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Adhesion Cell junctions

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  1. Adhesion Cell junctions Dr. habil. Kőhidai László Assoc. Professor Dept. Genetics, Cell- and Immunobiology Semelweis University 2008

  2. Significance of cell-adhesion: formation of cell layers

  3. Significance of cell-adhesion: Formation of multiple layers of cells

  4. Lymphocytes cross the endothel „Rolling” Entry Adhesion Migration homing receptor vascular addressin

  5. Main groups of cell adhesion molecules

  6. Main adhesion molecules expressed on the cells during adhesion • Cadhedrins homophil • Selectins heterophil • Integrins heterophil • Adh. mol. with immunoglobulin homophil domain { Ca2+

  7. i.e. cadherin cyto- skele- ton i.c. linker prot. i.e. integrin ECM

  8. Cadherin Ca2+ Ca2+ • Homophil connection • Cell-cell • Ca2+-dependent binding • I.c. anchored to actin or • intermedier filamentum • Significant role in • development • of vertebrates Ca2+ catenin • Tissue-specificity: • N - nerve • P - placenta • E - epithelial actin or IF

  9. CAM = Cell Adhesion Molecules • 5 pcs. Ig-type domain • Ca 2+ indep. adhesion • Homophi connection - typical • Heterophil connection - rare • More than 20 variations • Expressed in the critical phase of • development Ig-like domains • Tissue-specificity: • N-CAM - neuron • L-CAM - liver In melanoma – relation between ICAM-1 density and the Metastatic activity of the tumour

  10. Selectins Lectin type proteins, Carbohydrate specificity Tissue-specificity: E - epithelial L - lymphoid P - placenta L selectin: it has role in the initial phase of adhesion; in newborns the level of L sel. is low – the low number of inflammations (?!)

  11. Integrin b • Ca2+-dependent binding • Heterophil connection • Focal contacts • Its i.c. linker proteins are • i.e.. talin, a-actinin, vinculin • RGD sequ. Is significant in • e.c. binding • Partner molecules: • fibronectin • laminin • collagen a S S Deficiency(b) – the adhesion of leukocytes affected, results the increase of inflammations

  12. Cell-cell junctions

  13. Junctional complexes • Tight junction • Zonula adherens • Desmosome • Gap junction • Hemidesmosome • Interdigitation

  14. Intercellular space 0.6 mm Transmembrane proteins occludin Lipid bilayer Cytoplasmic face Tight junction = zonula occludens

  15. Negative staining to detect „insulating” effect of tight junction

  16. Transport accross tight junction

  17. System of occludin – lines

  18. Role of tight junction • Mechanical connection • Barrier • Inhibits: • entry of water-soluble molecules • lateral diffusion of membrane-components • Ca2+ is required for the connections of occludins • Permeability: inorganic small substances • amino acids • monosaccharides

  19. Septate junction • on the apical part of the cells • they form a continous belt (like z. adherens) • promote to stick together the cells • actin is anchored in this junction

  20. Desmosome = macula adherens Cell to cell, snap-like junction

  21. cytoplasmatic plaque desmoplaquin, plactoglobin Desmosome actin intermedier filaments desmosomal cadherins i.e. desmoglein, desmocollin

  22. Components of desmosomes

  23. TEM structure of desmosome Cytoplasmatic plaque Intermedier filaments (i.e. keratin) cadherins

  24. Submembraneous network connecting desmosomes

  25. Gap junction (1958, 1968) • Bridges the 2-4 nm gap between the neighbour cells • Hexagonal channel is formed (connexon) • The wall of the channel is composed by 6 connexins • (4 helical components) • The distribution of channels is tissue- or cell-specific • due to the difference of connexins • Accross channels substances are transmitted • (max MW. 1000) by a regulated mechanism

  26. Gap junction

  27. Gap junction

  28. Role of gap junction • Transportofneurotransmitters, cAMP, • Ca 2+ • Signaling in early embryo

  29. Plasmodesmata sER cytoplasm desmotubule cellwall membrane plasmodesmata Gap junction-like function Viral infection results in the increase of pore diameter

  30. Plasmodesmata ER membrane desmotubule

  31. Hemidesmosome Fixing of epithelial cells to the basal membrane

  32. Basal striation

  33. Interdigitation Characteristic between epithelial cells

  34. Structure of focal contact actin filament a actinin vinculin paxillin talin integrin fibronectin

  35. Focal contacts actin vinculin

  36. Extracellular Matrix

  37. Extracellular matrix - Function • Influence on migration of the cells • Regulation of activity of molecules released • Co-receptors

  38. Extracellular matrix – Building blocks • Glycosaminoglycans (GAG-s) • heparan sulfate - basal membr., cell surface • keratan sulfate - cornea, bone • chondroitin sulfate – cartilage, bone, heart • hyaluronate - synovial fluid • dermatan sulfate - blood vessels, heart • „Core-proteins” aggrecan – decorin • collagen – elastin - structure • fibronectin – laminin - adhesion

  39. Fibronectins collagen cell RGD Dimer composed by different channels – alternative splicing heparin

  40. Fibronectins Gly Arg Asp • Glycoproteins • Dimer-structure • RGD (Arg-Gly-Asp) • Plasma fibronectins • Gene „K.O.” experiments

  41. Basal lamina Cell Connective tissue Layers: lamina lucida lamina densa lamina fibroreticularis Components: IV. collagen laminin perlecan entactin

  42. SEM image of basal lamina epithelial cells basal membrane collagen fibrils

  43. Main proteins composing the basal lamina

  44. Collagen IV Entactin Perlecan Laminin

  45. Collagen • Fibrils(diam.10-300 nm) • More than 15 types • I., II., III., V., XI. – formation of fibrils • IV., VII. – network • IX., XII. – association of fibrils

  46. Synthesis and association of collagen filament synthesis of a-chain Pro, Lys hydroxilation glycosylation assembly organization into a fiber formation of triple helix secretion splitting of procollagen building into fibrill

  47. Negative staining of collagen fibrils gaps between collagen molecules collagen

  48. SEM image of collagen fibrils

  49. B2 chain B1 chain A chain a-helix Globular domains Laminin • each chain has more types • 18 isoforms of laminin • diversities in tissues

  50. strech relax Elastin fibre of elastin cross-links