Function Of Intercellular Junctions Research Articles

Kinetic Measurements Reveal Enhanced Protein-Protein Interactions at Intercellular Junctions.

The binding properties of adhesion proteins are typically quantified from measurements with soluble fragments, under conditions that differ radically from the confined microenvironment of membrane bound proteins in adhesion zones. Using classical cadherin as a model adhesion protein, we tested the postulate that confinement within quasi two-dimensional intercellular gaps exposes weak protein interactions that are not detected in solution binding assays. Micropipette-based measurements of cadherin-mediated, cell-cell binding kinetics identified a unique kinetic signature that reflects both adhesive (trans) bonds between cadherins on opposing cells and lateral (cis) interactions between cadherins on the same cell. In solution, proposed lateral interactions were not detected, even at high cadherin concentrations. Mutations postulated to disrupt lateral cadherin association altered the kinetic signatures, but did not affect the adhesive (trans) binding affinity. Perturbed kinetics further coincided with altered cadherin distributions at junctions, wound healing dynamics, and paracellular permeability. Intercellular binding kinetics thus revealed cadherin interactions that occur within confined, intermembrane gaps but not in solution. Findings further demonstrate the impact of these revealed interactions on the organization and function of intercellular junctions.

Viral Interactions with PDZ Domain-Containing Proteins-An Oncogenic Trait?

Many of the human viruses with oncogenic capabilities, either in their natural host or in experimental systems (hepatitis B and C, human T cell leukaemia virus type 1, Kaposi sarcoma herpesvirus, human immunodeficiency virus, high-risk human papillomaviruses and adenovirus type 9), encode in their limited genome the ability to target cellular proteins containing PSD95/ DLG/ZO-1 (PDZ) interaction modules. In many cases (but not always), the viruses have evolved to bind the PDZ domains using the same short linear peptide motifs found in host protein-PDZ interactions, and in some cases regulate the interactions in a similar fashion by phosphorylation. What is striking is that the diverse viruses target a common subset of PDZ proteins that are intimately involved in controlling cell polarity and the structure and function of intercellular junctions, including tight junctions. Cell polarity is fundamental to the control of cell proliferation and cell survival and disruption of polarity and the signal transduction pathways involved is a key event in tumourigenesis. This review focuses on the oncogenic viruses and the role of targeting PDZ proteins in the virus life cycle and the contribution of virus-PDZ protein interactions to virus-mediated oncogenesis. We highlight how many of the viral associations with PDZ proteins lead to deregulation of PI3K/AKT signalling, benefitting virus replication but as a consequence also contributing to oncogenesis.

Introduction to the “Paradigm Shifts in Perspective” Series

The history of human knowledge has so uninterrupt-edly shown that to collateral, or incidental, or acci-dental events we are indebted for the most numerousand most valuable discoveries, that it has at lengthbecome necessary, in any prospective view ofimprovement, to make not only large, but the largestallowances for inventions that shall arise by chance,and quite out of the range of ordinary expectation.—Edgar Allan Poe, The Mystery of Marie Rogeˆt,1842These words, voiced by Auguste Dupin, a fictional amateursleuth, contain an inalienable truth regarding the nature ofdiscovery. In science, the truly major advances, whichsubstantially change the way we think, termed ‘‘paradigmshifts’’ [1], often arise from the most unexpected quartersby individuals not considered to be in the mainstream ofinvestigators associated with a disease or observation. Withthis issue, Digestive Diseases and Sciences introduces anew series of articles entitled ‘‘Paradigm Shifts inPerspective’’ which is aimed at highlighting scientificfindings that have had a major impact on the field ofgastroenterology. One of the motivations for creating thisseries is to increase the appreciation for ‘‘small’’ science,driven mostly by intellectual curiosity informed by a desireto understand disease pathogenesis, the principal well-spring for these advances. We plan to highlight advancesthat were initially under-appreciated, scorned, or evenforgotten, only to resurface or gain acceptance as the‘‘game changers’’ of gastroenterology. Since it can takedecades for the full import of a discovery to manifest, mostof the articles highlighted will be from the 1980s at thelatest.The first of these articles is by Daniel Hollander, whowrites of his remarkable 1986 discovery in which hereports increased intestinal permeability in unaffected rel-atives of Crohn’s patients [2]. Although the familial natureof inflammatory bowel disease had been documented fordecades previous, few disease biomarkers that would pro-vide clues regarding its etiopathogenesis existed. Further-more, at that time the concept of intestinal permeability asa static, intrinsic property of epithelia was widely held.Lastly, the concept that increased intestinal permeabilitycould predispose to disease was virtually unknown.The publication of Dr. Hollander’s paper in 1986 markedan important year for the understanding of the nature ofintercellular junctions, with the publication of the cloning ofone of the first junctional proteins, zonula occludens [ZO]-1.This finding, along with Dr. Hollander’s, marked the start ofthe current understanding of intercellular junctions as com-plex, dynamically regulated multiprotein structures, whichhave strong implications for disease pathogenesis. Althoughinterventions have not yet targeted permeability, the obser-vation that increased permeability could be a cause and notthe effect of mucosal inflammation and injury changed theway we thought about IBD specifically and about mucosalinjury in general. That junctional permeability could beunder genetic control, as Dr. Hollander first reported, was arevolutionary finding, which helped ignite the current wideinterest in the structure and function of intercellular junc-tions. Indeed, 20 years after its publication, several groupsreportedthatincreasedintestinalpermeabilitywaspresentinrelatives of patients with familial Crohn’s disease who borespecificmutationsinthenucleotide-bindingoligomerizationdomain-containing protein [NOD]2/caspase recruitment

Structure and Function of Intercellular Junctions in Human Cervical and Vaginal Mucosal Epithelia1

The mucosal epithelium is a major portal for microbial invasion. Mucosal barrier integrity is maintained by the physical interactions of intercellular junctional molecules on opposing epithelial cells. The epithelial mucosa in the female reproductive tract provides the first line of defense against sexually transmitted pathogenic bacteria and viruses, but little is known concerning the structure and molecular composition of epithelial junctions at this site. In the present study, the distribution of tight, adherens, and desmosomal junctions were imaged in the human endocervix (columnar epithelium) and ectocervix (stratified squamous epithelium) by electron microscopy, and permeability was assessed by tracking the penetration of fluorescent immunoglobulin G (IgG). To further define the molecular structure of the intercellular junctions, select junctional molecules were localized in the endocervical, ectocervical, and vaginal epithelium by fluorescent immunohistology. The columnar epithelial cells of the endocervix were joined by tight junctions that excluded apically applied fluorescent IgG. In contrast, the most apical layers of the ectocervical stratified squamous epithelium did not contain classical cell-cell adhesions and were permeable to IgG. The suprabasal and basal epithelial layers in ectocervical and vaginal tissue contained the most robust adhesions; molecules characteristic of exclusionary junctions were detected three to four cellular layers below the luminal surface and extended to the basement membrane. These data indicate that the uppermost epithelial layers of the ectocervix and vagina constitute a unique microenvironment; their lack of tight junctions and permeability to large-molecular-weight immunological mediators suggest that this region is an important battlefront in host defense against microbial pathogens.

The TRPV4 Channel Contributes to Intercellular Junction Formation in Keratinocytes

Transient receptor potential vanilloid 4 (TRPV4) channel is a physiological sensor for hypo-osmolarity, mechanical deformation, and warm temperature. The channel activation leads to various cellular effects involving Ca(2+) dynamics. We found that TRPV4 interacts with beta-catenin, a crucial component linking adherens junctions and the actin cytoskeleton, thereby enhancing cell-cell junction development and formation of the tight barrier between skin keratinocytes. TRPV4-deficient mice displayed impairment of the intercellular junction-dependent barrier function in the skin. In TRPV4-deficient keratinocytes, extracellular Ca(2+)-induced actin rearrangement and stratification were delayed following significant reduction in cytosolic Ca(2+) increase and small GTPase Rho activation. TRPV4 protein located where the cell-cell junctions are formed, and the channel deficiency caused abnormal cell-cell junction structures, resulting in higher intercellular permeability in vitro. Our results suggest a novel role for TRPV4 in the development and maturation of cell-cell junctions in epithelia of the skin.

Implication of direct host–tumor intercellular interactions in non-immune host resistance to neoplastic growth

The hallmark of cancer as a disease is impaired homeostasis, which in normal tissue is maintained by the network of direct intercellular contacts. The cell–cell interaction machinery consists of intercellular junctions of various types, each of which has a role in the control of cell growth, differentiation, and motility. In cancer, the function of intercellular junctions is altered, often at quite advanced stages of tumor progression, while proper intercellular interactions between normal and tumor cells may control and even suppress, otherwise, aberrant growth and behavior of neoplastic cells. This type of host resistance to neoplastic growth implies a homotypic functional partnership between tumor cells and their normal host counterparts and, thus, is to a certain extent complementary to immune defense against tumorigenesis, which is effective only when tumor cells became ‘foreign’ for the host. Functional interactions between host and tumor cells could be lost at different stages of tumorigenesis through a range of mechanisms. In some cases, host–tumor interactions may be impaired reversibly, which in turn gives rise to the possibility of restoring this component of host defense against cancer by correctional interventions. This review highlights the role that direct intercellular host–tumor interactions may play in natural host resistance against neoplastic growth, with an emphasis on the underlying mechanisms of both their function and impairment.

Structural modifications of intercellular junctions.

Structure and function of intercellular junctions were studied under the electronmicroscope using conventional thin sectioning and freeze-etch replicas. Alterations of tight and gap junctions were analyzed 1. of exocrine pancreatic cells under cell isolation conditions and pancreatic duct ligation and 2. of hepatocytes during extrahepatic cholestasis.During the different steps of cell isolation of exocrine pancreatic cells, gradual changes of tight and gap junctions were observed. Tight junctions, which formed belt-like structures around the apex of control acinar cells in situ, subsequently diminished, became interrupted and were concentrated into macular areas (Fig. 1). Aggregations of membrane associated particles, which looked similar to gap junctions, were intermixed within tight junctional areas (Fig. 1). These structures continously disappeared in the last stages of the isolation procedure. The intercellular junctions were finally separated without destroying the integrity of the cell membrane, which was confirmed with porcion yellow, lanthanum chloride and horse radish peroxidase.

Ultrastructure of Intercellular Junctions in the Freeze Fractured Alveolar-Capillary Membrane of Mouse Lung

Intercellular junctions are specialized regions of contact between the apposed membranes of adjacent cells, which allow cells to interact with each other, and to form structures of higher order. While at least 4 different types of intercellular junctions have been recognized in mammalian tissues, 1 Staehelin LA Structure and function of intercellular junctions. Int Rev Cytol. 1974; 39: 191 Crossref PubMed Scopus (1049) Google Scholar in the case of the alveolar-capillary membrane we shall be concerned with only 2 types: the tight junction or zonula occludens, and the gap junction or macula communicans.2 Schneeberger EE Karnovsky MJ Substructure of intercellular junctions in freeze-fractured alveolar-capillary membranes of mouse lung. Circ Res. 1976; 38: 404 Crossref PubMed Scopus (72) Google Scholar Tight junctions, present near the apex of epithelial and endothelial cells, form a continuous, belt-like region in which, on thin section, the membranes of adjacent cells are so closely apposed that the intercellular space between them appears to be obliterated. Physiologic studies indicate that such junctions constitute a permeability barrier to the passage of small water-soluble solutes between the lumen and intercellular spaces. Gap junctions, on the other hand, facilitate cell-to-cell communication by providing channels which allow the passage of small molecules between the interiors of adjacent cells.

Effect of osmotic gradients on intercellular junctions of the toad bladder

Effect of osmotic gradients on intercellular junctions of the toad bladder