Cell Adhesion and ECM PDF

Cell Adhesion and Cell Signalling I. Adhesion in epithelia (Inke Nathke) II. The extracellular matrix (Alan Prescott) III.Cell-cell and cell-matrix adhesion (Alan Prescott) 1  Learning Objectives Cell Adhesion & Cell...

Cell Adhesion and Cell Signalling I. Adhesion in epithelia (Inke Nathke) II. The extracellular matrix (Alan Prescott) III.Cell-cell and cell-matrix adhesion (Alan Prescott) 1  Learning Objectives Cell Adhesion & Cell Signalling After these lectures you should be able to: Describe the molecular components of the extracellular matrix (ECM) and discuss their structures, properties and functions. Understand how the ECM contributes to tissue structure and function. Discuss the various families of adhesion molecules that allow cells to adhere to the ECM and to each other. Understand how these adhesion molecules are important in cellular functions particularly in the context of the cells of the immune system. Understand the role of adhesion in tissues, particularly epithelial tissues. Understand the general principles of cellular signalling and discuss examples of signalling pathways and their components. 2 Cell Adhesion and the ECM recommended textbook: Alberts et al. Molecular Biology of the Cell, Chapter 19 3 Cell Adhesion and Cell Signalling I. What is the extracellular matrix? II. How do cells adhere to each other and to the extracellular matrix? BS31004: Biochemistry and Cell Biology Dr Alan Prescott 4  What holds us together? cells have to be able to stick to each other and to other components to form a multicellular organism cells and other components are organised into tissues tissues are made of cells and extracellular space – filled with a network of macromolecules forming the extracellular matrix (ECM) cell adhesion mechanisms and the extracellular matrix are critical for the organisation, development, function and dynamics of tissues the contributions of each varies in different tissue types: 5 There are 2 extremes of animal tissue organisation epithelial tissues – sheets of tightly bound cells, cell-cell adhesions linked to cytoskeleton, thin layer of ECM connective tissues – rich in ECM components (e.g. collagen fibres), few cells (e.g. fibroblasts, fat cells, immune cells), few cell-cell adhesions, cell- matrix adhesions important e.g. epidermis e.g. dermis Tissues can be a combination of these extremes 6 Fibroblasts in rat cornea 7  Connective tissue Provides routes for communication and supply e.g. blood vessels, nerves, lymphatics In connective tissues, ECM determines the tissue’s physical properties 8  Types of connective tissue ECM in different tissues is adapted to particular functional requirements: Tendon - ropelike, high tensile strength (collagen fibrils) Blood vessel walls – resilient, flexible (elastic fibres) Cartilage – tensile strength and elastic properties (collagen and proteoglycan aggrecan) Bone – rigid and incompressible (calcified collagen) Vitreous content of eye - transparent jelly (collagen fibres and hyaluronan) Consist of similar components but with different variants, proportions and geometrical arrangement. 9  Components of the extracellular matrix 2 main types of component: (1) glycosaminoglycan polysaccharide chains (GAGs) e.g. heparin sulphate, hyaluronan - usually covalently linked to protein (proteoglycan) e.g. aggrecan, decorin, serglycin, perlecan and syndecan (2) fibrous proteins e.g. collagen, fibrillin, elastin, laminin Also adhesive glycoproteins which act as adapters, providing molecular interactions by binding matrix proteins, cells or both e.g. fibrinogen, fibronectin, osteopontin, tenascin, vitronectin etc 10  ECM Macromolecules Protein-green GAG-red 11  GAGs unbranched polysaccharide chains composed of repeating disaccharide units one of the 2 sugars is always an amino sugar (N-acetylglucosamine or N-acetylgalactosamine) second sugar usually a uronic acid (glucuronic or iduronic) highly negatively charged (sulphate and carboxyl groups) 4 main groups: - hyaluronan - chondoitin sulphate and dermatan sulphate - heparan sulphate - keratan sulphate heparan sulphate repeating disaccharide 12 Hyaluronan extremely long chain length – up to 25,000 disaccharide units non-sulphated like other GAGs adopts highly extended conformation attracts water, creating pressure non-compressible space filler 13  Proteoglycan synthesis translocated into linker added by polysaccharide modification e.g. ER glycosyl elongated by epimerisation, transferase in glycosyl sulphation in ER/golgi transferases golgi in golgi secretory pathway 14  Examples of proteoglycans glycoproteins usually contain 1-60% carbohydrate by weight proteoglycans can be 95% carbohydrate highly heterogenous – a single core protein can have variable numbers and types of GAGs 15 Aggrecan in cartilage 16  Rat cartilage GAG chains Core protein 17  Collagens the major fibrous extracellular matrix component 25% of total protein mass of mammals (major component of skin and bone) 42 human genes for collagen -chains (form triple helix) different combinations expressed in different tissues (~ 30 different molecules found) 18  Collagen fibrils in tadpole skin 19  Some collagens form fibrils bundles of collagen fibrils in connective tissue of embryonic chick skin 20 Collagen -chains form trimers each chain folds into a helix with 3 amino acids/turn (gly-X-Y; commonly proline and hydroxyproline) glycine proline wrap round each other to form tightly packed triple helical rod 21  Collagen trimers can form fibrils collagen trimers self-assemble into trimers (1.5nm diameter) fibrils (extracellular) covalent crosslinks form between fibrils (10-300nm diameter) lysines and hydroxylysines fibres (0.5-3 m diameter) collagen fibrils bundle into fibres 22  Synthesis and assembly of collagen scurvy 23  Fibril-associated collagens don’t form fibrils - non-helical domains interrupt triple helix, making molecule more flexible - retain propeptides, so don’t aggregate into fibrils bind to fibrils of fibrillar collagens - mediate fibril interactions with each other and with other ECM molecules to determine fibril organisation e.g. type IX binds type II fibrils in cartilage type XII bind type I fibrils in tendons 24 Collagens 25 Elastic fibres in dog Aorta 26  Elastin collagen fibrils provide tensile strength (resistance to stretch), but some tissues need to be strong and elastic e.g. blood vessels, lungs, skin elastic fibres provide resilience i.e. ability to recoil after stretch main component is elastin: - hydrophobic protein - secreted as tropoelastin, then highly crosslinked to form network of fibres and sheets elastic fibres also covered in microfibrils – made from other glycoproteins e.g. fibrillin 27  Fibronectin helps attach cells to the ECM binds integrins fibronectin forms dimers (usually heterodimers – differential splicing) each subunit comprises multiple functionally distinct domains and repeated modules (e.g. type III fibronectin repeat) – different adhesive functions can also form insoluble, crosslinked fibrils - only when binding cells and subject to tension 28  The basal lamina (basement membrane) the basal lamina is a very thin, tough, flexible sheet of ECM essential mechanical role e.g. connecting epidermis to dermis underlies epithelia, surrounds muscle and nerve cells 29 Examples of basal lamina physical support selective cell barrier filtration act as template for tissue regeneration determine cell polarity influence cell metabolism organises plasma membrane proteins promote cell survival, proliferation and differentiation 30 Basal lamina in chick embryo cornea 31 Molecular structure of basal lamina 32  Laminin structure heterotrimer of , ,  chains (multiple isoforms of each) multiple binding sites for other components and cells assembles into network via heads 33  The extracellular matrix is secreted and organised by cells within it fibroblasts, chondroblasts (cartilage), osteoblasts (bone) secrete and assemble ECM components (e.g. collagen fibrils) bind ECM components and apply tension via integrins and cytoskeleton (e.g. formation of fibronectin fibrils) Rat cornea can orientate ECM 34  Remodelling/degradation of the ECM occurs during: - normal tissue development - wound healing - bone remodelling - cell migration e.g. inflammation (for white blood cells to infiltrate tissues), tumour cell invasion and metastasis carried out by cellular proteases: - matrix metalloproteases (MMPs) e.g. MMP-9 (collagenase) - serine proteases e.g. Urokinase (urokinase-type plasminogen activator uPA) – implicated in metastasis. activity confined to cells by: - local activation from inactive precursors - cell surface localisation e.g. MMP-14 - inhibitors e.g. TIMPs, serpins 35 Dendritic cells use MMPs to degrade ECM 36  Roles of the ECM structural integrity of connective tissues scaffold for cells reservoir for growth factors and cytokines provides pathways for cell migration regulates cell shape, polarity, survival, proliferation and function regulates tissue development 37 ECM can immobilise chemokine gradients labelled dendritic cells added to dermis of skin explant cells migrate into skin lymphatic vessels in response to chemokine gradients (40 min) 38 Weber, M. et al., (2013) Science, 339, 328 ECM can immobilise chemokine gradients chemokines are bound to ECM Weber, M. et al., (2013) Science, 339, 328 39  Extracellular matrix summary found in all tissues and plays an important structural role - connective tissue: resistance to compressive forces and provision of resilience (elasticity) and tensile strength - basal lamina: scaffold for cell organisation made of polysaccharides (GAGs), which can be in the form of proteoglycans, fibrous proteins and adhesive glycoproteins which act as adaptors – these are secreted and remodelled by cells within the ECM these components are found in varying forms, amounts and arrangements giving different tissues different properties environment provided by ECM is important for regulation of cell shape, polarity, differentiation, survival, proliferation, migration, function Frantz, C. et al., (2010) The extracellular matrix at a glance. JCS, 123, 4195-2000 40