Cell signalling Flashcards
how is cell signalling altered in cancer?
3
- signalling turned on or unresponsive to inhibition
- volume of signalling increased (more receptors or more ligand)
- signalling at wrong time or place
alteration of cell signalling enable the cell to evade normal regulation
what is gefitinib?
a targeted therapy for EGFR mutations in non small cell lung cancer. It works by binding to the intracellular enzyme (tyrosine kinase) of the EGFR to directly block signals turned on by triggers outside or inside the cell.
what is cell signalling?
the mechanisms that cells use to perceive and adapt to their state and surroundings
- an interconnected series of molecular events that enables perceptions and transmission of information
what is signal transduction?
the biochemical process that facilitates information processing by the cell
how is information transmitted through pathways?
4| changes in protein state
- ligand and receptor (binding and dissociation)
- protein phosphorylation (post translational modification)
- G protein bound to GTP/GDP (conformational change)
- nucelocytoplasmic shuttling (localisation)
altered protein state is mediated by what two types of proteins
writers (eg kinases)
erasers (eg phosphatases)
cellular regulation is controlled by cell signalling and gene expression, compare these two parts
cell signalling
- enables transmission from outside cell to nuc;eus
- fast ON and OFF (secs to mins)
- transient changes (mins to hrs)
- spatial/directional repsonses and organisation
- energenticallt cheap (no protein synthesis)
gene expression
- slow ON and OFF (mins to hrs)
- stable changes (hrs to yrs)
- limited spatial responses
- energentically costly (transcription and translation)
whats the difference between positive and negative feedback?
Positive feedback occurs to increase the change or output: the result of a reaction is amplified to make it occur more quickly.
Negative feedback occurs to reduce the change or output: the result of a reaction is reduced to bring the system back to a stable state
what are the reasons to think signalling occurs in a network rather than a pathway?
- cross talk (interaction of signalling pathways)
- convergence (multiple signals activate one, integration of multiple signals)
- divergence (one signal elicits multple outcomes, many proteins function in multiple pathways)
what are the reasons to think signalling occurs in a network rather than a pathway?
-cross talk occurs between signalling pathways
-integration of multiple signals
-many proteins function in multiple pathways
what three ways can information cross the membrane?
- membrane permeable signals (eg lpid soluble hormones (steroids))
- gated channels (eg ions)
- transmembrane receptors (eg growth factors)
what are the three domains in transmembrane receptors?
- Discriminator domain binds specific ligand
- Transmembrane domain anchors in membrane
- Effector domain directly or indirectly linked to intracellular enzymatic activities
describe the indirect and direct function of the effector domain in transmembrane receptors?
Indirect: receptor associates with separate kinase protein
Direct: kinase domain in same protein structure as transmembrane receptor
after ligand binding to receptor tyrosine kinases, what do conformational changes in the cytoplasmic domains lead to?
- auto-phosphorylation and recruitment of signalling proteins
- phosphorylation of scaffold proteins that organises signalling complexes
oncogenic mutations in receptor tyrosine kinases increase signalling through what
over expression of receptor and mutations affecting structure lead to ligand independent firing
mutations in receptor tyrosine kinases lead to
ligand independent firing
what two ways can ligand independent firing occur?
- overexpression of receptor
- mutations affecting structure
Egfr mutations are found in what 4 exons of the egfr gene
18 19 20 21.
Mutations in exons 19 and 21 (L858R) account for 90%
what are the three most commonly modified amino acids in eukaryotes
phosphorylated
Ser > Thr > Tyr
give five possible consequences of phosphorylation
o Addition of phosphate group induces conformational changes
o Activation/inactivation
o Form/hinder protein interactions
o Sub-cellular relocalization
o Degradation via proteasome
what percentage of cellular protein may be ubiquitylated at any one time
20%
whats the function of E1, E2 and E3 in ubiquitylation?
E1 - recruits ubiqitin protein (2 in humans)
E2 - activated ubiquitin transfers E2 conjugating enzyme (50 in humans)
E3 - ligase that transfers ubiquitin to lysin group on target protein, primary determinants of substrate specificity (500 in humans)
give 4 different protein modifications that occur in signalling
Phosphorylation
Acetylation
Methylation
Ubiquitylation
give 4 different protein modifications that occur in signalling
Phosphorylation
Acetylation
Methylation
Ubiquitylation
give a method of identifying ubiquitylation sites
using proteomics
mass spectrometry proteomics;
o Digest proteins into peptides leaves a di-Glycine tag at ubiquitylated sites
o This tag can be identified on peptides using mass spectrometry
o Measure abundance and exact sites of ubiquitylation of 1000s proteins
give two trancriptional targets of beta catenin in the wnt pathway
- Cyclin D1 (CCND1)
Drives G1 to S phase transitions in cell cycle - Myc
Proto-oncogene encoding multifunctional transcription factor involved in cell cycle, apoptosis
Wnt pathway activation induces expression of genes that lead to proliferation