TKR 2 - cell survival Flashcards
alternative mechanisms of TKR
EGFR
- EGF binds to EGFR
= conformational change that allows association of 2 activated receptors
INSR
- homodimeric structure where intracellular domain held apart
- insulin binding induces conformational change
- > brings kinase domains together
RTK activation of SH2/SH3 domain proteins by…?
PI 3-kinase
-> cell survival pathway
Ras-MAP-kinase
-> cell proliferation pathway
Phospholipase C
- > activates IP3 pathway
- cross-talk with GPCR signalling
adaptor proteins
- what are they?
contain no catalytic domains
serve as link between receptor + intracellular signalling proteins e.g. GNRP/GEF
GNRP/GEF
- what are they?
- does what?
guanine nucleotide releasing protein
Ras-guanine nucleotide exchange factor
activates Ras monomeric GTPase
Ras superfamily
small monomeric GTPase
(unlike trimeric GTPases in GPCR signalling)
relay RTK signals
-> cell proliferation
GNRP/Ras-GEF activates Ras
- process
recruitment of Grb2 and Ras-GEF to activated receptor
-> brings them into proximity with Ras molecules
interaction of Ras-GEF with Ras -> conformational change of Ras -> releases GDP -> acquires GTP -> conformation change = activate Ras
-> downstream signals leads to proliferation
what 2 factors are key to GNRP/Ras-GEF activating Ras?
signal protein localisation
conformational change
Ras molecular switch
GEF/GNRP
-> promotes GDP release
= activates Ras
GAPs promote Ras GTPase activity
-> inactivates Ras via GTP hydrolysis
activated RTK promotes transient Ras activation
indirect association of GEF with RTK via Grb2
-> rapid activation of Ras
some GAPs associate directly with RTKs
why is Ras self-inactivating?
has intrinsic GTPase activity
how is RTK phosphorylation reversed?
by tyrosine-specific protein phosphatases
Ras activates a cascade of serine/threonine-kinases
via phosphorylating Raf
- > phosphorylates Mek
- > phosphorylates Erk
- > produces proteins or regulatory proteins
-> change protein activity or gene expression
Ras-MAPK pathway
- discovery
in Drosophila genetic experiments
based on inability of mutant flies to detect UV light
- > screen offspring
- > looking for genes that regulate eye development
drosophila eye development
R8
- > R5 + R2
- > R4 + R3
- > R6 + R1
- > R7
R7 specialised to detect UV light
Sevenless mutants
lack R7 cell
Sevenless
- molecule type
an RTK
Sev
- ligand
- Ras-GEF
- receptor kinase
Boss
Sos
Drk
Boss and Sev
anchored to PMs
- can only ‘talk’ to adjacent cells
i. e. R8, R6 + R1 cells with R7 cell
Boss-Sev pathway in R7 cells
- boss binds to Sev RTK = activated
- Drk binds to phosphate on Sev
- Drk binds to Sos
- Sos releases GDP from Ras
- GTP binds to Ras
- Activated Ras sends downstream signals
(proliferation)
PI-3 kinase
- what do they do?
forms products with P groups at 3rd position of 6-carbon inositol ring of PI
(phosphatidylinositol)
= forms PIP
PI-3 kinases promote cell survival
- proteins recruited
PI-3 is rapidly recruited to active RTK
PDK1 + PKB are recruited to membrane via interactions with their PH domains + IP products of PI3-kinase
PI-3 kinases promote cell survival
- process to BAD phosphorylation
proteins brought into close proximity
- > PDK1 activated by PIP
- > phosphorylates PKB
- > PKB conformation change + dissociates from PIP3
- > PKB phosphorylates target protein = BAD
PI-3 kinases promote cell survival
- post BAD-phosphorylation
BAD normally associated with death inhibitory protein
phosphorylated BAD
-> conformation change
-> releases death inhibitory protein
= prevents apoptosis
= cell survival
3 types of molecular activation
- what are they?
- what do they all result in?
phosphorylation
GDP to GTP exchange
protein-protein interaction
–> conformation change
