Receptor Tyrosine Kinases Flashcards
RTK Structure
Extracellular – ligand-binding
Transmembrane – α-helix
Cytoplasmic – tyrosine kinase activity (phosphorylate tyrosine aa)
- needs adapter proteins
- Ras-GTP —> signals downstream kinases
Activate RTKs
- bind ligand
- auto-phosphorylation of cytoplasmic domain
- phosphorylate additional tyrosine residues for SH2 docking
Adapter Proteins
- domains that recognize specific sequences
- SH2
Discover First Oncogene
- inject cell free extract from chicken tumor into healthy chicken —> developed tumors
- gene in virus encodes tyrosine kinase
- normal = cellular src (inhibitory phosphorylation)
- viral = viral src (missing terminus – always on)
Ras-GTP Switch Protein
- lipid anchored protein
Inactive (GDP) –> GEF activates Ras, removes GDP
Active (GTP) –> GAP inactivates Ras, removes GTP
Cancer — can’t bind GAP, no GTP removal = always on
FGF-Induced Ras Activation Step 1
- Ras inactive
- FGF binds to FGF receptor
- autophosphorylation of tyrosine residues
FGF-Induced Ras Activation Step 2
- GRB2 has SH2 domain – binds to phosphotyrosine
- GRB2 has 2 SH3 domains – bind to proline in SOS (GEF)
FGF-Induced Ras Activation Step 3
- Sos remove GDP from Ras
- GTP binds and activates Ras
- Ras activates downstream kinase cascade
Ras/Map Kinase Pathway
- Ras activated by GTP –> binds + activate Raf
- GTP hydrolysis = Ras dissociate from Raf
- Raf activates MEK activates MAPK activates TF’s
Oncogenic Receptors
- mutation in Her2 receptor = activate w/o ligand
- deletion in EGF receptor = always active cytoplasmic kinase domain w/o ligands
Human Epidermal Growth Factor Receptors (EGF)
- 4 RTKs = Her1 –> Her4
- Her2 does not bind ligands (gene amplification + targeted by monoclonal antibodies)
Herceptin Mode of Action
Block cleavage of extracellular domain of Her2
- no activation of signal transduction
Inhibit dimerization
- reduce Her2 signalling
Recruit immune cells
- destroy tumor cell
Endocytosis of Her2
- less Her2 available to trigger cell growth
Controlled Destruction of Cells
Necrosis = rupture + release (inflammation)
Apoptosis = phagocytosis of apoptotic body
Block Apoptosis in C.elegans
- dead cells detected by DIC microscopy
- ced-3 and ced-4 —> (promote apoptosis)
- ced-9 –> (suppress apoptosis)
Caspases Function
- Fragment DNA, Nucleus, Golgi
- cytoskeletal disruption
Initiator vs Effector Caspases
Initiator
- activated by dimerization
- cleave inanctive effector caspases –> to activate
Effector
- cleave protein substrates within cell
- trigger apoptotic process
Apoptosome
- Apaf-1 + Cytochrome C + Caspase-9
- bind cytochrome C = Apaf-1 forms disk heptamer
- recruits Caspase-9
- activates initiator caspase
Bcl-2 Family Proteins
- inhibits apoptosis
Pro-survival = Bcl-2 homology + TM domain (Bcl-2) Pro-apoptotic = lack BH4 domain
BH3 only proteins = counter effects of Bcl-2
Evolutionary Conservation of Apoptosis
- Bax/Bac form pores = release cytochrome C
- inhibited by Bcl-2
- BH3 proteins inhibit Bcl-2 (cytochrome C released)
Trophic Factor Withdrawal
Cell Survive
- growth factor or cytokine = phosphorylation of RTKs
- phosphorylation of Bad (interact with 14-3-3 inhibitor)
Cell Death
- no growth factor = less phosphorylation of RTKs + Bad
- inhibition of Bcl-2 = Bak releases cytochrome C
- forms apoptosome to activate effector caspase
Death Signal
- death signals from other cells bind to receptor
- activates initiator caspase 8
- cleavage of BID –> t-BID inhibits Bcl-2 –> release cytochrome C = cell death
- activates effectors proteins directly = cell death
Unregulated Apoptosis
Too Little = increase cell survival, cancer, weak immunity
Too Much = neurodegenerative disorders, aging, autoimmune diseases
