The document discusses receptor tyrosine kinases (RTKs), a class of cell surface receptors that possess intrinsic tyrosine kinase activity. RTKs are activated through ligand binding and dimerization, which leads to autophosphorylation and downstream signaling. This signaling involves phosphorylation of proteins by RTKs and recruitment of adaptor proteins, ultimately regulating processes like cell proliferation and differentiation. Examples of RTKs include receptors for growth factors like EGF. Mutations in RTKs can cause them to be constitutively active and contribute to cancer.

1. Introduction Recruitment of kinases in signalling pathways Consequences of protein phosphorylation RTK family: Classification & structure/function RTK ligands Receptor dimerization & autotransphosphorylation

2. RTK-mediated pathways: Ras-Raf-MAP kinase pathway, use of dominant negative mutants to map pathway

3. Cell surface receptors recruit activity of protein kinases in two general ways: Non-receptor tyrosine kinases : Receptors lacking self-contained kinase function recruit activities of intracellular protein kinases to the plasma membrane 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.)

4. Implicated in diverse cellular responses: Cell division Differentiation Motility At least 50 RTKs identified: Subdivided into 10 subclasses based on differences within extracellular, ligand-binding domain of receptor “ Oncogenic” RTK mutants exist: erbB gene encodes an N-terminal truncated, constitutively active form of EGF receptor

5. Four common structural features shared among RTKs: Extracellular ligand-binding domain Single transmembrane domain Cytoplasmic tyrosine kinase domain(s) Regulatory domains

7. Extracellular ligand-binding domain. Cytosolic domain with tyrosine kinase (tk) enzyme activity.

8. Regulatory domains

9. Typically small soluble proteins Work in autocrine and paracrine manner Dimerize (may aid in receptor dimerization) Some RTK ligands membrane-bound

10. Ligand-induced RTK activation induces Receptor dimerization, leading to activation of catalytic domains Receptor autotransphosphorylation: Further stimulates kinase activity Leads to phosphorylation of additional proteins involved in receptor signalling pathway Provides “docking sites” for downstream signalling proteins (Grb2, PI3-kinase, phospholipase C  , etc.)

12. SH2 domains: bind P-Tyr-containing sequences SH3 domains: bind to pro-rich (PxxP) sequences

14. Receptor tyrosine kinase mediated signal transduction does not involve G-proteins does involve phosphorylation of proteins … at tyrosines

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

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…

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

18. Ras-Raf-MAP kinase pathway R7 photoreceptor development in drosophila (fruitfly)

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

20. Regulates cell growth and cell reproduction Tyrosine kinase catalyzes transfer of phosphate group from ATP to to tyrosines Can trigger ten or more signal transduction pathways at once Abnormal tyrosine kinases that work even without a signal molecule may contribute to some cancers See next slide