Biology 2382B Lecture Notes - Lecture 9: Epidermal Growth Factor Receptor, Protein Kinase, Signal Transduction
23 Aug 2016
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RECEPTOR TYROSINE KINASES (RTKs)
objectives:
• structure
• dimerization
• autophosphorylation
• adapter proteins, GRB2
o PTB
o SH2
o SH3
• Ras and its regulation (GEF, GAP, Sos)
• HERs and human breast cancer
• Ras/MAP kinase pathway operation (Raf, MEK, MAPK), EGF
Receptor Tyrosine Kinases (RTKs)
• Extracellular (ligand binding) domain
o ligands include growth factors and insulin
• single transmembrane -helix
• cytoplasmic domain has intrinsic tyrosine kinase activity which is activated by ligand
binding and receptor dimerization
• subsequently, adapter proteins are required which activate further effector proteins
• Ras ats as a GTPase sith protei to sigal further dostrea kiases
o aberrant signaling is at root of many human cancers
notes:
• hundreds of RTKs with many different functions
• 3 domains: extracellular, transmembrane, cytoplasmic
• adapter proteins bind to receptor at activated phosphate, pass the signal along to
another molecule
Activation of RTKs
• dimerization allows for trans-
autophosphorylation of
cytoplasmic domains (enzyme
domain)
• phosphotyrosines serve as
docking sites for downstream
signal-transduction proteins
containing SH2 or PTB domains
(adapter proteins)
find more resources at oneclass.com
find more resources at oneclass.com
notes:
• tyrosine kinase activity is activated after ligand binding to extracellular domain
• ligand binding causes conformational change to RTK → homodimerization
o forms a dimer with an identical RTK → activates tyrosine kinase
o activation lips of cytoplasmic domain (enzyme domain) are phosphorylated first
• trans-autophosphorylation after dimerization
o trans = one RTK phosphorylated the other and vice versa
• different RTKs have a different number of phosphorylated tyrosines on their cytosolic
domains
• phosphotyrosines serve as docking sites for adapter proteins
o bind to phosphotyrosines, recognize them and pass on the signal
o have specific phosphotyrosine binding domains
Adapter proteins
• adapter proteins contain unique domains that recognize
specific sequences
• transmit signal to next enzyme cascade (RAS)
• common adapter domains:
o SH2 – src homology 2 domain (src stands for sarcoma)
▪ also an SH3
o PTB – phosphotyrosine binding domain
▪ found on multi-docking proteins
▪ serve as docking sites for other signal
transduction proteins
o IRS1 – insulin receptor substrate protein
note:
• SH2 domains are present in at least 100 human proteins
• different adapter proteins can bind to the same activated RTK which then leads to
multiple signal transduction pathways
o adapter proteis do’t eessarily tell you the futio of the RTK
Discovery of First Oncogene
• in 1911 Francis Peyton Rous injected a cell free extract from a chicken tumour (sarcoma)
into healthy chickens
o all developed tumours
• the transmissible agent was determined to be a retrovirus (Rous Sarcoma Virus)
• one of the genes within the virus encodes a tyrosine kinase protein (src)
• highly conserved and found in humans
• normal version is called cellular src (c-Src)
o regulated by phosphorylation
• viral version is called viral src (v-Src)
o this version is constitutively active (not
regulated)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Receptor tyrosine kinases (rtks) objectives: structure, dimerization, autophosphorylation, adapter proteins, grb2, ptb, sh2, sh3, ras and its regulation (gef, gap, sos, hers and human breast cancer, ras/map kinase pathway operation (raf, mek, mapk), egf. Step 3: sos does its work as a gef; exchanges gdp on active ras for. Gtp: ras-gtp is now active and triggers the downstream kinase cascade, activates a signaling cascade of kinases signal amplification, mapk is the end point of the signaling pathway, also known as erk, a protein kinase. Egfr leads to constitutive activation of cytoplasmic kinase domain. Erbb oncoprotein note: in both cases the oncogenic receptors are constitutively active even in the absence of ligand constitutively promote proliferation. Rtk: overexpression of her2 leads to greater signaling activation at very low egf concentrations, 25% of breast cancer patients have amplified. *note: her2 is targeted by monoclonal antibody, herceptin.
