Transmembrane Signalling and Phosphorylation Flashcards
What is paracrine singalling?
A signal which induces a response in nearby cells
What is autocrine signalling?
Signalling which acts on itself
What is endocrine signalling?
Signals which are produced by endocrine cells
Can signal a long distance
What is synaptic signalling?
Moves small distances across a synapse (neurotransmitters)
What is contact dependent signalling?
Cell to cell junctions
types of compounds which use matrix dependent signalling
- Cadherins
- Integrins
What are cadherins?
Types of cell adhesion molecules - important in forming adhesion junctions
What are integrins?
Any class of animal transmembrane protein which is involved in adhesion of cells to each other and their substrate
Form of cellular dependent signalling
matrix dependent
Form of cell to cell communication
gap junctions
Types of compounds which use gap junctions
Second messengers e.g, cAMP
Ions e.g. calcium and sodium
What are the different modes of signal transmission?
Conformational coupling (preformed complex)
Conformational coupling (diffusion-dependent complex formation)
Post translational modification
Protein degradation
Explain preformed complex
Signal changes the shape of A, causes B to change shape, join together = signal
Explain protein degradation
A and B are a preformed complex. Stimulus causes them to dissociate and degrade
What are the classes of transmembrane receptors?
GPCR Cytokine receptors Receptor tyrosine kinase TGF-beta receptors Hedgehog receptors Wnt receptors Notch receptor
What is different about notch receptors than others?
Requires cleavage and then it will become a receptor
What are protein:protein interactions?
Where one protein activates another
What are macromolecular complexes?
Where all of the proteins bind to a scaffold and they activate one another on there
What is the effect of an asymmetric dimer?
weak EGFR dimer = sustained effect = differentiation
What is the effect of symmetric dimer?
strong EGFR dimer = transient effect = proliferation
What are the fives ways which target cells can be desensitised to a signal molecule?
- Receptor sequestration
- Receptor downregulation
- Receptor inactivation
- Inactivation of signalling protein
- Production of inhibitory protein
Explain receptor sequestration
Where the receptor binds a ligand, moves into the cell via an endosome where the ligand is released and then reinserted on the membrane.
When the receptor is in the endosome there can be no signal detection.
Explain receptor downregulation
The receptor is internalised into an endosome. The endosome fuses with a lysosome. Receptor degradation.
Explain receptor inactivation
An inactivator binds to the receptor
Explain inactivation of a signalling protein
An inactivator binds to the signalling protein downstream of the receptor
Explain inhibitory protein production
The receptor signals to a signalling protein in the cell -> the signalling protein signals to an inhibitory protein -> inhibits the signalling protein
Negative feedback
Treatment for receptor induced cancers
use monoclonal antibodies which stop the ligand from binding
Example of a EGFR lung cancer drug
Gefitinib
What is TGF-beta important in?
During development and adult tissue homeostasis
Cancer biology
What does TGF-beta stand for?
transforming growth factor-beta
Examples of TGF-beta
Bone morphogenetic proteins
Growth and differentiation factor
What are TGF-beta cytokines involved in?
Regeneration Differentiation Development Apoptosis Immunosuppression Proliferation Migration Angiogenesis
What type of type II receptor does TGF-beta bind?
TbetaRII
What type of type I receptor dos TGF-beta bind?
ALK5 and ALK1
What R-smads does ALK5 cause?
Smad2
Smad3
What R-smads does ALK1 cause?
Smad1
Smad5
Smad8
What co-smad does ALK1 and ALK5 cause
Smad4
What does TGF-beta get secreted as part of?
A latent complex
What are the components of the latency complex?
LAP - latency associated protein
LTBP - Latency TGF-beta binding protein
LLC - Large latent complex
How do you activate TGF-beta?
Need to chop the latency component
1) Proteolysis with MMPs
2) Activation by integrins
3) Activation by:
- thrombospondin-1
- ROS
- Low pH
- Mechanical force
Process of TGF-beta signalling
1) Release from ligand traps (extracellular milleau)
2) Interaction with receptors (plasma membrane)
3) ALK5 (anaplastic lymphoma kinase) activation (plasma membrane)
4) Smad activation (plasma membrane, early endosome, cytoplasm)
5) Smad hetero-obligomerisation
6) Smad transcription factor interaction on DNA
7) Pathway termination
Explain how release from ligand traps work
homodimeric ligand
Interacts with the ECM domain in the type II receptors
The homodimeric structure means it binds two receptors at the same time = lower affinity for the type I receptors
What is the structure of R-SMAD?
MH1 and MH2 domains
The MH2 has a hydrophobic corridor, basic pocket and a site of receptor phosphorylation
What is the function of R-SMAD MH1?
- DNA binding
- Nuclear localisation
- Binding DNA to co-factors
What is the function of R-SMAD MH2?
- Receptor interaction and phosphorylation
- Homo- and hetero- oligomerisation
- Nuclear export
- Binding to co-activators and co-repressors
What is the structure of Co-SMAD?
MH1 and MH2 domains
MH2 domains - basic pocket and SAD domain
Function of Co-Smad MH1 domain
DNA binding
Function of Co-Smad MH2 domain
R-Smad binding
Interactions with transcriptional activators and repressors
What is SAD?
Smad activation domain
transcription activator
What does Smad7 complex with?
p300 and Smurf
What is smurf?
E3 ubiquitin ligase - polyubiquitylate the receptor to target it for degradation
What are the antitumour properties of TGF-beta?
- tumour suppressor
- induces cell growth arrest
- induces senescence
- TGF-betaRII inactivation promotes recruitment of myeloid progenitor cells
Loss of smad promotes genomic instability - induces apoptosis
What are tumour promoter properties of TGF-beta?
- potent immunosuppressor
- promotes invasion, intravasation, extravasation and metastatic colonisation
- promotes angiogenesis
- promotes tumour cell survival
What kind of vesicles are used in receptor 1 and receptor 2 degradation?
Caveolin
What homolog was discovered across animal species? And what was it called in flies?
Int-1
Wingless (Wg)
What are the names of the genes which encode the Int-1?
Wingless-related integration site-1 (WNT1)
Describe WNT ligands
Glycoproteins
Heavily glycosylated
Signal in paracrine and autocrine routes
What is the WNT signalling receptors?
FZD receptor
Describe FZD receptors
Similar to GPCRs
Bind to the N-terminal of extra-cellular Cys-rich domain
Co-receptors required
Define Groucho
A type of non-DNA binding corepressor for specific transcription factors
Give two examples of transcription factors which bind to groucho
LEF
TCF
What happens to beta-catenin in the presence of a WNT ligand
1) WNT ligand binds to FZD receptor
2) Dishevelled (DVL) becomes activated by phosphorylation
3) Destruction complex phosphorylates beta-catenin
4) Beta-catenin is targetted for ubiquitylation and degradation
Common target genes for WNT/beta-canenin
c-Myc
Axin2
CyclinD1
What are the two WNT ligand signalling pathways
beta-catenin dependent pathway
beta-catenin independent pathway
Where does beta-catenin exist?
plasma membrane - E-cadherin bound
cytoplasmic
Name a common WNT/beta-catenin pathway in cancer
APC - frameshift and deletion mutations so you cannot degrade beta-catenin
What cancers does APC effect?
- small intestine
- smooth muscle
- liver
- pancreas
- stomach
- large intestine
