Cancer Bio exam 2
SIGNALING PART 1
•Growth factor overview- tissue maintenance and wound healing
- Growth factors signal to cells grow via receptor tyrosine kinases (RTKs)
- help maintain tissue architecture (coordination of cells growth for the whole tissue not
only individual cells)
- FBS contains growth factors for cells growing in tissue culture.
- How FBS is made: from fetal blood that is allowed to clot, which activates platelets,
releasing platelet derived growth factor (PDGF) which usually is responsible to attract
fibroblast to wounds and stimulate their proliferation (for wound healing)
• Receptor Tyrosine Kinase (RTK) overview
- 60 human RTK genes
- In common: go through membrane with single alpha helix, have a Tyrosine Kinase
domain in cytosol, most dimerize upon ligand binding
- De-regulation of RTK (oncogene formation):
1. Site-specific mutation/truncation (ex) causes ligand independent firing)
- Truncated EGF as an oncoprotein: v-ErbB = EGF receptor lacking receptor
ectodomain (outside the cell), which allows for constitutive signaling
unregulated by EGF
2. or overexpression (increases chances of RTK collision and thus spontaneous
dimerization and increased sensitivity to GFs)
• Paracrine vs. autocrine signaling via RTKs
- Paracrine signaling: most cells depend on GF produced by other cells for
proliferation
- Autocrine signaling: independent cell growth (grow in response to GF made by
themselves) → typical in cancer (allows for independent sustained proliferative
signaling)
• RTK activation by dimerization
1. EGF-R moves laterally within cell membrane → Randomly,
they meet and form homodimer (needed configuration for
EGF binding)
2. EGF binding stabilizes the homodimer
3. Transphosphorylation on tyrosines then occurs within the C
terminal cytoplasmic tails
4. The signaling pathway is activated
Gene fusion: Ex) The Ros RTK can freely move laterally in normal cells. In some glioblastomas,
the Ros reading frame is fused with the Fig reading frame, a protein that forms strong homodimers.
→ Fig then brings the Ros monomers together, resulting in constitutive dimerization/activation
, • RTK signaling to Ras
Reminder: Ras oncogenic mutation prevents GTPase activity (stays always in active form)
Bound to GTP = conformational
changes (switches I & II) that allow to
bind to other downstream ligands (PI3K,
Raf, Ral-GEF)
• Positive and negative feedback of Ras signaling
Positive feedback loop:
- Degradation of NF1 tumor suppressor(inhibitor of active Ras by inducing GTP
hydrolysis)
- GF + RTK = PKC phosphorylate NF1, targeting it for ubiquitination and degradation
Neurofibromatosis type 1 (NF1) disorder that makes patients more likely to develop tumors
in nervous systems due to mutation in NF1 gene (which makes the tumor suppressor protein
Neurofibromin/NF1 protein) located in brain cells.
Negative feedback loop:
- Sprouty protein activation by Raf/MEK/Erk
downstream cascade of Ras. Sprouty binds
to adaptor protein (Grb2) blocking Ras
activation. It can also inhibit Raf.
- Ras-GAP can bind to RTK and inhibit
activation of Ras by facilitating GTP
hydrolysis.
SIGNALING PART 1
•Growth factor overview- tissue maintenance and wound healing
- Growth factors signal to cells grow via receptor tyrosine kinases (RTKs)
- help maintain tissue architecture (coordination of cells growth for the whole tissue not
only individual cells)
- FBS contains growth factors for cells growing in tissue culture.
- How FBS is made: from fetal blood that is allowed to clot, which activates platelets,
releasing platelet derived growth factor (PDGF) which usually is responsible to attract
fibroblast to wounds and stimulate their proliferation (for wound healing)
• Receptor Tyrosine Kinase (RTK) overview
- 60 human RTK genes
- In common: go through membrane with single alpha helix, have a Tyrosine Kinase
domain in cytosol, most dimerize upon ligand binding
- De-regulation of RTK (oncogene formation):
1. Site-specific mutation/truncation (ex) causes ligand independent firing)
- Truncated EGF as an oncoprotein: v-ErbB = EGF receptor lacking receptor
ectodomain (outside the cell), which allows for constitutive signaling
unregulated by EGF
2. or overexpression (increases chances of RTK collision and thus spontaneous
dimerization and increased sensitivity to GFs)
• Paracrine vs. autocrine signaling via RTKs
- Paracrine signaling: most cells depend on GF produced by other cells for
proliferation
- Autocrine signaling: independent cell growth (grow in response to GF made by
themselves) → typical in cancer (allows for independent sustained proliferative
signaling)
• RTK activation by dimerization
1. EGF-R moves laterally within cell membrane → Randomly,
they meet and form homodimer (needed configuration for
EGF binding)
2. EGF binding stabilizes the homodimer
3. Transphosphorylation on tyrosines then occurs within the C
terminal cytoplasmic tails
4. The signaling pathway is activated
Gene fusion: Ex) The Ros RTK can freely move laterally in normal cells. In some glioblastomas,
the Ros reading frame is fused with the Fig reading frame, a protein that forms strong homodimers.
→ Fig then brings the Ros monomers together, resulting in constitutive dimerization/activation
, • RTK signaling to Ras
Reminder: Ras oncogenic mutation prevents GTPase activity (stays always in active form)
Bound to GTP = conformational
changes (switches I & II) that allow to
bind to other downstream ligands (PI3K,
Raf, Ral-GEF)
• Positive and negative feedback of Ras signaling
Positive feedback loop:
- Degradation of NF1 tumor suppressor(inhibitor of active Ras by inducing GTP
hydrolysis)
- GF + RTK = PKC phosphorylate NF1, targeting it for ubiquitination and degradation
Neurofibromatosis type 1 (NF1) disorder that makes patients more likely to develop tumors
in nervous systems due to mutation in NF1 gene (which makes the tumor suppressor protein
Neurofibromin/NF1 protein) located in brain cells.
Negative feedback loop:
- Sprouty protein activation by Raf/MEK/Erk
downstream cascade of Ras. Sprouty binds
to adaptor protein (Grb2) blocking Ras
activation. It can also inhibit Raf.
- Ras-GAP can bind to RTK and inhibit
activation of Ras by facilitating GTP
hydrolysis.
