Lecture 5 - Receptor mechanism III Flashcards
Growth factor receptors (3)
Single transmembrane domain receptors EXCEPT INSULIN.
Activation –> Activation of a receptor kinase
–> Activation of multiple signalling pathways
Tyrosine receptors kinase - examples (8)
Insulin - Epidermal growth factor - Platelet-derived growth factor JAK/STAT - Growth hormone - Interferon Serine Threonine receptor kinase - TGFB(beta)
Enzyme-linked reactions, involved in the regulation of: (5)
Cell growth Division Differentiation Survival Migration
Tyrosine kinase receptors - Signal transduction mechanism (4)
Ligand binds to monomers induces dimerisation –> Monomers phosphorylate tyrosine residue in each another –> Phosphorylated intracellular domains bind enzyme/other cellular proteins –> cellular function
Tyrosine kinase receptors (6)
1 single protein subunit - monomer. 1 transmembrane domain. N terminal EXTRAcellular - binds ligand C terminal INTRAcellular - bind effector Slow response: minutes, hours, days. Phosphotyrosine + surrounding aa are recognised by SH2 domains of other proteins, allowing them to bind and undergo activation.
SH2 protein domain (3)
SH2 domains of other proteins, allowing them to bind and undergo activation.
SH2 is structurally conserved protein domain found within Src oncoprotein/intracellular signal-transducing proteins.
SH2 domains allow proteins containing those domains to dock to phosphorylated tyrosine residues on other proteins.
Activation of tyrosine kinase receptors activates multiple pathways (10) - Draw out the diagram
Phosphorylated tyrosine acts as docking site for SH2 domains (on other proteins).
Grb-2 is adaptor protein.
RAS important in the regulation of cellular activation/growth.
Grb2 binds to SH2 domain. RAS GEF binds to Grb2 as it detects SH3 domain, RAS is then activated. This has a biological effect and has downstream protein activity. GDP to GTP.
Leads to growth/differentiation and cellular function.
OR
Activation of the receptor.
A single receptor can be modulated depending on which protein is activated.
Proteins are activated and phosphorylated by PI 3-Kinase which can react with PIP2 which can be phosphorylated to PIP3 (PDK1) and then activate PKB (active form).
Insulin receptors (9)
Acts on liver and muscle.
Acts to oppose the effects of glucagon and adrenaline.
Consists of 2a/2b subunits linked by disulphide bridges.
Binding of insulin auto[P] of 2B subunits.
Activation of receptor –> activation of IRS (small protein substrates).
Stimulates lipid synthesis in adipocytes, ps, cell growth/proliferation.
Similar to EpidermalGrowthFactor (EGF) but it is already dimerised –> suggests dimerisation is required BUT NOT sufficient for activation.
Insulin receptor substrate recruits RAS and PLC.
Same steps as tyrosine kinase receptor.
PKB regulates enzymes in glycogen/ps.
How are receptor kinases inactivated? (4)
Dephosphorylation leads to inactivation.
If the receptor is not activated = phosphatase inactivated = signalling process sets in motion events that lead to signal termination.
Small G-proteins have intrinsic GTPase activity.
Receptor internalisation.
Small G proteins (6)
Ras.
Related to Ga subunit of cAMP.
Inactive GDP bound, replaced by GTP by GEF.
Growth/cell differentiation/motility.
Contains GTPase activity, slow dephosphorylation helped by GTPase-activating proteins (GAP).
Mutated Ras found in 30% of tumours.
Dephosphorylation of Ras takes 30 mins, GAP speeds this up 105 fold.
Mutation prevents dephosphorylation/hydrolysis of GTP –> GDP, leading to pituitary tumours.
Regulation of RAS activity (6)
Mutations in GAP NF1 results in a benign tumour.
RAS GEF activates Ras (GDP –> GTP). Ras can now bind with other proteins e.g. RAF. GEF allows process to carry on with greater efficiency.
Ras is a docking site for GTPase (responsible for activation/deactivation).
Activation faster than deactivation
Deactivation = GTPase removal of phosphate of GTP –> GDP. Ras/RAF seperated.
Mutations in key regulatory mechanisms can lead to cancer (4)
EGF receptor - important in mechanisms e.g. breast cancer.
Ras mutated = Cancers = Deactivation of GTPase (so Ras can’t be deactivated).
GTP –> may not be converted into GDP.
In breast cancer the receptor itself maybe the target = e.g. Herceptin is a monoclonal antibody that targets a member of EGF receptor family.
Jak-STAT signalling pathway activated by growth hormone (10)
STAT - Signal transducer and activator of transcription.
Growth hormone receptor (GHR) does not have any enzyme activity, to overcome this the receptor associates with diff types of Jak.
Receptors act as monomers when unbound to GH.
GH + R –> Conformational change = one GH binds to 2 receptors = co-operative effect.
Jak 2 anchored to membrane. Contains two kinase domains.
Dimerisation leads to phosphorylation of Jak.
Activated Jak = [P] of other proteins which [P] receptors on tyrosines.
GHR = [P] of regulators of gene expression = STAT.
[P] of tyrosine is important step.
Phosphotyrosine acts as docking site for SH2 domain. STAT dissociates from receptor and dimerise via SH2 domain.
Stable dimer has strong affinity for specific DNA binding sites and regulates gene expression.
A model Smad-dependent signalling pathway activated by TGFB (7)
TGFB - Transforming growth factor B
Smads are a family of structurally similar proteins.
Main signal transducers for receptors of TGFB = important in cell growth/development.
TGF-B [P] specific serine/threonine residues rather than thymine.
TGF-B binds to receptor and allows dimerisation/[P] to take place, acts as docking site for Smad.
4 types of Smad.
[P] Smad 2/3 dissociates and recognise/actiavted by Smad 4 becoming a dimer.
Dimer enters nucleus and binds to specific region of DNA and leads to transcription of specific genes.
Comparison of signal transduction pathways (12) - Draw table
On table.
Pathways don’t act in isolation but work to modulate each others activity.
