhesion of the human epidermal keratinocyte cell line (HaCaT cells). HaCaT cells spread on dermatopontin and formed actin fibers. Adhesion of HaCaT cells to dermatopontin was inhibited by both EDTA and heparin and was mediated in part by alpha3beta1 integrin. A synthetic peptide (DP-4, PHGQVVVAVRS; bovine dermatopontin residues 33-43) specifically inhibited adhesion of cells to dermatopontin, and when the DP-4 peptide was coated on the well, it promoted cell adhesion in a dose-dependent manner. An active core sequence of the DP-4 peptide was localized to an eight-amino acid sequence (GQVVVAVR). These results indicate that dermatopontin is a novel epidermal cell adhesion molecule and suggest that the DP-4 sequence is critical for the cell adhesive activity of dermatopontin. Adhesion of cells to DP-4 was strongly inhibited by heparin. When HaCaT cells were treated with heparitinase I, the cells failed to adhere to DP-4 but chondroitinase ABC treatment did not influence the adhesion activity. DP-4 specifically interacted with biotinylated heparin, and this interaction was inhibited by unlabeled heparin. DP-4 peptide significantly promoted the adhesion of cells overexpressing syndecans, and syndecan bound to a DP-4 peptide affinity column. These results suggest that HaCaT cells adhere to dermatopontin through alpha3beta1 integrin and a heparan sulfate proteoglycan-type receptor, which is likely a syndecan. We conclude that dermatopontin plays a role as a multifunctional adhesion molecule for epidermal cells.

Bisecting GlcNAc residues on laminin-332 down-regulate galectin-3-dependent keratinocyte motility

Laminin-332 (Lm332; formerly laminin-5) is a basement membrane protein in the skin, which promotes cell motility in wound healing and cancer invasion. In a previous study, we reported that the introduction of bisecting GlcNAc into Lm332 (GnT-III-Lm332), catalyzed by N-acetylglucosaminyltransferase III (GnT-III), reduced cell migration (Kariya, Y., Kato, R., Itoh, S., Fukuda, T., Shibukawa, Y., Sanzen, N., Sekiguchi, K., Wada, Y., Kawasaki, N., and Gu, J. (2008) J. Biol. Chem. 283, 33036-33045). However, the underlying molecular mechanism by which GnT-III-Lm332 suppresses the normal biological functions of Lm332 remains to be elucidated. In this study, we show that galectin-3, which is a beta-galactoside-binding protein, strongly bound to unmodified Lm332 but not to GnT-III-Lm332 and that binding of galectin-3 was completely blocked by lactose. Exogenous galectin-3 significantly enhanced keratinocyte cell motility on control Lm332 but not on GnT-III-Lm332. A functional blocking antibody against galectin-3 inhibited Lm332-induced alpha3beta1 and alpha6beta4 integrin clustering and focal contact formation. Co-immunoprecipitation revealed that galectin-3 associated with both beta4 integrin and epidermal growth factor receptor, thereby cross-linking the two molecules. The associations were inhibited by either the presence of lactose or expression of GnT-III. Moreover, galectin-3 consistently enhanced ERK activation. Taken together, the results of this study are the first to clearly identify the molecular mechanism responsible for the inhibitory effects of GnT-III on extracellular matrix-integrin-meditated cell adhesion, migration, and signal transduction. The findings presented herein shed light on the importance of N-glycosylation-mediated supramolecular complex formation on the cell surface.

Biologically active sequences in the mouse laminin alpha3 chain G domain

The laminin alpha3 chain is mainly expressed at the skin, and its C-terminal G domain has a critical role in multiple biological functions. We screened for biologically active sites on the mouse laminin alpha3 chain G domain using 107 synthetic peptides on coated plates and conjugated to Sepharose beads with HT1080 human fibrosarcoma cells, HaCaT human skin keratinocyte cells, and human dermal fibroblasts (HDFs). Eleven peptides exhibited cell attachment activity with respect to the peptide-coated plates and/or peptide-Sepharose beads. MA3G28 (WTIQTTVDRGLL) strongly binds to HaCaT cells. Four peptides promoted PC12 cell neurite outgrowth. Heparin inhibited attachment of HDFs to eight peptides on the coated plates. In contrast, EDTA significantly inhibited attachment of HDFs to MA3G27 (NAPFPKLSWTIQ) and MA3G28 but had no effect on the attachment of the other peptides. HDF cells formed well-organized actin stress fibers and focal contacts with vinculin accumulation on MA3G27. Additionally, attachment of HDFs to MA3G27 was inhibited by anti-alpha6 and anti-beta1 integrin antibodies, suggesting that MA3G27 promotes alpha6beta1 integrin-mediated cell adhesion. MA3G57 (NQRLASFSNAQQS) exhibited cell attachment activity only in the peptide bead assay. MA3G57 conjugated to a chitosan membrane promoted HDF attachment and spreading with well-organized actin stress fibers. The anti-beta1 integrin antibody partially inhibited attachment of HDFs to the MA3G57-chitosan membrane, suggesting that the MA3G57 site is involved in beta1 integrin-mediated cell attachment. These active sites are likely important in the biological activities of the laminin alpha3 chain G domain and would be useful for the study of molecular mechanisms of laminin-receptor interactions.

A biologically active sequence of the laminin alpha2 large globular 1 domain promotes cell adhesion through syndecan-1 by inducing phosphorylation and membrane localization of protein kinase Cdelta

Laminin-2 promotes basement membrane assembly and peripheral myelinogenesis; however, a receptor-binding motif within laminin-2 and the downstream signaling pathways for motif-mediated cell adhesion have not been fully established. The human laminin-2 alpha2 chain cDNAs cloned from human keratinocytes and fibroblasts correspond to the laminin alpha2 chain variant sequence from the human brain. Individually expressed recombinant large globular (LG) 1 protein promotes cell adhesion and has heparin binding activities. Studies with synthetic peptides delineate the DLTIDDSYWYRI motif (Ln2-P3) within the LG1 as a major site for both heparin and cell binding. Cell adhesion to LG1 and Ln2-P3 is inhibited by treatment of heparitinase I and chondroitinase ABC. Syndecan-1 from PC12 cells binds to LG1 and Ln2-P3 and colocalizes with both molecules. Suppression of syndecan-1 with RNA interference inhibits cell adhesion to LG1 and Ln2-P3. The binding of syndecan-1 with LG1 and Ln2-P3 induces the recruitment of protein kinase Cdelta (PKCdelta) into the membrane and stimulates its tyrosine phosphorylation. A decrease in PKCdelta activity significantly reduces cell adhesion to LG1 and Ln2-P3. Taken together, these results indicate that the Ln2-P3 motif and LG1 domain, containing the motif, within the human laminin-2 alpha2 chain are major ligands for syndecan-1, which mediates cell adhesion through the PKCdelta signaling pathway.

MMP7 shedding of syndecan-1 facilitates re-epithelialization by affecting alpha(2)beta(1) integrin activation

Background

Lung injury promotes the expression of matrix metalloproteinase-7 (MMP7, matrilysin), which is required for neutrophil recruitment and re-epithelialization. MMP7 governs the lung inflammatory response through the shedding of syndecan-1. Because inflammation and repair are related events, we evaluated the role of syndecan-1 shedding in lung re-epithelialization.

Methodology/Principal Finding

Epithelial injury induced syndecan-1 shedding from wild-type epithelium but not from Mmp7^−/− mice in vitro and in vivo. Moreover, cell migration and wound closure was enhanced by MMP7 shedding of syndecan-1. Additionally, we found that syndecan-1 augmented cell adhesion to collagen by controlling the affinity state of the α₂β₁ integrin.

Conclusion/Significance

MMP7 shedding of syndecan-1 facilitates wound closure by causing the α₂β₁ integrin to assume a less active conformation thereby removing restrictions to migration. MMP7 acts in the lungs to regulate inflammation and repair, and our data now show that both these functions are controlled through the shedding of syndecan-1.

Clustering of syndecan-4 and integrin beta1 by laminin alpha 3 chain-derived peptide promotes keratinocyte migration

Syndecans function as receptors for extracellular matrix (ECM) with integrins in cell spreading. However, the molecular mechanism of their specific involvement in cell migration or in wound healing has not been elucidated yet. Here, we report that a synthetic peptide, PEP75, which contains the syndecan-binding sequence of the laminin alpha 3LG4 module, induces keratinocyte migration in in vitro and in vivo. Soluble PEP75 induced the clustering of syndecan-4 and conformation-modified integrin beta1 colocalized with syndecan-4 in soluble PEP75-induced clusters. Treatment of cells in solution with PEP75 resulted in the exposure of the P4G11 antibody epitope of integrin beta1 in immunostaining as well as in flow cytometry and augmented integrin beta1-dependent cell adhesion to ECM. Pulldown assays demonstrated that PEP75 bound to syndecan-4, but not to integrin beta1. A siRNA study revealed a role for syndecan-4 in PEP75-induced up-regulation of P4G11 antibody binding and migration of HaCaT cells. We conclude that binding of soluble PEP75 to syndecan-4 induces the coupling of integrin beta1, which is associated with integrin beta1-conformational changes and activation, and leads to keratinocyte migration. To activate integrin function through syndecans could be a novel therapeutic approach for chronic wound.

Tyrosine dephosphorylation of the syndecan-1 PDZ binding domain regulates syntenin-1 recruitment

Heparan sulfate proteoglycan receptor syndecan-1 interacts with the carboxyl-terminal LG4/5 domain in laminin 332 (alpha3LG4/5) and participates in cell adhesion and spreading. To dissect the function of syndecan-1 in these processes, we made use of a cell adhesion model in which syndecan-1 exclusively interacts with a recombinantly expressed alpha3LG4/5 fragment. Plating HT1080 cells on this fragment induces the formation of actin-containing protrusive structures in an integrin-independent manner. Here we show that syndecan-1-mediated formation of membrane protrusions requires dephosphorylation of tyrosine residues in syndecan-1. Accordingly, inhibition of phosphatases with orthovanadate decreases cell adhesion to the alpha3LG4/5 fragment. We demonstrate that the PDZ-containing protein syntenin-1, known to connect cytoskeletal proteins, binds to syndecan-1 in cells plated on the alpha3LG4/5 fragment and participates in the formation of membrane protrusions. We further show that syntenin-1 recruitment depends on the dephosphorylation of Tyr-309 located within syndecan-1 PDZ binding domain EFYA. We propose that tyrosine dephosphorylation of syndecan-1 may regulate its association with cytoskeleton components.

Effect of chain length on physicochemical properties and cytotoxicity of cationic vesicles composed of phosphatidylcholines and dialkyldimethylammonium bromides

This study investigated the physicochemical characteristics of cationic vesicles that were prepared from two phosphatidylcholines and three dialkyldimethylammonium bromides (DXDAB) with differing in dialkyl chain lengths, ranging from 2-C(14) to 2-C(18), by measuring particle size and zeta potential. The dependence of particle size, zeta potential and short-storage stability of mixed phosphatidylcholine/DXDAB vesicles on the chain length and composition were also elucidated. Transmission electron microscopy analysis verified that vesicles were formed as a phosphatidylcholine film to which DXDAB was added in a phosphate buffer saline (PBS, pH 7.4). Furthermore, the toxicity to the human keratinocytes (HaCaT) and squamous cell carcinomas (SCC25) cells that were incubated with these vesicles, evaluated by a cell viability assay, increased with the percentage of DXDAB that was incorporated and was inversely proportional to the chain length of DXDAB. The morphological features (round shape, chromatin condensation and apoptosis bodies) and results of flow cytometry analysis (increased sub-G(1) fraction) confirmed the induction of apoptosis in HaCaT and SCC25 cells by cationic vesicles. Apoptosis caused by cationic vesicles without the addition of any drugs was observed for the first time in HaCaT and SCC25 cells. The results of this investigation suggest that cytotoxicity is related to the zeta potential of the cationic vesicles.

N-Glycosylation of laminin-332 regulates its biological functions. A novel function of the bisecting GlcNAc

Laminin-332 (Lm332) is a large heterotrimeric glycoprotein that has been identified as a scattering factor, a regulator of cancer invasion as well as a prominent basement membrane component of the skin. Past studies have identified the functional domains of Lm332 and revealed the relationships between its activities and the processing of its subunits. However, there is little information available concerning the effects of N-glycosylation on Lm332 activities. In some cancer cells, an increase of beta1,6-GlcNAc catalyzed by N-acetylglucosaminyltransferase V (GnT-V) is related to the promotion of cancer cell motility. By contrast, bisecting GlcNAc catalyzed by N-acetylglucosaminyltransferase III (GnT-III) suppresses the further processing with branching enzymes, such as GnT-V, and the elongation of N-glycans. To examine the effects of those N-glycosylations to Lm332 on its activities, we purified Lm332s from the conditioned media of GnT-III- and GnT-V-overexpressing MKN45 cells. Lectin blotting and mass spectrometry analyses revealed that N-glycans containing the bisecting GlcNAc and beta1,6-GlcNAc structures were strongly expressed on Lm332 purified from GnT-III-overexpressing (GnT-III-Lm332) and GnT-V-overexpressing (GnT-V-Lm332) cells, respectively. Interestingly, the cell adhesion activity of GnT-III-Lm332 was apparently decreased compared with those of control Lm332 and GnT-V-Lm332. In addition, the introduction of bisecting GlcNAc to Lm332 resulted in a decrease in its cell scattering and migration activities. The weakened activities were most likely derived from the impaired alpha3beta1 integrin clustering and resultant focal adhesion formation. Taken together, our results clearly demonstrate for the first time that N-glycosylation may regulate the biological function of Lm332. This finding could introduce a new therapeutic strategy for cancer.

Laminin isoforms containing the gamma3 chain are unable to bind to integrins due to the absence of the glutamic acid residue conserved in the C-terminal regions of the gamma1 and gamma2 chains

Laminins are the major cell adhesive proteins in basement membranes, and consist of three subunits termed alpha, beta, and gamma. Recently, we found that the Glu residue at the third position from the C termini of the gamma1 and gamma2 chains is critically involved in integrin binding by laminins. However, the gamma3 chain lacks this Glu residue, suggesting that laminin isoforms containing the gamma3 chain may be unable to bind to integrins. To address this possibility, we expressed the E8 fragment of laminin-213 and found that it was incapable of binding to integrins. Similarly, the E8 fragment of laminin-113 was expressed and also found to be inactive in binding to integrins, confirming the distinction between the integrin binding activities of gamma3 chain-containing isoforms and those containing the gamma1 or gamma2 chain. To further address the importance of the Glu residue, we swapped the C-terminal four amino acids of the gamma3 chain with the C-terminal nine amino acids of the gamma1 chain, which contain the Glu residue. The resulting chimeric E8 fragment of laminin-213 became fully active in integrin binding, whereas replacement with the nine amino acids of the gamma1 chain after substitution of Gln for the conserved Glu residue failed to restore the integrin binding activity. These results provide both loss-of-function and gain-of-function evidence that laminin isoforms containing the gamma3 chain are unable to bind to integrins due to the absence of the conserved Glu residue, which should play a critical role in integrin binding by laminins.

Laminin-332 and -511 in skin

The extracellular matrix (ECM) was long thought to be merely a structural tissue support and/or a filter. However, recent studies have suggested that ECM proteins regulate many intracellular and extracellular events, including cell growth, cell adhesion, cell division, cell movement, and apoptosis. They do so through activation of several families of cell surface receptor, including the integrins and syndecans. The focus of this review is on two laminin isoforms expressed in the skin. Laminins are an important molecular component of the basement membranes in a variety of tissue types. They have a cruciform shape, and are composed of three chains-alpha, beta, and gamma. Keratinocytes of the skin secrete numerous laminin isoforms, including laminin-511 and laminin-332. The latter are known to affect the behaviour of keratinocytes through binding to membrane-penetrating receptors (outside-in signal transduction). Conversely, the expression, secretion and assembly of laminin-rich matrices is regulated by cell surface receptors through inside-out signal transduction. We will review how integrins regulate laminin matrix assembly and the signals elicited by laminins that support either migration or stable adhesion of keratinocytes. We will also discuss recent data indicating that laminins plays key regulatory roles in the development of skin appendages and contribute to the pathogenesis of skin cancer.