Receptor tyrosine kinases.ppt


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Receptor tyrosine kinases.ppt

  1. 1. <ul><li>Introduction </li></ul><ul><ul><li>Recruitment of kinases in signalling pathways </li></ul></ul><ul><ul><li>Consequences of protein phosphorylation </li></ul></ul><ul><li>RTK family: </li></ul><ul><ul><li>Classification & structure/function </li></ul></ul><ul><ul><li>RTK ligands </li></ul></ul><ul><ul><li>Receptor dimerization & autotransphosphorylation </li></ul></ul>
  2. 2. <ul><li>RTK-mediated pathways: </li></ul><ul><ul><li>Ras-Raf-MAP kinase pathway, use of dominant negative mutants to map pathway </li></ul></ul>
  3. 3. <ul><li>Cell surface receptors recruit activity of protein kinases in two general ways: </li></ul><ul><ul><li>Non-receptor tyrosine kinases : Receptors lacking self-contained kinase function recruit activities of intracellular protein kinases to the plasma membrane </li></ul></ul><ul><ul><li>Receptor tyrosine kinases : Possess an intrinsic tyrosine kinase activity that is part of the receptor protein. Examples include receptors for growth factors (PDGF, EGF, insulin, etc.) </li></ul></ul>
  4. 4. <ul><li>Implicated in diverse cellular responses: </li></ul><ul><ul><li>Cell division </li></ul></ul><ul><ul><li>Differentiation </li></ul></ul><ul><ul><li>Motility </li></ul></ul><ul><li>At least 50 RTKs identified: </li></ul><ul><ul><li>Subdivided into 10 subclasses based on differences within extracellular, ligand-binding domain of receptor </li></ul></ul><ul><li>“ Oncogenic” RTK mutants exist: </li></ul><ul><ul><li>erbB gene encodes an N-terminal truncated, constitutively active form of EGF receptor </li></ul></ul>
  5. 5. <ul><li>Four common structural features shared among RTKs: </li></ul><ul><ul><li>Extracellular ligand-binding domain </li></ul></ul><ul><ul><li>Single transmembrane domain </li></ul></ul><ul><ul><li>Cytoplasmic tyrosine kinase domain(s) </li></ul></ul><ul><ul><li>Regulatory domains </li></ul></ul>
  6. 7. <ul><li>Extracellular ligand-binding domain. </li></ul><ul><li>Cytosolic domain with tyrosine kinase (tk) enzyme activity. </li></ul>
  7. 8. Regulatory domains
  8. 9. <ul><li>Typically small soluble proteins </li></ul><ul><li>Work in autocrine and paracrine manner </li></ul><ul><li>Dimerize (may aid in receptor dimerization) </li></ul><ul><li>Some RTK ligands membrane-bound </li></ul>
  9. 10. <ul><li>Ligand-induced RTK activation induces Receptor dimerization, leading to activation of catalytic domains </li></ul><ul><li>Receptor autotransphosphorylation: </li></ul><ul><ul><li>Further stimulates kinase activity </li></ul></ul><ul><ul><li>Leads to phosphorylation of additional proteins involved in receptor signalling pathway </li></ul></ul><ul><ul><li>Provides “docking sites” for downstream signalling proteins (Grb2, PI3-kinase, phospholipase C  , etc.) </li></ul></ul>
  10. 12. <ul><li>SH2 domains: bind P-Tyr-containing sequences </li></ul><ul><li>SH3 domains: bind to pro-rich (PxxP) sequences </li></ul>
  11. 14. <ul><li>Receptor tyrosine kinase mediated signal transduction </li></ul><ul><li>does not involve G-proteins </li></ul><ul><li>does involve phosphorylation of proteins </li></ul><ul><li>… at tyrosines </li></ul>
  12. 15. ligands inactive tyr kinase monomer … cross-phosphorylation of tyrosines Receptor Tyrosine Kinase Activation ATP ADP Phosphorylated tyrosines on activated signaling proteins  cell response active tyr kinase dimer P- P- P- -P -P -P X X X
  13. 16. ligands inactive tyr kinase monomer cross-phosphorylation of tyrosines MAP ( mitogen-activated protein ) kinase activation: ATP ADP active tyr kinase dimer GDP GTP Ras inactive active MAP kinase-kinase-kinase active nucleus P- P- P- P- P- -P -P -P X X X adaptor protein Ras-activatingprotein MAP kinase-kinase MAP kinase translocation to nucleus…
  14. 17. P | nucleus P- P- MAP kinase Transcription factors Other nuclear proteins DNA binding Changes in protein activity changes in gene activity Cell proliferation, differentiation
  15. 18. <ul><li>Ras-Raf-MAP kinase pathway </li></ul><ul><li>R7 photoreceptor development in drosophila (fruitfly) </li></ul>
  16. 19. Tyr-P Grb2 SH3 domains Proline-rich regions (-PXXP-) Sos Ras (inactive) Pi Ras (active) Raf MEK MAP kinase P P P Nucleus MAP kinase P P fos jun P P Increase gene expression SH2 domain GDP GTP DNA
  17. 20. <ul><li>Regulates cell growth and cell reproduction </li></ul><ul><li>Tyrosine kinase catalyzes transfer of phosphate group from ATP to to tyrosines </li></ul><ul><li>Can trigger ten or more signal transduction pathways at once </li></ul><ul><li>Abnormal tyrosine kinases that work even without a signal molecule may contribute to some cancers </li></ul><ul><li>See next slide </li></ul>