Tgfβ activation and signaling


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Tgfβ activation and signaling

  1. 1. TGFβ ACTIVATION AND SIGNALING Presented by: Fathimath Shibana M. Sc Biotechnology 3rd Semester, 2013 University of Mysore Guided by: Dr. Geetha N.P . Assistant Professor DOS in Biotechnology
  2. 2. WHAT IS TGF? • It is transforming growth factor or tumor growth factor. • There are two types, TGF-α and TGF-β • TGF-α is a single growth factor which is upregulated in some human cancers. It is produced in macrophages, brain cells and keratinocytes (basal cells in epidermis) and induces epithelial development. • TGF-β is a diverse family of growth factor. Many different members and subfamilies are within it. TGF-β is a protein that controls proliferation, cellular differentiation, and other functions in most cells. • It is a type of cytokine which plays a role in immunity, cancer, bronchial asthma, heart disease, diabetes, Marfan syndrome, etc
  3. 3. • In human TGF-β exist in 3 subtypes. They are TGF-β1, TGF-β2 and TGF-β3 which upregulates Marfan syndrome
  4. 4. STRUCTURE OF TGFβ Crystal Structure of TGF-beta 1 Crystal Structure of TGF-beta 2 Crystal Structure of TGF-beta 3 Structure of TGF-β consists of 3 domains. 1. N-terminal domain which associate with the precursor molecule to proper cellular secretory pathways 2. Peptide domain which support folding or dimerization of mature cytokine 3. C-terminal domain which are approximately 100-114 amino acid long, they help autocrine signaling molecule which is highly conserved across the superfamily.
  5. 5. TGFβ ACTIVATION • Some currently known factors which activates TGF-β are Protease, Integrins, PH and oxygen reactive species (ROS) • Disruption of these activating factors can leads to unregulated TGF-β signaling levels that may cause several complications including inflammation, autoimmune disorders, fibrosis, cancer and cataracts. • In most cases activated TGF-β ligand will initiate TGF-β signaling cascade as long as TGF receptors I and II are within reach. This is due to high affinity between TGF-β and its receptors.
  6. 6. TGFβ Activation continued..... LATENT TGFβ COMPLEX • TGF-β1, TGF-β2 and TGF-β3 are synthesized as Precursor molecule which contains propeptide region in addition to TGF-β homodimer. • After synthesized TGF-β homodimer interact with Latency Associated Peptide (LAP). [LAP is a protein derived from N-terminal region of TGF-β gene product]. • Interaction of TGF-β homodimer with LAP forms Small Latent Complex (SLC) • This complex remains in cell unit is bounded by another protein called Latent TGF-β Binding Protein (LTBP) forming large complex called Large Latent Complex (LLC) • It is LLC that get secreted to Extracellular Matrix (ECM)
  7. 7. TGFβ Activation continued..... Latent TGFβ Complex continued..... • In most cases before LLC is secreted, TGF-β precursor is cleaved from propeptide but remains attached to it by non-covalent bonds . • After its secretion it remains in ECM as inactive complex containing both LTBP and LAP which needs to be further processed to release active TGF-β. • The attachment of TGF-β to LTBT is by disulphide bond which allow it to remain inactive by preventing it from binding to its receptors. • Because of different cellular mechanism require distinct levels of TGF-β signaling, the inactive complex of this cytokine gives opportunity for proper mediation of TGF-β signaling.
  8. 8. INTEGRIN DEPENDENT TGFβ ACTIVATION TGFβ Activation continued..... 1. ACTIVATION BY PROTEASE AND METALLOPROTEASE • Plasmin and no. of Matrix Metalloprotease (MMP) play a key role in promoting tumor invasion and tissue remodeling by inducing proteolysis of several ECM components. • TGF-β activation process involves release of LLC from matrix, followed by proteolysis of LAP to release TGF-β to its receptors • MMP9 and MMP2 are known to cleave TGF-β • LAP complex contains protease sensitive hinge region which can be target for liberation of TGF-β. Despite the fact that MMP plays a key role in activating TGF-β, mice with mutation in MMP9 and MMP2 gene can still activate TGF-β and do not show any TGF-β deficiency phenotypes. It may be due to unknown proteases.
  9. 9. TGFβ Activation continued..... Integrin dependentTGFβ activation continued..... 2. ACTIVATION BY PH • Acidic condition can denature the LAP. • Treatment of medium with extremes of pH (1.5 or 12) result in activation of TGF-β as shown by radio receptor assays. • Mild acidic treatment (pH 4.5) yielded only 20-30% of the competition achieved by pH 1.5 3. ACTIVATION BY REACTIVE OXYGEN SPECIES (ROS) • LAP structure is important to maintain its function • Structure modification of LAP leads to disturbing the interaction between LAP and TGF-β and thus activates it. • Factors that may cause this modification may include hydroxyl radicals from ROS. TGF-β was rapidly activated after in vivo radiation exposure ROS
  10. 10. Fig: The construction and extracellular activation of latent TGF-β1. The TGF-β1 dimer is synthesized intracellularly and combines with LAP to form a latent precursor (SLC). The SLC then forms a LLC with LTBP-1 via covalent bonds. The hollow arrows show the activating sites of TGF-β1. Proteases and integrins can activate latent TGF-β1 via direct proteolytic cleavage and/or by inducing a conformational change in LAP.
  11. 11. TGFβ SIGNALING PATHWAY MECHANISM Ligand binding Receptor recruitment and phosphorylation SMAD phosphorylation Co-SMAD binding Transcription
  12. 12. TGFβ SIGNALING PATHWAY • TGF-β signaling pathway begins with a TGF-β dimer binding to Type II TGF-β receptor at cell surface. • TGF-β dimer induce formation of complex between type II and type I TGF-β receptors, both of which are transmembrane serine/threonine kinases. • Once TGF-β dimer binds to type II receptor, type II receptor phosphorelates and activates type I receptor. • The activated type I receptor phosphorelates a receptor regulated Smad (R-smad) which then dimerizes with a Co-smad. • The smad dimer translocates into the nucleus and with a DNA binding partner activates transcription of target genes.
  13. 13. BIBLIOGRAPHY • • Function-a-5894.html • • • naling_schematic.jpg • 01.htm?v=category&i=14010.01&s=00010&n=14000&o=00PRS