thrombospondin

							  Tumor angiogenesis: chapter13


Thrombospondin and
   Angiogenesis
          Farzana Alam
              Thrombospondin
•   Glycoprotein

•   Function:

    •   Support cell attachment through interaction with multiple cell-
        adhesion

    •   Regulate cell shape, adhesion and migration

•   Family:

    •   Subclass A : TSP-1 and TSP-2

    •   Subclass B : TSP-3, TSP-4 and TSP-5
            Structure of thrombospondin




Amino acid terminal : heparin binding domain
Pro-collagen or vWF region
Three type-1 or properdin repeats
Three type-II or EGF-like repeats
Seven type-III or calcium binding domains
Carboxy terminal binding domain
                 Functional properties


•   TSP-1 and 2 regulates matrix structure of cell via its ability to bind
    directly to fibronectin, fibrin and fibrillar collagens and by modulating
    MMP and plasmin activities

•   Convey migratory, proliferative, apoptic and adhesive signals to cell by
    creating a cellular matrix bridge within or in to the cell.

•   Responses to wound healing

•   Role in platelet aggregation, inflammatory responses and angiogenesis
    in both angiogenesis and wound healing
       The link between function and
                 expression


•   TSP-1 expression is frequently associated with epithelial/endothelial
    tissues; TSP-2 is more stromal/mesenchymal nature

•   TSP-1 rapidly induced by inflammatory and injury mediators; TSP-2
    doesn’t have the impact of inflammation

•   Both proteins have effect on angiogenesis inhibition
        Structure-function studies: anti-
              angiogenic activity
•   The anti-angiogenic domain of TSP-1 and 2 is Type-I or TSR (repeating unit) or
    properdin (TSR)

•   These TSR unit has anti-parallel three-stand structure; first stand (A) is irregular and the
    second and third (B and C) has beta-structure and they are stabilzed by hydrogen bond
    between glutamic acid residues of B and C with first tryptophan of A strand.

•   The TSR repeats in TSP-1 and 2 shows bind with CD36 and to support attachment of
    multiple cell types. (related with supression of anti-angiogenesis)

•   Other factors mediated by the binding with CD36 are

    •   Induction of endothelial cell apotosis

    •   Inhibition of endothelial cell migration

    •   Direct interaction with growth factors (MMP9, Pro-MMP etc)

•   Cells affected by the mediation of CD36 (apopotic effect) with TSP-1 are- monocytes,
    endothelial cells and platelets
                  Anti-angiogenic effect

•   TSP-1 mediates different pathways in angiogeneis,

    •   It binds with TGF-beta and supress the functional properties of VEGF and FGF-2

    •   The main mechanism is: TSP-1 is inhibitor of plasmin, uPA, neutrophil elastase,
        matrix metallo-protease (MMP)2 and MMP9

    •   So, for example, TSP-1 inhibit the activation of pro-MMP9 by MMP3 and thus lack
        of MMP9 activation, prevents VEGF release from the extracellular matrix. Results,
        supression of tumor progression and angiogenesis in tumor

•   These proteins have other functions:

    •   Cell-cell and cell-matrix interactions

    •   Neouronal guidence

    •   Extracellalr proteolysis
                Pro-Angiogenic effect


•   Either by, presentation of the protein (bound Vs soluble)

•   And/or, to the ability of this protein to mediate the recruitment and
    migration of smooth muscle and inflammatory cells that release pro-
    angiogenic factors

•   Example- the heparin-binding domain, amino terminal, when s bound or
    soluble status, it convey opposite effect on the because of it’s de-
    adhesiveness (soluble condition) and it supprots cellular adhesiveness in
    imbolized (bound) condition
Different action of different structure of
                  HBD

•   Monomeric - inhibits FGF-2 induced chemotaxis

•   Trimer stimulates chemotaxis

•   Reason –

    •   It has different array to bind with multiple region of one receptor or
        different receptors

    •   And convey altered affinity or uptake receptor turnover
TSP function in wound healing
       Wound healing process of TSP
•   During the tissue damage, degranulation of platelets mediates the
    release of growth factors and adhesive proteins that facilates the
    inflammtory response and stimulates the proliferation of fibrobvlasts and
    keratinocytes. Along the growth factors, TSP1 is also released and
    facilates the formation of multi-protein complex through it s ability to bind
    with fibronectin and fibrin in hemostatic plug

•   This fibrin-fibronectin-TSP-1 provisional matrix act as a frame work that
    facilitates stimulates the cell adhesion and migration

•   TSP-2 also secreted by dermal fibroblasts

•   The matrix assembly of both TSP 1 and 2 protein properties, directly
    perticipate in the reorganization of the wounded matrix

•   More over, TSP-1 activate TGF-beta during wound healing by TSR;
    resulting effect of Proteolysis

•   In this case, the presence of TSP delays a rampant angiogenic process
    and enables the organization of capillary growth in a more orderly
    fashion, less permeable and with thinner diagram.
•
        Effects of TSP in cellular level
    Lists of receptors of TSP are

    •   CD36 of monocytes, endothelial cells and platelets

    •   Integrins

    •   Integrin associated protein

    •   Proteoglycans

•   Integrin receptor- bind with TSP1 by alphaIIb beta 1 on platelets, alpha4
    beta1 in lymphocytes and alphaV beta3, alpha3 beta1 and alpha6 beta1
    on vascular cells

•   Here the beta3 integrins recognize the TSP as RGD-dependant manner,
    thought other integrins appear to interact with their regions

•   Examples :

    •    TSP-1 mediates chemotaxis of smooth muscle cells through CD47
        and alphaV beta3. it promotes the smooth muscle cell proliferation by
        same integrins
       Themes for future research


• Different fragment have different activities
• Based on the action of different fragments,
  thrombospondin protein fragments or peptides
  can be used for different targeting moieties.

• Example: Type-I fragments for targeting MMP9
  in tumor angiogenesis
Thank you