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İng tip adezyonmoleküll


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İng tip adezyonmoleküll

  1. 1. Cell Adhesion Molecules (CAM) Medical Biology Müjgan Cengiz
  2. 2. Cellular Junctions and Adhesion • In multi-cellular cells have junctions that occur with: • 1- Other cells • 2- The Extra-Cellular Matrix (ECM): • a network of secreted macromolecular complexes
  3. 3. Two main ways in which animal cells are bound together: •Connective tissue •Epithelial cells. Figure 19-1 Molecular Biology of the Cell (© Garland Science 2008)
  4. 4. Selective Adhesion Determines Specificity of Tissue and Cellular Associations • Townes & Holtfreter (1950) separated embryonic cells of frogs and combined them together again. To be able to identify the different cell types, they mixed together cells from normal (pigmented) frogs with cells from albino frogs Identification of CAM through experiment:
  5. 5. Selective Adhesion Determines Specificity of Tissue and Cellular Associations
  6. 6. Identification of CAM through experiment: Antibodies were developed against specific types of CAM. Antibody treatment of the target cells was found to disturb the cell aggregation.
  7. 7. • What are the factors that keep the cells together? • how do the same type of cells recognize each other?
  8. 8. Adhesion Adhesion = molecules sticking to a substrate
  9. 9. CELL ADESİON MOLECULES • Cell-cell interactions • Embryogenesis • Immunity(migration of immun cells to the inflamation center) • Cell tissue organ development • wound healing • Cancer metastasis
  10. 10. Cell adhesion molecules • 1-Holding cells together • 2-Cells detect their extracellular environment through interaction employing a variety of cell adhesion molecules (CAMs)
  11. 11. Cells adhere to each other and to the extracellular matrix through cell-surface proteins called cell adhesion molecules (CAMs) • Many adhesion molecules are mosaics of multiple distinct domains • (1) extracellular domain: – Mediate adhesion (2) transmembrane domain • • • • (3) cytosolic domain: -recruit sets of multifunctional adaptor proteins --adaptor proteins: link to cytoskeleton/ signaling molecules * outside-in and inside-out effects: connectivity and communication
  12. 12. Cell adhesion molecules (CAM) --Many adhesion molecules are mosaics of multiple distinct domains (1) extracellular domain: mediate adhesion *homotypic adhesion—adhesive interactions between cells of the same type *homophilic adhesion—a CAM on one cell can directly bind to the same kind of CAM on an adjacent cell. (2) cytosolic domain: --recruit sets of multifunctional adaptor proteins --adaptor proteins: link to cytoskeleton or signaling molecules * outside-in and inside-out effects: connectivity and communication
  13. 13. Heterophilic Binding- Binding to a different kind 1) extracellular domain of molecule on adjacent cells Homophilic Binding- Binding of same kind of molecules in adjacent cells Linker-dependent BindingBinding through a secreted linker molecules to other molecules. The binding of a cell-surface receptor to a secreted ECM molecule immobilized on the substrate.
  14. 14. cell adhesion molecules ↑ 1- cell adhesion molecules : glicoproteins ↓ 2- linker-protein connects the junction to (micro- or intermediate) filaments
  15. 15. Cell-cell adhesions can be • A- tight and long junctions • e.g. nerve cells in the nerve cells/ the metabolic cells in the liver • B- relatively weak and transient • e.g. immune –system cells in the blood
  16. 16. Cell Adhesion Molecules What are they? Cell adhesion molecules (CAMS) are cell surface proteins involved in the binding of cells, usually leukocytes, to each other, to endothelial cells, or to the extracellular matrix. Most CAMS can be placed into one of four general families of proteins: 1) Cadherins 2) Integrins 3) Immunoglobulin (Ig) super family 4) Selectins
  17. 17. epithelial cells non-epithelial cells tight junctions actin adhesion belt (CADHERINS) CELL CELL ADHESION desmosomes (CADHERINS) Gap junctions (connexins) CELL MATRIX ADHESION hemidesm. (integrins) focal contacts (integrins) basal lamina JUNCTIONAL ADHESION MECHANISMS CADHERINS IG-LIKE CAMS INTEGRINS SELECTINS integrins NO attachment plague Non-JUNCTIONAL CONTACTS
  18. 18. • Cell Adhesion also occurs in the blood • Under most circumstances, all blood cells try to keep from sticking to the wall. • When a Leukocyte goes on the hunt… – Cell Rolling – Cell Adhesion
  19. 19. CELL-CELL adhesion Cadh. repeats CELL ADHESION MOLECULES Cadherins Ca 2+ -dep. homophilic adhesion functional unit = dimer Ig and Fn III repeats Immunoglobin superfamily (CAMs) homophilic or heterophilic lectin repeats Selectins heterophilic P selectin + counter-receptor PSGL-1, glycosylated I-CAM Integrins heterodimers, heterophilic bind to ECM, Ig-CAMs, cadherins adhesion, polarity, migration Hynes: TiCB: 9:M33 1999
  20. 20. Immunobiology, 6th Edition, Janeway, Travers, Walport, and Shlomchik
  21. 21. Some CAMs are Ca2+-dependent, some others are Ca2+-independent. • Ca2+-dependent Cadherins, Selectins, İntegrins • Ca2+-independent Ig superfamily
  22. 22. 1-CADHERINS • A family of Ca2+dependent CAMs • Ca2+ causes dimerization of Cadherins • The binding is homophilic-hold cells of one tissue type/subtype together by binding to the same cadherin on a neighbouring cell • greater the number of cadherins, greater the strength of adhesion
  23. 23. Compaction of an early mouse embryo. At the 8-cell stage they start expressing E-cadherins Figure 19-5 Molecular Biology of the Cell (© Garland Science 2008)
  24. 24. 1) CA-DEPENDENT CAMs (CELL ADHESION MOLECULES): a) classic CADHERINS: involved in both junctional and non junctional adhesions E-, N- and P- cadherins (Epithelial, Nerve, Placenta) single-pass transmembrane glycoproteins (~700-750 AA s), 5 cadherin repeats selective adhesion, homophilic differential expression during development + morphogenesis the extracellular side: 5 cadherin repeats of 100 AA, (3 are Ca2+ -binding) in the absence of Ca >>> rapid proteolysis the cytoplasmic side: the intracellular attachment proteins: catenins α,β,γ (bind actin) (required for cell-cell adhesion) Nonclassical cadherines cannot bind actin filaments . They can bind to intermediate filaments and forms desmosomes.
  25. 25. Cadherin structure Extracellular domains of a classical cadherin (C-cadherin) Figure 19-9a Molecular Biology of the Cell (© Garland Science 2008)
  26. 26. If Ca2+ is removed, the extracellular part of the protein becomes floppy and is rapidly degraded by proteolytic enzymes Ca2+ causes dimerization of Cadherins
  27. 27. Cadherins -Ca-dependent adhesion molecules Extracellular domains adhere cells together Participate in intracellular signalling Link and help assemble the cytoskeleton via actin or intermediate filaments
  28. 28. Cadherins Are Linked To Actin Cytoskeleton • The linkage of cadherins to actin filaments.
  29. 29. Different CAMs function in different junctions
  30. 30. Zonula adherens- E-cadherin •Cadherins interact with actin filaments by CATENINs.
  31. 31. Cadherin-containing junctions connect cells to one another and are linked to either the actin or IF cytoskeleton α,β,γ, catenins Figure 22-5
  32. 32. Localization of sub-types: E-epithelial N-neuronal P-placental VE-endothelial For instance: N-cadherin binds to other N-cadherins, but not P or VE-cadherins This keeps neurons attached to other neurons! to E,
  33. 33. Table 19-3 Molecular Biology of the Cell (© Garland Science 2008)
  34. 34. Embryogenesis & Cadherins • Expression of specific cadherins accompanies morphogenetic movements during embryogenesis
  35. 35. Embryogenesis & Cadherins • E-cadherin is the first cadherin expressed during mammalian development. It helps cause compaction, an important morphological change that occurs at the eight-cell stage of mouse embryo development. • During embryogenesis, production of cadherins promotes cells of similar type to adhere when cells need to migrate to newly growing tissue (e.g. limbs), they lose adhesive properties – cadherins must be endocytosed •
  36. 36. Cadherins and Catenins participate in transduction of extracellular signals and Med various cellular response. interior cell Ca2+ external interior GTP cell Small GTPaz GTP effectors Cell- cell Adhesion The changes in cell shape Cell differentation?
  37. 37. 2-Integrins: • Mediates Ca+2 dependent adhesion Integrin makes cell-substrate interaction • Ligands: ECM molecules, soluble ligands, CAMs • ( fibronectin, fibrinogen, ICAM, laminin) • Two transmembrane glycoprotein subunits: α and β • both required for matrix binding
  38. 38. D R transmembrane linkers of the ECM and the cytoskeleton G β chain bind ligands with low affinity present at very high concentration on the cell surface α chain Cys-rich Cells both bind to and respond to the ECM via integrins. 3-4 Ca2+ or Mg2+ binding domains on the α chain Diversity of integrins: 9 types of β, 14 types of α ~ 20 different heterodimers identified so far Integrins are modulated by additional cell-specific factors RGD” sequence is the specific substrate
  39. 39. Integrins On the extracellular side integrins bind to the sequence Arg-Gly-Asp found in adhesion molecules including fibronectins On the intracellular side they bind Vinculin and a-Actinin, these proteins bind to Actin filaments This dual binding allow cells to move by contracting Actin filaments against the EM
  40. 40. integrin plays a major role in assembly of the hemidesmosome, or stable stable anchoring contact.
  41. 41. 2007 TUS • Hücrenin, hücreler arası matriks ile etkileşimini sağlayan transmembran yapıdaki adezyon reseptörleri aşağıdakilerden hangisidir? A) Kateninler B) Selektinler C) Kaderinler D) İntegrinler E) Vinkülinler
  42. 42. Aralık 2010 • Asagıdaki hücre baglantılarından ̧ ̆ ̆ hangisinin yapısında hücre adezyon molekülü olan integrin yogun olarak ̆ bulunur? A) Zonula occludens B) Zonula adherens C) Macula adherens D) Konnekson E) Hemidesmozom
  43. 43. Integrins Interact with The Cytoskeleton Integrins are linkers between cytoskeleton and extracellular matrix. Bind to actin filaments Need intracellular anchor proteins for bindig to actins. These intracellular anchor proteins are: 1. Talin 2. α –actinin 3. Filamin
  44. 44. Integrins Are TM Heterodimers (αβ Combinations) That Mediate Weak Cell-Matrix and Cell-Cell Interactions Cell-matrix adhesion is modulated by changes in the activity and number of integrins De-adhesion factors promote cell migration and can remodel the cell surface
  45. 45. interactions and the three binding modes of various integrins Adherent Cell PMN Platelet 1 2 3 Fibrinogen ECM Vasc. Endo. Cell 1. Integrins bind to ECM proteins via specific amino acid recognition sites 2. Integrins bind to other cell adhesion molecules 3. Integrins promote platelet aggregation through soluble miltivalent mediator molecules Platelet
  46. 46. 2. Integrins bind to other cell adhesion molecules
  47. 47. 2- Integrins promote platelet aggregation through soluble miltivalent mediator molecules Integrin and platelet aggregation (Karp, 2001)
  48. 48. Activation of some integrins may require to bind their ligand Ex: Platelet aggregation Leukocyte migration
  49. 49. Fibrinojen Trombin thrombin activation of platelets causes an induction of platelet agregation mediated by fibrinogen binding to the integrin
  50. 50. Disintegrins • Disintegrins are peptides isolated from the venom of various snakes of the viper family. They interact with the beta 1 and beta 3 families of integrin proteins. • They cause the bleeding.
  51. 51. Disintegrin drugs Drug Function Bitistatin platelet aggregation inhibitor, which binds with high affinity to the alphaIIbbeta3 integrin Kistrin Kistrin has an RGD site that competes for the platelet IIb/IIIa integrin Barbourin that function as potent inhibitors of both platelet aggregation and integrindependent cell adhesion Batroxostatin They were first identified as inhibitors of platelet aggregation and were subsequently shown to bind with high affinity to integrins and to block the interaction of integrins with RGD containing proteins for example they block the binding of the platelet integrin _IIb_3 to fibrinogen
  52. 52. Integrins and Signal Transduction: • Integrins play an important role not only in structure & architecture of tissues, but also for signal transduction leading to regulation of functions in cell.
  53. 53. 3-Immunoglobulin (Ig) Superfamily: •Mediate Ca2+-independent Cell-Cell Adhesion • • • Contain one or more Ig-like domains that are characteristic of antibody molecules a homophilic mechanism (between N-CAM molecules on adjacent cells). Some Ig-like cell-cell adhesion proteins, however, use a heterophilic mechanism Function: ICAM and VCAM molecules play an important role in T cell interactions and binding of leukocytes to activated or resting endothelial cells
  54. 54. 3-Immunoglobulin (Ig) Superfamily : members • Intercellular adhesion molecules (ICAMs)on endothelial cells Vasculer adesion molecules: VCAM • the neural cell adhesion molecule (N-CAM), • Platelet-endotel..: PECAM
  55. 55. 4- Selectins • Integral proteins • Extracellular domain bind specific carbohydrates on other cells • Most commonly found on epithelial cells, used to mediate interactions with leukocytes (white blood cells/immune cells)
  56. 56. P-selectin glycoprotein ligand-1
  57. 57. 4- Selectins • 3 types: - P-selectin- blood platelets,endothelial cells -L-selectin- white blood cells -E-selectin- endothelial cells
  58. 58. Selectins are calcium-dependent (C-type) lectins (carbohydrate binding proteins) • L-selectin – on lymphocytes (neutrophils) – binds specialized sulfated mucins (‘peripheral node addressins’ or PNAd) made by high endothelial venules (HEV) – Can be shed upon lymphocyte activation • P-selectin - early role in entry to site of inflammation – in Weibel-Palade bodies in endothelial cells and α-granules of platelets – translocates to membrane in response to thrombin, histamine, C5a, etc – binds PSGL-1, a tyrosine sulfated mucin - on neutrophils, some effector T cells • E-selectin - delayed role in entry to site of inflammation – cytokine inducible on endothelial cells (especially cutaneous) – binds carbohydrate ligand (sialyl-Lex) on neutrophil glycoproteins /glycolipids and cutaneous leukocyte antigen (CLA) on effector T cells L = C-type lectin domain E = EGF-like domain C = complement regulatory domain
  59. 59. Lymphocyte Extravasation
  60. 60. Selectins are involved in extravasation Inflammatory signals activate endothelial cells making PSelectin undergo exocytosis P-Selectin on the surface of endothelial cells binds a specific carbohydrate ligand (Sialyl Lewis -x) on leukocytes The leukocytes attach to the endothelial wall and roll slowly on it PAF and integrins are then activated and the leukocytes start to extravasate
  61. 61. Selectins
  62. 62. functions of selectins animation Figure 19-19b Molecular Biology of the Cell (© Garland Science 2008)
  63. 63. Lökosit Endotel 1-K.H P-selektin 2- İntegrin ICAM 3-İntegrin ECM
  64. 64. Diseases of cell adhesion molecules
  65. 65. Integrin diseases-1 • Leukocyte adhesion deficiency (LAD) type I: – – • • defects in β2 integrin -> defective neutrophil migration to inflammed skin, peritoneum; lymphocytes less affected due to continued use of α4β1, α4β7 LAD patients have recurrent bacterial infections Other types of LAD involve defects in expression of glycosyltransferases needed to make selectin ligands and defects in intracellular signaling molecules needed for chemokinemediated integrin activation EX: LAD 2 results from a lack of sialyl LewisX (defect of carbohydrate fucosylation). Interaction with endothelial E-and P-selectins is impaired
  66. 66. Integrin diseases-2 • Glanzmann Thrombasthenia • : is an inherited bleeding disorder fibrinojen – IIbß3 integrin expression deficieny – ↓ • adequate formation of the platelet plug » ↓ Susceptibility of bleeding trombin
  67. 67. Immunoglobulins • One Ig cell adhesion protein known as L1, assists in growth of nerve cells – mutants can have severe neural problems: – Mental retardation – Hydrocephaly (fluid accumulation in ventricles of brain - arrows)
  68. 68. Cancer Metastasis and adhesion Alteration in expression of adhesion molecules cell- cell a recognition- adhesion system breaks down in cancer
  69. 69. 6 basic steps for metastasis For metastasis 1. Detachment No need for cell to cell interaction 2. Invasion and intravasation 3. Circulation 4. Stasis 5. Extravasation and invasion 6. proliferation
  70. 70. Cancer Metastasis and adhesion cell- cell a recognition- adhesion system breaks down in cancer
  71. 71. • A loss-of-function allele of a Cadherin, a Desmocollin, or a Ca++independent CAM can lead a cell to a lose its adhesion to proper neighbors and start to wander(tour) • About 85% of cancers are epithelial in nature (due to high replication rate), metastasis is linked to a loss of E-cadherins E (Cadherins is down regulated in most carcinomas and is therefore a tumor suppressor
  72. 72. E (Cadherins: •. Loss of cadherin is accompanied by a loss of zonula adherens junctions and a dramatic reduction in cell-cell adhesion. •Experimentally increasing the levels of E-cadherin can restore many of the normal •epithelial properties of carcinoma cells including loss of their ability to cause tumors • when injected into animals. cadherins
  73. 73. Circulation Stasis Extravasation and invasion Changes in cell adhesion behavior