2024-25 Cell-Cell and Cell-ECM Interactions PDF

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Warning The contents of these slides are the exclusive property of the Instructor and/or granted by third parties (textbooks’ reference for pictures) and are therefore protected by the current regulations governing the Protection of Copyright. All rights are reserved. The reproduction and/or diffusion, even partial, by any analogical and/or digital means, without the consent of the rights holder is FORBIDDEN. Any unauthorized use of the above mentioned "Contents" is under the full and exclusive responsibility of the users who will be responsible for it, according to the laws and regulations in force. It is allowed the use of the material for private and study use, however not for profit and without commercial purposes. Prof Wanda Lattanzi Dept Life Science and Public Health Section of Biology Room 352bis 1st Floor Istituti Biologici [email protected]  Cell-cell and cell-substrate interactions Tight junction Adherens junction Gap junction Desmosome Hemidesmosome Cell-substrate anchorage Cells adhere to the substrate in the external environment through two alternative types of junctional complexes: Focal adhesions Hemidesmosomes The two types share some similarities Cell-substrate anchorage focal adhesions (FA) Discrete sites of the cell surface through which the cell adheres to the substrate and «senses» the extracellular environment Focal adhesions are sites where cells adhere to the ECM and transmit signals in both directions across the plasma membrane. Cell-substrate anchorage focal adhesions (FA) During cell locomotion integrins dynamically an transiently interact with the extracellular environment and transduce a mechanical signal inside the cell causing actin filament contraction  Cell-substrate anchorage focal adhesions (FA) Large macromolecular assemblies through which mechanical force and regulatory signals are transmitted between the extracellular matrix (ECM) and the cell. Serve as the mechanical linkages to the ECM, and biochemical signaling hub to concentrate and direct numerous signaling proteins at sites of integrin binding and clustering. Cell-substrate anchorage focal adhesions (FA) FOCAL ADHESIONS are integrin-enriched regions: complex plasma membrane-associated macromolecular assembly engages with the ECM via integrin physically connects with the actin filmaents through the recruitment of numerous FA-associated proteins. the cytoplasmic domains are connected to actin filaments of the cytoskeleton through adaptor proteins (talin, actinin and vinculin) Cell-substrate anchorage focal adhesions (FA) The binding of ECM components induces conformational changes in the cytoplasmic domains of the integrins that bind to actin filaments of the cytoskeleton through actin‐binding proteins (talin, actinin, vinculin) → integrin clustering at the cell surface The association of myosin molecules with the actin filaments can generate traction forces that are transmitted to sites of cell–substrate attachment Cell-substrate anchorage focal adhesions (FA) During FA formation, talin undergoes a conformational change that exposes binding sites on talin’s rod domain. The attachment of integrin to an extracellular ligand can activate protein kinases and start a chain reaction that transmits signals throughout the cell. Cell-substrate anchorage focal adhesions (FA) The attachment of integrin to an ECM ligand activates protein kinases and start a chain reaction that transmits signals throughout the cell. Talin undergoes a conformational change that exposes binding sites on talin’s rod domain → actin binding and activation. Cell-substrate anchorage hemidesmosomes Discrete sites of the cell surface through which the cell adheres to the basement membrane * * transmembrane glycoprotein of basal keratinocytes that spans the lamina lucida of the dermal‐epidermal junction. HEMIDESMOSOMES in human diseases Bullous pemphigoid Production of auto-antibodies directed against proteins of hemidesmosomes leading to the detachment of the lower layer of the epidermis from the underlying basement membrane The leakage of fluid into the space beneath the epidermis results in severe blistering of the skin  HEMIDESMOSOMES in human diseases Epidermolysis bullosa Mutations in several different genes expressed in hemidesmosomes Detachment of epidermal layers → skin fragility, blistering, infections Cell-cell junctions Tight junction Adherens junction Gap junction Desmosome Hemidesmosome Cell-cell junctions Cell-cell junctions  Adherens Junctions Ca‐mediated binding based on integral proteins that link the two cells across a narrow extracellular gap. Two types of AJ: (belt desmosome) Zonula adherens Cell‐cell adhesions are mediated by extracellular cadherin domains, whereas the intracellular cytoplasmic Macula adherens (desmosome) tails associate with numerous adaptor and signaling proteins, collectively referred to as the “cadherin adhesome”. Adherens junctions Selectins Immunoglobulin superfamily Cadherins  Adherens Junctions Cadherin superfamily includes different TM Ca2+‐ dependent proteins, subdivided in multiple classes: Cadherins Protocadherins Desmogleins Desmocollins By TelmaGL ‐ Handmade, CC0, https://commons.wikimedia.org/w/index.php?curid=31371740 They share cadherin repeats: five tandem extracellular domain repeats that act as the binding site for Ca2+ ions on the extracellular side. Cells containing a specific cadherin subtype tend to cluster together both in cell culture and during development Zonula adherens («belt desmosome») Form belt‐shaped junctions that encircle each cell within an epithelium The cytoplasmic domain of cadherins interacts with catenins that enable binding actin filaments Composed of: Cadherins (homophylic interactions between identical extracellular domains) p120 (aka delta catenin) binds the juxtamembrane region of the cadherin γ-catenin (aka plakoglobin) binds the catenin-binding region of the cadherin. α-catenin binds the cadherin indirectly via β- catenin or plakoglobin and links the actin cytoskeleton with cadherin By Mariana Ruiz LadyofHats - https://commons.wikimedia.org/w/index.php?curid=756087 Macula adherens (desmosome) Forms disc‐shaped junctions, strong spot‐like adhesions randomly arranged on the lateral sides of plasma membranes of adjacent cells Found in tissues subjected to mechanical stress: myocardium, bladder tissues, gastrointestinal mucosa, epithelia Macula adherens (desmosome) Mediated by subclass of cadherins known as desmocollins and desmogleins (heterophilic interactions in the extracellular space near their N‐termini) The cytoplasmic domains binds to intermediate filaments through intermediate proteins: «desmosome‐intermediate filament complexes» (DIFC), a network of cadherin proteins, linker proteins and keratin intermediate filaments. Their intracellular anchor secures the position in the cell membrane By Mariana Ruiz LadyofHats - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6197348 Cell-cell junctions Tight junction Adherens junction Gap junction Desmosome Hemidesmosome  Tight junctions (zonulae occludentes) Occluding junctions or zonulae occludentes are multiprotein junctional complexes At the very apical end of epithelial cells, sealing adjacent cells; serve as ✓ barrier to the free diffusion of water and solutes (paracellular way) ✓ Fence to maintain cell polarity Tight junction Tight junctions (zonulae occludentes) occludin Claudin  Tight junctions (zonulae occludentes) Occludin (~60kDa) 4 transmembrane domains and both the N‐terminus and the C‐terminus of the protein are intracellular It forms 2 extracellular loops and 1 intracellular loop, which regulate paracellular permeability Claudins Family of >27 different proteins (~20kDa) 4 transmembrane domains and similar loop structure compared to occluding Serve as the backbone of tight junctions and play a significant role in the tight junction's ability to seal the paracellular space JAM , Junctional Adhesion Molecules Part of the immunoglobulin superfamily (~40kDa) 1 transmembrane domain Help to regulate the paracellular pathway function of tight junctions and to maintain cell polarity Angulins 3 protein members (Angulin‐1/LSR, Angulin‐2/ILDR1, and Angulin‐3/ILDR2) 1 immunoglobulin‐like domain in the extracellular region and one PDZ‐binding motif at the carboxy‐terminus Responsible for establishment of tight junctions and regulate the paracellular barrier function Cell-cell junctions Tight junction Adherens junction Gap junction Desmosome Hemidesmosome Gap junctions Specialized sites of inter‐communications between animal cells Connexones on plasma membranes, connecting the cytoplasms of adjoining cells and allowing the passage of ions Connexones are made up by integral proteins named connexins Gap junctions Individual cardiac muscle cells (myocardiocytes) are linked by gap junctions that form low resistance pathways along which the electrical impulse flows rapidly and repeatedly between all the cells of the myocardium, ensuring their synchronous contraction. Cell junctions in human diseases